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.

Thrust Reversers

There will be cases when the aircraft is required to land on runways that are shorter than those for which the aircraft can normally land.  It is also beneficial to use less runway than that available in order to have a safety margin in the event of a failure.  Although the brakes on the aircraft are designed to be adequate under all normal operating conditions, the engine can assist in shortening the landing distance by using the thrust reversal systems.In this system the engine thurst is vectored to the front to slow down the aircraft.

On a propeller engine this is very simply done by reversing the pitch of the propeller blades so that they now thrust air forward instead of backwards. Therefore the prop aircraft can change the direction of thrust by 180 degrees. But, This is impossible to achieve with a jet engine, The result of this is that the reversed thrust from a jet engine can never be as fully effective as that from a propeller.  The thrust level obtained from the engine can be as high in reverse as it is in forward thrust but, because of the angle involved, the effect can never be the same as the forward thrust.

types of reversers

As far as jet engines are concerned there are three basic types of thrust reverser: 

• Clamshell Door
• Retractable Ejector
• Cold Stream Cascade Reverser