6.9- Transmissions Flashcards
How is power transmission achieved from engine to flying controls?
Through the use of belts, cables, control chains, chain wheels, pulleys and levers.
What other components may you find in transmissions?
Shafts, pull and push rods, cranks, eccentrics, threads, friction wheels, hydraulics and compressed air.
What do chains provide?
Strong, flexible and positive connections.
Where are chains generally used?
Where it becomes necessary to change the direction of controls runs in systems where considerable is exerted.
What 3 systems might chains be used in?
Control columns
Aileron and elevator controls
Trim controls
How are chains classed?
Pitch, roller diameter and width between plates.
What are some benefits of roller chains?
Low frictional loss
low maintenance.
What purpose does a chain cover serve?
Prevents jumping of the chain creating separation between chain and teeth.
What type of couplings do you get?
Solid
moveable and disconnectable
safety
What are the two best known solid couplings?
Sleeve couplings and disk couplings.
Where is a moveable coupling used?
If the shafts are not in alignment or if the position changes during operation?
What class of coupling is an elastic coupling?
Moveable.
Cross links such as universal joints are used to transfer what and what’s their benefit?
Stronger forces
They require no maintenance.
If a drive gear has 50 and the driven gear has 100 teeth what is the ratio, the mechanical advantage and what does that mean?
1:2
MA is 2
Which means the power required to drive the driven gar is halved.
What does a toothed wheel gear provide?
Transfer rotational movement at low speed without slip.
Where are external spur gears used?
When a change of speed is required and the shafts lie parallel to each other.
What are helical gears used for?
Used to transmit drive between parallel shafts.
What is an advantage of helical gears?
They have more teeth in mesh to provide a larger contact area.
What is rack and pinion?
Linear actuator. The pinion is the circle and the rack the bar.
What are bevel gears used for?
Used to transmit drive between shafts with intercepting axis.
What’s the benefit of herringbone over helical gears?
The axial forces are eliminated, therefore they are used for large forces.
What is a gear ratio?
Direct measure of the ratio of rotational speeds.
If the driven gear is smaller than the drive gear will it turn faster or slower?
Faster.
How do you work out gear ratio?
Driven gear teeth divided by drive gear teeth.
If a gear ratio is 1.5, what does that represent?
That the driven gear must turn 1.5 times before the drive gear has done 1 turn.
What is gear backlash?
The clearance between gear teeth at the mesh point. Excessive backlash would be indication of wear.
What is an idler gear?
The gear interposed between the driven and drive gear.
What is an intermediate gear?
Positioned between the drive and one or more driven gear in a train, it could transmit its own drive.
What is the pinion?
The term used to describe the smaller of two mating gears.
What is the lay shaft?
The shaft that supports an idler gear or intermediate gear.
What is a gear train?
Two or more gear wheels, can be used to alter output directions.
What is a compound gear?
A gear with more than one driving face.
What is a reduction gear?
An arrangement where the output is slowed but the torque remains the same or higher.
What does a planetary (epicyclic) reduction gear train consist of?
Sun (driving) gear driving three or more equi-spaced gears known as planet pinions, and the annulus gear.
What is the principle of planetary (epicyclic) reduction gear train?
The input comes through the sun gear which in turn spins the planet pinions within the annulus. The result is the annulus ring spinning the same direction as the sun gear but much slower.
What number of stages is rarely used on single pulley drives?
More than 5, because it would take up too much space.
What happens if two three stage belts are arranged in series?
There will be 9 rotational speeds not 6.
What are the two types of variable gear?
Caster swivel wheel gears and driven key type transmission.
What can driven key type gears only be used for?
Transmit small forces at low rotational speeds.
What’s the benefit of cable transmission?
They are versatile, offer movement free of play, and weight saving.
