Here is a table of prop pitch angles as a function of MPH.
Column B is the zero angle of attack of the prop for the speed.
Column C is the theoretical angle of attack for a fixed pitch prop designed
for about 240 MPH at 2700 RPM.
The chart below is the lift coefficient of an airfoil
at different angles of attacks. It is seen that the airfoil stalls
around 16 to 18 degrees. The range of this number can be increased only
by several degrees by making the prop airfoil thicker or
using a highly cambered airfoil. Therefor this fixed pitch
prop would be stalled at anything less than about 116 MPH.
Obviously the engine will not reach 2700 RPM at slow speeds so
the angle of attack will be much higher than that shown
and the engine HP will be severely limited.
This is why it is very important to have a variable pitch prop
if you intend to go fast and takeoff in a reasonable period
of time on a runway of reasonable length. It is also why
a variable pitch prop is almost mandatory on a seaplane.
A B C
MPH = 0.7 0.14 40.19
MPH = 7.5 1.49 38.84
MPH = 14.3 2.84 37.49
MPH = 21.1 4.18 36.15
MPH = 28.0 5.52 34.81
MPH = 34.8 6.86 33.47
MPH = 41.6 8.19 32.14
MPH = 48.4 9.50 30.83
MPH = 55.2 10.81 29.52
MPH = 62.0 12.11 28.22
MPH = 68.9 13.40 26.93
MPH = 75.7 14.67 25.66
MPH = 82.5 15.92 24.41
MPH = 89.3 17.17 23.16
MPH = 96.1 18.39 21.94
MPH = 103.0 19.60 20.73
MPH = 109.8 20.79 19.54
MPH = 116.6 21.96 18.37
MPH = 123.4 23.11 17.22
MPH = 130.2 24.25 16.08
MPH = 137.0 25.36 14.97
MPH = 143.9 26.45 13.88
MPH = 150.7 27.52 12.81
MPH = 157.5 28.58 11.75
MPH = 164.3 29.61 10.72
MPH = 171.1 30.62 9.71
MPH = 178.0 31.61 8.72
MPH = 184.8 32.58 7.75
MPH = 191.6 33.53 6.80
MPH = 198.4 34.46 5.87
MPH = 205.2 35.36 4.97
MPH = 212.0 36.25 4.08
MPH = 218.9 37.12 3.21
MPH = 225.7 37.97 2.36
MPH = 232.5 38.80 1.53
MPH = 239.3 39.61 0.72
Paul Lamar
The Aircraft Rotary Engine Newsletter. Powered by Linux.
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