As far as I know, it’s only been used for military aircraft. Why not passengers and freight? Doesn’t it have the potential to have a significantly higher volume and payload capacity?
Flying wings are unstable, and very difficult to fly. In fact, I think modern flying-wing aircraft all rely upon computer assistance to mitigate this problem.
Instability gives you a more maneuverable aircraft, but it also gives you a more dangerous one. That’s a bad tradeoff for freight service, and a worse tradeoff for passenger service.
Mr. Excellent summed it up, well, excellently.
There was an article years ago about how the B-2 bomber, a flying wing, would have been impossible without computers to keep it stable. A quick bit of Google revealed this.
Here is a Wiki article on flying wings for anyone interested.
I’d say that the initial capital costs would be more of a detriment than instability in the design. Modern jets aren’t inherently stable without computer controls anyway, but a flying wing design would be much more expensive initially than a conventional freight air craft, and I doubt the ROI would be worth the initial costs.
-XT
If you want to fly fast with efficiency, you need small(ish) wings. If you want to haul significant numbers of passengers / tons of cargo with efficiency, you need to put these in a tolerably narrow fuselage to which those smallish wings are attached.
The task of making a large flying wing controllable is manageable. But flying it at airline speeds will be inefficient. Its efficient speed will be unacceptably slow (which is another form of inefficiency).
I saw a program on this (Discovery Channel?) a couple of years ago. There’s another issue besides the stability problem: passengers like windows, and flying wings don’t have very many. It seems like a trivial issue, but apparently, it’s actually a huge barrier. Airlines don’t want planes that passengers don’t want to board.
There are two other factors that I know of.
Cost of construction. The fuselage of most jets is just a tube. Easy to build, and easy to engineer to take the loads and pressurization cycles. The 707, 727, 737, and 757 all had the same fuselage cross section. The joke was that Boeing had a big sausage machine that churned it out, and they just cut off whatever length they needed.
Passenger experience. This is sort of hard to explain, but it has to do with the movement the passengers feel when the plane turns. When a plane banks to enter a turn, one wingtip goes up, the other goes down. The passengers don’t feel it much because they’re sitting so close to the centerline of the plane. (The people in the window seats only go up or down a couple feet.) A flying wing is designed to spread the load out along the whole length. For the people sitting at the extremes, it’s gonna feel like the floor just fell out from under them.
I was going to mention the same thing.
But, it could definitely add to the whee! factor. Make flying an adventure again.
Would inertia be a factor as well? I mean, the B-2 carries all the heavy stuff in the belly. How much would the wings need to be beefed up to carry freight or people in 'em?
As I have grown older, I have come to realize that the adventure factor is not a positive concern in most people’s lives.
In a sense, a flying wing could be less strong. That’s their advantage.
Find a picture of a modern airliner and look at where the wings attach to the fuselage. That connection has to be incredibly strong. All the lift that holds the plane up comes from the wings. All the weight that’s trying to pull it down is in the fuselage.[sup]*[/sup] Build that too weak and the wings go up while the rest of the plane goes down.
In a true flying wing, with the payload spread across the whole span, you don’t have that connection. There’s no one part of the plane that’s carrying another; each part kind of carries itself. The structure is just strong enough to keep all the parts flying together.
Not strictly true, if you count the fuel. Most of it is stored in the wings.
So I can see why passenger aircraft wouldn’t use it. People get overly fearful in airplanes and shaving off a few hours in a long flight matters a lot for them.
What about freight? It’s much more patient than passengers, doesn’t care about windows and requires more lift than passengers (doesn’t the flying wing design give you more lift?). What’s so different about carrying explosive freight you unload at 30 000 feet vs unexplosive freight you unload at ground level? It should be easier and cheaper, if anything.
Related question: Does air resistance increase at the square of velocity? Does lift increase in the same way?
Google “Boeing Blended Wing”. Even without worrying about stability flying onboard a blended wing airliner would be a rather different experiance. There should be more cabin space which would normally translate to more seats (800-1000 in BBW’s case), but the cabin layout would be radically different then other airliners. Going with an amphitheater like layout might help alleviate some of the claustrophobia from the lack of windows, but it’s a huge gamble. Airliners could try to lure passengers by opting for more amenties (like lounges, sleeping berths, etc), but that’s unlikely. Everytime a bigger jetliner comes on the scene those get suggested and airlines always opt to cram in more seats.
Modern aircraft already carry a significant amount of weight on the wings: fuel and engine pods. Flying wings (or equivalently, an airfoil-shaped fuselage) only make sense if you have an airplane so ginormous that with a conventional design the wings would have to be that thick anyway, and transferring load from the wings to the fuselage would become too difficult. Even then it might make more sense to have multiple fuselages/nacelles linking wing segments.
Making them stable requires careful design, but the Hortonshad worked all that out prior to WW2.
The majority of hang-gliders are flying wings, yet manage with wetware based control systems.
All the freight-carrying planes I can think of are either designed for the military (which means they have to be able to operate from short, rough airfields) or are modifications of passenger-carrying jets. I don’t think the civilian freighter market is big enough to justify the expense of designing an aircraft just for that role.
Refitting a bomber would raise all sort of security issues. And bombers usually carry a small payload a very long way, so probably wouldn’t be a good fit anyway.
Hang gliders have a much lower center of gravity than say, a B-2 Spirit bomber.
As for “adventure”, most passengers don’t want a rollar coaster ride
There is also the cost of modifying airports to land a flying wing. Most commerical runways in the US are 150’ wide, then you need to have gate or ramp space to park the aircraft. If it’s only wing, the aircraft may be too wide to land or taxi at most airports.
Take a look at FedEx’s ramp at Memphis Airport (kind of an awful photo for Google). That is a lot of infrastructure committed to “normal” aircraft. To convert from conventionally designed aircraft to flying wings would require some huge changes to service those aircraft.
In my case vary much so. I just love flying on a clear day when I can sit and look out the window and see the ground roll up below me… Maybe it’s because I’m a mapoholic. 
The load is applied at “hang point” on the keel, at or at most a few inches below the lower wing surface. (assuming a lower surface) Most are reasonably stable when the pilot releases the control bar, and is hanging free. The airframe sees this as a point load at the hang point.
Anhedral is required in most flex wings to reduce roll stability and permit manageable control forces. This accomplished by designing the wing to fly in a nose high attitude, causing the sweep of the wing planform to translate to anhedral.
Roll stability in a flying wing is no different than conventional aircraft. Conventional aircraft have no surfaces beside the wing that influance roll stability. There is no reason a flying wing can’t incorporate dihedral, though most don’t require it. Roll instability is normally slow, tame, and not difficult for a pilot to manage.
Pitch stability in a flying wing is another kettle of fish. For stability, the CG needs to be ahead of the wings center of lift, which produces a nose down pitching moment. This must be countered, and conventional airplanes do this with upward force generated by the horizontal stabilizer. By placing the H. stab well aft, not much downward force is needed (long lever) so efficiency is pretty good.
Lacking the H. stab, pitch stability in a flying wing is accomplished by reflexing the trailing edge and/or washout in swept wing tips. A forward swept wing can use a bit of washin, working as a canard. I’m pretty sure the Genesis sailplane does this. The Genesis does have a small H. stab. This was a late addition to the design. It is much smaller and closer to the CG. than conventional gliders and is not the only source of pitch stability.
Because the trailing edge, or wingtips are not very far aft of the CG, large forces are required, and this reduces the efficiency of the wing. To improve this, the CG is moved aft, which reduces stability. It is a fussy bit of compromising, but as I stated, the Horton Brothers had gotten pretty good at this back in the early 1930s. Good enough to build contest winning gliders and Nazi medal winning jets which of course didn’t need yet-to-be-invented computers for stability augmentation. The brothers routinely flew the gliders yet managed to life until mundane deaths in the 1990s.
It is simply not true that aerodynamically stable flying wings flyable by ordinary pilots can’t be built. It has been done more or less routinely for many decades.
By reducing aerodynamic stability, and restoring it with electronic augmentation, it is possible to improve the efficiency and maneuverability, or reduce the radar signature of nearly any aircraft configuration. This is not unique to flying wings. The fact that well know contemporary flying wing designs use computerized stability augmentation does not mean they can’t be made controllable without such.
Another factor in a passenger plane is emergency exits. You’d have a lot of people a good long distance from anywhere a door can go, and meeting the certification requirements for total evacuation time could well be impossible.
Besides the difficulty of getting a wing up to a passenger gate, there’s the difficulty of getting loading/unloading equipment up to a freighter. For largely the same door-positioning reasons, it would be difficult to access containers in the plane’s interior. The extra time, even if it were feasible to do it at all, would be a serious impact on a freight firm’s operations.
And a wing is not a flexible design. With a conventional layout, it’s fairly easy to size the plane to optimize it for for a given market type and route length by lengthening or shortening the cube. There’s no way to do that with a wing - there’s only one sweet spot possible, and if you don’t meet it, you need a completely new design. Big bucks, of course. The most cost-effective way to make and fly a freighter is to base it on a passenger plane - not even conventional-layout planes designed from scratch as freighters have ever found a way to compete.
They do look cool, but unfortunately that isn’t enough.
(Assuming you meant downward force from the stabilizer.)
I’ve heard before that all aircraft (leaving aside the unusual canards) produce downforce with the horizontal stabilizer, but never any explanation for it. Is it really just that a stable wing must have the CG ahead of the center-of-lift, or is there any deeper explanation possible?
(For one thing, I always thought a taildragger needed some lift to get the tail off the ground before takeoff. I know the main landing gear must be ahead of the CG. Is it still the wings lifting the tail, while the tail itself is producing downforce?)