Flight, March 1935

AN EFFICIENT CARGO-CARRIER
The American Fairchild C-31: Useful Load of 5,678 lb. Carried 750 miles at 140 m.p.h.: Single 750 h.p. "Cyclone"

   AERODYNAMICALLY and structurally, there is little in the Fairchild C-31 freight-carrying monoplane that is startling, except perhaps the undercarriage, the wheels of which retract into the bottom of the fuselage; but what can be done by the judicious application to a well-designed aeroplane of such devices as variable-pitch airscrews, flaps and retractable undercarriage is exemplified in the performance figures which are given below. A sample machine has been supplied to the U.S. Army Air Corps.
   In order to provide maximum cargo space, a fuselage of approximately square section was adopted. This is made of welded chrome molybdenum steel tubes, with tie-rod bracing in most of the upper, lower and cross panels. Gusset plates, tie-rod lugs, and fittings are welded to the fuselage structure, which is covered with fabric.
   Embodied in the "hold" is a cargo chute which permits delivery by parachute of supplies in containers, and a large door (5ft. 10in. by 4ft. 11in.), the threshold of which, when the machine is on the ground, registers with the tail of a lorry. There is almost 775 cu. ft. of unobstructed cargo space, special fastenings being provided on the floor and walls for lashing every kind of load. For military use, six stretchers and a number of chairs for wounded may be carried, or fifteen chairs may be installed, or folding benches built into the wall may be lowered to accommodate fourteen soldiers.
   The fin is metal framed and bolted to the fuselage, and the rudder and elevators are of aluminium alloy with metal nose pieces and fabric covering. Trim is effected by adjustable trailing-edge tabs.
   Except for steel tube and wire bracing and fabric covering the wings are of duralumin. They embody solid web-type spars with extruded flanges. The leading edge, of sheet metal, reinforced by longitudinal stringers and nose ribs, is riveted to the front spar flanges, top and bottom.
   The duralumin-framed Frise ailerons operate differentially, 40 deg. "up" and 15 deg. "down." Zap tyre flaps are fitted. They are supported, with the ailerons, on the rear spar, and may be operated manually or by an electric motor. The lift struts, which run from the wing to a small wing "stub," are of streamline aluminium alloy tubing with strip alloy steel attachment fittings bolted into place.
   Another interesting feature of the U.S. Army version is the "dishpan" within the N.A.C.A. type cowling of the 750 h.p. Wright "Cyclone" engine, which, incidentally, is of the new R-1820-25 type, and which drives a Hamilton three-bladed controllable pitch airscrew. Data are as follows:-
   Dimensions. - Span, 75 ft, (22,86 m); length, 55 ft. 5 in. (16,9 m); height. 15 ft. 10 in. (4,8 m).
   Weights. - Weight empty, 7,322 lb. (3321,08 Kg); disposable load, 5,678 lb. (2575.58 Kg); gross weight, 13,000 lb. (5897 Kg.)
   Performance. - Maximum speed, 107 m.p.h. (269 Km/hr), cruising speed, 140 m.p.h. (225 Km/hr); landing speed (full load) 52 m.p.h. (83.7 Km/hr); cruising range (full load) 750 miles (1207 Km).