Trochoid
MLB used numerical optimization when first considering micro
air vehicle designs. Analysis results indicated that maximum
wing area (and lift capability) for a given size is critical
to achieving performance in an MAV. Circular wing planforms
have maximum area for a given size, but have poor aileron effectiveness
because the control surfaces are located close to the wing centerline
in a region of strong vortical flow. We tested several circular
wing designs and found that a slot between the upper and lower
wing surfaces restored control effectiveness, but reduced the
wing’s internal payload volume. Rudder control can also
be used for turning because low AR designs have strong yaw-roll
coupling due to side edge wing vortices, but this type of control
is very nonlinear with
angle of attack.
The trochoidal
wing planform has only 11% less area than a circular wing
for a given size, yet has the desirable aerodynamic properties
of a delta wing planform because its size normal to the flow
direction increases along the wing centerline. This allows
the control surfaces to be very effective even in the presence
of strong vortical flow. Our most successful version of this
design, a 20 cm Trochoid with a video downlink and a stability
augmentation system, has demonstrated 20 minute flight duration,
flight speeds from 10 to 60 mph, and turn radius of 15 feet.
It was regularly flown in gusty winds up to 20 mph.
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