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UNMANNED AIR VEHICLEMICRO AIR VEHICLES

Abhishek K V

3rd 

SEM, Department of Mechanical Engineering,

 REVA ITM, Bangaloreabhishek.spacescience65@gmail.com 

Ajay T S

3rd 

SEM, Department of Mechanical Engineering, REVA ITM, Bangaloreajayts54@gmail.com

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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