![]() ![]() The experiment may require a couple different diameters and pitches to produce a reasonable matrix of outputs. He should employ the school's machine shop to cut the wood and fit the wood with precision and also employ his more experienced family members to assemble the 3 blader precisely. The way I would approach it is to make a 3 bladed prop from 2 bladers (wood would be easier of course), to make certain important factors such as blade shape, area, thickness, stiffness and construction are as identical as a CNC mill can reproduce. May have another "Rocket Boy" here?ĬaryWell, I like this kid.Kudos to you for the encouragementĪlthough hard data may or may not exist (Boeing and NASA websites perhaps?), the experimental phase should be straight forward. I searched the web for 2-3 prop blade efficiency-thrust and could not find "Hard data" that he could use in a Review of Literature.May have to look at this another way. Kid has a lot of potential and I like the experiment he is attempting-Something new and refreshing- instead of the old same experiments that always gets repeated. Yeah, I know what you're saying.He knows I'm into modeling, and the students father/grandfather are older modelers themselves, so the student already has a interest in model aviation that I believe can be cultiated. How many blades required to get the appropriate blade area is what they're after. The reason the old saw has lasted so long is there is almost no way for modelers to make anywhere near a sensible conclusion.įull scale aeronautical engineers have put little effort into it because it's of no real consequence. If it was turned by 1.5 times the power that is. The old saw that, "2 blades are more efficient than 3" has led so many astray because there really isn't proof other than the irrefutable fact one prop has an additional tip and therefore 1.5 times the tip drag. It is almost impossible to isolate the effect of tips on the efficiency of a propeller because they have so little effect compared to blade area, blade aspect ratio, blade profile, blade twist, blade stiffness, operating rpm, operating speed, etc etc. There are way too many details that affect efficiency. If he adjusts the blades to have equal aspect ratio, they certainly won't have similar total blade area, also unfortunate since "wing loading" affects efficiency. Then unfortunately, how does he prove the difference in efficiency isn't the difference in propeller blade aspect ratio, a detail of wings and props that very strongly affects efficiency. ![]() He will of course have to come up with two "identical" propellers, one of 2 blades and one of 3, that produce very close to identical thrust. That's because there are way too many things that affect the efficiency of propellers. He cannot find any technical data (supported by hard facts) to support his hypothesis that 2 blade is more efficient than 3 blade. ![]()
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