The Comet 7-cylinder radials were a family of air-cooled radial engines, designed and built by the Comet Engine Corporation at Madison, Wisconsin from around 1927.
Comet designed the 7-cylinder radial series to take advantage of the boom in private aviation in the late 1920s; intending to replace the large number of relatively unreliable wartime surplus engines that flooded the market in the early 1920s.
First produced by the Aircraft Engine Corporation of Oakland, California, new interests acquired the California company and the Comet Engine Corporation was formed under the sponsorship of Air Investors Inc., the Crocker First Company of San Francisco and the Gisholt Machine Company.
Production transferred to workshops adjacent to the Gisholt Machine Company in Madison, which acted as production supervisor.
A Comet 7-E on display at the Hiller Aviation Museum, San Carlos, California.
The Comet radial was fairly standard with steel finned cylinders, cast light alloy cylinder heads and two valves per head. The valves are operated by a single rocker arms and push-rods, to the rear of the cylinder, which are in turn operated positively by inner and outer cam tracks operating rollers on the pushrod.
Oil pumps and magnetos are driven by the camshaft drives as well as the Heywood air starter and tachometer.
The two-piece crankshaft, with counter-weights, is carefully forged from heat-treated chrome-vanadium alloy steel and drilled for lightness and lubricating oil flow. Master and slave connecting rods are forged and machined from the same material as the crank-shaft. The rear of the crankshaft carries an induction rotor to ensure even mixture distribution to the cylinders from the Stromberg carburettor.
The two-piece crankcase is split in the plane of the cylinder centres, with the forward half supporting the fwd crank /prop-shaft bearing and the rear half housing the rear bearing, induction rotor, cam drives and accessories.
^Horsefall, J.E., ed. (September 1929). "The new Comet radial engine". Aero Digest. Vol. 15, no. 3. New York City: Aeronautical Digest Publishing Corp. p. 158.
