I fly a Cessna C-172, and if I have any bank when stalling, I have to use rudder to level the airplane. If I use aileron, the bank angle will increase and bring the airplane into a spin.
My question is, if there is no rudder or vertical stabilizer, like a B-2 bomber for example, how could a plane recover from a stall?
This question is different from others because this is not focus on the stability or control of 6 freedom. I would like more discussion on the recovery of spin and stall.
The answer depends on the type of flying wing aircraft.
The B2 for example is an example of a flying wing aircraft with rudders. It's just that it doesn't use conventional boat style rudders attached to vertical stabilisers since it doesn't have any vertical stabilisers. Instead it uses drag rudders.
There are several different types of drag rudders. The B2 uses one of the most effective designs as proven by countless experiments: the split elevon (sometimes called duckerons since they look sort of like duck bills). If you look at pictures of B2 landing you can clearly see them open at the wingtips.
Regardless of the type of drag rudders, they work via 2 principles:
The simple to understand one whereby if you increase the drag on one wing you make it advance slower than the other wing thus inducing a yaw.
The less obvious principle of shifting the center of drag backwards. This is the same principle of how badminton shuttlecocks work. Indeed, this is the same principle of how vertical stabilizers work. If the center of gravity is in front of the center of drag you get a weathervaning effect where the draggy part would swivel to the rear. The B2 achieves this by opening both drag rudders. In effect the B2 is creating a less efficient, more draggy, virtual vertical stabilizer. In practice you'd only need this extra stability when flying slow. At cruise speeds the drag rudders would be mostly closed (especially if you have them gyro stabilized, if you don't have computer controls and gyros you'd keep them partially open for stability).
Some flying wings don't have drag rudders. Instead the wing is twisted to achieve a lift distribution that would cause the wing to have proverse yaw. The Dunne series of flying wings were promoted as inherently stable aircraft because they didn't experience adverse yaw. If you have proverse yaw you can simply use your ailerons to turn the plane without rudders.
The big disadvantage designs that don't use drag rudders or any vertical stabilizers is that you depend on banking in order to yaw. This makes landing on straight runways impractical so most such planes land on grass fields which allows the pilot to choose landing direction so that crosswind is not an issue. A lot of Dunne flying wings were seaplanes.
Similar to the vertical tail on your Cessna, a flying wing produces only little lift or even a downforce over the rear part of its wing. A swept flying wing uses washout for the same effect. In all cases, the idea is to produce relatively more lift increase with an angle of attack increase in the rear parts of the wing (or the tail in conventional configurations) so the aircraft stabilizes itself.
This also means that the center of lift is ahead of the quarter chord point of the wing, and the same goes for the center of mass. At high angle of attack you need to create a pitch-up moment with the elevons in order to trim the high angle, and once the wing stalls, this pitch-up moment is reduced. As a consequence, the flying wing will pitch down and recover. Again, this is very similar to what happens on your Cessna, only that the function of the tail is performed by the rear part of the wing.
Wing sweep helps a lot to pull the aircraft into the wind, and the yaw inertia of the big wing helps to keep rate changes down. Stalling in banking flight produces a very similar reaction as a straight and level stall while the airplane continues to turn. Of course, pulling too hard and preventing the wing from correcting the high angle of attack itself will risk to force the flying wing into a spin.
Flying wings have only a steep spin mode. Flat spins are not possible because the flying wing lacks the lengthwise mass distribution of conventional airplanes which creates a strong pitch-up moment in a spin. If the flying wing has no fuselage protruding in front, it also lacks the stabilizing nose vortices which are a contributing factor for flat spins.
Spinning the SB-13 was quite harrowing: The nose points almost straight down and the aircraft loses about 100 m in one turn. But ending the spin was simple: Just pitch down and stop the rolling motion by allowing the roll damping of the wing to kick in.
