Seversky P-35

The Seversky P-35 was a US fighter aircraft. The first aircraft were transferred to the US Army Air Corps in 1937.

The aircraft was the first single-seater ordered by the Air Corps which featured a fully enclosed cockpit and retractable landing gear.

A single P-35 was modified and redesignated as the Seversky XP-41.

Early Seversky Aircraft, P-35 and P-35A

The first Seversky design was the "SEV-3" amphibian, The SEV-3 was an all-metal, low wing monoplane that was powered by Wright J-6 air-cooled radial engine, offering 420 horsepower (310 kW), and had an interesting arrangement of retractable floats that allowed it to land on water or a runway. The rear edges of all flight surfaces were in the form of elliptical curves, a feature that would be retained in its descendants.

The "3" in the SEV-3 designation indicated that it was a three-seat aircraft. It was intended for commercial use. It was fast for its time, and in October 1933, De Seversky set an international speed record of 290 km/h (180 mi/h) with it.

In 1934, the SEV-3 design was modified into a trainer configuration, designated the "SEV-3XAR". The float system was replaced by fixed landing gear with spats, the canopy was redesigned, and the engine was changed to a Wright R-975 radial with 950 horsepower (710 kW). The SEV-3XAR was entered in a USAAC competition for a flight trainer, and the Army ordered thirty examples of a derivative, the "BT-8 (Basic Trainer 8)".

Unfortunately, USAAC regulations required that the engine of a trainer must be limited to 400 horsepower (300 kW), and the BT-8 was powered by a Pratt & Whitney R-985-11 radial rated at 400 horsepower (300 kW). As a result, the aircraft was seriously underpowered and dangerous to inexperienced pilots, and was quickly replaced by the North American BT-9, which evolved into the famous T-6 Texan trainer.

Although the BT-8 was a loser, Kartveli had also designed a fighter derivative of the SEV-3, initially designated "SEV-2M" but quickly redesignated "SEV-2XP", where the "2" indicated a two-seat aircraft.

The SEV-2XP used a Wright R-1670 14-cylinder air-cooled radial engine with 735 horsepower (550 kW) for take-off. It had fixed landing gear with spats, and was armed with a 7.62 mm (0.30 in) and a 12.7 mm (0.50 in) Browning machine gun firing through the prop, plus a 7.62 mm machine gun on a rearward-facing hand-held mount for use by the back-seater.

In May 1935, the USAAC announced a competition for a new single-seat fighter. De Seversky believed the SEV-2XP could win, even though it was a two-seat fighter and entered in the competition. However, the SEV-2XP was damaged in mid-June while flying to Wright Field in Ohio for the fly-off.

The SEV-2XP went back to the shop. Second thoughts arose about the aircraft's configuration, and so it was reworked into a single-seat fighter designated the "SEV-1XP". Along with the new single-seat cockpit and the elimination of the flexible gun, the fixed landing gear was changed to gear that retracted into underwing fairings. The Wright R-1670 had proven not powerful enough, and so, after experiments with different engine fits, the Seversky Company installed a Pratt & Whitney R-1830-9 Twin Wasp radial, offering 850 horsepower (630 kW) for takeoff.

The Seversky Company was able to make these changes because the USAAC postponed the fighter competition, with the fly-off rescheduled to March 1936. The SEV-1XP was entered in the competition, and ended up as a finalist against the Curtiss Model 75 Hawk.

The SEV-1XP was selected as the winner of the competition on 16 June 1936, and a production order for 77 of the aircraft, with the USAAC designation "P-35", was confirmed in early 1937. However, as tensions rose in Europe, the USAAC also ordered 210 Hawks under the designation "P-36".

The actual P-35, which had the company designation "AP-1 (Army Pursuit 1)", entered service in 1937, with the last of the batch delivered in August 1938. 76 P-35s were actually built instead of the 77 ordered, with the 77th aircraft finished as an experimental variant with a supercharged engine and designated "XP-41".

The production P-35 differed from the SEV-1XP by featuring partial mainwheel fairings instead of full mainwheel fairings, seven degrees of dihedral to the outer wing panels, and a more aerodynamic front canopy.

Seversky P-35

spec	metric	imperial
wingspan	11 m	36 ft
length	7.67 m	25 ft 2 in
height	2.77 m	9 ft 1 in
empty weight	1,960 kg	4,315 lb
normal loaded weight	2,540 kg	5,600 lb
max speed at altitude	454 km/h	282 mi/h / 245 kn
service ceiling	9,325 m	30,600 feet
range	1,850 km	1,150 mi / 1,000 nmi

The P-35's performance was poor even by contemporary standards, and although USAAC fliers appreciated the P-35's ruggedness, the aircraft was already obsolescent by the time deliveries were finished.

Kartveli continued to refine the P-35 design while the aircraft was being produced.

Incidentally, Seversky also built a refinement of the original two-seat fighter concept embodied by the SEV-2XP, resulting in a fighter-bomber designated the "2PA", which was available with retractable landing gear or floats. The USSR bought one with each landing gear option, plus a manufacturing license, but never put the type into production.

The Japanese Imperial Navy actually bought 20 2PAs, apparently through a subterfuge to conceal the ultimate customer, but found them disappointing. Two of them were passed on the Asahi Shimbun newspaper as hacks. Sweden ordered 52 2PAs as dive-bombers, but only two were delivered before the US embargoed exports of fighters to Sweden in October 1940, and the other 50 ended up in USAAC hands as the "AT-12 Guardian".

Seversky Company also sold Sweden a refinement of the P-35 designated the "EP-1 (Export Pursuit 1)". The EP-1 was powered by a P&W R-1830-S1C1 Twin Wasp engine with 1,000 horsepower (750 kW), improving its performance by over 40 km/h (25 mi/h). The Swedes ordered a total of 120 EP-1s, with initial order placed in mid-1939. 60 of these aircraft were delivered to Sweden. They were armed with two 7.9 mm guns in the nose and one 13.2 mm gun in each wing, for a total of four guns.

After the embargo against Sweden, the other 60 were taken over by the USAAC as the "P-35A". 48 were sent to the Philippines, where they fought in the futile defense of the islands in December 1941 and January 1942, but were hopelessly outclassed by Japanese fighters. The other P-35As were used as USAAC trainers.

Designation Series: XP-33 - XP-34 - P-35 - P-36 - XP-37 - P-38

• USAF Museum: P-35 (http://www.wpafb.af.mil/museum/research/p35.htm)

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