# 20/20 Hindsight - different armament?



## Squeelig (Jun 7, 2006)

This is mone of those hindsight questions that don't take into account the realities of why fighters ended up with the armaments they did.

Do you think the Americans would have been better off with 20mm's on their planes? Could the P-51 have handled four 20mm's? Could the P-47 have handled six 20mm's? Would the P-38 have been better with three 20mm's in the nose?


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## red admiral (Jun 7, 2006)

Answers in order;

Yes

Not without changing the wing, 2x20mm and 2x0.5" easier

No, but could carry 4x20mm

Probably not as the 20mm they were armed with wasn't that good and only had a 120round drum. It was often removed.


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## Sal Monella (Jun 7, 2006)

P-51A's did in fact have 4 x 20mm cannons.

One look at the wings of the P-51 and Hurricane (both of which had models sporting 4 x 20mm cannons) leads me to believe that the P-47 would have done just fine with 6 x 20mm cannons. It would have been pretty devastating too. As it was though, eight .50's did just fine. 

The USAAF toyed with the idea of less cannons vs more .50's when outfitting the ground attack versions of the A-26 and settled on a nose package of 8 x .50's. 

The .50 is a fine weapon. Very flat trajectory and decent AP capability.

3 x 20mm cannons in the nose of the P-38 is an interesting idea.


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## delcyros (Jun 7, 2006)

I am confident that such an improvement wasn´t really necessary for the USAAF in ww2 over europe. If the GAF would have deployed far more bombers than they historically did against the western allies, this would make more sense. With the historcial thread scenario in mind there is no justification for this step. Fighter and fighterbomber would be the prime enemy and these can be dealed with by 0.50.
Beside of this, a 20 mm armament would reduce the performance of the Mustang, P-38 and P-47 considerably by pure weight of gun ammo, not to speak of the structural reinforcements necessary in order to deal with the heavier recoil forces of mid wing / outer wing placed 20 mm guns.
This would make more sense to me for the P-38 anyway.


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## Glider (Jun 7, 2006)

The American, British and German forces generally had well armed planes and probably wouldn't have bothered making any changes. The Russians had excellent weapons and took a deliberate decision to limit (in most cases) the number carried.

Now if you were to ask the Italians and JAAF the same question, I am sure they would have made some changes. The Machi 202 was crying out for a couple of 20mm, it ruined what was a perfectly good fighter. 

As for the JAAF you have to almost feel sorry for those pilots going up against B25/B26/B17/B24's with only a couple of HMG's and pretty poor HMG's at that.


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## Sal Monella (Jun 7, 2006)

On the Mc-202 -- Two .50 Bredas and two 7.7mm's is pretty pathetic.

The Mc-205, too late to see really widespread service replaced the 7.7's with 20mm's. That and the improved engine made it a truly top notch fighter.

The final evolution of Italian aeronautics, the G.55, had three 20mm's, two .50's and an even more powerful powerplant. Very few saw combat though.

I'm not sure that structural reinforcement would have been necessary on the P-47 for six 20's. She might have just limited her bomb load to 500 pounders under each wing instead of 1,000 pounders. There would, of course, have been some trade off in performance due to the additional weight of the guns and ammo.

As has been indicated already. Eight .50's were more than ample for dealing with axis fighters. I suspect that the air to ground role wopuld have been enhanced with a complement of six 20's though.


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## delcyros (Jun 7, 2006)

For 6 20mm guns? Absolutely sure. Take the off center recoil forces into account, that´s pretty much a doubling of recoilforces in case of the P47. No good news for a mid wing configuration. The airframe as a whole would hardly be able to susatin more than 0.1 recoil/weight ratio (above that margin the gunplatform isn´t stable enough for prolonged shootings). And there would arise a need in wing modification to carry the guns, the ammo and more important: To distribute the recoil forces. 234% the recoilforces of a "normal" P47 would make structural reinforcements necessary.

P-47D: recoil force each wing: 167.04 Kp per salvo
gas effects: 8.352 Kp
Total energy: 350.7 Kp

P47-Hispano MK II mod (3 guns each wing, mid wing configuration):
recoil force each wing: 343.2 Kp per salvo
gas effects: 68.64 Kp
total energy: 823.68 Kp

The heavier wings would probably reduce the performance somehow (higher wingload), a significant reduced rate of roll is obvious.



> :
> "As has been indicated already. Eight .50's were more than ample for dealing with axis fighters. I suspect that the air to ground role wopuld have been enhanced with a complement of six 20's though."
> 
> Agreed upon that.


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## Jank (Jun 7, 2006)

All that math and those numbers make me dizzy.

All I know is that if a Hawker Hurricane Mk IIC weighing in at 8,000lbs combat loaded can do just fine with 4 twenty milimeter guns, a 14,500lb combat loaded P-47 would handle 6 twenty milimeter guns no problem.

The P-47's wings and other structure is a hell of a lot more robust that a Hawker Hurricane. 

The Republic XP-72 had the same wings and tail as the P-47D. It was ordered to be produced having four 37mm guns! The XP-72 had a loaded weight that was 70lbs less than the P-47D.


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## Sal Monella (Jun 7, 2006)

delcyros said, "The airframe as a whole would hardly be able to susatin more than 0.1 recoil/weight ratio (above that margin the gunplatform isn´t stable enough for prolonged shootings)."

What does this theory tell you about the Hawker Hurricane's ability to handle 4 x 20mm's? How about the P-51A?


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## Squeelig (Jun 7, 2006)

Did the Hurricane have recoil problems when it fired its guns?


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## plan_D (Jun 7, 2006)

Nope. The Hurricane was a stable gun-platform and the recoil off four Hispano II 20-mm cannon caused little, if any trouble to the plane. The Hurricane IIC was the most widely deployed Hurricane and this would not be the case if the plane had problems with the cannon armament.


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## Grampa (Jun 7, 2006)

For me about the P-38 L. 
3 cannon in the nose and 2 placed in the wingroots. total 5 cannons. hows that?


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## Jank (Jun 7, 2006)

I wonder if the two in the wing roots would be too close to the pilot for comfort's sake. The gun barrels would literally be within arm's reach!


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## delcyros (Jun 8, 2006)

All I did is a lot of research regarding the recoil-weight ratios of different fighter airplanes. From what I can summarize, the ratio over 0.1 was never exceeded (including Me-262 and Fw190-those variants to exceed that ratio had a worrisome performance, the MK 103 equipped Fw190 was dropped because it reached horrible recoil forces), except for specialized ground attack planes (e.g.Hurricane, Hs-129, Il-2), which may exceed this. However, all these designs had structural reinforcements to carry the additional loads and recoil forces. The Huricane is no example for a fighter. So if You want to stay with a fighter is primary role, You should care about a decent recoil-weight ratio. I do suspect that the 0.5´s improved the steadiness of the gunplatform for US fighters in comparison with german ones, since US fighters barely exceeded a ratio of 0.05. The gunlayout in midwing position is also worrisome, they have more impact on the steadiness (in direct relation to the off centre rule). 
The XP-72 is a good example that You simply cannot put as many weapons on a n airplane as You want. This may also be a reason to drop the project.


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## syscom3 (Jun 8, 2006)

Grampa said:


> For me about the P-38 L.
> 3 cannon in the nose and 2 placed in the wingroots. total 5 cannons. hows that?



Not Good. That would take away some of the fuel cells and decrease range considerably.


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## Dac (Jun 8, 2006)

There's some interesting information on this subject at this site:

http://www.geocities.com/CapeCanaveral/Hangar/8217/fgun/fgun-in.html


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## Jank (Jun 8, 2006)

The XP-72 was ordered by the USAAF in two armament variants. One was to have six .50's. The other was to have four 37mm cannons.

The project was dropped because the writing was on the wall with respect to what the USAAF wanted and that was extreme range. The P-47N fit the bill nicely with it's 2,300 mile maximum range and souped up performance.


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## Grampa (Jun 8, 2006)

syscom3 said:


> Not Good. That would take away some of the fuel cells and decrease range considerably.


Ah well It looks like you have a point here when I see on a X-raydrawing on the P-38. the ammo is no problem if you place them behind the pilot but for the gun It looks like It have to make bout the main thank and the reserve port thank 5-10 % smaller wide. that mean losing 12,5-25 Imp gal (56,8-113,6 litres) fuel. I wonder if there was possible to place some or even more of the lost fuel betwen the supercharger and the engine coolant. like make some modifications in a way when they did on the P-51 B Mustang. Putting a Extra fuelthank in the rear. would that solve the problem whit 5 cannons on the P-38?


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## delcyros (Jun 8, 2006)

If You ask me, the XP-72 armed with four 37 mm would be good for some bad surprises.

We may discuss this more in detail, if You desire.
-impact of altitude-
low latitude=high airdensity=higher drag
-stabilising the airframe due to more airflow, the plane gets "stiffer".
One reason why the Ju-87 could use two 3,7cm BK, however, as such, the plane wouldn´t really execute prolonged sustained firing.
high altitude=low airdensity= low drag, rapidly increasing due to earlier Mach effects
-from hi alt dogfights -or interception- reports it is obvious that the recoil played a huge and often unnoticed role. There are several reports of hi alt engagements with Spits armed with two 20 mm guns. The most often recorded failure was loss of controll due to excessive recoilforces.

A six 20 mm upgrade for the P-47 would therefore have more worse tradeoffs than benefitials, except for the use as specialized ground attack plane. The Hi alt performance would be terrible when shooting. The recoil force is also much more pointed: originally: 350.7 Kp distributed to eight structural fixpoints in the wing (each 43.84 Kp), post refit: 823.68 Kp distributed to only six structural fixpoints (each 137.28 Kp). This causes a TRIPPLING of powerimpact for structural issues.

I do not question that it might be possible to fit 6 20mm guns into the wing of a Thud but I am confident that this could only be achieved with structural reinforcements of the midwing section, thus further increasing the weight and lowering the performance.


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## R988 (Jun 8, 2006)

Wouldn't a mix of armament like a Spitfire provide a reasonable gun load, four 20mm is a lot of firepower against a fighter, though I guess you want a lot of quick killing power in a boom and zoom aircraft. 2x 20mm and 2x or 4x .50cal with extra ammo would be a good mix of armament for many situations. Many other fighters got on fine with 2 cannon and 2 mgs, the 109E and Zero for example, they also had tons of mg ammo.


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## Jank (Jun 8, 2006)

"A six 20 mm upgrade for the P-47 would therefore have more worse tradeoffs than benefitials, except for the use as specialized ground attack plane."

I thought it was clear that that was what we were talking about. 

Since the P-47 did just fine in the air to air role with eight .50's, (Almost all of the other fighters in the U.S. arsenal did fine with six .50's.) an outfit of six 20's would have been an improvement for the air to ground role which the P-47 assumed heavy responsibility for later in the war.

Anyway, in light of the little Hurricane's ability to handle the recoil of four 20mm's, it wouldn't have been difficult for the P-47 to have handled six. The trade off in increased weight on performance would have been a benefit in the air to ground role.

R988 has an interesting take as well. Perhaps some mix of cannon and machine gun.

It was no engineering feat to make the Hurricane (originally designed to be outfitted with .303 guns) work with four 20mm's. Any re-engineering, if required per your opinion, would have been easily effected. There aren't any fuel tanks in the wings of the P-47D.


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## Squeelig (Jun 8, 2006)

delcyros - 

It's easy to get caught up in equations and mathematical formulas. Sal Monela asked earlier how the Hurricane fared under your analysis with 4 x 20mm guns. I'm curious myself but am gonna go out on a limb here and say I bet it would have failed far worse than the Thunderbolt with 6 x 20mm guns and yet, it was a success as far as I know. 

The Hurricane had less weight for each of its four 20mm guns than the Thunderbolt had for each of six and the Thunderbolt wing was already designed to handle far, far greater stress. It often carried 1,000 pound bombs under each wing. I don't think the the Hurricane could even handle 500 pounders. 

Anyway, maybe an armament of 2 x 20mm's and 4 x .50's would have been a better trade off along the lines of what R988 said.


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## Glider (Jun 8, 2006)

Re the discussion of the P47 with 6 x 20 I suspect your missing one vital factor. WHICH 20mm.
If you choose the Russian B20 that weighs less than an .50 M2, you can probably have 6 with ease and maybe 8 at a push


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## delcyros (Jun 8, 2006)

Since it is matter of interest, lets have a look to the Hawker Hurricane MK IIc:

exteriors:
flight envelope: low-med altitudes, GROUND ATTACK PLANE
airfoil: 19% at wingroots, 12% at wingtips (actually thicker than a Pe-2 wing)
ergo:
unlike the P47 wing, the Hurricane has a huge cross sectional wing airflow area = stiff wing stability

interiors:
steel pipes as structural elements, MKIIc wings were REWORKED METALWINGS 
guns in mid wing position
loaden weight: 8250 lbs (3746 Kg)
recoil of 4 HS MK II 20mm: 457.6 Kg
gas effects: 91,52 Kp
total recoil energy: 549 Kp
recoil/weight ratio: 0.146 for a full loaden and 0.18 for a lightly loaden plane

Conclusion: This specialized ground attack plane exceeds the 0.1 margin in recoil/weight ratio, which would effect the fighter role of this plane severely.
For a GROUND ATTACK plane it has a mediocre recoil/weight ratio.
Do not mix up fighter with ground attack issues, the statements that low alt strafing was no problem doesn´t mean that precise prolonged firing in dogfights, esspecially at altitude wasn´t a problem either.
Attention, the original Hurricane wings had to be modified AND STRUCTURALLY REINFORCED IN ORDER TO DEAL WITH THE RECOILFORCES. This added 129 lbs weight to the wings (not counting the weight for guns and ammo)! The results of these reinforcements were suboptimal, so further structural wing modifications of the MK III and subsequent MK IV and MK V had to be executed.

The problem with the P-47 is that the plane had a comparably light airframe weight and much weight for fuel, ammo, engine and loadings. However, only the airframe deals with the recoils (except for engine mounted guns, which do share a good percentage with the engine as well) at all. A fully loaden P-47(20mm mod) will have a recoil/weight ratio of 0.097, which is ok. So from this point of view, You are right. However, for a lightly loaden plane this ratio quickly rises to 0.18. 
Next problem is P-47 design. The ship is litterally designed around a huge and powerful turbosupercharger for hi alts. This isn´t necessary for a low alt ground attack plane and adds only dead weight. An optimized P-47 redesign therefore would be a major issue and could include the removal of the supercharger units, making the plane lighter. It is possible. 

I stay to my statement, the wing would need a structural reinforcement to deal with the recoilforces as did the Hurricanes wing. The plane as a whole may sustain the recoils, I admit.


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## Glider (Jun 8, 2006)

Re the statement 
Conclusion: This specialized ground attack plane exceeds the 0.1 margin in recoil/weight ratio, which would effect the fighter role of this plane severely

The records that I have seen comparing the IIB and the IIC showed that the extra firepower made precious little if any difference to the planes performance as a fighter. Can you amplify that asspect

Some strengthening is of course to be expected, you cannot expect to go from one of the most lightly armed fighters around to the most heavily armed fighter without some support but the figures were very similar.

Small point, the first IIC wings were reworked metal wings, but the vast majority were of course built that way. The switch to metal wings I always believed to be in hand for some time and you are not going to try to fit 4 x 20mm in a canvas wing, its asking for trouble.


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## Sal Monella (Jun 8, 2006)

Glider, it was my understanding as well that the Mk IIC's performance was not hampered (at least not enough to warrant any comments) in the air to air realm by the realtively massive upgrade from .303's to 20mm's. 

Delcyros, do you have any information on any purported loss of performance attributed to the 20mm's?


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## delcyros (Jun 8, 2006)

My mistake with the wings, I should go sleeping (tomorrow have to see the World Championship opening in Berlin, yeah!).
My database contains 89 types and subtypes of ww2 fighter and fighterbomber. I recalculated the recoil issues for each of them and noticed that very few FIGHTER PLANES exceeds a recoil / weight ratio of 0.1. (those to exceed have fuselage mounted or inner wing mounted guns)
Several planes had to be redesigned because of unproper recoil estimations (He-162 is a good example, the two fuselage mounted MK108 exceed the critical margin heavily to 0.143, hence the plane got a pair of 20 mm MG 151, which fit well (0.06). The later A-2 subtype was heavier and structurally enforced to carry the MK 108 again (0.11). Nethertheless this subtype had a lower performance, of course) 
However, to be more correct I would need to recalculate against the airframe weight (structural parts). This task is ongoing.
The wing / fuselage positions also play a role, the more offcenter a recoil, the more worrisome it will be (ergo, the Yak9T´s and P-39´s 37 mm centerline mounted guns produce comparably low recoil issues) generally spoken.
The VVS analyzed MK IIc and found the plane to be well suited in the ground attack and very worse for dogfights (the report quotes that prolonged deflective shooting is very difficult with the heavy recoilforces). Eventually the VVS DOWNGRADED their few MK IIc Hurricane to 0.50 cal guns which again fitted the critical recoil/weight margin of 0.1!


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## Sal Monella (Jun 8, 2006)

"The problem with the P-47 is that the plane had a comparably light airframe weight ..."

Huh? Look at the unloaded weight of the F4U Corsair, F6F Hellcat and the P-47 Thunderbolt. (The Corsair and Thunderbolt are very close in size) 

No, the P-47 did not have a comparably light airframe weight. In fact, The Thunderbolt weighed about 1,800lbs more than the Corsair in empty trim. 

Both planes sported R-2800's and the airframe of the Corsair was very robust as it was designed to crash land onto carrier decks.


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## pbfoot (Jun 8, 2006)

an interesting sidenote this little snippet is from Jim Coyne Dfc 263 Squadron who flew Whirlwinds " The crop of new pilots was posted in and the Sqn moved to Zeals to work up . This airfield was as a training ground used by the "airfield commandos" ground crews who would accompany the aircraft to europe after D Day they would be trained to defend the airfield from attack as well a refueling an servicing. The commando unit CO happened to mention that his people needed real practice at refueling and arming . Since they had no aircrew on strength he suggested that I might be interested in flying some of his a/c .Always game I did a few flights in his 
Hurricane MkIV then had a go with his Spit IX both without benefit of handbook or even good advice . I took the Spit down to the gunnery range in the channel and fired away and was startled when the Spit went into a great slide I immediatly ceased firing and pulled out of the dive realizing the slide had been caused by the a cannon jamming "


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## Sal Monella (Jun 8, 2006)

That's a really interesting account. The Hurricane Mk. IV, by the way, sported two 40mm guns! 

I wonder if anyone else knows of accounts where small fighters with wing moiunted cannons experiences such problems. Based on that account, one would expect the Hurricane Mk. IIC to have had serious problems.


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## Jank (Jun 8, 2006)

Folks, I don't think we're talking about any weight increase. 

From: http://www.geocities.com/CapeCanaveral/Hangar/8217/fgun/fgun-pe.html

Eight M2 .50's weigh in at 510.4 lbs.

Six Hispano Mk. V 20mm's weigh in at 554.4lbs. (I chose the Mk. V because it would have been later in the war after the P-47 assumed the air to ground role where six 20's would come in handy. If anyone prefers that I use the Mk. II 20mm instead, just add another 150lbs total weight for all six guns.)

The P-47 was designed to carry 425 rounds per gun of .50 cal ammo.

The projectile weight of the 20mm is just under three times that of the .50. If we assume the entire catridge weight of the 20mm is three times the entire cartidge weight of the .50, a 175 round 20mm load would weigh the same as 525 .50 rounds.

That ammunition weight x 6 guns would be equivalent to 3,150 .50 rounds.

With a full ammo load, a P-47 is already carrying the weight of 3,400 .50 rounds.

The point here is that the extra 45 pounds of gun that six Mk V 20mm's would have over eight .50's would be pretty well offset by the reduced weight of the total ammunition load because the 20mm cannon ammunition weight at 175 rounds for six guns would be less than the total ammunition weight of 425 .50 cal rounds for eight guns.

This would represent no detriment to the performance of the P-47.

Now even if they were to add 50 more pounds of steel to strengthen each wing, that would cause a negligible decrease in performance. 

Now, if you are really concerned about the small weight increase, you could reduce the 20mm ammo load to 150 rounds per gun (like any other aircraft carrying 20mm's) thereby reducing the ammunition weight to that equivalent to 2,700 .50 cal rounds. Again, the P-47 is already set up to carry the weight of 3,400 .50 cal guns. Now, even adding an extra 100 pounds of steel (on top of the 100 pounds we already added) to the wings would still leave you with an airplane lighter than a P-47 with a full load of eight .50's.

For the foregoing reasons, I say the P-47 would have maintained its air to air performance as well.


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## Glider (Jun 8, 2006)

pbfoot said:


> an interesting sidenote this little snippet is from Jim Coyne Dfc 263 Squadron who flew Whirlwinds " The crop of new pilots was posted in and the Sqn moved to Zeals to work up . This airfield was as a training ground used by the "airfield commandos" ground crews who would accompany the aircraft to europe after D Day they would be trained to defend the airfield from attack as well a refueling an servicing. The commando unit CO happened to mention that his people needed real practice at refueling and arming . Since they had no aircrew on strength he suggested that I might be interested in flying some of his a/c .Always game I did a few flights in his
> Hurricane MkIV then had a go with his Spit IX both without benefit of handbook or even good advice . I took the Spit down to the gunnery range in the channel and fired away and was startled when the Spit went into a great slide I immediatly ceased firing and pulled out of the dive realizing the slide had been caused by the a cannon jamming "



I would expect any aircraft with two cannon to have this problem if one of them should jam or fail. Must have been a nasty moment at low level.


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## Squeelig (Jun 9, 2006)

Interesting analysis Jank. I think the P-38 carried 150 20mm rounds.


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## red admiral (Jun 9, 2006)

> I think the P-38 carried 150 20mm rounds.



120round drum. The 20mm was often removed in service.


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## Twitch (Jun 9, 2006)

Since we just went through this in April I'll cut and paste what I concluded then.

Setting aside idiosyncrocies of brands of weapons within the same caliber the 20 mm round should have been the acknowledged all around most usefull. The caliber itself seems best suited to the demands of the job in mid to late WW2. While we look at 30 mm types and conclude they are almost specialized in nature as they were mounted on machines in all countries whose role was anti-heavy bomber. On the other end of the spectrum the .30 caliber was about useless except in the very early stages of the war and then mostly in the hands of virtuoso shooters. Those with thirty caliber weapons mostly used them for ranging in their heavier cannon only.

One of the problems with 20 mm magazines was simply that they held too few rounds. 60-100 rounds might have been ample for Saburo Sakai or Adolf Galland who were the products of the cream of the elite best pilots. For the pliots who weren't trained for extended periods due to the need for them to appear in action, it was woefully inadequate.

The .50 caliber weapon of any manufacture had a tradeoff that lessened punch but retained fire time. Frankly it didn't matter if a "good" grade pilot took 700 rounds to bring down an enemy with fifties where an elite pilot used 70 rounds of 20 mms. The good pilot had ample ammo for a couple kills in the magazines even at that poor strike rate. Until much later with somewhat larger mags, 20 mms could not be spread around liberally in the air by trigger-happy pilots.

In later .50s, and 20s ROF was about the same- 740 RPM. The math is easy. You got 200 20mms or 400 .50s. No the 20mm doesn't have exactly twice the killing power to make up for it. It's pretty close but weight and size restrictions make compromise necessary depending on the plane and the ordnance used if we diverge into that area beyond simple caliber cross section alone. All 20 mms are not equal. 12.7/.50s have more parody of universal application.

It's one thing to easily stick a quartet of 20 mm Hispanos inside a Tempest's wing and quite another to get four MG 151s in a Bf 109's. Even if it were possible what about room for ammo?

The pre and early war rifle caliber mentality for aerial weaponry was a throwback to WW I as was the bolt action arm for soldiers- inadequate for the modern combat that was about to unfold. 

The contention of low velocity of early 20 mm weapons is superfluous since the pilots knew their weapons and compensated to whatever degree was necessary. Any halfway sharp aerial gunman could alternate between high and lower velocity weapons by selecting their different triggers then mentally and physically compensate lead, drop and deflection. This was primary stuff. We idiot savants who know all the statistics of all the planes and weapons haven't got a clue to aerial gunnery beyond flight sims.

.50 calibers were acceptable but becoming inadequate by late 1944 were as 20 mms had improved in velocity to the point of being the ideal caliber for times. Even so few planes carried a lot of rounds per gun. 20s should be considered the prime caliber of the aerial war as most effective I believe.

American pilots liked the 20 mm weapon when they had it. P-38, Spit, and F6F pilots I know were happy with it as they should be. Of course they were mixed with .50 cals. None gave a bucket of spit for .30s no matter how many were mounted. 

I still stand by the statement, "Frankly it didn't matter if a "good" grade pilot took 700 rounds to bring down an enemy with fifties where an elite pilot used 70 rounds of 20 mms." - Because you gotta be good enough to put ordnance on target in the first place, it matters not what caliber gun you got. An "average" skill shooter can simply procure more hits with fifties than with 20s because he's not hording rounds.

Idealy 20/50s would be the perfect armament. You range in and begin damaging with the fifties and touch the cannon trigger to follow up. Repeat as necessary for results. 

It is interesting to note that even cannon-trained air forces like the Luftwaffe continued to mount .30/.50 calibered weapons in addition to cannon. They were there for 2 reasons- to range in and to actually shoot down E/A when cannon shells were gone. Of course almost immediately .30 caliber was obsolete as a killing tool in WW 2. If the half inch caliber wasn't better the Luftwaffe wouldn't have used them on Bf 109s and Fw 190s in place of the .30 cal equivenent- MG 131 vs MG 17.

Every American pilot I know liked 20s too. 

There was a P-38 the 49th had with 6 50s in the nose. Bong didn't like it and most of the pilots felt the plane's balance was ruined. So the weight of more 20 mms would have been detrimental.


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## Glider (Jun 9, 2006)

If I may comment on parts of your posting:-

a) In later .50s, and 20s ROF was about the same- 740 RPM. The math is easy. You got 200 20mms or 400 .50s. No the 20mm doesn't have exactly twice the killing power to make up for it.
Reply) The USN considered the Hispano 20mm to be three times as effective as the .50M2

b) The contention of low velocity of early 20 mm weapons is superfluous since the pilots knew their weapons and compensated to whatever degree was necessary. 
Reply) Most pilots had huge difficulty hitting anything. Only the real experts had any idea as to compensating for differing trajectories.

c) You range in and begin damaging with the fifties and touch the cannon trigger to follow up. 
Reply) My comment is similar to my previous observation. If you saw your opponent ranging with the smaller caliber before firing with the larger, you knew that you were in trouble as the person doing it was a highly experienced pilot. The vast majority of pilots would let fly with whatever they had. Tragically a lot of pilots died before they had a chance to fire at anyone.

D) They were there for 2 reasons- to range in and to actually shoot down E/A when cannon shells were gone. 
Reply) The reason that I have seen was to give you some self defence capability once the cannons had run out of ammo. Most planes didn't have a gauge to tell you how many rounds you had left. Some airforces put different coloured tracer into their guns to give an indicator that ammo was running low. 

E) .50 calibers were acceptable but becoming inadequate by late 1944 were as 20 mms had improved in velocity to the point of being the ideal caliber for times.
Reply) Totally agree


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## delcyros (Jun 9, 2006)

Sal Monella said:


> "The problem with the P-47 is that the plane had a comparably light airframe weight ..."
> 
> Huh? Look at the unloaded weight of the F4U Corsair, F6F Hellcat and the P-47 Thunderbolt. (The Corsair and Thunderbolt are very close in size)
> 
> ...



-"comparably" means in comparison to the Hurricane (not absolutical but relative, e.g. in percentages)
I do enjoi the postings, all very interesting discussion. If anyone may help me out with a typical weight comparison Huricane / P 47D25 I could be more concrete with a calculation of structural loadings due to recoil forces.
-The idea to change HS MK II with MK V is a good one. The later has a slightly reduced recoil due to lower muzzle vel. Nethertheless, I do believe that 50 lbs are insufficiant for 6 fixpoints.
-The big advantage of 20 mm rounds are the higher HE content. Did the RN also developed mine rounds for them?


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## Glider (Jun 9, 2006)

red admiral said:


> 120round drum. The 20mm was often removed in service.


I admit to never having heard of the 20mm being taken out in actual service. Must have played hell with the weight distribution.


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## Jank (Jun 9, 2006)

Glider said, "The USN considered the Hispano 20mm to be three times as effective as the .50M2"

That is true for close range. It dropped to 2-1/2 times beyond that. The Report of Joint Fighter Conference mentions the 2-1/2 times to 3 times at close range figure from the USN tests. 

On a related note, it is too bad the USAAF's high velocity .60 cal gun never went into production. That would have been a sweet gun. 3,600 feet per second with a very high ballistic coefficient.


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## Sal Monella (Jun 9, 2006)

delcyros, when I said, "No, the P-47 did not have a comparably light airframe weight., I was referring to a comparison with the Hurricane. I used the Corsair's similar size and less weight to illustrate that the P-47 really was built like a tank - unlike the Hurricane.

You mentioned that the Hurricane had 129 lbs of steel reinforcement in each wing in order to upgrade from .303's to 20mm's. In going from .303's to 20mm's, you are asking far more from the Hurrican'e existing wing structure than you would ask from the Thunderbolts in going from .50's to 20mm's.

The Thunderbolt was overengineered where structural integrity was concerned. I have a publication from Republic Aviation that states that the maximum wing carried bomb load for a P-47M is 1,600lbs under each wing. As you probably know, the P-47M had the same wing and wing to body structure as the P-47D.

Allow me to analogize here. Pretend you don't know that the P-47D's wings were designed to handle 1,600lb bombs. 

If I told you that I think the P-47 could handle some new powerful bomb weighing 1,350lb under each wing, I would expect you to lecture me on how the wings would need to be reinforced since we all know that the heaviest bombs the P-47 carried were only 1,000lbs.

Well, we all know that the P-47 carried eight .50's with 425 rounds per gun. Why are you so sure that the wings would need to be reinforced at all, and even if so, with more than 100 pounds of steel, to handle a compliment of 20mm guns and ammunition that weighed the same amount as eight .50's with full loads of ammunition?

You are about to exclaim, "The recoil! The recoil!"

Yes, the recoil. Keep in mind that the Hurrcane wasn't over engineered for tank-like strength. Unlike the Hurricane, the Thunderbolt's wings were designed to handle bomb loads that were full 60% heavier than the heaviest bombs that could be carried by fighters (1,000lbs.) when the Thunderbolt was designed. 

It is quite possibole that those same wings designed to carry 1,600lb bombs might do just fine with 100 pounds of steel reinforcement. Hell, the little Hurricane, designed to handle .303's, was successfully structurally re-engineered with just 129lbs of steel reinforcement!


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## Jank (Jun 10, 2006)

F6F Hellcat

Length - 33'7"
Wings - 42'10"

Empty weight - 9,042lbs.

F4U-1 Corsair

Length - 33'4"
Wings - 41'

Empty weight - 8,980lbs.

P-47D Thunderbolt

Length - 36'2"
Wings - 40'9"

Empty weight - 10,700lbs.


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## delcyros (Jun 10, 2006)

Thanks Jank.
I originally had a weight distribution table in mind, like this example (He-162A1, excerpt from my database)

airframe: 839 Kg (1847.5lbs)
engine and related equipment: 673 Kg (1482lbs)
all time equipment: 11 Kg (24lbs)
--------------------------------
empty weight: 1523 Kg (3353lbs)
--------------------------------
+ additonal equipment(including guns, optics, ejection seat): 339 Kg (746.5lbs)
+ crew: 100 Kg (202 lbs)
--------------------------------
"Rüstgewicht": 1862 Kg (4100 lbs)
--------------------------------
Fuel: 780 Kg (1718 lbs)
ammo: 58 Kg (128 lbs)
--------------------------------
loadings: 838 Kg (1845 lbs)
--------------------------------
usual take off weight: 2800 Kg (6166 lbs)
--------------------------------
additional weight (not included): jettisonable rocket assitence take off booster
--------------------------------
-guns are fuselage mounted, guns do not share recoil with the engine.
relative loading factor: 100%
off centre recoil: little
gun recoil factor (2 MG 151/20): 0.0593
composite structural recoil-weight: 0.198
relative structural recoil strength (1.0=average, higher=better): 1.685
--------------------------------

Sal, I do see Your points. But I cannot shift from Hurricane to F4U that easily (lag of database), thats a lot of computing for me. So please tell me F4U or Hurricane? 
No, I didn´t know that the P47 wings were designed for 1600 lbs bombs, thanks for Your clarification.
The ammo You had in mind would weight more thanks to non projectile weight related equipment (cases, boxes, "Gurte"(don´t know the correct engl. translation), but this isn´t my concern as You recognized.
Bombloads and recoil are physicly different loadings with different vectors, loads and different loading types (recoil=impulse). You cannot draw experience from one to the other.



> It is quite possibole that those same wings designed to carry 1,600lb bombs might do just fine with 100 pounds of steel reinforcement. Hell, the little Hurricane, designed to handle .303's, was successfully structurally re-engineered with just 129lbs of steel reinforcement!"
> 
> 
> > succesfully is relative, low cross sectional strength remained an issue for the MK IIc and lead to repeated redesign and structural reinforcements of the wings in subsequent types. The plane was able to handle four 20 mm wingmounted guns, agreed upon that.
> > I do have one factor for my argumentation left: A six 20 mm gunned version (either P-47, F4U or P-80) was never executed. So I ask why, if the relative loads would be the same in comparison with 0.5´s? The answer only can be because of the issues of recoil and / or recoil related structural reinforcements.


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## Jank (Jun 10, 2006)

delcyros said, "I do have one factor for my argumentation left: A six 20 mm gunned version (either P-47, F4U or P-80) was never executed. So I ask why, if the relative loads would be the same in comparison with 0.5´s? The answer only can be because of the issues of recoil and / or recoil related structural reinforcements."

First, I never said the relative loads would be the same with six 20's as eight .50's. I pointed out that the weight load could be the same or less depending on the ammunition load carried. I also indicated that given the overengineered strength of the P-47's structure (By way of example, it was designed to handle a far greater bomb load for instance than it actually carried into combat and thus may have been able to handle far greater gun recoil forces as well.) it was possible that little if any additional weight would be required to reinforce the wing. Keep in mind that the little Hurricane, designed to handle a compliment of .303 machine guns, only required 129lbs of reinforcement (your claim) in each wing to handle 20mm cannons.

As for your calling into question why 20mm guns weren't used if they were possible, I think you know better than to pose such a specious point. You know very well that there are a whole host of considerations that go into the choice of armament for an aircraft that have nothing to do with whether it is possible or better.

The .50 was performing just fine and to quote one P-47 pilot, ""When eight fifty caliber machine guns converge at 200 yards, things happen." A switch to 20mm cannons would have only had a benefit for ground attack as eight .50's often caused enemy fighters to just desintegrate or explode. Targets succeptible to 20mm fire were usually succeptible to damage from .50 rounds as well. The USAAF also liked uniformity in production and application for reasons of efficiency.

We all know that the .50 was obsolete in the Korean conflict as an air to air weapon. Quite often, Mig-15's made it back with many hits from .50 cal guns. The USAAF knew the same thing the USN knew in WWII and that was that the 20mm was 2-1/2 to 3 times more effective than the .50. So why did the F-86 utilize six .50's instead of four 20mm's? The answer to that question tracks the answer to your question about why the USAAF outfitted its late war WWII fighters with 20mm guns.


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## delcyros (Jun 11, 2006)

Jank said:


> First, I never said the relative loads would be the same with six 20's as eight .50's. I pointed out that the weight load could be the same or less depending on the ammunition load carried. I also indicated that given the overengineered strength of the P-47's structure (By way of example, it was designed to handle a far greater bomb load for instance than it actually carried into combat and thus may have been able to handle far greater gun recoil forces as well.) it was possible that little if any additional weight would be required to reinforce the wing. Keep in mind that the little Hurricane, designed to handle a compliment of .303 machine guns, only required 129lbs of reinforcement (your claim) in each wing to handle 20mm cannons.
> 
> The .50 was performing just fine and to quote one P-47 pilot, ""When eight fifty caliber machine guns converge at 200 yards, things happen." A switch to 20mm cannons would have only had a benefit for ground attack as eight .50's often caused enemy fighters to just desintegrate or explode. Targets succeptible to 20mm fire were usually succeptible to damage from .50 rounds as well. The USAAF also liked uniformity in production and application for reasons of efficiency.



To the earlier part of Your post I want to underline that the P-47 may carry these loads (6 HS MKV, wingmounted) with a structural reinforcement of the wing. I am not familar with the P-47 wingstructure, only knowing she is thick skinned and has a rugged fuselage. Nethertheless it makes a difference to handle bombs or recoils. Whether or not the original wing structure was overdesigned enough to handle the recoil of three times a 0.5 cal. without reinforcement is very much of speculation. I do hear it for the first time. Would be interesting to know if and to what degree structural redundance played a role in her design.
At least, there are tradeoffs for such an overgunned P-47:
heavy off-centre recoil (always makes problems at prolonged aiming&shooting and may cause loss of controll once assymetric recoil [due to one jammed or damaged gun] ocurred), recoil-weight on the upper edge of what is usual, at least for fighterplanes (this may have low impact at low alts but grave impacts at hi alts), a lower ammo-load with a reduced total firing time (reducing the tactical flexibility of the A/C), higher vulnarability (due to unprotected ammoboxes in the wing), possible performance reduction (due to increased weights of the wings). 

Does any of You have the weight of the P-47D-airframe? (exclude all equipment, fueltanks and engine related equipment. Only weight for load distributing structural parts of the airframe and the fuselage)

I cannot agree more on the latter part, Jank. The 0.50 was a decent gun and more than adaequate for USAAF needs, at least against the Luftwaffe fighter force. My estimation is that the use of 0.50 was excellent for hi alt fighter, such as the P-47.


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## wmaxt (Jun 11, 2006)

red admiral said:


> 120round drum. The 20mm was often removed in service.



Where did you find this I've never heard of either. 20mm is often mentioned as the pilots favorite gun, and 150 is the standard ammo capacity though some references cite slightly reduced count (120) for added reliability but not as the capacity.

wmaxt


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## Glider (Jun 11, 2006)

If it helps one P80 was tried with 4 x 20 instead of the 6 x .50 but it wasn't taken up. If anyone knows why it might be a valuble input into this debate.


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## Twitch (Jun 12, 2006)

I would bet that the 20 mm P-80 was tried after a whole bunch of .50 cal. planes were already flying and standardization was what the USAF was thinking. Just a guess but the military brass thinks in those strange ways.

Here's some more random thoughts on guns and pilots. We assume and make excuses for the "average" pilot's ability to hit targets with ordnance. As we know the Imperial Japanese Navy, Air Force and the Luftwaffe had towering requirements for pilots which exceeded more than just gunnery. The men accepted were few and they were the elite of the elite in all around perfection in aerial combat.

These men were shooters and could hit with any weapon given them. They made no excuse that their ordnance was too slow or too weak. They knew how to shoot and hit the target even alternating between weapons of different projectile velocities.

They weren't equal to newly graduated American pilots by 1944 who went on to fly 149 missions and score 2 kills. While the mass training of men that came out as "pretty good" pilots was enough by that time in the war, it was not comparable to IJN or Luftwaffe meistros that were trained in 1939 and were "excellent." The "average" pilots from those ranks were far above the American "average" of 1944.

Of course we know the loss of the elite cadre was devastating to the Germans and Japanese. They couldn't be easily or quickly replaced. Neither country envisioned a conflict where vast hordes of airmen would be required in a protracted struggle. The American system produced quantities that simply overwhelmed its foes.

Fifty calibers could kill at a mile and there were cases of that happening. There were gunnery virtuosos in the USAF. Being that I have long associated with aces I never heard "average" guys whining about real or perceived advantages the enemy had. Fifties were adequate weapons. 20 mms had more punch but magazines held fewer rounds. So were fifties better for the "average" pilot who could squander ammo to some extent? Perhaps. But not hitting with 400 rounds of .50 ammo is the same as not hitting with 150 rounds of 20 mm. If you can't hit with 50s, 20s aren't going to do you any good!

The truly great American aces had the "force" like Japanese and German aces did. They killed with fifties at up to 1/2 a mile away on a regular basis. Their planes had enough ordnance to make multiple kills. What else do you need if you have skill?

This was hammered home to me by 10 victory Korean War ace Hal Fischer. Remember the F-86's fifties had a faster firing rate than the WW 2 weapons. They carried 297 RPG. I was thinking that was not much ammo like most people here asked him about it. 

Fischer grinned in amusement to my lame question. "More than enough. A one second burst was all that was needed," he nearly whispered. "And it doesn't take much to damage a turbine, he added. 

When I asked if the 6 guns was sufficient his soft voice continued," Four would have been enough. It takes less rounds to kill a jet due to its fewer engine parts."

Another 10 kill ace Ralph Parr answered my question of the adequacy of fifties with, "sure 20 mms would have been great." Yet in the next sentence explained how he used the F-86F's A-4 lead computing gun sight to take out his seventh victim at a phenomenal 4,800 feet!! 

Gunther Rall smiled when he explained how it was "quite easy really if you have the experience to alternate bewteen the MG FF and the MG 17 or 131," when I asked about velocity differentials.

It was an even sixty rounds per plane times six. That's all it took for Hans-Joachim Marseille to down six Tomahawks of the British Desert Air Force (DAF). What's more amazing is that the 20-millimeter nose cannon had jammed after only ten rounds were fired. The Star of Africa finished them all off with the pair of 7.9 mm MG 17s above the cowl!

So if .50s were so "average" why the heck did the military continue to arm planes with them? I can see that in WW 2 the industial-military complex was geared for the Brownings' production. This is like the many other weapons, vehicles or equipment produced- even if something demostrably better was found the alteration to production facilities might have been more than was deemed acceptable at the time. IE., don't rock the boat. 

I think that goes back to the 20 mm vs the .50 calibered P-80. There was probably a USAF comment like "yeah we already produced 1,000 with fifty calibers and maintence and is set up for that on form # AP-34590 for ordnance procurement, bla, bla, bla."


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## plan_D (Jun 12, 2006)

Excellent post, Twitch. But I do not think anyone has stated the .50 cal to be average. The feeling of most people on this site is that the .50 cal was enough to bring down any fighter. But the 20mm was, obviously, more destructive and probably more flexiable because of it's ability to take on both fighters and bombers. 

I have to ask, did any of the Korean pilots you spoke to mention anything about MiGs escaping with the battle damage they'd inflicted on them?


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## Jank (Jun 12, 2006)

Twitch said, "It takes less rounds to kill a jet due to its fewer engine parts."

Perhaps but in Korea, the planes had far sturdier construction as the speeds and g-forces they were subjected to were greater. I understand that the non-explosive .50 was obsolete due to the greater resistance the thicker skin and structural pieces posed to the non-explosive .50.

I have read a number of accounts of .50's not getting the job done. That's not to say that there weren't plenty of instances where it obviously did but a lot of Migs made it back peppered pretty good with .50 hits. F-86's, on the other hand, didn't fare so well against non-critical hits from the Mig's 23mm (.92 cal.) explosive rounds.

The USAF was stubbornly wedded to the .50 in an era where literally everyone elso had figured out the advantages of the 20mm. The USN was ahead of the curve and outfitted even its propeller driven Corsairs and Skyraiders with 20mm's. In WWII though, against enemy fighters, it did just fine.


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## Glider (Jun 12, 2006)

I think you will find that the 20mm armed P80 was around the 380th to be built which was early in the production run.

Janks posting sums it up.


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## delcyros (Jun 12, 2006)

Korea was different in many ways.
Funny thing is I just read the opposite opinion from a veteran, describing how much it took to knock it out with 0.50 cal. because the engine had fewer parts and could take more punishment. Sounds logical if we factor the vulnarability of piston engines due to cooling equipment properly.
I think the P80 was tried with four 20mm, am I correct?


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## Glider (Jun 13, 2006)

Re the damage I suspect it would depend on where you hit. If a .50 hit the blades then its almost certain to almost disintigrate as the early engines didn't contain damage very well. The blades would fly in all directions and totally take out the engine and anything else around it. 
If the .50 hit any other part of the aircraft then it wouldn't cause as much damage due to the additional strength required.

If a Mig 15 hit the F86 then it was almost certain to go down. Few survived a hit from the 37mm and one hit from the 23mm had a high probability of destroying the F86. It should be remembered that her engine was equally liable to self destruct and the 23mm chucks out a lot of shrapnel any piece of which would take out the engine if it hit the blades.

The ability to contain damage is still a major part of the engine design and is a difficult test to pass.


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## Twitch (Jun 13, 2006)

Thicker skin mentioned by Jank is exactly why you'd want armor-piercing power such as the API belts had. Explosive shells exploding outside the fuselage do far less damage than ones going boom inside.

The NS-23 cannon had a low cyclic speed of just 550 RPM and a slower muzzle velocity of 690 meter per second. Forget the NS- 37 unless sheer luck was at work with a 250 RPM but with a quicker 900 MPS.

Actual muzzle power scales show the MiG 15 lower at 2,070 vs the Sabre's 2,200 but wins in weight of fire per second at 8.69 kg to the F-86A's 5.82 with the .50 M3 weapons firing at 1,200 RPM.

The FJ-2 Fury with 4- Mk. 12 20 mm cannon had a muzzle power of 3,740 and a weight of fire of 7.32 kg. The 4X20 mm Panthers and Banshees with Hispanos had a 2,600 muzzle power with 7.37 kg weight of fire. 

When the F-86H arrived in combat with 4 M39 20 mms it boasted a muzzle power of 6,070 with 11.44 kg weight of fire. 

The MiG 15's NS 23s had just 80 rounds per gun! Early on the inadaquacy of these weapons was a concern so the Nudelmann 37 mm was installed but carried just 40 rounds. This gave 8.7 seconds of 23 mm fire and 10 seconds of 37 mm. The 267 RPG of the F-86A-F gave 13.3 seconds of fire.

While we all know if the MiG 15's performance abilities it still comes down to putting ordnance downrange and on target. Since MiG drivers didn't have G suits the F-86 guys had it all over them in that respect all the time. You can't shoot strait when you're being slammed by Gs. The radar controlled, lead computing Mk. 18, A-1CM and later A-4 gunsights had no Soviet counterpart. THAT alone compensated for any perceived advantage of armament.

The MiG 17 carried over the same 23/37 mm mix but the newer NR 23 mms fired at 1,100 RPM now. The 37 was finally dumped and replaced by a 3rd 23 mm weapon.

In fact the only saving grace was the intrusion of experienced Russian pilots in the mix. There were only 2 North Korean aces with 6 and 8 kills respectively. The Chinese produced 6 aces with a combined total of 48 kills. So if it was up to indigenous pilots their performance was sadly lacking.

This is the same kind of results as with the Gulf War- decent imported hardware but the inability to successfully engage in the air and scored ZERO kills.


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## Glider (Jun 13, 2006)

Twitch I seem to have different numbers to you. According to my records the NS 23 had a ROF of 690 RPm not 550 and a MV of 740m/s not 690m/s.

These are not fantastic but not bad for the size of the weapon and make it quite a dangerous weapon against other fighters. You are correct re the 37mm which was only useful against bombers. 
The observations re the radar gunsight are also spot on once it arrived in theatre. However the early F86 didn't carry it and neither did the other aircraft so the Mig 15 still made a decent showing.


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## DAVIDICUS (Jun 23, 2006)

Sal, you may have the same or a similar publication as I have. The surprising thing is that not only is the P-47M designed to carry 1,600lb bombs under each wing but also a 1,000lb bomb under the belly. That's 4,200lbs of bombs!

The P-47N has the same bomb capacity under the wings but only a 500lb bomb under the belly for a 3,700lb bomb load.

While the design capacity was high though, I have never heard of P-47's carrying more than 2,500lbs of bombs.


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## Tony Williams (Jul 3, 2006)

Sorry to arrive late for this one, gentlemen - I have a few comments.

The US outfit of six (or eight) .50s was entirely adequate to deal with fighter opposition in WW2. However, good 20mm cannon offered a better power-to-weight ratio because of the explosive/incendiary contents of their shells, so you could achieve equal destructive effect with a lighter armament weight - or faster destruction with the same weight. The RAF found that their normal allocation of 120 rpg for the 20mm was adequate, few pilots expended all of their ammo on a mission.

I have never read of any inherent problems caused by the recoil of 20mm cannon. The British found specific installation problems which had to be solved on every plane with wing-mounted Hispanos, but solving them was a matter of fine-tuning the installation. The Hurricane IIC was not designed as a specialised ground-attack plane (that was the IID, with two 40mm guns and more armour) but as a fighter: the fact that from about 1943 it was used for ground attack was simply because its performance as a fighter was outclassed by then. 

Note that in every air force which had a choice of good HMGs or cannon, they went to cannon even when they didn't have heavy bombers to deal with (the Soviets had the excellent 12.7mm Berezin UB series, as powerful as the .50 M2 and lighter and faster-firing, but they still switched to the heavier, slower-firing 20mm ShVAK where they could). Even the USN wanted to move to cannon, being held up by the unreliability of the US-built Hispano. The USAAF was the only organisation to prefer the HMG.

In Korea, it took an average of over 1,000 .50 cal rounds to down each MiG-15. The MiGs sometimes returned to base with up to fifty .50 cal holes in them. The USAF responded to criticism of the .50's ineffectiveness by setting up Project GunVal, equipping some F-86's with 20mm cannon and trying them in combat. After Korea, every new US fighter had 20mm cannon.

If you're interested in aircraft guns, you'll find a lot of articles, data, illustrations etc on my website.

Tony Williams: Military gun and ammunition website and discussion forum


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## pasoleati (Jul 3, 2006)

Finnish pilots found the .50 inadequate to deal with planes like the Il-2 and the Pe-2 and even the I-153 had pilot armour often sufficient to resist .50 fire.


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## Tony Williams (Jul 3, 2006)

pasoleati said:


> Finnish pilots found the .50 inadequate to deal with planes like the Il-2 and the Pe-2 and even the I-153 had pilot armour often sufficient to resist .50 fire.


True, but IIRC their fighters only had a couple of .50s and they were synchronised, drastically reducing their rate of fire. The .50 was effective in USAAF planes because it was used in quantity.

Tony Williams: Military gun and ammunition website and discussion forum


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## delcyros (Jul 3, 2006)

Tony Williams said:


> I have never read of any inherent problems caused by the recoil of 20mm cannon. The British found specific installation problems which had to be solved on every plane with wing-mounted Hispanos, but solving them was a matter of fine-tuning the installation. The Hurricane IIC was not designed as a specialised ground-attack plane (that was the IID, with two 40mm guns and more armour) but as a fighter: the fact that from about 1943 it was used for ground attack was simply because its performance as a fighter was outclassed by then.
> 
> forum




Welcome to our discussion, Tony Williams!
The recoil phenomen is a troublesome one. There are few docs, dealing completely with them and even in cases when the recoil made use impossible (Fw-190 with underwing mounted MK 103), recoil isn´t adressed as the main problem. I may submit an excerpt from my database which clearly shows that recoil/weight ratios are specific ones for fighter A/C, which -beside from a very few exception- generally avoid a ratio over .1. Attack A/C do have a higher ratio, but are often limited to low level (high air density) purposes.

best regards,


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## Tony Williams (Jul 3, 2006)

Recoil is a complex subject with a number of different aspects.

First of all, guns of equal power do not necessarily produce equal recoil effects on the aircraft. There is a difference between the recoil impulse generated by a cartridge - which basically equals (projectile weight x muzzle velocity) + (propellant weight x escape velocity) - and the severity of the recoil kick transmitted to the mounting. Heavy guns recoil more slowly than light ones. Certain types of gun action also soften the recoil kick by spreading it out over a longer period, for example long-recoil designs (the P-39's 37mm M4 and the Hurricane IID's 40mm Vickers) and API blowbacks (Oerlikon FF, MG-FF, MK 108 ).

Then there was the effect of the mountings, some of which could absorb and smooth out the recoil kicks better than others. The US Edgewater mounting was particularly good in this respect and was promptly adopted by the British. This is an extract from 'Flying Guns – World War 2: Development of Aircraft Guns, Ammunition and Installations 1933-45' by Emmanuel Gustin and myself:

"To give some examples, the .50" Browning in the Spitfire IX had a peak recoil load of 2,700 kg (which was reduced to 1,000 kg when the absorbent Edgewater mounting was used); the 20 mm Hispano peak load varied between 1,450 kg (Edgewater) to 4,000 kg depending on the mounting; while the 40 mm Class S peaked at just 2,270 kg and the 57 mm Molins gun at 2,900 kg. Of course, the total recoil of the big guns was far greater than the smaller ones, but it was spread much more evenly through the firing cycle."

It is worth noting that there are different effects on the aircraft where recoil is concerned; the effect on the aircraft's structure and the effect on its flight attitude. The effect on the structure mainly concerns the degree of vibration caused, and this is where the type of mounting matters such a lot. The effect on the flight attitude depends on the total recoil, and the location of the guns. Firing powerful underwing guns tended to make the nose drop, which meant that only two or three shots could be fired before reaiming. This certainly affected the Il-2M3 with its NS-37 cannon, and also the Hurricane IID. It may also have partly explained why the Fw 190 + MK 103 was not a successful combination (another possible reason is that the mounting and/or wing were not rigid enough to maintain accuracy).

And of course, if a powerful wing-mounted gun jammed, the aircraft would slew sideways from the recoil of the gun(s) on the other side, making aiming impossible. As a matter of interest, with modern fighters in which the only gun is mounted to one side of the centre line, the rudder automatically corrects for this when the gun is fired.

Tony Williams: Military gun and ammunition website and discussion forum


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## Jank (Jul 3, 2006)

Tony, I have read your work and it is very illuminating.

To cut to the chase, do you think that recoil forces would have prohibited the P-47 from carrying six 20mm cannons (three in each wing as opposed to the two in each wing that the Hurricane carried)?


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## delcyros (Jul 3, 2006)

Old question.
wOULD IT BE POSSIBLE? YES IT WOULD.
Would it be possible without structural reinforcements? Probably not.
Would the recoil effects have an impact for prolonged firing aiming in hi alt?
Depends. The mountings will play a role. But I suspect that the dispersion field of the 20mm would be larger in such an event. Nose / engine mounted guns do behave somehow better than mid wing mounted ones.

regards,


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## Jank (Jul 3, 2006)

To put a sharper focus on the question, you contend that the structural reinforcements (if they were necessary) would inhibit performance due to excess weight.

I have already shown that the weight of 8 .50's with maximum reserves of ammo in a P-47 would weigh about the same as six 20mms with 175 rounds per gun. (My earlier post follows in Italics)
------------------------------

From: http://www.geocities.com/CapeCanaver...n/fgun-pe.html

_"Eight M2 .50's weigh in at 510.4 lbs.

Six Hispano Mk. V 20mm's weigh in at 554.4lbs. (I chose the Mk. V because it would have been later in the war after the P-47 assumed the air to ground role where six 20's would come in handy. If anyone prefers that I use the Mk. II 20mm instead, just add another 150lbs total weight for all six guns.)

The P-47 was designed to carry 425 rounds per gun of .50 cal ammo.

The projectile weight of the 20mm is just under three times that of the .50. If we assume the entire catridge weight of the 20mm is three times the entire cartidge weight of the .50, a 175 round 20mm load would weigh the same as 525 .50 rounds.

That ammunition weight x 6 guns would be equivalent to 3,150 .50 rounds.

With a full ammo load, a P-47 is already carrying the weight of 3,400 .50 rounds.

The point here is that the extra 45 pounds of gun that six Mk V 20mm's would have over eight .50's would be pretty well offset by the reduced weight of the total ammunition load because the 20mm cannon ammunition weight at 175 rounds for six guns would be less than the total ammunition weight of 425 .50 cal rounds for eight guns."_

------------------------------

The only issue then is the recoil of the six 20mm's and whether structural reinforcments (if even necessary) would be too heavy and inhibit the performance of the P-47.

I say no. You say yes.

Shaving the 20mm ammmunition load from 175 to 150 rounds per gun would decrease the weight by an amount equivalent to 450 .50 cal rounds. (six 20mm guns times 25 rounds each = 150 20mm rounds. Each 20mm round weighs as much as three .50 cal rounds so that's equivalent to 450 .50 cal rounds.)

Bottom line is that you could easily add over 100 pounds of steel to each wing with no adverse effects on performance.


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## delcyros (Jul 3, 2006)

Jank said:


> I say no. You say yes.
> 
> Shaving the 20mm ammmunition load from 175 to 150 rounds per gun would decrease the weight by an amount equivalent to 450 .50 cal rounds. (six 20mm guns times 25 rounds each = 150 20mm rounds. Each 20mm round weighs as much as three .50 cal rounds so that's equivalent to 450 .50 cal rounds.)
> 
> Bottom line is that you could easily add over 100 pounds of steel to each wing with no adverse effects on performance.



I am open to change my mind for good arguments, Jank. You very well factored gun weights and projectile weights but what about the space? It certainly is possible to storage 175, maybe even as much as 200 rounds pg into the wing. So, I admit that this is possible in the layout You suggest. 
Revising the entire thread isn´t necessary. 
However, let´s assume there are no significant recoil issues performance issues, would this armement be benefitial?
For ground attack purposes without doubt, for interceptions as well but what about dogfights in hi alt? The dispersion pattern for 20 mm´s is larger than for .50´s, the effective firing distance drops, with reaching Mach 1.5 at ~450m for the MK V and ~ 600 m for the MKII (compare 900 m for the .50 cal), implying a less favourable projectile trajectory beyond these distances. Still, I believe 450m are well beyond usual firing distance prior to the introduction of computing gunsights late in ww2. However, increasing the velocity by 50% means doubling the chance of hitting in deflection shootings. The battery output of the P-47 drops from ~100 rounds per second to ~70 rps. Take notice that convergance firing requires a good output. All in all the chances to hit are reduced in effective firing range and probability to hit for a rapid improve in destructive force. I personally question that this is a good development, at least with the thread scenario for the P-47 in mind. There were no bombers to take down but Luftwaffe fighter A/C.


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## Jank (Jul 3, 2006)

delcyros,

In post #19 above, you said, *"A six 20 mm upgrade for the P-47 would therefore have more worse tradeoffs than benefitials, except for the use as specialized ground attack plane."*

I responded in the following reply at post #21 saying, *"I thought it was clear that that was what we were talking about. 

Since the P-47 did just fine in the air to air role with eight .50's, (Almost all of the other fighters in the U.S. arsenal did fine with six .50's.) an outfit of six 20's would have been an improvement for the air to ground role which the P-47 assumed heavy responsibility for later in the war."*

Yes, all along, I have been talking solely about increasing the air to ground destructiveness.


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## Tony Williams (Jul 3, 2006)

I have no specific information relating to the installation of cannon in the P-47; I don't know if it was ever considered. However, on the face of it I doubt that there would have been any problems in fitting six Hispanos. Don't forget that a six-cannon installation was plannned for the Spitfire Mk IV (and a mock-up of the installation constructed) and the Martin Baker MB3 was designed around six wing-mounted Hispanos. These were intended to be air-superiority fighters, not ground attack planes. As they were very small and light aircraft by comparison with the P-47 (which also had a reputation for great strength and ruggedness) then I can't imagine that the big fighter would have had any problems with such an armament, and it would have significantly magnified its destructiveness in both aerial combat and ground attack.

I doubt very much that accuracy would have suffered either: the Hispano was actually a more accurate gun than the Browning (which was one of the least accurate aircraft guns). 

The absolute range of the .50 Browning was greater than the Hispano, simply because the bullets had a superior aerodynamic shape compared with the rather blunt cannon shells - the muzzle velocities were similar. However, this was not an issue at normal combat ranges and, of course, the higher the altitude, the less significant air resistance becomes. 

The RAF seemed satisfied with four cannon, because they found them enough to do the job. The first jet, the Meteor, was planned to have six Hispanos (possibly because it was expected that the high speeds of jet combat would have minimised firing opportunities) but the installation of the extra two caused problems so they were dropped.

Tony Williams: Military gun and ammunition website and discussion forum


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## Jank (Jul 3, 2006)

Tony, I obviously agree with your opinion on the issue of six 20mm's in a Thunderbolt.

On another note. I'm curious as to your statement that *"I doubt very much that accuracy would have suffered either: the Hispano was actually a more accurate gun than the Browning (which was one of the least accurate aircraft guns)."*

I was under the impression that the M2 was quite accurate. The .50BMG cartridge is considered an inherently accurate round. I have seen guys consistently hit 8" gongs at 600 yards with rifles chambered for the round.

Why was the M2 not considered accurate? Was it poor mounts that failed to hold the gun securely in place under fire? 

Can you point me to some souces for information on the lack of accuracy of the M2?


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## Tony Williams (Jul 3, 2006)

The problem was not the ammunition but the gun. The Browning was a short-recoil design in which the barrel moved to and fro - it was not fixed in relation to the rest of the gun, as it was in the Hispano. Short-recoil guns can still be accurate if they are assembled carefully with tight tolerances, but tight tolerances reduce reliability, so the guns were made deliberately 'sloppy'. 

A friend of mine made some studies of aircraft gun dispersion and came up with figures of 4 mils for the Browning and 3 mils for the Hispano (for 75% of the shots - double for 100%). Mountings - and especially wing mountings - added more dispersion due to flexibility, and what the RAF called 'aim wander' (the tendency for the plane to slide off-target while the pilot was firing) had even greater effects. I discovered some official stats about the RAF's fighters with eight .303 Brownings which showed that in ground tests each gun had a dispersion of 10 mils as installed (which is to say a spread of one metre at 100 metres range), with 5 mils for the 75% figure.

Tony Williams: Military gun and ammunition website and discussion forum


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## Jank (Jul 3, 2006)

I hope you stick around on this forum Tony.

I think we're all going to learn a thing or two from you.

What do you think of the proposed .60 cal gun that the USAAF was testing as a replacement for the .50 BMG? They appeared to be more impressed with it than the 20mm guns in use. The following information is taken from the Report of Joint Fighter Conference / Oct. 1944 pp. 165-166.

A 140 lb gun firing a .60 cal round with 3,600 fps (about 1,100 m/s) velocity and a ROF in the range of 500 to 700 rpm. Armor penetration was reportedly 1-1/4" at 600 yards and 20 degree obliquity.


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## Tony Williams (Jul 3, 2006)

I'm happy to stick around for as long as there are interesting things to talk about 

There's quite a history behind the .60 cal. The cartridge was originally developed for a tripod-mounted semi-automatic anti-tank rifle, but by the time it was ready ATRs had gone out of fashion. So the cartridge was then spotted as a potential aircraft gun round to replace the .50 BMG. Interestingly, the gun chosen to fire it was a modified Mauser MG 151, captured examples of which had been studied. This gun was designated T17 and about 300 were built, but it was not adopted. I suspect that this was because it was substantially heavier than the .50 Browning and also slower-firing, but it lacked the destructive power of a cannon (note that the Luftwaffe preferred the 20 mm version of the MG 151 over the 15 mm for exactly that reason).

However, the USAAF had a thing about high muzzle velocity, arguing that it would increase hit probability by reducing the effect of aiming errors. They even produced a necked-down .50/60 round with an extremely high velocity. After WW2 when the M39 revolver cannon (also based on a wartime Mauser design) was being developed, a .60 version of the gun featured. But eventually, it was decided to follow the Luftwaffe's example and neck the case up to 20mm calibre to take explosive shells. The result was the 20x102 cartridge which was adopted for the M39 and is still in service in the M61 'gatling' gun used in present-day US fighters.

You can find comparative photos of the ammo on my site (Ammo Photo Gallery, also Military Cartridge Relationships), together with basic cartridge data (Ammo Data Tables).

Tony Williams: Military gun and ammunition website and discussion forum


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## delcyros (Jul 4, 2006)

Tony Williams said:


> Don't forget that a six-cannon installation was plannned for the Spitfire Mk IV (and a mock-up of the installation constructed) and the Martin Baker MB3 was designed around six wing-mounted Hispanos. These were intended to be air-superiority fighters, not ground attack planes. website and discussion forum



..and actually now you named the exceptions from the rule, I already mentioned. But as You know, none of them were used in combat so evaluation of them is impossible. No combat prooven fighter A/C exceeded the recoil/weight ratio that much. I have grave doubts about the usefuleness of this armement layout in dogfights.


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## Tony Williams (Jul 4, 2006)

delcyros said:


> No combat prooven fighter A/C exceeded the recoil/weight ratio that much. I have grave doubts about the usefuleness of this armement layout in dogfights.


It's a question of the balance of advantages. A P-47 with four Hispano Mk V would be carrying less weight than with eight .50s, but would still have the edge in destructive power. A P-47 with six Hispanos would be a little less quick and agile, but enjoy a 50% advantage in destructive power meaning that the guns would only need to be 'on target' for two-thirds as long for each kill. 

As far as 'recoil ratios' are concerned the Hurricane IIC had four Hispanos for a normal loaded weight of 7,300 lbs, while the P-47 weighed 13,500 lb (normal loaded). Clearly, a six-cannon P-47 would have had to cope with less recoil per unit weight than the Hurricane. I have never read any suggestion that the Hurricane couldn't cope with four Hispanos. The reason that it was eventually relegated to ground attack was that the basic design simply couldn't be made fast enough to compete with the latest German fighters (its performance was already pretty marginal even during the BoB) - but that applied to the MG-armed Hurri IIB just as much as it did to the IIC. 

Tony Williams: Military gun and ammunition website and discussion forum


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## Jank (Jul 4, 2006)

Deja vu.

I advanced the same argument at post #8 about the recoil forces per pound between the Hurricane (4 x 20mm) and the Thunderbolt (6 x 20mm) favoring the Thunderbolt. Delcyros, your counterpoints were as follows:

*"Conclusion: This specialized ground attack plane exceeds the 0.1 margin in recoil/weight ratio, which would effect the fighter role of this plane severely."* Post #24

*"The VVS analyzed MK IIc and found the plane to be well suited in the ground attack and very worse for dogfights (the report quotes that prolonged deflective shooting is very difficult with the heavy recoilforces). Eventually the VVS DOWNGRADED their few MK IIc Hurricane to 0.50 cal guns which again fitted the critical recoil/weight margin of 0.1!"* Post #27

I have not read anything, anywhere indicating that the 4x20mm armed Hurricane was a dog in the air to air role compared to it's lighter armed bretheren.

Now keep in mind that the Hurricane experienced an increase in weight by going to 4x20mm's over it's other configured armaments. This, though, would not be so with the P-47. And, adding 100 pounds of steel to each wing of the Hurricane for reinforcement would represent a greater burden than a 100 pound increase to each wing of the Thunderbolt (not that the Thunderbolt would even need such reinforcement as its wings are far, far stronger to begin with).

Just look at the difference in size between the Thunderbolt and the Hurricane!













I hope that made you smile.


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## Tony Williams (Jul 5, 2006)

An afterthought: some Spitfires fought with a four-Hispano armament, which became standard with the Mk 21. As the weight of a Spit was around two-thirds that of a P-47, that obviously compares with six cannon for the Jug. The Mk 21 may have been a shade too late to see action, but I don't think that anyone would it regard as an unsatisfactory fighter...and the postwar Spiteful weighed little more.

Tony Williams: Military gun and ammunition website and discussion forum


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## delcyros (Jul 5, 2006)

Speculation. By the time of Spiteful Spit XXI the thread scenario already changed. Dogfighting at hi alt with 4 mid wing mounted 20mm is an awesome idea in a Spit. The twin 20mm + .3 cal Hi alt Spit suffered from worrisome recoileffects according to RAF reports.
Four 20mm MK V would have around 2 times the recoil energy of two 20mm and four 0.33 cal. And because the recoil is spread out across half as many pulses per second, it's going to be much more severe. Therefore, it's going to be a lot harder to hold your aim with wingmounted 20mm cannons due to off centre recoil caused sideways slew.


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## Tony Williams (Jul 6, 2006)

"Speculation" that the Spitfire 21 and Spiteful would have proved to be successful in combat if the war had lasted slightly longer? Well, I'm not a betting man but would regard a bet on that as being a sound investment, since they were no more than evolutionary developments of the most successful fighter design of the war. 

You seem to be combining two issues: the total recoil generated by the armament, and the vibration caused by the firing pulses. These were related, but by no means the same. As I have pointed out previously, the use of the Edgewater mounting reduced the Hispano's peak recoil blow (the source of the vibration) to less than that of a .50 Browning with an ordinary mounting. Instead of being a quick, sharp hammer-blow the recoil-force graph became levelled off, more of a smooth oscillating curve than a sharp on/off. 

As far as the total recoil is concerned, you are quite right that a gun jam would cause assymmetric effects which would make it difficult to hold the plane in the aim - but that's one of the penalties of powerful wing-mounted armament. As you can see from this article I favour armament concentrated in or close to the centreline - but that just wasn't possible with RAF or USAAF fighters (with the single exception of the P-39/63). They seemed to perform pretty well all the same.

Tony Williams: Military gun and ammunition website and discussion forum


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## Jank (Jul 6, 2006)

If one of the six guns were to jam on one side, that would represent less of a recoil differential between the two sides than a single jam on one side of a 4 x 20mm armed plane.

If two 20's on one side jammed and one 20 on the other side all jammed, that would also represent less of a differential between the sides. 

Two of the 20mm's jamming on one side only would present a problem that could be easily overcome by the use of a firing trigger than allows the four inboard guns to be fired either independently of or in conjunction with the two outer guns. You would still have firepower, albeit less, without significant recoil differential.

This would also be an easy fix (lots of guns had similar alternative/conjunction firing switches) to the issue raised by Delcyros about six 20mm's shaking the plane too much for air to air applications. I don't agree with Delcyros on that point but it would provide a solution to what he views as a problem. You could bring 4 20mm's to bear in air to air (for perfectly suitable lethality) and all six in air to ground applications.

The chance of a single 20mm jamming (which would have been much more common that two 20mms jamming on one side only) on the several 4 x 20mm armed planes was never a consideration that prohibited that armament arrangement. The loss of one 20mm, is a loss of 50% recoil forces on one side. Again, apparently this was not significant enough of a problem to keep Hurricanes, Tempests, Typhoons, F6F Hellcats and Corsairs (4x20mm armed versions of the latter two may have not seen combat but were in the pipeline) from being pressed into service.


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## Tony Williams (Jul 6, 2006)

Jank said:


> This would also be an easy fix (lots of guns had similar alternative/conjunction firing switches) to the issue raised by Delcyros about six 20mm's shaking the plane too much for air to air applications. I don't agree with Delcyros on that point but it would provide a solution to what he views as a problem. You could bring 4 20mm's to bear in air to air (for perfectly suitable lethality) and all six in air to ground applications.



Actually the requirements tended to be the other way round. Maximum firepower was needed in aerial combat, because the firing opportunity might only be a fraction of a second. In ground attack, there was time to line up the target and a longer burst was possible. I have read that pilots of the Hawker Hunter jet (possibly overgunned with four 30mm Adens) switched off two of the cannon for ground attack, in order to conserve ammo.

Tony Williams: Military gun and ammunition website and discussion forum


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## Twitch (Jul 6, 2006)

All the P-47 Pilots I ever talked to agreed that the 8 fifties was ample for any role. With bombs and rockets added for ground pounding duties the Jug had enough power ti do the job. But pretty much in the end it didn't matter what any attacking plane had as armament since every German airfield bristled with a huge variety of defensive weapons and they brought down many of the aces who dared to strafe them.

If ever cannons were to be added to the P-47s 4 20mms would have been ample. There is enough space to have 250 RPG or more that way. A few smaller Italian fighters carried 250 RPG for 2 wing-mount 20s.  The Thunderbolt certainly could have.

It was not unheard of for one wing's weapons to not fire for assorted reasons. Pilots simply adjusted rudder and went about their business. No big deal.


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## delcyros (Jul 6, 2006)

Tony Williams said:


> "Speculation" that the Spitfire 21 and Spiteful would have proved to be successful in combat if the war had lasted slightly longer? Well, I'm not a betting man but would regard a bet on that as being a sound investment, since they were no more than evolutionary developments of the most successful fighter design of the war.
> forum



Succesful is relative, by the time of their arrival they would have been totally outdated by first gen. jets, at least over europe.

Do You have an idea about hi alt decremental effects of recoil?
Lunatic actually studied this before. A long time ago he calculated that each round coming out the pair of Ho155's on the Ki-84-1c would slow the plane approximately 11 mph. Such huge recoil forces are a real issue for effective weaponry in any aircraft.
Note that a single Ho-155 has around 1.4 times the recoil of a Hispano 20mm MK II, a six 20 mm upgunned P-47 would have TWO TIMES AS MUCH recoil force, even if it is a slowly applied force as the gunmount Tony suggest, imply. (By the way, interesting aspect, Tony!) 
What to expect in dogfights? I suspect that it would have been hard to hold Your aim for more than 2-3 shots.
I would still prefer the eight .5 cal for dogfighting, against ground targets 4 20 mm are decent, as Twitch suggests. Only in case a large air target (heavy bomber) has to be intercepted in a single pass such weaponry makes sense, but their was no such thread scenario in 1944/45 requiring this weaponry.
best regards,


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## wmaxt (Jul 6, 2006)

In WWII the problem with 20mm was ammo count and and the slower rate of fire. I agree with Del that I want at least a few .5s. The mix gives good time of fire as well as a great punch. As the 20mm rate of fire increased and the capacity to hold enough ammo for more than 15-20 seconds of fire they became the weapon of choice.

I think that applies to both ground attack as well as Ariel attack. Whatever gun you use has to get enough in the air to hit then destroy the target. If your spread is to wide due to a slow rate of fire, have to make repeated passes or run out of ammo prior to destruction of the target you've failed.

wmaxt


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## Tony Williams (Jul 7, 2006)

delcyros said:


> Succesful is relative, by the time of their arrival they would have been totally outdated by first gen. jets, at least over europe.


We have been talking here about whether a given weight of armament would have been practical in a piston fighter, or whether it would have had unacceptably detrimental effects on the plane. How piston fighters compare with jets in combat is an entirely different issue.



> Do You have an idea about hi alt decremental effects of recoil?
> Lunatic actually studied this before. A long time ago he calculated that each round coming out the pair of Ho155's on the Ki-84-1c would slow the plane approximately 11 mph. Such huge recoil forces are a real issue for effective weaponry in any aircraft.


Actually I do know something about recoil - and the calculations you quote do not make sense. I have suddenly understood why you are so concerned about recoil, if you are basing your opinions on this. Let's take the example you quote - the Ki 84: this weighed much the same as the Hurricane or Spitfire (give or take a bit). So logically, if the recoil from each Hispano shot generates about 70% of the recoil of the Ho-155, then each pair of rounds fired from Hispanos would slow the British planes down by about 11 mph x 70% = 8 mph (16 mph with four-cannon layouts). The RAF did an analysis during WW2 of the use of cannon ammo in combat, and discovered that an average of 17 rounds per gun were fired in each burst of fire, taking 1.7 seconds (five bursts were fired on average, for 85 rpg total). So according to the calculations you quote, the Spitfire would have been slowed down by 8 x 17 = 136 mph after each burst, the Hurricane by 272 mph - which means it would have fallen out of the sky before it finished one burst! This is clearly wrong.

I think I may have posted this already, but it obviously bears repeating (along with a bit more) - from *Flying Guns – World War 2: Development of Aircraft Guns, Ammunition and Installations 1933-45*:

"This might be an appropriate moment to dispel one of the favoured myths of big-gun aircraft; that the recoil had a drastic effect on their speed. To take the example of the USAAF's B-25 fitted with a 75 mm M4 gun; the aircraft weighed around 12,000 kg and attacked at perhaps 400 km/h, the gun fired a 6.8 kg projectile at around 2,200 km/h. A simple rule of thumb is to multiply the weight by the speed to achieve a rough "momentum index" (it is actually a bit more complicated than this, as the expanding propellant gasses contribute to the recoil). It will be apparent that the aircraft has at least 200 times the momentum of the projectile, and a single shot will therefore not greatly slow it. In fact, at the end of an attack run in which several shots were fired, the plane would typically be slowed by 10-15 mph. The effect on fighter speed of long bursts of heavy gunfire (especially from automatic cannon) could be noticeable, particularly in a turning battle when the aircraft might be manoeuvring at the extremes of the flight envelope, close to stalling."

Now let's do some calculations about what the effect might have been. I explained the methodology in some detail here: BASIC BALLISTICS Each Hispano round fired a 130 g projectile at about 860 m/s. Each contained around 32 g of propellant, with an escape velocity of about 1,200 m/s (this is a typical average for high-velocity guns). This gives a recoil momentum factor of (130 x 860) + (32 x 1,200) = 150,000 g/m/sec (let's convert the grams to kg to make the calculation easier, giving 150 kg/m/sec). Assuming a typical loaded aircraft weight of 3,600 kg, one shot would generate enough recoil to move the aircraft backwards at 150/3,600 = 0.04 m/s. So a burst of 17 rounds per gun would push the aircraft back at 17 x 2 x 0.04 = 1.35 m/s (2.7 m/s for four-gun layouts). Now if the aircraft is flying at 400 kmh when it fires, that is equivalent to 110 m/s. So after firing their 17-rpg bursts, a two-cannon Spitfire would be slowed by 1.25 %, a four-cannon Hurri by 2.5 % (all figures rounded), which amounts to 5 or 10 kmh respectively.

I have no argument with the proposition that four 20mm Hispanos would have been quite enough for almost any target - that's what the RAF concluded, anyway. But what we are debating is whether the P-47 could have coped with six, and remained an effective fighter. My conclusion to that is yes, certainly.

Tony Williams: Military gun and ammunition website and discussion forum


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## mosquitoman (Jul 7, 2006)

In my opinion, 20mm cannon weren't needed by the USAAF because there weren't any heavy bombers being operated by the Luftwaffe, these would have needed 20mm to take down, just like the Luftwaffe fighter armament went to higher and higher calibre eg 2cm, 3cm etc. The RAF and USAAF mainly had fighters and fighter-bombers to deal with


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## Twitch (Jul 7, 2006)

We must realize that guns are fired for very brief periods. A 3 second burst is a VERY long burst. Recoil of all guns firing does slice a bit of speed off but its effects were alwayd dealt with. I have never met a fighter pilot that said the shaking of his ship was so severe due to recoil that he could hit the enemy once he had a good gun solution. We have inertia at work in its best form too so that diving and zooming crates that lose any speed from breach recoil reactions are extremely negligable. That few MPH is quickly regained.
We are analyzing and over analyzing what was never a problem to begin with.


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## Jank (Jul 7, 2006)

Mosquitoman said, *"In my opinion, 20mm cannon weren't needed by the USAAF because there weren't any heavy bombers being operated by the Luftwaffe, these would have needed 20mm to take down, just like the Luftwaffe fighter armament went to higher and higher calibre eg 2cm, 3cm etc."*

Yes, and no one disagrees with that position. This thread, like so many others, concerns a question of what if and whether it could have been practically done. This thread is really about whether the P-47, later in the war, in the ground straffing and close support role, would have benefitted from an outfitting of 6 x 20mm cannons and whether their installation would have been practical in terms of degradation of flight performance.


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## delcyros (Jul 7, 2006)

Tony Williams said:


> I have no argument with the proposition that four 20mm Hispanos would have been quite enough for almost any target - that's what the RAF concluded, anyway. But what we are debating is whether the P-47 could have coped with six, and remained an effective fighter. My conclusion to that is yes, certainly.



I want to point out first that I enjoi our debate, so if You ever had the impression that my statements are unpolite, be sure I don´t want to be agressive anyway.

According to Your calculations (which make sense to me as did Lunatics one´s), a late war P-47 (M) would be slowed down by a three sec. burst of six 20mm guns by 10 mp/h or ~16 Km/h. 
mv: 880 m/s Lunatic's WWII Aircraft Gun Ballistics Page
proj. weight: 0.13 Kg
cartridge load: 32g
powder vel.: 1200 m/s
rof: 600 rpg (3 sec burst equals to 30 rounds per gun)
P-47 M typical loaded weight: 6029 Kg Republic P-47 Thunderbolt
net recoil: 152.9 Kp per gun (917.4 Kp for a six gun burst)
recoil / weight relation: 0.152
brutto deceleration for 3 sec. bursts: 4.56 m/s (16.41 Km/h or 10.19 mp/h)
compare original P-47M:
recoil / weight relation: 0.067 (for eight 0.50 M2)
brutto deceleration for 3 sec. bursts (a 40 rounds): 2.68 m/s (9.64 Km/h or 6 mp/h) That´s typical for ww2 fighter A/C (between 5 and 10 km/h deceleration) but once a single gun is out of calibration (rof is always slightly different for individual guns due to gunwear, condition, etc.), the mid wing layout causes problems in aiming, esspecially for long to medium range deflection shots. I have always taken the comparably low recoil / weight relation USAAF fighter A/C had, as an advantage, overcoming the shortcomings of the mid wing layout. They do imply a very stable gunplatform even at hi alt, so I conclude that the long range gunnery is much easier with them.
Note that the brutto deceleration of 6 gunned P-47 exceeds typical ww2 fighter A/C values according to my database.
This is significantly more than any Fighter A/C of ww2 had, so I conclude this weapon layout would be impractical for hi alt, hi speed engagements. I would like to be more concrete here but I have a lack in cartridge loads for different guns of my database.
This layout could be used for low alt strafing / attacking purposes as Jank pointed out, but I do think this is lot of overkill.


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## Tony Williams (Jul 7, 2006)

mosquitoman said:


> In my opinion, 20mm cannon weren't needed by the USAAF because there weren't any heavy bombers being operated by the Luftwaffe, these would have needed 20mm to take down, just like the Luftwaffe fighter armament went to higher and higher calibre eg 2cm, 3cm etc. The RAF and USAAF mainly had fighters and fighter-bombers to deal with


I would put it slightly differently: 

.50 = OK against fighters, as long as you have at least six of them.

20mm = OK against fighters, as long as you have two of them; great against fighters and fine against medium bombers/attack aircraft also, if you have four of them. 

30mm = optimum against heavy bombers, as both the Germans and the Japanese discovered.

Tony Williams: Military gun and ammunition website and discussion forum


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## Tony Williams (Jul 7, 2006)

delcyros said:


> I want to point out first that I enjoi our debate, so if You ever had the impression that my statements are unpolite, be sure I don´t want to be agressive anyway.


You are not, and I hope I don't appear to be so either. There is nothing I enjoy more than a well-argued debate on an issue like this!



> According to Your calculations (which make sense to me as did Lunatics one´s), a late war P-47 (M) would be slowed down by a three sec. burst of six 20mm guns by 10 mp/h or ~16 Km/h.


I have no argument with that, except that three seconds is a very long burst of fire.



> Note that the brutto deceleration of 6 gunned P-47 exceeds typical ww2 fighter A/C values according to my database.
> This is significantly more than any Fighter A/C of ww2 had, so I conclude this weapon layout would be impractical for hi alt, hi speed engagements.


That would be true *if *more lightly armed planes were felt to be on the limit of recoil tolerance. I am not aware of any evidence that they were. In fact, the only mentions I have found of recoil affecting shooting accuracy, so the pilot had to re-aim after a few shots, is for planes carrying very powerful cannon: the Hurricane IID (2x40mm), Il-2M3 (2x37mm), Yak-9T (1x37mm). I have read no such reports concerning the 4x20mm RAF fighters. So I must therefore conclude, unless hard evidence to the contrary can be found, that 6x20mm would not have caused the P-47 significant problems.

Tony Williams: Military gun and ammunition website and discussion forum


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## delcyros (Jul 7, 2006)

Something worth to spent some thoughts. I would like to hypothezise for a moment.
Hypothesis is: There was a "rule for useful recoil" of ww2 fighter A/C altough it was never credited as a design feature this way. (By the way, the VVS credited the 4 20mm upgunned Hurricane as unsuited for dogfighting and reduced the armement to soviet .50´s) Impossible to prove and to some degree will remain speculation. But perhaps we can make it plausible?
Can You give me the cartridge datas for MG 151/15; -20; Berezin .50; Shvak and MK 108 + Ho-155 and Ho-5?
I would like to compare the recoil values for typical and prooven ww2 fighter A/C but still miss the cartridge loads (probably 20+-% plus) for recoil addings:
(typical weights: clean configuration and 50% fuel)

P-40N (weight: 3500 Kg, six 0.50cal: 228.6 + gaz effects): 0.065 
P-39D (weight 3810 Kg, one 37mm M4 + four 0.50cal: 546.8 + gaz effects): 0.143 -heavy recoil gun is nose mounted, plane not suitable for hi alt 
P-38L (weight 6875 Kg, one 20 mm + four 0.50cal: 266.4 + gaz effects): 0.038 -plane suited for hi alt dogfights
P-47D-(weight 6350 Kg, eight 0.50cal:304.8 + gaz effects): 0.048 -plane suited for hi alt dogfights
P-51D (weight 4355Kg, six 0.50 cal: 228 + gaz effects): 0.0525 -plane suited for hi alt dogfights

US fighter planes preferred very stable gunplatforms, recoil (netto)/weight ratios well under 0.06 with the notable exception of the P-39, altough this plane received critizism because of the 37mm gun, which was barely used except for ground attacks or bomber interceptions

Ki-61 Ib (weight 3050 Kg, two 20mm Ho-5 +two 0.50cal: 189.6 + gaz effects): 0.062 -plane suited for hi alt dogfights
Ki-84 Ib (weight 3275 Kg, four 20mm Ho-5: 274.56 + gaz effects): 0.083 -plane with limited fighter use at hi alts 
A6M5b: (weight: 2750 Kg, two 20mm type99, one 13mm type 3, one 7.7mm type 97: 238 + gaz effects): 0.086, plane suited for hi alt dogfights
J2M (weight 3500 Kg, four 20mm Ho-5: 274.56 + gaz effects):0.078 -plane suited for hi alt dogfights / engagements
N1K1J (weight 3600Kg, four 20mm type 99, two 7.7mm type 97: 400.7): 0.111 -plane suited for high alt bomber interceptions 

Typical mid-late war japanese fighter had a very high recoil (netto) / weight relation which usually was between 0.06 and 0.09 with the notable exception of specialized bomber interceptors such as the Ki-84Ic and N1K1J, which performed worser in the fighter role.

Hurricane IIb (weight 3150 Kg, twelve 0.303cal: 95.4 +gaz effects): 0.030-plane suited for dogfights (hi alt wasn´t tactical envelope of Hurris)
Spitfire Vc (weight 2700 Kg, two 20mm MKII+four 0.303cal: 260.6 + gaz effects): 0.096 -plane suited for medium alt dogfights
Typhoon (weight 4600 Kg, four 20mm MKV: 436.8 + gaz effects):0.095 -plane suited for interceptions
Meteor-III (weight 5500 Kg, four 20mm MK V: 436.8 + gaz effects):0.079 -plane suited for hi alt engagements, all guns nose mounted

RAF fighter A/C seems to have put emphasis on maximum useful gunpower (at least so in the case of Hurricane IId and Spit Vc, altough numerous accounts concerning the recoil of the guns exist in this case) for their mid war fighter A/C, late ware fighter A/C (Tempest, Meteor, Spitfire XIV) had a more balanced recoil-weight relation, indicating a somehow increased importance of recoil issues. 

Me-109G10 (weight 2735 Kg, one 30mm MK 108, two 13mm MG131: 219.45 + gaz effects) : 0.080 -plane suited for hi alt dogfights, all guns nose mounted
Fw-190 A8 (weight 4400 Kg, four 20 mm MG151/20, two 13mm MG131:357.3 +gaz effects): 0.081 -plane suited for interceptions
Fw-190D9 (weight 4200 Kg, two 20mm MG 151/20, two 13mm MG131:205 + gaz effects): 0.488 -plane suited for hi alt dogfights
Me-262 (weight 6000Kg, four 30mm MK 108:666.6 +gaz effects): 0.111 -plane suited for high alt interceptions -all guns nose mounted
He-162A (weight: 2700Kg, two 20mm MG 151/20: 152.25 + gaz effects): 0.056 -plane suited for hi alt dogfights

German planes favoured the nose mounted guns and hance enjoied some heavy recoil-weight relations. I suspect that this was a reason why no Bf-109 had a 30mm MK103, this would exceed the "rule" by much! The dogfighters (Fw-190D and He-162) had a significantly lower ratio, implying a more stable gunplatform 

Yak-3 (weight 2400 Kg, one 20mm Shvak, two 12,7mm: 160.7 +gaz effects): 0.067 -plane suited for dogfights (hi alt wasn´t tactical envelope of the Yak)
La-7bic (weight 3100 Kg, 3 20mm B20: 213.75 + gaz effects): 0.069 -plane suited for hi alt dogfights

VVS fighter A/C with all nose mounted guns also enjoied a comparably low recoil-weight relation, implying a very stable gun platform with little or no recoil issues. (Note that tank hunters such as the Yak-9T with 37 mm NS 37 exceeded the typical ratio.)

What to conclude? Generally spoken, each nation / air force preferred a typical recoil-weight relation for typical purposes. Fighte A/C rarely exceed 0.1. (THEY DO NEVER EXCEED 0.10 FOR MID WING MOUNTED GUNS!) It seems to me that the nose gunned Fighter A/C had sometimes a higher recoil-weight relation than the mid wing mounted ones.
Note that a six 20mm upgunned P-47 would rather fall in the envelope of ground attackers than dogfighters, esspecially with the emphasis of USAAF in mind to limit the recoil-weight ratios. Keep an eye on the distribution of the values. They are typical and not randomly choosen. The "rule" gives a limit of 0.10 (not counting gaz effects) for wing mounted armement for fighter purposes (interceptor do slightly, ground attackers do heavily exceed this limit) with a nation related typical window below. 
best regards,


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## Jank (Jul 7, 2006)

Delcyros said, *"P-47D-(weight 6350 Kg,"*

A combat loaded P-47D-22 and later series came in at 14,500lbs or 6,591 kg in combat loaded trim. (Full internal fuel and full ammunition load.)


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## delcyros (Jul 7, 2006)

I used to reduce all weight figures by a bit to reflect the fuel weight left for climbing to altitude and so.
For some planes no combat load figures were avaiable the last 20 min. in the net (..or I used to take the wrong sources..), so I used some approximations from empty and max weight figures...
best regards,


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## Tony Williams (Jul 8, 2006)

There is one general comment I would make about your theory: that as far as I'm aware, the limitations on the number and size of fighter guns were concerned primarily with weight, and to a lesser extent with space and difficulty of access, but not with recoil. In particular, weight out in the wings affected the handling of the plane (it slowed the roll-rate) which could make it more vulnerable in combat. Weight anywhere in the plane restricted the agility, the rate of climb, the rate of acceleration (except in a dive) and the maximum altitude. So plane makers usually restricted the armament to the minimum they thought would be effective in doing the job. 

The most interesting examples of this were the heavily armed and armoured late-war Bf 109 and Fw 190 variants intended to attack USAAF bomber formations, while their more lightly armed and armoured comrades tried to hold off the bomber escorts. The extra armament (and armour) affected the performance and handling of these planes, which is why those engaging the fighters didn't want the extra gunpods - recoil had nothing to do with it.

Similarly, most Russian planes were lightly armed, with the guns usually in the fuselage. This had nothing to do with recoil problems, everything to do with the serious performance limitations caused by the low-powered Russian engines.

Do you have any contemporary sources which raise recoil as a significant issue in limiting the armament of fighter planes? I did a lot of research into original British documents on WW2 aircraft armaments held in the National Archives, when collecting information for the *Flying Guns *books, and did not find any such concerns.

A few more detailed points: 



delcyros said:


> (By the way, the VVS credited the 4 20mm upgunned Hurricane as unsuited for dogfighting and reduced the armement to soviet .50´s)


Not according to my co-author Emmanuel Gustin, who had this to say (from *Flying Guns – World War 2: Development of Aircraft Guns, Ammunition and Installations 1933-45*):

"The armament of Browning .303 guns installed in early Hurricanes was considered deficient, as having an effective range of only 100 to 150 meters. It was considered to install four ShVAK cannon, four UBTs, or two ShVAK and two UBT guns; although a preference existed for the second option the last one was chosen, because there were not enough UBT guns. So about a 1000 Hurricanes Mk.IIA and Mk.IIB were modified to have two ShVAK cannon and two UB machine guns, a quite powerful combination by Soviet standards. The Hurricane's armour protection also fell below Russian standards, and it was replaced. The Mk.IIC with its four Hispano Mk.II cannon retained its armament, and was used as a ground attack and anti-shipping aircraft. By 1941 the Hurricane was obsolescent as a fighter, and it was not highly regarded."

Sources I have state that the Soviets had a very low opinion of the Hurricane as a fighter (so did the Finns who fought against them) because its performance was too poor (possibly because high-octane fuel wasn't readily available?) so they did not use it in aerial combat if they could help it.



> Can You give me the cartridge datas for MG 151/15; -20; Berezin .50; Shvak and MK 108 + Ho-155 and Ho-5?



I presume you mean the propellant weights (the projectle weights and muzzle velocities are available on my site here: WORLD WAR 2 FIGHTER GUN EFFECTIVENESS

I do not have propellant weights for all of the rounds, but have the following(results are averages, these did vary): MG 151/15 = 25 g; MG 151/20 = 18 g; 12.7 mm Berezin = 18 g; MK 108 = 28 g; Ho-5 = 21 g. The Ho-155 probably weighed around 30 g as its muzzle energy was similar to the Hispano's, but I have no sources for that.



> US fighter planes preferred very stable gunplatforms, recoil (netto)/weight ratios well under 0.06 with the notable exception of the P-39, altough this plane received critizism because of the 37mm gun, which was barely used except for ground attacks or bomber interceptions


On the contrary, the P-39 was valued by the Soviets as an air combat fighter, and some of their highest-scoring aces used it. They were not bothered about its poor high-altitude performance because most Eastern-Front combat was at lower altitudes. Although any fighter (in any air force) might be called upon to attack ground targets from time to time, the Soviets generally left that to the well-armoured Il-2.



> RAF fighter A/C seems to have put emphasis on maximum useful gunpower (at least so in the case of Hurricane IId and Spit Vc, altough numerous accounts concerning the recoil of the guns exist in this case) for their mid war fighter A/C, late ware fighter A/C (Tempest, Meteor, Spitfire XIV) had a more balanced recoil-weight relation, indicating a somehow increased importance of recoil issues.


No, as planes grew heavier the armament weight did not increase because the RAF felt that its gunpower was adequate. Although having said that, the prototype Meteor did have six Hispanos but two were removed because their installation was dangerous (they could not be worked on or removed unless the armourer was standing directly in front of the muzzle).



> German planes favoured the nose mounted guns and hance enjoied some heavy recoil-weight relations. I suspect that this was a reason why no Bf-109 had a 30mm MK103, this would exceed the "rule" by much! The dogfighters (Fw-190D and He-162) had a significantly lower ratio, implying a more stable gunplatform


The MK 103 was too big to be fitted to the little Bf 109. A special version with a revised design for the gas-operated action, the MK 103M, was experimentally fitted to a Bf 109K-10, but proved unsuccessful. There is no doubt that the Luftwaffe wanted to see the MK 103 fitted to the Bf 109, but it could not be made to work.



> VVS fighter A/C with all nose mounted guns also enjoied a comparably low recoil-weight relation, implying a very stable gun platform with little or no recoil issues. (Note that tank hunters such as the Yak-9T with 37 mm NS 37 exceeded the typical ratio.)


The Yak-9T was not a tank-hunter - it was designed for aerial combat, and proved very successful in skilled hands (the Yak-9K, with the even more powerful NS-45, was given to an elite fighter squadron to test and they claimed one kill for every 10 rounds fired). As I have said, the armament of Russian fighters was limited by their weak engines. It increased later in the war, as their planes became more powerful.

To sum up, it seems to me that you have become very fixed on your theory that gun recoil was a major limitation on aircraft armament, but I have seen no evidence to support this. On the other hand, it is clear that armament weight (especially out in the wings) was a major concern because of its effect on performance and handling, and this caused all air forces to restrict the number and size of guns.

Tony Williams: Military gun and ammunition website and discussion forum


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## delcyros (Jul 8, 2006)

Tony Williams said:


> To sum up, it seems to me that you have become very fixed on your theory that gun recoil was a major limitation on aircraft armament, but I have seen no evidence to support this. On the other hand, it is clear that armament weight (especially out in the wings) was a major concern because of its effect on performance and handling, and this caused all air forces to restrict the number and size of guns.



I may be fixed to the idea, but only because I believe it is not covered enough and because I think in ww2 there was little if even any covering of the problem, altough it undoubtly existed.
Actually, the Yak-9T unsurprisingly suffered from heavy recoil issues:
"Yak-9T - Yak-9 armed with a 37 mm Nudelman-Suranov NS-37 cannon with 30 rounds of ammunition instead of the 20 mm ShVAK cannon, cockpit moved 0.4 m (1 ft 3 in) back to compensate for the heavier nose. Initially poor quality control lead to multiple oil and coolant leaks from cannon recoil. Recoil and limited supply of ammunition required accurate aiming and 2-3 round bursts. Yak-9T was widely used against enemy shipping on the Black Sea and against tanks, but also successful against aircraft with a single cannon hit usually sufficient to tear apart the target." The designation alone implys a specialized tank hunter variant:
Yak 9 Tyazhelowooruzheny" (Heavily Armed), the design bureau was asked for a -tank destroyer -altough it now is generally assumed to be a fighter plane because of the use in this role by VVS-Garde units. (It actually served in the tunk hunter role as well). Even with this in mind, nobody claims the Yak-9T to be good in the dogfighting role, it´s one and only reputation is incredible devastating firepower.
According to the Hurricane, Yakolev wrote (translated):
"...the GKO accepted the Hurricane, but the armement was considered to weak by Suprun and others, so subsequent changes in weapon layout to two Shvak and two 12.7mm guns became necessary. Later Hurricane with four high velocity 20mm guns suffered from heavier weight and lower firing accuracy and thus were deligated to the ground attack role or refitted with 4 12.7mm guns". (Yakolev, zehl dschisin, p.402)
Note that "lower firing accuracy" may be caused due to heavier recoil as plausible explenation.
According to the P-39 in VVS use, Yakolev wrote (translated):
"The airplane Airacobra was well known to us since the land lease treaties. Initially it made problems because of the weak tailplane, a number of planes were lost without enemy actions due to this weakness. Eventually we removed parts of the armour and sometimes even the 37mm gun in order to improve the dogfighting abilities and the stability of the gunplatform. With more experience, pilots soon learned to use the advantages of this big gun against german bombers, so most Airacobras retained the centreline gun in the end, despite it´s negative aspects" (ebd.p.418 )

This leads us to a certain point: Altough you made clear that other reasons may cause the lower armement, You did not disproved my theory. It is interesting to note that certain recoil-weight relations were never exceeded for fighter A/C and some ratio´s are too close to be explained as random events:
(Yak-3 and La7bis for example but also Bf109G10/G6 and Fw190A8, Ki-84Ib and A6m5b, Spitfire Vc and Typhoon, P47D and P51D)
And there were enough examples to put more firepower on planes, however, none of them reached combat status. Best example for this is the tiny He-162A1 with originally two 30mm MK 108 mounted in the lower fuselage (better than mid wing), but the recoil exceeded 0.1 (actually 0.123 plus gaz effects), hence test pilots were concerned about the comparably large recoil issues for the pretended fighter role. Subsequent changes (He-162A2) to a twin 20mm armement eased the problem, the later A-3 variant again with 30mm had substantial structural reinforcements and a heavier weight to match 0.100 (plus gaz effects). All random? 

Question still remains wther or not the recoil of a six mid wing mounted 20mm high velocity guns would detrementally affect the stability of the fighter gunplatform rating. I do believe it does, You disagree.
the brutto recoil is around 152 Kp per one single shot. Depends on the geometry of the placement of the gun. assume the gun is placed in the middle of the wing, ~4.5 ft. away from the centreline and ~1 ft. below the central, longitudinal energy axe of the plane. Any recoil impulse generated there will cause some rapidly or slowly applied force (depending on gunmount) to the airframe, which may slew the plane out of course by a tiny fraction. (Note that fractions are important here) Rof for one gun is as low as 600 rpm, but maybe as high as 1000 rpm for a tweaked gun. This implys there will be never absolute, contemporary balance in firing. (this is also true because of different barrelwears=slightly different mv, different gunstate, different ammo type mixings and so on) A single, uncoupled shot will aplly 152Kp to the right wing 4.5ft. from the energy axe, if the right gun is fired. For the energy axe, this results to a course difference of 1.8712 deg (assuming some stabilizing factors by speed [~300 mp/h] and air density [500 hectopascal or~18000ft alt]) or in other words, a 20ft. wide, circular target originally aimed at 306 ft. distance will be thrown completely out of aim due to the recoil of a single shot fired from a mid wing mounted Hispano 20mm MK II in our example. That´s pretty much recoil for fighter purposes, if You ask me. Now, we know that firing 6 guns simultaneously will positively affect the gunstability but only to some degree (debatable), there is no question that eight 0.50cal do perform much better in this respect than would do six 20mm.

By the way, thanks for the cartridge infos!
best regards,


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## Tony Williams (Jul 8, 2006)

delcyros said:


> I may be fixed to the idea, but only because I believe it is not covered enough and because I think in ww2 there was little if even any covering of the problem, altough it undoubtly existed.


I have already agreed that it existed with certain heavily-armed planes, and provided examples of this. I don't agree that it was a significant problem with 20mm fighter armament; 'standard weight' fighters could cope with four 20mm without suffering any significant disadvantage, which means that the big and heavy P-47 could have coped with six.



> Actually, the Yak-9T unsurprisingly suffered from heavy recoil issues:


Yes, I'd already mentioned that one in my post No.88.



> The designation alone implys a specialized tank hunter variant:
> Yak 9 Tyazhelowooruzheny" (Heavily Armed), the design bureau was asked for a -tank destroyer -altough it now is generally assumed to be a fighter plane because of the use in this role by VVS-Garde units. (It actually served in the tunk hunter role as well).


"Heavily Armed" is an accurate translation and is certainly correct, but does not imply use against tanks, or any other specific targets. As I have already pointed out, any fighters could be tasked with ground attack missions when needed, which may have involved shooting at tanks, but that didn't make them anti-tank planes. The fact that, as you say, it served with fighter units (rather than ground attack ones), is a clear indication of its primary purpose.



> According to the Hurricane, Yakolev wrote (translated):
> "...the GKO accepted the Hurricane, but the armement was considered to weak by Suprun and others, so subsequent changes in weapon layout to two Shvak and two 12.7mm guns became necessary. Later Hurricane with four high velocity 20mm guns suffered from heavier weight and lower firing accuracy and thus were deligated to the ground attack role or refitted with 4 12.7mm guns". (Yakolev, zehl dschisin, p.402)
> Note that "lower firing accuracy" may be caused due to heavier recoil as plausible explenation.


Speculation - not proof.



> According to the P-39 in VVS use, Yakolev wrote (translated):
> "The airplane Airacobra was well known to us since the land lease treaties. Initially it made problems because of the weak tailplane, a number of planes were lost without enemy actions due to this weakness. Eventually we removed parts of the armour and sometimes even the 37mm gun in order to improve the dogfighting abilities and the stability of the gunplatform. With more experience, pilots soon learned to use the advantages of this big gun against german bombers, so most Airacobras retained the centreline gun in the end, despite it´s negative aspects" (ebd.p.418 )


The P-39 was notorious for stability problems, which could cause it to go into a dangerous spin. These were not caused by gun firing.



> This leads us to a certain point: Altough you made clear that other reasons may cause the lower armement, You did not disproved my theory. It is interesting to note that certain recoil-weight relations were never exceeded for fighter A/C and some ratio´s are too close to be explained as random events:


If you propose a new theory, it's your job to provide convincing evidence to prove it, not my job to disprove it. Other things being equal, the heavier the weight of armament, the more recoil it is likely to produce. As I have pointed out, it is very clear that armament weight affected aircraft performance, so (generally speaking) no more armament was fitted than was thought necessary to do the job. That this also restricted the recoil was a side-effect, not the main priority.



> Best example for this is the tiny He-162A1 with originally two 30mm MK 108 mounted in the lower fuselage (better than mid wing), but the recoil exceeded 0.1 (actually 0.123 plus gaz effects), hence test pilots were concerned about the comparably large recoil issues for the pretended fighter role.


According to my information, the main problem with the MK 108 installation was the nose was too lightly built and was damaged by the gufire, so MG 151s were fitted while the nose was strengthened. I've not read anything to suggest that the effect of recoil on the flight performance caused aiming problems.



> Question still remains wther or not the recoil of a six mid wing mounted 20mm high velocity guns would detrementally affect the stability of the fighter gunplatform rating. I do believe it does, You disagree.


Indeed. It looks as if we will have to agree to disagree  



> Any recoil impulse generated there will cause some rapidly or slowly applied force (depending on gunmount) to the airframe, which may slew the plane out of course by a tiny fraction.


The more guns you have, the less significant is a single firing impulse from any one gun - so a six-cannon layout would have had a smoother total recoil push than a four-gun layout. If your theory was correct, the shooting accuracy of most Spitfires - with just two, wing-mounted cannon - should have been terrible, with the plane being shaken from side to side. I do not ever recall reading such a complaint, and the fact that most Spitfires were built with this armament indicated that it did not cause the problems you suggest.

Tony Williams: Military gun and ammunition website and discussion forum


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## delcyros (Jul 8, 2006)

Tony Williams said:


> The P-39 was notorious for stability problems, which could cause it to go into a dangerous spin. These were not caused by gun firing.
> 
> 
> According to my information, the main problem with the MK 108 installation was the nose was too lightly built and was damaged by the gufire, so MG 151s were fitted while the nose was strengthened. I've not read anything to suggest that the effect of recoil on the flight performance caused aiming problems.
> ...



Well, if the P-39 was that unstable (which is true due to bad stall behavior) it doesn´t make sense to remove the M4 as a mean to improve dogfighting performance (all under the assumption that the recoil issues are neglectable)
and stability. Actually, VVS did so, that´s why I conclude there have been recoil related issues on that plane.

The He-162 is something different. Here we have an example, where the weight of the plane is identic to the variant with 30mm MK 108 and 20mm MG151/20. So any explenation why the MK 108 was dropped is recoil related . The He-162 fuselage was metal structure (except the nose, which was plywood, but the nose has nothing to do with the gunmounts) with an inclined 12mm fireproof St52 bulkhead beeing the structural backup for the gunmounts. Factoring standart production methods in 1944/45, this still is a very strong structural part of the plane. I will dig out something, but I am sure I read somewhere that THK was concerned with the recoil effects on static tests (structural) and test pilots beeing concerned about low lateral stability for firing in flight tests ("Schiessanflugtests").

And regarding the Spitfire, there do exist such concerns in flightreports. One might first collect them all but I have a note somewhere about a specific Spitfire recoil issue at hi alt from a pilot report. Will check it out. (have to wait to return home for my books a week)
best regards,


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## Jank (Jul 8, 2006)

This discussion has broken down into a complex, myriad of equational monstrosities and as such, the forest is being lost through the trees. The fact remains that the Hawker Hurricane handled four six 20mm's just fine. No evidence has been produced that the ensuing recoil of that set up caused stability problems. 

Ergo, a 6 x 20mm set up in the Thunderbolt would not present any such concerns either.

It is not disputed that the set up of 6 x 20mm with 175 rounds per gun would have about the same weight as 8 x .50's with full ammunition loads.

It is claimed, but without evidence, that a 6 x 20mm setup in a Thunderbolt would presernt recoil serious problems resulting in stability issues. Why then no such recoil issues with the Hurricane?

The production run of 4 x 20mm armed Hurricanes was large. Any recoil associated problems would be peppered throughout the RAF's records and the numerous pilot accounts that have been memorialized to writing. Can you produce a single one?

On a semi-related note, the XP-72, an evolutionary development of the P-47, was ordered to be produced in two variants. One with six .50 cal guns (I assume for air to air engagements) and the other with four 37mm cannons, two in each wing, which I assume was for air to ground applications. Would this second version have presented difficulties?

Republic XP-72

Bear in mind that if so, that is not constitute proof that a 6 x 20mm armed Thunderbolt would have experienced significant stability related issues as the recoil of four 37mm guns must have been quite jarring indeed. Alternatively, however, if a four 37mm gun set up would have worked, as the USAAF believed it would have, that would tend to support that a 6 x 20mm set up would have worked just fine.

I would just point out that the production of the XP-72 was cancelled not because of any armament related issues but because the USAAF had decided that it was in need of long range escorts instead.

Enter the P-47N.


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## Glider (Jul 8, 2006)

I may well be getting into areas where you know more than me about recoil forces but I would suggest that they were not the be all and end all of the various problems.

The P39 being unstable could be more to do with the weight sensitivity. The P39 was very suseptible to changes in weight to the extent that the ammo (or ballast) needed to be retained before flight. As such, a plane in combat that has fired the ammo and may well have suffered damage may well seem to be unstable. This alone would be an argument for keeping the M4.

He162. 2 x 20 would appear to make more sence as an armament. The 162 was fast and had high closing speeds whilst the 108 had a short range with poor ballistics. This is not a good combination. Space presumably was a concern. The 108 was short but bulky and ammo limited. Another good reason for the 20mm.

The Spit at high altitude may have recoil problems but this could be to do with the limitations of flying and fighting at high altitude where its easier to stall. I admit that I have heard that the Spit wasn't as good a gun platform as a Hurricane, but not that it was a poor platform. 

The observation about the later Hurricanes with 4 x 20 being relegated to GA in Russia probably had more to do with the fact that the Russians considered them outclassed by German fighters of the period. Whereas they do pack a significant punch in the GA role and the Hurricane could carry bombs something that most light Russian fighters didn't do that well. 
Its also worth remembering that Russian fighters had their guns on the certre line where gun forces had a minimal effect due to it being on the thrust line of the plane. Wing mounted guns (all wing mounted guns) had a tendancy to be less accurate if the plane was turning, as the wings themselves obvoiously flex. When manouvering one wing is normally going faster than the other introducing differing forces. I cannot remember which Allied Ace but one of of the British pilots always checked his turn slip before firing which suprised me at the time, but made sense when I thought it through.


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## Tony Williams (Jul 8, 2006)

delcyros said:


> Well, if the P-39 was that unstable (which is true due to bad stall behavior) it doesn´t make sense to remove the M4 as a mean to improve dogfighting performance (all under the assumption that the recoil issues are neglectable)
> and stability. Actually, VVS did so, that´s why I conclude there have been recoil related issues on that plane.


I have a book on the P-39 which includes many first-hand accounts by pilots who used it in combat. One complained about the cannon because it jammed a lot. Three said that the low velocity meant that it had a curving trajectory, so they had to get close before firing (although a couple commented that once you understood the trajectory, it was very accurate and could be shot with precision). One complained about the small magazine capacity. *Not one *mentioned recoil at all. If you want to quote the P-39 as an example of a plane with recoil problems, you're going to have to provide some very hard evidence - your case is based on pure supposition.



> The He-162 is something different. Here we have an example, where the weight of the plane is identic to the variant with 30mm MK 108 and 20mm MG151/20. So any explenation why the MK 108 was dropped is recoil related .
> 
> I am sure I read somewhere that THK was concerned with the recoil effects on static tests (structural) and test pilots beeing concerned about low lateral stability for firing in flight tests ("Schiessanflugtests").


The damage was not necessarily caused by recoil. The very short barrel of the MK 108 produced spectacular muzzle blast, and this might have caused damage to the wooden nose cone. Even if it was recoil-related, it doesn't necessarily support your case. It is obvious that the MK 108 produced more recoil than the MG 151, and the He 162 was designed with the lightest possible structure, so might have needed some reinforcement around the gun mounting. I don't see that that is relevant to your point about the recoil affecting the flying or shooting qualities of the plane. There is no evidence that it would not have performed very well with the MK 108 once the strengthening took place. 'Low lateral stability' was an aerodynamic issue, unconnected with gun firing.

In fact, the main reason for the change may have been simpler: Kosin in his study 'The German Fighter' states that "the Russian advance brought a halt to production of the MK 108 in Poznan, which necessitated converting the aircraft to take the MG 151/20..."



> And regarding the Spitfire, there do exist such concerns in flightreports. One might first collect them all but I have a note somewhere about a specific Spitfire recoil issue at hi alt from a pilot report.


I do recall reading one account in which a high-altitude interception was attempted. One of the cannon jammed because of the extreme cold, and the pilot was unable to hit the target because the plane immediately slewed to one side when the single cannon fired. Which is exactly what one would expect. 

To support your case that a plane with the size, weight and strength of the P-47 would have been adversely affected by the recoil of six cannon, you need hard evidence. So far, you have produced none. 

Tony Williams: Military gun and ammunition website and discussion forum


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## Tony Williams (Jul 8, 2006)

Glider said:


> I admit that I have heard that the Spit wasn't as good a gun platform as a Hurricane, but not that it was a poor platform.


That's a different issue. The Spitfire had marginal lateral stability, which made it difficult to aim steadily. The upside of that was that it was instantly responsive to the controls, making it very agile. The Hurricane was more stable, which made it easier to keep in the aim, but the handling wasn't as responsive. None of this was affected by the armament they were carrying.

Tony Williams: Military gun and ammunition website and discussion forum


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## delcyros (Jul 8, 2006)

Tony Williams said:


> To support your case that a plane with the size, weight and strength of the P-47 would have been adversely affected by the recoil of six cannon, you need hard evidence. So far, you have produced none.



I showed that the recoil of this layout exceeded typical ww2 Fighter A/C values by much. This may not be a hard evidence but it cannot be neglected either. We should remember that no such weapon layout was tried out and tested so far.
In this light nobody will be able to give hard evidence for an armement layout not tried. You want me to quantify the unquantifyable. I am not going to do so, I am only able to make it plausible to some degree or to throw my concerns into the discussion.
One step out of my possibility (but probably possible for You) would be to ask fighter pilot´s with combat experience about their specific recoil experience. I do not think this was properly done. I suspect this would be more enlighting on this highly interesting subject. Such a study would be worth the expense.

In case of He-162 M2, the damage caused by static firing of the MK 108 was not due to blast effects but due to recoil. The metal structure wasn´t prone to damage caused by blast effects (the metal skin did not differ from that executed in the Me-262 or Me-163B, which also had a plywood nose). Compare the He-162M4 with two MG 151/20, it´s test records do still exist.
The He-162M6, again with MK 108 for ground firing tests confirmed the recoil related problems known from the M2-prototype. (note that the plywood nose wasn´t damaged, the gunmount itself was repeatedly thrown out of calibration). 
Neither weight nor space was a major concern and initially the Luftwaffe wanted this plane to carry 30mm guns instead of 20mm ones (the later A-3 subtype again carried 30mm guns). Personally, I regard 20mm guns as better for the specifc purposes in retrospect.
And no, low lateral stability was a concern during firing of the guns according to "schiessanflug" reports, it may be eased by aerodynamic issues (which must be proofed first) of the He-162, but it is not caused by them independent from recoil issues in this case.
Note that Koznan wasn´t the prime production centre for MK 108 and note that MK 108 were well avaiable to wars end from various decentralized production rings around Bernburg, Schwechat, Holstein, Wien and others (to name those avaiable in march 45). Neither the Me-262 production, nor the Ta-152, Bf-109K, Me-163B or even the Ju-388 production suffered from a Mk 108 shortage till wars end.
I am not going to say recoil was the only factor to define the gunplatform charackteristics of a plane, the opposite is the case, the gunplatform charackteristics do allow a certain amount of recoil without detremental effects on firing accuracy. That´s why I studied recoil-weight relations for different planes. So far, I have not found anything to exceed 0.10 for pure fighter A/C, which made it into combat. Interceptors: yes, Ground attackers: yes, pure fighter: no. 

According to the Hawker Hurricane IId the fact remains that this plane with this weapon layout wasn´t primarely used for dogfights. Attack planes usually had not to aim long range, wide deflection shots, so recoil related issues naturally were of less importance to them. Nethertheless, I would like to hear a Hurri´s pilot opinion on this matter, esspecially with the differences between 0.303 cal and 20mm armement.
As a sidestep concerning the XP-72: This plane also did not reached combat status, the proposed armement layout was not accepted by official standarts (no firing in flight tests were acomplished), so it totally remains speculation and not fact. With a typical weight of 6575 Kg and a netto recoil of 1578 Kp (pluz ~20% gaz effects= 1894Kp) for four 37mm M10, a 3 sec. burst will slow down the plane by approximately 33.2 Km/h or 20.6 mp/h, a significant deceleration, not to speak of recoil issues due to much fewer pulses! 
The P-47 would need significant wing modifications. At first it would need structural (spacial) modifications in order to handle the larger ammo feed belts and cases, then it would need a stronger gunmount with special applications to reduce the peak of recoil (which was new to me), both would increase the weight. At next it would need structural reinforcements of the wing structure to handle the impulses, again increasing weight. Why wasn´t this tried if there were no such obstacles, Jank?


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## Tony Williams (Jul 8, 2006)

delcyros said:


> I showed that the recoil of this layout exceeded typical ww2 Fighter A/C values by much. This may not be a hard evidence but it cannot be neglected either. We should remember that no such weapon layout was tried out and tested so far.
> In this light nobody will be able to give hard evidence for an armement layout not tried. You want me to quantify the unquantifyable. I am not going to do so, I am only able to make it plausible to some degree or to throw my concerns into the discussion.


Of course hard evidence could be provided, if it existed. Your thesis is that fighter designers deliberately kept the recoil/weight ratios of the armament below a certain figure. So all you have to do is to find evidence that fighter designers were aware of this problem, and deliberately aimed to keep the recoil/weight ratio below the limit you have identified. 

I have to say that in all the decades I have been reading technical histories of WW2 aircraft, I have never come across any such concern. Neither have I come across any mention of it in pilot's reports, nor any comments in any independent evaluatons of aircraft, with the few exceptions I have mentioned (of which only the Yak-9T and Yak-9K were fighters). I must therefore conclude that it did not exist.

I will sign off from this thread with this post, because it is becoming repetitive. I will just reiterate the key point I have made before: that keeping weight down was a major issue, and provides a much simpler and well-evidenced reason for limiting armament.

Tony Williams: Military gun and ammunition website and discussion forum


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## delcyros (Jul 8, 2006)

Tony Williams said:


> Neither have I come across any mention of it in pilot's reports, nor any comments in any independent evaluatons of aircraft, with the few exceptions I have mentioned (of which only the Yak-9T and Yak-9K were fighters). I must therefore conclude that it did not exist.



"The Spitfire was less stead when the guns were firing because, I have always thought, they were spread further along the wing, and the recoil effect was noticeable."
-Douglas Bader

"We had to close on dicke Auto´s before we open fire to a point, from which we couldn´t miss the target, because beside of other reasons, the recoil of wingpod guns made prolonged aiming very unreliable."
-Pipps Priller

but:

"*"- What effect does the weapons' recoil have?* 
Nnooo, it has no effect, you don't push the trigger all the time. You fire accurate shots. And you don't have so many rounds. Firing prolonged rounds was no problem without pod guns"
- Väinö Pokela, Finnish Me 109 pilot. 

I expect there is more in the net and will start to collect pilot informations regarding recoil informations. Thank You, Tony for participating in our discussion!
Best regards,


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## Jank (Jul 8, 2006)

*"Why wasn´t this tried if there were no such obstacles, Jank?"*

Simple. The USAAF was wedded to the .50. The P-47 did just fine with 8 x .50's in ground attack as most targets succeptible to 20mm damage were also succeptible to .50 API damage. 

Later in the war when the P-47 assumed primarily a ground attack / close air support role in the ETO, existing Thunderbolts were pressed into action. Why go through refits? The Germans at this point in the war were playing defense. The Allied advantage came from sheer numbers of aircraft. There was no reason to rethink a problem that didn't exist to begin with. We're talking here about making the P-47, which was already highly effective, even more effective and not about correcting a noted deficiency on the part of the P-47.

The fact that it was not done is not evidence either that it could not have been done or that it was not feasible due to recoil.

*"I showed that the recoil of this layout exceeded typical ww2 Fighter A/C values by much."*

So what. I'm sure that in 1940, had you been in the USAAC, you would have told Alexander Kartvelli that his idea for an 11,500lb behemoth, armed with 8 x .50 cal machine guns "exceeded typical ww2 Fighter A/C values by much" and that therefore, it could not possibly be a success and was a waste of time and money.

Well looky here (the prototype ended up weighing even more than his 1940 proposal for the XP-47 design):

Republic XP-47B Thunderbolt
_The XP-47B prototype (40-3051) flew for the first time on May 6, 1941, piloted by Lowry L. Brabham. This was only eight months after the order had been placed. The XP-47B was the largest single-engine fighter built up to that time. At a loaded weight of 12,086 pounds, the XP-47B dwarfed all previous fighters, being almost twice as heavy as most of its contemporaries. On the first flight, the pilot was forced to make an unplanned emergency landing because of a leakage of exhaust fumes into the cockpit. Its eighteen-cylinder XR-2800-21 radial engine offered 1960 hp at 25,800 feet, and gave it a maximum speed of 412 mph, 12 mph faster than Kartveli had projected. An altitude of 15,000 feet could be attained in five minutes. Empty and normal gross weights were 9189 pounds and 12,086 pounds respectively._

As to the Xp-72, you said, *"This plane also did not reached combat status, the proposed armement layout was not accepted by official standarts (no firing in flight tests were acomplished), so it totally remains speculation and not fact."*

Well, you are right, of course, the plane was cancelled after having been ordered to be produced with 4 x 37mm guns. The fact that the 4 x 37mm layout was ordered into production by the USAAF does, however, constitute an "official acceptance" of that layout. It is also speculative to say that no flight tests were performed with that layout. I would just say that it would seem to be rather odd that in 1944, given what the USAAF knew about fighter design and performance that it wouldn't have determined that this layout would have worked. Of course, we'll never know and I'm not going to argue the point further because it is rather speculative. I wonder if Tony has any thoughts on the XP-72.

I will, however, refocus you on the point raised above in my post:

"This discussion has broken down into a complex, myriad of equational monstrosities and as such, the forest is being lost through the trees. The fact remains that the Hawker Hurricane handled four six 20mm's just fine. No evidence has been produced that the ensuing recoil of that set up caused stability problems.

Ergo, a 6 x 20mm set up in the Thunderbolt would not present any such concerns either.

The production run of 4 x 20mm armed Hurricanes was large. Any recoil associated problems would be peppered throughout the RAF's records and the numerous pilot accounts that have been memorialized to writing. Can you produce a single one?"

You point out that the Hurricane was primarily used in the air to ground role with the 4 x 20mm configuration and that this is evidence that it didn't work in the air to air realm. I would point out that the P-47, later in the war also assumed primarily an air to ground roll. Are we to conclude that this was because it was found that a compliment of 8 x .50's produced too much recoil to be effective in the air to air realm? Of course not.

You know very well why the Hurricane was relegated primarily to air to ground operations and it had nothing to do with the unacceptability of the 4 x 20mm layout. In war you attempt to direct resources efficiently. If there are planes with better air to air performance (Spitfire), you put them there in that role. The Hurricane was obsolete as an air to air resource whether with 8 x .303's or 4 x 20mm's.


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## delcyros (Jul 8, 2006)

Jank said:


> So what. I'm sure that in 1940, had you been in the USAAC, you would have told Alexander Kartvelli that his idea for an 11,500lb behemoth, armed with 8 x .50 cal machine guns "exceeded typical ww2 Fighter A/C values by much" and that therefore, it could not possibly be a success and was a waste of time and money.
> 
> 
> In war you attempt to direct resources efficiently. If there are planes with better air to air performance (Spitfire), you put them there in that role. The Hurricane was obsolete as an air to air resource whether with 8 x .303's or 4 x 20mm's.



You raise two points here. The first beeing something wrong, I think. The XP-47B wighting 11500 lbs does not exceed the typical 0.10 limit for fighter A/C: total netto recoil is 338 Kp for eight 0.50cal guns (400 including gaz effects), so the recoil weight ratio is: 0.064 (0.076 with gaz effects), well below 0.10. and in within the typical ratios for US fighter planes. I would have nothing to concern about this layout.
The second point You arise is different. The Hurricane is quoted by You for an example of a plane beeing a very stable gunplatform despite the fact that it exceeds the "rule". You have to be careful with this. Are the pilot reports stressing the good gun platform rating relative to the Hurricane II mod with four 20mm or to those with 0.303cal guns? Is this in every case clear or not? The recoil weight ratios for both planes differ a lot (with twelve 0.303: 0.030; with four 20mm: 0.14), so this question is justified. I above posted that at least the VVS might have concerns with the 20mm Hurris (debatable).
I agree with You that ground attack purposes may justify the use of extra 20mm guns.
best regards,


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## Jank (Jul 8, 2006)

*"You raise two points here. The first beeing something wrong, I think."*

No. You misunderstood the point. Perhaps I am at fault for not being clear. This was an analogy. The point of the example of the XP-47 was just to demonstrate that it was WELL BEYOND the size and weight of ANY single engine fighter in existence. You could have easily calculated the average weight and size of existing fighters that were successful and shown that the proposal for the P-47 was a recipe for disaster because the "values" for average maximum size and weight would have been greatly exceeded and that therefore the propasal should have been deep sixed by the USAAC.

As it turned out, the P-47 can be credited with great responsibility for breaking the back of the Luftwaffe.


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## delcyros (Jul 9, 2006)

I got Your point. However total values and relations are something different. Our topic is related to whether or not it would be practical to use six 20mm guns on the P-47 airframe. The P-47 indeed is an extraordinary design, which turned out to be something very usefule for it´s pretended role as escort (later ground attack) fighter.


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## delcyros (Jul 9, 2006)

Tony, if You are still around here, I have a question regarding MK 103 projectile weights:
WORLD WAR 2 FIGHTER GUN EFFECTIVENESS
this page gives the projectile weight for the MK 103 with 330g for HE (M) rounds (MK 108 HE(M): 330g),
altough Lunatics values are:
Lunatic's WWII Aircraft Gun Ballistics Page
MK 103: 330g; MK 108: 312g, both for HE(M) Ausf.A rounds 
to make things more complicated
The Bf 109´s guns
and my books list the projectile weight of the MK 103 with 530 g with a round weight of 980 g instead of 780g. (MK 108: 330g with a round weight of 480g)
???
And a second question regarding the gunmount weights for 0.50cal and 20mm guns. Esspecially the later with recoil damping applications.
Thanks in advance,


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## Jank (Jul 9, 2006)

*"Our topic is related to whether or not it would be practical to use six 20mm guns on the P-47 airframe."*

I know what our topic is. It was an analogy. You are not just missing the forest through the trees but through individual branches as well now. That was analogy too. I know we are not talking about forests, trees or branches. 

*"However total values and relations are something different."*

There can be no relationship between number of pounds (value) per number of engines (value)? At 11,500lbs, the P-47 was by far the heaviest single engined fighter ever to be proposed in 1940. Because of this, there was great casternation by some in the corps about invresting in its development.


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## Tony Williams (Jul 9, 2006)

delcyros said:


> Tony, if You are still around here, I have a question regarding MK 103 projectile weights:
> WORLD WAR 2 FIGHTER GUN EFFECTIVENESS
> this page gives the projectile weight for the MK 103 with 330g for HE (M) rounds (MK 108 HE(M): 330g),
> altough Lunatics values are:
> ...



Many similar but different 30mm projectiles were used in the MK 108 and the MK 101/103 towards the end of the war. These are quite comprehensively listed, but it is sometimes difficult to tell which were common and which were rare or experimental. However, the M-Geschoss were the standard for aerial combat and they almost all weighed 330g, +/- 8 g.

The MK 108 weighed 483-487g total, the MK 101/103 varied a lot because some of the older, thick-walled HE and steel AP could also be loaded, and these were much heavier. Total cartridge weight therefore ranged from 778g (+/- 30) for the M-Geschoss to 935g.

I have no information on mounting weights, these would have varied according to the installation. It could in any case be difficult to separate the mounting from the surrounding aircraft structure.

Tony Williams: Military gun and ammunition website and discussion forum


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## delcyros (Jul 10, 2006)

Tony Williams said:


> Many similar but different 30mm projectiles were used in the MK 108 and the MK 101/103 towards the end of the war.



Thanks for clarifcation, Tony. I just noticed that the heavier 530g projectile was primarely used for tank hunter Hs 129. Didn´t knew that the lighter 330g projectile was exclusively used for HE-mine rounds. I find it interesting to note that muzzle velocity figures for both unsimilar projectiles are pretty identic. Probably explainable by the larger cartidge with more propellant contents.
I do suspect that the trajectory of the heavier projectile is far superior due to a better sectional density with all other factors beeing identic. Should be noted that the brutto recoil of a gun firing the heavier projectile is ~ 75% bigger !


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## delcyros (Jul 10, 2006)

I continue to search for statements regarding recoil on fighter planes. From another thread posted by V2:

"Q: Did you have problems hitting targets with the 37 mm’ gun of the YAK?
A: No, it had strong recoil but I had my sight and had no problems hitting targets. " -A.
_(it should be noted that this statements is not relative to air targets)_

If any of You has pilot information, please poste them here or pm me, we are trying to collect infos. Thanks in advance.


However, if any of You guys has the opportunity to interview a veteran, please use the possibility to ask for!
(example of questions regarding recoil):

Q) What armement do you remind, had the plane You flew?
Q) Under which circumstances /loads / targets did You opened fire?
Q) Did you noticed any recoil affecting the plane´s handling?
Q) Did you noticed any recoil affecting the aiming?
Q) Charackterize typical recoil. 
Q) How long were average firing bursts in your Memory?
Q) Do You noticed recoil differences for different loads or weapon configurations?
Q) Do you noticed different recoil charackteristics for different planes?


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## Tony Williams (Jul 10, 2006)

delcyros said:


> Thanks for clarifcation, Tony. I just noticed that the heavier 530g projectile was primarely used for tank hunter Hs 129. Didn´t knew that the lighter 330g projectile was exclusively used for HE-mine rounds. I find it interesting to note that muzzle velocity figures for both unsimilar projectiles are pretty identic. Probably explainable by the larger cartidge with more propellant contents.
> I do suspect that the trajectory of the heavier projectile is far superior due to a better sectional density with all other factors beeing identic. Should be noted that the brutto recoil of a gun firing the heavier projectile is ~ 75% bigger !


The primary tank-hunting ammo used in the MK 103 was the tungsten-cored Hartkernmunition, which weighed in at 355 g and was fired at 940 m/s. The M-Geschoss weighed 330 g and were fired at 860 m/s (although the MK 101 fired them at 930 m/s). The reason for these odd figures is that the MK 101 was a stronger gun than the MK 103, so the M-Geschoss loading for the MK 103 was reduced in pressure and velocity. The Hartkern round was not reduced because velocity was so important for penetration, so they took the risk of a short gun life when using it. Incidentally, the speed of operation of the MK 103's mechanism was sensitive to the ammo - it fired at 420 rpm when using M-Geschoss, 360 when firing Hartkern.

The main alternative loadings for the MK 101/103 were as follows:

HE: 433 g at 800 m/s
APHE: 500 g at 690 m/s
APHEI: 455 g at 760 m/s.

The APHEI was probably used more than the others; it stayed in use because the Hartkern round was less effective against tanks with spaced armour plates.

Tony Williams: Military gun and ammunition website and discussion forum


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## Twitch (Jul 11, 2006)

Jank- yes the now obscure topic question has been completely eclipsed. All the statistical data flying about is grand but has absolutely nothing to do with the reality of the actual combat situation by 1944. Fifties and 20 mms were just fine for fighter vs fighter. I don't know of any A/C that had so much recoil so as to be too bothersome to actually shoot and kill effectively.

Strapping 6 20 mms or whatever PC flight simulator armament hacks you all envision is fine but they were overkill on the Allied A/C of which you are speaking. The only crates that "needed" that heavy or heavier armament were Zerstorers! Spitfires and Thunderbolts had NO NEED for 6- 20mm cannon whether they would work smoothly or not. A ship as massive as the Jug could have handled them as was demonstrated with the XP-72. Just remember that the heavily armed Zerstorers had Umrüst-Bausätze -factory conversion and Rüstätza -field conversions sets for armament and they completely lost their ability to perform well.

Did an Fw 190 with 8 20 mms lay rounds on target? Yes. Did its excessive armament degrade performance. Sure. Would a P-47 require 8 20 mms? Hell no! 

A/T weapons are just that- used against stationary or slow moving targets on the ground where recoil versus long burst of fire are irrelevent. If A/T cannon on strike aircraft DID have huge recoil it doesn't matter because the limited number of rounds actually fired at targets negated the perceived problem. They didn't swoop in spitting out ordnance like .30 caliber 1,000 RPM rate of fire!

All the ballistics nonsense comes down to pilots hitting with whatever weapons they were given. Decent shooters could hit their targets with slow of fast moving rounds and experienced shooters could do it using both alternately. How the hell could Imperial Navy pilots routinely range in with 1,000 RPM Type 97 MGs with ordnance traveling at 750 meters per second and switch to 520 RPM Type 99-1 cannon firing at 525 M/S and make kills? Training and experience.

The comparisons are fun to a limited extent of course, but there is no need to belabor the nonexistent problem of recoil affecting kill performance in a negative way or comparing Axis and Allied fighters armament sets which were arrived at for the specialized roles each had.


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## delcyros (Jul 11, 2006)

That´s nice info, Tony.
Do You know what the HE-content for HE and APHE/APHEI and HE(M)rounds was?


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## Tony Williams (Jul 11, 2006)

delcyros said:


> That´s nice info, Tony.
> Do You know what the HE-content for HE and APHE/APHEI and HE(M)rounds was?


The M-Geschoss varied with type, the original blunt-nosed Ausf.A containing 80-85 g, the streamlined Ausf.C more like 70-75 g. 

The 'old-fashioned' 433 g HE-T contained 29 g within its thick walls. The 500 g APHE contained 14-15 g, the 455 g APHEI just 11 g.

WW2 ammunition is described and illustrated ((including sectioned drawings to show the designs) in *Flying Guns – World War 2: Development of Aircraft Guns, Ammunition and Installations 1933-45 *by Emmanuel Gustin and myself - details on my website! 8) 

Tony Williams: Military gun and ammunition website and discussion forum


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## delcyros (Jul 12, 2006)

Thanks again. I was just asking becuase I do still not know, how to rate projectile effectiveness at impact relation (not at muzzle relation).
I have seen several attempt, so far none of them convinced me:
1.) "influencal zone" (ignores HE content, impact velocity and obliquity but takes fragmentation into account): shell weight / 4pi r2.
2.) Via blast effect (ignores true impact velocity but takes HE content into account)
3.) Via momentum (takes impact velocity and shellweight into consideration, only)

Twitch, which Fw-190 variant had 8 20mm guns? So far, I only know about the Fw-190 A5/U12 with a dual 20mm pod under each wing, but the outer wing gun was always removed with this configuration, leaving six 20mm guns + 2 MG. Perhaps You refer to something, which slipped under my radar, would be interesting.
The XP-72, however, prooved nothing. No XP-72 had four 37mm guns attached to the airframe, so we impossibly can say that this plane demonstrated how good the airframe could handle the recoil.


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## Tony Williams (Jul 12, 2006)

delcyros said:


> Thanks again. I was just asking becuase I do still not know, how to rate projectile effectiveness at impact relation (not at muzzle relation).
> I have seen several attempt, so far none of them convinced me:
> 1.) "influencal zone" (ignores HE content, impact velocity and obliquity but takes fragmentation into account): shell weight / 4pi r2.
> 2.) Via blast effect (ignores true impact velocity but takes HE content into account)
> 3.) Via momentum (takes impact velocity and shellweight into consideration, only).


There is no simple answer to that question, mainly because AP bullets and HE shells have different destructive mechanisms, which are differently affected by distance. They will also have different effects depending on the structure of the plane, and where they hit it.

There is also the question of destructiveness v hit probability; to give an hypothetical example, fighters could have carried a battery of bazookas into combat, which would have had devastating effectiveness if they'd hit - but the chance of hitting would have been negligible. So projectile time of flight - i.e. velocity - is an important factor.

I took all of these factors into account when devising the formula used in this article: WORLD WAR 2 FIGHTER GUN EFFECTIVENESS I will be the first to admit that it is fairly rough and ready, but it does seem to match pretty well with the few actual assessments of relative effectiveness we have. I really don't think that there is any point in trying to devise anything more sophisticated.

Tony Williams: Military gun and ammunition website and discussion forum


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## delcyros (Jul 13, 2006)

I fully agree with You. Something of particular interst for me are the different trajectories at distance for the different aircraft rounds. They do seem to limit the effective range as well (in case the projectile drops below Mach 1). 
Other factors may play a role, too: gunsights, skill, stability of the gunplatform.
For the latter I have found so far 8 quotes regarding them, rating from "no signifcicant importance" to "I could swear I flew backwards when firing". Up to now I have not found anything to contradict the "rule" but this hasn´t to mean anything.


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## Twitch (Jul 13, 2006)

Rüstätza were field conversions sets for armament mods and there were tons of them done with the official sets and by inventive Luftwaffe armorors. Geez there were 410s with 6 20mms and 2 30mms too and just about everything we can imagine.

Yeah the XP-72 was little more than your basic T-Bolt and if could handle 4 37mm it could certainly handle 4 or 6 20mms, right?


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## delcyros (Jul 13, 2006)

The difference in design expectations and combat proofed are significant. The XP-72 was designed to handle six 0.50 cal guns but one production variant should have four 37 mm guns. This variant was canceled long before it went to the assembly plant, so we cannot judge her stability as a gunplatform. It simply had no chance to proof itself in flight. Well possible (..and I believe probable...) that it shares the same fate the He-162 suffered: Recoil of the designed weaponry was underestimated.
There is a significant difference in recoil produced from 37 mm and 0.50 cal guns, the four 37 mm guns do produce 6-7 times (including gaz effects) the recoil of the six .50 cal. And because the recoil is spread over fewer pulses it´s going to be much more severe.
So if You say that the P-47 will handle the problem in analogy to the XP-72, You will draw critizism on You regarding the point that no XP-72 was build with such a weaponry. No proof, no deal.
The Me-410 is a destroyer, no fighter plane. But even with this in mind, there was no version with six 20mm AND two 30mm guns. Either two 30mm + (two 13mm) + two 20mm or four 20 mm + two 8mm (means defensive remotely controlled guns)
Even the heaviest variant, the Me-410 A2/U4 had two 8mm +(two 13mm) + a single 50 mm gun.
The Me-410 A2/U1 with six 20mm + (two 13mm) + two 8mm does not exceed
the "rule" for a good gun platform rating.
The P-47 surely will be able to handle four 20 mm guns without significant performance reduction or impact on stability, whether or not the plane will be able to handle as much as six 20mm guns depends on the purposes and what do You accept in performance losses. There is space for debate left. There are good chances to fit six 20 mm Hispano MK V with the limitations Jank suggested, altough there might be some performance reduction or reduction in stability of the gun platform when firing all guns simultaneously. For the ground attack role, as You already recognized, such concerns do not play a major role.


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## delcyros (Jul 15, 2006)

...taken an example from Lunatic from an earlier post, regarding recoil forces on mid wing mounted guns, the A1D Skyraider suffered very worsely if one of her two 20mm guns jammed, the recoil always was to strong to be trimmed out.
This eventually lead to the four 20 mm gunned Skyraider (Recoil-weight ratio:0.076), not because they wanted more firepower but because if one gun jammed and the other mate was out due to recoil issues they had one pair left.
This shouls be true for the P-47 as well.
The Spitfire IXc is listed with four 20mm cannons (recoil-weight ratio: 0.16) but due to recoil and performance issues almost always flew with only two 20mm guns. The RCAF No. 421 squad flying the four gunned version almost entirely flew ground combat sorties with them. 
Factoring recoil, weight and jamming rates, the six 20mm are truly no improvement over eight 0.50cal guns. You gain destructive power but You do loose accuracy, platform stability, performance. Personally I would upgun the P-47 with six to eight 0.60cal guns. They do not have such a strong recoil compared to 20mm, significant more projectile weight than a .50cal, a decent muzzle velocity + a comparable rof (which is improvable had they concentrated on this). The higher sectional density gives them extreme accuracy due to an even flatter trajectory and shorter time to distance figures, a better punch, a longer effective firing range and I do suspect a better armour penetrating capability as well (at least for low impact obliquities). So You get improvements in both main aspects with this gunnery layout for our P-47: Improved hit probability and better punch instead of trading the former for the latter. With only six 0.60cal and 350 rpg, the planes weight +their handling performance remains almost the same, the recoil-weight ratio is 0.059, well in within excellent figures for fighter A/C.


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## Jank (Jul 16, 2006)

*"Factoring recoil, weight and jamming rates, the six 20mm are truly no improvement over eight 0.50cal guns."*

Earth to Delcyros, we've already been over this. The weight of six 20's with 175 rounds per gun is about the same as eight .50's at full ammunition load. Thus, weight is not an issue to be factored in.

As to recoil, if the Hurricane handled 4 x 20mm's just fine, then a P-47 would handle 6 just fine and with less recoil force per pound of aircraft. You still have produced nothing convincing me or anyone else that the 4 x 20mm armed hurricanes "suffered" in the air to air role or were relegated to the air to ground role because of that. The Hurricane, to be brief and simple, sucked, and was no longer useful as an air superiority fighter. That is why the 4 x 20mm armed Hurricane as well as the others, were generally withdrawn from air to air duty. It did, however, perform well in the close support ground attack role where speed and climb were not determinative of success. 

The issue of jamming favors a six vs. a four gun installation as well. Again, I am only making the point that a six 20mm armed Thunderbolt, late in the war, after they had largely been shifted to ground attack and close ait support, would have benefitted from such an installation.


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## delcyros (Jul 16, 2006)

Jank said:


> Earth to Delcyros, we've already been over this. The weight of six 20's with 175 rounds per gun is about the same as eight .50's at full ammunition load. Thus, weight is not an issue to be factored in.



The key word was "improvement". Using six 20mm will make the airframe heavier (compensated to some degree by the reduced ammo and the use of MK V instead of MK II, as You suggest. However, ammo boxes, belt weight and gunmount weights are not taken into consideration by Your calculation and they do weight a lot, also). Cutting the ammo to 175 rpg equals to only 14 s. of firing volume instead of 34 s. for M2 with 450 rpg and 29 s. for cal.60 with 350 rpg. Something to worry about for a ground attacker.
The recoil length of the shorter barelled MK V also points to a higher peak recoil despite a somehow lower brutto recoil in comparison to the MK II. Special gunmounts may reduce this effect, as Tony suggested, altough I am sure they don´t come with zero weight. 
Regarding to the Hurricane, I found many quotes regarding the repeated redesign of the wing structure to handle recoil weight´s of the 20mm and I found no pilot quote stating that the plane was "just fine" with four 20mm. All comments regarding the excellent gunstability to proof the Hurricane was fine relate either to the 0.303 cal equipped version if You trace them back (numerous accounts at BoB) or to the soviet modified, which shouldn´t surprise us much.
In the end I am confident that The P-47 with six 20mm is both, overgunned, and unnecessarily limited in purposes. This weaponlayout has more limiting factors than benefits. If You pretend on this, I do believe now that it may be possible to modify the plane in the way You suggested, but as I did earlier, I question the sense of such measures.


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## Twitch (Jul 16, 2006)

Isn't this where it all began like 9 pages ago with most folks agreeing that the P-47 could handle 4 or 6 20 mms? I am mystified as to why anyone needs to ponder that one! I simply look at XP-72 armament variants and figure the Republic engineers had a better handle on it that we do. Whatever. Anyhow, right the P-47 did just fine the way it was and didn't "need" a brace of 20 mils.

Rüstätza were field conversions sets for armament mods in the field. Please note there were many custom "one off" conversions of Luftwaffe aircraft that were not mainstream depicted in the ubiquitous "stat" books. Rüstätza were "kits" to beef up armament on just about every type and sub-model of plane in combat. Luftwaffe armorers were very creative with these and they created alternate armament layouts that were not officially recognized in any way. Hence there aexist narratives describing these overkill gunships that pilots hoped would give them the ultimate advantage in firepower against the bomber stream. Simply because it seems improbably to us armchair crew chiefs 60+ years hence doesn't mean it is impossible.


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## Jank (Jul 16, 2006)

*"Factoring recoil, weight and jamming rates, the six 20mm are truly no improvement over eight 0.50cal guns."*

The USN did testing, the methodology of which was unassailed, that indicated that round for round, a 20mm was 3 times as destructive at close range and 2.5 times as destructive at longer ranges than a .50.

For the air to ground role, it would indeed "truly" have been an improvement over an existing situation that was not a problem to begin with. No one ever said it was needed or necessary. This thread, like zillions of others, is just a "what if" inquiry. 

*"I found no pilot quote stating that the plane was "just fine" with four 20mm."* That was funny because you wouldn't generally come across comments that things are "just fine" if that was the case. "Just fine" is simply not noteworthy. On the other hand, if things were "not fine," you would generally hear about it. Therefore if no evidence exists of comments that things were "just fine" and no evidence exists of comments that things were "not fine," and you had to draw a conclusion, the reasonable and logical inference would be that the absence of "not fine" comments means that it was "just fine."

*"the A1D Skyraider suffered very worsely if one of her two 20mm guns jammed, the recoil always was to strong to be trimmed out."*

I don't believe that for a second.

Sounds like you're arguing just for the sake of arguing which is "just fine" but I think this issue was resolved to everyone's satisfaction long ago.


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## Squeelig (Jul 16, 2006)

I have read that it was a simple task to reduce a guns ROF which increased relaibility and reduced wear on the barrel. If the ROF was reduced to 600 rpm for the twenty milimeter, then the firing time would be increased from 14 seconds to 17.5 seconds which is very respectible. Less jams too. The total output would still be 3,600 ROF per minute which would be more than the 3,000 ROF per minute for a four gun armed 20 milimeter set up. 

3,600 ROF per minute is equivalent to 9,000 RPF per minute in destructive power (2.5 X .50). The P-47 only had 6,000 ROF per minute for its fifty calibers. That's 50% more power at longer ranges.

At closer ranges, that would be like 10,800 ROF per minute of fifty calibers.


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## delcyros (Jul 16, 2006)

Jank said:


> The USN did testing, the methodology of which was unassailed, that indicated that round for round, a 20mm was 3 times as destructive at close range and 2.5 times as destructive at longer ranges than a .50.
> 
> For the air to ground role, it would indeed "truly" have been an improvement over an existing situation that was not a problem to begin with.
> 
> ...



For the latter part, ask Lunatic in his post 52
http://www.ww2aircraft.net/forum/aviation/why-us-only-nation-rely-50-a-2747-4.html
He is reputated for knowing what he said. So believe it or not, the Skyraider suffered from recoil issues.

The former part of your post, while interesting, tends to simplicate the matter. There is no overall agreed solution how to rate gunnery effectiveness, altough the comparsion in gunnery effectiveness
WORLD WAR 2 FIGHTER GUN EFFECTIVENESS
implys that the MK II is even four times as damage effective as was the .50cal.
However, against ground targets You need: armour penetration and a high volume of fire. Explosives have limited benefits most cases (unlike against airframes), except for soft targets like trucks etc. (altough the eight .50cal were sufficiant in destroying them and even steel made locomotives).
Regarding pure volume of fire, six 20mm (or .60cal) gives 75 rps while eight .50 cal give 104 rps, which is a significant disadvantage and don´t ease the probability of hitting something. 
Regarding pure armour penetration the 20mm round is superior at high impact obliquities due to weight advantage but it shows no striking advantage over the 0.50 cal (and I suspect it is about the same or even less effective than 0.60cal) at low impact obliquities. 
It´s ballistic coefficient of 0.555 allows for a quite significant drop in impact velocity for the MK V at 300 m (~630 m/s + planes vectoring speed), so I get via M79 APCLC an armour penetration sligtly less than 40 mm at best possible impact obliquities. In comparison to this the 0.50 cal 736 m/s @300 m + planes speed would give a penetration of slightly more than 41mm, the 0.60cal guns even slighly more than 44mm! -the higher the impact obliquity, the better the 20mm, of course-
Beside this, I would rate the .50 cal even better, because it may defeat thicker plates by repeated hits due to better accuracy and higher volume of fire.
What left from the big advantage of the 20mm? Explosive charge carried. But if You pretend on this advantage I would rather suggest to load more bombs for ground attacks...

Regarding the Hurricane issues, we already have overrun the repititive limit. I posted that the plane was redesigned in the VVS- surely not without good reason. I also posted that the wingdesign had to be modified repeatedly because of the problems associated with handling and firing the large 20mm guns. I am collecting pilot information and will post them later in case I get a sufficiant statistical base (I will also post in case it disproves my theory, anyway). But I suspect You rely on a position not justified to be an argument for or against.


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## Jank (Jul 16, 2006)

Lunatic said, *"With .50's, the recoil can be trimmed out so the mated gun can still be fired. Even on the AD Skyraider (a huge plane), if one 20mm jammed the mate on the opposite wing was useless."*

To which you draw the obvious (to you) conclusion that, *"He is reputated for knowing what he said. So believe it or not, the Skyraider suffered from recoil issues."*

Like I said, "I don't believe that." That does not constitute evidence of anything. Just your faith in a "Lunatic"

*"Regarding pure armour penetration the 20mm round is superior at high impact obliquities due to weight advantage but it shows no striking advantage over the 0.50 cal (and I suspect it is about the same or even less effective than 0.60cal) at low impact obliquities."*

You have a vivid imagination. The issue of armor piercing effectiveness between the .50 and the 20mm has been the topic de jure on this forum before. Bottom line - A 20mm AP projectile has superior armor piercing ability vis a vis the .50 AP at ALL angles. In fact, as the angle increases, the margin of superiority over the .50 increases. 

I suggest you read through the "Armor Penetration - 20mm vs. .50 cal." thread where "Lunatic" discusses the absolute armor piercing superiority of the 20mm over the .50 cal. at all ranges and at all angles. I suspect that given your predilection for favoring "Lunatic" as a definitive source, you will be swayed by his reasoning.

This discussion ceases to hold my interest. It is beginning to resemble the thread about the B-25 being a carrier operable aircraft. We will just have to agree to disagree.

I leave you with the following relevant British tests to mull over:


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## delcyros (Jul 16, 2006)

"I leave you with the following relevant British test:"

Ahh, now You changed Your opinion and swift to the MK II with higher muzzle velocity? Ok-so far, I know the resports.
However, You cannot draw a simple conclusion from them except for that the Hispano 20mm MK II was superior at those test in comparison to other contenders under (unknown) circumstances, because:
1.) mv for ech gun is not noted (gunwear factor)
2.) true impact velocity is not noted
3.) plate penetration circumstances are unknown (the closer the impact was on the plate edges, the easier it makes to penentrate)
4.) individual plate property and condition is unknown ( with ~27 mm penetration, I suspect something like higher grade FH armour of thin thicknesses, which typically was hardened to much higher degrees than the plate hardness, I used for comparison)
5.) remaining striking velocity (post impact logic) is unknown
6.) Quality of penetration is unknown (e.g. condition of projectile behind the plate)
7.) Quantity of penetration is unknown (10 out of 12? 10 out of 10?)

M79 APCLC makes penetration more comparable because it reduces this complex matter to the physical backgrounds of the processes. Against a standart armour plate (average 1.0 Quality (220BRH), Elongation 20%), the samples are taken. Resulting impact force therefore is:
20 mm MK V (!) -true impact velocity*@ 300m: 741 m/s (2452 fps); projectile weight: 129,6 g; energy / unit hole volume: 35078 ft-lbs/in^3 (actual energy density), plate thickness: 1.56" (39,64mm), impact obliquity: 0 deg; result: penetration, ballistic limit for penetration is 2450 fps, remaining striking velocity is 89 fps for post impact logic
0.50 cal M2: -true impact velocity* @300m: 847 m/s (2803 fps),projectile weight: 48,6g; energy / unit hole volume: 41057 ft-lbs/in^3 (actual energy density), plate thickness: 1.62" (41,16mm), ballistic limit for penetration is 2803 fps, remainingstriking velocity is 35 fps for post impact logic. 
And for comparison the MK II 20 mm: -true impact velocity*@300m: 784 m/s (2595 fps), projectile weight: 129,6 g.; energy / hole volume: 35997 ft-lbs/in^3 (actual energy density), plate thickness: 1.705" (43,32 mm), ballistic limit for penetration is 2595 fps, remaining striking velocity: <10fps for post impact logic.
As You see, the 20mm MK II unsurprisingly is superior to the .50 cal at even 0 deg. impact obliquity but the MK V of Your suggested layout, Jank, is inferior due to the lower initial velocity. Cut these datas in half and You get penetration figures for 400 BRH high grade FH armour, which match very well those posted in the test above.

You can do the maths on Your own, there is no cheating in them.


*) calculated with a vector speed of 400 km/h relative to target (111 m/s)

It should also be noted that M79 APCLC used the shell properties from the US M79 APC round, which is in the middle between blunt shaped and very pointed, thus slight differences may occur. However, these tend to benefit the 20mm round (at least the AP MK I), because the .50cal round has a very pointed nose, improving armour penetration at low impact obliquity ( and degrading penetration at high impact obliquities).
It should also be noted that the differences between AP MK I (20 mm) and AP MK II (27 mm) at 200m seem to reflect a completely different projectile type. I have not found anything regarding 20 mm AP MK II ammo but I suspect something like tungsten cored. Maybe Tony may help out here.


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## Jank (Jul 16, 2006)

*"Ahh, now You changed Your opinion and switch to the MK II with higher muzzle velocity?"*

Huh? I selected the Mk. V instead of the Mk. II. To reiterate, I said,

_Six Hispano Mk. V 20mm's weigh in at 554.4lbs. (I chose the Mk. V because it would have been later in the war after the P-47 assumed the air to ground role where six 20's would come in handy. If anyone prefers that I use the Mk. II 20mm instead, just add another 150lbs total weight for all six guns.)_

I have no idea where you are pulling your data from but I wouldn't smell my fingers if I were you. The difference in muzzle velocity between the Mk V and Mk II is just 100fps! (830mps vs. 860mps - please see Tony's tables at WORLD WAR 2 FIGHTER GUN EFFECTIVENESS) And the projectile weight of the AP for both is the same. 

In any event, Delcyros, even assuming the use of less penetrative Mk I as per the British tests, that ammunition has an advantage over the .50 at all but perfectly perpendicular strikes with AP at 200 yards. At 20 degrees, the Mk I has a 36% armor piercing advantage. At 40 degrees, the armor piercing advantage rises to 53%. 

Do you want to talk about the chance that strikes will just happen to strike at perfectly perpendicular angles? 

Do you want to talk about the advantages realized with the Mk II? A six gun compliment would weigh a grand total of 150lbs more! So we can go that route quite easily. That's just 75lbs more per wing over the use of Mk. V guns.

Delcyros, I just want to make sure I understand your tactical strategy in this discussion. "Lunatic" makes a statement without resort to extrinsic data for support and you draw a simple conclusion stating that, *"He is reputated for knowing what he said. So believe it or not, the Skyraider suffered from recoil issues."* 

I offer actual data from tests carried out by the Research and Development Arm of the Ministry of Air Production and you dismiss it saying, 

*"However, You cannot draw a simple conclusion from them except for that the Hispano 20mm MK II was superior at those test in comparison to other contenders under (unknown) circumstances, because:
1.) mv for ech gun is not noted (gunwear factor)
2.) true impact velocity is not noted
3.) plate penetration circumstances are unknown (the closer the impact was on the plate edges, the easier it makes to penentrate)
4.) individual plate property and condition is unknown ( with ~27 mm penetration, I suspect something like higher grade FH armour of thin thicknesses, which typically was hardened to much higher degrees than the plate hardness, I used for comparison)
5.) remaining striking velocity (post impact logic) is unknown
6.) Quality of penetration is unknown (e.g. condition of projectile behind the plate)
7.) Quantity of penetration is unknown (10 out of 12? 10 out of 10?)"*

In addition, I notice that while you rely in conclusory fashion on what "Lunatic" said about the Skyraider, you are apparently not prepared to rely on his opinions concerning the armor penetration superiority of the 20mm vs. the .50 cal. as set out in the other thread specifically addressing this point. Again, see the "Armor Penetration - 20mm vs. .50 cal." thread.

Also, "Lunatic" accepted the exact tests above that you are now questioning. In fact, he quoted them in his discussion on that thread. Therefore, I might add that "He is reputated for knowing what he said. So believe it or not, the 20mm is superior to the .50 in armor penetration."

You are transparent and indeed worthy of a good laugh.


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## Tony Williams (Jul 17, 2006)

Armour penetration is a complex subject, and was made much more so in aircraft because a projectile would never just strike an armour plate first - it would have to work its way through the aircraft skin, structure and ancillary bits and pieces before it even reached the armour. This tended to destabilise the projectiles so that they wouldn't hit the armour point-first. The problem is that this 'destabilising effect' varied enormously from one projectile design to another. Some quotes from *Flying Guns – World War 2: Development of Aircraft Guns, Ammunition and Installations 1933-45*:

_Comparisons between the penetration achieved by different armour-piercing cartridges are problematic for several reasons. First, penetration figures are often quoted at different distances and striking angles (incidentally, striking angles in this work are all quoted using the convention that the most favourable angle for penetration, perpendicular (or "normal") to the armour, is measured as 90º; some other conventions have described this as 0º). Much less obviously, different qualities of armour are sometimes assumed. There have also been various national definitions of "penetration"; some (e.g. the US) specified that 50% of the shots fired have to pass through the target, others required significantly higher percentages, or do not require the shot to pass completely through the target. Finally, AP performance was usually measured on the ground. When fired from an aircraft, the actual figure would be slightly reduced in a tail chase due to increased air resistance (less of an effect at high altitude), but would be increased when firing at ground targets because the speed of the aircraft was added to the muzzle velocity, and considerably increased in a head-on attack.
In addition to these problems, the actual performance of AP projectiles in battle can vary considerably from that achieved on test. In particular, passing through the thin aluminium aircraft skin can induce yaw, i.e. disturb the straight flight of the projectile away from travelling point-first, so that it fails to hit the armour head-on, thereby significantly reducing its penetrative abilities. In fact the degree of obstruction caused by aircraft structures is such that armour much thinner than theory indicated would be necessary was often found to give satisfactory results. 
The most exhaustive tests during the Second World War seem to have been carried out in Germany. Official penetration curves for 7.92 mm AP rounds tested in 1942 are worth examining in detail because they reveal the variations which can occur. The SmK-v (Spitzgeschoss mit Stahlkern verbessert; improved pointed bullet with steel core) achieved the following: 
at 100 m: 12 mm / 90º, 8 mm / 60º,	3.5 mm / 30º
at 300 m: 9 mm / 90º, 6 mm / 60º,	3 mm / 30º
at 600 m: 6 mm / 90º, 3.5 mm / 60º,	1.5 mm / 30º
However, if the bullet first penetrated a 3 mm dural (light alloy) aircraft skin angled at 70º, armour penetration at 100 m dropped to 4 mm / 90º, 3 mm / 60º and 2.5 mm / 30º.
A different 7.92 mm AP loading, the Pz-v (Panzerdurchschlagsleistung verbessert; improved armour penetration) penetrated less than 11 mm / 100 m / 90º but was much more tolerant of unfavourable circumstances, achieving 9 mm / 60º and 4.5 mm / 30º. Even more significantly, after penetrating the same angled dural skin the Pz-v could still penetrate 8.5 mm / 90º, 7 mm / 60º and 3 mm / 30º. Clearly, bullet design made a huge difference.
These results are supported by tests carried out by the British in January 1941 to compare British and German rifle-calibre steel-cored AP ammunition. The performance of the .303" (11.28 g at 735 m/s) and the 7.92 mm (of unspecified type, but measured at 11.53 g at 788 m/s) was first tested against "homogeneous hard armour". The thickness necessary to achieve immunity from this ammunition at 183 m was 12.0 mm for the .303", 12.5 mm for the 7.92 mm, when striking "at normal" to the armour (i.e. at 90º). The British ammunition was significantly worse when the striking angle changed to 70º; only 6.6 mm was needed for immunity in comparison with 8.9 mm to protect against the German round. 
The test then changed to shooting at the rear of the long-suffering Bristol Blenheim at the same distance, involving penetrating the rear fuselage before reaching the 4 mm armour plate protecting the rear gunner, which was angled at 60º to the line of fire. The results in this case were reversed; 33% of the .303" rounds reached the armour and 6% penetrated it. In contrast, only 23% of the 7.92 mm bullets reached the armour, and just 1% penetrated. The British speculated that the degree of stability of the bullets (determined by the bullet design and the gun's rifling) might have accounted for these differences. 

_and:_

Continuing with the German ammunition (for which more detailed records seem to survive than any other nation's during this period) it is instructive to compare some of the standard AP types in different calibres. The little 13x64B Pzgr for the MG 131 was capable of penetrating 17 mm / 100 m / 90º but this dropped to just 10 mm / 60º and 4 mm / 30º (equivalent figures at 300 m being 11 mm / 90º and 7 mm / 60º). On the other hand, the consequences of hitting the dural plate first were negligible, only reducing penetration by 1 or 2 mm. The 15 mm Pzgr for the MG 151 at 300 m penetrated 25 mm / 90º, 19 mm / 60º and 12 mm / 30º, but the effects of the dural plate were catastrophic, with figures dropping to 11.5 mm / 300 m / 90º. Clearly, this projectile was not very stable and yawed heavily on passing through the light alloy. This may have been because it was significantly heavier than the usual HEI; the barrel's rifling twist needs to be steeper for a heavy projectile, so it could be that the designers opted for an intermediate twist which only just stabilised the AP. The tungsten-cored 15 mm Hartkernmunition achieved an impressive 42 mm / 300 m / 90º, dropping sharply to 20 mm / 300 m / 60º and 10 mm / 300 m / 30º (a characteristic of the German Hartkern designs). Figures are not given for the effect of dural, presumably because this special ammunition was supposed to be reserved for attacking armoured vehicles only.

Before turning to the 20 mm cannon it is worth mentioning the performance of the .50" Browning. The official requirement for the M2 AP was to penetrate 22 mm steel at 183 m (the M8 API was expected to match this figure at 92 m). The striking angle is not specified but is assumed to be 90º. Official US tables for the M2 show penetration at 300 m as follows: 21 mm / 90º, 13 mm / 60º and 5 mm / 30º. These measurements were to the USN criterion which called for 50% of shots to penetrate. British tests at 183 m determined that the M2 would penetrate 21 mm at 0º angle of yaw (i.e. the bullet was flying perfectly straight) but this dropped to 15 mm with only 10º of yaw (such as might be caused by passing through an aircraft’s skin before hitting the armour). Further tests at 90 m firing through a heavy bomber fuselage demonstrated an ability to penetrate between 14 and 20 mm when firing at angles of between 57 and 77º. German tests credited the M2 with a penetration of 25 mm /100 m / 90º, falling to only 10 mm after passing through the dural skin (the 12.7 mm Berezin API was even worse affected, falling from 25 mm to 8.5 mm). Taking the effects of typical ranges, striking angles and fuselage structures into account, it seems likely that the practical penetration of either the M2 or M8 was in the region of 10-15 mm in normal circumstances. This was generally adequate for dealing with aircraft armour although it should be noted that Finnish pilots using Brewster Buffalos armed with .50" Brownings reported considerable difficulty in shooting down Soviet fighters from directly behind and recommended attacking from a slight angle in order to fire past the rear armour plate. 

_and:_

The Allied 20 mm Hispano was significantly more powerful than the MG 151/20, but little attempt seems to have been made to exploit this in terms of armour penetration. As already described, the RAF settled on a mixture of HEI and a SAPI projectile which was specified to penetrate 20 mm / 200 m / 90º and ignite petrol in cans behind the plate. This was regarded, with some justification, as entirely adequate to deal with enemy aircraft. The US M75 AP shot for this cartridge was claimed to penetrate 18 mm homogenous plate or 16.5 mm face-hardened armour at 457 m / 70º. Another US official source gives penetration at 300 m as follows: 31-39 mm / 90º (depending on the armour hardness), 19 mm / 60º and 10 mm / 30º (presumably for average armour hardness). The Germans surprisingly credited this loading with only 25 mm / 100 m / 90º, although noted that passing through the usual dural skin only reduced this to 21 mm. The British did experiment with a tungsten cored type, similar to Hartkernmunition, (the AP Mark III.z) designed by Janecek of "squeezebore" gun fame, which was intended to penetrate up to 60 mm / 200 m / 70º, but it seems that it was ballistically unsatisfactory and was not adopted._

Tony Williams: Military gun and ammunition website and discussion forum


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## delcyros (Jul 17, 2006)

Squeelig said:


> I have read that it was a simple task to reduce a guns ROF which increased relaibility and reduced wear on the barrel. If the ROF was reduced to 600 rpm for the twenty milimeter, then the firing time would be increased from 14 seconds to 17.5 seconds which is very respectible. Less jams too. The total output would still be 3,600 ROF per minute which would be more than the 3,000 ROF per minute for a four gun armed 20 milimeter set up.



True. The volume of fire per sec. would have been drastically reduced in this layout to 60 rps in comparison to 100 rps with eight 0.50cal. Still, 60 rps is impressive for cannon fire.


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## delcyros (Jul 17, 2006)

Jank said:


> Huh? I selected the Mk. V instead of the Mk. II.
> 
> I have no idea where you are pulling your data from but I wouldn't smell my fingers if I were you. The difference in muzzle velocity between the Mk V and Mk II is just 100fps! (830mps vs. 860mps - please see Tony's tables at WORLD WAR 2 FIGHTER GUN EFFECTIVENESS) And the projectile weight of the AP for both is the same.
> 
> ...



To this point I enjoied the discussion but now I see no justification to continue (with the attitude You have) so this is my last post in this thread.
The difference between MK-II and MK V is due to true impact velocity in the comparison I made. I actually calculated with a 40 m/s difference according to:
The WWII Fighter Gun Debate: Gun Tables
And if You check this with the true impact velocities for MK V and MK II, the difference at 300 m is only 43 m/s according to Balltraj. The weight of both AP-rounds is the same, You don´t need to worry about this.
From Tony´s 20mm datas:"Another US official source gives penetration at 300 m as follows: 31-39 mm / 90º (depending on the armour hardness)".
This almost exactly match my calculations, altough now I am confident that 220BRH hardness for such thin plates is highly improbable. Thin plates can be treated better than thick ones and usually are hardened to high degrees:
typical BRH values for (homogenious) target plate thicknesses (in mm):
5 to 15------435 to 465
16 to 30-----338 to 382
31 to 50-----323 to 368
51 to 80-----309 to 338
81 to 120----279 to 309
121 to 150---235 to 265
151 to 275---206 to 235
(all from german sources)
typical BRH values for homogenious target plates (in mm):
6 to 13------330 to 370
25-----------240 to 350
38-----------240
51-63--------240
76 to 127----220 to 240
>127---------220
(all from US sources)
typical BRH values for homogenious target plates (in mm)
3 to 30------440 to 475 
15 or more---300 to 331  
3 to 14mm---340-388 
15 to 30-----262-321
31 to 80-----262-321
85 to 120----255-302
125 to 160---241-285
>160--------?
(all from british sources)
The underlined figures are those relevant to the tests.
This may explain the significant differences between the tests to some degree. Esspecially for british tests it is impossible to draw conclusions if those plate properties are not given because several, different specifications (four!) were used contemporary for target plates.
Now if You factor the different 20mm AP results from Tony:
from german test: 25 mm / 100 m / 90º (impact obliquity= 0 deg) [BRH= 338-382]
from british test: 27 mm /200 m / 0 deg [BRH= [U]262-475[/U]] 
from US tests: 31-39 mm/ ? / 90º [BRH = 240-350]
None of the tests is comparable to each other since the plate hardeness remains unknown. The german target plates differ less in hardness for this thickness than do US plates and particularly british plates (due to different specifications).
The M79 APCLC results from me give results for the same plate hardeness, so a comparison between the guns is possible (all using AP-rounds):
20 mm MK II: 43,3 mm / 300 m / 0 deg [BRH= 220]
20 mm MK V: 39,6 mm / 300 m / 0 deg [BRH = 220]
.50 cal M2: 41,1 mm / 300 m / 0 deg [BRH = 220]

There is nothing wrong with my datas, except for the plate hardness, which seems to be too soft, hence the deifferences to the recorded datas. I also suspect the germans used something more around BRH 380 for their tests, while the british actually may used something in the region between 300 and 350 BRH. The US plates, which match my calculations most are also made from comparably soft material (BRH 240-350, depending on hardness, as the quote imply). I cannot be sure here as long as the plate properties are not given, but the calculations give an idea what happens. Better armour penetration tests do not give the plate thickness, which is defeatable (this is dependent on more factors) but the minimum necesaary striking velocity for a specific projectile at a certain impact obliquity to defeat the plate, which also always is charackterized regarding ductility and hardeness (both is missing in these records). 
There is no doubt that the MK V (unlike the MK II) has no advantage over the 0.50 cal in penetration abilities at 300 m and 0 deg impact obliquity. That´s what I said. I do also confirm that the superiority of the 20mm round is significant as the impact obliquity rises. The tungsten cored and tungsten tipped AP rounds for 20mm and .50cal. respectively, do have different plate penetration curves.
By the way, thanks for the datas, Tony, esspecially the yaw inducing datas are interesting. 

best regards,


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## Tony Williams (Jul 17, 2006)

delcyros said:


> The M79 APCLC results from me give results for the same plate hardeness, so a comparison between the guns is possible (all using AP-rounds):
> 20 mm MK II: 43,3 mm / 300 m / 0 deg [BRH= 220]
> 20 mm MK V: 39,6 mm / 300 m / 0 deg [BRH = 220]
> .50 cal M2: 41,1 mm / 300 m / 0 deg [BRH = 220]


I have penetration curves for the .50 Cal AP M2 and the 20mm AP M75, both from the Ballistic Section, Technical Division, USN, and both dated December 1943. We may therefore assume that the data is comparable.

The .50 Cal was measured against homogenous plate of 350 BHN. At 300m this gave the following figures: 
Striking velocity (from aircraft gun: 36" barrel) = 740 m/s. 
Penetration at 0 degrees = 22 mm

The 20mm was fired against plates of various hardnesses. Against 350 BHN plate, the following figures are given:
Striking velocity at 300m = 655 m/s
Penetration at 0 degrees = 39 mm

Tony Williams: Military gun and ammunition website and discussion forum


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## Squeelig (Jul 17, 2006)

Wouldn't the effect of yawing have a greater effect on the fifty's ability to penetrate than the twenty milimeter? 

I still don't see how any of this is relevant guys. You still have a situation where each round of twenty milimeter is at least 2.5 times as effective as each one from a fifty.


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## Jank (Jul 17, 2006)

I think the loss of velocity that Delcyros listed at 300 meters is frankly too little. A start of 880ms and still travelling at at 847ms at 300 meters? The .50had a great BC but there would be more velocity loss. That much I know.

The differences in striking velocity at 300 meters between the data that Delcyros used and Tony used is as follows:

For the .50, Delcyros used 847ms and Tony used 740ms

For the 20mm, Delcyros used 741ms and Tony used 655ms.

Tony said,*"The .50 Cal was measured against homogenous plate of 350 BHN. At 300m this gave the following figures:
Striking velocity (from aircraft gun: 36" barrel) = 740 m/s.
Penetration at 0 degrees = 22 mm

The 20mm was fired against plates of various hardnesses. Against 350 BHN plate, the following figures are given:
Striking velocity at 300m = 655 m/s
Penetration at 0 degrees = 39 mm"*

I take it that we have closure now. The 20mm has a penetration superiority on the order of 77%. At angles of deflection, that superiority would increase.

It is simply not possible that, pursuant to Delcyros' assertion, increasing the velocity by 107ms for the .50 and 86ms for the 20mm (a 20ms difference in increase between the two) would then result in the .50 now outpenetrating the 20mm.

Besides, "Lunatic" would disagree with you. That settles it.


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## Jank (Jul 17, 2006)

Squeelig said, *"Wouldn't the effect of yawing have a greater effect on the fifty's ability to penetrate than the twenty milimeter?"*

Good point. Yes. The .50 has greater sectional density than the 20mm and given its comparatively low weight, relies on that for penetration so yawing would indeed be more detrimental to the penetration of the .50 than the 20mm.

You will also notice that the .50 is affected by angles of deflection much more than the 20mm. 

I think that ideally, comparing perpendicular hits (90 degrees or 0 degrees depending on how you figure it) is unrealistic. All comparisons should be at 45 degrees. Comparing penetration at 90/0degrees gives a false boost to the .50 cal's armor penetration abilities under circumstances that would be a rarity in the real world of combat. Even Delcyros' data wouldn't support an outcome where the .50 is superior to the 20mm at 45 degrees. 

For an illustration of the effect on penetration due to angle of deflection between the .50 and 20mm, look below. Looking at the Mk I vs. .50 tests, we see 100% parity at 90/0 degrees, then at 20 degrees, the .50 is down to 70% and the 20mm is down to 95%, then at 40 degrees, the .50 is down to 40% and the 20mm is down to 75% of it's ability to penetrate. The 20mm retains penetrative ability at angled strikes far better than the .50 does. (This is Mk I and not the Mk II)

And why just examine armor penetration? Look at the penetration through sand. The .50 at 200 yards penetrates 15" while the 20mm Mk I penetrates 24" (a 60% increase over the 50's ability to penetrate). (This is Mk I and not the Mk II)


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## Jank (Jul 17, 2006)

Delcyros, 

As I said above, _I think the loss of velocity that Delcyros listed at 300 meters is frankly too little. A start of 880ms and still travelling at at 847ms at 300 meters? The .50had a great BC but there would be more velocity loss. That much I know._

From "Lunatic's" website at Lunatic's WWII Aircraft Gun Ballistics Page

Note that the .50 BMG is listed as having a velocity of *736ms* at 300 meters and not the *847ms* figure you are using. 

As you well know, Lunatic knows what he's talking about which, of course, necessarily means that you don't know what you're talking about. 

Lastly, it just so happens that Tony's data matches Lunatic's. This makes perfect sense because Lunatic bases his information on Tony's data. Tony lists 740ms at 300 meters.

Again, Tony's data states:

*The .50 Cal was measured against homogenous plate of 350 BHN. At 300m this gave the following figures:
Striking velocity (from aircraft gun: 36" barrel) = 740 m/s.
Penetration at 0 degrees = 22 mm

The 20mm was fired against plates of various hardnesses. Against 350 BHN plate, the following figures are given:
Striking velocity at 300m = 655 m/s
Penetration at 0 degrees = 39 mm*

Even if the data above was realized with Mk. II as opposed to Mk. V, (difference at the muzzle of less than 35ms) that wouldn't diminish the penetration at 300m by more than 17 mm (a reduction of 17mm is 2/3 of an inch and would represent a 43% decrease) which would be required in order to put it at below the .50's ability to penetrate 22mm.


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## delcyros (Jul 17, 2006)

Jank said:


> Delcyros,
> 
> As I said above, _I think the loss of velocity that Delcyros listed at 300 meters is frankly too little. A start of 880ms and still travelling at at 847ms at 300 meters? The .50had a great BC but there would be more velocity loss. That much I know._
> Note that the .50 BMG is listed as having a velocity of *736ms* at 300 meters and not the *847ms* figure you are using.
> ...



Dear Jank, dear Tony,

The impact velocities are correct, as I stated above:
"*) calculated with a vector speed of 400 km/h relative to target (111 m/s)"
so I used Lunatics values for 300 m (for example: 20mm MK II: 673 + 111 = 784 m/s; .50cal: 736 + 111 = 847 m/s) to get a true impact velocity (including plane vectoring speed, the gun is not fired with speed zero). Altough all will be a bit lower due to the higher initial rate of deceleration. Note that the 20mm round even benefits from this (!) and puts the .50 cal to a disadvantage, factoring the higher BC (= less deceleration) of the 0.50 cal rounds. I would be glad to have a computing system for deceleration rates of small calibre rounds, but sadly I do only have them for medium to large calibre rounds (50 mm and up), so these are approximations but very close ones, relied on Lunatics page (whom´s calculation I trust unless You present better results).

Tony, can You give me more datas or a copy about this specific test. All I have studied so far implies that 39 mm @ 300 m / 0 deg with a plate hardeness of 350 BRH is totally contradicting even british datas and sources (not to speak of other US and german tests). A testplate of 39 mm is quite difficult to process with a specification calling for 350 BRH, hence specifications do call for 240 BRH for these thickness and US tests. I know there are plates of this hardeness used by germans but for the US I know only two experimental plates, which match those requirements, and none of them actually was tested against 20mm rounds. I am not aware of other special plates used for .50 cal tests on prooving grounds (it may have happened), so this source would interest me in particular. Indeed such a figure would surprise not only me but also friend and expert Dr. Wegener. In case this plate indeed has 39 mm and 350 BRH and has no major internal flaws (bubbles, pipings (long tube-like bubbles), cracks, laminations, and any other irregularities, this would exceed even the special treated plates with about 300 Brinell (32 Rockwell "C") hardness for plates under 51mm thickness!
This penetration value is also totally off-line if I use the official Ministery of Defense british penetration formula for homogenious armour, announced 1942:
B0 = 500 - (160)(0.434294482)[LOGe(D / 1.5648 )]

B1 = 54000 / (B0 - BHN)

FOB1 = 11800 / (65o - OB)

FOB2 = (43.4)(PQF)(T/D)[SQRT(BHN)]/COS[(1.5)(OB)]

FOB3 = 929 - B1 - FOB1 + FOB2

BRITNBL = FOB3 / SQRT[W/D3]

But it fits very well with a plate hardeness of 250 BRH (.8% difference). 
This would indeed imply an actual energy density above 65000 ft-lbs/in^3, which is hard to believe (impact force necessary to cause such energy densities would even be higher than a 37 mm NS37 impact from this distance!).

Thanks in advance,


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## Jank (Jul 17, 2006)

*"The impact velocities are correct, as I stated above:
"*) calculated with a vector speed of 400 km/h relative to target (111 m/s)"
so I used Lunatics values for 300 m (for example: 20mm MK II: 673 + 111 = 784 m/s; .50cal: 736 + 111 = 847 m/s) to get a true impact velocity (including plane vectoring speed, the gun is not fired with speed zero)."*

You are correct and I am an ***. 

I am still not convinced that the .50 cal would out penetrate a Mk V 20mm at 300 meters though. Perhaps Tony can give his thoughts. 

And what about at a 20 degree angle? What about at a 40 degree angle? As I indicated above, pependicular strikes would be rare. Tony indicated that after striking the aluminum skin, the bullet yaws thereby not striking with the maximum ability to bring its sectional density to bear. And lastly, the penetrative ability of the .50 would be affected more by both yaw and angled strikes than the 20mm.

Additionally, when the USN determined that ther 20mm was 2.5 times as destructive at longer ranges, how exactly did they define destructive? Even the Mk II doesn't have 2.5 times the armor penetration ability so I believe that were referring to effects beyond mere armor piercing ability. Whatever effects they include, they would favor the 20mm over the .50.

And finally, the 6 x Mk V setup can still be swapped out for a 6 x Mk II setup at a total increase in weight of 150lbs for all six guns. As you may recall, I originally advanced the idea of using Mk V instead of Mk II because you were concerned with weight degrading the flight performance of the Thunderbolt. I always maintained that it wouldn't make a hill of beans difference, especially in the ground attack role.


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## delcyros (Jul 17, 2006)

I actually liked the idea with the MK V due to their lower recoil , weight higher rof. The long barreled MK II with recoil-damping gunmount might offset the larger brutto recoil as I learned from Jank, but it still is a very bulky weapon.

Regarding higher impact obliquities, the 0.50 penetration curves drops with a steady rate, much steeper than the 20 mm. This may be partly caused by the thickness / diameter relation and mostly because of the blunter nose of 20 mm projectiles. I can perform calculations, if You desire (all factors beeing the same as above=300m, 220 BRH):
20mm MK II: 41,6mm(20deg), 37,5mm(40deg), 33,4 mm (45 deg)
Note that it takes only a loss of 4 mm between 20 and 40 deg and further 4mm between 40 and 45 deg. impact obliquity for the 20mm AP MK I fired from 20mm HS MK II. 
0.50 cal AP: 39,1mm(20deg), 33,0mm(40deg), 28,9mm (45deg)
Note that the .50 cal projectile loses 6 mm penetration between 20 and 40 deg. impact obliquity and further 6 mm for 40-45 deg. impact obliquity.
Loss is relative to armour quality. The 220 BRH are too low, as we recognized, so I estimate that the .50 cal round would have more detremental losses with higher grade armour material than this softer "comparison steel". Also, the less pointed nose of the 20mm round will perform better at high impact obliquities (program credits only for a standart middle shaped nose), which is not reflected by the calculation above (the significance rises with impact obliquity).
Yawing effects are not that important for ground attacks, since few vehicles (unlike planes!) had layered armour layout (or inner mounted plates). They are not quantifyable according to recent knowledge. They do happen and this is expressed with an "estimated percentage of Yaw" rather than with "a loss of penetration" -figure, altough Tonys infos covering this aspect are highly interesting. Too much factors play a role: impact velocity, plate 1 thickness, plate 2 (..3...4) thickness, angles, spacial distribution (the larger the distance beween the more probable are yawing effects), spin of projectile and weight (=stability border to induce yaw) and much others. Yawing effects can be considerable but more "stable" projectiles (not necessarely heavier ones) need more inducing force for them. 
There is no doubt that the 20mm round carries more HE charge, is heavier, has more source for fragmentation and therefore will cause more damage against air targets and "soft" ground targets.


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## Jank (Jul 17, 2006)

What would the armor penetration be for a .50 vs a 20mm fired from a Mk V at 300 meters at 20 degrees deflection? At 40 degrees deflection?


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## delcyros (Jul 17, 2006)

...38,0mm at 20 deg. with a similar 4mm dropping rate to the MKII with 33,9mm at 40 deg and 29,8mm at 45 deg. (true values should be slightly better due to less pointed nose with higher impact obliquity, note). 0.50cal as above, so there is parity in penetration at around 30 deg (probably more close to 25 deg.) and beyond this the 20mm MK V, despite the lower muzzle velocity, has a better penetration according to M79 APCLC.


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## Tony Williams (Jul 17, 2006)

A few comments:

The USN penetration graphs to which I referred I have only in the form of poor-quality photocopies. I do not know how the results were obtained, but I can hardly imagine that they had a huge variety of plates of different thicknesses and fired at each one at every range and striking angle - I expect that they carried out a few actual tests at critical points and interpolated the rest (that would be the only practical way to do it IMO).

I should emphasis that the 20mm AP tested was the US M75, which was different from any British rounds. It was solid steel, weighed 165 g and was fired at 775 m/s. The British developed several Marks of 20mm AP, but the RAF appeared to make relatively little use of them; the most common seems to have been the Mk II, which had a hollow cavity and weighed 141 g (I don't have a muzzle velocity figure, but it was presumably around 820-850 m/s from the Mk II).

The penetration figures most often quoted for the British 20mm refer to the SAPI, which was the hollow HE shell filled with incendiary material and fitted with a hardened steel nose-cap instead of a fuze. This had the advantage of matching the trajectory of the HEI, and the two types of round were usually mixed in equal numbers in the ammo belt. Obviously, the penetration of the SAPI would not have been as good as a solid AP. I don't have directly comparable figures, but the penetration of the SAPI at around 20-25mm was similar to that of the .50 AP - i.e., good enough to deal with aircraft armour. Incidentally, I have never seen any penetration claims for the .50 AP which exceed 25mm armour plate, at any distance or striking angle.

I also have penetration graphs for the German 20mm AP (which also had small cavities, often filled with incendiary material), these show that the low-velocity MG-FF (117 g at 585 m/s) would penetrate 18mm at 300m (against 150 kg/mm2 armour), reducing to 11mm after penetrating a 3mm dural skin at 70 degrees. The MG 151/20, which fired the same proj at just over 700 m/s (v around 530 m/s at 300m), penetrated 23mm (or 12mm after passing through the dural). Obviously, with similar projectiles the Hispano would penetrate significantly better than this, as the cartridge was far more powerful.

The USN charts for the fall-off with striking angle show that the .50 AP (which gives 22mm/300m/0 degrees) sees a fall-off to 17mm at 20º, 13mm at 30º, 11mm at 40º, 9mm at 45º, 7mm at 50º and 4.5mm at 60º.

The USN chart for the 20mm AP is less helpful, because although it shows penetration at 0º for 300, 350 and 400 BHN plate (46mm, 39mm and 32mm respectively), it only gives one figure for other angles. However, it is reasonable to assume that these figures probably relate to 350 BHN plate as that is the middle one of the three, and the same used for the .50. Anyway, they show a sharp initial fall-off to 21mm/20º, before levelling off at 19mm/30º, 18mm/40º, 17mm/45º and 10mm/60º.

Tony Williams: Military gun and ammunition website and discussion forum


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## Jank (Jul 17, 2006)

Tony said, *"I should emphasis that the 20mm AP tested was the US M75, which was different from any British rounds. It was solid steel, weighed 165 g and was fired at 775 m/s."*

Geez, that's like 6 ounces!


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## delcyros (Jul 18, 2006)

Tony Williams said:


> I expect that they carried out a few actual tests at critical points and interpolated the rest (that would be the only practical way to do it IMO).
> (...)I have never seen any penetration claims for the .50 AP which exceed 25mm armour plate, at any distance or striking angle.



It´s not surprisive. With a plate QF:1.0 and BRH 220 there will be no target plates of such thin thicknesses to test vs. .50cal impacts. A BRH of 300-400 is more plausible, ergo a plate QF of between 1.2 an 1.4. For such properties and under assumption that the gun does not move (unlike an airplane), I get fairly comparable results for the .50cal: 21,9-25,8mm at 300m/ 0 deg.
USN penetration specifications are usually very reliable sources. I understand that plates have been penetrated under controlled circumstances and most records do also give a remaining striking vel. for the projectile (I suspect but am not sure, that this was recalculated via distance travelled behind the plate either in air or through sand). So actually there was no 39 mm plate with 350 BRH but (probably) a usual 1" plate of 350 BRH. The penetration at 300m distance was recorded and the remaining striking velocity was calculated back to reach 39mm with the M75 20mm AP for Navy ballistic limit of full penetration. This was common practice also for larger projectiles, which are more familar to me.
With the update in the datas (heavier projectile, striking vel), I still have problems to recall this result via M79 APCLC:
M75 20mm AP(165 g plain steel), impact vel.: 655m/s, plate QF: 1.1 (equals 280 BRH), obliquity: 0 deg; max. penetration: 1.41" (35,8mm)
plate QF: 1.3 (equals 350 BRH): max penetration: 1.19" (30,2 mm), so either the projectile performs much better than estimated or the program has severe failures or the plate does not fit to the specification calling for 350 BRH. There is still a significant gap in energy density, something to keep in mind.


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## schwarzpanzer (Aug 3, 2006)

I think that for a fighterbomber or heavy fighter, HE and AP performance is vital.

I have often thought that the P47 should have had 4 Hispano 20mm's instead of 8 .50's. Instead of another pair of 20mm's, I'd have extra ammo or fuel.

Would it be possible to have a 40mm, or even 57mm, under each wing of a P47?

I know America couldn't make the Hispano work though, so it's pie in the sky.


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## Tony Williams (Aug 16, 2006)

...to the debate on gun recoil any more, but I came across some new and relevant information while looking for something else (which is usually the way  )

Tim Mason's book "The Secret Years - Flight Testing at Boscome Down 1939-45" is concerned with the official tests of new or modified aircraft to ensure that they were ready for service. Boscome Down was the home of the "Aeroplane and Armament Experimental Establishment" (or A&AEE), which tested every aspect of the planes' performance, handling, and armament. The book summarises the results of the tests, picking out points of interest. 

One of the planes tested was Hurricane Mk 1 L1750, which in late 1939 was fitted with two Hispano cannon in underwing gun pods (obviously a less aerodynamic solution than the later in-wing installation). The book contains this comment: "Aircraft handling remained unchanged, although firing one gun induced slight yaw; performance suffered only marginally."

Several Hurricane Mk IIC were tested, as they tried to 'debug' the cannon installation. There were only two complaints concerning the cannon: that the ammo capacity of the original drum-fed version was inadequate, and that the guns froze up at altitude - which proved difficult to solve as they couldn't get enough hot air to them.

Some Spitfires with four 20mm cannon were tested. The installation was regarded as satisfactory, the main comment being that the installation added 200 lb (91 kg) and shifted the CG rearwards, required a 7.5 lb inertia weight. Four cannon also proved more difficult to keep warm than two plus MGs (I have read before that this was a key reason for not fitting Spitfires with four cannon - the guns froze at altitude). This problem took until mid-1944 to solve - although it then returned with the Griffon-engined versions as the engine ran much cooler than the Merlin so didn't provide as much gun heating. It is stated that the Hispano+Browning combo was preferred because the Browning was much less prone to freezing up.

The Spitfire XXI seems to have resolved these problems, the only comment about the four 20mm cannon being that they gave "accurate shooting from the steady platform".

To sum up, there is not a single reference to the recoil of the cannon causing any issues with either the Hurricane or the Spitfire, except for the comment that firing just one gun in the Hurricane caused "slight yaw". The main reason for the RAF avoiding the four-cannon layout was the gun freezing problem at altitude, which was tolerable in the Hurricane as it soon became used for ground attack anyway. It is probably significant that the only reference I can recall to the use of four-cannon Spitfires was in the Mediterranean theatre, where ambient temperatures were higher.

Tony Williams: Military gun and ammunition website and discussion forum


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## Jank (Aug 16, 2006)

Thanks Tony. These reports on four 20mm installations in the Hurricane and Spitfire indicate that a six 20mm installation in a P-47 would not have presented recoil related issues of any significance.

Thanls for the follow up.


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## merlin (Dec 27, 2006)

To my mind the question is round the wrong way. The US managed perfectly well with the 0.5" machine gun till the korean war. Perhaps we should be wondering if the RAF got it right with opting for eight 0.303"? Wouldn't four or six 0.5" have been better? Come the Battle of Britain, such puny rifle calibre guns were only saved by the Dixon (usually mistakenly referred to as De Wilde) ammunition.


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## Jank (Dec 27, 2006)

"Perhaps we should be wondering if the RAF got it right with opting for eight 0.303"

That was funny.


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## Tony Williams (Dec 27, 2006)

merlin said:


> Perhaps we should be wondering if the RAF got it right with opting for eight 0.303"? Wouldn't four or six 0.5" have been better? Come the Battle of Britain, such puny rifle calibre guns were only saved by the Dixon (usually mistakenly referred to as De Wilde) ammunition.


Aircraft went through a process of up-armouring as a result of battle experience during 1940. At the start of the fighting, eight .303s were probably the best armament of any fighter in service. As aircraft toughened up, so .303s became less effective. By the end of the BoB, a quartet of .50s would probably have been better (although heavier). Even so, the RAF continued fitting .303s to fighters for several years, so they can't have regarded them as useless. 

The B Mk VI ("De Wilde") incendiaries were a definite improvement on any other type at the time, but they weren't that common initially. See my analysis of BoB armament HERE

The RAF had realised that the .303 would no longer be adequate as soon as planes started to adopt armour plate, and were planning as early as 1935 for fighters armed with 20mm cannon - but the Hispano took longer than expected to de-bug, so it just missed contributing to the BoB.

Tony Williams: Military gun and ammunition website and discussion forum


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## Jank (Dec 28, 2006)

It wasn't just the advent of armor plate that rendered the .303 less than adequate but the structural and other "hard" components of the aircraft itself. 

A .303 with Mk. I AP would penetrate just 5mm of armor plate at 200 yards at 20 degree deflection. A .50 AP round under the same circumstances would penetrate 14mm. Even at 600 yards, the .50 under the same circumstances could still penetrate 9mm of armor plate. Obviously, it was far easier to critically damage your opponents engine with a few .50's than a dozen or more .303's.

Yes, obviously the Brits didn't regard it as useless but their ongoing use of it does not mean it was effective relative to other available armaments like the .50 either. Case in point. The USAAF persisted in using the .50 on its F-86 when it would have been far more effective with even three 20mm's. Many, many Migs made it back to base peppered with .50 rounds.


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## Tony Williams (Dec 28, 2006)

Jank said:


> It wasn't just the advent of armor plate that rendered the .303 less than adequate but the structural and other "hard" components of the aircraft itself.



I agree. The RAF were also aware of this, which is why they decided in the mid-1930s that they needed to fit their fighters with eight of the guns, at a time when most fighters in service only had two. They were working on the calculation that a high volume of hits would compensate for the low effectiveness of each one, but this was not entirely successful. 

The Luftwaffe also perservered with rifle-calibre guns, of course, with the 109 and 190 carrying 7.9mm cowling guns until about 1943 IIRC.

Tony Williams: Military gun and ammunition website and discussion forum


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## Soren (Jun 5, 2007)

Interesting discussion guys.

As to armor penetration and the effect the size of the incoming projectile has is here explained by Robert D. Livingstone, Co. author of "World War II Ballistics: Armor and Gunnery".

"Armor obliquity effects decrease as the shot diameter overmatches plate thickness in part because there is a smaller cylindrical surface area of the displaced slug of armor which can cling to the surrounding plate. If the volume which the shot displaces has lots of area to cling to the parent plate, it resists penetration better than if that same volume is spread out into a disc with relatively small area where it joins the undisturbed armor. Plate greatly overmatching shot involves the projectile digging its own tunnel, as it were, through the thick interior of the plate. It was found experimentally that the regions in the center of the plate produced the bulk of the resistance to penetration, while the outer regions, near front and rear surfaces, presented minimal resistance because they are unsupported. Thus, an overmatched plate will be forced to rely on tensile stresses within the displaced disc, and will tend to break out in front of the attacking projectile, regardless of whether the edges cling to the parent material or not. Plate obliquity works in defeating projectiles partly because it turns and deflects the projectile before it begins digging in. If there is insufficient material where the side of the nose contacts the plate, stresses will travel all the way through the plate and break out the unsupported back surface. The plate will fail instantaneously rather than gradually".

"You can angle the armor any way you want, and beyond a certain point of shot overmatching plate, the obliquity will cease to be relevant. In fact, at certain conditions of shot overmatching plate, the cosine rule is broken and the plate resists less well than the simple cosine relationship would predict (LOS thickness is greater than effective thickness). The above only applies to WWII era AP and APC/APCBC, and WWII sub caliber ammunition. The long rod penetrators of today are greatly overmatched but they bring so much energy to the plate that they penetrate by "ablation" in which both projectile and armor behave like fluids. Hollow charge also enters the field of fluid dynamics, with a very thin jet penetrating overmatching armor with ease, regardless of obliquity"

Was he's talking about here is the effect of the T/D coefficient between the incoming projectile and the armour it opposes.


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## merlin (Jun 5, 2007)

I note in an earlier reply Tony referred to the "De Wilde" incendary shells for the 0.303" machine guns. Isn't it about time the De Wilde reference was dropped - it was only retained to fool the Germans! The real hero was Captain Dixon, who realised that the De Wilde shell being hand made without any 'measured' amount ingredients, couldn't be mass-produced. It was fortunate that he unofficially conducted tests until he came up with the solution - which was passed on the the Americans!
Hence he deserves the credit for his achievement.

Sorry for being slightly off-topic!!


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## Tony Williams (Jun 6, 2007)

That is quite true, but they are still popularly known as "De Wilde" bullets. if I want to be technically precise, I refer to them as the B Mk VI (superseded by the B Mk VII), which is their official designation.


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## renrich (Jun 9, 2007)

Earlier in this thread someone mentioned an English ace who always checked to see if he was in a turn before firing his guns. I believe that was Stanford Tuck and he was not checking whether in a turn but checking whether he was in a skid or uncoordinated flight. I also believe that the eight gun armament of the British fighters was partly because of the Tactics they were using and because of the poor marksmanship of the pilots. They theorised that they would open fire at long ranges with a lot of guns and get hits because of the many bullets in the air. Sort of a shotgun approach. Also I don't know if this has been mentioned but a significant number of Corsairs were armed with 4- 20mm cannon in WW2 and some night fighter versions of the Hellcat had 2-20mm cannon plus 4-.50 MGs.


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## Tony Williams (Jun 10, 2007)

renrich said:


> I also believe that the eight gun armament of the British fighters was partly because of the Tactics they were using and because of the poor marksmanship of the pilots. They theorised that they would open fire at long ranges with a lot of guns and get hits because of the many bullets in the air. Sort of a shotgun approach.


No - the decision to go to eight guns was taken in around 1934/5, as a result of theoretical studies which showed that the increasing speed of aeroplanes meant that a pilot may only be able to fire at a target for about two seconds (IIRC). So they did some sums to work out how much damage one machine gun could do to an aircraft in two seconds, and reckoned that they would need eight of them to do the job.

They started out with the guns harmonised for 400 yards, on the assumption that a typical attack run would start at that distance and finish off at 200 yards. They estimated that the spread of fire at short range would cover the fuselage and engines of a twin-eingined plane, so all the bullets should still be hitting. Early WW2 experience showed these figures were too optimistic, so they dropped the harmonisation range to 250 yards.

The RAF became concerned at standards of pilot accuracy in deflection shooting in the late 1930s, so started working on the gyro gunsight. That had no effect on the choice of armament though.


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## renrich (Jun 10, 2007)

Thanks Tony for your explanation. I had read somewhere about the theory you discussed but was quoting from memory which was quite hazy. According to John Lundstrom in "The First Team" the European air forces did not place much reliance on deflection shooting in contrast to the US Navy perhaps partly because of visibility problems in inline engined a/c. An aside, I saw gun camera film of a German fighter firing at a P38 from the 6 o clock position about 30 degrees high. What a target with a lot of vital parts.


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## renrich (Jun 10, 2007)

PS, good work of fiction, "Piece of Cake" can't remember author goes into British fighter tactics and gunnery it seems with some accuracy. Good book!


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