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Old 09-22-2008, 05:42 AM
Look out for that tree!!!
Larry3215's Avatar
Join Date: Mar 2006
Location: Gig Harbor, Wa USA
Posts: 7,061

Originally Posted by BEC View Post
I suppose one way to get closer to the answer to question 1 is to fly a low powered setup with a BIG battery (so that voltage is "stiff" and sags little) though of course the added weight will work against that objective. I don't see how you can completely eliminate the variable of power to the prop when the load is - by definition - not constant in this situation regardless of what means is used to twist the prop. That is, unless we go back to some huge overpowering means and the wind tunnel/dyno combo mentioned before.

Thats why I wanted the raw data files - so I could "see" even very small voltage drops. It takes very little voltage drop to make a significant power drop when power changes as the cube of the change in voltage.

The answer to two is probably as varied as power system/plane/prop/altitude/flight profile combinations.

I suspect thats true - but it would be nice to see if there is a trend we can spot - or if the general beliefs are correct

The answer to three, as I understand it, can be "yes" in the case of high speed aircraft with deeply pitched props that are partially stalled until the airplane gets moving. I imaging Schneider Cup racers from between the wars and early WWII types like the Hurricane Mk. I that had fixed pitch props would be examples.

Id like to see if there is a case with our models where that actually occurs. So far there is no sign of it on any of the graphs we have seen so far. Trams hi speed setup didnt show any of that behaviour.

I have one setup that may have a chance of showing it - a warmliner turning a 14x12 prop at around 550 watts or so. Its a relatively slick airframe as well. I wont be able to try it for a while - it needs some repairs.

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