Groundhog Thread Part Deux - P-39 Fantasy and Fetish - The Never Ending Story (Mods take no responsibility for head against wall injuries sustained) (1 Viewer)

[pbehn]

The British were in need of good aircraft, they would have taken Allison engine Mustangs any time up to the end of the war. The P-39 was not better than what the British had for the uses they had and with the invasion of Russia and Pearl Harbor the British need for aircraft was third in any queue. In addition to P-39s going to Russia so were Hurricanes.

 

[P-39 Expert]

I would note that the US fitted pretty much the same equipment to the P-39D (ordered in the spring of 1940) got pretty much the same weight gain and pretty much the same drop in performance. Only thing is the US Army knew it, and the Army and Bell negotiated the contracts to suit after a long and sometimes contentious negotiation.
So far there is no evidence the British added anything the USAAC didn't. In fact they used a lighter cannon.

The P-39D was about 200# lighter than the export P-400/P-39D-1 which were virtually alike. Both were intended as export models while the D was for the AAF. Empty the D weighed 5462# and the F weighed 5409# because the only difference in the D and F was the hydromatic propeller on the F which was about 50# lighter than the Curtiss Electric prop on the D. With a load of 1700# those Ds and Fs would have weighed 7162# and 7109# respectively and had performance like the P-39C in post #388. That's fully equipped with self sealing tanks, revised armor plate/glass, 120 gallons of fuel and armed with the 37mm canon and twin .50 caliber MGs.

The performance difference was all weight since the aerodymanics and engines were the same. All that performance lost over 4 .30 caliber MGs and about 120 pounds of armor plate that wasn't needed. Items that could be removed in a short amount of time at a forward air base. Would you rather have the 4 peashooter MGs and useless armor plate (due to location) or the extra 1000fpm climb? The Russians figured this out after they tested the first Airacobras delivered to them.

 

[pbehn]

The P-39D was about 200# lighter than the export P-400/P-39D-1 which were virtually alike. Both were intended as export models while the D was for the AAF. Empty the D weighed 5462# and the F weighed 5409# because the only difference in the D and F was the hydromatic propeller on the F which was about 50# lighter than the Curtiss Electric prop on the D. With a load of 1700# those Ds and Fs would have weighed 7162# and 7109# respectively and had performance like the P-39C in post #388. That's fully equipped with self sealing tanks, revised armor plate/glass, 120 gallons of fuel and armed with the 37mm canon and twin .50 caliber MGs.

The performance difference was all weight since the aerodymanics and engines were the same. All that performance lost over 4 .30 caliber MGs and about 120 pounds of armor plate that wasn't needed. Items that could be removed in a short amount of time at a forward air base. Would you rather have the 4 peashooter MGs and useless armor plate (due to location) or the extra 1000fpm climb? The Russians figured this out after they tested the first Airacobras delivered to them.

Wasn't the performance difference in part due to filling and polishing of an aircraft for test? I am sure we went through all this.

 

[Shortround6]

The British never got out of the contract because the Japanese bombed Pearl Harbor and the AAF needed all the planes they could get, including the P-400s that Britain didn't want.

Well, we are part way there.

Now we just need the proof that the British KNEW in the fall of 1940 that there would be no German invasion in the spring of 1941 so they could try to get out of the contracts.
We just the proof that the British specified hundreds of pounds of "equipment" that the USAAC was NOT specifying at the same time for their P-39Ds.
and we need the PROOF that the British did this in 1940 with the intention of getting out of the contracts 9-15 months before the planes were to be deleivered and 6-9 months before lend lease was passed into law (giving them planes for "free")

 

[P-39 Expert]

Wasn't the performance difference in part due to filling and polishing of an aircraft for test? I am sure we went through all this.

I believe you are thinking of the April 1941 tests of the P-400 with the smaller tail, polished surface, etc. I don't believe any of the govt/military tests in wwiiaircraftperformance.org showed a polished P-39. That's only good for 2-3mph anyway.

 

[pbehn]

I believe you are thinking of the April 1941 tests of the P-400 with the smaller tail, polished surface, etc. I don't believe any of the govt/military tests in wwiiaircraftperformance.org showed a polished P-39. That's only good for 2-3mph anyway.

We did go through it all at length though, didn't we, starting off with the same statement about the British not wanting to pay?

 

[P-39 Expert]

Well, we are part way there.

Now we just need the proof that the British KNEW in the fall of 1940 that there would be no German invasion in the spring of 1941 so they could try to get out of the contracts.
We just the proof that the British specified hundreds of pounds of "equipment" that the USAAC was NOT specifying at the same time for their P-39Ds.
and we need the PROOF that the British did this in 1940 with the intention of getting out of the contracts 9-15 months before the planes were to be deleivered and 6-9 months before lend lease was passed into law (giving them planes for "free")

French/British ordered the P-400 in 1940 because they DIDN'T know that they would win the battle of Britain in the fall of that year. After they DID win the BoB they no longer needed the P-400. They didn't try to get out of paying for them until they knew that they didn't need them.

See post #442 for the weight differences.

 

[Shortround6]

I believe you are thinking of the April 1941 tests of the P-400 with the smaller tail, polished surface, etc. I don't believe any of the govt/military tests in wwiiaircraftperformance.org showed a polished P-39. That's only good for 2-3mph anyway.

What Bell did was worth a whole lot more than 2-3mph. More like 15-20mph minimum


I also have serious doubts about how much yanking the four .30 cal guns is going to do for performance.
Yanking the under wing .50s from a P-63 was only supposed to be good for 110fpm in climb.
The under wing wing .50s weigh more than the .30s,in fact the four .30 cal guns weigh about 95lbs. This does not include mounts/brackets and accessories. The under wing .50 cal guns on late P-39s and P-63s went 220lb for the pair of guns, the pods, mounts/brackets stc.

The 4 guns in the P-39 wing had the exposed barrels and cartridge ejection slots to cause drag.
The P-63 had

Now perhaps the test of the P-63 was falling into the ends of the allowable or expected errors?

However please note (as I have mentioned before) that a Spitfire MK V could be fitted with a 90 imp gallon drop tank, gross weight increased by 790lbs and yet it's climb performance only went down to 10 minutes to 20,000ft from 8 minutes and to 14.000ft (critical altitude at climb speed) it needed 6.6 minutes instead of 5.35 (an increase of 1 1/4 seconds)
while the P-39 carrying 2 extra ,30 cal guns (2 had been moved from the nose) , more ammo and a bit of extra armor loses 1000ft a minute????

 

[Shortround6]

French/British ordered the P-400 in 1940 because they DIDN'T know that they would win the battle of Britain in the fall of that year. After they DID win the BoB they no longer needed the P-400. They didn't try to get out of paying for them until they knew that they didn't need them.

See post #442 for the weight differences.

So, the British didn't increase the weight until the fall of 1940, months after the initial order?
And months after they knew (and the USAAC knew) they wanted armor and self sealing tanks?

Differences for the British might be different oxygen equipment, different radios, fitting IFF gear (I don't know if the US was using it at the time)
Or other bits and pieces like landing lights or somthing

the difference in armor is about 40lbs at the most and may be nothing depending on which source or which airplane is tested/ weighed.
The difference in .303 ammo and US .30 ammo is trivial and it is in favor of the .303.

British didn't know in 1940 that Germany would invade Russia in 1941 which is what really took the invasion of Britain off the table.

 

[Peter Gunn]

I believe that Bell pulled a bit of a fast one, pardon the pun, when they polished up the demonstrator for the RAF, it had to be good for more than just a 2-3 MPH increase. On the P-80, polished and filled surfaces were good for a 10-11 MPH increase from SL to 20,000 for both top speed and cruising speed.

Admittedly I didn't dig out any P-39 data for polished or unpolished simply because I knew where to find the P-80 data.

P-80 Performance Tests

 

[Glider]

French/British ordered the P-400 in 1940 because they DIDN'T know that they would win the battle of Britain in the fall of that year. After they DID win the BoB they no longer needed the P-400. They didn't try to get out of paying for them until they knew that they didn't need them.

See post #442 for the weight differences.

So far there is nothing in your evidence, in fact there is no evidence at all, that the British tried to avoid paying for anything. The UK took on the entire French order for US aircraft even those they had no interest in and didn't avoid paying for anything.
All you have is conspiracy theories that lack any fact. Timescales that are out and an aircraft that clearly didn't meet it's promised performance. I am pretty confident that any halfway decent lawyer had they wanted to would have won a case against Bell

 

[P-39 Expert]

What Bell did was worth a whole lot more than 2-3mph. More like 15-20mph minimum


I also have serious doubts about how much yanking the four .30 cal guns is going to do for performance.
Yanking the under wing .50s from a P-63 was only supposed to be good for 110fpm in climb.
The under wing wing .50s weigh more than the .30s,in fact the four .30 cal guns weigh about 95lbs. This does not include mounts/brackets and accessories. The under wing .50 cal guns on late P-39s and P-63s went 220lb for the pair of guns, the pods, mounts/brackets stc.

The 4 guns in the P-39 wing had the exposed barrels and cartridge ejection slots to cause drag.
The P-63 had
View attachment 531916
Now perhaps the test of the P-63 was falling into the ends of the allowable or expected errors?

However please note (as I have mentioned before) that a Spitfire MK V could be fitted with a 90 imp gallon drop tank, gross weight increased by 790lbs and yet it's climb performance only went down to 10 minutes to 20,000ft from 8 minutes and to 14.000ft (critical altitude at climb speed) it needed 6.6 minutes instead of 5.35 (an increase of 1 1/4 seconds)
while the P-39 carrying 2 extra ,30 cal guns (2 had been moved from the nose) , more ammo and a bit of extra armor loses 1000ft a minute????

In wwiiaircraftperformance.org there is a Memorandum at the bottom of the P-39 section titled "Speed Test, Smoothed Camouflage Finish" where they were sanded and rubbed down with pumice and water. Speed difference was 2mph at military power.

See the graph in post #442 to see the difference in performance between a 7100# P-39 and a 7850# P-39 as compared to a contemporary Spitfire V. Straight from wwiiaircraftperformance.org.

 

[Shortround6]

I believe that Bell pulled a bit of a fast one, pardon the pun, when they polished up the demonstrator for the RAF, it had to be good for more than just a 2-3 MPH increase. On the P-80, polished and filled surfaces were good for a 10-11 MPH increase from SL to 20,000 for both top speed and cruising speed.

Admittedly I didn't dig out any P-39 data for polished or unpolished simply because I knew where to find the P-80 data.

P-80 Performance Tests

It wasn't "polished",
It had 20 coats of primer sanded between each coat. It had wood filler smoothing the metal to plexiglass (canopy ) fit/joints. It had a one piece engine cover to eliminate gaps/joints in that area. There were a few other 'tricks" employed too.

Polishing would have been minor compared to what Bell did

 

[P-39 Expert]

I can't resist, 20 coats of primer sanded between each coat is going to be 15mph faster than an identical plane that was sanded and polished?

 

[Shortround6]

In wwiiaircraftperformance.org there is a Memorandum at the bottom of the P-39 section titled "Speed Test, Smoothed Camouflage Finish" where they were sanded and rubbed down with pumice and water. Speed difference was 2mph at military power.

except the Airacobra I tested at the end of April 1941 was NOT sanded/ rubbed down with pumice and water. You know it.
See the Birch Mathews book pages 119-120.

See the graph in post #442 to see the difference in performance between a 7100# P-39 and a 7850# P-39 as compared to a contemporary Spitfire V. Straight from wwiiaircraftperformance.org.

yep, straight from wwiiaircraftperformance.org. except the P-39s are running at either the 5 minute rating (up until the jog in the lines to left) while the Spitfire is running at it's 30 minute rating, a nice fair comparison.......................not.

 

[Shortround6]

I can't resist, 20 coats of primer sanded between each coat is going to be 15mph faster than an identical plane that was sanded and polished?

Rather depends on the fit an finish of the panels doesn't it?

If 20 coats of primer (20 trips through the spray booths) isn't better than a quicky 2-3 day polish job on the top coat coat why do it?

perhaps because they are using the multiple coats of paint to seal cracks/gaps, fill in low spots (or dents) that no polish job to to the top coat ever could.

From the book, page 120. "This treatment covered all seams, screws and rivet heads. Standard British camouflage was applied for a finish coat. This was lightly sanded to remove seams left by the edges of the camouflage templates. As a final note, the test airplane was 169 pounds lighter than a standard production model".

 

[pbehn]

Some time around about now the discussion moves on to the Russian front (from memory)

 

[CORSNING]

Some time around about now the discussion moves on to the Russian front (from memory)

Polished and spit-shined?......No $#!+, what the Bell direction are we going now?...

 

[P-39 Expert]

except the Airacobra I tested at the end of April 1941 was NOT sanded/ rubbed down with pumice and water. You know it.
See the Birch Mathews book pages 119-120.



yep, straight from wwiiaircraftperformance.org. except the P-39s are running at either the 5 minute rating (up until the jog in the lines to left) while the Spitfire is running at it's 30 minute rating, a nice fair comparison.......................not.

The five minute rating was increased to 15 minutes mid 1942.

 

[Glider]

The five minute rating was increased to 15 minutes mid 1942.

Just when the Spit IX entered service, a comparison which the P39 is guaranteed to lose.