In 1933 Kellett announced a new model, the K-4. The most noticeable change was the absence of the familiar turned-up wing tips. A beautiful wing, tapered in plan and thickness had a single dihedral angle which put the tip at exactly the same place as the top of the turned-up tip. The landing gear, too, was somewhat simplified. The rotor pylon used the same large diameter forward member with only one aft member. But retaining the side braces as in the K-3. The appearance of the horizontal tail caused some confusion. When the K-3 was built, the horizontal tail had been redesigned to a rounded elevator. The K-4 showed the old K-2 square elevators. Actually the K-2, serial #3, was modified to make the K-4. A later Continental R-670 giving 210hp was installed with a ground-adjustable Hamilton Standard aluminum propeller.
The fuselage, of course, coming from the K-2 serial #3, was gas welded steel tubes. The wing was wood with a plywood cover. The tail was wood with a fabric covering.
No price was announced. Only one was built. There is no record of a CAA approved Type Certificate being obtained. The autogiro was reported to have been sold to the Steel Pier in Atlantic City, New Jersey.
G.Townson "Autogiro. The Story of the Windmill Plane", 1985
Technical data for Kellett K-4
Gross weight: 1089kg, empty weight: 735kg, useful load: 354kg, top speed: 183km/h, cruise speed: 151km/h, rate of climb: 286m/min, absolute ceiling: 4250m, service ceiling: 3810m