20/20 Hindsight - different armament?

[Jank]

"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.

 

[Squeelig]

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.

 

[Glider]

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

 

[delcyros]

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.

 

[Glider]

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.

 

[Sal Monella]

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?

 

[delcyros]

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!

 

[Sal Monella]

"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.

 

[pbfoot]

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 "

 

[Sal Monella]

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.

 

[Jank]

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.

 

[Glider]

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.

 

[Squeelig]

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

 

[red admiral]

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

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

 

[Twitch]

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.

 

[Glider]

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

 

[delcyros]

"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.

-"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?

 

[Glider]

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.

 

[Jank]

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.

 

[Sal Monella]

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!