Honing the MicroAirship's Configuration-
Several promising configurations and related design ideas were competitively
assessed (by scoring matrix) for potential speed, maneuverability, reliability,
and simplicity of construction.
The baseline for review was classic airship design which is pendulum stable
with nonvectored bilateral thrusters. Two other candidate designs incorporated
vectored thrust; one was a typical twin vectored thrust design with rudder and
elevator. Another was a futuristic neutrally balanced concept with tri-radially
mounted vectored thrusters and no control surfaces.
The top dog is a Vee-Tailed Twin In-Line Thrust design which scores high in
every functional category. Its fast, agile, robust, and simple.
The dashing vee tail is an update on classical blimp tail design that
reduces part count by a third, plus a surprise; a quality microblimp's vee-tail
can be quickly adapted from off the shelf RC glider wings. Well known vee-tails
include the Stealth Fighter and classic vee-tail Bonanza civil aircraft.
-By locating the chord mounted elevon just above the
propwash it avoids a high speed drag penalty in cruise but
can still dip into the wash for aggressive maneuvers. Thus the
tradeoff between agility and speed is substantially avoided.
An elastic restraint will assist the high torque servos
retrieving the leading edge from the propwash.
(7/14/96)
The In-line twin propulsion units, mounted just aft of center, provide as
much balanced power as the blimp can carry. The advantages of this mounting
approach, as popularized in the Lear Jet and DC-9, apply to blimps. In this case
visualize a fat wingless vee tailed Lear Jet. This picture also resembles
NASA's early lifting bodies leading to the space shuttle design. Twin electric
propulsion offers vigorous yaw inputs allowing the vee-tail to be flattened in
favor of pitch control. The degree of flattening is balanced against the urgent
need for rudder steering in the case of a single propulsion unit failure.
-Mount propulsion units with a slightly toed in
fore and aft stance so that at full cruise power they
align at the most efficient angle. Provide for field
tunability of the prototype to determine best toe factor.
(7/14/96)
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