proppastie
Well-Known Member
Prop Safety Question (Another Prop Questions)
I have purchased an Engine, 200 CC, 20 hp at 7500 RPM. I would like to start out with off the shelf propellers for break in, thrust testing, and playing with. They are rather reasonable compared to certified, full size, or custom props ($50-60 range). There is lots of stuff here at HBA and on the net about design of your Optimal prop. That is not where I am at......at this point in time. The Valley Calculator, and several other spread sheets, rule of thumb, sanity check etc....point to a 4" pitch for my 25 mph best L/D climb. They also point to 27-28 inch diameter as being the largest prop I can mount to stay at 81% max speed of sound. I have only found 6" pitch so far in 26", 27", 28" and they are for smaller 160 CC engines (I think).
Now for the Questions: Should I worry about these smaller propellers coming apart? Is it safe to assume the smaller propellers are designed for higher RPM.
That these smaller props are for less hp, does going to 7500 rpm with them make any more sense than going at a lower rpm with a prop designed for 200 cc. Will the smaller prop be not as wide and not be able to transmit the power to the air or perhaps not any more power than a wider prop at lower rpm.
I have purchased an Engine, 200 CC, 20 hp at 7500 RPM. I would like to start out with off the shelf propellers for break in, thrust testing, and playing with. They are rather reasonable compared to certified, full size, or custom props ($50-60 range). There is lots of stuff here at HBA and on the net about design of your Optimal prop. That is not where I am at......at this point in time. The Valley Calculator, and several other spread sheets, rule of thumb, sanity check etc....point to a 4" pitch for my 25 mph best L/D climb. They also point to 27-28 inch diameter as being the largest prop I can mount to stay at 81% max speed of sound. I have only found 6" pitch so far in 26", 27", 28" and they are for smaller 160 CC engines (I think).
Now for the Questions: Should I worry about these smaller propellers coming apart? Is it safe to assume the smaller propellers are designed for higher RPM.
That these smaller props are for less hp, does going to 7500 rpm with them make any more sense than going at a lower rpm with a prop designed for 200 cc. Will the smaller prop be not as wide and not be able to transmit the power to the air or perhaps not any more power than a wider prop at lower rpm.
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