I’m curious, and thought I’d ask his question here rather than in The Pit.
I’m not an aircraft designer. The YB-49 had vestigal vertical stabilizers, but I think the N1M didn’t. So it can be done. (Of course there were stability problems – which is my we have Edwards AFB instead of Muroc AFB.) I used to build balsa airplanes, and frequently I could get a straight wing to glide without a fuselage. As I said, I’m not a designer; but just off the top of my head here’s what I think:
A swept wing would put weight at the front, so it would have lateral stability and fly in the right direction. Longitudinal stability could be provided by sufficient dihedral, or by having enough weight on the bottom to provide a “parasol” effect. I think vertical stability would come from the sweep of the wings.
Can anyone say how close I am? Am I completely wrong? How would they have been able to make a flying wing stable without a computer making constant adjustments?
The YB-49’s problem was yaw stability. IIRC yaw contol was made with speed brake like devices that opened on the trailing edge of each wingtip. Effective control but kind of touchy since they are so far from the C.G. Existing autopilot systems didn’t work well with them giving it a yaw osscilation that was said to make bombardiers nauseous when looking at the ground through the optical bombsight. I’m sure an analog yaw damping system could have been made if they had identified that as the problem instead of blaming the aircraft design.
There were lots of stable flying wings before computers, as there are now that aren’t using computers. Look at all of the Horten wings, to name just a few of them. Most hang gliders don’t have tails, and many are rigid wings.
Flying wings, in a way, are more stable than conventional wings, as they don’t need a stabilizer. It’s closer to the truth to say that both types need stability…conventional planes have a stabilizer, and wings have reflex. Conventional planes are more efficient than flying wings, but you can increase the efficiency of wings by reducing reflex, and you can add stability by adding a stabilizer, and many people with rigid wings are doing just that.
Wasn’t the problem with the YB-49 a ‘Dutch Roll’? The problem is that if the airplane yaws, one swept wing presents more of its surface to the airflow, and tends to lift. I seem to recall reading that looking through the bombsight could literally make you ill as the thing Dutch-rolled back and force subtly.
No reason it should be by intentional design or from being a flying wing. As a general rule stability and maneuverability are tradeoffs. Bombers need more stability and fighters nees the opposite quality. IIRC the Grumman X-29 was in the unstable category with C.G. forward of center of pressure and required computer control corrections several times a second to keep the pointy end forward and the greasy side down.
Johnny…no, washout refers to twist from the root to the tip. Washout adds stability and drag, by decreasing the angle of attack at the tips. Reflex refers to an “upward tilt” of the leading edge, and is generally seen only on flying wing airfoils…which is probably why Boyo Jim & others have never heard the term. I fly them all the time, including the radio-controlled variety, so the term is common to me.
This is true, but another reason for using computer stability is fuel efficiency. Stable conventional aircraft achieve stability through applying a downforce with the tail to oppose the rotational moment created by having the center of lift behind the center of gravity. That extra force causes increased induced drag. This is the reason canards can be more efficient - both surfaces are providing a lifting force.
So by making the aircraft marginally stable and augmenting it with computers, you can increase range and/or payload capability. In a combat aircraft, you gain the added advantage of increased manoeverability when you need it.
Flying wings can be very stable. I fly R/C gliders and swept flying wings with elevons are very popular. They are sold as training planes that can perform full aerobatics and combat. What makes ANY aircraft unstable is it’s weight loading and balance point. Most flying wings use “reflex” or an upward sweep at the trailing edge. This forces the back end of the wing down, and takes the place of a conventional stabilizer. “Washout” is a twist in the wing so that if the wing stalls the center section will stall before the tips. This is desirable because if the center stalls first, the plane dives a bit to gain airspeed, and then recovers. If either tip stalls first the aircraft goes into a spiral dive, and does not naturally recover.
The balance point or CG (Center of gravity) of the wing is normally just in front of the center of lift for that wing. So if you pick up the Spruce Goose right at the center of the wing, the nose of the plane should tip down. In slow flight, every plane should want to nose down a little. This increases the airspeed which also increases the flow of air across the stabilizer or reflexed section. That forces the back down and the nose up. If the nose goes up too far the speed drops, the airflow drops, and its back to scene one. The plane will find a happy medium between diving and stalling. Stability.
There is a tradeoff though. If you move the CG too far forward the plane will become so stable that you cannot change its attitude or direction easily. This adversely affects manuvreability.
As the CG gets moved back, the plane becomes more manuvreable and less stable. If the CG gets near or behind the center of lift the plane becomes super manuvreable and unstable. People cannot keep up with the control inputs needed. But computers can.
