09-08-2012, 10:20 AM
Design and Feasibility Analyses of Morphing Airfoil Used to Control Flight Attitude
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ABSTRACT
Morphing technology, inspired by bat and bird flight can enable an aircraft to adapt its shape
to enhance mission performance and optimize flight attitude controlling efficiency. A morphing airfoil
concept is proposed to replace the traditional flap, ailerons, elevator and rudders in order to improve
aerodynamic efficiency in this paper. A procedure is used to virtually simulate a morphing wing to perform
fast, relatively accurately and efficiently. A set of optimal airfoil shapes obtained are aimed at minimizing
the aerodynamic drag character by optimizing morphing configurations at different Cl under the twodimensional
steady-flow simulation. These airfoil shapes are used to maneuver flight attitude, minimize
drag and take place of traditional control surfaces of different rolling, yawing and pitching moment.
Then, the basic relationships between optimized morphing airfoil and the traditional control element on
rolling, pitching and yawing moment are simplified to the relationship of Cl. The morphing airfoil shapes
at different Cl are represented. The configuration of traditional airfoil and morphing airfoil at different Cl
are compared. It is proved that morphing wing can be used to take the place of a traditional wing.
©2011 Journal of Mechanical Engineering. All rights reserved.
INTRODUCTION
Since the Wright brothers’ first successful
flight, aircraft designers have been focusing
on improving the aircraft flight efficiency,
and especially airline companies are anxious
to improve the commercial aircraft efficiency
nowadays. Usually aircraft wings are designed
to be most efficient at cruising flight but suffer
performance penalties under other conditions,
such as taking off, landing and controlling flight
attitude. Inspired by the bald eagle which can
change its own flap configuration to fit different
flight conditions and control the rolling, pitching
and yawing performance [1] many researchers
have investigated different ways to change the
flight efficiency in different environments. Many
research works have been published on smart
wing and morphing aircraft technique in recent
years.
MATHEMATIC AIRFOIL MODEL
Numerous mathematic methods have
been devised to represent airfoil geometry in
aerodynamic design, optimization and parametric
studies. In this paper “CST” mathematical method
[30] to [32] proposed by Brenda Kulfan is chosen
to describe the airfoil configuration; there are n
control parameters which can be defined by the
customer according to the required accurate which
are used to control the different part of airfoil
configuration.
THE MORPHING WING CONTROLLER
CONCEPT
The traditional flaps, ailerons, elevators
and rudders consist of hinged control surfaces
that are attached to the trailing edge of the wing
on a fixed-wing aircraft. The ailerons are used
to control the aircraft in roll, the two ailerons are
typically interconnected, so that one goes down
when the other goes up: the down going aileron
increases the lift on its wing while the up going
aileron reduces the lift on its wing, producing a
rolling moment about the aircraft’s longitudinal
axis [33]. The elevating and yawing rudders are
used to control the aircraft in pitch and yaw. All
the control elements above can control the flight
attitude by changing the lift of the control surfaces,
so the flight controlling can be simplified to force
on different control elements. Any control element
that can change the force of the whole airfoil can
take the place of the traditional control element.
It has been found that morphing airfoil control
element can take the place of the traditional
control element and provide a smaller drag.
OPTIMIZATION OF THE MORPHING
AIRFOIL
The optimization of the morphing airfoil
is necessary in order to compare the morphing
airfoils and the traditional hinged control surfaces.
The airfoil was optimized to get the optimal
airfoil shapes which can provide the same Cl with
a much smaller Cd punishment than any other
shapes. To achieve this, a tool that can search the
optimal airfoil geometry is used. First the generic
constrain was represent by Eqs. (1) to (3) based
on the Bernstein polynomial. Second, the XFOIL
program is used to get the polar ratio of the airfoil
shape in the aerodynamic analysis.
RESULTS AND DISCUSSION
A set of optimal airfoil shapes which can
provide different Cl with the minimum drag are
obtained by the procedure at Mach 0.045, Re
300000. In 5.1, the particular polar characteristics
of the optimal airfoil configurations are compared
with the traditional hinged control surfaces
which include a different angle of attack and
hinged control surfaces. In 5.2, the optimal airfoil
shapes are obtained by the procedure limited by
a minimum drag coefficient at different Cl which
correspond with the different angle of traditional
hinged control surfaces, the optimal airfoil shapes
can take place of all the control surfaces of a flight.
CONCLUSION
The morphing wing is designed according
to the morphing airfoil theory represented. It has
been proved that the morphing airfoil can replace
the hinged control surfaces to control the rolling,
pitching and yawing moment with a smaller drag
and increasing the flight efficient at different
rolling, pitching and yawing moment.
The morphing airfoil control element
can reduce the drag from 20 to 60% (showed in
Fig. 5) than the traditional airfoils with control
surface when they provide a same Cl, if the Cl is
bigger than 0.1. The morphing airfoil can lead to a
smaller adverse yaw when they provide the same
rolling moment.