4 ms·

> Throw on a brace for support, though, and suddenly the high-aspect ratio concept becomes plausible. So, high aspect ratio is desired, but needs support... wh

by uticus 3y ago

> Throw on a brace for support, though, and suddenly the high-aspect ratio concept becomes plausible. So, high aspect ratio is desired, but needs support... why not extend the trusses for a biplane design? Not an aeronautical engineer, but from my armchair seems like high-aspect ratio and support are both gained by using a more familiar technology (I've seen pictures of real biplanes flying, have not yet seen a truss-braced like this concept in the air).

pfdietz 3y ago
Biplanes have supports between the wings that add drag. Also, biplanes typically don't have swept wings; here, the truss sweeps forward while the wing sweeps backward. Mentour Now! video on Boeing and transonic truss braced wings: https://www.youtube.com/watch?v=zkrdIw8LWrM https://www.youtube.com/watch?v=zkrdIw8LWrM
nvy 3y ago
The reason why you use a biplane design is to get more lift per unit span, so you can keep wingspan within some arbitrary constraint. As with all engineering, there is a tradeoff involved, and with biplanes you don't get double the lift because of the boundary layers of the wings interacting. You also pay a drag penalty as you have twice as much skin area exposed to airflow, and it complicates the design because in the transonic région you can get interactions between shockwaves causing flutter and other not so fun effects.
deleted 3y ago
[deleted]
huthuthike 3y ago
Biplanes have twice the number of wingtip vortices, so lots more drag. I suspect the reason biplanes existed in the first place was due to materials constraints. We didn't know how to make the wings strong and light enough to be very long, so kept them short and added a second set. This caused both more lift and drag. The drag was compensated for by running the engine harder (or using more powerful ones). We now have sufficient materials knowledge that we don't have a problem making wings long enough to lift the plane. We're instead working on reducing the drag, so we can make engines work less hard.

by uticus 3y ago

pfdietz 3y ago

Biplanes have supports between the wings that add drag. Also, biplanes typically don't have swept wings; here, the truss sweeps forward while the wing sweeps backward. Mentour Now! video on Boeing and transonic truss braced wings: https://www.youtube.com/watch?v=zkrdIw8LWrM https://www.youtube.com/watch?v=zkrdIw8LWrM

nvy 3y ago

The reason why you use a biplane design is to get more lift per unit span, so you can keep wingspan within some arbitrary constraint. As with all engineering, there is a tradeoff involved, and with biplanes you don't get double the lift because of the boundary layers of the wings interacting. You also pay a drag penalty as you have twice as much skin area exposed to airflow, and it complicates the design because in the transonic région you can get interactions between shockwaves causing flutter and other not so fun effects.

deleted 3y ago

[deleted]

huthuthike 3y ago

Biplanes have twice the number of wingtip vortices, so lots more drag. I suspect the reason biplanes existed in the first place was due to materials constraints. We didn't know how to make the wings strong and light enough to be very long, so kept them short and added a second set. This caused both more lift and drag. The drag was compensated for by running the engine harder (or using more powerful ones). We now have sufficient materials knowledge that we don't have a problem making wings long enough to lift the plane. We're instead working on reducing the drag, so we can make engines work less hard.