Chapter 17: Bearing and Seals

Question 1

characteristics of bearings

Answer 1

withstand pressure and permit movement

close tolerances while permitting freedom of motion

Question 2

primary loads for both radial & axial directions in bearings

Answer 2

1) weight of rotating mass
2) axial thrust force
3) gyroscopic effect while maneuvering
4) compression & tension loads btwn stationary casing & rotational system
5) vibration induced from engine

Question 3

loads on bearings

Answer 3

1) axial ( resultant of thrust loads)
2) radial (right angle of shaft, due to RPM changes or maneuvering)

Question 4

what types of load can ball bearing support?

Answer 4

both radial and axial

Question 5

what types of load can roller bearing support?

Answer 5

only radial

Question 6

what is good about ball bearings?

Answer 6

less friction than other types (less contact area)

Question 7

what is good about roller bearings?

Answer 7

allows thermal growth as engine expands

has greater surface area to absorb most of radial loads

Question 8

what does lubrication of bearings help with?

Answer 8

1) reduce transmission of vibration
2) cleaning debris
3) reduce temperature
4) extend life of bearing

Question 9

purpose of seals

Answer 9

prevent oil or air leakage from engine bearing chambers & components on accessory gearbox

Question 10

types of seals

Answer 10

O-ring
C-ring/clamp
Carbon seals
Labyrinth seals

Question 11

how does labyrinth seals work?

Answer 11

has a rotating member & static casing
pressurised bleed air seals oil path from leakage (knife edge, air can pass through, oil cant)