Sailplanes have much higher L/D than jetliners. But they are three times slower.

Is it practical to make a vanilla sailplane glide at 600mph by lifting it to a ridiculous altitude? If so, what would be the quantitive effect on L/D?

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    $\begingroup$ Check out Perlan 1 and Perlan 2 high altitude glider projects. According to Wikipedia, Perlan 2 has a $V_{ne}$ of 434 mph (TAS). When at it's service ceiling of 90k feet, it is designed to fly at around around 400 mph. $\endgroup$ Feb 3 at 4:07
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    $\begingroup$ aerodynamic flutter has entered the chat $\endgroup$
    – tedder42
    Feb 3 at 5:52

1 Answer 1


Use this calculator to work it out. If your glider reaches it's L/D max at 70 kt indicated, pretty typical, and you tow it to 50000 ft, its max L/D will still be 70 kt indicated, but the TAS will be 140 kt.

To get to 600kt TAS, you'd be flying it at 300 kt indicated at 50000 ft. Well past the typical glider's Vne of, say, 120kt. So you would be diving vertically, and it would likely come apart first.

At 90000 ft, at 70kts indicated, TAS is 196kt. To get to 600 kt, you'd need to be at over 200kt indicated, still well exceeding the Vne of a typical glider. Best you could hope for is 350-400 kt and not exceed Vne, and that would still be a vertical dive. If you're gliding for best range with a Max L/D at 70kt indicated, 196 kt TAS is it.


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