ENGÎNE CONTINENTAL 210HP
The one and only Kellett K-4. No Department of Commerce certificate. (Kellett Photo)
This head-on iuew shows the beautiful tapered wing. This Series Continental, originally 165 hp had been upgraded to 21U hp by this time. The lip of this wing was at the same point as the turned-tip tip on K2-K3 models. It was said thai this wing gave the same stability of the turned-up tips. (Smithsonian Photo)
Kellett KD-1 (Army Air Corps YG-1)
About 1935 Keilett announced a new model, the KD-1. The "D" denoted Direct Control. This meant that the control of the autogiro did not depend on airspeed for effectiveness.
As long as the rotor turned, control was adequate—even at zero airspeed. Control responses came from tilting the entire rotor head with the control stick in the direction that control was desired. This was similar to the Pitcairn PA-22, PA-35, PA-36, PA-34, PA-39 and XOP-2. Actually, Wallace Kellett and Chief Engineer Dick Prewitt went to Europe to see Cierva's C-30 Autogiro. The KD-1 was made more nearly a copy to that autogiro.
Several departures from earlier Kellett machines were noticeable. Seating was now tandem in open cockpits. The landing gear was nearly directly under the engine. The engine selected was a locally manufactured seven-cylinder radial air cooled Jacobs L4MA-7, developing 225 hp. The rear of the engine was especially modified to drive the rotor prior to takeoff using the engine starter pad.
Rotor blades were different from earlier Kellett blades. The chord was reduced to 12 inches from K-3, K-4's 23 inches. The airfoil section was a Goettingen 606. All other Kellett rotor airfoils had been nearly symmetrical while this one had nearly a flat underside. The upper curve was a high lift airfoil. Attachment of the ribs to the steel tube spar departed from the pinned-on method previously used in favor of the spot welded attachment used by Pitcairn. The ribs were routed from specially made 3-ply wood using vertical grain mahogany over horizontal grain birch. The mahogany layers were 1/16" thick and the birch 1/8". The trailing edge was spruce, the leading edge was ash. The entire blade was covered with 1/32" mahogany 3-ply, then covered with balloon cloth and doped to a smooth finish. The blades were balanced chord-wise with a brass bar right at the nose and balanced spanwise by filling any of three boxes near the blade tip with lead shot as required.
The number of blades was reduced to three. The droop cables were eliminated by installing
Kcllett YG-1 Autogiro assembly line where she eutogiro fuselages are shown.
Kellett blade shop showing blades in jigs. The right fop side of blade frame next to right bottom side of blade being covered with 1/32" plywood. When both sides were covered with plywood they were then covered with cotton fabric and doped These arc KD-l/YG-1 blade*. (Kcllett Photo)
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