An aircraft propeller is used to transform a rotary wave from an engine or other manual power source to produce a spinning force. It has a centre to which multiple radial airfoils are attached to ensure that the mechanism rotates longitudinally. The pitch of the blade should be fixed by hand at certain fixed locations or electronically at a constant speed. The propeller should be attached either directly to the drive shaft of the power source or via a reduction gear. Most aircraft propellers run at an airspeed of 770 km/h. Mechanical problems can arise if the propeller reaches this speed. It is therefore vital to ensure that airplane propellers are well maintained and repaired to reduce cases of airplane crashes. The paper will discuss the various types of propeller damages and proper measures to maintain and inspect a propeller.
Several types of damages make the propellers fail or become airworthy. The magnitude of the damage determines the type of maintenance required. Loss of airworthiness in a propeller is caused by corrosion. Rusting of metal blades may cause external corrosion and hubs while internal corrosion is caused when moisture enters in certain internal cavities such as blade clamps, hubs, and pitch control mechanisms (Huang et al., 2016). Corrosion threatens the structural performance of the propeller without being noticed. It takes place regardless of whether the aircraft is flying or not. Moreover, propellers are rarely exposed to fire damage such as engine fire.
In the event of a fire, most of the propellers parts are damaged, which may eventually lead to an aircraft crash. A propeller may also be prone to an over-speed situation and fail to give an alert of the condition happening. The situation may lead to severe damage to the propeller because of the dramatic increase of the centrifugal loads. Furthermore, dents and cracks grow over time rapidly which may eventually lead to propeller failure (Huang et al., 2016). Dents can be dangerous depending on their location, size, and configuration. They can lead to local stress risers around the parameters and the bottom undersurface of the propeller.
Proper Maintenance and Inspection
Proper cleaning of a propeller is essential to maintain its airworthiness. The cleaner should take care when cleaning the surfaces of a propeller to avoid damaging the surfaces being cleaned. This is because most of these areas have finish requirements, which can be damaged by cleaning agents and hard brushing. Furthermore, other surfaces have unique finish textures like a glass bead peening, which can be destroyed by polishing with steel wool and other rough materials. It is not recommended to use high-pressure washers when cleaning propellers because the high pressures may drive water into the cavities of the propeller and the hub. This is because the water can cause corrosive internal environment if it enters the propeller (Hafenrichter, Georgeson & Lea, 2017). Acidic and alkaline solutions should also be avoided when cleaning the propeller. Additionally, if there is evidence of grease or oil leakage, the source of the leakage should first be established before cleaning because the oil or grease may be leaking from a crack or lubrication fitting. Cleaning should be done with clean water and then dried with a soft cloth.
The same methods used to inspect the entire aircraft should be used in propeller inspection. The methods are set in such a way that if a defect exists, it will be detected. Detection of errors allows inspection intervals to be established. To ensure that a propeller is airworthy, it is essential to use inspection to accurately and reliably detect the defects. The process of review requires that review of the same part is done uniformly to enhance the correct probability of defect detection. An inspector should be trained on how to carry out the inspection. Moreover, the inspection device should be in good condition and standardized as required. A detailed procedure of carrying out inspection should be contained in the manufacturer’s propeller maintenance document (Tsagkas, Nathanael & Marmaras, 2014). The examination may detect the following flaws: bent blade, loose blade in the hub, diameter reduction, corrosion, and cracks. Additionally, other defects such as surface damage, erosion, and oil and grease leakage can be detected. Inspection can be done in three levels; walk around inspection, teardown inspection, and detailed inspection.
An appropriately rated mechanic should be the only one to install propellers. Propeller manufacturers should provide instructions on how the propellers should be fixed. Only correct seals and O-rings should be used during the assembly of propellers (Tsagkas, Nathanael & Marmaras, 2014). In case the propeller begins to vibrate after installation, the propeller should be removed for reinstallation or rotated 180 degrees on the engine crankshaft. An aircraft’s propeller should be checked for proper installation before it is allowed to fly.
It is essential to establish proper propeller maintenance and inspection techniques to avoid propeller failure. Aircrafts are prone to propeller damages such as corrosion, erosion, fire, dents, cracks, and leakages. To control these losses, propellers should be well cleaned with clean water and inspected for any damages. Furthermore, only trained mechanics should be allowed to install the propellers to ensure correct assembly of propeller components.
Hafenrichter, J. L., Georgeson, G. E., & Lea, S. W. (2017). U.S. Patent No. 9,643,313. Washington, DC: U.S. Patent and Trademark Office.
Huang, D., Li, K., Tian, G. Y., Sunny, A. I., Chen, X., Tang, C., & Zhao, A. (2016). Thermal pattern reconstruction of surface condition on freeform-surface using eddy current pulsed thermography. Sensors and Actuators A: Physical, 251, 248-257.
Tsagkas, V., Nathanael, D., & Marmaras, N. (2014). A pragmatic mapping of factors behind deviating acts in aircraft maintenance. Reliability Engineering & System Safety, 130, 106-114.