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Aerospace Glide Ratio and Scale

  1. Jul 12, 2010 #1

    I am looking into the design of gliders with good L/D / Glide Ratio.

    It seems hard to find what is the most efficient full size glider, and the same goes to a scale r/c type one too.

    So any ideas?

    If i was to start from scratch, what should i be looking at to get the best l/d ratio possible?

    The AIM is to get the most airtime and/or distance.

    I read in a book that speed has little effect on the L/D ratio, is this true? If so, is this only true down to a certain speed, ie, stall speed?

    Project needs to address to if the aircraft can be used with a powerplant.

    Is the use of a glider for adaption to a low power, and long distance aircraft better than building an aircraft from scratch for this purpose?

    My area of study is Mech Eng, but I want to get into Aero Engineering after graduation, and i have an interest in fluids and aviation in general, thus having an Aero themed project to try get some knowledge about Aero Engineering.
  2. jcsd
  3. Jul 12, 2010 #2

    Filip Larsen

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    Gold Member

    Flying gliders but not R/C model I'm not sure what you ask. A modern glider has a glide ratio around 40-50 with the airspeed for maximum glide a bit above the speed for minimum sink rate, as calculated as the "tangent" from the glide polar [1]. The glide ratio do vary with speed, enough so that flying with the "correct" speed is significant in competition flights [2] and you would usually also correct for wind speed so that you fly a bit faster in head wind and a bit slower in tail wind.

    I assume the performance of a R/C glider somehow can be transformed from the performance figures of a real size glider using the "standard" scale laws in aerodynamics, but I suspect "heuristic" knowledge about build and flying R/C models is far more important than general theoretical knowledge about aerodynamics.

    [1] http://en.wikipedia.org/wiki/Polar_curve_(aviation)
    [2] http://en.wikipedia.org/wiki/Speed_to_fly
  4. Jul 12, 2010 #3
    Any aerodynamic behavior of a vehicle is a function of its angle of attack and sideslip. Airspeed does not dictate best L/D ratio, angle of attack does.
  5. Jul 14, 2010 #4
    All i was wondering, thanks.
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