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TYRE SELECTION

TYRE DESCRIPTION

The main landing gear of our aircraft is set at a camber to increase load

carrying capacity. As a result, the tires footprints can change based on the

aircrafts weight. Extreme operating parameters like these demand tires with

incredible durability.

Michelin AIR X radial tires were thus chosen as they are designed to excelunder these conditions. They offer longer life and weigh less than bias ply tires,

yet they are competitively priced.

Important Tire Features:

Advanced Rubber Compounds.

Sidewall compound provides ozone and UV protection for longer wear and

resistance to weather checking. Tread compound is optimized to provide cut

resistance and long life.

Protector Ply.

Design provides excellent cut resistance and durability for extra protection

against foreign objects.

Enhanced Belt Design.

Belt plies help stabilize the tread and dissipate heat for a longer tire life.

Advanced Radial Constructed Nylon Casing Plies.

Lightweight, yet strong nylon plies reduce heat build up, resulting in faster

turnaroundtimes between sorties.

Mass Optimized Casing Design.

Exclusive Michelin process distributes stress more evenly throughout the tire,

allowing for weight reduction.

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Streamlined Profile. Contoured

Shoulder assists in absorbing lateral impacts associated with landing, helping the

tire achieve a full life, even under extreme conditions.

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DETAILED DESIGN OF A SEGMENTEDROTORDISK BRAKE SYSTEM

Due to heavy landing loads and speeds we are using Segmented rotor brakes. They

are heavy duty brakes especially adapted for high pressure pneumatic systems. Braking can

be accomplished by means of several sets of stationary, high friction type brake linings

making contact with rotating (rotor) segments. This brake system was designed in DS

SolidWorks modeling

A segmented rotor brake is a multiple disk system. The Brake assembly consists of

1. Carrier

2. Piston

3. Pressure plate

4. Rotor disk

5. Stator disk

6. Backing plate

7. Flange bolt

8. Pusher

9. Pipe

The above parts are explained in brief.

CARRIERThe Carrier is the basic unit of the brake. It is the part which is attached to the

axle. A groove is machined on the carrier to receive the piston. Air is admitted through the

pipe attached to the outside of the carrier. Inside the pipe it consists of the pusher with a

return spring. It also consists of slots to house the pressure plate and the stator disk.

Fig. 24 Carrier Fig. 25 Pusher Fig. 26 Piston

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PRESSURE PLATE

The pressure is a flat, non rotating plate notched on the inside diameter which fits

over the slot in the carrier. It is also an auxiliary stator plate. The Brake lining is present onone side of the plate. Ceramic brake linings are used for more efficiency at higher

temperatures,noise control, increased life and better braking performance.

Fig. 27 Pressure Plate Fig. 28 Stator Disk

STATOR DISK

Stator disk also a non rotating plate notched on the inside diameter to fit on the

carrier. In this brake linings are present on both sides of the disk. The brake lining are in the

form of separate multiple circular blocks to aid the dissipation of heat. For maintaining

clearance between stator and rotor an automatic adjuster with a spring and conical pin is

provided.

ROTOR DISK

The assembly consists of two rotor disk (1) in between pressure plate and stator, (2) in

between backing plate and stator. The rotor segments are notched on the outside

circumference, so that it is keyed to the wheel and rotate with it. Many holes are provided to

aid the dissipation of heat.

Fig.29 Rotor Disk

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BACKING PLATE

It is the final unit of the assembly. It is a non rotating plate with brake linings present

on one side. It receives the ultimate force resulting from brake application, so it is provided

with the stiffeners on the outside. It is bolted to the front face of the carrier.

Fig.30 Backing Plate

OPERATION

During the application of brakes through the pneumatic system, the force first acts on

the pusher rod forcing the piston outward. In this process the spring attached to the rod get

compressed over the back face of the carrier. The piston applies the force against the pressure

plate which contacts the first rotor disk.

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This lateral movement continues till the brake linings are in contact with the rotor.

The pressure plate, stator disk and backing plate are prevented against rotation. Thus the non

rotating linings are all forced in contact with the rotors, creating enough friction to stop the

wheel, to which the rotors are keyed.

The function of the automatic adjustor is to maintain the correct friction between the

disks. When the stator is engaged with the rotor, the conical pin touches the groove in the

rotor. This process compresses the small spring in the adjuster and allows the brake lining to

touch the rotor disk.

When the pneumatic pressure in the brake is released, the return spring forces pusher

rod and piston to return to its initial position. During this process, spring in the adjuster forces

stator and pressure plate to move to its position thus maintaining the clearance between the

rotor segments.

Fig.31 Exploded view of Segmented Rotor Disk Brake System

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MATERIAL SELECTION

The general considerations guiding material selection on our aircraft are

listed in order of importance are:

1) Strength to weight ratio

2) Cost

3) Manufacturing

4) Availability

Two types of materials are used, metal alloys and composites. The metals will be

used in low load areas where large amounts of material are required such as

frames, bulkheads, ribs and the fuselage skin. This is due to the higher

availability of metals compared to composites, as well as easing manufacturing

costs. Composites are used in the high load areas in the wings, control surfaces,

and longerons.

COMPOSITES

Aluminium 7075 was also considered for low stress areas. High stress

areas require materials such as fibre based composites with either a

thermoplastic or thermoset matrix. The wing of the aircraft needs very high

strength components, so varieties of composites are considered. The materials

considered for the spar are listed below. The skin is made out of Hexcel with a

high temp thermoplastic matrix with a honeycomb core. The thermoplastic

Celazole Polybenzimidazole or PBI is used as the matrix material in high heat

areas because it can withstand 580F for over 20000 hours before degrading.

The material properties can be seen below. The wing spars use Spectra 1000 as

the fibre as it has a higher specific strength compared to Hexcel. The matrix

material for the Spectra 1000 parts is RTP 3000, a low temperature matrix

material that has a mould temperature below the critical temperature of 147Cof Spectra 1000. The spars also contain a honeycomb core to prevent buckling of

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the load carrying Spectra by increasing the stiffness and increasing the strength.

The core increases the strength up to 9 times the strength of the panel and up to

37 times the stiffness, if the core is 4 times the plates thickness. The

honeycomb used is aluminium based material because it has the highest

strength to weight ratio.

Other areas that use composites are the longerons and control surfaces.

The forward fuselage longerons are made of Spectra fibres and the rear

longerons are made of Hexcel. The Hexcel is required for the rear longerons as

they undergo the heat produced by the engine. The control surfaces are made of

a Hexcel based skin, and have a honeycomb core. To assemble the composite

sections, thermoplastic flanges will be attached to the bulkheads. The

thermoplastic of flange and adjoining piece can then be heated locally to bond

the flange and adjoining piece together.

Composite comparisons

Thermoplastics used and their properties.

METALS

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Composites arent the only materials integrated in our aircraft. While

composites represent 50 percent by weight (80 percent by volume) of the

structure, other materials represented are aluminium ( 20 percent); titanium( 15

percent); steel (10 percent) and others(5 percent). Most notable among the

other is the first-time widespread use in aircraft structures of plastic heat

sinks. Plastics that are highly loaded with heat-removing materials such as

carbon or ceramics have been around for a while, but have not yet penetrated

the aircraft market. Their great advantage is their ability to be moulded into net

shapes. The economics for plastics can be favourable depending on total tooling

and finishing costs. They can be designed with additional surface areas as fins

and ribs to improve convective heat transfer.

Costs and properties can be balanced depending on which engineering

thermoplastics are used. For example, nylon can improve economics while liquid

crystal polymer can improve properties. They are typically loaded 30 to 40

percent with thermally conductive materials.

Metals such as aluminium are a staple in aircraft structures. Aluminium is

a material with strength to weight ratio better than steel and is much cheaper

than composites. Stainless steel is a very high strength material and has very

good high temperature properties, so it will be used around the engine to shieldthe composite longerons from the extreme engine heat. Aluminium lithium is

lighter than typical 7075 aluminium and will therefore be used in the high load

bulkheads where the weight savings over aluminium 7075 would be the greatest.

Aluminium lithium is also used for the skin of the fuselage and tails for the same

reason. Aluminium 7075 is acceptable for the frames.

Aluminum alloy comparisons

Other new materials highlighted on the ground-breaking aircraft are:

Titanium: The aircraft will be the first big user of a new advanced alloy from

titanium in the aircraft industry. The new grade, designated 5553 (Ti-5Al-5V-5Mo-

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3Cr), supersedes another high-strength alloy, 1023 (Ti-10V-2Fe-3Al). Typically,

titanium has been used in engine applications for rotors, compressor blades,

hydraulic system components and nacelles.

Aluminium: New technologies are emerging for extrusions in plates in aluminium-lithium alloys that finds its application in our aircraft. Its well known that

aluminium-lithium alloys have lower density, good and often higher strength

than conventional aluminium alloys, and provide higher modulus, and therefore,

enable weight savings.

Thermally conductive plastics offer significant improvements over

conventional plastics.

CONCLUSION

The requirements for the design of six seater trainer aircraft are immense.

We have continued our work form ADP-I and we have successfully managed to

tweak our design further. The structural analysis of the aircraft members carried

out has yielded acceptable results. Apart from the structural analysis, the

landing gear positioning and retraction mechanisms were also analysed.

The flight envelope of our aircraft was also defined and was found again to

be within acceptable limits. To increase the lifespan of our aircraft, we have gone

in for a composite material structure, as they have the distinct advantage of not

failing easily under the action of high stress and temperatures, thereby making

our structure strong and efficient. We have utilized the best hardware and

software available on our aircraft. Our design is damage tolerant in nature. This

is proved by the fact that we are using composite structures and added features

such as self sealing fuel tanks, redundant flight control computers etc

The ability to blend modern technology along with proven techniques and

applied on an efficient platform allowed for the creation of a trainer aircraft

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which would definitely be an invaluable asset to any countrys offensive and

defensive aerial capabilities to produce very efficient pilots.

BIBLIOGRAPHY

1. Introduction to Flight by J.D.Anderson, Tata McGraw-Hill Publishing Company

Limited, Edition 2007.

2. Aerodynamics by Clancy, This edition Longman Group UK Limited 1996

3. Fundamentals of Aerodynamics by J.D.Anderson, Tata McGraw-Hill Publishing

Company Limited, Edition 2007.

4. The Design of the Aeroplane by Darrol Stinton

5. Preliminary sizing of airplanes by Dr. Jan Roskam, Roskam Aviation and Engineering

Corporation, 1985.

6. Janes All the Worlds Aircraft

7. Aircraft Design: A Conceptual Approach by Daniel. P. Raymer, Americal Institute Of

Aeronautics and Astronautics, Inc.370 LEnfant Promenade, S.W., Washington,

D.C.2002

WEBSITE REFERENCES

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1. www.wikipedia.org

2. www.naca/aerofoil.gov

3. www.worldaircraftdierctory.com

4. www.airfoilinvestigationdatabase.com

5. www.lockheedmartin.com

6. www.airliners.net

7. And other websites related to design of aircrafts.