P-39- Did the engine behind the pilot cause any problems?

DarrenW · May 14, 2020

GregP said:
The Japanese went from a V-12 to a radial in going from the Ki-61 to the Ki-100, and they didn't seem to have much trouble.

The Ki-100 is a bad example. It was developed out of pure necessity and desperation which was never experienced by US aircraft manufactures. It's success could have went either way. In my opinion it garners a reputation that far exceeds it's virtues but that's another topic for another thread...

Though most likely doable it would have been a total waste of time, energy, and money to re-engine the P-39 with a Merlin, especially with far superior aircraft like the P-51B in need of them. By the summer of 1943 it was outclassed by all major US fighter types and Bell already had the much-improved P-63 in the works, so why even bother?

GregP · May 14, 2020

Bad example I agree, but still an example.

If they can adapt a radial for use where they had formerly use an inline, then changing between two V-12 inlines of very similar weights and dimensions is simply not that big of an issue. I would not have tried it because of the other issues. Changing to a Merlin would not correct the design flaws in the P-39. It would still have insufficient fuel and the CG would still shift aft when the ammunition was used up. Waiting and going to a 2-stage Merlin in the P-63 would make a LOT more sense, but the P-63 still didn't have enough fuel to meet the U.S. / British needs of 1944 and beyond. Basically, the P-39 was a flawed machine and a fresh, new design would have been the way to go rather than try to "rescue" the P-39.

They tried rescuing it with the P-63, and it was a good aircraft. But it was also associated with the P-39 and its existing reputation, so nobody who mattered was all that anxious to "buy in" on the design. We didn't really use all that many in the U.S.A. . Most were exported to the U.S.S.R., who DID like it as they liked the P-39 because their operational envelope was right where the P-39 excelled, not necessarily as all ground attack, either. They used them as fighters, but low ceilings, short mission and good tactics made them fitted for Soviet use.

I don't really know what the Soviets specifically thought of the P-63, but they used some 2,500+ of them and would have accepted more if we had made them.

chipieal · May 14, 2020

This is WAY OFF TOPIC and if it gets thrown off oh well. I am personally tired of hearing about covid. Please no serious talks about it. If I want that I can just turn on the talking heads.

tomo pauk · May 14, 2020

chipieal said:
This is WAY OFF TOPIC and if it gets thrown off oh well. I am personally tired of hearing about covid. Please no serious talks about it. If I want that I can just turn on the talking heads.

So in all of this thread you've found that worthy of your comment?

P-39 Expert · May 14, 2020

I honestly don't know what to say.

Merlin in a P-39? I guess it's possible but hardly worth the effort. If you want two stage performance just use the -93 engine in production from April 1943. 1150hp at 21500'. Then immediately move the carb from the auxiliary stage to the engine stage supercharger (like the P-38) and add another 2500'-4000' critical altitude. In April '43.

But the P-39 used single stage engines throughout its life. Only two ways to improve performance, more engine power or less weight. Not getting more power so reduce the weight. In the earlier models with the 8.8 supercharger gears (D-L) remove the small .30 caliber wing guns and the nose armor plate and save 300 pounds. About 360 feet per minute improvement in climb and about 3500' in ceiling cures the biggest problem in the early models.

The 9.6 geared engines (-83, -85) in the P-39M-Q were a big help, another 100hp above 15000'. The N model was actually competitive with anything in combat in 1943, good speed and a great rate of climb. Only real drawback was endurance, just get rid of the .30 caliber wing guns and put fuel tanks in their place.

The ideal timeline would be:

April '41-November '42: Lighter D-L models with better climb/ceiling. No wing guns or nose armor. 1150hp at 12000'.
November '42-April-'43: 9.6 geared engines give good performance at full weight in N model. 1150hp at 15000'
April '43-August '45: Don't build the Q model with the performance killing wing gondola .50 caliber guns. Instead install the two stage -93 engine and move the carb up from the auxiliary stage to the engine stage. 1150hp at 24000'. From April '43. Pretty simple really.

Csch605 · May 14, 2020

B-25 Pilot said:
Hey everyone,

I am doing a school project and
I chose the P-39 to be on of the planes in my book. But I have a question, did the engine behind the pilot cause any problems?

Thanks ahead of time.

It made the CG and spin characteristics different. Many pilots thought it was dangerous some used it to their advantage. The rear engine was vulnerable to a 6 o'clock attack but head to head the other guy was dead since the nose had two 50's and a 37mm made possible by a rear engine.

ktank · May 15, 2020

B-25 Pilot said:
Hey everyone,

I am doing a school project and
I chose the P-39 to be on of the planes in my book. But I have a question, did the engine behind the pilot cause any problems?

Thanks ahead of time.

Firstly, why have the engine behind the pilot?

One in theory was that it would increase maneuverability by reducing the polar moment of inertia, ie the main masses would be close to the centre of gravity and so there would be less resistance to turning. I don't know whether that worked, but it certainly gave it a vicious fast spin when the cg got too far back after expending ammunition. This, along with the aircraft failing to meet its performance claims, meant that it had a very brief career with the RAF, who passed the whole lot onto the USSR.

Second, it would allow better streamlining by having the point of greatest width (the engine) in the middle of the fuselage rather than the nose. However, as stated, its performance, not only at altitude, was disappointing compared to what had been promised.

Third, it would allow heavy nose armament. Which in the true P39 it did, with a filthy great 30mm cannon that the Russians loved in ground attack roles. However, in the original export version, the P400, this was replaced by a 20mm cannon (why?) which had nowhere near the hitting power.

So the only justification that worked out was the heavy cannon armament, and the P400 didn't even have that.

Interestingly the Italians used the same three justifications for a prototype mid-engined fighter called the Piaggio P119.

More about the cg problem: on normal ww2 fighters ammo and fuel were kept around the cg, notably in the wings, so that as they were expended the cg stayed about the same. However, with the engine occupying all the fuselage space around the cg, they had to be moved and for goodness knows what reason Bell calculated the static margin (distance from cg to centre of aerodynamic pressure) with a full ammo load. The result is that once the ammo had run down the static margin was reduced and the aircraft was only marginally stable and a potential widow maker.

Part of the reason for the success the Russians had was that rather than giving up on the aircraft (they were desperate for any modern fighters) was that they extensively researched the cg problem and came up with precautions and work-arounds. (I see parallels with the Finns and the Buffalo, where for lack of alternatives they took an aircraft the Western allies loathed and steadily turned it into something decent).

Incidentally, I wonder how much the smaller caliber cannon in the P400 made the cg problem worse by reducing nose weight. I read once (can't confirm it) that the last straw for the RAF after only a handful of missions in their P400s was when they sent four out on one raid and on the way home, with ammo expended, two of the four (including pilots) were lost to flat spins!

Overall for me the most appropriate epitaph for the P39 is the British phrase "Too clever by half".

And why on earth did they use those car doors, making it very difficult to get out of an already dangerous aircraft in an emergency?

Best of luck with your project. BTW, one lesser-known user was the RAAF who refurbished twenty or so war weary and damaged P39s and P400s for interim home defence for a few months in 1942.

ktank · May 15, 2020

GregP said:
I like the looks of the F myself, but the performance gain was very little, and wasn't worth the effort.

I thought the advantage wasn't so much outright performance, but that the Merlin versions were effective for a few thousand feet higher, even single-staged.

Koopernic · May 15, 2020

GregP said:
The UK made the last WWII debt payment to the U.S.A. and Canada in 2006.

The USSR never did repay the WWII lend-lease debt. They paid part of it and, since we never really expected any payment, maybe it was a win.

I'm sorry there was ever a reason for WWII debt in the first place. It would be interesting to go back to the 1880s and find a way to keep the Triple Alliance and other agreements alive. Maybe WWI would never have happened, thus maybe not generating a way or a need for Hitler to come into the limelight. von Metternich set up alliances that were allowed to expire and set up WWI. Funny how agreements penned in the mid-1800s managed to lead to WWI and WWII so many years later after they expired. I suppose that's off-topic, so I'll just let it die here.

The Germans made their last debt repayments for WW1 only a few years ago and are still paying for WW2. It just goes to show bankers always seem to win wars.

P-39 Expert · May 15, 2020

ktank said:
Firstly, why have the engine behind the pilot?

One in theory was that it would increase maneuverability by reducing the polar moment of inertia, ie the main masses would be close to the centre of gravity and so there would be less resistance to turning. I don't know whether that worked, but it certainly gave it a vicious fast spin when the cg got too far back after expending ammunition. This, along with the aircraft failing to meet its performance claims, meant that it had a very brief career with the RAF, who passed the whole lot onto the USSR.

Second, it would allow better streamlining by having the point of greatest width (the engine) in the middle of the fuselage rather than the nose. However, as stated, its performance, not only at altitude, was disappointing compared to what had been promised.

Third, it would allow heavy nose armament. Which in the true P39 it did, with a filthy great 30mm cannon that the Russians loved in ground attack roles. However, in the original export version, the P400, this was replaced by a 20mm cannon (why?) which had nowhere near the hitting power.

So the only justification that worked out was the heavy cannon armament, and the P400 didn't even have that.

Interestingly the Italians used the same three justifications for a prototype mid-engined fighter called the Piaggio P119.

More about the cg problem: on normal ww2 fighters ammo and fuel were kept around the cg, notably in the wings, so that as they were expended the cg stayed about the same. However, with the engine occupying all the fuselage space around the cg, they had to be moved and for goodness knows what reason Bell calculated the static margin (distance from cg to centre of aerodynamic pressure) with a full ammo load. The result is that once the ammo had run down the static margin was reduced and the aircraft was only marginally stable and a potential widow maker.

Part of the reason for the success the Russians had was that rather than giving up on the aircraft (they were desperate for any modern fighters) was that they extensively researched the cg problem and came up with precautions and work-arounds. (I see parallels with the Finns and the Buffalo, where for lack of alternatives they took an aircraft the Western allies loathed and steadily turned it into something decent).

Incidentally, I wonder how much the smaller caliber cannon in the P400 made the cg problem worse by reducing nose weight. I read once (can't confirm it) that the last straw for the RAF after only a handful of missions in their P400s was when they sent four out on one raid and on the way home, with ammo expended, two of the four (including pilots) were lost to flat spins!

Overall for me the most appropriate epitaph for the P39 is the British phrase "Too clever by half".

And why on earth did they use those car doors, making it very difficult to get out of an already dangerous aircraft in an emergency?

Best of luck with your project. BTW, one lesser-known user was the RAAF who refurbished twenty or so war weary and damaged P39s and P400s for interim home defence for a few months in 1942.

Engine was put behind the pilot to make room for the 37mm cannon. It couldn't be synchronized.

37mm was replaced in the P-400 (and P-39D-1, a virtual copy) by a British 20mm cannon for commonality and logistics since those planes were for export to Britain. And their 20mm cannon was more reliable than our copy of the same 20mm cannon.

Stability was nowhere near marginal even with the nose ammo fully expended. In order to spin a plane must stall first and the P-39 had good stalling characteristics. No danger whatsoever in normal flight, approach or landing.

The 37mm cannon weighed 300# including ammo as installed in the P-39. The 20mm cannon weighed 160#. Virtually all planes use ballast for balance and this weight disparity was corrected through ballast. Consider that the P-39 was designed to use propellers of different size and weight, different reduction gears, varied nose armament, varied radio equipment and varied armor. The 100# nose armor (out of the 240# total armor including armor glass) was likely for ballast as heavier propellers were anticipated since they would be larger or have more blades.

The Soviet P-39 was successful (likely their best fighter in '43-'44) because they received the much improved N and Q models with the higher rated 9.6 supercharged engines. They deleted the wing guns on both the N and Q making them virtually the same plane. This reduced weight enhanced their performance substantially over American models which were already very competitive with the German 109 and 190. Three of the top four Soviet aces and scores of 20+ victory aces flew the P-39. Considering that they received less than 5000 P-39s it would seem that it was their best plane.

Concerning the car doors, I would have preferred a simple conversion to a bubble canopy. But the car doors were retained throughout P-39 production and even retained throughout P-63 production.

tomo pauk · May 15, 2020

ktank said:
Firstly, why have the engine behind the pilot?

One in theory was that it would increase maneuverability by reducing the polar moment of inertia, ie the main masses would be close to the centre of gravity and so there would be less resistance to turning. I don't know whether that worked, but it certainly gave it a vicious fast spin when the cg got too far back after expending ammunition. This, along with the aircraft failing to meet its performance claims, meant that it had a very brief career with the RAF, who passed the whole lot onto the USSR.

Second, it would allow better streamlining by having the point of greatest width (the engine) in the middle of the fuselage rather than the nose. However, as stated, its performance, not only at altitude, was disappointing compared to what had been promised.

Third, it would allow heavy nose armament. Which in the true P39 it did, with a filthy great 30mm cannon that the Russians loved in ground attack roles. However, in the original export version, the P400, this was replaced by a 20mm cannon (why?) which had nowhere near the hitting power.

So the only justification that worked out was the heavy cannon armament, and the P400 didn't even have that.

I'm not sure that P-39 needed justification for the 37mm cannon (no 30 mm cannon) - it was a part of a requirement laid down by the costumer (USAAC/AAF). Without the ability to carry the cannon the user deemed essential, there will be no P-39. Since the V-1710 was not able to have armament going withing the Vee, it was 'shifted' back so the big cannon can be comfortably installed.
The 'Russians used 37mm cannon from P-39 for ground attack' myth is past it's sell date. The P-39s were used in fighter regiments, ground attack was what Il-2s and Su-2s were for.

Overall for me the most appropriate epitaph for the P39 is the British phrase "Too clever by half".

Yes, pretty much.
Bell tried to pour 1.5L of liquid into a 1L bottle. The (X)P-39 was supposed to have it all - turbocharged liquid-cooled engine, tricycle U/C, heavy armament, 200 gals of internal fuel. Did not worked, and a lot of the items were not present by the time P-39D entered service (some items were added, like the s-s fuel tanks).

And why on earth did they use those car doors, making it very difficult to get out of an already dangerous aircraft in an emergency?

Car doors were there to make exit easier, on both sides.

cherry blossom · May 15, 2020

There is another issue with mid engined aircraft. If you make a crash landing, it is nice if the engine does not hit the pilot in the back. This may require a strengthened and thus heavier fuselage compared to the conventional designs. Of course, the engine may allow you to remove some of the armour from the pilot's back and thus save weight. However, you might need some extra armour in front if you want to attack well armed bombers.

Dinger · May 16, 2020

Best of luck with your project. You have certainly picked a topic that creates controversy. The subject of the P39 and its success with Soviet forces in WW2 and its lack of success with the US and British is a cause for constant debate on forums.

A few points about the British experience with the P-39 are directly related to the engine position. These points are almost never bought up in modern discussions of the type, being largely forgotten. So they might interest other readers of this forum as well as adding a unique slant to your project.

On 1st March 1940, an article appeared in the British weekly "Aeroplane" magazine. It was highly critical of the new Bell P-39 Airacobra and the performance claims made for it. One point the author kept repeating was that a mid-engined aircraft requires a long extension shaft to the prop. That adds extra weight to the aircraft, weight that is avoided in a traditional front-engined design. So, all things being equal, a properly designed front-engined fighter would always be superior to a mid-engined one because it would not carry the additional weight of the extension shaft. The added weight and complication of the big steerable nose-wheel would only compound the matter. The author also had a particular issue with the location of the carb air intake behind the cockpit, which he asserted would be highly inefficient. The position of the engine behind the pilot was also criticised as in a crash it could "run over" the pilot (this was a particularly British concern reflecting the experience with "pusher" aircraft such as the FE2B and Vickers Gunbus in the First World War). The tone of the whole article was downright nasty and it ended on a particularly sour note.

"As a serious fighter the Bell is all wrong. We trust the British Purchasing Commission in the USA will not be hood-winked into placing an order"

The article was anonymous, but no one had any doubts who had written it – the dreaded Charles G Grey.

It is hard now to realise just what influence this ridiculous old fool had in Britain at the time. The founder of the "Aeroplane" magazine he had used it as a mouthpiece for his own racist, xenophobic, world-view in both the weekly editorial and the comments he felt free to insert into other writer's articles. His own pet-theories and prejudices were given great coverage and he became a man of great influence. A sort of aeronautical Piers Morgan, one half of his readership agreed with him while the other half read his editorials to see what nonsense the old man was spouting this week. He was the man that had led the campaign to close down the Royal Aircraft Factory during World War One just as it was about to deliver some very advanced designs and an outstanding engine. The Air Ministry ran scared of him on a number of issues. His pro-German attitude eventually proved too much even for the publishers of "The Aeroplane" and he was "retired" as editor when war broke out in September 1939. However he continued to have his articles printed in the magazine (often anonymously) and he was snapped-up as air correspondent of various newspapers, so if anything his influence spread.

So you can imagine the trepidation of the Air Ministry and RAF when the British Purchasing Committee selected the P-39 for production for the RAF in its modified P-400 "Caribou" form with 20mm cannon instead of 37mm cannon. It would only need a letter from some pilot to his MP or to a newspaper complaining of even the slightest problem with the new aircraft to have CG Grey down on them complaining of incompetence in the Air Ministry. When the new aircraft were tested after arrival in the UK and found to have a performance well below that expected, just as CG Grey had prophesied 12 months earlier, you can imagine alarm bells started ringing in the Air Ministry! Is it any wonder they looked for ways of unloading this machine onto someone else, especially as, at the time, supplies of Hurricanes and Spitfires were on the up (How things would change at the end of 1941 with opening up of the war in the Far East!)

The other problem with the P-400 was the timing of its arrival in the UK. In early 1941 there was every expectation that the Luftwaffe would renew their daylight attacks on Britain. When the Battle of Britain had petered out in 1940 combats had been happening at increasing heights. The RAF expected that when the battle was re-joined it would start off where it had left off, with combat at increasing altitude and maybe with the Germans using new high-altitude pressurised bombers. This had led to the emergency development of the mark VII and VIII high-altitude versions of the Spitfire and the fitting of the Merlin XX in the Hurricane II to give a better high-altitude performance. Again, you can imagine the dismay when the new P-400 arrives on the scene and proves to have a particularly disappointing performance at altitude. Even when the Germans invaded Russia everyone assumed that the Soviets would be defeated in a matter of weeks and that the Germans would resume their attack on the UK in the autumn of 1941 or spring 1942.

The other issue that came to light during testing was the time it took to "turn around" the aircraft. During the Battle of Britain, when a Hurricane or Spitfire squadron returned to base after combat they would usually come back in "dribs and drabs", a few aircraft at a time. The armourers would work on the machine-guns in the wings, and even though they had 8 machine guns the way they were installed made them easy to reload without getting in anyone's way. While this was going on the fuel could be refilled and oil and coolant topped-up. So the turn-around time was remarkably quick and the aircraft was ready for the next "scramble" in a very short time. Largely because of its mid-engine layout P-39/ P-400 took much longer to turn-around. With the armament in the nose and awkward to get at the armourers were in the way of the fuel-replenishers. Time to turn-around is a powerful FORCE-MULTIPLIER and remained a central feature of RAF thinking into the cold-war (the cannon packs on the Hunter jets being a case in point).

The RAF defence structure, based on sector stations each controlling a limited number of squadrons had been a great success in 1940. – But it was also inflexible. All Day Fighter Squadrons were EQUAL. They all had to be capable of being sent against any incoming force and at whatever height, be they bombers or an enemy fighter sweep (one of the reasons for the withdrawal of the Defiant from the Day-fighter role in 1940). It simply would not have been possible to have some P-39 /P-400 squadrons limited to only low-altitude interceptions, and also taking twice the time to turn-around.

So you see, the P-39 was just not suitable for the battle RAF Fighter Command thought it was going to have to fight in 1941 or 1942 once the Germans were through with defeating the Russians. Of course, neither the altitude or turn-around time matters when you go into OFFENSIVE operations or if you provide air defence over your front line by flying standing patrols. Then, as the Russians did, you can dictate yourself what altitude you want to fight at and take your time re-arming and refuelling your aircraft ready for the next mission.

So when you add this evaluation to the possibilities of the "CG Grey" issue you can perhaps appreciate why the Air Marshals jumped at the chance to unload the P-400s onto the Soviets!

CG Grey was only months away from getting his own comeuppance. Firstly the German invasion of Russia made allies of a nation he had spent a lifetime denigrating. Then the US entry into the war made Allies of a nation he had often offended ( the American aeronautical press often featured letters from the British people apologising for Greys latest outbursts, the B-17 and US aero-engines were also regular targets for his ire). Then a piece he wrote just weeks before Pearl Harbour about the abilities of Japanese Aviators sealed his fate as an aviation pundit.

Heck, I've ended up writing an essay! - Best of luck with yours!

gjs238 · May 16, 2020

Dinger said:
Best of luck with your project. You have certainly picked a topic that creates controversy. The subject of the P39 and its success with Soviet forces in WW2 and its lack of success with the US and British is a cause for constant debate on forums.

A few points about the British experience with the P-39 are directly related to the engine position. These points are almost never bought up in modern discussions of the type, being largely forgotten. So they might interest other readers of this forum as well as adding a unique slant to your project.

On 1st March 1940, an article appeared in the British weekly "Aeroplane" magazine. It was highly critical of the new Bell P-39 Airacobra and the performance claims made for it. One point the author kept repeating was that a mid-engined aircraft requires a long extension shaft to the prop. That adds extra weight to the aircraft, weight that is avoided in a traditional front-engined design. So, all things being equal, a properly designed front-engined fighter would always be superior to a mid-engined one because it would not carry the additional weight of the extension shaft. The added weight and complication of the big steerable nose-wheel would only compound the matter. The author also had a particular issue with the location of the carb air intake behind the cockpit, which he asserted would be highly inefficient. The position of the engine behind the pilot was also criticised as in a crash it could "run over" the pilot (this was a particularly British concern reflecting the experience with "pusher" aircraft such as the FE2B and Vickers Gunbus in the First World War). The tone of the whole article was downright nasty and it ended on a particularly sour note.

"As a serious fighter the Bell is all wrong. We trust the British Purchasing Commission in the USA will not be hood-winked into placing an order"

The article was anonymous, but no one had any doubts who had written it – the dreaded Charles G Grey.

It is hard now to realise just what influence this ridiculous old fool had in Britain at the time. The founder of the "Aeroplane" magazine he had used it as a mouthpiece for his own racist, xenophobic, world-view in both the weekly editorial and the comments he felt free to insert into other writer's articles. His own pet-theories and prejudices were given great coverage and he became a man of great influence. A sort of aeronautical Piers Morgan, one half of his readership agreed with him while the other half read his editorials to see what nonsense the old man was spouting this week. He was the man that had led the campaign to close down the Royal Aircraft Factory during World War One just as it was about to deliver some very advanced designs and an outstanding engine. The Air Ministry ran scared of him on a number of issues. His pro-German attitude eventually proved too much even for the publishers of "The Aeroplane" and he was "retired" as editor when war broke out in September 1939. However he continued to have his articles printed in the magazine (often anonymously) and he was snapped-up as air correspondent of various newspapers, so if anything his influence spread.

So you can imagine the trepidation of the Air Ministry and RAF when the British Purchasing Committee selected the P-39 for production for the RAF in its modified P-400 "Caribou" form with 20mm cannon instead of 37mm cannon. It would only need a letter from some pilot to his MP or to a newspaper complaining of even the slightest problem with the new aircraft to have CG Grey down on them complaining of incompetence in the Air Ministry. When the new aircraft were tested after arrival in the UK and found to have a performance well below that expected, just as CG Grey had prophesied 12 months earlier, you can imagine alarm bells started ringing in the Air Ministry! Is it any wonder they looked for ways of unloading this machine onto someone else, especially as, at the time, supplies of Hurricanes and Spitfires were on the up (How things would change at the end of 1941 with opening up of the war in the Far East!)

The other problem with the P-400 was the timing of its arrival in the UK. In early 1941 there was every expectation that the Luftwaffe would renew their daylight attacks on Britain. When the Battle of Britain had petered out in 1940 combats had been happening at increasing heights. The RAF expected that when the battle was re-joined it would start off where it had left off, with combat at increasing altitude and maybe with the Germans using new high-altitude pressurised bombers. This had led to the emergency development of the mark VII and VIII high-altitude versions of the Spitfire and the fitting of the Merlin XX in the Hurricane II to give a better high-altitude performance. Again, you can imagine the dismay when the new P-400 arrives on the scene and proves to have a particularly disappointing performance at altitude. Even when the Germans invaded Russia everyone assumed that the Soviets would be defeated in a matter of weeks and that the Germans would resume their attack on the UK in the autumn of 1941 or spring 1942.

The other issue that came to light during testing was the time it took to "turn around" the aircraft. During the Battle of Britain, when a Hurricane or Spitfire squadron returned to base after combat they would usually come back in "dribs and drabs", a few aircraft at a time. The armourers would work on the machine-guns in the wings, and even though they had 8 machine guns the way they were installed made them easy to reload without getting in anyone's way. While this was going on the fuel could be refilled and oil and coolant topped-up. So the turn-around time was remarkably quick and the aircraft was ready for the next "scramble" in a very short time. Largely because of its mid-engine layout P-39/ P-400 took much longer to turn-around. With the armament in the nose and awkward to get at the armourers were in the way of the fuel-replenishers. Time to turn-around is a powerful FORCE-MULTIPLIER and remained a central feature of RAF thinking into the cold-war (the cannon packs on the Hunter jets being a case in point).

The RAF defence structure, based on sector stations each controlling a limited number of squadrons had been a great success in 1940. – But it was also inflexible. All Day Fighter Squadrons were EQUAL. They all had to be capable of being sent against any incoming force and at whatever height, be they bombers or an enemy fighter sweep (one of the reasons for the withdrawal of the Defiant from the Day-fighter role in 1940). It simply would not have been possible to have some P-39 /P-400 squadrons limited to only low-altitude interceptions, and also taking twice the time to turn-around.

So you see, the P-39 was just not suitable for the battle RAF Fighter Command thought it was going to have to fight in 1941 or 1942 once the Germans were through with defeating the Russians. Of course, neither the altitude or turn-around time matters when you go into OFFENSIVE operations or if you provide air defence over your front line by flying standing patrols. Then, as the Russians did, you can dictate yourself what altitude you want to fight at and take your time re-arming and refuelling your aircraft ready for the next mission.

So when you add this evaluation to the possibilities of the "CG Grey" issue you can perhaps appreciate why the Air Marshals jumped at the chance to unload the P-400s onto the Soviets!

CG Grey was only months away from getting his own comeuppance. Firstly the German invasion of Russia made allies of a nation he had spent a lifetime denigrating. Then the US entry into the war made Allies of a nation he had often offended ( the American aeronautical press often featured letters from the British people apologising for Greys latest outbursts, the B-17 and US aero-engines were also regular targets for his ire). Then a piece he wrote just weeks before Pearl Harbour about the abilities of Japanese Aviators sealed his fate as an aviation pundit.

Heck, I've ended up writing an essay! - Best of luck with yours!

Would be interested to hear his thoughts of the B-17.

Dinger · May 16, 2020

gjs238 said:
Would be interested to hear his thoughts of the B-17.

Give me a day to two to dig through old copies of "The Aeroplane" and other magazines and books of the time I'll put them up. Along with some of his more outrageous comments on other subjects. - But rather than do it on this thread I'll create a new one. Then anyone else who comes up with other quotations from him can add them for comment.

Deleted member 68059 · May 16, 2020

P-39 Expert said:
I honestly don't know what to say.
Merlin in a P-39? I guess it's possible but hardly worth the effort. If you want two stage performance just use the -93 engine in production from April 1943.

A lot of engineers in America at Wright-Field wanted very much to put a V-1650 into the P-39, and went as far as having Rolls-Royce do all the calcs on if the extension shaft would be
permitted by them as a concept (they said yes).

NARA-6566652

The documents do not state why it did not go further, but a reasonable guess would be that as the project progressed - the number of 61`s and 1650`s was limited and soon the Spit IX and Mustang were ready, which were probably far better "value" to use them in at that stage. These discussions were 15months before your date of April 1943.

P-39 Expert · May 18, 2020

Dinger said:
Best of luck with your project. You have certainly picked a topic that creates controversy. The subject of the P39 and its success with Soviet forces in WW2 and its lack of success with the US and British is a cause for constant debate on forums.

A few points about the British experience with the P-39 are directly related to the engine position. These points are almost never bought up in modern discussions of the type, being largely forgotten. So they might interest other readers of this forum as well as adding a unique slant to your project.

On 1st March 1940, an article appeared in the British weekly "Aeroplane" magazine. It was highly critical of the new Bell P-39 Airacobra and the performance claims made for it. One point the author kept repeating was that a mid-engined aircraft requires a long extension shaft to the prop. That adds extra weight to the aircraft, weight that is avoided in a traditional front-engined design. So, all things being equal, a properly designed front-engined fighter would always be superior to a mid-engined one because it would not carry the additional weight of the extension shaft. The added weight and complication of the big steerable nose-wheel would only compound the matter. The author also had a particular issue with the location of the carb air intake behind the cockpit, which he asserted would be highly inefficient. The position of the engine behind the pilot was also criticised as in a crash it could "run over" the pilot (this was a particularly British concern reflecting the experience with "pusher" aircraft such as the FE2B and Vickers Gunbus in the First World War). The tone of the whole article was downright nasty and it ended on a particularly sour note.

"As a serious fighter the Bell is all wrong. We trust the British Purchasing Commission in the USA will not be hood-winked into placing an order"

The article was anonymous, but no one had any doubts who had written it – the dreaded Charles G Grey.

It is hard now to realise just what influence this ridiculous old fool had in Britain at the time. The founder of the "Aeroplane" magazine he had used it as a mouthpiece for his own racist, xenophobic, world-view in both the weekly editorial and the comments he felt free to insert into other writer's articles. His own pet-theories and prejudices were given great coverage and he became a man of great influence. A sort of aeronautical Piers Morgan, one half of his readership agreed with him while the other half read his editorials to see what nonsense the old man was spouting this week. He was the man that had led the campaign to close down the Royal Aircraft Factory during World War One just as it was about to deliver some very advanced designs and an outstanding engine. The Air Ministry ran scared of him on a number of issues. His pro-German attitude eventually proved too much even for the publishers of "The Aeroplane" and he was "retired" as editor when war broke out in September 1939. However he continued to have his articles printed in the magazine (often anonymously) and he was snapped-up as air correspondent of various newspapers, so if anything his influence spread.

So you can imagine the trepidation of the Air Ministry and RAF when the British Purchasing Committee selected the P-39 for production for the RAF in its modified P-400 "Caribou" form with 20mm cannon instead of 37mm cannon. It would only need a letter from some pilot to his MP or to a newspaper complaining of even the slightest problem with the new aircraft to have CG Grey down on them complaining of incompetence in the Air Ministry. When the new aircraft were tested after arrival in the UK and found to have a performance well below that expected, just as CG Grey had prophesied 12 months earlier, you can imagine alarm bells started ringing in the Air Ministry! Is it any wonder they looked for ways of unloading this machine onto someone else, especially as, at the time, supplies of Hurricanes and Spitfires were on the up (How things would change at the end of 1941 with opening up of the war in the Far East!)

The other problem with the P-400 was the timing of its arrival in the UK. In early 1941 there was every expectation that the Luftwaffe would renew their daylight attacks on Britain. When the Battle of Britain had petered out in 1940 combats had been happening at increasing heights. The RAF expected that when the battle was re-joined it would start off where it had left off, with combat at increasing altitude and maybe with the Germans using new high-altitude pressurised bombers. This had led to the emergency development of the mark VII and VIII high-altitude versions of the Spitfire and the fitting of the Merlin XX in the Hurricane II to give a better high-altitude performance. Again, you can imagine the dismay when the new P-400 arrives on the scene and proves to have a particularly disappointing performance at altitude. Even when the Germans invaded Russia everyone assumed that the Soviets would be defeated in a matter of weeks and that the Germans would resume their attack on the UK in the autumn of 1941 or spring 1942.

The other issue that came to light during testing was the time it took to "turn around" the aircraft. During the Battle of Britain, when a Hurricane or Spitfire squadron returned to base after combat they would usually come back in "dribs and drabs", a few aircraft at a time. The armourers would work on the machine-guns in the wings, and even though they had 8 machine guns the way they were installed made them easy to reload without getting in anyone's way. While this was going on the fuel could be refilled and oil and coolant topped-up. So the turn-around time was remarkably quick and the aircraft was ready for the next "scramble" in a very short time. Largely because of its mid-engine layout P-39/ P-400 took much longer to turn-around. With the armament in the nose and awkward to get at the armourers were in the way of the fuel-replenishers. Time to turn-around is a powerful FORCE-MULTIPLIER and remained a central feature of RAF thinking into the cold-war (the cannon packs on the Hunter jets being a case in point).

The RAF defence structure, based on sector stations each controlling a limited number of squadrons had been a great success in 1940. – But it was also inflexible. All Day Fighter Squadrons were EQUAL. They all had to be capable of being sent against any incoming force and at whatever height, be they bombers or an enemy fighter sweep (one of the reasons for the withdrawal of the Defiant from the Day-fighter role in 1940). It simply would not have been possible to have some P-39 /P-400 squadrons limited to only low-altitude interceptions, and also taking twice the time to turn-around.

So you see, the P-39 was just not suitable for the battle RAF Fighter Command thought it was going to have to fight in 1941 or 1942 once the Germans were through with defeating the Russians. Of course, neither the altitude or turn-around time matters when you go into OFFENSIVE operations or if you provide air defence over your front line by flying standing patrols. Then, as the Russians did, you can dictate yourself what altitude you want to fight at and take your time re-arming and refuelling your aircraft ready for the next mission.

So when you add this evaluation to the possibilities of the "CG Grey" issue you can perhaps appreciate why the Air Marshals jumped at the chance to unload the P-400s onto the Soviets!

CG Grey was only months away from getting his own comeuppance. Firstly the German invasion of Russia made allies of a nation he had spent a lifetime denigrating. Then the US entry into the war made Allies of a nation he had often offended ( the American aeronautical press often featured letters from the British people apologising for Greys latest outbursts, the B-17 and US aero-engines were also regular targets for his ire). Then a piece he wrote just weeks before Pearl Harbour about the abilities of Japanese Aviators sealed his fate as an aviation pundit.

Heck, I've ended up writing an essay! - Best of luck with yours!

Main problem with the P-39 and P-400 was weight. In 1941 a SpitfireV weighed 6600#. A P-400 weighed 7850# with a slightly less powerful engine. If they had simply deleted the wing guns and a little of the redundant armor plate performance was about the same as the SpitfireV. With 20% more fuel, tricycle landing gear and better visibility.

Dinger · May 18, 2020

gjs238 said:
Would be interested to hear his thoughts of the B-17.

Have started the new thread under "Stories" (only heading I could see that was anywhere near applicable). - Includes a quote of his on the B17.

gjs238 · May 22, 2020

Rolls-Royce Mustang Mk.X - Wikipedia developments
In June 1943, Rolls-Royce proposed to re-engine the Mustang with a Griffon 65, although the resultant "Flying Test Bed" (F.T.B.) would involve a dramatic redesign. Three surplus Mustang I airframes were allotted by the Ministry of Aircraft Production (MAP) and were dismantled in order to provide the major components for a mid-amidships installation of the more powerful Griffon engine, somewhat like the V-1710 Allison installation in both the American Bell P-39 Airacobra and Bell P-63 Kingcobra. The project culminated in a mock-up, albeit with a Merlin 61 temporarily installed, serialed as AL960, that was examined by representatives from the Ministry in 1944, but was not given priority status. Further studies involving more powerful engines or turboprops were not given approval and the development contract was cancelled in 1945 with the mock-up being destroyed.[2]

P-39- Did the engine behind the pilot cause any problems?

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