CHAPTER-1

INTRODUCTION OF MICRO AIR VEHICLES

There has been recent interest in unmanned air vehicles with a largest linear dimension no

greater than 6 inch Micro air vehicles (MAVs) are intended to operate in close proximity to a

point of interest without being detected and should provide surveillance teams with critical

information in a rapid-deployment urban-environment mission scenario.

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 of

mission including reconnaissance, surveillance, targeting, tagging etc in hazardous locations

and for bio-chemical sensing in defence 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. MAVs are not the small versions of ordinary

aircrafts but are affordable fully functional, military capable, small flight vehicles in a class

of their own.

Figure 1.1: A Micro Air Vehicle (MAV) flies over a simulated Combat area during an operational test flight.[7]

The mechanism used for the flapping wing is a six-link mechanism, which is designed from

nature i.e. from the motion of the wings of a type of insect called Encarisa Formosa.

1

The advantage of this special mechanism is that, it is having more lift compared to a fixed

wing mechanism. Also it can increase the lift without increasing the vehicle speed. Since the

proposed mechanism helps for lift generation and not for the full 3-d movement this model

have not been used for more functions. The future work will be for designing for the forward

motion and also for reducing the weight by using light materials.

1.1 COMPARISON WITH OTHER AIR VEHICLE

Figure 1.2: The micro Air Vehicle Flight Regime Compared to Existing Flight Vehicles [9]

The low Reynolds number regime is significant in that it projects a fundamental shift in

physical behaviour at MAV scales and speeds - an environment more common to the smallest

birds and the largest insects. While naturalists have seriously studied bird and insect flight for

more than half a century, our basic understanding of the aerodynamics encountered here is

very limited. Neither the range - payload performance of bees and wasps nor the agility of the

dragonfly is predictable with more familiar high Reynolds number aerodynamics traditionally

used in UAV design. And if our understanding of low Reynolds number effects is limited,

our ability to mechanize flight under these conditions has been even more elusive.

2

With the small size of the MAV come high surface-to-volume ratios and severely constrained

weight and volume limitations. The technology challenge to develop and integrate all the

physical elements and components necessary to sustain this new dimension in flight will

require an unprecedented level of multi functionality among the system components. The

traditional "stuffing the shell" paradigm of conventional aircraft design is not likely to be

workable for MAVs. Yet to be developed, Micro Air Vehicles will be roughly one-tenth the

scale of the Sender, and the weight of a six-inch, fixed-wing MAV may be only 50 grams or

so, just one one-hundredth the weight of the Sender. The above figure illustrates the

difference in size. Yet MAVs must be capable of staying aloft for perhaps 20 to 60 minutes

while carrying a payload of 20 grams or less to a distance of perhaps 10 km. finding high

density sources of propulsion and power is a pivotal challenge. And while the Sender is a

conventional, moderate aspect-ratio, fixed wing aircraft, MAVs may require more unusual

configurations and approaches ranging from low aspect-ratio fixed wings to rotary wings, or

even more radical notions like flapping wings.

1.2 COMPARISON BETWEEN FIXED WING, ROTARY-WING AND

FLAPPING-WING DESIGNS

Micro air vehicles are either fixed-wing aircraft, rotary-wing aircraft (helicopter), or flapping-

wing (of which the ornithopter is a subset) designs; with each being used for different

purposes. Fixed-wing craft require higher, forward flight speeds to stay airborne, and are

therefore able to cover longer distances; however they are unable to effectively manoeuvre

inside structures such as buildings. Rotary-wing designs allow the craft to hover and move in

any direction, at the cost of requiring closer proximity for launch and recovery. Flapping-

wing-powered flight has yet to reach the same level of maturity as fixed-wing and rotary-

wing designs. However, flapping-wing designs, if fully realized, would boast a

manoeuvrability that is superior to both fixed- and rotary-wing designs due to the extremely

high wing loadings achieved via unsteady aerodynamics

1.3 PRACTICAL IMPLEMENTATIONS

The Tamkang University (TKU) in Taiwan recently (in Jan., 2010) realized automatically

control of the flight altitude of 8-gram flapping-wing MAV. The MEMS Lab in the TKU has

been developing MAVs for several years and since 3 years ago the Space and Flight

Dynamics (SFD) Lab has joined the research team for the development of autonomous flight

3

of MAVs. The MAVs developed in the TKU are 20 cm in wing span and 8 gram in weight.

Instead of traditional sensors and computational devices, which are too heavy for most

MAVs, the SFD combines stereo-vision system and ground station to control the flight

altitude. This seems to be the first flapping-wing MAV of weight under 10 grams which

realizes autonomous flight (or partly autonomous flight).

The TU Delft University in the Netherlands has developed the (in 2008) smallest ornithopter

fitted with a camera, the Delfly Micro, the third version of the Delfly project that started in

2005. This version measures 10 cm and weighs 3 grams, slightly larger (and noisier) than the

Dragonfly it was modelled after. The importance of the camera lies in remote control when it

is out of sight and eventually completely autonomous flight. This version has, however, not

yet been successfully tested outside, although it performs well indoors.

Robert Wood at Harvard University developed an even smaller ornithopter, at just 3 cm, but

this craft is not autonomous in that it gets its power through a wire and is led along a rail.

.

4

CHAPTER-2

LITERATURE REVIEW

The concept of micro-sized Unmanned Aerial Vehicles (UAVs) or micro Air Vehicles

(MAVs) has gained increasing interest over the past few years, with the principal aim of

carrying out surveillance missions. The primary payload of these tiny aircraft

(~15centimetres or 6 inches wingspan) is usually a miniature image sensor.

The history of micro air vehicles really began with the development of model airplanes in the

19th century and the development of radio controlled model airplanes in the 20 th century. The

improvement in propulsion systems from rubber bands to liquid fuel internal combustions

engines and later battery powered electric motors made it possible to produce longer and

longer flights. The development of miniature radio receivers and control components in the

1990s also had a large impact on the ability to design a very small flying vehicle. Once the

aerodynamics and control of small aircraft models with a mass less that 100 grams were

better understood, the micro-air-vehicle was born.

After the Montgolfier brothers made their first unmanned balloon flight in Paris in 1783,

experimental aviation accelerated by 1799, Sir George Cayley produced the first design for

the modern airplane configuration. Cayley tested a boy-carrying glider in 1849, and by 1853

he made a controlled flight of a man carrying glider. Cayley became known as the “Father of

Aeronautics” due to these experiments and corresponding publications. Alphonse Penaud,

another Frenchman, began selling rubber band powered pusher-propeller ready-to-fly model

airplanes in 1871. Penaud recognized that longitudinal stability was crucial. In 1879, Victor

Tatin flew a tethered monoplane model in France using a compressed air motor. Nikola

Tesla, a Serbian immigrant and inventor, allegedly arrived in New York in 1884 with plans

for a remotely controlled unmanned airplane. Fourteen years later he entered a remotely

controlled four-foot-long boat in the Electrical Exposition in Madison Square Garden. Tesla

manoeuvred his boat to stop or go, turn left or right by blinking its lights using different radio

frequencies. Before Tesla showcased his boat in Madison Square Garden, Louis Brennan, an

Irish inventor, demonstrated his wire-guided torpedo in 1888. Two decades later, Rene Lorin,

a French Artillery Officer, proposed a jet powered flying bomb that would be controlled from

a manned escort. Because of the possible military applications, a growing interest in remote

controlled vehicles emerged in a number of countries.

5

The first appearance of winged insects is shrouded in the past, but they probably took to the

air almost 350 million years ago (Wotton, 1981; Ellington, 1991a). Wingspans of the early

fossils ranged from 10 to 710 mm, and the form of the wings suggests a variety of adaptations

in flight style. The Protodonata, which were the ancestors of dragonflies, were among the

early fliers; their wings were similar enough to modern forms to suggest comparable flight

capabilities, although perhaps with less refinement. Through natural selection, the insects

have been experimenting successfully with wings, kinematics, aerodynamics, control and

sensory systems for hundreds of millions of years. Much more recently, interest has

developed in small autonomous flying vehicles, largely motive by the need for aerial

reconnaissance robots inside buildings and confined spaces. Industry, commerce and the

military have all identified potential roles for such micro-air vehicles (MAVs). Research on

MAVs is primarily conducted by aerodynamic and robotic engineers who are attempting to

improve the performance at small sizes of conventional fixed wings and rotary wings.

However, there already exists a very successful design for intelligent MAVs with much better

aerodynamic performance than conventional wings and rotors.

2.1 USAGES:

The Black Widow is the current state-of-the-art MAV and is an important benchmark. It is

the product of 4 years of research by Aerovironment and DARPA. The Black Widow has a 6-

inch wingspan and weighs roughly 56 grams. The plane has a flight range of 1.8 kilometres, a

flight endurance time of 30 minutes, and a max altitude of 769 feet. The plane carries a

surveillance camera. In addition it utilizes computer controlled systems to ease control.

Figure 2.1: Black Widow [6]

The Black Widow is made out of form; individual pieces were cut using a hot wire

mechanism with a CNC machine allowing for greater accuracy.

6

The University of Florida has been very successful over the past five years in the MAV

competitions. In 2001 they won in both the heavy lift and surveillance categories. Their plane

was constructed of a resilient plastic attached to a carbon fibre web structure. This resulted in

a crash resistant airfoil. Figure shows a picture of the University of Florida design for the

heavy lift competition.

Figure 2.2: University of Florida 2001[6]

Brigham Young University has been involved with the MAV competition for a number of

years now, and their concept has been different. They have chosen to increase the wing area

without increasing their largest dimension by making a biplane. The two wings double the

surface area without affecting the maximum dimension of the aircraft. Another technique that

was employed by the Brigham Young team was to bring multiple planes to the competition.

Figure 2.3: Brigham Young 2001[6]

7

Some of these planes were much larger than others. The idea behind this was that the large

plane could be flown to guarantee a qualification for ranking, and once that was done; they

would attempt to make their smaller planes fly for the necessary two minutes to qualify.

Figure2.4 shows some of the MAVs that were designed by Brigham Young.

Arizona State University has also been involved with the competition for a number of years.

Their design featured a simple swept, flying wing design. It also uses the COX .01 TEE-DEE

engine for thrust. The control surfaces are at the trailing edge of the wing, and it uses an

aileron system for turning. The 2001 MAV from Worcester Polytechnic Institute placed 4th

in the 2001 competition. Their plane was constructed out of a carved block of polystyrene.

The electric propulsion system, control system, and payload were stored in a rectangular

fuselage below the wing. The team also used a folding propeller to gain an advantage on its

maximum dimension. The rules have since been changed to stipulate that the largest

dimension is measured in the flight condition. There are some similarities in many of these

aircraft. Almost all of the designs use the COX .01 TEE-DEE engine. Almost all of the

designs also use a leading edge that is swept back from the propeller, which allows for a

slightly more efficient thrust from the engine, or motor.

Notre Dame’s MAV design was entered in both the heavy lift and the surveillance

competitions also. The plane was constructed out of balsa and foam. It should be noted can

also see that the design has a large fuselage, which would increase the drag greatly, however

this design also utilized the COX .01 TEE-DEE. Control was provided by an aileron/elevator

system mounted below the wing and a rudder on a vertical tail above the wing.

8

CHAPTER -3

CONSTRUCTIONS AND WORKING DETAILS

3.1 CONSTRUCTION

Thus far we have relied on an Edisonian approach to design our aircraft. No mathematical

models would have lead to the development of our new concept. In order to use this approach

we made some significant advances in the construction methods so that design iterations

could be made quickly and each design could be thoroughly tested.

Following step-by-step construction techniques used to fabricate a MAV fuselage and wing

are described here.

3.1.1 FUSELAGE CONSTRUCTION

Step1. A drawing is made of the fuselage panels to act as a guide for placement of the carbon

fibre.

Step2. The drawing is taped onto the fiat tool.

Step3. Transparent skin material (Vacuum bag material) is then placed over the drawing.

Step4. Unidirectional carbon fibre tape is cut into long narrow tacky strips.

Figure 3.1: Initial wing designs [12]

Step5. The carbon fibre strips are placed on the transparent skin material manually using the

drawing as a guide or by automated process. Multiple layers are used in places where high

stiffness is required. Overlap at the corners assures a mechanically sound joint.

9

Step6. Hinge material is placed between layers of carbon fibre at the location of the control

surfaces.

Step7. Nonporous Teflon release film is then placed over the assembly.

Step8. The assembly is then placed into a vacuum bag and subsequently into a vacuum oven

for cure.

Figure 3.2: New wing design: [12]

Step9. Aider the cure cycle is complete; the parts are removed from the bag. The fuselage

panels are then cut out.

Step10. The parts are glued together with cyanoacrylate adhesive.

Step11. Kevlar thread is used to lash the parts together. Without lashing, the glue joints

would fail.

Step12. The motor, servos, receiver, control rods and horns are installed.

3.1.2 WING CONSTRUCTION

Step1. A drawing is made of the wing plan form to act as a guide for carbon fibre placement.

Step2. The drawing is taped onto a curved tool.

Step3. A layer of nonporous Teflon release film is placed over the drawing.

Step4. Unidirectional carbon fibre tape is cut into long narrow tacky strips.

10

Step5. The carbon fibre strips are placed on the release film using the drawing as a guide.

Multiple layers are used in places where high stiffness is required. Overlap at the comers

assures a mechanically sound joint.

Step6. Nonporous Teflon release film is then placed over the assembly.

Figure 3.3: Illustration of the wing construction process. [12]

Step7. The assembly is then placed into a vacuum bag and subsequently into a vacuum oven

for cure.

Step8. After the cure cycle is complete, the carbon fibre wing skeleton in separated from the

tool.

Step9. Spray mount adhesive is applied to the skeleton.

Step10. Thin latex rubber material is then applied to the wing.

Step11. Cyanoacrylate adhesive is used to reinforce the bond line.

Step12. Excess latex rubber is trimmed away.

11

Figure 3.4: Illustration of different carbon fibre skeletons tested in flexible wing development. [12]

3.2 COMPONENT SELECTION

3.2.1 MOTOREarly on the decision was made to pursue electric propulsion over an internal combustion

engine. Preliminary calculations of fuel consumptions for the smallest available combustion

motor; furthermore, an electric solution has the weight advantage of powering all components

off one common power source. In addition, an electric motor is more reliable and does not

pose the difficulties of a moving center of gravity caused by an emptying fuel tank. Micro-

R/C motors have a larger power output than the commercial motors we considered but at the

cost of increased weight

3.2.2 BATTERIES

Most R/C vehicles use rechargeable nickel cadmium (Ni-CAD), nickel zinc (Ni-Zn), or

nickel metal hydride (Ni-MH) batteries because of their high current draw, long life and very

slight recharge memory. Rechargeable batteries are preferred for this type of application

because they are cost effective and would not need to be removed from the plane. However

these batteries are very heavy and are designed for long life. The ideal batteries would fit

completely inside the wing of the MAV. To fit inside the wing the battery would need to be

very thin, less than 8mm in one dimension. The only batteries of that size and shape did not

meet the electrical requirements of the motor. These batteries are available in 3 and 6 volts

with different sizes and capacities.

12

3.2.3 PROPELLER

(A) GEOMETRY

There are two dimensions that are used to describe propellers, diameter and pitch. These two

dimensions can be seen in Figure below. Diameter is simply the length from tip to tip of the

propeller. The pitch is the length the propeller would move forward in one revolution in an

ideal fluid. It can be explained as similar to the wavelength of a wave, the distance moved in

one cycle. The pitch of the propeller is dependent on the angle of twist of the blades on the

prop. On most propellers however the angle of the blades changes with the position on the

radius of the prop.

Figure 3.5: Schematic of Propeller Dimension [6]

(B) CHARACTERISTIC

The propeller supplies the thrust for the propulsion system. The thrust that is created by the

propeller is difficult to predict because there a several inter-related parameters that effect the

thrust. Parameters include are prop dimensions, flow speed, prop angular velocity, air

density, and prop efficiency. The equation for propeller efficiency is:

EFFICIENCY=VT/P

Where V is the plane velocity, T is the output thrust, and the P is the power output of the

motor.

13

(C) TESTING AND SELECTION

Many propellers are designed for specific motors, or rpm, while others are designed for

specific size planes. This necessitates experimental testing in selecting a prop for a plane. At

the start of the component selection process the propeller selection was driven by both the

weight and diameter, which affect the maximum dimension of the MAV. When motors were

first purchased for the MAV, several different propellers, in the correct size range, were also

purchased for testing.

3.2.4. RECEIVER

A receiver is the part of the plane that receives the information from the pilot controlled

transmitter. Receivers have an antenna attached to them and also have a power input plug and

output plugs to the servo flap controllers. The type of receiver required by the Hi-Tech

transmitter was FM channel 37. The weight was the most important parameter to the design,

providing the receiver was compatible with the transmitter. Some of these receivers have a

speed controller built into them for controlling the motor speed. Speed controllers are not

entirely necessary for a model plane but do allow the pilot to "throttle back", which can save

battery life significantly.

3.2.5 ANTENNA

The antenna that comes with a receiver is usually a 39 inch light wire antenna soldered to the

receiver. This antenna is designed to hang off the back of the plane and receive the

communications. It seemed however that this type of antenna would create a noticeable drag

force at this scale of aircraft. For that reason alternate antenna designs were researched. Upon

further reading it was found that the antenna was stiff and was 5 inches long. The normal

antenna is just a wire connected to the receiver. This antenna is simply an inductor and small

capacitor wired in parallel at the base of the wire antenna. The capacitor and coil effectively

tune the receiver to pick up a 72 MHz signal from the transmitter, at a much shorter length

than normal.

3.2.6 SERVOS

Servo motors are small electric motors that move the control surfaces of the plane. Servos are

plugged directly into the receiver, which powers and controls the servo motors. The lightest

servos found were the Wes-Technique 2.4 gram linear servo. The Wes-Technique servos

work quite well but are rather fragile. Several servos were broken during initial flight tests. A

14

3 gram model of the same design was tested as well and seemed to be much more crash

resistant that the smaller servos. The 2.4 grams servos are ideal however and will last if they

are mounted and protected adequately.

3.3 WORKING PRINCIPLE

Newton’s first law states a body at rest will remain at rest or a body in motion will continue

in straight-line motion unless subjected to an external applied force. That means, if one sees a

bend in the flow of air, or if air originally at rest is accelerated into motion, there is force

acting on it. Newton’s third law states that for every action there is an equal and opposite

reaction. As an example, an object sitting on a table exerts a force on the table (its weight)

and the table puts an equal and opposite force on the object to hold it up. In order to generate

lift a wing must do something to the air. What the wing does to the air is the action while lift

is the reaction.

Let’s compare two figures used to show streams of air (streamlines) over a wing. In figure 3.6

the air comes straight at the wing, bends around it, and then leaves straight behind the wing.

We have all seen similar pictures, even in flight manuals. But, the air leaves the wing exactly

as it appeared ahead of the wing. There is no net action on the air so there can be no lift.

Figure 3.7 shows the streamlines, as they should be drawn. The air passes over the wing and

is bent down. The bending of the air is the action. The reaction is the lift on the wing.

Figure 3.6: Common depiction of airflow over a wing. This wing has no lift. [10]

15

Figure 3.7: True airflow over a wing with lift, showing up wash and downwash. [10]

As Newton’s laws suggests, the wing must change something of the air to get lift. Changes in

the air’s momentum will result in forces on the wing. To generate lift a wing must divert air

down; lots of air.

3.3.1 FORCES ACTING ON AN AIRCRAFT

There are four forces acting on the airplane all the time during airplane is flying. The four

forces are (1) Lift, (2) Gravity force or Weight, (3) Thrust, and (4) Drag. Lift and Drag are

considered aerodynamics forces because they exist due to the movement of the Airplane

through the Air.

Figure 3.8: Forces acting on the aircraft [10]

LIFT: It is produced by a lower pressure created on the upper surface of an airplane's wings

compared to the pressure on the wing's lower surfaces, causing the wing to be lifted upward.

The special shape of the airplane wing (airfoil) is designed so that air flowing over it will

have to travel a greater distance and faster resulting in a lower pressure area (see illustration)

thus lifting the wing upward. Lift is that force which opposes the force of gravity (or weight).

Figure 3.9 Air passes through the airfoil [10]

16

Lift depends upon (1) shape of the airfoil (2) the angle of attack (3) the area of the surface

exposed to the airstream (4) the square of the air speed (5) the air density.

WEIGHT: The weight acts vertically downward from the center of gravity (CG) of the

airplane.

THRUST: It is defined as the forward direction pushing or pulling force developed by

aircraft engine. This includes reciprocating engines, turbojet engines and turboprop engines.

DRAG: It is the force which opposes the forward motion of airplane. Specifically, drag is

retarding force acting upon a body in motion through a fluid, parallel to the direction of

motion of a body. It is the friction of the air as it meets and passes over an airplane and its

components. Drag is created by air impact force, skin friction, and displacement of the air.

17

3.4 HOW TO CONTROL MICRO AIR VEHICLES

Pilot reports and video recording through a small on-board camera indicate that our flexible

wing micro air vehicles have unusually smooth flying characteristics. Most of our test flying

is done using conventional RC equipment at close range, keeping the vehicle in continuous

visual contact. Because of the small size of the vehicles, flying at distances greater than about

100 feet can quickly cause loss of orientation unless the pilot is flying by monitoring the

video output from an on-board camera. The RC transmitter produces a radio frequency signal

that causes the RC receiver carried in the vehicle to develop a series of pulses of varying

pulse widths (pulse width modulated or PWM) that are delivered to the control surface servos

as the command signals for the desired positions of these surfaces. On the equipment we use,

the pulses are generated at a constant frequency of 40 Hz. To capture this control input

information, we have developed a simple system that uses a second RC receiver on the same

RC frequency as the flight unit to monitor the pulse widths of the servo signals on the various

servo terminals on the receiver and store the data on a notebook PC. With this system, stick

input data is recorded without any contact or interference with the pilot or the micro air

vehicle and the recording can be done at any reasonable range within the operating range of

the RC system (at least 1100 meters).

18

CHAPTER-4

INTRODUCTION OF FLAPPING WING MECHANISM

When we go through the flying creatures of the nature all of them are capable of initiating lift

in flight by flapping of wings. Thus the wing flapping is a universal method of sustained

biological flight propulsion. There are flying creatures weighing up to 15 Kg, which

effectively use this wing flapping for flying. Thus the idea of adopting this feature to the

Micro Air Vehicle was a good one.

Consider the case of MAV with fixed wing and propeller. The lift for flying is created by the

airflow from the propeller of the vehicle towards the wings and the wings will support its

weight. This lift is proportional to the wing area and square of the velocity of airflow over the

wings. Smaller the linear dimension of the vehicle the less lift it can apply because the area of

the wing decreases as square of the linear dimension. One solution to counter this effect is to

increase the velocity of the vehicle. But the velocity cannot be increased in situations such as

indoor missions where a MAV makes the most sense. So for creating more lift the flapping

wings are used. By the flapping wing mechanism the vehicle can hover in the air like insects.

Only helicopter presently achieve hovering. But micro helicopters are not feasible because of

the mechanical problems of balancing them with tail and gyroscope etc.

4.1CHARACTERISTICS OF FLAPPING WING MECHANISM

In the micro air vehicles with flapping wings the lift is generated in two ways,

(1) By the air flow created by the vehicle speed.

(2) Wing flapping to support the weight of the vehicle.

So if the scale is reduced, i.e. the size of the vehicle is reduced, the frequency of beating can

be increased without affecting the minimum velocity of the vehicle. Since this design is not

affected by the scale changes the size of an air vehicle can be reduced to a size of millimetres

as observed in nature.

Another feature of this flapping-wing mechanism relates to the minimum speed of the vehicle

and the ability to perform short take offs and landings. Actually a vehicle with flapping wing

provided with enough power can take off and land vertically. So the fixed wing mechanism is

19

very limited in low speeds, thus requiring significant distance to increase its speed before

attaining flight speeds. The lift is generated in the flapping wings mainly by shedding of

vortices. Initially, as the two wings starts motion from the clap position at the back, according

to Kelvin’s circulation theorem, the net circulation around the insect body is zero. Then as the

insect beats its wings back and forth, high lift coefficient is built up due to vortices shedding

from the trailing edge to generate necessary circulation around the wings.

In ordinary insects, this build-up of high lift coefficient is delayed, because it takes some time

after flapping is initiated for the insect to attain the required velocity of wing beating and the

circulation around the wing to be developed. Hence to counter the delay, one species of

insects, Encarsia Formosa, precedes each beat with a special movement, which causes the

necessary circulation to occur immediately and avoid any delay in built up of maximum lift.

This model, named after the discoverer Weis Fogh, consists of a pure rotation, followed by a

translation and a rotation of the wings.

4.2 WIES FOGH’S 2-D MODEL

For a body starting to move in a fluid at rest retains zero circulation of fluid around it. This

retards the generation of lift on the body. But when the body brakes into two pieces, there

may be equal and opposite circulation, around these, each suitable for generating the lift

required.

Figure 4.1: Different movements of wings [4]

20

This model is based on the sequence of motions of the wings of an insect, Encarsia Formosa.

The figure given above illustrates the wings movements, which constitute the Weis Fogh

mechanism.

At certain instant in the wing flapping cycle, the insect performs a clap, i.e. both the wings

are clapped together [(a), (b)]. The two wings then starts to fling open but are still connected

to each other at the bottom so that these effectively form a single body [(c)—(e)]. Then the

wings break apart and are completely separated [(f), (g)]. When the wings break apart, the

circulation around each wing is in the opposite directions to generate enough lift. The motion

of the wings described above is not one of pure rotation, or pure translation. To generate this

class of motion accurately, multiple drives with feed back position control on each axis are

required.

4.3 FLAPPING MECHANISM

The mechanism used for flapping of the wings is a six-link mechanism. This is designed

according to the position of the wings in the Weis Fogh’s model. The positions (a), (e) and

(h) are the three main positions of the wings, on which synthesis is done by kinematic

inversion method.

This mechanism is driven by an electric motor, and the output is an extension attached to the

coupler AB.

21

4.3.1 DESIGN STEPS

The guidance mechanism is a double rocker. To power this, Weis Fogh’s mechanism using a

continuously driven motor, a crank rocker arrangement has been designed. In the figure

O3CAO2 represents the driving crank rocker arrangement, with O3C as crank and O2A the

rocker. O1BAO2 represents the rocker-rocker pair and the coupler BA has the wing attached

to it. The procedure for developing the mechanism is as follows. First the flapping

mechanism O1BAO2 is designed. For the known positions of the wing, assume positions of

fixed pivots O1 and O2. Subsequently, if a good solution is not obtained iteration with

alternate solutions are needed.

Inverting about the extended coupler (wing), the points A and B on link coupler are

determined. The links O1A and O2B are the driver and the follower of classical four-link

mechanism, respectively. The criterion for a feasible solution is that the links should be in the

range 1 cm to 4 cm for ease of manufacture and miniaturization. Hence if the criterion is not

satisfied then steps 1 and 2 are repeated until this criterion is satisfied for all the links.

Next the driving mechanism, O3CAO2 is designed. In this case the position of link O2 is

known from the design of flapping mechanism. It is also known that the link O 3 is a crank. A

position for O3 is first chosen on the bisector of the angle formed by the two extreme

positions of link O2. Iterate for some lengths of O3C, and different positions of O3. A good

design, satisfying the conditions in step 3, was obtained after six iterations.

22

CHAPTER-5

ADVANTAGES, DISADVANTAGES AND ITS APPLICATION

5.1ADVANTAGES

a) It can be packed to 1/10 of original size.

b) It has Low mass.

c) It requires Low power requirements.

d) It has High reusability.

e) Outdoor NBC emergency reconnaissance

f) It has High stability and control.

g) It has High lift and slow landing speed.

h) Direct connectivity.

i) It can be individually controlled.

j) It can be used for a wide range of new missions.

5.2 DISADVANTAGES

a) The most important problem encountered so far is the quality of images taken from

onboard TV equipment.

b) Micro air vehicles have small range of communication with controller.

c) It is very difficult to design flapping wing mechanism.

d) It is very difficult to control it in bad weather condition such as heavy rains etc.

e) It is very expensive to design micro air vehicles.

f) Lithium batteries which are generally used in MAVs are relatively expensive,

particularly with reference to the common alkaline batteries with their widespread

commercial use.

5.3 APPLICATION

In contrast to higher-level reconnaissance assets like satellites and high altitude UAVs,

MAVs will be operated by and for the individual soldier in the field as a platoon-level asset,

providing local reconnaissance or other sensor information on demand, where and when it is

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needed. MAVs may also be used for tagging, targeting, and communications, and may

eventually find application as weapons, as well. The reconnaissance application is a primary

driver behind the first generation of MAVs. Micro sensors like those mentioned earlier

suggest the possibility of reduced latency and greatly enhanced situational awareness for the

small unit or individual soldier. Additionally, the MAV's ability to operate in constrained

environments like urban canyons and, eventually, even the interior of buildings, gives these

systems a level of uniqueness unmatched by other concepts. MAVs are not replacements for

previously manned air vehicle missions; because of their size, they will be capable of

completely new missions not possible with any existing systems.

MORE ON MISSIONS

Micro Air Vehicles will be capable of a wide range of useful military missions. The one most

often identified by users is the textbook, "over the hill" reconnaissance mission illustrated in

Figure 5.1. The current concept suggests that reconnaissance MAVs need to range out to

perhaps 10 km, remain aloft for up to an hour, reach speeds of 10 to 20 m/s (22 to 45 mph),

and be capable of real time day/night imagery.

Figure 5.1: The "Over-The-Hill Reconnaissance" Mission for the MAV [8]

In contrast, some surveillance applications may require less range - payload performance. In

these instances, the MAV would relocate to a suitable vantage point and serve as a fixed,

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unattended surface sensor with capabilities ranging from imagery to seismic detection. At the

same time, MAVs must be launched and operated relatively simply with an easy-to-operate

ground station. Ground stations may employ directional antennas to maintain contact with the

MAV at long range.

In urban operations (see Figure 5.2), MAVs, acting in small, cooperative groups, will enable

reconnaissance and surveillance of inner city areas, and may serve as communication relays.

Figure 5.2: Urban Operations Missions for the MAV [8]

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, illustrated in Figure 5.3 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.

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Figure 5.3: The MAV as a Mobile Immersion Sensor [8]

MAVs may also find application in search and rescue operations. An MAV could be packed

into the ejection seat mechanism on fighter aircraft. If the pilot has to "punch out", the MAV

is released from the ejection seat and lingers in the air for up to an hour, providing the

downed pilot with reconnaissance information, or sending a signal to rescue vehicles.

A large number of potential commercial applications also exist. These include traffic

monitoring, border surveillance, fire and rescue operations, forestry, wildlife surveys, power-

line inspection and real-estate aerial photography.

5.4 FUTURE WORK

Development of a mechanism that simulates Wies Fogh’s model is the first step towards

developing an MAV. A robust model of the MAV using this concept is being fabricated to

measure the resulting lift. 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.

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CONCLUSION

Micro Air Vehicles are a class of UAVs whose time has just about come. 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. Simple flapping, which is an oscillatory

motion of the wings about a fixed axis does not generate sufficient lift. Although biological

have reported the efficiency of the Wies Fogh model the design using this model has not been

attempted so far. In the seminar, we highlight the recent research and development in

establishing a flexible-wing-based technology for MAVs. Our effort addresses the entire

scope comprehensively, including basic concept, novel fabrication approaches, aerodynamics

investigations, and flight test data. The outcome is improved understanding of the key issues

related to robust and stable flight and vehicle durability.

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REFERENCES

[1] Bret Stanford, Peter Ifju, Roberto Albertan, Wei Shyy, “Fixed Membrane Wings for

Micro Air Vehicles: Experimental Characterization, Numerical Modeling, and Tailoring”,

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

[03-09-10].

[2] Peter G.Ifju, David A. Jenkins, Scott Ettinger, Yongsheng Lian and Wei Shyy, “Flexible-

Wing-Based Micro Air Vehicles”, Department of Aerospace Engineering, Mechanics and

Engineering Science.

University of Florida, Gainesville,[03-09-10].

[3] Francis Barnhart, Michael Cuipa, Daniel Stefanik, Zachary Swick, “Micro-Aerial Vehicle

Design with Low Reynolds Number Airfoils”, 7th March 2004[28-08-10].

[4] www.wikipedia.com[28-08-10].

[5] Hundley Richard, O Gritton, Eugene C, "Future Technology-Driven Revolutions in

Military Operations”, Documented Briefing of the RAND National Defence Research

Institute, December 1992[03-09-10].

[6] James M. McMichael, Col. Michael S. Francis, “Micro Air Vehicles - Toward a New

Dimension in Flight”, Program Manager Defense Advanced Research Projects Agency

8/7/97 [29-08-10].

[7] www.Thaitechnic.com [08-09-10].

[8] Thomas J. Mueller, “On the Birth of Micro Air Vehicles”, Department of Aerospace and

Mechanical Engineering, University of Notre Dame,

Notre Dame, Indiana, USA, 46556[03-09-10].

[9] Peter G. Ifju, Scott- Ettinger, David Jenkins, and Luis Martinez, “Composite materials for

micro air vehicles”, Aerospace Engineering, Mechanics and Engineering Science Department

University of Florida, Gainesville [03-09-10].

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