General Aircraft Hamilcar - Variants

Variants

Several variants on the Hamilcar Mark I were planned, although only one was actually produced. The Hamilcar Mark X, also known as the GAL. 58, was designed to specification X 4/44 in an attempt to allow Hamilcars to be used in the tropical climate of the Pacific, where high temperatures and the high altitudes of many airfields reduced the efficiency of piston-engined aircraft. This meant that Halifax bombers could not tow Hamilcars without a drastically reduced fuel load, which in turn narrowed the range of the Hamilcar. Two initial solutions were proposed to correct this problem; the first was to convert a Hamilcar into a rocket-assisted take off (RATO) aircraft. Two cylindrical steel cylinders filled with twenty-four three-inch rockets were attached to either side of the glider to provide it with 20,000 lbs of mean thrust as it took off; they would then be jettisoned once the glider was airborne. Initial trials conducted in January 1943 proved to be successful, but was not pursued any further for unknown reasons. The second solution was double towing, where two Halifax aircraft, one stripped of all unnecessary equipment, attached tow ropes to a Hamilcar and then took off from an airfield; once airborne the normal Halifax would then detach its towrope and land, and the modified Halifax would tow the glider to its destination. However, this idea went no further than initial trials in England, as it was considered to be a high risk operation with a high probability of a serious accident occurring. As such, a powered version of the Hamilcar, the Mark X, was decided upon, as it offered the possibility of long-range airborne operations and the ability to retrieve the glider once it had been used. The decision was taken to start developing the Mark X in November 1943 when the potential for airborne operations against Japan itself began to be considered by the Allies; however, for some reason a relaxed view was taken to the development of the production models, and the first was not available until the early months of 1945.

The first prototype was converted from a Hamilcar Mark I. Two Bristol Mercury radial piston engines, capable of producing 965 hp, were added to the wings of the glider, and the wings and fuselage were strengthened so they could take the weight of the engines. Extra controls were added to the cockpit and duplicated in the two pilot positions, although space restrictions meant that the glider could only be started from the rear seat, and fuel tanks were added to the wings, with the possibility of a third being carried in the fuselage. These additions increased the glider's weight to 47,000 pounds (21,000 kg), but its other dimensions remained unchanged, including the carrying capacity in the fuselage. The first flight of the Mark X, under its own power, took place in February 1945 and the initial flight and further trials showed that the glider operated as had been expected. With engines installed, a Mark X could be towed by a fully loaded Halifax and achieve an operational radius of approximately 900 miles (1,400 km). However, if the glider itself was fully loaded and took off on its own power, it was discovered that it could not maintain height even at full power; this resulted in a decision to decrease the amount of cargo it could carry under its own power, which in turn decreased its weight to 32,500 pounds (14,700 kg). Two Hamilcar Mark Is were converted for initial trials, and when these proved satisfactory a further eight Mark Is were converted and ten Mark Xs built from scratch; any further orders were cancelled when the conflict ended in August 1945, although further tests were conducted in the United States. One other Hamilcar variant was proposed, although it never went into production or appeared to go further than the design stage. This was a proposal to mate a Lockheed P-38 Lightning fighter to the top of a Hamilcar, as the fighter would provide enough power to keep both aircraft in flight and relieve the glider pilots of the task of controlling the glider until it cast off to land.

While the unpowered glider needed ballast to be flown empty, the Hamilcar X was less sensitive to centre of gravity issues. The performance of the Hamilcar X under its own power was not dissimilar to performance under tow, notwithstanding the low load. At 32,500 1b, it could take off in 1,385 yards. Its maximum speed was 145 miles per hour (233 km/h) but it could cruise at 120 miles per hour (190 km/h). With 400 gallons of fuel it could manage 705 miles (1,135 km) in still air or 1,675 miles (2,696 km) with 860 gallons onboard replacing the cargo capacity.