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Reading about recent Boeing's high aspect ratio wing concepts for commercial aircraft, such as TTBW and SUGAR, I couldn't help but think of the Hurel-Dubois aircraft, where similar aerodynamic choices seem to have been made back in the 1950s.

Why has there been such a long gap in aircraft history, to see a rebirth of such a high aspect wing ratio transport/commercial aircraft family, since advanced materials to improve the concept were already available in the 1970s?

enter image description here

(TTBW)

sugar

(SUGAR)

hd34

(Hurel-Dubois 34)

hd10

(Hurel-Dubois 10)

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High aspect wings provide the best efficiency, but the current airline business model needs more than just efficiency; it also needs to keep speeds up.

Modern airlines could save on fuel by flying slower, but they would lose some business to other forms of transport or airlines that did not slow down as much. As long as fuel prices remain under a certain limit, this trend will continue. In this answer, Peter Kämpf speculates that limit might be around 200USD per barrel (originally gallon, but likely a typo).

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    $\begingroup$ +1 There is also the limited gate space (I think the first two photos show narrow-bodies). $\endgroup$ – ymb1 Jul 29 '19 at 11:46
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    $\begingroup$ Per barrel, not per gallon. Peter can make misspellings too. $\endgroup$ – Therac Jul 29 '19 at 19:09
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    $\begingroup$ @Therac to be honest I did vacillate when copying that, but decided to trust his words because freedom units are not my forte. Upon review it does make more sense; fixed $\endgroup$ – AEhere supports Monica Jul 29 '19 at 19:10
  • $\begingroup$ Gate space in theory should not be a problem - there's boeing 777x with folding wing tips. $\endgroup$ – Electric Pilot Jul 31 '19 at 18:13
  • $\begingroup$ As per Boeing links, you can make a braced wing with a high sweep too. Boeing claims that speeds of 0.8M is achievable with new braced wings boeing.com/features/2019/01/spreading-our-wings-01-19.page $\endgroup$ – Electric Pilot Jul 31 '19 at 18:27
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The "historical gap" has been created by sheer size, speed, and weight differences in modern transport. Although the Hurel Dubois 34 features a high aspect wing, note it is also heavily cambered and designed for 175 mph flight. A non starter.

High aspect wings are very efficient, but their stall AOA is much lower than a low aspect wing.

The pitch inertia of a very large aircraft will much more readily torque the fuselage past stall AOA of a high aspect wing. Notice that this would be a consideration for larger tail volume, and is a problem high efficiency/low drag designs are struggling with even today. Take a look at a Boeing 707 plan form. See how much wider the wings were and bigger the tail was. This all adds to higher stability, but alas, higher fuel consumption.

But there is a solution to this dilemma, known 100 years ago, have another wing forward of the main wing as a stall "feeler". This is the poor man's MCAS. This wing would stall first and drop the nose. A bi-plane? Technically, yes, but how big should the forward wing be? The range would include canard all the way up to second wing.

Perhaps something resembling the Rutan Model 76 Voyager - with Hstabs/elevators added on rear for (larger scale) adequate pitch control - and LNG in the booms! (the jets could be mounted on the central fuselage).

But if they want very high aspect wings, 21st century engineers can't just scale up a sail plane any more than the dolphin can be scaled up to a blue whale without major design considerations, which must include safety.

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  • $\begingroup$ In first picture, adding some swept angle to high aspect ratio wing may sovle pitch inertia issue $\endgroup$ – qq jkztd Jul 30 '19 at 15:17
  • $\begingroup$ @qq jkztd That's a thought. Dunne helped control it with down wash on the wing tip. Note that with a swept wing tip control surfaces are possible, but tail usually provides more torque. The fore wing in my proposal really takes the slat and moves it to the FRONT of the fuselage. Look at the Rutan Voyager, and also what he is doing with Virgin Galactic. Imagine a fuselage carried around by the Knight (LNG in the booms). It's the 21st century, maybe time for something new! $\endgroup$ – Robert DiGiovanni Jul 30 '19 at 21:39
  • $\begingroup$ sorry what's/who's Dunne? $\endgroup$ – qq jkztd Jul 30 '19 at 21:53
  • $\begingroup$ (rutan voyager wasn't made to land or behave at high AOA either.) $\endgroup$ – qq jkztd Jul 30 '19 at 21:56
  • $\begingroup$ Dunne made the swept wing biplane early 1900s, rejected for being too stable (Etrich Taube had the same problem). Yes, noticed a few things with the Voyager on takeoff that may have needed some adjustment, but it flew around the world without refueling. Putting control surfaces at both ends should give superior stability control, if needed. And yes, larger slats too. $\endgroup$ – Robert DiGiovanni Jul 31 '19 at 0:38

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