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The P-400's were heavier because they had more armour and what did they do with them, they shot up some invasion barges. Maybe that's what we needed them for in the first place, but no invasion, no P-400's required.
Until the British actually got some in England to test to they didn't realize what a dog it was at altitude. There was no quick and easy fix. They were flying a P-40 with a Merlin engine
on June 30th 1941 about the time the P-39Cs show up in England, and even the first of these lightweight machines only manages 359mph around July 6th. You can't put a Merlin in a P-39 (not without months and months of work and there aren't enough Merlins anyway)
The useless backfire screens were finally discarded around the same time as the five minute rating was increased to 15 minutes, mid 1942. The 15 minute rating was for most of the combat engines including Allison and P&W.Hello Shortround6,
I suspect the British had a pretty good idea what kind of altitude performance to expect from the Airacobra before they every got one. Note that although they may have ended up with a few P-40s with Merlin engines, they had been flying early Tomahawks and Kittyhawks before the Merlin versions came along. The engine in the P-39D, D-1, and F would have been almost the same as that in a P-40E.
In one of the Airacobra books (I forget which one), there was a mention of the British requirement for snow filters on the intake which caused a significant loss of performance. In addition, it was pretty common practice for US Army operators to remove the anti-backfire screens from their engines which gave a noticeable (about 1000 feet) increase in critical altitude.
- Ivan.
For the thousandth time, delete the wing guns AND THE USELESS 100# NOSE ARMOR PLATE and substitute 50 gallons of fuel at 300#, the weight of the self sealing tanks would be mostly offset by removing the gun mounts, chargers, heaters and ammunition boxes. Very minor weight gain if any.Except you don't.
Four .30 cal guns = 99lbs
1200 rounds of 30 cal ammo= 72lbs
50 gallons of fuel weighs 300lbs
Weight of the self sealing tanks to put the fuel in???????
Wonder what the Mustang could do if you magicly took out 180lbs and added 400lbs of "stuff" with no penalty?
Please see above.They had maybe, repeat, maybe 30-40 pounds more armor than the P-39D did. Which strangely disappeared when one was weighed for US service? (AHT Dean Page 193) Armor plate/glass weighed 292# on the P-400 including the nose gearbox armor, armor for the oxygen bottles and armor just outside the rear armor glass. Delete these items (not used on other comtrmporary aircraft) and the weight of armor plate and glass is reduced to around 140#.
Most new squadrons, regardless of what they intended to use them for tended to get sent on barge, coastal shipping or coastal target strikes for their first few missions. Over two years later the first P-51B mission with the 354th fighter group was a fighter sweep over Belgium and France. Meeting no German Aircraft they did some ground strafing.
It was a way to ease a unit into combat by only keeping them in a dangerous area for a few minutes.
By the summer of 1941 the British had little or no need of the P-39 as a barge buster. Let alone in Oct/Nov of 1941. The P-400 mounted a single 20mm with a drum feed gun for barge busting plus the two .50 cal guns. Spitfires were getting two 20mm cannon, the unloved Whirlwind had four. Beaufighters had four and they were starting to be belt feed. Four 20mm cannon for Hurricanes were in the works. (showing up the fall of 1941?). The 20mm cannon in the P-400 was a non-starter with only a 60 round magazine good for 5-6 seconds firing time. It also jammed a lot. Give it the British belt fed 120 round magazine like the SpitfireV (just the logical development) and it would be a very useful gun.
Until the British actually got some in England to test to they didn't realize what a dog it was at altitude. There was no quick and easy fix. They were flying a P-40 with a Merlin engine
on June 30th 1941 about the time the P-39Cs show up in England, and even the first of these lightweight machines only manages 359mph around July 6th. You can't put a Merlin in a P-39 (not without months and months of work and there aren't enough Merlins anyway) Due to rediculously heavy weight as specified by the British. Removing the weight was a very quick and easy fix. British are comparing their 6450# Spitfire with their 7850# P-400 creation and wondering why performance is down. They knew all along. Again, please see the graph in post #388.
This is a big part of this particular argument about the P-39, who knew what and when. Bell knew all along that it wasn't a 400mph fighter at 20,000ft or even 390mph at 15,000ft.
They have hoped it was, they may prayed that some miracle would make it so. But they never had a test airplane in 1939-40 come close to those numbers (at least one even remotely equipped for service use.) We know that the American army didn't expect that speed and climb performance from it either or they wouldn't have signed/agreed to the contracts for the P39D with lower performance.
So the question is when did the British know, or again, who knew when ( British test pilot and purchasing delegation in the US, British air ministry officials in England, or British pilots/squadron commanders who would have to use it) The P-39 was being touted as a 400mph airplane in ads and articles in British publications like Flight magazine during 1940.
Granted you don't put full details (especially short comings) in a public magazine in war time but the average Briton interested in aviation in 1940 expected the P-39/P-400 to be a 400mph airplane. Bell promoted the P-400 as a 400mph airplane in '39 and '40 when it weighed 5000#, not after that. There were six weight increases under this contract between Feb 1940 and June 1941 increasing the weight from 5849# to 7635# of which the British were certainly aware since this was a direct purchase contract and they had to sign off on all changes. The big test (reflecting the decreased performance) was in April '41 and the final revision to the contract increasing the order from 170 to 675 planes was signed in June. That the British were somehow tricked or fooled by Bell is rediculous. The British had the best intelligence service in WWII and had already contracted for and built a large quantity of very high performance airplanes themselves. They knew exactly what they were doing.
For the thousandth time, delete the wing guns AND THE USELESS 100# NOSE ARMOR PLATE and substitute 50 gallons of fuel at 300#, the weight of the self sealing tanks would be mostly offset by removing the gun mounts, chargers, heaters and ammunition boxes. Very minor weight gain if any.
Please provide the weight/s for the gun mounts, chargers, heaters and ammunition boxes. No idea, but I do know that they would need to be removed if fuel tanks were replacing them.
large flat fuel tanks weigh a lot more than short deep ones for the same fuel capacity.
The bullet proofing material weighs about the same per sq ft of tank to be covered, the more sq ft you need per gallon the heavier the tank.
A rough estimate of tank weight is from page 380 of "Aircraft Power Plants" by Arthur P Fraas ( a Packard engineer) who says that plain aluminum tanks can go from 3/4 lb per gallon for small tanks to 3/8lb per gallon for large tanks of 100 gal or more.
Bullet sealing tanks weigh between 0.7 and 1.5 lbs per gallon. So, at one pound per gallon the new tanks would weigh 25 pounds each (for two)? The normal tanks in the P-39 weighed about 1pound per gallon. The weight would have increased by 300# of fuel and 50# of new tanks for a total of a 350# increase. Weight would have been reduced by the .30 cal guns 99#, ammo 77#, the unneeded nose and selected other armor 140#, and the gun mounts, chargers, heaters and ammo boxes. If these last items weighed 34# (8.4# per gun) then the weight penalty for the additional fuel and tanks would have been exactly zero.
Tying to use the space where the .30 cal guns and ammo were for fuel tanks is going to result in about the worst possible shape of a tank from the standpoint of wall area to volume.
How much weight did Bell save by getting rid of the 33 gallons in the outer fuel cells? 200# plus the tanks.
And you want to add 50 gallons in an even thinner part of the wing? I have never been in favor of less fuel for the P-39. With more than the standard 120gal the P-39's effectiveness would have been increased. The standard 120 gallons carried by the P-39 was more than was carried internally on Spitfires, 109s, (and the 190 if it's much larger engine is considered) and most Russian fighters.
And how are you going to compensate for the resulting rearward CG shift in a plane that's already borderline tail heavy? Move the battery and the radio boxes forward? Where you going to find room for them to gain back the moment arm you lost by deleting the armor? The farther the battery gets from the starter and generator, the fatter (and heavier) your cables are going to get and the more starting problems you're going to have. The farther from the CG your battery and radios are, the more G abuse they'll suffer in Air Combat Maneuvering. Tube radios located in the nose next to a 37 (or a 20) and two 50s are going to be subject to intense high frequency vibration stresses whenever you squeeze the trigger. There's more to it than just yanking the armor.delete the wing guns AND THE USELESS 100# NOSE ARMOR PLATE
And how are you going to compensate for the resulting rearward CG shift in a plane that's already borderline tail heavy? Move the battery and the radio boxes forward? Where you going to find room for them to gain back the moment arm you lost by deleting the armor? The farther the battery gets from the starter and generator, the fatter (and heavier) your cables are going to get and the more starting problems you're going to have. The farther from the CG your battery and radios are, the more G abuse they'll suffer in Air Combat Maneuvering. Tube radios located in the nose next to a 37 (or a 20) and two 50s are going to be subject to intense high frequency vibration stresses whenever you squeeze the trigger. There's more to it than just yanking the armor.
Cheers,
Wes
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Armor plate/glass weighed 292# on the P-400 including the nose gearbox armor, armor for the oxygen bottles and armor just outside the rear armor glass. Delete these items (not used on other comtrmporary aircraft) and the weight of armor plate and glass is reduced to around 140#. Armor plate/glass weighed 292# on the P-400 including the nose gearbox armor, armor for the oxygen bottles and armor just outside the rear armor glass. Delete these items (not used on other comtrmporary aircraft) and the weight of armor plate and glass is reduced to around 140#.
The 20mm cannon in the P-400 was a non-starter with only a 60 round magazine good for 5-6 seconds firing time. It also jammed a lot. Give it the British belt fed 120 round magazine like the SpitfireV (just the logical development) and it would be a very useful gun.
Due to rediculously heavy weight as specified by the British. Removing the weight was a very quick and easy fix. British are comparing their 6450# Spitfire with their 7850# P-400 creation and wondering why performance is down. They knew all along. Again, please see the graph in post #388.
Bell promoted the P-400 as a 400mph airplane in '39 and '40 when it weighed 5000#, not after that. There were six weight increases under this contract between Feb 1940 and June 1941 increasing the weight from 5849# to 7635# of which the British were certainly aware since this was a direct purchase contract and they had to sign off on all changes.
The big test (reflecting the decreased performance) was in April '41 and the final revision to the contract increasing the order from 170 to 675 planes was signed in June. That the British were somehow tricked or fooled by Bell is rediculous. The British had the best intelligence service in WWII and had already contracted for and built a large quantity of very high performance airplanes themselves. They knew exactly what they were doing.
And how are you going to compensate for the resulting rearward CG shift in a plane that's already borderline tail heavy? Move the battery and the radio boxes forward? Where you going to find room for them to gain back the moment arm you lost by deleting the armor? The farther the battery gets from the starter and generator, the fatter (and heavier) your cables are going to get and the more starting problems you're going to have.......... There's more to it than just yanking the armor.
Not to mention the multiplied dynamic lateral and vertical loads from abrupt maneuvering the farther these delicate electronics are from the CG.It would have never occurred to me when redesigning a WW2 fighter that they wanted the radio close to the center of the plane due to g forces.
Thank you, Sr6, I stand corrected. Now Cobra 'spurt, where you going to find the extra moment to make up what you lost by stripping the nose armor? Huh?The battery was already in the nose
Yes the P-39 carried more fuel, 120 gallons vs 103 for Spitfire and 106.7 for the 109. I am not going to get all excited over the P-39 because it carried 16% more fuel than standard Spitfire.
Didn't the standard capacity become 87USG for later models?