Landing Gear

SEMINAR ON LANDING GEAR PRESENTED BY ABHIJITH.VP REGNO:13021896

INTRODUCTION 

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Aircraft landing gear supports the entire weight of an aircraft during landing and ground operations. They are attached to primary structural members of the aircraft. For snow it will be skis type For water it may of pontoon type For ground and water An amphibious aircraft with retractable wheels

Purpose of Landing Gear To provides structural support to the aircraft for ground operation  To provides maneuverability for ground operation  To provides a mean to absorb unusually loads incurred during landing and ground operation 

TYPES OF LANDING GEAR ARRANGEMENT A. B. C.

Tail wheel type (Conventional) Tandem loading gear (longitudinally Aligned) Tricycle type landing gear

Fixed Landing Gear- A gear is attached to the airframe and remains exposed to the slip stream as the air craft is flown.

Retraction Type – Stowed in fuselage or wing compartments while in flight . As speed of aircraft increases the drag caused by the landing gear becomes Greater and a means to retract the gear to eliminate parasite drag is required.

Shock Absorbing-The shock energy is altered and transferred throughout the airframe at a different rate and time than the single strong pulse of impact. Non Shock Absorbing- The shock is absorbed by converting the energy into heat energy.

Design considerations       

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Maximum strength Minimum weight High reliability Overall aircraft integration Low cost Airfield compatibility Landing Gear should locate near the center gravity (CG) of the plane CG location are depended on aircraft configuration, loading, fuel state

CONSTRUCTION

Typical Landing Gear Arrangement It consists of an upper and lower link hinged at the centre that permits the brace to jackknif0e during retraction of the gear.  The upper end pivots on a trunnion attached to structure in the wheel well overhead. The lower end is attached to the shock strut.

A locking link is incorporated between the upper end of the shock strut and the lower drag link.  This locks the gear securely in the down position to prevent collapse of the gear.  To adjust the over-centre position of the side brace locking link, the aircraft must be placed on jacks. With the landing gear in the down position, the lock link end fitting is adjusted so that the side brace links are held firmly over - centre.

Landing Gear Alignment ,Support and Retraction Components of a LGS ,Typically these are the torque links, trunion and bracket arrangements, drag strut linkages, electrical and hydraulic gear retraction devices, as well as locking, sensing, and indicating components.

Alignment This is set by the manufacturer and only requires occasional attention such as after a hard landing. The aircraft’s main wheels must be inspected and adjusted, if necessary, to maintain the proper tow-in or tow-out and the correct camber. Tow-in and tow-out refer to the path a main wheel would take in relation to the airframe longitudinal axis or centreline if the wheel was free to roll forward. Three possibilities exist. The wheel would roll either:

eel alignment on an aircraft a) Parallel to the longitudinal axis (aligned) b) Converge on the longitudinal axis (tow-in) c) Veer away from the longitudinal axis (tow-out)

Support  Aircraft landing gear are attached to the wing spars or other structural members.  Retractable gear must be engineered in such a way as to provide strong attachment to the aircraft and still be able to move into a recess or well when stowed. The trunion is a fixed structural extension of the upper strut cylinder with bearing surfaces that allow the entire gear assembly to move.

Retraction Systems

The simplest contains a lever in the flight deck mechanically linked to the gear. Through mechanical advantage, the pilot extends and retracts the landing gear by operating the lever. Use of a roller chain, sprockets, and a hand crank to decrease the required force.  To decrease drag in flight some undercarriages retract into the wings and/or fuselage with wheels flush against the surface or concealed behind doors; this is called retractable gear.

Air Craft Brakes  The brakes slow the aircraft and stop it in a reasonable amount of time. They hold the aircraft stationary during engine run-up and, in many cases, steer the aircraft during taxi.  On most aircraft, each of the main wheels is equipped with a brake unit.  The nose wheel may have or may not have a brake. In the typical brake system, mechanical and/or hydraulic linkages to the rudder pedals allow the pilot to control the brakes. Brakes principle is the conversion of kinetic energy of motion into heat energy through the creation of friction.

Types of Brakes 1. Single Disc Brakes or Floating Disc Brakes 2. Dual Disc Brake 3. Segment Rotor Disc Brakes 4. Carbon Disc Brakes 5. Expander Tube Disc brakes 6. Boosted brakes 7. Power Brakes A cross-sectional view of a Goodyear single-disc brake calliper illustrates the adjusting pin assembly that doubles as a wear indicator.

Landing Gear Developments Noise Reduction 

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As engines become quieter, landing gear is now making a dominating component of noise in large commercial aircraft European co-financed research project Silencer is trying to create low noise landing gear design Desires 10db reduction in landing gear noise by 2020, has only dropped 3db so far

Gear up landing prevention system 

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NTSB reports that the majority of gear up landings are due to equipment malfunctions. Gear up landing prevention systems will disengage autopilot and alarm at a preset safety altitude if every piece of landing gear is not extended and locked. It can be disengaged if a belly landing is the only option.

Materials 

Composites will be integrated into gear because they are stronger and cheaper than the current used high strength steels and titanium

Materials 

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Ultra-High Tensile Steels are already being integrated into the A400M and the B-787 landing gear, replacing the low-alloy steels. Research into organic matrix composites and metal matrix composites using titanium are promising, though still very expensive.

Corrosion - Many modern aircraft have cadmium in the landing gear to prevent corrosion and chrome plating to reduce friction wear. - Advancements in stainless steels and titanium will replace the cadmium in landing gear.

ANTISKID SYSTEM 

Antiskid system is a feature found in high performance aircraft braking system. It is important because if a wheel goes into skid, its braking value is greatly reduced.

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The skid control system performs four functions: i) normal skid control, ii) locked wheel skid control, iii) touchdown protection and iv) fail-safe protection.

Normal Skid Control 

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It comes into play when wheel rotation slows down but has not come to a stop. When this slowing down happens, the wheel sliding action has just begun and not reached a full scale slide. In this situation the skid control valve removes some of the hydraulic pressure to the wheel, which permits the wheel to rotate a little faster and stop its sliding. The skid detection and control of each wheel is completely independent of the others.

Touchdown Protection The touchdown protection circuit prevents the brakes from being applied during the landing approach even if the brake pedals are depressed.  This prevents the wheels from being locked when they contact the runway.  Two conditions must exist before the skid control valves permit brake application: i) The squat switch must signal that the weight of the aircraft is on the wheels. ii) The wheel generators sense a wheel speed over 15-20 mph. 

Fail-safe Protection The fail-safe protection circuit monitors operation of the skid control system. It automatically returns the brake system to full manual in case of system failure. It also turns on a warning light.