Types Of Landing Gears

The various types of landing gear are dependent on the design and manufacture of the undercarriage units, 

The main type of landing gear for aircraft over 5700 Kg is termed the TRICYCLE UNDERCARRIAGE.

The tricycle undercarriage landing gear comprises two main undercarriage units and one nose undercarriage unit.  However, there are THREE main variations of the tricycle undercarriage as follows:

Standard (Boeing 737)

·         Two main undercarriage units
·         One nose undercarriage unit

Centreline (Airbus A340)

·         Two main undercarriage units
·         One center-line undercarriage unit
·         One nose undercarriage unit

Wing/Body (Boeing 747)

·         Two main (outer) wing mounted, undercarriage units
·         Two main (inner) body mounted, undercarriage units
·         One nose undercarriage unit

Solid Rivets

In the construction of a metal air frame, permanent joints are made either with rivets or bolts. To securely attach structures together, rivets are cheaper to use, lighter and more rapidly fitted than nuts and bolts, but in the case of power operated machine riveting, more extensive equipment is usually required to make the permanent joints.

Solid rivets have the greatest strength and are therefore preferable to any other type of rivet, but they can only be used where there is access to both sides of the structure.

Rivets are always supplied to the operator with one head already formed and the shank plain to permit insertion into the hole, the opposite end being formed into a head by manual or mechanical means. The size of a rivet is expressed as the diameter and length of its shank; the exception is the countersunk rivet where the length is inclusive of the head

1. SNAP HEAD : for general purposes where strength is required but not a streamline finish.
2. MUSHROOM HEAD: for skin covering to give maximum strength.
3. FLAT HEAD: for internal work where heads are not easily accessible
4. COUNTERSUNK:  for flush finish (90°, 100°, 120° head) in aviation mostly used 100°
5. RAISED COUNTERSUNK : for more streamlined surfaces.
6. UNIVERSAL HEAD
7. 100° COUNTERSUNK TRUNCATED RADIUS HEAD:  

Ball Bearings

These bearings are used where it is not practical to use plain bearings, and where a high degree of reliability and precision is required.

The advantages are:

·         Low frictional losses

·         Wide range of loads may be accepted

·         Simple lubrication requirements

Ball Bearings

The most common type of bearing used on aircraft.  The ball bearing has many variations in design allowing it to be used in a wide variety of situations/

They carry radial loads and moderate axial loads in both directions and where a high axial load may be experienced, the balls run in a deep groove in the races.Two types of ball bearings are in general use.  The caged type and the crowded type.

Caged Ball Bearings

In general use, for engine applications and for equipment with rotational speeds in excess of 100 rpm.  When used within engine/gearbox casings they are lubricated with engine oil supplied by jets or by splash.  When used outside casings, they are lubricated by the application of grease which may be applied at specified intervals by grease gun, or may be of the pre-packed type where lubricating grease is packed and sealed into the bearing on assembly.

Crowded Ball Bearings

This bearing has filling slots in one or both races and has no cage or separators.  The balls therefore touch each other during operation, hence the term ‘crowded’.  They are suitable only where slow rotation or part rotation (oscillations) are found, and are usually of the sealed or pre-packed type.

Angular Contact Ball Bearings

Accept radial loads, and axial loads in one direction where a single bearing may be used.  For axial loads in both directions  an opposed pair of bearings is often used.