My friend Bernardo Malfitano gave me permission to post this email he wrote to me explaining why there aren't any blended wing body commercial aircraft.
I think it's just "too different".
A couple years ago, someone used a picture of McDonnell Douglas' BWB model, and a CG image from Popular Science from about 8 years ago, and created a fake press-release/leak type thing saying that the "797" would be a BWB. (Do some Googling, you can find it) Despite the obvious fakery (the next "7 N 7" will almost certainly be a 737 replacement, and aviation fans like myself recognized the images used, and the specs listed for the BWB were insane like 900 seats), many aviation sites ended up seeing discussions about the feasibility of introducing of a BWB into commercial service. Some of the points raised were:
- The way that cargo/luggage, food, trash, people, etc, are loaded onto a commercial jet today assumes that you have access to the side of the fuselage, i.e. these mechanisms depend on systems that push people and things horizontally into or out of the side. In a BWB, the "sides" are the leading and trailing edges, and it might not be possible to put doors there, so things would have to be loaded up straight into the belly. That would require a whole new fleet of carts and belts and stairs and so on to get people and luggage and cargo and food and trash into/out of the jet. You'd need to load a BB pretty much the same way you load a bomber.
- Since you can't really put doors on the sides (except perhaps at the very front), how do people get out in case of a belly landing or water landing? You'd probably need a way to get them out onto the top.
- If you're seated in a conventional tube-shaped fuselage, you're at MOST a few seats from the centerline. When the airplane banks, your butt goes up and down a few inches, maybe a foot. But in a BWB you'd have many more people per row, and some of them would be seated way out, and would move up and down several feet when the plane banks. Would people be ok with this? (Then again, people get used to stuff like this. Notice that air sickness bags are not regularly seen anymore. And I would guess that fewer people get carsick today than they did, say, 70 years ago).
- It's harder for the manufacturer to release modified versions. If you want a bigger or smaller version of a 737 or 787 or A320 or whatever, you add or remove a cylindrical section to the tube (and maybe add some area to the wingtips). With a BWB, the cross-section is nowhere near constant in any direction, so you can't really take one and make a bigger or smaller version without redoing the whole thing.
- It's not 100% understood how BWBs stall, or how they spin. A strong gust of sideways wind could induce some funky spinning, and it may or may not be possible to recover. Controllability at the slow-speed edge of the envelope could depend drastically on what we now think are minor aspects to the configuration, like where the engines are and where the control surfaces are relative to each other and to the curvature of the wing. And dynamic stability could be an issue (it has been for all the Northrop flying wings). These are the kind of thing that a fly-by-wire system and big control surfaces (as in the F-22) can overcome, but we don't know 100% for sure, and for commercial operations you'd want something less draggy than the F-22's huge control surfaces. I think it's this set of questions that the X-48 program aims to clear up.
Here are some links about the "797 BWB" thing:
More BWB stuff from the last time this idea was "hot" (late 90s), when McDonnell Douglas and NASA Dryden and Stanford were cooperating in looking into the technology:
And of course, the X-48: