7.12 Transmissions Flashcards
What is the primary function of a gear?
Transmission of power through motion
What are the common defects found during gear inspection?
- Cracks
- Chipped teeth
- Pitting
- Excessive wear
What maintenance action can be taken for minor scratches on gear surfaces?
Use a fine abrasive cloth
What is gear backlash?
The play between teeth in a gear system
What are the causes of gear failure or premature wear?
- Excessive backlash
- Poor lubrication
- Misalignment
What can cause corrosion in gears?
Exposure to corrosive conditions and moisture in the lubricant
What happens to gear teeth when lubrication breaks down?
Overheating occurs, leading to brittle teeth
What is overload wear?
Wear caused by heavy contact and sliding action between gear teeth
What causes pitting and spalling in gears?
Thin oil films and high temperatures
What causes cracking in gears?
Failure in heat treatment or improper machining
What is interference wear?
Wear caused by misalignment of gears
What is abrasive wear?
Wear from scratching and scoring due to particles in lubricant
What is a wear pattern in gear inspection?
Impressions left by one set of gear teeth on another set
How can the tooth contact pattern be established before final assembly?
Using Prussian blue
What is the function of backlash in gear systems?
Prevents gears from jamming and allows for lubricant space
What is the definition of minimum backlash?
Occurs when all tolerances give the shortest centre distance and thickest teeth
What is the formula for backlash variation?
Difference between maximum and minimum backlash in a gear rotation
How can backlash be measured in a gear train?
By locking one end and measuring limits of movement at the other end
True or False: Excessive backlash is always acceptable in gear systems.
False
Fill in the blank: The amount of backlash can be affected by changes in _______.
[centre distance]
What is the consequence of deep scratches or scoring on gears?
Not acceptable for continued use
What type of wear results in polished gear tooth surfaces?
Normal wear
What indicates impact overloading in gear breakage?
New metal over the break area
What is required for chain assemblies according to the aircraft maintenance manual?
Chain assemblies are required to be inspected at specified intervals.
What is the primary purpose of inspecting chains during maintenance?
To ensure the chain passes smoothly over the sprockets.
What percentage limit of deflection/elongation is typical when a chain is loaded?
Typically ranges from 1.5% to 3%.
What should be checked during the inspection of chains?
- Damage
- Cleanliness
- Adequacy of lubrication
- Absence of corrosion
When must a chain be replaced according to inspection results?
If the chain shows signs of corrosion or other defects.
What must be ensured when adjusting the tension of a chain with turnbuckles?
The chain must not be twisted during adjustment.
What is the correction for abnormal wear rubbing on guides?
Replace chain when 5% worn and check chain alignment or increase clearance.
What causes pin galling in chains, and how can it be corrected?
Caused by inadequate lubrication; reduce load or chain drive speed and provide proper lubrication.
What causes tight joints in chains, and what is the correction?
Caused by dirt or foreign substance; clean and re-lubricate the chain or replace it.
What should be done if sprocket teeth are hooked due to excessive chain wear?
Replace the chain and the sprocket.
What is the probable cause of cracked plates due to fatigue?
Loading beyond the chain’s dynamic capacity.
What causes rusted chains, and how can they be corrected?
- Exposed to moisture
- Water in lubricant
- Inadequate lubrication
Replace the chain and protect from moisture.
What materials are commonly used to manufacture sprockets?
- Steel
- Alloy
- Hard fibre material
- Plastic
What is the main role of a sprocket?
To convert rotary motion into linear motion or vice versa.
What can a visual inspection of a sprocket determine?
If the sprocket has worn beyond its limits.
What abnormalities should be looked for when inspecting a sprocket?
- Worn teeth
- Misalignment
What are the key inspection points for drive belts?
- Wear and degradation
- Cracking and splitting
- Chipping and fraying
What can cause cracking and splitting of drive belts?
Slipping of the belt causing heat build-up.
What is the procedure to check belt tension?
Push on the belt in an unsupported location and observe the deflection.
What should be referenced when checking the belt tension?
The relevant Aircraft Maintenance Manual (AMM).
What must be done after adjusting belt tension?
Carry out a further test to ensure the correct tension has been achieved.
What is a screw jack transmission commonly used for in aviation?
Lowering and raising the trailing edge flaps, stabiliser, and rudder trim mechanisms.
Name the three basic types of screw jacks used in aviation.
- Worm and peg mechanism
- Worm and nut mechanism
- Recirculating ball mechanism
Why is the worm and peg mechanism rarely used on aircraft?
Due to excessive backlash which causes localized wear on the peg and worm screw.
How does the worm and nut mechanism operate?
Actuation is generated by turning the shaft to drive the nut, or by turning the nut to drive the shaft.
What is the recirculating ball mechanism also known as?
Ball screw actuator.
How does the recirculating ball mechanism reduce friction?
All of the threads are filled with ball bearings that recirculate through the gear as it turns.
What are the primary maintenance concerns when inspecting a screw jack arrangement?
- Lubrication
- Backlash
List the typical inspection procedures for a screw jack.
- Checking screw shaft for wear (micrometer or Vernier)
- Checking ball nut for end float
- Checking ball nut lubrication level
- Checking screw jack full travel and stop limits
What happens if a defect exceeds inspection limits during a screw jack inspection?
The screw jack and its components will need to be replaced.
What are push-pull rods commonly used for in aircraft?
They are used in the aileron and trim tab mechanisms to transfer compression (push) or tension (pull) forces.
What material are push-pull rods typically made from?
Aluminium alloy tubing.
What should be inspected on a push-pull control rod?
- Straightness
- Wear in the eye ends
- Security of the check nuts and end fittings
- Corrosion
- Scratches
- Dents
- Chafing
- Buckling
What does a witness hole in the adjustable eye-end fitting indicate?
It allows inspection to determine if the adjustable end is sufficiently screwed onto the threaded portion of the control rod.
What is the purpose of bell cranks in aircraft?
- Transmit force or motion
- Permit a change in direction of that force or motion
Is adjustment usually required for a bell crank?
No, there is usually no adjustment required.
True or False: Control rod bearings are subjected to both radial and axial loads.
True
What must be checked for control rod bearings during inspection?
Play in both radial and axial planes.
Fill in the blank: The recirculating ball mechanism primarily uses _______ to reduce friction.
ball bearings
