Bill,
If you ever get time I would love to have the specs for a fixed pitch prop optimised for a 70" length, 225 HP and 200 to 225 MPH.  I have prop carving on my LONG list of things to learn.

Ken Powell

Ken Powell
kenpowell@aristotle.net

Perry is building something close to that Ken for test with the LAEV
hub as we speak.

Paul Lamar

You did not specify shaft rpm for that power level, so I assumed prop rpm of 2700.
Inputting a design top speed of 210 mph , with your 70 inch diameter, I got the following
recommended size. The program assumes a flat bottm clark Y type foil, with pitch
measured to this surface. The lift coeff for this foil at that zero angle is roughly 0.4
and drag for typical prop aspect ratio about  0.02. The program picks a true helical pitch
for that angle of attack - relative to disk flow thru velocity, and comes up with a tad over
87 inch pitch. The disk delta V at that point is only about 19 ft per second. tip airflow
speed is about 887 fps (faster tan a 45 slug, and about 10 percent above recommended
for a wood prop.predicted  thrust is about 340 lbsf for a bit over 83 percent eff.
Proposed dimensions would be
      radius            blade width       blade angle        eff air velocity
       0.9 R                   4.9                  23.7                   811
       0.7R                    6.0                  29.5                   663
       0.5R                    7.7                  38.4                   526
       0.3R                     8.0*               52.9                   410
* the 0.3 radius zone  is usually highly blocked, and even theoretical  contribution
to thrust is less than 10 percent. The only prop I have seen that carries the width
for constant HP per square foot  this far in is the prop for the Carter Copter.

This is a theoretical undisturbed inlet prop - pushers need more pitch
to compensate for the velocity accelleration around the fuselage.
Berkuts routinely use over 90 inches of pitch. Also for this to be valid
- you really need to have a plane clean enough to go 210 with 225 HP
Vance

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