Lesson 8: Landing Gear Type and Configurations

 Landing Gear Type and Configurations

Landing Gear Type and Configurations


Landing gear provides support and directional control of the aircraft while on the ground, and is a means for the aircraft to transition from the ground to the air. During landing and taxiing, the gear will provide a cushion effect that absorbs shock. A landing gear assembly consists of a shock strut, actuating cylinders, side and drag brace, torque links, and a wheel and brake assembly. When the landing gear is retracted during flight, drag is reduced. On most aircraft, the landing gear will be enclosed in an opening either in the nacelle, fuselage, or wings, and streamlined with doors.

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Click here for the previous lessons, to learn about: Principle of Airframe; Principles of Aerodynamics; Airfoil Characteristics; Primary Flight Control Surfaces; Description and Operation of Helicopter; Miscellaneous Components of an Aircraft…

Points discussed:

Landing gear type and configurations, bicycle landing gear,  modified tricycle landing gear,  quadra-cycle landing gear, shock strut of landing gear, shock strut shock strut, Trunnion of landing gear, nose landing gear, torque links of landing gear, steering system of landing gear, nose wheel steering switch, rudder pedals/steering wheel, centering cams/motors, type of wheels, wheel markings, torquing instructions, arresting systems, drag chute,

 Start from Lesson 1: Principle of Airframe

Go to Lesson 2 : PRINCIPLES OF AERODYNAMICS

Go to Lesson 3 : AIRFOIL CHARACTERISTICS

BICYCLE Landing Gear,

The bicycle type landing gear, figure 1-37, consists of a main gear mounted in the forward fuselage and a second steerable main gear in the aft fuselage. Outriggers or wing tip protection gears may be provided to support and balance the aircraft wings during takeoff, landing and ground operations.

 

BICYCLE Landing Gear,

Figure 1-37, Bicycle Type Landing Gear

TRICYCLE. The most common type of landing gear pattern is the tricycle type. Figure 1-38. This arrangement consists of a nose landing gear and two main landing gears. The main landing gears are located slightly aft of the center of gravity (the forward and aft balance point of the aircraft). The distance between the main landing gears will vary with the size of the fuselage and wings.

 

Tricycle Type Landing Gear

Figure 1-38, Tricycle Type Landing Gear

 MODIFIED TRICYCLE Landing Gear,

The C–5 landing gear is a fully retractable modified tricycle type with four main landing gear shock struts with six wheels mounted on bogie type units that retract into pods on each side of the aircraft. Figure 1-39. The nose gear is a four-wheel steerable unit, which retracts aft into the fuselage nose wheel well.

 

Modified Tricycle Type Landing Gear

 Figure 1-39, Modified Tricycle Type Landing Gear

 QUADRA-CYCLE LANDING GEAR,

The quadra-cycle landing gear, Figure 1- 40, is used on the B–52 aircraft. It consists of four main gears mounted in the fuselage in the form of a rectangle and two outriggers or wing tip protection gears, as shown. The wing tip protection gear is located near the outboard end of each wing to provide lateral stability.

 The quadra-cycle landing gear retracts into the fuselage, which allows the use of a thinner wing design and results in greater speeds.

Quadra-cycle Landing Gear


Figure 1-40, Quadra-cycle Landing Gear

Aircraft Shock struts:

SHOCK STRUT of Landing Gear,

 The purpose of the shock strut is to absorb shock during take off, landing, and ground operation. The shock strut is a pneudraulic unit that consists of several components. Each component serves a specific purpose. Refer to Figure 1-41 as we discuss each of these components.

OUTER AND INNER CYLINDER of Landing Gear,

The inner cylinder or piston is on the lower part of the strut and the axle is at the lowest point. The inner cylinder slides inside the outer cylinder to give the desired shock absorbing qualities. This shock strut is serviced with hydraulic fluid and nitrogen or dry air. A set of seals at the lower part of the outer cylinder keeps the unit from leaking oil or the air charge.

 

aircraft shock strut assembly

Figure 1-41, Shock Strut

TRUNNION of Landing Gear,

 At the top of the outer cylinder is the trunnion. Figure 1-42. This is the point at which the landing gear is attached to the aircraft structure. It is also the pivot point for extending and retracting the landing gear.

 

Landing Gear Trunnion

Figure 1-42, Landing Gear Trunnion

Nose landing gear

TORQUE LINKS of Landing Gear,

TORQUE LINKS of Landing Gear


 The torque links are attached at the base of the outer cylinder and just above the axle on the inner cylinder. The torque links are hinged in the middle and at their attaching points. This allows the inner and outer cylinder to telescope. Torque links also keep the inner cylinder from rotating or spinning.

STEERING SYSTEM of Landing Gear,

STEERING SYSTEM of Landing Gear,


 Most aircraft have steerable nose wheels. Nose wheel steering provides a means of directional control when the aircraft is taxiing, during takeoff and on landing roll. Certain conditions must be present for nose wheel steering to operate. There must be DC electrical power, hydraulic pressure, and the ground safety switch must be closed.

NOSE WHEEL STEERING SWITCH,

NOSE WHEEL STEERING SWITCH


 To energize the nose wheel steering system on some fighter aircraft, the nose wheel steering switch must be depressed, opening a solenoid controlled shutoff valve. This switch is located on the control stick grip. On most heavy type aircraft, the nose wheel steering is automatically engaged when weight is on the landing gear or when the landing gear is down and locked.

RUDDER PEDALS/STEERING WHEEL,

RUDDER PEDALS/STEERING WHEEL


 On fighter type aircraft the rudder pedals allow the pilot to select the direction and degree of travel. The rudder pedals are connected to the nose gear steering system by mechanical linkage and electrical circuits. These allow the steering power unit/servo valve to control nose wheel steering.  On many large aircraft, the nose wheel steering system is controlled by a steering wheel located to the left and forward of the pilot. The steering wheel controls the direction and degree of travel of the nose wheel. When small amounts of movement are required for corrections on takeoff and landing, the rudder pedals will give the pilot up to 8° of steering. This minor amount of steering aids in high speed ground movement because the normal steering wheel control could easily over control the aircraft.

CENTERING CAMS/MOTORS,

One notable difference between main and nose gear shock struts is the centering device found in nose struts. Two types of centering devices are shown in Figures 1-43 and 1-44. The upper cam is attached to the top of the piston (inner cylinder), and the lower cam is connected to the inside bottom of the outer cylinder. When the weight of the aircraft is removed from the gear, the shock strut piston extends and forces the upper cam into the lower cam. The seating of the two cams aligns the wheel for proper retraction into the wheel well. When the weight of the aircraft is on the gear, the upper cam is unseated from the lower cam and the wheel is free to swivel.

 

Figure 1-42, Figure 1-43,

 V Type Centering Device Nose Strut, Centering  (Cam and Lobe Type)

Wheels/Tires,

TYPE OF WHEELS,

One type of aircraft wheel is the split type wheel mostly used on large aircraft. This type of wheel is in two halves and it is bolted together. When bolted together both halves must have identical part numbers and manufacturer. The second type of aircraft wheel used is the split rim (removable flange) wheel; this is primarily used on fighters. The flange portion of the wheel is held on with a locking ring, this type of wheel is faster in changing out the rubber (tire), making it go back into service faster. Aircraft wheels are usually made of aluminum, magnesium, or steel alloy. These materials are susceptible to corrosion. To help reduce corrosion and failure, all aircraft wheels will be cleaned, inspected and repaired. This maintenance will be accomplished at the time of tire change.

WHEEL MARKINGS,

On each wheel there are markings very much like those on a tire. Each wheel is made for a specific type of tire. Each half of a split wheel has a part number and manufacturer stamped on it. Wheel halves must be matched with respect to wheel part number and manufacturer when assembled.

• Size. The wheel size is stamped on each half of the split wheel.

• Serial Number. Each wheel half has a serial number stamped on it. This number will be used when turning in the wheel after a wheel and tire change

• Disassembly Warning. A warning is stamped on the wheel which reads: Deflate tire before loosening tie bolts. The tie bolts hold the wheel halves together on a split wheel. If tie bolts are loosened before the tire is deflated, the wheel and tire may explode.

• Torquing Instructions,

The tire shop puts the wheel halves together. The bolts must be torqued in a specific way and to a specific torque. These instructions are stamped on the wheel.

TIRE SHOP,

The tire shop is where the tires and wheels are put together and inflated. A modern tire shop uses pneumatic tools for disassembly an reassembly of the wheels. The tire shop will also have vats of solvent for cleaning the used parts. This is so a through inspection can be made to determine if the part can be reused.

Arresting Systems,

aircraft arresting systems


Arresting gear is usually installed on fighter type aircraft. The arresting gear is made to stop the aircraft on the runway in case of an emergency. The arresting gear is located underneath and at the rear of the aircraft. DO NOT walk or crawl under the arresting gear. This is a very dangerous area and can cause serious injury or death. Always make sure the arresting gear is safely pinned when the aircraft is stationary.

DRAG CHUTE,

drag chute aircraft


With high landing speeds, drag chutes are often installed to assist the aircraft braking system. These drag chutes allow aircraft to land on shorter runways at higher speeds and weights.