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Old 11-10-2009 | 05:35 PM
  #37  
pe reivers
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From: Arcen, , NETHERLANDS
Default RE: A matter of thrust


ORIGINAL: Sport_Pilot

Some “square” props (diameter & pitch numbers same) or over square props (pitch number greater than diameter) tend to partially stall or are in turbulence when ran statically.
I don't think the plane would take off if the prop was stalled, unless only part of the prop is stalled. When the prop is turning on the ground the air speeds up and has velocity before entering the prop. It would likely only be stalled when revving up quickly from idle.
I have a nice example of foil stall.
When extending the AoA of the blade, the lift does not drop all that much, and there is sufficient lift to propel a plane. At certain aspect ratios, there even is a second lift peak! However, the drag at these high angles becomes very large, and a lot of engine power is wasted in just stirring the air. The realm of low drag is the region before the first lift peak has occurred. That is where the engine can unload, and produce best power/thrust ratios.
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