Thursday, April 3, 2014

A Comparison of the WWII GAL 49/50 Hamilcar Mk I and AS.51 Horsa Mk I Gliders

Because of the sustained popularity of the pages in this blog regarding the WWII General Aircraft Ltd. GAL 49 Hamilcar Mk I Heavy Assault Glider, as well as the Airspeed AS.51 Horsa Mk I Glider, thought it might be beneficial to present a one-on-one comparison of both aircraft.

As can be seen in some of the photographs of personnel standing under the wing of a Horsa, it was not a small aircraft. However, it was dwarfed by the Hamilcar. Even though it was only a foot longer in overall length, the fuselage and the wing span and area of the Hamilcar far exceeded that of the Horsa. Obviously it was these dimensions that provided the massive payload capacity of the glider, which was well over double that of the Horsa. The wing span of the Hamilcar exceeded that of the Horsa by 22 ft. and the wing area by 553.5 ft2.

A AS.51 Horsa Mk I showing the 25 air landing troops
embarking, which comprised the glider's full capacity

Also note the disparity in the vertical stabilizer design of the two aircraft. Stability and control is a compromise between the two factors. And overly stable airplane will tend to resist any change in direction, and a very nimble aircraft would require constant adjustments to keep flying straight .

The stabilizing effect of the vertical tail surface is a function of its size and the distance between its location and the position of the center of gravity of the airplane; so a smaller tail located further aft would be as stable as a larger tail that is kept closer. A simple matter of leverage. Compared to the Horsa, the center of gravity of the Hamilcar was much further forward on the glider due to the positioning and distribution of their vastly differing payloads.

While not of a calculated precise scale, the drawings which are shown are approximately proportional to each other (with a slight error which occurs in transferring images; this can be corrected by enlarging and copying off-line), affording a direct comparison of the size of the two gliders. It is unfortunate that accurate original plans for the Hamilcar seem to be non-existent.

Profile of the General Aircraft Ltd. GAL 49 Hamilcar Mk I

Top View of the GAL 49 Hamilcar Mk I

General Aircraft Ltd. GAL 49 Hamilcar Mk I General characteristics
  • Crew: 2
  • Capacity: 7 tons (17,500 lbs)
  • Length: 68 ft (20.73 m)
  • Wingspan: 110 ft (33.53 m)
  • Height: 20 ft 3 in (6.17 m)
  • Wing area: 1,657.5 ft2 (153.98 m2)
  • Airfoil: RAF.34 modified
  • Empty weight: 18,400 lb (8,346 kg)
  • Max. takeoff weight: 36,000 lb (16,329 kg)

Profile of the Airspeed AS.51 Horsa Mk I

Top View of the AS.51 Horsa Mk I

Airspeed AS.51 Horsa Mk I General characteristics
  • Crew: 2
  • Capacity: 25 troops (20-25 troops were the "standard" load – 7,130 lbs)
  • Length: 67 ft 0 in (20.43 m)
  • Wingspan: 88 ft 0 in (26.83 m)
  • Height: 19 ft 6 in (5.95 m)
  • Wing area: 1,104 ft² (102.6 m²)
  • Empty weight: 8,370 lb (3,804 kg)
  • Loaded weight: 15,500 lb (7,045 kg)
  • Maximum speed: 150 mph on tow; 100 mph gliding (242 km/h / 160 km/h)
  • Stall speed (fully loaded)69 mph (flaps up), 55 mph (flaps down).
Wing loading: 14.0 lb/ft² (68.7 kg/m²)

A side-by-side profile view of the two gliders showing the more box-like voluminous fuselage of the Hamilcar, as compared with the narrower tubular fuselage of the Horsa. 

The following are detailed cut-aways of each glider showing both design and structural features. As can  be seen both aircraft had an airframe constructed entirely out of wood.

An additional segment of historical film footage showing the Hamilcar glider in flight, as well as unloading some of the many heavy payloads it could carry.