Propellers and Propeller Systems

Added on -2020-02-18

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A Review on Propellers and Propeller Systems: PropulsionPlant InvestigationAircraft accidents could occur due to a number of reasons and propeller damage isone of the best indicators of aircraft accidents. While checking for propeller damages time foroverhaul, repair records and operation times are checked whether the repairs are carried outas per the rules and regulations as improper repairs can lead to failures caused by surfacediscontinuities ( Anderson, 2009). Irregular welding and straightening activities can lead topropeller failure but physical damage to the propeller physical damages are the mostdestructive. Damages caused by water impact and ground impact are thoroughly investigatedin case of propeller damage.Ground impact damage could be determined by evaluating the bending of the blade,slash marks caused by ground, breakage, tip curl, span wise and chord wise scratches. Tipcurl shows that the engine was rotating and the power developed by the engine is indicated bythe amount of tip curl (Anderson, 2009). If the propeller tips are curled backwards then itsuggests that the propeller was rotating with low RPM relative to forward velocity and if thepropeller was rotating with high RPM with respect to the speed of the aircraft, then the tipcurls in the forward direction.Bending is caused due to crash impact and its direction will be opposite to that of thedirection of rotation is the propeller is powered. Low aircraft speed and high power bends thepropeller in the forward direction. But if the aircraft creates an impact at right angles to theground the propeller bends in the backward direction. Vibration, imbalance and impropermaintenance also bends the propeller blades (Kroes and Wild, 2010). Misalignments in thecrankshaft and bearings are good indicators of bending because problems in the propeller aretransmitted to the crankshaft and bearings. If the engine is not rotating then it could break the propeller blade, scratches alongpropeller blade face is due to propeller rotation. Chord-wise scratches are caused when thepropeller rotates at the time of impact, but this sign not necessary indicate that the engine wasrunning it can also be caused due to wind-milling (Kroes and Wild, 2010). Rotation of thepropeller can cause slash marks on the ground which could be used to estimate the RPM ofthe propeller.

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