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8/12/2019 Unmanned Air Vehicle
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UNMANNED AIR VEHICLEMICRO AIR VEHICLES
Abhishek K V
3rd
SEM, Department of Mechanical Engineering,
REVA ITM, [email protected]
Ajay T S
3rd
SEM, Department of Mechanical Engineering, REVA ITM, [email protected]
Abstract — Micro Air Vehicles (MAV’s) are class of Unmanned
Air Vehicles (UAV) that has a size restriction and is a semi-
autonomous air vehicle. The improvements in the propulsion
system, battery powered electronic motors, development ofminiature radio receivers and control components, advancement
in aerodynamics brought change over in the design and
development of these vehicles. Modern MAV’s are based on the
body design of birds and insects which give them better stability,
control, up thrust and lower landing speed and finally require
low power. The main advantage of MAV is that it hover for 2-3
hours at an altitude of 600 meters or above, ranging from 20-30
mph in speed which cannot be detected by most of the Radars.
Major applications of MAV’s include military surveillance,
biochemical sensing, Traffic monitoring, defense applications,
Wildlife study and Photography and tracking criminals and
illegal activities.
Keywords — Micro Air Vehicle, Aerodynamics, Fixed-wing,
Rotary wing, Flapping-Wing, Reynolds Number, Biologically
inspired air vehicles
I. I NTRODUCTION
A micro air vehicle (MAV), or micro aerial vehicle,
is a class of unmanned aerial vehicles (UAV) that has a size
restriction and is a semi-autonomous air vehicle. The DefenseAdvanced Research Projects Agency (DARPA) is working on
the development of a new class of flight vehicles called micro
air vehicles (MAVs). The high level of current interest in
developing small flight vehicles is the result of the nearlysimultaneous emergence of their technological feasibility and
an array of compelling new military needs, especially in urban
environments. A more flexible definition includes aircraft
whose flight is characterized by low Reynolds number. Micro
Air Vehicle is a small flight vehicle that uses lift-generating
mechanism different from the mechanism used for larger
aircraft. These machines are used to perform a variety ofmission including reconnaissance, surveillance, targeting,
tagging etc. in hazardous locations and for bio-chemical
sensing in defense sector. The design features and the
configurations of MAVs are different from that of normal
aircrafts. The speed of MAV is very low and the size is less
than 38.10 cm length, width or height [1]. MAVs are not the
small versions of ordinary aircrafts but are affordable fullyfunctional, military capable, small flight vehicles in a class of
their own. The mechanism for lift generation in these smaller
vehicles is of different types like using rotary wings and using
flapping wings. The current goal is to develop aircraft with a
15cm maximum dimension that have a mass less than 90g and
an endurance of 20 to 30 min at speeds between 30 to 65 km/h[2]. In addition to being a compact system transportable by a
single operator, MAVs have other advantages including rapid
deployment, real time data acquisition capability, low radar
cross section and low noise.
II. DESIGNIn order for practical MAVs to be created for either
indoor or outdoor applications, they must first be able to fly, be
controllable, and have a useful endurance. Key to the ability to
fly is an efficient aerodynamic structure with a sufficiently high
lift-to-drag ratio that it can support the weight of its structure in
flight. Weight and strength of materials are essential elements to
the creation of any flying vehicle. It is logical and expected that
the first MAVs would be designed as scaled-down manned
aircraft, since that is the most familiar design space. Fixed-wing
MAVs and rotary-wing MAVs are naturally modeled after
conventional airplanes and helicopters. Closer investigation
reveals that one cannot simply scale down large designs to the
15 cm scale and below, because the interaction of objects
moving through air changes as the size of the objects diminish.
Classical aerodynamics used to design airfoils in manned
airplanes and helicopters no longer applies as the scale of the
airfoil approaches that of small birds and insects because of the
reduction in Reynolds number which describes the behavior of
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the air as seemingly much more viscous. Reynolds number
(Re) is a dimensionless number that relates inertial forces of
an object such as an airfoil, to viscous forces in a fluid
(air).Thinner airfoils are a typical result of designs optimized
for lower Reynolds numbers. [3]
A better engineering approach
is to use ―biological inspiration‖ rather than bio mimicry.
Using biological inspiration, function, and then figures out
how to leverage the physical principles involved, to create a
mechanical analog that is not an exact copy, but works with
similar principles and is able to be implemented. Implement
ability is essential to a valid MAV design philosophy. MAV
structures must be strong, but moreover, lightweight. Because
the strength of materials does not scale proportionately as
things get smaller, we find that materials that would be
otherwise unsuitable for aircraft use at a larger scale can
become quite useful at the 15 cm MAV scale and below [4]
.
The Reynolds number is defined as:
(1)
Where:
v is the mean velocity of the object relative to the fluid (SIunits: m/s)
L is a characteristic linear dimension, (travelled length of the
fluid; hydraulic diameter when dealing with river systems)
(m)
µ is the dynamic viscosity of the fluid (Pa·s or N·s/m² or kg/
(m·s))
is the kinematic viscosity ( =
) (m²/s)
ρ is the density of the fluid (kg/m³).
III. MORPHOLOGY
MAVs fall into three basic categories: fixed-wing,
rotary wing, and flapping-wing configurations. Combinations
of these are of course also possible. The selection of a particular configuration is usually driven by mission
requirements.
1. Fixed-Wing MAV’s
Propeller-driven MAVs are essentially flying wings
where all of the avionics, energy storage, and propulsion are
contained within the plan form of the wing. As such, these
usually end up being ―fast flyers ―reaching 65 km hr−1 (40
mph) at chord Reynolds numbers from about 45 000 to
180 000 and at altitudes from 30 to100m (98 to 328 ft.)).
Fig-3.1.1 shows the various parts of Fixed-wing MAVs.
Fig-3.1.1 Fixed-Wing MAV
Fig-3.1.2 Rotary-wing MAV
2. Rotary-Wing MAVs
Many of the problems associated with the fast flight
of fixed wing MAVs can be overcome through the use ofrotary-wing implementations because of their ability to fly
slowly and even hover. Still, indoor flight or operations inconfined spaces pose the risk of rotor strikes. Weight is also
an issue when small redundant propellers are used with
multiple motors.Fig-3.1.2 shows the details of the Rotary-
wing MAVs.
3. Flapping-Wing MAVs
Unparalleled in the ability to fly slowly and robustly
indoors and in confined spaces is the flapping-wing MAV.
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Just like a moth or small bird can fly about in a building,
sometimes even grazing the walls with its wings, a flapping-
wing MAV[5]
would provide the greatest survivability and
performance indoors (see Fig 3.1.3 ). While all classes of
MAV can function outdoors and are susceptible to the same
environmental affects that keep insects and birds from flying
effectively during periods of high winds or during thunder
storms, the ability of flapping wing MAVs to safely negotiate
tight quarters is based on high lift mechanisms evolved over
the surface of the wing, which allow slow controlled flight.
The reason that a flapping wing is more survivable than a
rotor is that its energy is distributed over a wider chord and
oscillates from a minimum of zero thrust and lift at either end
of the flapping stroke, to its maximum at mid stroke.
Manoeuvrability derives from the flapping-wing’s differential
kinematics, which can vary in flapping speed, angle of attack,
span, or cycle excursion [6]
.
Fig-3.1.3 Flapping-Wing MAV
IV. FUNCTIONS OF MAV
The concept of MAV's has had significant interest,
especially where the military is concerned; the idea of a back
packable spying device which could be used by soldiers to
scout enemy positions, provide real-time tactical combat
information and take aerial photographs of the immediate
area, with no risk to the soldiers life is very appealing. The
MAV's could also be upgraded with useful technologies like
Optical and infrared cameras, signal boosters and a radar
module if the devices could be miniaturised enough the
possibilities are great.
From some sources it also seems like the MAV's may be
made into weapons of war, with roles such as:
Target finding - fly into the vicinity of a target and
'paint' (point a laser) at the target, or even fly to the
target and transmit positional information using the
GPS system for cruise missile.
Flying explosives - One source described multiple
MAV's destroying bridges by flying to weak spots
and detonating.
Controllable debris - the MAV’s could fly into
engines of aircraft and cause heavy damage.From these examples it is easy to see the potential of micro
air vehicles for use as a high precision tactical weapon.
In Civil operations the idea of using a MAV for
reconnaissance could also be replicated by Police forces
when they want to see inside a building discretely for
example during a hostage situation.
Using MAV’s with flapping wings ('Entomopters')
to explore Mars is a project already underway. Having a
flying scout for exploration that accompanies the rover will
be very beneficial because the exploration will no longer be
restricted by natural barriers. and furthermore exploration ofthe atmosphere can be achieved.
In urban operations MAVs, acting in small,
cooperative groups, will enable reconnaissance and
surveillance of inner city areas, and may serve as
communication relays. They may also enable observations
through windows, and sensor placement on vertical and
elevated surfaces. Their application to building interiors is the
most demanding envisioned. The capability to navigate
complex shaped passageways, avoid obstacles and relay
information will require yet another level of technology.
Biochemical sensing, is another potential mission for MAVs.
With gradient sensors and flight control feedback, MAVs will
be able to map the size and shape of hazardous clouds and
provide real time tracking of their location [7]
.
V. LIMITATIONS:
The development and fielding of militarily useful
MAVs will require overcoming a host of significant
technology and operational obstacles. The physical
integration challenge is believed to be the most difficult
problem, the degree of which increases dramatically with
decreasing vehicle size or increasing functional complexity.
At and below the 15 cm scale size, the concept of "stuffing"
an airframe with subsystems - our conventional approach to
hardware integration - becomes extremely difficulties. Flight
control is the single technological area, which harbors the
largest numbers of unknowns for the MAV designer. The
laminar-flow-dominated flight environment can produce
relatively large forces and moments, and they are difficult to
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predict under all but the most benign flight conditions.
Unsteady flow effects arising from atmospheric gusting or
even vehicle maneuvering are far more pronounced on small
scale MAVs where inertia is almost nonexistent, that is,
where wing loading is very light. Platform stabilization and
guidance will require rapid, highly autonomous control
systems. Beyond the difficulties in developing MAVs, few
designs adequately address control issues. The MAVs' small
size makes tele operation impractical because a ground
station pilot cannot see it beyond 100 meters. An onboard
camera allowing the ground pilot to stabilize and navigate the
craft was first demonstrated in the Aerovironment Black
Widow, but truly micro air vehicles cannot carry onboard
transmitters powerful enough to allow for tele-operation. For
this reason, some researchers have focused on fully
autonomous [8]
.
VI. FUTURE WORK
The future work involves the design for forward
moving, reducing the weight of the device using lighter
materials, including the structure of the device, the
controllers, the gyroscope for stabilizing, and developing
small power sources. Also there will be design improvements
to achieve high flight speeds better stability in air, etc. The
overall aim will be to minimize the size and weight, to
increase the speed, and to maximize the battery life for this
MAV.
Other capabilities under development include:1. Smaller size and lighter – there is active research on
―Nano air vehicles‖ [9]
2. More capabilities – live video and
chemical\biological monitoring [10]
3. Sensors for tracking enemy troop movements and
other activities
4. Longer flight times
5. Longer range
6. Advanced flight control
7. Navigation and communications capabilities
8. Lower cost9. Fly at higher altitude
[11]
VII. CONCLUSION
Micro Air Vehicles are the new development of the
technology by which a variety of operations are done. An
approach to design a flying mechanism different from the
approaches being followed by the researchers around the
world has been described. MAVs design presents new
challenges to the aerospace engineer because they operate in
relatively new flight regimes where classical design methods
begin to fail for reasons associated with the physical
characteristics of air flow around small surfaces.
Compounding the aerodynamic design issues are those of
miniaturization, energy storage, and non-scaling items.
Beyond the engineering of efficient MAVs are many
logistical problems yet to be considered: air traffic
management, manned aircraft ―sense and avoid‖ issues,
certification of the MAV and its support systems, and how to
deal with autonomous operations where the vehicle is too
small to see, may be impossible to communicate with, and of
very limited endurance.
VIII. ACKNOWLEDGEMENT
The Authors would like to express a deep sense of
gratitude and thank profusely our guide Mr. Santhosh B D for
his able guidance and valuable suggestions. Without his wise
counsel and able guidance, it would not have been possible to
complete the Technical Paper in this manner. The constant
guidance received from Mr.Raju B S and Mr. Varadraj K R
has been of great help in carrying out the present work. We
are thankful to all the faculty members who have directly or
indirectly helped us in completion of this paper.
REFERENCES
[1] T. J. Mueller, ―Fixed and Flapping Wing Aerodynamics for Micro
Air Vehicle Applications‖ (I-IV)
[2] Garcia-Polanco, N. and Palencia, J., "Aerodynamic Design of aMicro Air Vehicle: Study of Propeller-Engine Performance,"
SAE Technical Paper
[3] James M. MC-Michael, Col. Michael S. Francis; Micro AirVehicles: Toward a New Dimension in Flight.
[4] Robert Michelson ―Encyclopedia of Aerospace Engineering,‖Online © 2010 John Wiley & Sons, Ltd
[5] Zufferey, J.-C. (2008). Bio-inspired Flying Robots: Experimental
Synthesis of Autonomous Indoor Flyers. EPFL Press/CRC Press.
[6] Robert Michelson ―Encyclopedia of Aerospace Engineering,‖Online © 2010 John Wiley & Sons, Ltd
[7] James Upton, ―Paper on Computing Assessment 1 on MicroAir Vehicles.‖(Page 2)
[8] C. Galiński and R. Żbikowski ―Some problems of micro airvehicles development‖, Bulletin of the Polish academy ofTechnical sciences Vol.55, No.1, 2007.
[9] ―Nano Air Vehicle‖, Defense Sciences Office, DARPA. [10] Garcia-Polanco, N. and Palencia, J., "Aerodynamic Design of a
Micro Air Vehicle: Study of Propeller-Engine Performance,"SAE Technical Paper
[11] Mike Bame, ―Paper on Micro Aerial Vehicles‖
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