Flight, November 1933

FAST AMERICAN AMPHIBIANS

   THE Seversky Aircraft Corporation, of 570, Lexington Avenue, New York, is producing three very interesting amphibians, all characterised by an extremely high performance. The basic layout of all three aircraft is similar, so that the following description of the SEV-3 ("Sportsman"), the first of the series to be built, will give an idea of their design.
   The SEV-3 carries three passengers in two tandem cockpits. It is a typical American "high-speed" design, i.e., monocoque fuselage, low cantilever wing and radial engine, fitted with a low drag N.A.C.A.-type cowling.
   The wings are of the "cellular" or "multi-box" type. Their smooth outer skin is stiffened internally on the top side by corrugated sheets, with the corrugations running the length of the span. On the bottom the skin is stiffened by closed-channel type longitudinals. The fuselage, in the original model, has seating accommodation for three, but the interior may be altered to carry five. The main bulkhead is attached to corresponding webs of each "box" section of the wing, five points of attachment being provided at the junction of wing and fuselage. The fin is an integral part of the fuselage structure, and the tail plane is attached at four points, thus ensuring the distribution of stresses over a large area of skin. Welded-steel tubes are used for the engine mounting, with rubber vibration absorbers at the points of attachment to the fuselage.
   An air brake (known in America as a "descelerator") is carried under the trailing edge of the wing and stretches from aileron to aileron. It is stated that this brake halves the landing run and decreases the landing speed by 15 m.p.h.
   Perhaps the most interesting feature of the aircraft is the "universal" landing gear. Twin floats with their wheels are attached to the fuselage by cantilever struts, a pivoting movement being permitted at the points of attachment on the floats. This movement is controlled by small "V" struts located behind the main cantilever struts. As the floats are buttressed with interior keels, they can, in an emergency, be used as landing skids, when landings can be made on ice, snow and rough, marshy or sandy ground. The wheels, which are fitted with hydraulic shock absorbers, protrude through "wells” in the floats. As the result of special attention to the design of the float bottoms these "wells" do not have to be closed to aid take-off. For operation from land the small "V" struts are released, allowing an upward movement of the rear of the floats. Thus an ordinary three-point landing can be made on the two main wheels and a conventional tail wheel. On water the "U" struts are locked and the wheels retracted so that the machine possesses all the characteristics of an ordinary twin-float seaplane. In the event of a forced landing in a confined space the wheels could absorb the initial shock, and then, on the operation of a relief valve, they would retract into the floats, the under portions of which would act as effective brakes. Sudden application of brakes in an emergency is permissible owing to the extension of the floats in front of the machine. A normal retractable land undercarriage can be substituted for the amphibian gear in less than an hour. The wheels, when in the "up" position are housed partly inside the wings and partly in fairings.
   The cockpits of the SEV-3 type, which are fitted with dual controls using ball bearings, have sliding roofs and adjustable seats. The pilot has an excellent view for taking off, landing and taxying when his seat is in the uppermost position. An anchor is carried in the nose of one of the floats, and can be released by remote control by the pilot from the cockpit.
   As a landplane, when fitted with the 420-h.p. Wright "Whirlwind" engine, the top speed is given as 235. When the supercharged 700-h.p. Wright "Cyclone" is used, the speed, as an amphibian is 245 m.p.h., and 290 m.p.h. as a landplane. The flying radius is 800 miles.
   The two other models in the Seversky range are known as the SEV-5 ''Executive'' and the SEV-7 ''Transport." The former is a five-seater, while the latter has a cabin accommodating eight passengers and two pilots. This is in two compartments, one of which is quickly convertible into a "hold" for freight.
   On October 9, 1933, a Seversky aircraft established a world's record for amphibians with a speed of 180.3 m.p.h.