30 Questions
What can happen if a pulley is out of line?
It can cause wear to both the pulley and the cable
What is the primary purpose of pulley guards?
To prevent the cable from jumping out of the groove
Why are control chains used in aircraft control systems?
Because they can provide a relatively large amount of force to operate
What is the purpose of studying the pattern of contact left on the teeth of gears?
To set up the correct shimming or assembly relationship
What is unique about the manufacturing of aircraft control chains?
They are manufactured to closer tolerance and have more rigorous inspection criteria
What is an indication of normal wear on the teeth mating surfaces?
A polished surface on the tooth face
During an overhaul, what is examined to determine acceptability for further service?
The wear pattern on the gear teeth
What is the benefit of regular inspection of pulley bearings, bolts, and bushings?
It can ensure the serviceability of the pulley
What can happen if a pulley is not equipped with a guard?
The cable may jump out of the groove
What is the heel of a helical bevel gear?
The larger-width outer end of the gear
What type of chains are typically used in aircraft control chains?
Roller type
What is the purpose of chain keepers in aircraft control chains?
To stop the chain from coming off the sprockets
Which side of the tooth is under pressure during normal operation?
Drive side
What are the three parameters used to size chains?
Pitch, width, and roller diameter
What can the wear pattern examination reveal after a gear or assembly failure?
The cause of the failure
Why are non-reversible chains connected using end fittings?
To allow the chain to be fitted in one direction only
What is the purpose of chain guards in aircraft control chains?
To prevent the chain from coming adrift when tension is reduced
What should be done to the chain before checking for wear or damage?
Clean the chain
What is the formula to calculate the chain elongation percentage?
Extension (%) = (M - (X × P)) × 100
What is the consequence of excessive tension on the chain?
It causes the chain rollers to bind on the sprocket teeth
What should be done if the chain elongation is greater than 2%?
Replace the whole chain
How is the chain tension checked?
By applying a specified load and measuring the deflection
What is a common consequence of inadequate chain storage?
Chain corrosion or kinking
What is a criterion for rejecting a chain?
All of the above
What is the primary role of sprockets in many aircraft systems?
To convert rotary motion into linear motion and/or linear motion into rotary motion
What is the purpose of an idler sprocket in a chain system?
To support the chain run
What determines the gearing ratio of a chain system?
The number of teeth on the drive sprocket and the driven sprocket
What is the correct way to store chains?
Cleaned, dried, and coiled without twisting
What is the purpose of sighting along the length of a suspended chain?
To check for kinks or twists
What are sprockets usually made from?
Depending on the application, steel, alloy, hard fibre material, or plastic
Study Notes
Chain Maintenance
- To check for elongation, apply a specified load to the chain, measure the length, and calculate the extension using the formula: Extension (%) = (M - (X × P)) × 100 / (X × P)
- Replace the whole chain if elongation is greater than 2%, as it can compromise its strength
- Chain tension is checked by measuring chain deflection under a given load
Chain Tensioning
- Chain tensioning is adjusted using turnbuckles or adjustable sprockets
- The chain should be tightened enough to remove any backlash
- Too much tension causes the chain rollers to bind on the sprocket teeth
Criteria for Chain Rejection
- The chain section is elongated by more than 2%
- Any links are stiff or jammed
- Any part of the chain is kinked or twisted
- Any plates are cracked, worn, or corroded
- Any rollers are cracked, worn, corroded, or jammed
Chain Storage
- Correct storage of chains is important to minimize the possibility of corrosion or kinking of the links
- Chains should be cleaned, dried, and soaked in light lubricating oil before storage
- Chains should be coiled without twisting and checked for kinks or twists
Pulleys and Belt Inspection
- Pulleys should turn freely when the control cables are moved
- If a pulley is out of line, it causes wear to both the pulley and the cable
- Mountings for pulleys should be corrected and the cable carefully examined for wear
- Wear of pulley bearings, bearing bolts, and bushings should be checked for serviceability regularly
Chain Introduction
- Control chains are found in a number of applications in aircraft control systems
- Chains are made up of multiple links and can be joined together to make an endless loop
- Chains can be of a terminating type – a single length with a start and finish
- Chains are manufactured to closer tolerance and have more rigorous inspection criteria
Chain Components
- Chain keepers, similar to cable guards, stop the chain from coming off the sprockets
- Chains have drive and idler sprockets and a method of maintaining the tension of the assembly
- Chain link assembly consists of rollers, bushes, and inner link plates
- Pins are mounted in the outer plates, which are clamped together to join the whole assembly
Chain Sizing
- Chains are sized according to pitch, width, and roller diameter
- Non-reversible chains are joined or connected using end fittings similar to cable terminals
- Chain guards can be fitted to sprockets to prevent the chain from coming adrift when tension is reduced
Chain Inspection
- Chains need to be assessed regularly for wear, corrosion, and distortion, including elongation
- It is always best to clean the chain before checking for wear or damage
Sprockets
- Sprockets are used in many aircraft systems and in a variety of different applications
- Sprockets are usually made from steel, alloy, hard fibre material, or plastic
- Their primary role is to convert rotary motion into linear motion and/or linear motion into rotary motion
- Sprockets act as support for the chain in the form of an idler sprocket
Idler Sprocket
- An idler sprocket is a non-driving sprocket used to support the chain run
- Sprocket teeth are spaced to align with the chain pitch
- The number of teeth on the drive sprocket compared to the number of teeth on the sprocket being driven determines the gearing ratio of the chain system
Learn how to analyze the wear pattern on gear teeth to determine the condition of the gear assembly and identify potential issues. This quiz covers the techniques used to examine gear wear, including the normal wear patterns and signs of abnormal wear.
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