Partial Power Best Glide/range speed

Discussion in 'Flight Following' started by Matthew Rogers, Jul 18, 2021.

  1. Matthew Rogers

    Matthew Rogers Cleared for Takeoff

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    We are taught about normal operations and engine out emergency operations, but what about partial power operations? I have had a partial power emergency where my C150 had less power than required to remain aloft and I was 10 miles from an airport with dense forest or houses as the other choices. Mine was caused by a blocked fuel vent so the engine was not blowing itself apart and ready to depart the aircraft. Other examples could be fouled plugs (not likely to cause further damage), partially blocked intake, stuck throttle, one bad cylinder, etc. If that is the case, what speed is best to maximize the flying/glide range in order to have the best chance to make it to an airport.

    Let's assume that the airplane lost enough power that it is no longer able to maintain level flight at Vy speeds.
    Do you pitch for best glide speed in the POH?
    Remain at Vy speed?
    A higher speed since you have some power and it may get you somewhere faster in case the engine only has a certain number of minutes of running left?
     
  2. brcase

    brcase Pattern Altitude

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    Yes, Best glide speed is essentially the best lift per drag speed. technically it should also be thebest range speed, but I think the curve is very flat at that point so the difference between the published best range speed and best glide speed is very minimal.

    Brian
    CFIIG/ASEL
     
  3. Matthew Rogers

    Matthew Rogers Cleared for Takeoff

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    So best glide speed will extract the most amount of "UP" from the least amount of power? Even if the aircraft is falling, will the sink be lower at best glide than at Vy? But we also have to consider moving horizontally to make it to a far off landing zone. Like when we have to guess what is the best glide when pointing into a headwind (best glide + some fudge factor). And consider that the engine may still quit along the way. It is complicated, but my first thought was either Vy or Best Glide.