One off Curtiss P-40 prototype fitted with two stage supercharger version of the Twin Wasp

[fortrena]

I seem to recall that an early example of the P-40 was experimentally fitted with a two stage supercharger version of the R-1830 Twin Wasp.

Would anyone know when that one off machine first flew and what speed it eventually achieved, a few weeks or months later?

 

[Hardrada55]

I seem to recall that an early example of the P-40 was experimentally fitted with a two stage supercharger version of the R-1830 Twin Wasp.

Would anyone know when that one off machine first flew and what speed it eventually achieved, a few weeks or months later?

I gleaned this info from other sites on the web and my own files. In 1940, Pratt & Whitney purchased from Curtiss one of the first 199 P-40 (H81A-1) fighters, without an engine. The intention was to use this plane to test Pratt & Whitney's R-1830-SSC7-G Twin Wasp. R-1830-SSC7-G was an engine with a two stage supercharger. Figures for the P-40 airframe with the R-1830-SSC7-G engine, tested in September of 1942 showed a speed of 389 mph at 22,700 ft. I also saw reference to 389 mph at 19,000 ft. It climbed to 15,000ft in 5.5 minutes and to 20,000ft in 7,7 minutes using military power for the entire climb. In November of 1942 Pratt & Whitney reported that this plane performed much better than P-40F. The Pratt & Whitney engine sheet says the plane was a Hawk 81A and the photo doesn't seems to show guns in the wings or fuselage. The equipment and armament fitted is not known, but the P-40 (H81A-1) didn't have armor and self-sealing tanks.

 

[Justo Miranda]

The H75 inadequate performance at high altitude was a constant source of concern for the Curtiss Airplane Division staff.

In 1938 one H75 A-1 was modified as the H75 R high-altitude prototype, powered by one R-1830-SC2-G radial engine driving two centrifugal turbochargers, with ventral intercooler. During flight tests conducted in January 1939 the H75R reached a top speed of 330 mph flying at 15,000 ft. The USAAC considered insufficient the increase of performance and the H75 R unsuitable for operational service, due the complexity of the new propulsion system.

Curtiss continuing to perfect the concept, in 1943 the NX 28990 airframe of a H81A was powered by one R-1830-SSC7-G radial engine driving two centrifugal compressors housed in a new streamlined cowling. During flight tests conducted between July and October 1943, the high-altitude prototype reached a top speed of 389 mph and 25,000 ft of ceiling.

 

[jcf]

Justo, the R-1830 powered P-40 was not a Curtiss project, it was entirely a Pratt & Whitney development
and NX28990 was simply the civil registration assigned by the CAA on September 29, 1940.

The Curtiss serial number was 17816 which puts it directly in front of the final batch of Tomahawk IIB for the
RAF (c/n 17817 - 18116), it was not one of the first "199 P-40 (H81A-1)". The constructor numbers for the first
200 P-40s were 13033 through 13232.

 

[PabloSniper]

Forgive my ignorance.
But wouldn't it have been easier to use the same Alisson from the P-38 with the same compressor from the P-38?

 

[Kanga]

Justo, the R-1830 powered P-40 was not a Curtiss project, it was entirely a Pratt & Whitney development
and NX28990 was simply the civil registration assigned by the CAA on September 29, 1940.

The Curtiss serial number was 17816 which puts it directly in front of the final batch of Tomahawk IIB for the
RAF (c/n 17817 - 18116), it was not one of the first "199 P-40 (H81A-1)". The constructor numbers for the first
200 P-40s were 13033 through 13232.

For the sake of clarity, was this engine turbocharged by an exhaust driven turbocharger or supercharged by superchargers mechanically linked to and driven by the engine?

 

[Justo Miranda]

For the sake of clarity, was this engine turbocharged by an exhaust driven turbocharger or supercharged by superchargers mechanically linked to and driven by the engine?

Pratt&Whitney R-1830-19 with two compressors in tandem.

 

[fortrena]

If I read the data in https://www.enginehistory.org/Piston/P&W/R-1830/R-1830Index.pdf correctly, the R-1830-SSC7-G of the Curtiss H-81A seemed very similar to the R-1830-76 and -86 engines, both of them fitted with a mechanically-driven two-stage supercharger. Those engines were mounted on Grumman F4F-3 and -4 Wildcat fighter planes.

 

[Apophenia]

Forgive my ignorance.
But wouldn't it have been easier to use the same Alisson from the P-38 with the same compressor from the P-38?

As Jon noted in the post directly above yours, this re-engining exercise was a Pratt & Whitney project, not a Curtiss job.

Curtiss did experiment with the same GE turbosupercharger used in the P-38 - in the Allison-powered YP-37 prototype. A major problem was the excessively close proximity of the turbo to the exhaust ports directly in front. At this stage of their development, turbosuperchargers needed distance to adequately cool exhaust gases. The P-38's layout lent itself to providing that distance.

 

[PabloSniper]

As Jon noted in the post directly above yours, this re-engining exercise was a Pratt & Whitney project, not a Curtiss job.

Curtiss did experiment with the same GE turbosupercharger used in the P-38 - in the Allison-powered YP-37 prototype. A major problem was the excessively close proximity of the turbo to the exhaust ports directly in front. At this stage of their development, turbosuperchargers needed distance to adequately cool exhaust gases. The P-38's layout lent itself to providing that distance.

Thanks for the information.
Yes, I realized that it was a Pratt & Whitney development.
However, it seemed so obvious to me to use the same solution as the P-38.
But I didn't realize that it needed a larger space.

 

[Scott Kenny]

Curtiss did experiment with the same GE turbosupercharger used in the P-38 - in the Allison-powered YP-37 prototype. A major problem was the excessively close proximity of the turbo to the exhaust ports directly in front. At this stage of their development, turbosuperchargers needed distance to adequately cool exhaust gases. The P-38's layout lent itself to providing that distance.

Ironic that today we have people complaining if the turbo is more than a couple inches away from the exhaust ports...

 

[Apophenia]

Ironic that today we have people complaining if the turbo is more than a couple inches away from the exhaust ports...

Progress in metallurgy (including bearings) marches on, I guess.

For WW2 aircraft applications, I suppose the big advance was the introduction of intercoolers. Postwar, crossovers from growing gas turbine tech experience helped as well.

 

[Justo Miranda]

As Jon noted in the post directly above yours, this re-engining exercise was a Pratt & Whitney project, not a Curtiss job.

Curtiss did experiment with the same GE turbosupercharger used in the P-38 - in the Allison-powered YP-37 prototype. A major problem was the excessively close proximity of the turbo to the exhaust ports directly in front. At this stage of their development, turbosuperchargers needed distance to adequately cool exhaust gases. The P-38's layout lent itself to providing that distance.

- In February 1937 the USAAC contracted with Curtiss the installation of one advanced Allison V-1710-11 turbo-supercharged V-12 engine in the H75 B airframe. To make room for the experimental B-1 exhaust-driven turbo-supercharger, including the compressor, the Prestone intercooler and heavy tubing system, the cockpit was pushed very far to the rear, resulting in poor visibility during take offs and landings.

The extensively modified prototype, redesigned XP-37, was flown on April 1937 reaching 340 mph at 20,000 ft, but suffered frequent turbo-supercharger malfunction and tail plane flutter, the performance fell short of expectations.

On 11 December 1937 the USAAC ordered thirteen service test airplanes under the designation YP-37. These pre-production machines were fitted with elongated fuselages and Allison V-1710-21 engines with improved G.E. B-2 turbo-superchargers.

The first YP-37 flew on June 1939.

Although the new turbo-supercharger was quite troublesome, the YP-37 remained in experimental service until 1942.



Curtiss XP-37 technical data

Power plant: one 1,150 hp Allison V-1710-11, twelve cylinder, Vee, liquid-cooled engine with General Electric B-1 turbo-supercharger, wingspan: 37.33 ft (11.38 m), length: 30.46 ft (9.2 m), height: 10.5 ft (3.2 m), wing area: 235.94 sq. ft (21.92 sq. m), max speed: 349 mph (547 kph), max weight: 6,700 lbs (3,035 kg), service ceiling: 32,750 ft (9,984 m), armament: one 0.50 cal and one 0.30 cal nose mounted machine guns.



Curtiss YP-37 technical data

Power plant: one 1,150 hp Allison V-1710-21, twelve cylinder, Vee, liquid-cooled engine with General Electric B-2 turbo-supercharger, wingspan: 37.33 ft (11.38 m), length: 33.83 ft (10.3 m), height: 10.5 ft (3.2 m), wing area: 235.94 sq. ft (21.92 sq. m), max speed: 331 mph (532 kph), max weight: 7,167 lbs (3,255 kg), service ceiling: 34,000 ft (10,366 m).

The development of the P-37 high-altitude interceptor was discontinued in favour of a less complex conversion of the P-36 for the Allison engine.

In July, Curtiss got USAAC permission to install in the P-36A s/n 38-10 one V-1710-19 engine, with single-stage, single-speed engine driven supercharger.

The project had the designation Model 75 P (XP-40).