Why swept or delta shape flying wings

[rcairflyer]

Some design questions -

For model airplanes - why do Zagis and other "flying wings" have swept wings? Is the wing swept to get the winglets further back and make them more effective as fins? Is the shape of a delta wing aircraft related to the shape of a swept flying wing?

Deltas usually have a non-zero wing tip chord. Does that shape work better than a true triangle?

What is a "true flying wing", does it omit winglets?

Bill

[Ollie]

There can be several reasons for sweeping back the wings of a "flying wing" model.

Swept back wings have yaw to roll coupling somewhat like dihedral effect that imparts lateral stability.

If the airfoil does not have enough reflex to provide pitch trim efficiently, then sweepback plus wash out can provide the necessary pitch trim.

In flying wing design, almost every thing affects everything else. Sweepback has to be harmonized with taper, washout, airfoil selection, CG location, aspect ratio, vertical tail area and location, etc. for the model to fly well.

[propfan]

And don't forget... swept wings look pretty cool too ;)

[John Boren]

Here is my two cents worth. Sweeping back the leading edge of a wing acts like dihedral so less needs to be put in the wing to still have good stabilty. Delta wings don't need any dihedral beacuse of their even greater sweep of the leading. As why don't most deltas have their wing tips cut off so they don't come to a point. That one's easy, it is a pain to make them that way and almost impossible to do if it is made out of foam. Attached is a photo of my Up Scaled Lady Hawk Rocket powered plane. It is shown takeing off with a AeroTech G-35 Motor.

John Boren

[annihilator]

im currently building a 29" long delta wing with a 0 inch chord at the tip its max thickness is about 1.25" the thing should fly. flying wings are nice because the drag that is encountered on the portions of the wing behind the CG acts as a rudder. If you were to intentionally create drag on the wingtips of a triangular flying wing you probably wouldnt need a rudder at all. Thats how the b2 works. If im right the full scale plane just "splitting" an aileron and making a v shape to increase drag on one side.

Flying wings are naturally stable and i cant wait to get pics of mine up on the boards. I would say about 2 weeks more cuz i havent even ordered a motor 4 it yet :) oh well. ill play with my cobra and e starter till then. Im hoping for some runs in the high 70's to low 80's out of my delta wing. We'll see.

[Ollie]

There are only three requirements for controlled flight and none of them have to do with the shape of the planform. The CG has to be very near or ahead of the neutral point. There has to be more thrust available than drag. The control surfaces have to be big enough and with enough throw. Everything else is secondary. Proof? Flying lawnmowers, witches and other wierd contraptions.

Deltas and low aspect ratio flying wings have advantages and disadvantages. They have outstanding maneuverability but, they require more power and have poorer fuel economy. That's why you never see them on long range commercial aircraft. They appeal to "put a bigger engine on it" people.

[Robbie d]

the swept wing had another advantage. The further back you can place your control surfaces from the centre of gravity, the more effective they'll be. Even better if the elevons taper outward, so the widest part is closest to the wing tip

[Majortomski]

There were a lot of "Hershey bar" square flying wings back in the '70s and 80's. The trend was kind of kicked off by the RCM Plank. A great flyer with some creative solutions to ailievators with our old big heavy non-computerized radios. I think the plans are still available over at RCM

[Thomas B]

IIRC, the RCM Plank (I built a couple) was inspired by the full size Plank wing built by Al Backstrom over here in Texas.

[FlycastSeven]

Swept wings were originally thought of to get inside the shock wave of a supersonic aircraft- thus greatly increasing efficiency. That's why all supersonic aircraft, with an extremely low number of exceptions, have either delta or swept wing planforms. Obviously, as we have no models going supersonic, sweep adds "cool factor" and stability, similarly to dihedral.


George