morphing wing concept for small uav
TRANSCRIPT
Morphing wing concept for small UAV
VASILE PRISACARIU1,a , MIRCEA BOSCOIANU2,b, IONICĂ CÎRCIU2,c
1”Transilvania” University, 1 Colina Universităţii, Braşov, Romania 2 “Henri Coandă” Air Force Academy, 160 Mihai Viteazu, Braşov, Romania
a [email protected], [email protected], [email protected]
Keywords: morphing wing, airfoil, aerodynamic analysis, sensors, actuators
Abstract: The biological flight involves the movement of a wing (lift surface) in viscous medium
and it generates lift and resistance for going forward through friction compared to Reynolds
number. The morphing concept is generally based on optimizing the aerodynamic form during the
mission so it can execute a maneuver flight. This article desires a short passage through the
mathematical aspect in 2D of the morphing profile concept.
Introduction
Generally a biological flight involves the movement of a wing (lift surface) in viscous medium
and it generates bearing and resistance for going forward through friction compared to Reynolds
number. The lift force is generated by the airfoil of the wing due to pressure difference between the
two surfaces of the wings and the resistance for going forward is due to the friction principal in
contact with the air and the vortex from the downstream of the wing located in different incident
angles.
Morphing transformations
Starting from the recent studies from the big universities and research centers (Bristol
University, NASA, DARPA) we can establish a classification of the morphing concept (figure 1):
omni-morphing (internal morphology with multiple non planar dynamic volume); active poly-
morphing (local multidirectional geometrical modifications and the wing is aero-elastic active:
sliding wings, telescopic wings, folding rotating wings, folding wings); passive poly-morphing
(local multidirectional geometrical modifications); active mono-morphing (local multidirectional
geometrical modifications: interconnected flaps with flight stabilizer, spoilers, weight reduction of
the wings, variable volume, variable chord wing, vectorial traction); unidirectional and discreet
mono-morphing (local multidirectional geometrical modifications: discreet spoilers as controlled
surfaces, flaps)[1].
Fig.1 Morphing concept
Biomechanics of the flying wing
Senses/ sensors. Flying creatures and machines must be capable to detect and feel the weird
atmosphere near them as well as their own position, location and structural configuration to perform
the flight activity into a given medium.
Applied Mechanics and Materials Vol. 332 (2013) pp 44-49Online available since 2013/Jul/15 at www.scientific.net© (2013) Trans Tech Publications, Switzerlanddoi:10.4028/www.scientific.net/AMM.332.44
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Birds are capable of using these senses, like sight, hearing, smell but also special sensor systems
like: eco-location (bats), the linear and angular acceleration capacity with the help of the ears and
mechanic receptors at insects that feel a potential approach from something. Birds can feel the
electromagnetic field of the Earth that informs information for navigation.
Example of sensors (figure 2) and collected data: weather (temperature and humidity),
biometrical (the quality of the atmosphere-smoke, gas, contaminated atmosphere), navigation
(GPS), telemetry (speed, altitude, pressure), attitude (the position compared to other objects, the
position/form of the wing at every moment). This capacity can use special sensors like angular
gyroscopes for orientation and capitation widgets for air pressure through the wing.
a b c
Fig. 2 Ultrasonic sensor (a), pressure and temperature sensor (b), video sensor (c) [2]
Processing/ hardware. The signal entries from the birds senses (eyes, ears), must be integrated
and worked in the brain or flight computer. The processes and functions include special algorithms
for control, flight stability and navigation. Stability during the flight is the most important function
because without it you can not fly. At aerial vectors the processes which serve for the flight stability
are executed at top speeds.
In biological flight the commands are electrical impulses from the brain which stimulates
muscles and specific organs. At aerial vectors the commands are electrical signals that activate the
execution elements (actuators). Within the navigation processes we compare the information from
the passing points with a known geographical orientation so that we can calculate the best flight
course to our destination. The control function executes information and guidance and it generates
commands tot the action system to fly through the calculated course.
Actuation / actuators. The natural biological flight requires a special skeleton structure and
muscles [3] so it can perform flight figures and acrobatics (figure 3).
Fig. 3 Pterosaurs: first vertebrates in the flight Fig. 4 Morphing wing mechanisms
Oxford University 2008
Flight in the morphing concept requires specialized structures and elements so that it can modify
the position of the elements and structures the way we desire (figure 4). Also, the new types of
servo-actuators, movable winglets [4] and morphlets [5] extend the operational envelopes of the
future UAV together with the introduction and use of the GPS modules and autopilot for command
and control, (figure 5).
Applied Mechanics and Materials Vol. 332 45
Fig.5 Kestrel [6] and MP 2128x autopilot [7]
Advanced materials. The advanced morphing technologies, like compliant structures [8] with bi-
stable materials and aero-elastic manufacturing [9] should allow a multi-role design for aircrafts
with the same level of performance and flight quality.
.
The proposed morphing concept
The presented morphing concept is based on the wing torsion along of the wing span. The
extreme end of the wing will realize a difference of the incidence 200.
Fig. 6 Morphing by wing torsion
Fig. 7 Clark YH airfoil, morphing angle ± 100
[10]
Calculations regarding the airfoil with morphing. Starting from a classic aerodynamic profile,
we will calculate the aerodynamic features depending on the skeleton profile initially not deformed
and the morphing angle equivalent to β, (figure 8) [11].
we have increased incidence τ∆ :
βππ
βτ
−≅
−+=∆
c
c
c
c
c
c
c
c
c
c 11111 17,014
1arcsin2
Experimental we obtained the following relation
c
c1βτ ≅∆ (1)
where
c-the rope of the modified profile
c1-the rope of the morphing profile
β -morphing angel
46 OPTIROB 2013
Fig. 8 Morphing airfoil (medium torsion)
and the modification of the momentary coefficient
β3
11 12
−−=∆
c
c
c
cCm (2)
The hinge moment of the command surfaces. By turning o morphing command surface we will
modify the aerodynamic force which will produce a hinge moment (Eq.3), will be written as a form
that will obvious stake out the dependence on aerodynamic pressure, the geometrical features of the
commanded surface and the dimensionless coefficient:
mMAc CcSVM 2
2
ρ= , (3)
where Sc- the command surface area
CMA-the medium chord of the same surface
Cm- the moment coefficient
The dimensionless coefficient of the virtual hinge moment depends on the incident angle of the
fixed surface α and the turning angle δ of the command surface (Eq.4):
Ch=Ch(α, δ). (4)
With the help of the Profili v.2.25 software [12] we can obviously stake out the command on
each half-wing (simultaneously and alternative) which will lead to a handling grade that will be
according to the geometrical and mass features of the flying wing (figure 9, figure 10). We will
need to pay special attention to the internal structure of the lift surface because the handling
difficulty directly depends on the elasticity/rigidity of the flying wing [13].
Analysis was performed at Re = 272,000, for a speed V = 10m / s and c = 0.40 m chord profile.
We observe, as expected, in figures 9 and 10, a significant difference in lift and moment
coefficients. In Table 1 are shown the values of the coefficients on the three morphing angles.
Applied Mechanics and Materials Vol. 332 47
morphing 00 angle morphing 10
0 angle morphing -10
0 angle
Fig.9 Chart Cl-α and Cd-α
Fig.10 Chart Cl/Cd- α and Cm- α
Table 1. Data for morphing angles
morph 00 morph 10
0 morph -10
0
Conclusions
The special UAV missions require exceptional evolutions from UAV (evolutions at small
speeds, small turns, and quick maneuver). The proposed, implemented, analyzed morphing
solutions compared to a global indicator on reliability, control, maneuver and low fabrication costs
are all important for the selection of a morphing strategy.
Advanced sensors used to measure response features for flight maneuvers; the latest software
together with quality analysis methods for performances will lead to a global improvement of the
bearing surfaces.
Acknowledgment
The authors wish to thank the “Transilvania” University of Braşov and "Henri Coandă" Air
Force Academy of Braşov for supporting the research necessary for writing this article.
48 OPTIROB 2013
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