20/20 Hindsight - different armament?

[Tony Williams]

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

 

[delcyros]

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,

 

[Jank]

"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.

 

[delcyros]

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,

 

[Jank]

"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.

 

[delcyros]

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.

 

[delcyros]

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,

 

[Jank]

"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.

 

[Tony Williams]

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,

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

 

[delcyros]

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 !

 

[delcyros]

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?

 

[Tony Williams]

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

 

[Twitch]

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.

 

[delcyros]

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

 

[Tony Williams]

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

 

[delcyros]

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.

 

[Tony Williams]

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

 

[delcyros]

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.

 

[Twitch]

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?

 

[delcyros]

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.