Aircraft power plant systems - exam 2 with complete solutions

Propeller efficiency - measure of how well a propeller transfers engine power to thrust - Propeller deflects air and creates lift, propeller produces thrust, engine produces power - Constant speed props are able to change the angle of attack to perform at the most efficient angle of attack in all phases of flight (PURPOSE) - A more efficient propeller (under the same condition) will transfer more of the provided engine power to thrust number of propeller blades adjustable factors (thrust dependent on lift produced by the propeller) 1. Velocity (RPM)/Airspeed = more air moved by airfoil then more lift is produced, faster you spin propeller more thrust it will produce 2. WING AREA/SURFACE AREA OF A WING (number and size of propeller blades) = directly determines lift - Prop blade angle changes to maintain constant RPM - Propeller RPM can no longer change with manifold pressure - have propeller at most efficient angle of attack Blade angle can be set to be most efficient for each phase of flight (constant speed prop) - Cruise - high pitch/low RPM - faster cruise - Climb - low pitch/high RPM - better acceleration prop spinning faster than selected RPM (constant speed prop - overspeed) the L shape weights will open up the pilot valve prop spinning slower than selected RPM (constant speed prop - under speed) L shape weights will close the pilot valve If I have an under speed condition how does the pilot valve move down? Moves down allowing oil to move down back from the propeller hub. if my propeller in overspeed condition - prop spinning faster than selected RPM (constant speed prop) - pilot does not do anything with LEVER - does tension on speeder spring change NO - condition of flyweights in OPEN - pilot valve RAISES UP - oil will flow in standard constant speed into propeller hub and push piston back INCREASING BLADE ANGLE if my propeller in under speed condition - prop spinning slower than selected RPM (constant speed prop) - pilot does not do anything with LEVER - does tension on speeder spring change NO - condition of flyweights in CLOSED - pilot valve LOWERS DOWN - oil will flow back from propeller hub to oil sump/engine and push piston forward DECREASING BLADE ANGLE Nothing else happens to the speeder spring or the lever Beyond what the pilot sets Constant Speed Prop Diagram How do the parts of this system adjust to certain conditions? (overspeed & underspeed) operational considerations - Throttle controls manifold pressure - Blue knob controls RPM - Prop will maintain set RPM at all times, if able - Too much manifold pressure with low RPM will damage engine (DETONATION) - RPM is no longer a direct indication of carb ice, power changes number of propeller blades keep propeller blade diameter as long as possible while having as much of propeller blade area as possible while still being able to maintain RPM in all phases of flight why are some propeller blades swept (scimitar)? keep propeller blade subsoni