20/20 Hindsight - different armament?

[Jank]

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

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.

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!

[Jank]

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.

[delcyros]

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.

[quote] 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!" [quote]

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.

[Jank]

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.

[delcyros]

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.

[wmaxt]

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