Swanson-Freeman SF-4

Flight, February 1924

THE SWANSON-FREEMAN "SS4" TWO-SEATER BIPLANE

   IN our issue for May 17, 1923, we published a description of the Swanson Model 3 Sport 'Plane built by S. Swanson, of Vermillion, South Dakota, U.S.A., arid this week we give a brief description of a development of this machine. The new model is known as the Swanson-Freeman "SS 4," and while in general appearance it is similar to the Sport 'Plane, actually it differs from the latter machine in that it is a larger and more powerful 'bus, being, in fact, a "full-sized" two-seater biplane, fitted with an 80 h.p. Le Rhone engine. The Sport 'Plane, it may be remembered, was fitted with a 28 h.p. 2-cyl. horizontally opposed Lawrence engine.
   The "SS 4" was first tested on November 11 last by Lieut. M. E. Callender, who took the machine off after a short run, climbed to 2,000 ft. and circled over Vermillion for fifteen minutes, during which time he executed various manoeuvres, such as loops, dives, Immelmans, etc. On landing, the pilot reported that it handled like a fighting 'plane, but with more uniform and accurate action, and answered the controls wonderfully. He further stated that with the dual control and side-by-side seating arrangement he thought that he could teach anyone to fly it in a few hours. It "stunted" well and was a good glider.
   With full load this machine takes off in 75 ft., and lands within 150 ft. With the engine running at 900 r.p.m. horizontal flight can be maintained without losing altitude.
   The fuselage is of the girder type, built up of spruce and ash, the latter material being employed for the longerons forward of the cockpit. A good streamline shape is obtained by means of basswood fairings. Pilot and passenger are seated side by side, and dual stick and rudder bar control is fitted. A magneto switch is placed on the top of each control stick, and the aileron control cables are carried inside the wings. The petrol tank, which contains sufficient fuel for three hours, is located between the engine and the cockpit. The oil tank has a capacity of 10 gals.
   The wings are of the single-bay type, of equal span, with ailerons to upper and lower planes. U.S.A. 27 wing section, set at an angle of 1 1/2° (upper) and 0° (lower), is employed. The planes are set at a dihedral angle of 4°, and given a normal stagger of 1 ft. 8 ins. Both upper and lower planes are in three sections, comprising a centre section and two outer sections, the latter being interchangeable top and bottom. The upper centre section is supported above the fuselage by four struts, and the lower centre section passes below, and is attached to the fuselage. Spars are of routed I-beam section, and the ribs are of built-up truss construction. The wing bracing is of clean design and ample strength, the single I interplane struts being built up of spruce laminations, whilst the single landing wires and double flying wires are 5/32 in. cable.
   The tail plane is adjustable from the cockpit, and has one-third of its camber on the lower surface and two-thirds on the upper surface. All control surfaces have a high aspect ratio and are negatively raked. The vertical fin is built integral with the fuselage, a small portion projecting below the fuselage. The control surfaces are provided with a special hinge construction which leaves no gap between the surfaces. All control horns are built into the surfaces, thus eliminating external bracing.
   The tail skid is of ash, sprung by the usual rubber shock absorber. The undercarriage is of the Vee type, with a divided axle hinged near the centre. Streamline-section ash is employed for the chassis struts, and the wheels are 26 in. by 3 in. sprung, with the conventional rubber absorber cord; the wheel track is 5 ft.
   A 9-cyl. air-cooled Le Rhone 80 h.p. rotary engine is fitted. This engine has been found to throttle down fairly well on this machine. All instruments, viz., switch, altimeter, air speed indicator, rev.-counter, and oil gauge, are mounted on an instrument-board in full view of both pilot and passenger.
   This machine is very easily assembled, for once the centre-sections are adjusted the wings are self-aligning.
   The principal characteristics of the Swanson "SS 4" are :-
   Span 28 ft.
   Chord 4 ft. 4 ins.
   Gap 4 ft. 10 ins.
   Stagger 1 ft. 8 ins.
   O.A. length 21 ft. 7 ins.
   Height 8 ft. 6 ins.
   Wing section U.S.A. 27.
   Angle of incidence (top) 1 1/2°.
   Angle of incidence (bottom) 0°
   Decalage 1 1/2°.
   Dihedral 4°.
   Area of main planes 225 sq.
   Area of tail plane 16 sq.
   Area of ailerons 28 sq.
   Area of elevators 11 sq. ft.
   Area of fin 5 sq. ft.
   Area of rudder 5 sq. ft.
   Weight, empty 980 lbs.
   Weight, loaded 1,550 lbs.
   Weight per horse-power 19 lbs.
   Weight per sq. ft. 6.8 lbs.
   Speed range 35-95 m.p.h.
   Climb per minute 800 ft.
   Gliding angle 1 in 10.
   Petrol capacity 20 gals.
   Oil capacity 10 gals.