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angle to pitch relation
how exactly do you come up with pitch from a blade angle? i know it's supposed to be how far forward it would go in one turn if you screwed it into jello or something... I have a varying pitch blade (NOT variable) that is 50 degrees at the root, 15 at the middle, and 8.5 at the tip... any suggestions
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The angle at any point on the prop is based on the amount the prop advances during a revolution, which is determined by the radius of the point from the root. At the root, a complete revolution of the point moves thru a small distance.. to make that distance equivalent to the larger distances out along the blade the angle of the blade gets lower as the point moves from the center..
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Well, if I think it works out to:
2 * pi * radius / tan(angle) The radius being the radius up to the point you measure the angle. The angle will always decrease further from the centre in order to maintain the same pitch. I think there are instruments that measure the pitch. But measuring it is very tricky, because there is no easy definition of the direction the prop blade is facing. Props are rotating wings and there are several different possible lines to measure the angle from: flat-ish back of prop, geometric chord, aerodynamic chord... I've never tried it, but I've read that it's very difficult to replicate the manufacturer's measurement of pitch, and that manufacturers vary somewhat in how they define pitch. Stuart |
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If the prop were a flat plate airfoil, you could use the geometric relationship
pitch = pi * diameter * tan(angle) I dont have prop infront of me to measure, but if we use the numbers for your 10x6 the pitch comes out to pitch at tip = 3.14 * 10 * tan(8.5) = 4.7 inches pitch at mid = 3.14 * 5 * tan(15) = 4.2 inches It's a little shy of the advertised 6, but this simple equation ignores the airfoil shape which makes the prop more efficient at moving air than a flat plate. - Zoom - |
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Quote:
P=2*Pi*Tan(angle from horizontal) P=2*Pi/Tan(angle from vertical) And now for a prediction... No matter how many props you measure you will always find that the 'vertical' angle plus the 'horizontal' angle add up to 90 degrees. I wonder why they make props like this? |
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yeah, no kidding. but for 2pir DIVIDED it has to be the vertical angle. otherwise it doesn't work out. I was dividing, and using the horizontal angle. wrong result.
no, i did NOT remeasure the angle. I subtracted from 90. I may be dumb, but i ain't stupid. |
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