rainedave said,
"What's interesting is that Zingers are a lighter load than APCs, yet I still bettered their figure!"
That's 'cause they have a better shape for moving air. Or at least moving through air. A 'normally shaped' prop, like most wooden model props & even mostmetal full scale props, are only really efficientforabout half of each blade's length.
Aircraft propellers (airscrews)
A propeller's efficiency is determined by<dl> <dd>
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A well-designed propeller typically has an efficiency of around 80 percent when operating in the best regime.
Changes to a propeller's efficiency are produced by a number of factors, notably adjustments to the helix angle , the angle between the resultant relative velocity and the blade rotation direction, and to blade pitch (where θ = Φ + α ). Very small pitch and helix angles give a good performance against resistance but provide little thrust, while larger angles have the opposite effect. The best helix angle is when the blade is acting as a wing, producing much more lift than drag. However, due to the shape of the propeller, only part of the blade can actually be operating at peak efficiency. The outer part of the blade produces the most thrust and so the blade is positioned at a pitch that gives optimum angle to that portion. Since a large portion of the blade is therefore at an inefficient angle, the inboard ends of the blade are hidden by a streamlined spinner to reduce the resistance torque that would otherwise be created. Another method used is to have a curved pitch propeller, in which the individual blades are actually airfoils of varying camber and angle of attack across the span. This is achieved by
twisting the airfoil across its major neutral axis(span length). It is usually set with the inner airfoil section of the blade in the direction of travel; that is, axial speed, or U (here freestream velocity), and the outer edges at right angles to it.
Do the last three sentencesbring to mind the shape of a particular brand of model airplane propellor?
Terry in LP
edit: to fix the symbols that were made into emoticons!