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Do propellers really "unload" in flight?

Old 02-02-2014, 05:32 PM
  #126  
Larry3215
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Thats by far the safest way to proceed

Two other thiing to note are:

1) all the testing we did was 4 years ago. Many of the newer hi C batteries hold voltage significantly better than they did back then. That will reduce the % of "unloading" from battery voltage sag.

2) a small but significant % of the "unloading" in the air seemed to be due to heat losses in the motor/esc. That kind of power drop may look like "unloading", but it certainly wont help save your power system if your exceeding its limits
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Old 02-02-2014, 10:22 PM
  #127  
kyleservicetech
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Originally Posted by rcers View Post
That echo's my findings. Unloading in flight is variable, and the voltage drop is hard to differentiate from the "unloading" drop in current.

Square or over-square by far the most likely - on slippery ships.

I essentially account for little, if any, unloading and assume stalled static is about the right number to use for being safe with the equipment. If I was over on the ground I didn't use the setup, period. In other words I don't account for any unloading for safe margins with equipment.

Mike

Yeah
For those that have access to an ESC with data recording, such as the Castle Creations ICE series, make a wide open throttle pass over your field. Then return while in about a 20 degree climb out at WOT, and again return back with about a 20 degree descent.

The results might surprise you. The angle of attack of your model has a very significant effect on the watts pulled by the motor. Likely more than any prop unloading effect that might be present. One one flight at WOT, I actually had the current pulled by the motor drop from 75 Amps during a climb out, to less than 15 Amps during about a 30 degree descent. How much your model drops off really depends on how streamlined your model is, and what prop pitch your model has. If you don't see the current drop off notably from a climb out to a descent, IHMO, you might have the wrong prop on your model for general purpose flying anyhow.
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Old 02-03-2014, 12:43 AM
  #128  
rcers
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Originally Posted by kyleservicetech View Post
Yeah
For those that have access to an ESC with data recording, such as the Castle Creations ICE series, make a wide open throttle pass over your field. Then return while in about a 20 degree climb out at WOT, and again return back with about a 20 degree descent.
I have a Graupner Telemetry ESC with data logging and several ICE controllers. The Graupner gives me all the flight data and I can replay the data from the flight....

It shows widely varying AMP, and voltage data. It, like the Castle Ice Logging, is hard to match to an exact moment in flight. You can do better with the Graupner as I can also tie altitude to the log, had I attached the variometer.

It is super hard to determine exactly the amount of unloading, vs voltage drop, vs voltage sag, vs one of the other many factors.

There is no question a climb - takes more power. Similarly a descent takes less. Just hard to match it all up and be 100% certain that it is attributed ONLY to prop unloading.

Originally Posted by kyleservicetech View Post
The results might surprise you. The angle of attack of your model has a very significant effect on the watts pulled by the motor.
I completely understand it takes power to climb and less to descend.

Originally Posted by kyleservicetech View Post
Likely more than any prop unloading effect that might be present. One one flight at WOT, I actually had the current pulled by the motor drop from 75 Amps during a climb out, to less than 15 Amps during about a 30 degree descent. How much your model drops off really depends on how streamlined your model is, and what prop pitch your model has. If you don't see the current drop off notably from a climb out to a descent, IHMO, you might have the wrong prop on your model for general purpose flying anyhow.
Again - I am not talking about the power difference in climbs and descents. I am talking about level flight, propeller "unload". Some say as the model is at max speed, the load drops due to prop unload. I believe it does, but MUCH less than many think.

Hard to test in flight - even with excellent logging as you can't fly straight and level for very long, especially with the slippery, square or over-square props that propel fast, slippery models.

Mike
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