Design
The No.21 was a wire-braced monoplane with bat-like wings and triangular horizontal tail. There was no vertical fin, and lateral control was intended to be accomplished by shifting the pilot's body sideways.
The wings were constructed with radial bamboo ribs and covered with silk, and had a span of 36 ft (11 m). They had noticeable dihedral, which would have contributed to the aircraft's stability had it ever flown, and could be folded like a fan for transport.
The fuselage was of rectangular box section with constant height, curved to taper inwards at front and rear when seen from above. Four small wheels were fixed to the bottom.
Although having two engines and twin propellers, the aircraft was not a conventional twin. It had separate engines for ground running and flight, both designed and made by Whitehead. The ground engine was of 10 hp (7.5 kW) and drove the wheels to reach takeoff speed. Propulsion was then changed to a 20 hp (15 kW) acetylene engine driving two counter-rotating tractor propellers mounted on outriggers.. The aircraft could supposedly take off under its own power and without assistance.
Later analysis by aviation historians concluded that the design as a whole was flimsy and aerodynamically unsound.
Read more about this topic: Whitehead No. 21
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