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Glide speed

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General Aviation

dose there any formula to  calculate glide speed ??

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2 Answers

  1. Best Answer


    Brian on Jan 25, 2014

    There is no formula to calculate glide speed, if you are in a bind due to poor prep you can roughly estimate glide speed as twice your stall speed in a landing configuration. However, it’s far better to get your glide from the POH and keep it stored in your memory bank for the oh crap moments.

    There is a formula to adjust your glide speed for weight as in many aircraft you will only have a published gross weight speed and you’ll rarely fly at gross weight. That formula is:

    Glide speed adjusted for weight = Sqrt (actual weight / gross weight) * glide speed at gross weight.

    Example: Gross weight 2500. We are flying at an actual weight of 2000. Published gross weight best glide of 65…

    Glide speed adjusted for weight = Sqrt (2000/2500) * 65.

    ‘ ‘ = Sqrt (0.80) * 65

    Glide speed for this flight equals roughly 58 knots.

    —

    FWIW You can use a slightly altered formula that you can do on a basic calculator or in your head if you’re good with numbers. That formula is…

    Glide speed percent adjustment = [1 – (actual weight/gross weight)] / 2

    That formula yields a percent that you take off of your gross weight glide speed.

    Example using the numbers from above:

    Glide speed percent adjustment = [1 – (2000/2500)] / 2

    ‘ ‘ = [1 – (0.8)] / 2

    ‘ ‘ = 0.2 / 2

    ‘ ‘ = 0.1 or 10 percent reduction

    Since 10 percent of 65 is 6.5 we do 65 – 6.5 and arrive at an answer of 58.5 knots for our glide speed adjusted for this weight. The actual calculation from above was 58.14. As you can see it isn’t exactly the same, but it’s close enough if you need to do an on the fly calculation.

    —

    A few words in conclusion. All of the above is great on paper and wonderful to do on the ground before you fly. However, if you’re in the air and have not prepared yourself your best bet is to fly best glide. If you know you’re light fly a few knots slower.

    Whatever you do, don’t get so wrapped up in perfecting this speed that you slam into a mountain trying to attain a perfect glide speed. Set a pitch that is close, trim it, and find a place to land; these three steps are what is important. Losing your brain in endless checklists or calculations are not going to do you any good.

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  2. Mohammad Adaileh on Jan 26, 2014

    thank you very much wonderful information

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