Originally Posted by
Sport_Pilot
You would think that the velocity of the air would increase in proportion to the RPM but actually it does not. Also consider that the resistance of the blade will increase by the square of the velocity so that HP actually is much higher than 8% in your case. I ran this though a propeller calculator and the thrust was about 20% higher for your 8% increase in RPM. Now we have started another discussion I guess.
I'm a little confused. Are you talking about HP or thrust? I could see where an engine going from 12000 rpm to 13000 rpm would be putting out more than 8% more
HP due to air resistance on the blades...analogous to the fact that it takes much more than 10% more HP for a car to go 88 mph vs 80 mph. Bugatti makes a $1.5 million supercar called the Veyron with 1000 hp and a top speed of 253mph. In an interview, the car's lead engineer stated that the slippery car needs "only" about 500 hp for the first 215mph. The other 500 hp is needed to get the car from 215 to 253.
What I don't understand is how you came up with 20% more
thrust from an 8% increase in RPM. The engine might be producing 20% more
HP to obtain the 8% increase in rpm, but the increase in
thrust wouldn't be anywhere near 20%. It wouldn't even be 8%...I don't know what the exact number would be due to the many variables involved, but the increase in thrust would
always be
less than 8%.