US Navy's Pratt Whitney

[Marshall_Stack]

I have read that the US Navy worked with P&W to come up with a two-stage supercharger that was used on the F4U Corsair (and probably others).

Did this make a big difference? I know that the USAAF wanted to put turbochargers on the P-70 (night fighter variant of A-20) but they were not available (higher priority for bombers, P-47s and P-38s). I was thinking that if the Army had access to the Navy's supercharger, maybe it would have been more successful, not to mention that it could have benefited other planes....

 

[renrich]

The R2800 in the Corsair and Hellcat had a 2 stage, 2 speed supercharger. The PW and Wright engines in the Wildcat used 2 stage, 2 speed superchargers also. Republic elected to use a turbo supercharger on the R2800 in the P47. They could have used the same supercharger as used in the Navy AC but wanted to maintain engine power to a higher altitude than the Navy needed to do. Vought developed a turbocharged Corsair but the additional drag and complexity and possible lower reliability caused them to not put the AC into production. Interestingly the Merlin Mustangs used a 2 stage, 2 speed supercharger which had automatic controls. The Navy Corsairs and Hellcats had their superchargers controlled by the pilot from the cockpit. I always wondered about that as it seems to be a hassle to have to manually switch form low blower to high blower and vice versa as the AC goes higher or lower.

 

[Marshall_Stack]

Why didn't the AAF use this version of the P&W for such planes as the A-20, A-26, P-61A, etc. to get higher performance at altitude?

 

[renrich]

Good question as far as P61 is concerned but the A20 and A26 were not too concerned about very high altitude performance. The supercharged R2800 in the F4U 1-4 were good up to almost 30000 ft and the F4U5 was a good performer above 30000 feet. That is not to say that the WW2 Corsairs could not perform above 30000 feet. Their best performance however was around 21000 to 26000 ft with a service ceiling of between 37000 to 42000 feet.

 

[Marshall_Stack]

I just wondered how much better the P-61A/B and the P-70 would have been as night fighters. The P-70 was still slow (330 mph) but it may have done better against the Japanese bombers. Northrop realized that the P-61 needed better high altitude performance (as seen in the Philippine campaign) so they put turbos on the P-61C. This aircraft didn't see action.

Could the AAF modified the P&Ws per the Navy design in the interim?

 

[renrich]

The R280018W powered the F4U4 and was still pulling 1710 HP at military power at 25000 ft. The R280065 that powered The first P61s pulled 1650 HP at military power at 22500 ft. It seems like the Corsair engine would have been a better choice.

 

[Marshall_Stack]

Do you know how they modified the engine? Was the supercharger an external fit to the engine (as I believe they did for the Allison in the P-63)?

 

[red admiral]

I guess it was similar to that used in the R-1830. The two stage supercharger really was in in two separate stages, though not quite as separated as Allison's hash up in the V-1710. There was an intercooler between the two stages (as opposed to an aftercooler on the Merlin) and the second stage could be disengaged at low altitudes in order to provide more power. The system was complicated and added considerable bulk to the arrangement (I'm not so sure of weight) with the result that the two-stage R-2800 was longer than the Merlin 60. Of course, the system weighed less and took up less volume than the comparative turbocharged R-2800.

 

[renrich]

I believe that the PW 1830 and the PW 2800 shared a similar design in a 2 speed 2 stage supercharger. The first stage of the blower was always operative and it compressed the fuel air charge between the carburettor and the cylinders of the engine. This system was when the clutch was in neutral. When the pilot shifted the clutch to low blower the second stage came in which took the air from the outside compressed it, sent it though an intercooler and thence into the carb. The fuel air mixture was then further compressed by the first stage blower.This kept the power up until around 16000 ft. Shifting the clutch to high blower increased the speed of the second stage blower which allowed the power to be kept up to about 24000 ft.