How can a designer maximize the glide ratio of an aircraft with low aspect ratio wings, other than by increasing the aspect ratio?

Question

As I understand it, the gliding range is given by a lift to drag ratio—hence to increase the gliding range, I would want to increase the lift and reduce the drag as much as possible.

To that end, apparently, it seems that high AR fits both the bills. However, does that mean that I will not able to enhance the gliding range with low AR wings at all?

Sure you can. Shave off some of the wing chord to make them into higher aspect wings. The increase in wing loading won't decrease your gliding range in still air, and it will actually increase the gliding range if you are gliding into a strong headwind. Also, make like hawk and get some slotted wingtips, ideally ones you can close at will when you need to fly fast. — quiet flyer, May 02 '20 at 13:49
Highly related (if not a dupe): Relation between drag and aspect ratio — Manu H, May 02 '20 at 17:50
Does this answer your question? What dictates the aspect ratio of an aircraft's wing? — Manu H, May 02 '20 at 17:51

Peter Kämpf · Answer 1 · 2020-05-03T05:02:20.333

5

With a given wing span, everything that reduces drag will increase the gliding range. Aspect ratio is less of a factor here because induced drag depends on wing span, not aspect ratio. But increasing the aspect ratio with a given wing span will reduce the wetted surface and, consequently, friction drag.

What can be done to increase gliding range outside of increasing span?

retract the landing gear,
avoid struts or bracing wires,
minimize friction drag by allowing for more laminar flow and minimum surface area.
minimize pressure drag by streamlining everything

Generally, a low aspect ratio shifts the polar point of best gliding range to lower lift coefficients, so reducing all that parasitic drag becomes more important the stubbier the wings are.

The most effective way, however, to increase gliding range is indeed a larger wing span if all other parameters are held constant. Increasing span while keeping wing area constant will:

increase aspect ratio and reduce wing chord,
reduce induced drag at the same lift coefficient,
and, as a consequence, lower the optimum gliding speed, so the parasitic drag is lower as well.

edited May 03 '20 at 05:02

answered May 02 '20 at 17:41

Peter Kämpf

231,832
17
588
929

I think you should describe the effect of low and high aspect for the same wing area. – John K May 02 '20 at 21:41
@JohnK it has already been done in this answer – Manu H May 03 '20 at 07:23
No that answer also talks about different ARs with the same span, so one has less area than the other. I'm talking about two wings of the same area, say because I want to consider two cases with the same wing loading in order to have the same stall speed. A 1-26 has 160 sqf and 1-23 has 165 sqf, more or less the same, AR of 10 and 17 respectively. L/D of 23 and 31 respectively. For two wings of the same area, the higher AR does better even tho wetted area is the same. I believe the answer is related to lower tip losses and the higher AR is moving a larger package of air a smaller amount. – John K May 03 '20 at 12:50
@JohnK: The higher AR does better because wingspan is larger. 16 m versus 12.2 m - that is about the ratio if their respective L/Ds, too. – Peter Kämpf May 04 '20 at 05:33

How can a designer maximize the glide ratio of an aircraft with low aspect ratio wings, other than by increasing the aspect ratio?

1 Answers1