Post on 07-Apr-2018
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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.