Rotorcraft Ltd is a marketing company jointly owned by the Mitchell Engineering Group and Servotec Ltd, the latter being the ARB design-approved company which, under the leadership of Mr J. S. Shapiro, is developing this twinengined light helicopter. The aim is to sell a two-seater with twin-engined safety which will have a practical range of 200-250 miles at 100 m.p.h. A first prototype with 65 h.p. Walter Mikron engines flew in March 1962 and a more elaborate cabin machine with 105 h.p. Walter Minor engines in November.

These aircraft were intended to prove the aerodynamics and mechanics of the co-axial contra-rotating rotor system. This type of rotor has the advantages that all the engine power goes into the lifting system and that the weight and cost of a tail-rotor drive are eliminated. It is claimed that economics extend from reduced first cost to lower maintenance costs, while the simplicity means a safer fail-safe construction and good flying and handling characteristics. The use of two engines geared individually to the contra-rotating drive ensures independent operation in case of failure and level flight can be maintained on one.

The two-bladed rotors are semi-rigid and are suspended on see-saw hinges, pitch being changed by rotation about a torsion hinge. To obtain yaw control the collective pitch of the two rotors is altered in the opposite sense, thereby unbalancing the torque and causing the aircraft to turn by reaction.

In the prototype Grasshoppers the cabin was aft and the engines forward of the rotor, under a bonnet. The definitive model has a more conventional glazed cabin, which can carry up to four, with the two engines mounted horizontally aft and coupled to the rotor by a right-angled bevel drive. Rotor blades are of wood and the fuselage is mainly stressed skin, apart from the framework of the glazed areas. Butterfly tail surfaces in the downwash are used for yaw and pitch stability and trim. The landing gear consists of fixed skids, with energy absorption in the supporting legs, and retractable ground handling castor wheels. The 100 h.p. Rolls-Royce Continental O-200A, the 125 h.p. O-240-A, or the 125 h.p. Franklin 4A-235 are offered.