The SEV-2XP with an 800hp Wright XR-1670 engine, was damaged enroute to Wright Field and hurriedly converted into the single-place SEV-1XP with an 850hp Wright R-1820-G4 Cyclone engine
First flying as the NX18Y c/n 2 still, in August 1935 piloted by de Seversky, the SEV-1XP initially retained the R-1670 engine. By now featuring a semi-retractable undercarriage, the prototype was reengined with an ungeared nine-cylinder Wright R-1820 Cyclone. This engine failed to produce its rated power, however, the predicted 483km/h maximum speed proving unobtainable in consequence.
The USAAC Materiel Division’s decision to defer fighter choice pending further evaluation to be held in March 1936 enabled the SEV-1XP to be re-engined once more, this time with an 850hp 14-cylinder Pratt & Whitney R-1830-9 Twin Wasp. This was succeeded, in turn, by a geared R-1820-G5 offering 950hp for take-off, but the Twin Wasp was subsequently re-installed.
With this last engine and an armament of one 7.62mm and one 12.7mm gun, the SEV-1XP was selected on 16 June 1936, approval being given for production of 77 fighters against a contract confirmed early in 1937, with the designation P-35.
Repowered with a P&W R-1830B as the SEV-S1, and with a new tail and cowling, NX18Y raced at the 1935 Nationals, piloted by Frank Sinclair) to fourth place.
It was scrapped in 1937.
Sev-1XP
Engine: 850hp Wright R-1820-G4 Cyclone
Wingspan: 10.97 m / 36 ft 0 in
Length: 7.59 m / 25 ft 11 in
Height: 2.69 m / 9 ft 10 in
Wing area: 20.44 sq.m / 220.01 sq ft
Max take-off weight: 2274 kg / 5013 lb
Empty weight: 1681 kg / 3706 lb
Max. speed: 465 km/h / 289 mph
Range: 1918 km / 1192 miles
Seats: 1
Sev-1XP
Engine: P&W R-1830B
All Aero 