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REVIEW ARTICLES

# Membrane Wing-Based Micro Air Vehicles

[+] Author and Article Information
Wei Shyy

Clarence L. “Kelly” Johnson Collegiate Professor and Chair, Department of Aerospace Engineering,  University of Michigan, Ann Arbor, MI 48109weishyy@umich.edu

Peter Ifju

Department of Mechanical and Aerospace Engineering, University of Florida, Gainesville, FL 32611

Dragos Viieru

Department of Mechanical and Aerospace Engineering, University of Florida, Gainesville, FL 32611

Appl. Mech. Rev 58(4), 283-301 (Jul 01, 2005) (19 pages) doi:10.1115/1.1946067 History:

## Abstract

Micro air vehicles (MAVs) with a wingspan of $15cm$ or shorter, and flight speed around $10m∕s$ have attracted substantial interest in recent years. There are several prominent features of MAV flight: (i) low Reynolds number $(104–105)$, resulting in degraded aerodynamic performance, (ii) small physical dimensions, resulting in certain favorable scaling characteristics including structural strength, reduced stall speed, and impact tolerance, and (iii) low flight speed, resulting in order one effect of the flight environment and intrinsically unsteady flight characteristics. Flexible wings utilizing membrane materials are employed by natural flyers such as bats and insects. Compared to a rigid wing, a membrane wing can better adapt to the stall and has the potential for morphing to achieve enhanced agility and storage consideration. We will discuss the aerodynamics of both rigid and membrane wings under the MAV flight condition. To understand membrane wing performance, the fluid and structure interaction is of critical importance. Flow structures associated with the low Reynolds number and low aspect ratio wing, such as pressure distribution, separation bubble, and tip vortex, as well as structural dynamics in response to the surrounding flow field are discussed. Based on the computational capabilities for treating moving boundary problems, an automated wing shape optimization technique is also developed. Salient features of the flexible-wing-based MAV, including the vehicle concept, flexible wing design, novel fabrication methods, aerodynamic assessment, and flight data analysis are highlighted.

Topics: Wings , Membranes

## Figures

Figure 1

The Great Flight Diagram gives a relation between wing loading, weight and cruising speed. (The shaded region indicates the expanded parametric range surrounding the projected size, speed and weight for MAV.) Adopted by Shyy (1) based on Tennekes (27).

Figure 2

Lateral views of steady-speed flight illustrating the path of the wingtip (filled circles) and wrist (open circles) of a characteristic wingbeat in a pigeon (Columbia livia) flying at speeds of 6–20m∕s in a variable speed wind tunnel. The bird silhouettes illustrate the body posture at the upstroke/downstroke transition. By permission, after Tobalske and Dial (1996) (33).

Figure 3

Dorsal views of steady-speed flight illustrating the path of the wingtip (filled circles) and wrist (open circles) of a characteristic wingbeat in a pigeon (Columbia livia) flying at speeds of 6–20m∕s in a variable speed wind tunnel. The bird silhouettes illustrate the body posture at the middle of downstroke. Pigeons adducted their wrists during upstroke while flying at 6 and 8m∕s (indicating a vortex-ring gait), but left their wrists extended during upstroke at speeds of 12–20m∕s (indicating a continuous vortex gait). Wingbeat characteristics at 10m∕s were transitional during the two gaits. By permission, after Tobalske and Dial (1996) [33].

Figure 4

A 15cm MAV with membrane wing developed by Ifju at the University of Florida

Figure 5

Schematic of the wing with six battens developed by Ifju at the University of Florida

Figure 6

Streamlines and vortices for rigid wing at α=39deg. The vortical structures are shown on selected planes, adopted from Lian (44).

Figure 7

Pressure distribution around the rigid wing in the cross sections with streamlines at angle of attack of 39 deg, adopted from Lian and Shyy (39)

Figure 8

Evolution of flow pattern for rigid wing versus angles of attack. (From left to right, top to bottom, 6 deg, 15 deg, 27 deg, and 51 deg, adopted from Lian and Shyy (39).)

Figure 9

Spanwise pressure coefficient distributions at x∕c=0.4 for rigid wing at different angles of attack. (a) Pressure coefficient at upper surface; (b) pressure coefficient at lower surface. Adopted from Lian and Shyy (39).

Figure 10

Projected wing shape geometry. (a) Initial wing geometry. (b) Modified wing geometry.

Figure 11

Pressure contours in the wake behind the wing. (a) Initial wing; (b) modified wing, without end plates; (c) modified wing with end plates. Adopted from Viieru (48).

Figure 12

Vorticity contours in the wake behind the wing. (a) Initial wing; (b) modified wing, without end plates; (c) modified wing with end plates. Adopted from Viieru (48).

Figure 13

Horizontal velocity component and streamlines slightly above the wing surface. (a) Initial wing, NO end plates; (b) modified wing, NO end plates; (c) modified wing, WITH end plates. Adopted from Viieru (48).

Figure 14

Pressure contours on the upper wing surface. (a) Initial wing, NO end plates; (b) modified wing, NO end plates; (c) modified wing, WITH end plates. Adopted from Viieru (48).

Figure 15

Horizontal velocity component and streamlines slightly below the wing surface. (a) Initial wing, NO end plates; (b) modified wing, NO end plates; (c) modified wing, WITH end plates. Adopted from Viieru (48).

Figure 16

Pressure contours on the lower wing surface. (a) Initial wing, NO end plates; (b) modified wing, NO end plates; (c) modified wing, WITH end plates. Adopted from Viieru (48).

Figure 17

Pressure coefficient on the upper wing surface in the spanwise direction at location (a) x1∕c=0.34 and (b) x2∕c=0.53. Adopted from Viieru (48).

Figure 18

Pressure coefficient on the lower wing surface in the spanwise direction at location (a) x1∕c=0.34 and (b) x2∕c=0.53. c is the root chord. Adopted from Viieru (48).

Figure 19

Spanwise lift coefficient (Cl) distribution, adopted from Viieru (48)

Figure 20

Spanwise drag coefficient (Cd) distribution, adopted from Viieru (48)

Figure 21

Streamlines at different angles of attack for rigid wing. From top to bottom 6 deg, 15 deg, 27 deg, and 51 deg. Shown are single span shots of the individual time dependent flows. Adopted from Lian and Shyy (39).

Figure 22

Normalized chordwise velocity u∕U contours at root for rigid wing. From top to bottom the angles of attack are 6 deg, 15 deg, 27 deg, and 51 deg, adopted from Lian and Shyy (39).

Figure 23

Vortex shedding at α=51deg, adopted from Lian and Shyy (39)

Figure 24

Comparisons of cp on rigid wing at the root for steady and unsteady computations. (a) α=6deg; (b) α=15deg, adopted from Lian and Shyy (39).

Figure 25

Three versions of the flexible wing were tested in the wind tunnel, adopted from Waszak (57)

Figure 26

Lift coefficient versus angle of attack for configurations with varying wing stiffness, adopted from Waszak (57)

Figure 27

Wing deformation at three spanwise locations for various angles of attack, adopted from Waszak (57)

Figure 28

Wing deformation and airflow visualization experiment using smoke, adopted from Waszak (57)

Figure 29

Time history of trailing edge displacement for membrane wing at α=6deg. The camber at the root is 0.90cm. Adopted from Lian and Shyy (39).

Figure 30

Spectrum analysis of the trailing edge point vibration for membrane wing at α=6deg. Adopted from Lian and Shyy (39).

Figure 31

Averaged displacement of the membrane wing trailing edge. (a) α=6deg; (b) α=15deg. Adopted from Lian and Shyy (39).

Figure 32

Time-averaged spanwise angle of attack for membrane wing. (a) α=6deg; (b) α=15deg. Adopted from Lian and Shyy (39).

Figure 33

Comparison between optimized shape and base line shape at different span positions. The camber decreases from 4.8% at the root to 4% at the tip. Adopted from Lian (44).

Figure 34

Steps to fabricate a 6in. MAV

Figure 35

The flexible wing allows for wing warping to enhance vehicle agility

Figure 36

A foldable wing was developed in order to enhance MAV portability and storage

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