synopsy landing gear

8/4/2019 Synopsy Landing Gear

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INTRODUCTION

The landing gear of the very first airplanes was not

very complex. Specially designed landing gear and wheels

that absorbed the extreme loads imparted during takeoffs

and landings. In addition, braking systems were installed to

provide safer and more efficient control for solving an

airplane after landing. In later years, as aircraft designs

improved to flight to reduce aerodynamic loads, or drag.

With continued improvements in technology, landing gear

systems on modern aircraft are highly reliable and capable

of handling extreme conditions, enabling safe transitions

between flight and ground mobility.

Landing gear designs for aircraft vary from simple,

fixed arrangements to very complex retractable systems

involving many hundreds of parts.


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LANDING GEAR MECHANISM


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LANDING GEAR METHODOLOGY

One type of retractable main landing gear is

illustrated in the figure. The assembly consists principallyof the shock strut; the wheel; the brake assembly, the

trunnion, and side brace; the torque link, or scissors; the

actuating cylinder, the down-and-up locks; and the bungee

system.

To retract the gear, the actuating cylinder is

extended by hydraulic pressure. Since the actuatingcylinder can provide greater force during extension of the

cylinder than it can during retraction because of the greater

piston area exposed to fluid pressure, the extension

movement of the actuating cylinder is used to retract the

gear. Retraction of the gear requires greater force because

of gravity. Extension of the actuating cylinder causes the

gear to rotate on the trunnion pin until the gear is

approximately in a horizontal position. When the gear

reaches the full UP position, a pin on the strut engages the

UP latch and locks the gear in the UP position.

When the gear is extended, the first movement

of the actuating cylinder releases the UP lock. This permits

the gear to fall of its own weight, and the actuating cylinder

acts to snub the rate of fall. Usually there is an orifice checkvalve in the Up line of the landing-gear hydraulic system;

this restricts the fluid flow from the actuating cylinder to

the return line, thus slowing the rate of gear


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descent. As the gear approaches the DOWN position, the

actuating cylinder moves it to the full DOWN position. In

the DOWN position, a blade engages the DOWN-LOCKtrack and slides into the DOWN lock latch as shown in the

figure. The DOWN lock prevents the gear from retracting

after it has been lowered.

The landing gear shown in the figure is

equipped with pneumatic bungee system for emergency

operation. The purpose of the system is to provide air or gas

pressure to lower the gear in the event of hydraulic powerfailure. The bungee tank is charged with air or gas at a high

pressure, and when it becomes necessary to lower the gear

in an emergency, the air or gas is released from the tank by

means of a valve and is carried through tubing to a special

bungee cylinder. This cylinder provides enough force to

lock the gear in the DOWN position. In many systems, the

air or gas I directed to a shuttle valve, which blocks off thehydraulic system and opens the DOWN line to the main-

landing gear actuating cylinder, which then lowers and

locks the gear. In any case, the landing-gear control handle

must be placed in the DOWN position.


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LITERATURE SURVEY OF THE

LANDING GEAR

The landing gear of an airplane serves a

number of very important functions and is classified

by a number of different characteristics. It supports the

airplane during ground operations, dampens vibrations

when the airplane is being taxied or towed, and

cushions the landing impact. The landing of an

airplane often involves stresses far in excess of what

may be considered normal; therefore, the landing gearmust be constructed and maintained in a manner that

provides the strength and reliability needed to meet all

probable landing gear.

The landing gear of an airplane consists

of main and auxiliary units, either of which may be

fixed or retractable. The main landing gear providesthe main support of the airplane on land or water. It

may include a combination of wheels, floats, skis,

shock-absorbing equipment, brakes, retracting

mechanism, controls, warning devices, cowling,

fairing, and structural members needed for attachment

to the primary structure of the airplane.

The auxiliary landing gear consists of

tail or nose landing-wheel installations, skids,

outboard pontoons, etc., with the necessary cowling

and reinforcements.


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Large Aircraft Retraction Systems

The actual system for retracting and extending

the landing gear on large aircraft is similar to that just

described. However, there are several additional features

and component used because of the size and complexity

of the system.

Normally, large aircraft have wheel-well doors

that are closed at all times the landing gear is not actuallymoving up or down. Sequence values are used in the

system to ensure the doors are opened before the landing.

Most large aircraft use mechanical locks to hold

the landing gear in its UP or DOWN position. There

must be a provision in those systems for the hydraulic

pressure to release the locks before fluid is directed intothe actuating cylinders.

Most of the large aircraft landing-gear systems

use an orifice check valve in the fluid lines to the

actuators. The weight of the landing gear dropping out of

the wheel well could cause it to fall so fast that damage

to the structure is a possibility. Therefore, the return flow

from the actuator is restricted which preventsuncontrolled free fall. Unrestricted flow, however, is

allowed into and of the actuator when the gear is being

retracted.


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FISIBILITY STUDY


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DC GEARED MOTOR


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DESIGN OF LANDING GEAR

MOTOR

Power of motor = H.P = 746 x .25 = 186.5 N- m /s

Rpm of motor = 1800 rpm

Out put rpm required = 24rpm

Load of system = 100 kg = 100 x 9.81 = 981 N

Max load at landing = 120kg = 120x 9.81 = 1177 N

Number of stage in gear box = 2Ratio of gearing =1: 74.8

CALCULATION FO FINAL SPEED & TORQUE OF

JACK

Power of motor = P = 186.5 watt.

2 N T

P = -----------------

60

Where, N Rpm of motor = 1800

T = torque transmitted


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2 x 1800 x T

186.5 = ----------------------

60

T = 0.989N-m

T = 989.9 N-mm

T = 990 N-mm

CALCULATION OF TORQUE OBTAIN

BY GEAR BOX

In put torque of gear box = 990 N- mm

In put rpm of gear box = 1800 rpm

Torque & rpm obtain at gearing

1800 rpm

Main

motor shaft

N = 8

spiral

81 rpm

Worm

wheel out

put

N = 44

teeth

D = 46

mm


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As reduction ratio is 1:22

So,

Out put rpm of gearbox is

N 2 = N 1 / 22

1800N 2 =

22

N 2 = 81.8 rpm

N 2 = 82 rpm

TORQUE AT GEAR BOX OUT PUT

N 1 T 2

=

N 2 T 1

1800 X=

82 990


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X = 1800* 990

82

X = 21731 N-mmT2 = 21731N-mm

Load of system = 100 kg = 100 x 9.81 = 981 N

Max load at landing = 120kg = 120x 9.81 = 1177 N

TOTAL LOAD = 981 + 1177 = 2158 N

We know T = F x R

So

21731 = F x 46 / 2

F = 21731 x 2 \ 46

F = 944.8 N

F = 945 / 9.81 = 96 kg

As out put of gearing system is insufficient to lift the total

load of 300 kg so further more speed reduction is required

to increase the torque value.


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We use spur gearing having reduction ratio = 1: 3.4

So torque at out put speed of spur gearing

As reduction ratio is 1:3.4

N 2 = N 1 / 3.4

82N 2 =

3. 4

N 2 = 24.1 rpm

N 2 = 24 rpm

TORQUE AT GEAR BOX

OUT PUT

N 1 T 2

=

N 2 T 1

D=60 mm

N = 34 D=16m

N = 10


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82 X=

24 21731

X = 82 x 21731

24

X = 74247.58 N-mm

T2 = 74248 N-mm

Torque = force x distance

Torque = force x radius of out put gear

74248 = F x 60 /2

F = 74248 x 2 / 60

F = 2474.59 N

F = 2475 N

F = 2475 / 9.81 = 252.2 kg

F = 252 kg

This Force Value Is Sufficient To Lift construction Body

So Transmission Is Safe.


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FORCE REQUIRED FOR LANDING

MECHANISM Fr = 220 kg

SO OUTPUT FORCE OF SYSTEMFs= 252 kg

Fr < Fs

As out put force is more than required force value so design

of transmission system is safe.


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OBJECTIVE LANDING GEARSYSTEM

One of four methods is used to extent the landing

gear if hydraulic power is lost, preventing hydraulic

extension of the landing gear.

1. Some aircraft make use of an air bottle to blow thegear down, substituting air pressure for hydraulic

pressure. This pneumatic extension has the

disadvantages that the system must be bled of all air

before being returned to service.

2. Some aircraft make use of mechanical system, where

the operation of a hand crank or ratchet performs the

extension operation.

3. Other aircraft have a separate hydraulic system,

powered by various methods, including a hand pump,

to extension the gear.

4. The fourth method of emergency extension that

appears to be becoming very popular for aircraft is theuse of a mechanical system to release the UP locks,

allowing the gear to free fall into the down-and-locked

position.


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Here we use simple and reliable landing gearing

mechanism using lead screw mechanism in which the

action of hydraulic cylinder is done by dc powered motorand lead screw mechanism. As if any where in system

leakage is done causes presser drop in system that pressure

drop is in put signal to motorize mechanism and it operate

the landing wheel out as and when required.

synopsy landing gear

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