[jcampbell1]

The main argument against it is that it increases fuel consumption. Plowing your cargo area through the air sideways is just idiotic. There is some crazy public belief that it is more fuel efficient because the public doesn’t understand physics. These things keep getting getting publicity because even Hacker News folks don’t get it.

Long high aspect ratio wings and streamlined body are how you get fuel efficiency.

The fuel burn of a B2 is far higher pound for pound than a 737.

This idea gets even more ridiculous when you consider the cargo area is a pressure vessel. There is a reason the body is isomorphic with a welding tank.

Edit: I suppose I wouldn’t care about this, but the Biden Administration plowed climate money into a blended wing military concept, which 1 day with any CFD software shows is stupid.

[coredog64]

It’s not that simple. Aerodynamic drag is made up of surface drag and induced drag. Given the same coefficient of drag, drag goes up as S-wet goes up (which is what you’re referencing). Induced drag is a consequence of how much structure is required to create a flying vehicle. IF (and it’s a big if) the BWB turns out to be more structurally efficient, then the total drag for the plane might be less than for a conventional design.

(Source: I have an aerospace engineering degree from Embry-Riddle)

[dr_orpheus]

> There is some crazy public belief that it is more fuel efficient

There are a number of engineers at NASA and Boeing working on the X-48 who would disagree with you on this one.

The main advantage of the blended wing body is to reduce the skin friction drag [0] of the aircraft relative to the typical fuselage and wings. You have less surface area in contact with the air relative to the amount of internal volume. There may be some increase in the profile drag (i.e. the cross section of the aircraft) but is made up for by the reduction in the skin friction drag.

> The fuel burn of a B2 is far higher pound for pound than a 737.

This isn't really a fair comparison. They are two aircraft optimized for entirely different things.

[0] https://en.wikipedia.org/wiki/Skin_friction_drag

[jcampbell1]

Skin friction drag is a drop in the bucket compared to parasitic and lift induced.

I’m willing to accept that a gold bullion transporter can look closer to a flying wing, but with any reasonable cargo density you are back to the standard design.

Trying to intuitively explain CFD results is apparently just as hard as dispelling the Bernoulli nonsense about airfoils.

I’m right and high aspect ratio wings are a harder materials science and design challenge than blended wings. There is a reason 10000x as much engineering effort is going into folding carbon fiber wings for passengers/cargo. The folding is to increase fuel economy through aspect ratio and fit in terminal box.

Everything I have said is trivial to prove with CFD and experimentally. I get that popular science articles need to entertain the masses.

Let me ask you this, why is the tail of passenger aircraft upward sloping?

[dr_orpheus]

One, I'll admit I'm not an expert in this, I have an aerospace degree and took some aircraft classes but it was 90% on the space side of things. But I'm trying to be devils advocate here since its not just pop-sci articles.

> Skin friction drag is a drop in the bucket compared to parasitic and lift induced

I'm trying to rectify it with papers that say "In civil aviation, skin-friction drag accounts for around 50% of the total drag in cruise conditions" [0]

> I’m right and high aspect ratio wings are a harder materials science and design challenge than blended wings

I understand that higher aspect ratio reduces drag too and that the planes should all look like scaled up gliders with their long skinny wings. But as you said, it is harder. So is it a clear cut answer that exploring blended wing designs is a waste of time?

> Let me ask you this, why is the tail of passenger aircraft upward sloping?

To prevent tail strike during take-off and landing when you are at a high angle of attack.

[0] https://www.sciencedirect.com/science/article/pii/S037604212...

[jjk166]

Aerospace engineer here, this is incorrect.

Long thin fuselages dramatically increase drag due to skin friction. Blended wings have better lift to drag ratios, meaning for a given amount of fuel consumption (to overcome drag) you get higher payload/better range.

The B2 has twice the range of a 737 and cruises 20% faster.

[scarier]

I mean, aerodynamic drag scales linearly with both Cd and A. It isn’t too far-fetched to think that you might be able to trade them off in a blended wing design and come out ahead by reducing interference drag and wetted surface area.

The pressure vessel problem is much more concerning to me—I can’t think of a way to solve it that wouldn’t massively increase weight and/or reduce usable space.

To be fair, the B2/737 comparison isn’t particularly fair—they were optimized for wildly different things, and only one design was significantly constrained by acquisition and operational costs.

[runarberg]

I see. So this is why a flock of geese flies in a single file, rather then, say, a V shape.

[jcampbell1]

Goose wash is the problem with single file. Goose V takes advantage of the up current you get from the neighbors lift. Geese and evolution clearly understand areo better than current HN.

[shkkmo]

Do you have any sources for this? My understanding is that hybrid wings reduce weight needed for structural components. Since fixed wings basically trade drag for lift, reducing weight can more than offset increases in profile/shape that increase drag.

https://www.technologyreview.com/2013/01/24/180345/hybrid-wi...

[jdhendrickson]

I'm curious if your thinking on this matter has changed based on the replies you have received ?

[jcampbell1]

No. The points made seem to be like asking if it is a good idea buy something that costs 25% more when you have a 5% coupon.

[strongpigeon]

You seem knowledgeable about this. Do you mind expanding on why these aren’t more efficient?

[schiffern]

The problem is frontal area is higher, so more drag. Wetted area[1] is also much higher, so there's a lot of skin friction.

The advantages are (theoretically) lower structure mass per passenger. But airplane cabins are pressurized, and lightweight pressure vessels 'want' to be cylinders or spheres, not big flat boxes.

There's a aerospace engineering student who gave a thesis talk on the disadvantages of blended wing-body, and offers some possible solutions.[2]

[1] https://en.wikipedia.org/wiki/Wetted_area

[2] https://www.youtube.com/watch?v=IWBaddGG6z8

[kridsdale2]

I'm no aerospace engineer, but the flux through the air, driving resistance, seems obviously higher the more you move away from the shape of a missile.