Talk:Wingtip device

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The lede says "Such devices increase the effective aspect ratio of a wing without greatly increasing the wingspan." The words "aspect ratio" only appears in one other place in the article, also unreferenced. Could we have a reference and an explanation, please? What is the "effective aspect ratio" and how do wingtip devices increase it? cagliost (talk) 21:19, 18 March 2025 (UTC)Reply

My suspicions were raised by the mention of aspect ratio. As we all know, induced drag is reduced by increasing wingspan, not aspect ratio.

Looking at Wingtip Devices: What they do and how they do it by Doug McLean, he says "Trefftz-plane theory tells us that we can reduce the ideal induced drag by increasing the vertical height of the lifting system, as well as by increasing the horizontal span." He does not give aspect ratio as a mechanism by which winglets work, and there is no mention of "effective aspect ratio", whatever that is. @Ahunt: @Dolphin51: you might be able to help. cagliost (talk) 22:05, 18 March 2025 (UTC)Reply

Definition and discussion of the intrinsic efficiency of winglets by Dieter Scholz mentions "effective span", but it's not clear to me he means this literally. I think he just means the effect of winglets can be compared to the equivalent-sized effect of a sufficient increase in wingspan. cagliost (talk) 22:12, 18 March 2025 (UTC)Reply

As you know, the drag on an aircraft is dependent on the lift being generated, the airspeed, and other things. If we confine our attention to cruising flight (straight and level flight) we can say weight instead of lift. So the drag is dependent on the aircraft weight and its airspeed, and other things. When contemplating small changes to an aircraft design to alter the drag we need to keep in mind that the weight and airspeed must remain unchanged.

The stalling speed at a given weight is partly dependent on the wing area, and the parasitic drag is partly dependent on the wetted area of the aircraft. When contemplating small changes to an aircraft design to alter the lift-induced drag we also need to keep the wing area unchanged so we don’t change the stalling speed or the parasitic drag.

When contemplating a change in wingspan to alter the lift-induced drag we could say “weight and wing area remain unchanged.” Alternately we could make use of an already defined ratio, the wing loading (weight divided by wing area), and say wing loading remains unchanged.

We know that increasing the span reduces lift-induced drag providing weight and wing area remain unchanged, and we can say so in those words. Alternatively we can make use of already defined ratios, the span loading (weight divided by wing span); and the aspect ratio (span squared divided by the wing area). Therefore we regularly see statements about lift-induced drag such as:

Reducing the span loading reduces the lift-induced drag at a given airspeed.

Increasing the aspect ratio reduces the lift-induced drag at a given weight and airspeed.

Dolphin (t) 23:41, 18 March 2025 (UTC)Reply

Aspect ratio is a quantity that is highly relevant in the study of ideal wings - uniform downwash, elliptical spanwise lift distribution, elliptical planform etc.

For a real wing without these ideal characteristics see Oswald efficiency number. For such a wing, the aspect ratio is replaced by the effective aspect ratio which is the square of the wingspan divided by the wing area and multiplied by the Oswald efficiency number. Dolphin (t) 01:08, 19 March 2025 (UTC)Reply

Thanks. It would be helpful if we could add these details to the article:

• What effective aspect ratio is.
• How wingtip devices increase it.
• References.

cagliost (talk) 08:13, 19 March 2025 (UTC)Reply

Throughout the article there are numerous statements that wingtip devices reduce drag. The word "drag" appears 26 times in the article but it doesn't appear in the titles of any of the 50 cited sources in the References.

When we say wingtip devices work by reducing drag we are talking about models of aircraft being tested in wind tunnels. If two models of the same aircraft, identical in all respects except that one model has wingtip devices and the other doesn't, are tested in a wind tunnel at the same angles of attack and the same airspeeds, the model with the wingtip devices will show less drag than the model without.

However, if we are talking about an aircraft supported in flight by lift, and propelled by thrust from propellers or jet engines, the situation is significantly different because the drag is determined by the thrust. In level, unaccelerated flight, the drag is equal to the total thrust from the propellers or jet engines. If we imagine two aircraft, identical in all respects except that one aircraft has wingtip devices and the other doesn't, the two aircraft are producing the same thrust and experiencing the same drag; but the aircraft with wingtip devices is flying at a slightly faster airspeed than the aircraft without. The rates of fuel consumption in the two aircraft are identical; but the aircraft with wingtip devices is flying faster so its specific range (miles per gallon, litres per 100 km etc.) is better than in the aircraft without devices. That is the reason our article talks about wingtip devices delivering improved performance; and References 1, 2, 15 and 50 contain the word "performance" in their titles.

It is almost universal that pilots and non-specialist people talk about lift and drag acting on aircraft in flight. In contrast, when scientists and engineers are talking about the same thing, they more commonly talk about coefficients - lift coefficient and drag coefficient. Another example is that pilots and non-specialist people are likely to describe the benefits of wingtip devices in terms of reduced drag; whereas scientists and engineers are likely to describe the benefits in terms of improved performance, higher cruising speed, better specific range, higher Oswald efficiency number etc.

We need to adjust the article so it says less about wingtip devices reducing drag, and more about these devices delivering improved performance and the other benefits described in reliable published sources. Dolphin (t) 12:21, 6 April 2025 (UTC)Reply

You are right to say wingtip devices improve performance. Another way to put it, is they improve efficiency. Whether an airline chooses to take this as reduced fuel burn for a given airspeed, or increased airspeed for the same fuel burn, is a choice they must make. Probably they do a bit of both.

We could say wingtip devices reduce drag for a given airspeed. To say they "reduce drag" without qualification, is like giving a numerator without a denominator. cagliost (talk) 16:06, 29 May 2025 (UTC)Reply