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4 Answers

Glide range increase with incresed mass and a headwind

Asked by: 2833 views , ,
Aerodynamics

Hello All,

So apparently the glide range increase if you increase the total weight and add headwind.

Can anyone tell me how to calculate that?

 

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4 Answers



  1. KDS on Jun 19, 2018

    It doesn’t.

    The maximum glide ratio remains the same regardless of weight. What changes is the speed at which that maximum glide ratio is achieved. The heavier the airplane, the faster the speed for maximum glide distance.

    A headwind will always decrease the distance that is achievable regardless of any other factors.

    Few airplane pilots understand the nuances of gliding and a lot of glider pilots don’t understand them either, but once you do, it’s a fascinating subject.

    Here is a detailed explanation:

    https://www.maa.org/sites/default/files/pdf/Mathhorizons/MH-Apr2008_OptimalSoaring.pdf

    Here is KDS’s simple rule of thumb:

    If achieving distance is your objective, fly the Max L/D speed. Add one half of the headwind component or subtract one quarter of the tailwind component as applicable, but never fly slower than minimum sink speed.

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  2. KDS on Jun 19, 2018

    I left out one element.

    In lifting air, fly slower. In sinking air, fly faster. How much slower and how much faster depends on the rate of the vertical air change.

    However, for airplanes, you can pretty much ignore that part except in extreme situations.

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  3. Surenthan on Jul 06, 2018

    Hello,
    So here is the answer for my question;

    * A/C1 @ 1000kgs Best glide speed 90kts for best L/D ratio= 8
    * A/C2 @ 1400kgs Best glide speed 100kts for best L/D ratio=8
    With a condition of 0 (zero) wind, glide distance from 2500ft Altitude
    2500* 8 = 20000 ft (air distance)
    Time:
    @1000kgs : Ground speed= 90kts= 9000ft/min
    @1400kgs : Ground speed= 100kts=10000ft/min

    @1000kgs => 20000ft/9000ft/min => 2.22min
    @1400kgs => 20000ft/10000ft/min => 2.00min
    > At higher weight we travel the same distance but faster (because there is no wind)

    With 20kts headwind:
    The air distance is still 20000ft

    What is the ground distance?
    Based on time calculated before:
    (ground speed (ft/min)) x (time to reach the ground) = ground distance in feet
    @ 1000kgs: ground speed = 90kts – 20kts = 70kts => 7000ft/min
    7000ft/min x 2.22min = 15540ft (ground distance)
    @ 1400kgs: ground speed = 100kts – 20kts = 80kts => 8000ft/min
    8000ft/min x 2.00min = 16000ft (ground distance)

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  4. Brian on Sep 01, 2018

    Wow. I love math and that was painful! I just felt the need to point out that you came to the same conclusion as KDS. Glide ratio ,I’ll add within usable weights of most aircraft since I dislike absolutes, will remain unchanged with variations in weight. Headwinds will decrease your glide range. Tailwinds will increase. KDS said exactly that and your numbers support it.

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