Height vs. Velocity diagram explained

Jean Claude

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Jan 2, 2009
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Centre FRANCE
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I piloted gliders C800, Bijave, C 310, airplanes Piper J3 , PA 28, Jodel D117, DR 220, Cessna 150, C
Total Flight Time
About 500 h (FW + ultra light)
The windmilling is just beginning at this moment. But Increase the forward speed to 30 m/s and the engine will be driven by the propeller at say 2600 rpm (propeller at 1000 rpm). Then the representative blade element will have a circumferential speed of 65 m/s. Its angle of attack would be zero for a pitch of : Atan (30/65) = 25 degrees. This is about 5 degrees more than the pitch angle (Hence CL = - 0.5 ) and the propeller pull would then be about -350 N.
Such an increase in drag would be very noticeable

Sans titre.png

For simplicity, I have neglected the induced speed
 
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WaspAir

Supreme Allied Gyro CFI
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Oct 21, 2006
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Colorado front range
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Bell 47G-3B-1, A&S 18A, Phoebus C, SGS 1-26A, etc.
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stopped caring at 1000
Thanks - that agrees with my expectations.
 

Vance

Gyroplane CFI
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Oct 30, 2003
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Nipomo,California
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Givens Predator
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The Predator has a noticeably better glide with a stopped propeller compared to an idling propeller at 800 rpm direct drive.

I did not attempt to quantify it as I always assume a worse glide ratio than she has so I make it to my landing spot.

My GPS shows glide ratio and it can be anywhere from three to one to five to one depending on conditions.

The Propeller did not windmill at 50kts indicated airspeed.
 

Jean Claude

Junior Member
Joined
Jan 2, 2009
Messages
2,409
Location
Centre FRANCE
Aircraft
I piloted gliders C800, Bijave, C 310, airplanes Piper J3 , PA 28, Jodel D117, DR 220, Cessna 150, C
Total Flight Time
About 500 h (FW + ultra light)
The Propeller did not windmill at 50kts indicated airspeed.

Windmilling does not mean restarting the engine. It just means aerodynamic torque helping it rotation.
To restart the engine, a greater aerodynamic torque is needed to overcome the first compression.
Only then it can continue to run without any explosion
 
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