6.9

Question 1

Spur gear

Answer 1

Parallel teeth positioned around a circumference
Can be noisy
Shafts lie in parallel
The larger gear is called a wheel/spur
Smaller wheel is called pinion

Question 2

Helical cut spur gear

Answer 2

Teeth are cut at an angle
Quieter in operation
Can take heavier loads
More complex to manufacture

Question 3

Bevel gears

Answer 3

Used to transmit the drive between shafts which have intercepting axes.
Angle of interception varies with individual applications
Helical type bevel gears carry heavier loads d run more smoothly

Question 4

Hypoid gears

Answer 4

A progression of the spiral bevel gears, quieter and smoother in operation.
Suffer from sliding contact.

Question 5

Worm gears

Answer 5

Worm drives spur.
Large sliding movement can make them inefficient.
Found in flap and trim systems.

Question 6

Rack and pinion gears

Answer 6

Used to transmit motion between a rotating spur and a linear toothed rack.
Converts rotational motion to linear motion.
Often used on leading edge flaps for extension and retraction.
Used for aircraft nose wheel steering.

Question 7

Speed ratio of gears

Answer 7

Opposite of the ration of the number of teeth.

Question 8

Idler gears

Answer 8

Makes the output gear rotate in the same direction as the input gear.
Can be used to link gears when there is distance between them.
Makes no difference to the ratio of speed or mechanical advantage.

Question 9

Gear trains

Answer 9

Count number of gears between input + output.
If even then rotation is opposite
If odd then rotation is same direction.

Question 10

Epicyclic / planetary gears

Answer 10

Used as reduction gearing in aircraft engines.

Question 11

Gear meshing and wear pattern

Answer 11

If set to tightly, cannot mesh , no lube or room for thermal expansion.

If too loose then teeth will break.

Question 12

Gear backlash

Answer 12

The amount of play between gears, results in lost motion.

Excessive backlash would be a sign of worn gearing.

Question 13

Friction belt

Answer 13

Rely on friction between belt and pulley.
Requires adequate tension to maintain correct friction.

Question 14

Positive drive (synchronous) belt

Answer 14

Rely on engagement of teeth on belts with grooves on the pulley.

There is no slip besides ratcheting and jumping.

When malaligned can rub against pulley flanges, results in heavy wear.

Under tensioning causes performance problems: noisy or prematurely er during to ratcheting.

Can be double sided.

Question 15

V belts

Answer 15

Low cost, wedging action, more friction, easy to keep in grooves

Question 16

V rib belts

Answer 16

Can run at high speeds.
Grooves ensure belt stays on track making alignment less critical then on flat belts.

Question 17

Stepped or cone pulley drive

Answer 17

Changes the speed
(Like gears on a push bike)

Question 18

Chains and sprockets

Answer 18

Roller chains are preferred in aviation. Although not often used due to fly-by-wire systems.

Chain drives cannot slip

Non slip can be a disadvantage. Heavy and noisy too.