SMOG. Signal, mirrors, over the shoulder look, go.
This is probably only a very minor consideration, but on a high wing passenger airliner the wingbox runs through the top of the cabin, stealing space from the overhead bins. You can see it in this photo of a BAe-146 cabin.
You’re 100% right the BAE-146 does that. But that’s not a necessity, that’s a design choice. One can build a cargo/passenger airplane so the wingbox runs above the cabin. See the pix here for a design that ensures the cargo compartment is full height full length.
Agree. But see this interesting future direction. It’s quite possible the next clean-sheet Airbus design, and the next+1 clean sheet Boeing design will be like this
The wiki is a bit dated. Here’s more from Boeing
https://www.boeing.com/features/2019/01/spreading-our-wings-01-19.page
It’s almost like a biplane, right? The truss is an airfoil that generates lift as well as a structural support for the main wing.
Semi-biplane.
The truss generates lift and also helps manage interference drag. But that’s not really a matter of needing it for lift, as was the case back in the 1910s. They need it for structural reasons when building the main wing that long and that thin. And then once they’ve got that strut structure hanging out in the wind, modern iterative optimization kicks in and they make it earn its keep every which way they can. Which includes generating lift.
Aviation Week https://aviationweek.com/ has had some nice articles interviewing the engineers doing the wind tunnel & CFD stuff. Lots more meat than the fluff in those PR pieces wiki & I referenced above. All paywalled of course. I don’t know what their policy is on freebie articles , but a search for TTBW on their home page might net some good info for folks without the kinda pricy subscription.
Overall, my impression is the ideas behind TTBW have some real life to them. Unlike certain ideas about imminent hydrogen airliners.
I love that design. Who would have thought struts would make their way back into high speed aircraft?
But it makes sense. What you give up in intersection drag you get back in strength, alloiwing a super high aspect ratio wing that’s really the secret to the plane’s efficiency.
I wonder if they optimzed the airfoils on the struts for cruise speeds? If they were maybe twice as wide, that wing could be called a diamond planform rather than a strut based wing.
It has a 215 ft wingspn. That’s about the wingspan of a 747. That’ll create some interesting airport ops issues if it ever becomes a real plane in service.
But I like the approach. If you are going to fly on a lot less energy for a reasonable distance, this is a good way to go.
This thing has an aspect ratio of 26. That’s in the same range as ultra high performance gliders. In comparison, a 787 has an AR of 9.5. Efficiency is everything in this design.
Would the structure to attach the wing to the fuselage be heavier with that sort of design? IIRC a full height cargo compartment at the expense of some extra weight is a more acceptable tradeoff in a military transport than a civil airliner.
I yield to the real engineers who can run the numbers.
However, I would have thought the hybrid design would be more suitable to the DASH-8 or ATR series design regional aircraft. Replace the turboprop with a fuselage mounted generator. replace the heavy wing-based engines with electric, and the entire wing structure is lighter - plus add in the struts and there’s a lot less stress and less need for stronger, thicker structure at the wing root. Plus as I understand, wind resistance/drag goes up dramatically with speed, so turboprop speeds are more suited to the extra strut. Add a bit of battery to aid during the power demands of take-off (much as how Toyota hybrids use a much smaller engine because the acceleration is aided by the battery). Battery weight near the front helps balance the generator engine set presumably at the back.
The main point though is the strut reduces the need for bracing the box between the wing root and the landing gear pods - particularly lateral diagonal bracing. To avoid the lateral braces running through the cabin, the box needs to be stronger (i.e. heavier) which is why the external struts instead are a major benefit.
This airplane needs to,fly really high to get the efficiency up. A regional airliner would spend more of its flight down lower, and less time cruising at altitude. Maybe that’s the issue? Also, regionals often go into smaller airports, and this thing has the wingspan of a 747.
Some forms of drag go up, and some go down with speed. Induced drag, the drag created from lift, goes down as speed goes up. Other forms of drag go up. This is why aircraft have an optimum cruise speed for drag that is not zero.
The long wing on that thing is all about efficient flight at very high altitudes. The higher you go, the lower the indicated airspeed. The airplane feels like it’s flying slower because the air is thinner. So induced drag goes up while parasitic drag goes down. Increasing the aspect ratio of the wing reduces induced drag while increasing parasitic drsg (form drag, skin friction, etc). At optimum altitude the decrease in induced drag will overcome the increase in other drag, making the airplane fly more efficiently.
This airplane will want to get as high as it can, as fast as it can. That super long wing will probably make it slow in roll response as well. So getting above the weather and into the thin air is likely critical to its success…
The plan is that the wings will fold just outboard of where the strut attaches to the wing. So the as-folded planform will fit in the traditional narrowbody 737/A320 Size “C” parking box: Aircraft Size Table (ifatceg.com).
Interesting! That’s cool, if the folding mechanism doesn’t wind up adding too much weight.
The upcoming 777X will have folding wingtips too. Just 10-ish feet at each end, so not too impressive in the context of the size of the whole airplane. But enough to keep the new longer & higher aspect ratio wings within the size E parking box.
See Boeing 777X - Wikipedia and the adjacent pic.
The TTBW is planned to have a lot larger percentage of the wing outboard of the fold line.
In a sense, the 777X effort is a proof-of-concept for the TTBW feature. Debugging the design process, the FAA approval process, the build process, and any operational issues. At least with the 777X, the thing will fly just fine with one or both tips in the incorrect = up position. That would not be true on a TTBW.
Or liability.
As I said, I yield to those who know the aerodynamics.
I guess the main point I had was the wing root does not need to be anywhere nears as strong if there are diagonal braces, nor does the inner part of the wing spar. That has to be a lot of weight savings. Particularly, too, it reduces the structural strength (i.e. weight) needed for the spar to brace and support the load of fuel. Plus, the box between the upper wing spar and the landing gear attach point needs less sturdy lateral bracing.
Sure, no argument with that at all. It is what enables that long wing. The long wing is the primary factor in how efficiently the plane flies. I assume that more than compensates for the added drag of the struts.