The Spartan C3 is an American three-seat open-cockpit utility biplane from the late 1920s.
Design
The C3s fuselage and wing struts were built up from welded chromium-molybdenum alloy steel tubes, faired with wood battens. It had two open cockpits each protected from the wind with generously sized shatterproof-glass windscreens, and which could accommodated three people, with two in the front cockpit.
The wings on the prototype were built around spruce and plywood box beam spars that were replaced with solid spruce spars routed into I-beams on production examples. Ribs were built up from spruce and plywood, while on the C3-225, duraluminium sheet covered the leading edge of the wing to improve the aerodynamic form. The wings were braced with streamlined section steel wire. Both upper and lower wings used a Clark Y airfoil section, and had the same span and wing chord, with rounded wing tips. The wing was rigged without stagger, or washout and at a 0° angle of incidence. The upper wing was flat across, with no dihedral, while the lower wing had 2° of dihedral. Interconnected unbalanced ailerons were fitted to both wings inset from the wingtips. The rudder and elevators were constructed similarly to the wings.
Other than the metal panels around the nose, most of the airframe was covered in fabric that had been doped to tighten and seal it.
The fuel tank was fitted into the upper wing center section in such a way that it could be removed without removing the wings. On the C3-225, an additional removable fuel tank was added in the fuselage, and the wing tank acted as a header tank.
The prototype had a conventional undercarriage similar to those used on most World War One aircraft, with a pair of vees braced from the lower longerons, connected with a spreader bar and suspension provided by bungee cords. This was replaced with a split-axle undercarriage on the C3-1 and C3-2, which had the legs braced to the opposite lower longerons. From the C3-3 onwards, each undercarriage leg was triangulated with two struts braced to a central keel in the bottom of the fuselage, and one oleo strut on each side to the upper longeron, providing a greater range of movement and reducing camber changes. Early examples had a tail skid, while later ones had a tailwheel fitted.
The redesign of the undercarriage, and numerous other details changes coincided with Brown's visit to Europe to arrange for the use of the Siemens-Halske engine and had not been approved by him. He considered them unnecessary, and the fight over these changes led to his departure from the company.
The keel used to brace the undercarriage on the C3-3 and later models coincided with a deepening of the fuselage, with additional fairing strips added, including to the underside of the fuselage. A headrest would also be added for the rear cockpit on later models.
Development
The privately developed prototype to the C3 series first flew on 25 October 1926, originally powered with a stationary radial engine modified in the US from a Le Rhône 9J rotary engine called a Super LeRhône. The use of various engines was anticipated from the start, although the planned Hispano-Wright E-2 water-cooled V-8 engine was never used and only radial-engine powered versions were flown.
Despite the low-power engine, the type showed sufficient promise to warrant the formation of the Mid-Continent Aircraft Company in Tulsa, Oklahoma, to produce it, which would in turn be bought out and reorganized by prominent oilman William Skelly as the Spartan Aircraft Company in 1928.
The search for a suitable powerplant led to a number of different engines being installed. When production started, the Ryan-Siemens radial engine was chosen, but production of that engine stalled due to the worsening economic situation in Germany, where it was manufactured. Even before the supply problems had manifested themselves, the next engine chosen, the Fairchild Caminez, had already been tried out, and was found to be extremely unreliable, so only one aircraft was fitted with it. The search for a reliable replacement for the Siemens led to the use of the more successful Walter NZ 120.