6.9 Transmissions Flashcards
Physical power transmission from the engine to flight control surfaces is normally done by what?
Belts, cables, control chains, chain wheels, pulleys and levers
What is the purpose of chains
They provide a strong positive connection, generally used where change in direction is necessary and in runs where considerable force is exerted
How is change in direction achieved
By chainwheels and pulleys
What systems may chains be found in
- Control column installations
- Aileron or elevator control
- Trim Control Systems
Can chains be used with other forms of transmission
They can be used on their own or in conjunction with cable assemblies
How is the incorrect assembly of chains made impossible
By the use of non reversible chains
How are chains classified
By their pitch, roller diameter and width between plates
What component allows a chain to have a 90° change in direction
A bi planer block
What type of tower transmission are chains used for
Non slip power transmission
How many teeth should be the minimum on a chain wheel and why
12, otherwise wear of the chain will be too high
What type of chains require little maintenance
Roller chains
What chains are virtually silent in operation
Gear chains
How many teeth should be the minimum on gear chain wheels with regards to wear
17
What are couplings used for
They are used to connect 2 shafts together
What are the 3 types of couplings
- Solid
- Movable and dissconnectable
- Safety couplings
What are the best known solid couplings
Sleeve couplings
Disk couplings
What is achieved by using solid couplings
A rigid connection between 2 shafts
What are movable couplings used for
Used for shafts that may not be in alignment or if the position of the shafts change with operation
What is the purpose of extension couplings
They allow for a small amount of longitudinal movement
What is the purpose of using universal joints
They can transfer a strong force, like used in cars
To gain mechanical advantage when using gears what gear must have a different amount of teeth
The drive gear
What is the purpose of toothed wheel gears
They transfer rotational movement at low speeds with out slip
How would noise be reduced in toothed-wheel gears
They should have ground tooth flanks and should operate in an oil bath
How are accidents avoided in toothed-wheel gear runs
They are covered with protection devices which also prevent contamination
Why are spur gears used
When a change in speed is required and the shafts lie parallel to each other
When are internal spur gears used
When a change in speed is required whilst maintaining overall minimum diameter
What is the smallest set of spur gears referred to
The pinion
What are helical gears used for
To transmit drive between parallel shafts (like spur gears)
What is the difference with helical gears over spur gears
Helical gears are more complex to manufacture, but quieter than spur gears and helical gears have a larger contact area
What is the purpose of a rack and pinion
Transfers rotational movement into linear movement
What is the main benefit of the worm gear
High mechanical advantage
What angle should herringbone gears not exceed
20°
What is the purpose of backlash
Allows for expansion and lubrication
What is a pinion
It is the smaller of 2 mating gears
What is a lay shaft
A shaft which supports an idler gear
What is a step up drive
Provides an output drive higher than the input
What is a compound gear
A gear wheel with more than one driving face
What is the purpose of a planetary/elliptical gear
Used to reduce the speed of the aircraft engines output shaft to the propeller
What is the major disadvantage of a stepped pulley drive
They can take up a lot of space
What type of loads can the drive gear type key transfer
Small forces at slow rotational speeds
What type of forces can push rods transmit
Pull and push forces
What are push rods used to operate
Rudders, flaps etc
