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NB - Green numbers within brackets
refer to references.
TERRESTRIAL
HYPERSONIC FLEX-WING (THF).
The nose-cap and lower floor-pan are
rigidly fixed to one another, and the leading edges are
articulated, so that they may be extended, permitting the
nose angle to be changed to match the shock angle, as the
vehicle decelerates. The lower sail may be unfurled so that
the aspect ratio of the aircraft can be altered in flight,
as the geometry of the shockwave changes with progressively
lower air-speed. Since changes in pitch angle may be
necessary to maintain stability, the upper centreline strut
may also be lowered by means of a hydraulic strut, similar
to the struts controlling the leading edges. This mixture of
leading edge and keel separation, allows a wide range of
configurations into which the airframe may be adjusted,
depending on the prevailing angle and velocity of the
aircraft. The vehicle could be launched with the wing fully
retracted, greatly reducing drag, or packaged and stored in
the cargo bay of a U.S. or Russian space shuttle.
With such a degree of control over
the shape of a Waverider, emergency procedures such as
decelerating aerocapture reentries could be made possible.
Being able to unfurl large wing surfaces and increase the
aircraft's frontal area, either separately or in a
coordinated deployment, would allow greater choice of
landing footprints and touchdown sites.
Conversely the ability of the vehicle
to fold its wings if required, may prove useful. As in the
interplanetary design, atmosphere entries which required to
be aborted back to orbit could be effected by retracting the
wings. Simply folding up the wing during a high velocity
aerocapture manoeuvre could allow the vehicle to abort entry
and "skip" out of the atmosphere.
The design of the Terrestrial
Flexwing Waverider is based partly on the "lips" optimised
Waverider shape developed by the University of Maryland, and
partly on the standard Rogallo kite. The vehicle's main
features are: the relatively straight leading edges, flat
upper surfaces and the absence of a base or "transon" at the
trailing edge. The upper freestream-aligned surface is
constructed from the same woven carbon matting, but has to
remain taut and longitudinally rigid. The carbon spars are
braced internally by at least three extending struts. Since
shock angles may vary quite sharply, the leading edges may
have to rotate longitudinally, to cope with low or high
entry angles and flat or concave sail contours during
flight.
The low position of the payload
palette within the floor pan imparts static stability to the
aircraft, while the very low inertia of the microlight
airframe reduces the control input forces required to
manoeuvre the aircraft.
To preserve the structured shape of
the flexible "sail", the directional tensile strength of the
sail material must run in the spanwise direction. The
resistance of the sail extrusions to compression loads to
the movement of the leading edges, will act like a spring,
preserving the symmetrical geometry of the lower cavities.
This "spring effect" should allow the wing to "billow-shift"
in the same manner as a low speed hang glider. The
structural integrity of the complete airframe would be
increased as a consequence of having a flexible, but
resilient sail structure. In later studies, slight changes
in the sail material allow the possibility of variable
porosity and heat transfer. In another part of this paper,
the thermal equilibrium of the sail is "designed" for shock
environment, and is capable of being changed during flight,
if thermal conditions alter as a result of attitude or
geometry changes.
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