a single rotating seat besides the pilot. In addition to the passenger cabin, it had a separate luggage compartment. A specialised air ambulance model of the Sycamore was developed during the early 1950s. In this configuration, up to two patients were carried inside the cabin on stretchers stacked one above the other; this was different to the usual arrangement of the era of using externally-mounted "pods" for carrying patients. To provide the extra width necessary in the cabin, detachable Perspex blisters were fitted on each side of the cabin. The stretcher racks could be folded into the sides of the cabin, providing room for up to three sitting casualties instead; an electrical supply outlet was available for connecting electric blankets. Next to the pilot was a swivelling seat for a medical attendant. The blades of the three-bladed main rotor were attached to the rotor head with lightweight interleaving steel plates while tie-rods carried the centrifugal tension loads. The blade levers were connected using ball joints to the arms of a control spider, the cone of which was actuated up and down by the collective pitch lever which changed the pitch of all the blades; an irreversible mechanism was used to prevent blade loads being transferred back to the control stick. The blades were supported when stationary or turning slowly by droop stops, which maintained a minimum clearance between the blade tips and the tailboom even in high winds; these stops were withdrawn above 100 rpm so that full freedom of movement for effective flight was possible. The Sycamore was powered by a single Alvis Leonides piston engine of . The engine was mounted below and to the rear of the main rotor on a flexible mounting to reduce vibrations transmitted to the helicopter structure. It was isolated in a fireproof enclosure which was fitted with fire detection and extinguishing equipment to meet certification requirements. Air was drawn through a forward-facing grill to cool the gearbox before passing through the engine cowling and leaving the fuselage. The engine power was controlled by the collective pitch lever. In order to maintain the rotor speed at its required setting fuel to the engine had to be automatically varied as the rotor pitch setting commanded by the pilot changed the load on the engine; fine adjustment of engine power was achieved by twisting the pitch lever. The Sycamore had a relatively high rotor speed