Back Kellett K-2
1932

Kellett K-2

Undaunted, Kellett went on to design a machine similar to the Pitcairn and Cierva style, which had been successful. The differences were that Kellet's was a side-by-side seater, had larger blade area and a much simpler landing gear.

The first flight was on April 24, 1931 by Jim Ray, Pitcairn's chief test pilot. Approval by the Department of Commerce (1931's FAA) was obtained under a "group 2" type certificate #2431 on May 27, 1931, just about a month after the first flight. Joe Juptner's Volume 5, shows K-2 having ATC 437. The Chief of the Department of Commerce, Gilbert Budwig, flew the K-2 and complained of lack of aileron control at low speeds and slow rate of climb. Flight test notes fail to show any corrective work done between flights. Approval was granted on the promise that the aileron control would be improved.

The Autogiro was flown to Washington for the evaluation by the Department of Commerce. A note on the test report says it took 3.5 hours to fly from Philadelphia to Washington against a 32 kilometers per hour wind. The return trip required about two hours. The distance is about 210 kilometers.

The fuselage was gas welded of steel tubing using square tubes for longerons. It was lightly faired on the sides with deep fairing on the top with no fairing on the bottom.

A much simpler landing gear than the Pitcairn models was designed. A long-travel oleo shock strut was attached to the bottom of the wing at the front spar. The lower end was attached to the axle. A drag brace took the taxiing and aft loads. These were attached to a cabin assembly under the fuselage. The axle and drag braces faired into a streamline shape with balsa wood on the aft side which was wrapped with airplane fabric and doped.

The entire tail assembly was made from wood resulting in a very light structure. Spars were solid spruce, the ribs were light plywood web members with spruce cap strips and a few vertical members. The trailing edged of the rudder and elevators were round aluminum tubes which were pressed into a streamlined shape.

Wing beams were box spars with spruce longitudinal and vertical members. The web members were three-ply mahogany with a 45 degree face grain. Ash blocks were built into the spars at points of heavy loads. Most ribs were made of square spruce cap strips and diagonals; some were made with spruce cap strips and mahogany plywood members. The airfoil, a RAF 30 was symmetrical in shape.

The wings were braced to the fuselage with aluminum streamlined struts. The front spars carried the landing gear loads from the wing to the fuselage top longerons.

The entire autogiro including the rotor blades was fabric covered. The rotor system was similar to those used on the Pitcairn Autogiros with some exceptions. Most noticeable was the wider chord rotor blade; 0.58m instead of 0.45m used on the Pitcairn blades of similar gross weight autogiros, keeping the same thickness ratio for the rotor airfoil. The steel tube spar was made from 5.4cm diameter instead of the 4.4cm on the Pitcairn light autogiros. This had a secondary importance in the method of assembly of the rib to the spar. Instead of employing the delicate process of spot welding the rib collars to the spar, Kellett pinned the collars using a 3mm clevis pin through the spar kept in place with a cotter pin. The rest of the blade assembly was the same as the Pitcairn blade.

The same blade dampers were installed, the stainless steel trailing edge had the same slip joints, the same fittings were used to attach the droop cables which held the blades while they were not turning. The leading edge back to the spar was covered with preformed plywood and the entire blade covered with aircraft fabric. The rotor hub, universal blocks (which allowed flapping and lead and lag) and blade root end fittings were the same ones used on the light Pitcairn Autogiros; (PAA-l and PA-18 series). These hubs and parts were supplied by Autogiros Specialties Company, a mechanical engineering firm which supplied all the early autogiro hubs and parts to Pitcairn, Kellett and Buhl.

The rotor pylon was a pioneer effort by Kellett which they improved and refined all through their models. It was basically a single large round tube with auxiliary light weight struts going aft to the rear of the cockpit. After a few early flights with the K-2, 6mm diameter, streamlined rods had to be added to brace the pylon to the upper longerons.

The powerplant was a Continental A-70 seven cylinder radial aircooled engine giving 165hp at 2000 rpm. The weight of the engine was reported as "between 181 and 188kg."

Thrust was provided by a 2.89m diameter propeller, either fixed-pitched metal or ground adjustable metal.

In reviewing the flight test reports of early K-2 Autogiros, problems of rotor roughness are mentioned. One complaint was referred to as "wind wobbles" - a kind of lateral vibration caused by improper rotor damper settings or improperly adjusted interblade cables.

Overheating of the Continental A-70 is mentioned during the early flights but seems to be corrected by reworking the cowling around the cylinders. One other thing that seemed to give problems was the rotor run-up drive system. Broken ring gears and stripped pinion teeth are often mentioned. Because all these parts are common with the Pitcairn machines, no doubt Pitcairn had the same problems. But references, if any, were not available in research.

Balancing the Autogiro required much experimenting. The storage tank for the air starter was mounted in the tail to improve longitudinal balance. A lead weight was added inside the left-hand wing tip to improve the lateral balance. The pylon needed realigning to achieve proper rotor axis angle fore and aft and laterally. Because the blades have a fixed angle to the flap and lead lag hinges (after rigging), the lateral and longitudinal adjustment of the pylon helps offset the unequal lift on the upwind side of the rotor and the downwind side. This effect was referred to as "mechanical feathering." The rotor blade on the right side (advancing) climbs, and the one on the left side (retreating) descends. This equalized the lift on right and left.

G.Townson "Autogiro. The Story of the Windmill Plane", 1985

Kellett K-2

Technical data for Kellett K-2

Engine: 1 x Continental R-670 pistone engine, rated at 210hp, gross weight: 1027kg, empty weight: 705kg, useful load: 287kg, max speed: 161km/h, cruise speed: 129km/h, min speed: 39km/h, landing speed: 0km/h

Kellett K-2

Kellett K-2

Kellett K-2

Comments 
David Surace, e-mail, 01.05.2017

I am interested in any print for the Kellett K2

Penny Woods, e-mail, 04.04.2009

I have a negative and print of what I believe is this aircraft, taken by my grandfather. I would like information on what happened to this particular aircraft. Who would you suggest I contact for historical information? The numbers visible on the underside of the wing end in 766 and it is Kellett Autogiro is clearly marked on the tail of the aircraft. Thanks for any help that you can provide. Penny Woods

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