I understand prop design fairly well (I think) - I’ve dabbled enough in designing props and drive systems to know that variance of the Reynolds number, even changing it along the same blade, will have significant impact to lift produced and that the optimum tip speed for achieving low noise is 400 mph (For those that dont know.., guess why??? - The air compression and shock waves as the tip speed approaches Mach 1 causes huge amounts of drag) In addition to the above, being a hardcore RC Aircraft and heli enthusiast for more than 25 years hasn't helped...
So.. I apologise, as may have wrongly worded my prevous post/sentence.
When I said shaping the props I meant shaping i.e. tips in such a way as to make them least penetrating or flexible in design so that when the prop blade makes contact/impact with something solid/living it flexes enough or cleanly breaks resulting in minimal damage to the (unintended) victim, whilst still retaining lift properties in normal flight. |