Improve That Design: How Aircraft Could Have Been Made Better

[sazabi2001]

I think the top ally ACEs flew the P38 & P39... So why not Merlin-ed them like P51?

 

[wuzak]

I asked if the H-2600 had been given the go-ahead would the R-2800 have proceeded.

The R-2800 and H-2600 proceeded at the same time historically. The H-2600 would never have taken precedence over the R-2800.

 

[swampyankee]

I think the top ally ACEs flew the P38 & P39... So why not Merlin-ed them like P51?

The Soviet P-39 successes were at low altitudes, where the Allison engine performed quite well. The P-38 would require a lot of rework to fit Merlins and maintain its high-altitude performance. Also, the P-39 would require work to integrate a new engine with its driveshaft. I think the Allison had a different firing order, so it would have different vibration characteristics.

 

[GrauGeist]

I think the top ally ACEs flew the P38 & P39... So why not Merlin-ed them like P51?

To add to Swampyankee's explanation, it also takes time to refit an airframe to accept a new engine.
The P-38 and P-39 were critical fighters in the early stages of the war and such a design change would stop production of the much needed aircraft.

 

[sazabi2001]

The Soviet P-39 successes were at low altitudes, where the Allison engine performed quite well. The P-38 would require a lot of rework to fit Merlins and maintain its high-altitude performance. Also, the P-39 would require work to integrate a new engine with its driveshaft. I think the Allison had a different firing order, so it would have different vibration characteristics.

From Wiki:

Bell P-63 Kingcobra - Wikipedia

"The first prototype, 41-19511, flew for the first time on 7 December 1942. It was destroyed on 28 January 1943 when its landing gear failed to extend. The second prototype, 41-19512, followed on 5 February 1943. It, too, was destroyed, this time due to an engine failure. The Merlin-engined 42-78015 (as Merlins were primarily needed for the P-51 Mustang) was delivered with another Allison instead, a -93, which had a war emergency rating of 1,500 hp (1,120 kW) at sea level, making this prototype one of the fastest Kingcobras built, attaining 421 mph (678 km/h) at 24,100 ft (7,300 m)."

Seems like there was an attempt for Merlin KingCobra, and even without the Merlin engine inside yet that was the fastest KingCobra ever built.

==========

For the P38, I think it is a bit pointless for a Merlin version.

 

[sazabi2001]

To add to Swampyankee's explanation, it also takes time to refit an airframe to accept a new engine.
The P-38 and P-39 were critical fighters in the early stages of the war and such a design change would stop production of the much needed aircraft.

I think P39 never 'critical' to the American and British.

 

[P-39 Expert]

The Soviet P-39 successes were at low altitudes, where the Allison engine performed quite well. The P-38 would require a lot of rework to fit Merlins and maintain its high-altitude performance. Also, the P-39 would require work to integrate a new engine with its driveshaft. I think the Allison had a different firing order, so it would have different vibration characteristics.

For the bazillionth time, the vast majority of P-39s received by the Soviets (N and Q models) were not altitude limited. As the Soviets configured them (no wing guns etc) they had service ceilings over 38500' and would climb at just under 2000fpm at 25000'. This is substantially above the FW190A and about the same as the Bf109G. And at 25000' better than a P-47B/C or P-38F/G.

 

[Zipper730]

I think the top ally ACEs flew the P38 & P39...

I don't know about the P-39, but the P-38 was flown by several high scoring aces. I'm not sure how many scored well in the ETO and how many scored in the PTO, but Richard Bong scored in the Pacific.

So why not Merlin-ed them like P51?

They had toyed with the idea of putting a Merlin in the P-38, but I forgot the reason. The P-39 had to do with a limit on the number of aircraft.

 

[P-39 Expert]

P-39 couldn't take the Merlin because of different locations for the engine mounts and the Merlin didn't have the remote reduction gear. Would have taken a major reconfiguration by Rolls Royce or Bell to get the Merlin to fit.

 

[GrauGeist]

I think P39 never 'critical' to the American and British.

The P-39 was critical to the US in the Pacific and even moreso to the Soviet Union.

 

[Kevin J]

The P-39 was critical to the US in the Pacific and even moreso to the Soviet Union.

Perfect for the USSR. The only fighter available in the South Pacific in early 1942 when the Japanese were expanding their defensive perimeter, the P-40 was better of course.

 

[P-39 Expert]

At what?

 

[pbehn]

At what?

Preventing back strain.

 

[GrauGeist]

The P-39 was able to prove itself against the A6M ad long as they fought at lower altitudes.

Where the P-39 proved to be invaluable, however, was in the ground attack role. It literally saved Henderson field against a Japanese counter-attack and it sent many a Japanese troop transport to the bottom. It also was a crucial factor in the Aleutian theater early on, too.

It provided an irreplaceable platform at a precarious time in the war.

 

[P-39 Expert]

The P-39 was able to prove itself against the A6M ad long as they fought at lower altitudes.

Where the P-39 proved to be invaluable, however, was in the ground attack role. It literally saved Henderson field against a Japanese counter-attack and it sent many a Japanese troop transport to the bottom. It also was a crucial factor in the Aleutian theater early on, too.

It provided an irreplaceable platform at a precarious time in the war.

And most of those Japanese killed at Henderson were from the .30 caliber guns that I so dislike.

 

[drgondog]

From Wiki:

Bell P-63 Kingcobra - Wikipedia

"The first prototype, 41-19511, flew for the first time on 7 December 1942. It was destroyed on 28 January 1943 when its landing gear failed to extend. The second prototype, 41-19512, followed on 5 February 1943. It, too, was destroyed, this time due to an engine failure. The Merlin-engined 42-78015 (as Merlins were primarily needed for the P-51 Mustang) was delivered with another Allison instead, a -93, which had a war emergency rating of 1,500 hp (1,120 kW) at sea level, making this prototype one of the fastest Kingcobras built, attaining 421 mph (678 km/h) at 24,100 ft (7,300 m)."

Seems like there was an attempt for Merlin KingCobra, and even without the Merlin engine inside yet that was the fastest KingCobra ever built.

==========

For the P38, I think it is a bit pointless for a Merlin version.

There was no US role for either the P-39 or the P-63. They were both too limited in range for escort or recon, there was no interception mission that the P-38 was not capable of fulfilling. In 1943 the emerging XP-51F with merlin 1650-3 was FAR more capable than the P-63 at all altitudes, much faster, climbed much better, had almost as much range as the P-51B/D.
Then the most important reason of all (for both the P-39 and P38) is that ZERO Packard Merlin 1650-3/-7 were Available to any US aircraft except the Mustang. Packard never had the capacity.

 

[P-39 Expert]

Except that the P-38 did not see combat until December '42 (call it '43) and the P-51B did not see combat until December'43 (call it '44). Something (P-39 and P-40) had to hold the line in '42. There was really no high altitude escort until the P-47 reached combat in May '43. The original P-38s in England got sent to the Med in late '42 for Torch.

 

[drgondog]

Except that the P-38 did not see combat until December '42 (call it '43) and the P-51B did not see combat until December'43 (call it '44). Something (P-39 and P-40) had to hold the line in '42. There was really no high altitude escort until the P-47 reached combat in May '43. The original P-38s in England got sent to the Med in late '42 for Torch.

Agree your comments but the P-39 was dead with respect to future of both CAS/TAC in early 1943 when the decision was made by TAC-HQ to replace both the P-40 and P-39 with the P-51A, then P-51B when the Merlin Mustang was in production. My comments were focused on why their was no real consideration to re-design the P-39 to try to squeeze the Merlin into the airframe. Either the Allison 2s/2stage or the Merlin made the P-63 with extra fuselage length and wing change required for CG purposes and even though the P-63 was coming in parallel with the P-51A, it still had serious deficiencies in external bomb load and range.

 

[swampyankee]

Agree your comments but the P-39 was dead with respect to future of both CAS/TAC in early 1943 when the decision was made by TAC-HQ to replace both the P-40 and P-39 with the P-51A, then P-51B when the Merlin Mustang was in production. My comments were focused on why their was no real consideration to re-design the P-39 to try to squeeze the Merlin into the airframe. Either the Allison 2s/2stage or the Merlin made the P-63 with extra fuselage length and wing change required for CG purposes and even though the P-63 was coming in parallel with the P-51A, it still had serious deficiencies in external bomb load and range.

Because of its configuration, the P-39 had serious problems with growth, in general, and in re-engining. Since the size of a drive shaft is dictated by vibration properties and torque, and the path of the shaft has to be straight from the engine output to the propeller hub. This may require modifying the pilot so the shaft can pass through his chest or abdomen (not recommended) or modifying the Merlin for a remote gearbox (recommended). How difficult this would be, I have no knowledge. Obviously, a gearbox would also be needed. The Merlin and the Allison had different firing orders, which would have made differences in the forcing function for the shaft, which would require, at a minimum, analysis and testing. A Merlin P-39 would require, at a minimum, significant redesign of the fuselage center section and transmission from the engine to propeller; while this redesign could be done without slowing down production, introducing this into production would require new production tooling.

You still have an aircraft with severely constrained internal fuel capacity (the engine is right where you want to put fuel tanks) and a tendency to have its center of gravity move aft as combat proceeds, not infrequently resulting in flight characteristics that are somewhat unpleasant. While the P-39 was not as terrible as some have made out, it was at least a half-generation behind the P-51 (and F4U and P-47) and even the derivative design, the P-63, was no advance over the P-51 (and F4U and P-47).

 

[wuzak]

Because of its configuration, the P-39 had serious problems with growth, in general, and in re-engining. Since the size of a drive shaft is dictated by vibration properties and torque, and the path of the shaft has to be straight from the engine output to the propeller hub. This may require modifying the pilot so the shaft can pass through his chest or abdomen (not recommended) or modifying the Merlin for a remote gearbox (recommended). How difficult this would be, I have no knowledge. Obviously, a gearbox would also be needed. The Merlin and the Allison had different firing orders, which would have made differences in the forcing function for the shaft, which would require, at a minimum, analysis and testing. A Merlin P-39 would require, at a minimum, significant redesign of the fuselage center section and transmission from the engine to propeller; while this redesign could be done without slowing down production, introducing this into production would require new production tooling.

You still have an aircraft with severely constrained internal fuel capacity (the engine is right where you want to put fuel tanks) and a tendency to have its center of gravity move aft as combat proceeds, not infrequently resulting in flight characteristics that are somewhat unpleasant. While the P-39 was not as terrible as some have made out,

The Merlin could have been modified to have a direct output shaft rather than a reduction gear.

How long it would take to get such a modification into production I do not know.

You definitely wanted to use crankshaft speed at least, to minimise the size of the driveshaft which, as you pointed out, dictated by torque.

The Griffon in the Rolls-Royce Flying Test Bed had an output lower than the crankshaft centreline, being driven by a step up spur gear set (output shaft speed faster than crankshaft).