Seversky AP-4
1939
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Seversky AP-4

Preceded by the AP-7, the AP-4 possessed a superficial resemblance to the AP-2 and was intended as a high-altitude interceptor. The first Seversky fighter to feature flush-riveted skinning, the AP-4 was powered by a 1,200hp Pratt & Whitney R-1830-SC2G equipped with a belly-mounted turbo-supercharger. As a company- funded development, the AP-4 was intended to participate in a USAAC competition scheduled for 25 January 1939 and was expected to demonstrate the superior medium- and high-altitude performance obtainable with a turbo-supercharged R-1830. The same engine, fitted with a mechanical supercharger, had been specified by the USAAC for the XP-41. The AP-4 was evaluated at Wright Field during February- March 1939, demonstrating exceptional climb and altitude performance. Early 1939, it was fitted with a close-fitting, high-inlet-velocity engine cowling matched with an oversize propeller spinner as a continuation of a drag reduction programme supervised by the NACA and initiated earlier with the AP-1. The AP-4 was subsequently fitted with a modified engine cowling, without the spinner, but, on 22 March 1939, caught fire in the air, the pilot bailing out. On 12 May 1939, a contract was awarded for 13 service evaluation models under the designation YP-43.

Seversky AP-4


Specification 
 WEIGHTS
    Take-off weight3075 kg6779 lb
    Empty weight2462 kg5428 lb
 DIMENSIONS
    Wingspan10.97 m36 ft 0 in
    Length8.23 m27 ft 0 in
    Height3.81 m13 ft 6 in
    Wing area20.44 m2220.01 sq ft
 PERFORMANCE
    Max. speed534 km/h332 mph
    Range1255 km780 miles

Comments
Klaatu83, 21.02.2017

The AP-4 was powered by a Pratt & Whitney R-1830 engine with a turbo-supercharger mounted in the fuselage behind the pilot in order to give the fighter good performance at higher altitudes, which was an attribute sadly lacking in the Bell P-39 and Curtiss P-40. This aircraft became the prototype for the Republic P-43 Lancer and set the pattern for the larger and more powerful Republic P-47 Thunderbolt. It has been alleged that the Army Air Force only ordered the P-43 in order to keep Republic's production line operating until the fighter they really wanted, the far-superior P-47 Thunderbolt, was ready to go into production.

Don Friedman, 29.07.2010

I have another picture of the AP-4 and on the back it says first flight by Frank Sinclair December 22, 1938

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