15.8 Bearings and Seals Flashcards
(38 cards)
What is the main purpose of bearings in engine construction?
To support the main engine rotor.
What determines the number of bearings required in the engine rotor?
- Length of the engine rotor.
- Weight of the engine rotor.
What forces act on the weight rotor? (5)
- Weight.
- Gas.
- Shock.
- Gyroscopic.
- Imbalances.
What are the 2 forces that act on a bearing?
- Axial.
- Radial.
In what direction can radial forces be transmitted in, on a bearing?
In any direction.
In what direction can axial forces be transmitted in, on a bearing?
Only in the forward and aft direction.
What main type of bearings do aircraft use?
Anti-friction bearings.
What type of bearings do newer engines use?
Hydraulic bearings.
The outer race is surrounded by a thin layer of oil to reduce vibrations.
What are the advantages of Anti-friction bearings? (8)
- Little rotational resistence.
- Precision alignment.
- Inexpensive.
- Easily replaced.
- Withstand high momentary loads.
- Accomodate both axial and radial loads.
- Easy cooling, lubrication and maintanence.
- Resistent to elevated temps.
What’s the two disadvantages of Anti-friction bearings?
- They fail without warning.
- Vulnerable to FOD damage.
What type of load is the main example of an axial load?
Thrust load.
What forces do fixed bearings transmit?
Both axial and radial forces.
How are fixed bearings installed, in terms of the rotor?
They fix the rotor in axial direction, and support the rotor in the radial direction
What force do floating bearings transmit?
Radial forces only.
How do floating bearings ‘float’?
The shaft and inner bearing race can move axially in the outer race.
What type of bearing system do aircraft use?
A Triple-Bearing System.
What does a Triple-Bearing System consist of?
A fixed bearing in the middle of the rotor, with a floating bearing at each end of the rotor.
What’s the advantage of the Triple-Bearing System?
Minimises thermal expansion of the shaft end.
What’s the main type of fixed bearing used?
Large ball-bearings.
How are radial forces transmitted through a ball-bearing?
Through the bearing components to the bearing support.
How are axial forces transmitted through a ball-bearing?
Applied through the shaft fitting to the inner race.
What’s the purpose of the balls, in the ball-bearings?
Transmits the forces between the outer and inner races.
What’s the main type of floating bearing that’s used?
Roller bearing.
How do roller bearings transmit the radial forces?
The rollers are guided by the inner race, free to move in the axial direction in the outer race. (which transmits a radial force).
