Curved wing vs dihedral

[Cape Byron]

Just musing and some ugly sketching...

Is their an advantage to building a boost glider wing with say 5 degrees (as an example) dihedral compared to ammonia treating a balsa wing and curving it to give the same root to tip angle? Anyone have any experience in this area?

Hoping to achieve something like this:

 

[OverTheTop]

I would think the curved wing would be less oscillatory in roll as the change in lift with roll is applied more progressively and more towards the tip.

The flat dihedral would be easier to get consistency, especially side-side symmetry, that is important for efficiency I think.

Caveat: theoretical only, no experience.

 

[Cape Byron]

I would think the curved wing would be less oscillatory in roll as the change in lift with roll is applied more progressively and more towards the tip.

The flat dihedral would be easier to get consistency, especially side-side symmetry, that is important for efficiency I think.

Caveat: theoretical only, no experience.

I was thinking the curve would give a more gentle correction. Very early days on this idea, but I just want to know if the tree I'm barking up is full of drop bears.

 

[OverTheTop]

I think symmetry will be the challenge, and also keeping the same curve from creeping over time.

 

[Spitfire222]

Advantages? Not really, as they're two different things. Dihedral is something designed into the plane to provide roll stability. Glider wings curving upwards in flight is a product of their composite construction and large span, high-aspect ratio wings. It also provides stability similar to dihedral, but is not explicitly baked into the design the way dihedral is.

 

[Alan15578]

That is a straight wing that shows a lot of deflection under load. It may be a fiberglass structure at the end of its life cycle.

Curved wings are not worth the effort. However, HLGs with dihedral achieved with multiple flat panels seem to roll out and transition better.

 

[Spitfire222]

It may be a fiberglass structure at the end of its life cycle.

That's quite normal for sailplanes.

 

[David_Stack]

That sailplane pictured is the eta. Aspect ratio of 51.33:1, designed in an effort to realize improved lift to drag ratio. As Vince noted, spar bending in sailplanes is typical, the eta takes it to extremes as a result of the aspect ratio.

http://sailplanedirectory.com/sailplanes/eta/

 

[Cape Byron]

Thanks for those replies. I’ll take the traditional non-balsa-bending route I think.

 

[Ez2cDave]

"Elliptical Dihedral" . . . a good example is on the "Hobie Hawk" RC sailplane, from the 1970's . . .

https://hobiehawk.com/hist.html








Dave F.

 

[dhbarr]

I think symmetry will be the challenge, and also keeping the same curve from creeping over time.

Symmetry should be fairly straightforward -- same technique as FAI gyro blades, just much larger pipe and rotated 90deg.

 

[BEC]

Advantages? Not really, as they're two different things. Dihedral is something designed into the plane to provide roll stability. Glider wings curving upwards in flight is a product of their composite construction and large span, high-aspect ratio wings. It also provides stability similar to dihedral, but is not explicitly baked into the design the way dihedral is.

I'm quite sure that the effect of the spanwise curving of the wings under load is absolutely "baked into the design." Having the necessary control authority and knowing what the stability of the airplane is are both required if you're going to put a man in the airplane as well as certify it. This may be a visually obvious example, but it applies to pretty much any non-rigid wing....like every jetliner in the world. The designers (and the stress analysts) and the structural as well as flight controls certification engineers are all going to be looking at this sort of thing and taking it into account.

 

[Spitfire222]

I'm quite sure that the effect of the spanwise curving of the wings under load is absolutely "baked into the design." Having the necessary control authority and knowing what the stability of the airplane is are both required if you're going to put a man in the airplane as well as certify it. This may be a visually obvious example, but it applies to pretty much any non-rigid wing....like every jetliner in the world. The designers (and the stress analysts) and the structural as well as flight controls certification engineers are all going to be looking at this sort of thing and taking it into account.

.........
Yes, of course the engineers designing a gliders wing know that it will deflect when loaded. My point was that dihedral is implemented into the design for stability purposes only. The deflection of a sailplane wing is a by-product of the fact that it's a high-aspect ratio composite wing/cantilevered beam. That the deflected wing provides stability akin to that provided by dihedral is a secondary, known effect.

Source: am engineer who designs aircraft for a living.

 

[BEC]

… and of course whatever effort that is necessary to arrive at the right amount of roll stability knowing not only that the wing would deflect like that, but how much it would under which load conditions. The results of that analysis/understanding would have to be “baked into” the design, which is my point.

The deflection may be a “secondary, known effect” of the general structural design, but the aero guys involved would certainly have to know what those deflections looked like all through the flight envelope of the airplane and do whatever else was necessary (including having the structures guys redefine the composite structure‘s characteristics) in order to arrive at acceptable handling qualities. Torsional deflections would also have to be looked at, and characteristics tailored to have the controls work properly and to avoid flutter, as well. I wonder if that particular sailplane uses spoilers only for roll control rather than ailerons….though of course you can’t pick up a low wing with spoilers, as some B-52 pilots have found out much to their detriment.

It’s far more nuanced than “oh, the wings flex, giving us some dihedral effect so we don’t have to build any into the jig shape of the wing, so isn’t that handy.”

While I wasn’t an aerodynamic configuration designer, I am an engineer who helped design airplanes for a living.

 

[OverTheTop]

I'll throw this video in for interest .

 

[BABAR]

That sailplane pictured is the eta. Aspect ratio of 51.33:1, designed in an effort to realize improved lift to drag ratio. As Vince noted, spar bending in sailplanes is typical, the eta takes it to extremes as a result of the aspect ratio.

http://sailplanedirectory.com/sailplanes/eta/

Good observation, you can see ALL the curvature and most if not all the dihedral goes away as the glider comes to a halt.

i had the opportunity to see this when I was a Flight Surgeon for a KC-135 squadron, particularly with the B-52s (the KC-135s are likely the last tankers that have a boom operator laying flat on his/her belly looking out the back/down windows, with two “bunks” on each side for trainers observers. it’s a weird feeling looking out and DOWN from an aircraft and see the world fly away from you!). Anyhoo, the B-52 wings definitely look different in flight than they do on the ground.

 

[BEC]

I'll throw this video in for interest .

Those 150% of ultimate load static tests are amazing, frightening, expensive tests, in this case of a rather larger composite wing than the one in the OP.