1. National Conference on Innovative Trends in Mechanical and Aerospace Engineering (ITMAE-2014)
SVIT,Vasad Page 1
Numerical Analysis over Variable Sweep Wing in
Micro Air Vehicles
M M Oza, M B Joshi J R Vala, N M Mehta, D V Shah
UG students, Department of aeronautical engineering Asst. professor: Department of aeronautical engineering
Saradar Vallabhbhai Patel Institute of Technology Saradar Vallabhbhai Patel Institute of Technology
Vasad, India Vasad, India
manasvi_o@yahoo.in jigneshrvala@gmail.com
manavjoshi14@gmail.com dhruvin21@gmail.com
Abstract- Micro Air Vehicles (MAVs) are noted for their small
size and low-Reynolds number flight regime. Because they have
small mass, they are attractive for use in sensing of toxic plumes.
This mission requires high aerodynamic efficiency and the ability
to be quickly and easily launched. A variable-sweep wing is
investigated to meet these goals. One of the main objective is to
study the effect of flow on Micro air vehicle with different swept
back angle wings at different angle of attack. The computational
analysis is based on light weight, high lift, and low aspect ratio
wing with laminar flow. From the study of the MAV with
variable sweep wing, it is inferred that as the sweep angle
increases, parasite drag decreases and gives better aerodynamic
performance and also withstands at high wing loading due to
gust wind.
Keywords—Micro air vehicle, Aerodynamics, sweep back wing,
aircraft, CFD analysis.
I. INTRODUCTION
A Micro air vehicle (MAV), or Micro aerial vehicle
[1][2], is a class of unmanned aerial vehicle (UAV) that has a
size restriction and may be autonomous. Micro Air Vehicles
(MAVs) are small aircraft with potential applications ranging
from surveillance and communication to sensor networks in
both civilian and military applications. MAVs [3] are
distinguished by their small size and their often unknown
aerodynamic characteristics. Because MAVs operate in a flow
regime with Reynolds number below 200,000 they behave
much differently than conventional aircraft. At these low
Reynolds numbers, the ratio of lift to drag is significantly
lower than that of large-scale aircraft.
A variable-sweep wing [4] is an airplane wing that may be
swept back and then returned to its original position during
flight. It allows the aircraft's planform to be modified in flight,
and is therefore an example of a variable-geometry aircraft. A
swept wing is more suitable for high speeds. The variable-
sweep wing is most useful for those aircraft that are expected
to function at both low and high speed, and for this reason it
has been used primarily in combat aircraft. Traditionally,
variable sweep has been used to increase the critical Mach
number of transonic and supersonic jets while providing low-
speed maneuverability and decreased stall speed.
Typical flight speed is 20 m/s, it means that a wind gust can
increase relative airspeed by 50-100%. This increase in
Reynolds number and dynamic pressure causes a large
instantaneous increase in wing loading and may cause
structural damage. The use of flexible membrane wings allows
the MAV to decrease camber and hence lift coefficient in
response to a large wind gust, alleviating some of the adverse
effects of the gust.
A flexible wing MAV called CMAV [5] has already been
designed and built at the University of Colorado. It
represented the first generation of design concepts for the
project.
II. BRIEF DESCRIPTION OF WORK
A. Model Description
Eppler 387 airfoil[6] is used in model.
Fig. 1 Eppler 387 airfoil
The geometry of the model was drawn using CATIA V5.
Geometry setup was made for 2 different sweep back angles,
150
and 400
which respectively shown in figure 2 and 3 using
wireframe and surface design to draw the 3-dimensional
model of MAV.
The wings are each 0.5 m long and have a 0.1 m chord.
Dimension of fuselage is 0.14m * 0.12m *0.04m and Tail is
0.24m + 0.08m. Three versions of the model were generated
for two swept angles 150
and 400
.

2. National Conference on Innovative Trends in Mechanical and Aerospace Engineering (ITMAE-2014)
SVIT,Vasad Page 2
The top view of 150
sweep back angle model.
Fig. 2 150
sweep back angle model
The top view of 400
sweep back angle model.
Fig. 3 400
sweep back angle model
B. Computational work:
The computational steps in this project consist of three
stages: Pre-processing, numerical computation and post-
processing.The project began from pre-processing stage of
geometry setup and grid generation. The grid was generated in
ICEM 14.0. The mesh generator created an unstructured mesh.
Fig. 4 150
sweep back angle model mesh
Figure 4 and 5 shows mesh of 150
and 400
swept back angle
model. For 150
swept back angle model total element is about
966042 and for 400
swept back angle model it is 737663.
Fig. 5 400
sweep back angle model mesh
The second stage was computational simulation by FLUENT
solver using Finite Volume Approach. Final stage is post-
processing.
Below figures 6, 7 and 8 shows the pressure & velocity
contours from the analysis performer for 00
, 50
and 100
angle of
attack for 150
swept back wing model.
Fig 6.Pressure & velocity contour for 150
angle at 00
AOA swept back
Fig 7.Pressure & velocity contour for 150
angle at 50
AOA swept back
Fig 8.Pressure & velocity contour for 150
angle at 100
AOA swept back
Below figures 9, 10 and 11 shows the pressure & velocity
contours from the analysis performer for 00
, 50
and 100
angle of
attack for 400
swept back wing model.

3. National Conference on Innovative Trends in Mechanical and Aerospace Engineering (ITMAE-2014)
SVIT,Vasad Page 3
Fig 9.Pressure & velocity contour for 400
angle at 00
AOA swept back
Fig 10.Pressure & velocity contour for 400
angle at 50
AOA swept back
Fig 11.Pressure & velocity contour for 400
angle at 100
AOA swept back
From the above figures 6 to 11, from the pressure contours it
is clear that pressure decreases from leading edge to some
certain point then it start increasing throughout trailing edge. It
is seen that at upper edge of wing minimum pressure point is at
maximum thickness for 00
angle of attack. With increase in
angle of attack maximum lift point or minimum pressure point
is move away from maximum thickness point.
III. RESULTS DISCUSSION:
Flow simulations were run for several different conditions.
Each model was simulated at 20 m/s of far-field velocity and
three angles of attack (α), ranging from 00
to 150
in 50
increments [7]. The results were then tabulated and analysed.
Table 1: Aerodynamic coefficient for 150
sweep back angle
AOA(α) CL
(computational)
CL
(reference)
CD
(computational)
CD
(reference)
00
0.44 0.35 0.156 0.13
50
1.23 1.10 0.157 0.14
100
1.54 1.50 0.23 0.20
Table 1 shows value of coefficient of lift and drag with angle
of attack 00
, 50
and 100
for 150
swept back angle model.
Table 2: Aerodynamic coefficient for 400
sweep back angle
AOA CL
(computational)
CL
(reference)
CD
(computational)
CD
(reference)
00
0.31 0.3 0.06 0.075
50
0.59 0.6 0.08 0.08
100
1.08 1.0 0.11 0.12
Table 2 shows value of coefficient of lift and drag with angle
of attack 00
, 50
and 100
for 400
swept back angle model.
From the values obtain of coefficient of lift and drag, it is
clear that with increasing in angle of attack, lift is increase and
with increase of swept back angle drag is decrease.
D=½ ρ U∞
2
CD,OS+ 2W2
/ᴫeρb0
2
(U∞cos Ʌ) (1)
Equation (1) is drag equation[8] where ρ is density, S is
surface area, W is weight, e is Oswald’s coefficient and b0 is
span of wing. In (1) the first term represents the contribution of
parasite drag. The second term represents the induced drag,
which decreases with free stream velocity (U∞) but increases
with sweep angle (Ʌ). Which clearly shows with increasing the
swept angle (Ʌ) total drag (D) is decrease.
Fig 12. CL vs. AOA from observation
The most obvious effect of sweep angle on CL is the change
in lift-curve slope. The change in slope is caused by a decrease
in the effective camber. When the wing is swept, the effective
chord (C) length becomes C =c/cos Ʌ. The total camber (c) of
the wing remains unchanged, resulting in a decreased
percentage in camber of the wing and smaller a lift-curve
slope. In the coefficient of lift the only significant deviation is

4. National Conference on Innovative Trends in Mechanical and Aerospace Engineering (ITMAE-2014)
SVIT,Vasad Page 4
for the case of the aircraft with 150
sweep operating at 100
AOA, where CL = 1.54 for 20 m/s and 400
sweep operating at
100
AOA, where CL = 1.08 for 20 m/s. In both cases, the flow
has separated from the upper surface of the wing.
Fig 13. CD vs. AOA from observation
The swept configuration has a lower coefficient of drag, due
to its smaller frontal profile. Parasitic drag coefficient CD,0 for
the fully swept configuration is less than half that of the
unsweep counterpart, 0.15 compared to 0.06. The 150
sweep
vehicle also has greater induced drag due to the steeper lift
curve.
Fig 12. L/D vs. AOA from observation
The lift-to-drag ratio is critical for the MAV. In order to
achieve long duration flight, the aircraft must be as efficient as
possible. For all three configurations, the most efficient AOA
is around 50
. Level flight requires L =W, which is
approximately 1.96 (9.81*.02) N for the MAV. Under this
condition the lift coefficient is inversely proportional to the
square of velocity, requiring a change in AOA for level flight.
The reason for this is that the wing is larger than necessary
for a vehicle of 200 g. The light weight and large wing area
cause the vehicle’s operating point to be well away from the
optimum L/D, which occurs around 50
AOA. At the low
speeds, 150
sweep provides the greatest L/D.
IV. CONCLUSION
The use of variable sweep to improve MAV flight
characteristics over a different range of angle of attack. A
decrease in parasite drag due to a reduced in aspect ratio and
frontal profile results in decreased drag. By sweeping the wings
from 150
to 400
, CD can be reduced by nearly 52% for airspeed
of 20 m/s. It is possible to achieve L/D > 8 at 20 m/s.
IIV. FUTURE EXPANSION OF PROJECT
This research work can be expand further as generate a
different geometry with different specifications i.e with
winglet. Geometry can be made with anhedral angle to provide
more stability. MAV with morph wing i.e variable chamber.
V. REFERANCE
[1] K. Mohseni, D. Lawrence, D. Gyllhem, M. Culbreth, and P. Geuzaine.
Flow simulation around a micro air vehicle in a plume characterization
scenario. AIAA paper 2004-6598, American Institute of Aeronautics and
Astronautics, 3rd Unmanned Unlimited Technical Conference,
Workshop and Exhibit, September 20-22 2004.
[2] D.A. Lawrence, K. Mohseni, and R. Han. Information energy for sensor-
reactive UAV flock control. AIAA paper 2004-6530, Chicago, Illinois,
20-23 September 2004. 3rd AIAA Unmanned Unlimited Technical
Conference, Workshop and Exhibit.
[3] Y. Lian, W. Shyy, D. Wiieru, and B. Zhang. Membrane wing
aerodynamics for micro air vehicles. Prog. in Aero. Sci.
[4] Project merlin. University of Wisconsin College of Engineering,
August2005.http://homepages.cae.wisc.edu/_floatn/merlin/project.htm.
[5] D. Gyllhem, K. Mohseni, D. Lawrence, and P. Geuzaine. Numerical
simulation of flow around the Colorado micro aerial vehicle. AIAA
paper 2005-4757, American Institute of Aeronautics and Astronautics,
35th AIAA Fluid Dynamics Conference and Exhibit, Toronto, Canada,
June 6-9 2005.
[6] Theory of wing sections, summary of airfoil data by IRA H. ABBOTT
and ALBERT E. VON, research engineer nasa.
[7] P.G. Ifju, D.A. Jenkins, S. Ettinger, Y. Lian, W. Shyy, and M.R.
Waszak.Flexible-wing-based micro air vehicles. AIAA paper 2002-
0705, January 2002. 40th. Aerospace Sciences Meeting & Exhibit,
Reno, Nevada.
[8] J.D. Anderson Jr. Introduction to Flight, 5th Ed. McGraw Hill, Boston.