Tech Briefs Magazine - August 2022 - 34

Aeronautics
line to develop an opposing aerodynamic
force alleviating the load felt by the
wing. This passive gust alleviation control
covering 33 percent of the span of a
cantilever wing was tested in NASA Langley's
low-speed wind tunnel and found to
reduce wing response by 30 percent.
While ongoing experimental work with
new laser sensing technologies is predicted
to similarly reduce gust load, simplicity
of design of the present invention may be
advantageous for certification processes. In
addition, this passive technology may provide
further gust alleviation upon extending
the use of the control to the entire trailing
edge of the wing or upon incorporation
with current active gust alleviation systems.
Importantly, the technology can be
easily incorporated into to the build of
nearly all fixed-wing aircrafts and pilot
control can be maintained through a
secondary trim tab. Though challenging
Outer Aileron Yaw Damper
A lightweight alternative to rudders for aircraft with spanwise adaptive wings.
Armstrong Flight Research Center, Edwards, CA
I
n recent years, NASA, along with
partners Boeing and Area-I Inc., have
developed the spanwise adaptive wing
(SAW). SAWs leverage a thermally triggered
actuator made from a NASA-developed
shape memory alloy (SMA) to
allow outer portions of aircraft wings
and control surfaces to be folded to
achieve optimal angles during flight.
For supersonic aircraft, SAWs can reduce
drag and increase performance
during the transition from subsonic
to supersonic speeds. For subsonic aircraft,
SAWs offer increased control and
reduced dependency on the tail rudder
and associated hydraulic systems, a particularly
heavy part of the aircraft.
Engineers at NASA AFRC realized
the aircraft weight savings that could
be achieved by reducing or eliminating
rudder dependency, since this would allow
for rudder size to be reduced. They
set out to develop an alternative system
capable of providing the same " yaw conLess
rudder dependency enables aircraft designs with smaller rudders and vertical tail structures,
significantly decreasing vehicle weight. (Image: NASA)
trol " functionality as traditional rudders.
This work resulted in the invention of
NASA's outer aileron yaw damper system,
which includes novel control algorithms
that drive flight control surfaces
to produce desired flight conditions.
The benefits of reduced rudder dependency
led NASA to develop the outer
aileron yaw damper to further decrease
or eliminate rudder dependency for aircraft
using SAWs. As mentioned, SAWs use
shape memory alloy actuators to articulate
the outer portion of the wing, effectively
creating a movable wingtip. NASA's invention
uses an outer aileron located on the
wingtips, which is driven (along with the
inner ailerons) by a control algorithm.
The control algorithm, taking into account
the wingtip positions, manipulates
the outer ailerons to achieve the desired
yaw rate. At the same time, it positions the
inner ailerons to counter roll rate resulting
from the outer aileron.
In other words, the control algorithm
calculates a control surface ratio (i.e.,
position of inboard aileron and outboard
aileron) that produces desired
yaw and roll accelerations.
The system can also be used to offset
the existing rudder in current or future
aircraft designs. A second part of NASAs
novel outer aileron control algorithm
modifies the aircrafts rudder loop gain
in proportion to outer aileron usage.
This allows the outer ailerons and rudder
to work in tandem, while at the same
time reducing rudder usage.
Less weight and drag lead to reduced aircraft fuel consumption. (Image: NASA)
34
As a result of this NASA invention, required
rudder usage can be reduced or
eliminated for aircraft with SAWs. Consequently,
the size of rudders and vertical tail
structures can be reduced, which in turn
reduces weight and parasitic drag. The
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Tech Briefs, August 2022
to retrofit, passive gust alleviation could
enable use of thinner, more efficient
wings in new plane design.
NASA is actively seeking licensees to
commercialize this technology. Please
contact NASA's Licensing Concierge at
Agency-Patent-Licensing@mail.nasa.gov
or call at 202-358-7432 to initiate licensing
discussions. For more information,
visit https://technology.nasa.gov/patent/
LAR-TOPS-343.

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Tech Briefs Magazine - August 2022

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