> At 11:46 PM 12/19/2006, you wrote: >>1) Multi-bladed props climb better than 2 bladed props, as a rule. > > ++++++++++++++++++++++++++++++++++++++++++++++++++++++= > > But are less efficient in cruise, as a rule. >
why should that be ? Multiblade props have a couple of advantages, better ground clearance and lower tip speeds ( for the same power ). I cannot think of any logical reason why they should offer better climb performance given the fact that the inner half of a prop is battering air against the engine cowlings, you want longer blades not more shorter or wider blades. I think this is a case of extrapolating data from a vastly different aircraft. It is true that BIG radials ( Mustangs etc ) got better climb perf with multiblade props, but that was because the tips of their 14ft diam props went supersonic. That's not the case with VW/Corvair/Jabiru class engines. A 58inch prop is only doing about 0.8mach at 3400 revs. It is also not true that multiblades are easier to balance than 2 blade props, obviously it is easier to balance the blades of a warp drive than the blades of a wood prop - thats a inherant property of the design of the warp drive and has nothing to do with the number of blades, simply put:- 1 warpdrive blades are machined in a very accurate manner using modern manufacturing techniques, rather than being hand hewn from a material that can have a variable density. 2 each blade is then very accurately weighed Thus quality control on warpdrive blades is, by design, far tighter than is possible with wooden props. One last important consideration. It is more difficult to hand swing a 3 blade. This is because each blade is at a different angle when pulled through TDC, it's very easy to accidentally pull through TDC when you are not expecting to - watch your knuckles !! Pete
