The Command-Aire 3C3 and similar 4C3 and 5C3 are American three-seat open cockpit utility, training and touring biplanes developed by Command-Aire in the late 1920s and early 1930s.
Design and development
The Command-Aire did not at first appear to offer much of an advancement over the vast multitude of three seat biplanes built around the ubiquitous Curtiss OX-5 engine to similar designs, with similar dimensions and construction methods, many of which were already in production. Indeed, the OX-5 era was coming to an end. The vast quantities of war-surplus engines, which had swamped the market in the immediate post-war period, were running low. Only by the smaller details can it be distinguished from its brethren. The basic design was by Morton Cronk, and although it had excellent high altitude capabilities, it was slow. This setback nearly foundered the company before its first aircraft entered production.
The design's proportions were good, but Cronk's departure left the company without an engineer. It happened to be that Albert Vollmecke, a Heinkel engineer was in the US attempting to find a customer to build Heinkel HD 40 mailplanes under licence for the US market. Seeing that there was little prospect of any sales in the US, he decided to hire on with an American company, and Command-Aire lucked out. His first task was to rework the design to provide documentation for the new approval process. While there was only one major visible external difference, he undertook an extensive redesign based on his experience in the much more scientifically-grounded German aviation industry, and to bring the design into line with CAA (now FAA) certification requirements, which involved a lot of submissions, and alterations, and resubmissions before they signed off on it. Many parts had to be redesigned when it was easier to redo the design, than to use the existing design to calculate the necessary strength margins. The most obvious change was a switch from four small conventional ailerons at the tips to two slotted nearly full-span ailerons on the lower wing. This improved low speed control dramatically, allowing lateral control even after the aircraft had stalled - a novelty among American aircraft at the time, and a recurring advertising theme. The second change was the incorporation of a Phylax fire suppression system capable of putting almost any fire out in flight. The third novelty was the use of a rotisserie type fuselage jig, that ensured accuracy and consistency between the airframes they built, reducing the chance of building an airplane that couldn't be rigged to fly right. Although Command-Aire's advertising claims that Vollmecke invented this, he claimed he merely brought the idea from Europe.
Airframe details
The fuselage was built in a rotating jig that ensured accuracy from welded chromium-molybdenum alloy steel tubes, faired with wooden battens. The top of the fuselage was covered in large metal panels that could be readily opened to provide access, and a compartment for luggage was provided between the cockpits large enough for a suitcase.
The slightly staggered wings were built around solid spruce spars, with spruce and plywood warren truss type ribs. The wings were braced with cables.
The ailerons and the entire empennage were also built from chromium-molybdenum alloy steel tubing, and all controls were actuated through pushrods and bellcranks, with no cables or pulleys used. The ailerons on the prototype were conventional, however on production variants, they extended across nearly the full span on the lower wings only, and had a slot that allowed air to flow over the aileron at low airspeeds and high angles of attack, which helped ensure lateral control even after the wings had stalled. These were not Frise-type ailerons though, but conventional ailerons with a slot at the hinge line.
The undercarriage was a split axle type, braced to a steel tube four point pyramid that extended from the belly of the aircraft, with suspension provided with bungee cords which were protected by leather boots. Both cabane and interplane struts took the form of an N and were steel tubing as well. The 3C3 can be distinguished from later types by having an additional strut providing lateral bracing from the forward strut anchor point on the wing, to the lower longeron at the firewall, triangulating the structure. The 4C3 and later types dispensed with this extra strut, and coincided with an extensive redesign that otherwise had few external differences.