Hi there!I don't often post here on AVSIM, so I'm not sure what the culture of the community here is like, but from what I've seen I think this would be as good a place as ever to post a new-fangled aviation debate. A couple months back while doing work on an Aerodynamics project involving paper airplanes I came across a unique feature of airfoils that bend at the end: An airfoil with an upward bend, like those found on the 737 NG, will roll the aircraft a lot smoother than equal applications using an aileron.It got me wondering if it would be plausible to construct an aircraft that used winglets who's angle relative to the length of the wing could be changed in the same way an aileron could be manipulated. The change in angle, like the change in airflow caused by an aileron, should cause that aircraft to roll (I.E, turn) without the adverse yaw created by ailerons.

In this (exaggerated) example, I show an aircraft using ailerons to roll the aircraft to perform a turn, and an aircraft using winglets (which at this point is probably not called winglets) to turn. In the example I used the roll can be achieved with one wing facing up and the other facing down or one wing facing up/down and the other level. It really doesn't matter.So, with this all said, I'm wondering what you all think. I wasn't able to make a model to throw in the wind tunnel, and I am by no means anything more than a novice in aerodynamics (I only took a 200 level course), so I'm bringing the question here to Avsim: Mechanical difficulties aside, is it a plausible idea? :( Thank's for reading!

Angling the wing-tips up and down as you propose won't work as ailerons because angling the wing-tip up or down reduces the amount of lift equally on both sides of the fuselage (by the cosine of the angle to the spar), so there is not net rolling moment to roll the aircraft.What you will get is a net side force to the right in your diagram (equal to the lift per wing-tip times the sine of the angle to the spar.)One North-American Navion was modified to sport two vertical stabilizers, one each mid-wing, to allow turning without banking. (It also sported a fly-by-wire system and fast-acting automatic positive and negative flaps). It was known as the VRRA Variable Response Research Aircraft (See page 4).If you angled the wingtips to 90º, your proposal woud work similarly to the VRRA, but the size of the wing-tip that bends would have to be rather large to counter the centrifugal turning force so you would only obtain low turning rates.What has been tried is very elastic wings with very small ailerons that act as trim-tabs to the wing-tips themselves: As the aileron moves up, the wing-tip trailing edge moves down while the leading edge moves up, thus increasing airfoil angle of incidence at that wing-tip, increasing lift and making the wing move up as well, provided the aileron on the other wing-tip moves in the opposite direction. You will note aileron control is reversed, as the wing now moves in the direction the aileron moves. This is called "aileron reversal" and happened on certain aircraft at high speeds unintentionally as required aileron forces exceeded wing available stiffness. An F/A-18 was modified to sport intentionally aeroelastic wings to test reversed ailerons. Iwas called the X-53.Cheers,- jahman.

Jahman,Interesting little bit of information there. I never knew NASA tried that with the FA-18 (or X-53, I should say). I love reading about stuff like that. As for the winglet idea, the main idea would be to manipulate one winglet (for instance, one winglet is up while the other is flat) to initiate a roll. The loss in vertical lift should be immediately witnessed, and only small winglets would be required to see significant roll rates. (With one wing being manipulated, the airfoil shouldn't need to be bent to 90*; I imagine it would be similar to mechanically shrinking the overall length of one of the wings).Once again, thanks for the reply (and links).

Yaw I don't think would be diminished if this procedure were adopted. As it is a function of weight. Normally a/c wings have dihedral (that is the angle of pointing up or down of the wings). The dihedral angle increases the tendency for the CofG to remain central between the wings. Too much however would lead to instability causing severe oscillations and more importantly loss of lift. Also don't forget that swept back wings in themselves cause severe instability leading to convergent or divergent dutch roll. Thus if one yaw damper is inoperative then it's usually a no go for the flight.Also don't forget the moment arm. If you create a wing whereby the only method of turning the a/c is by deflecting its wingtip then that could create a lot of extra stress. In slow moving general aviation a/c it could be experimented with.A nice idea but it has been visited before.vololiberista

Yes, bending one wing-tip at the time would work, although it would be inefficient as the sideways component of the lift would be wasted (but the full impact of the associated drag on fuel burn would still be present.)Also wing structure is terrible at absorbing the sideways compression resulting from a wing-tip moving up, and would thus have to be stiffenned further, adding more weight and also increasing fuel burn.The wing-tip moving down, OTOH would increase wing tension and metal is good at that, so no problems there, but a wing-tip bent down would be a serious hazard during landing.Additionally, the drag components of standard ailerons would not be present and these are extremely useful to keep the aircraft from weathercocking into the wind when a crosswind component is present during takeoff and especially landing. That's why you will always see pilots lowering the wing into the wind: The up aileron on the upwind wing decreases angle of attack and thus decreases drag, while the dwonwind aileron moves down thus increasing angle of attack and associated drag. The net effect of the upwind wing reduced drag and downwind wing increased drag is to yaw the aircraft away from the wind, thus helping the rudder keep the aircraft pointing down the runway.Back to your proposal and regular turning, as the previous poster also said you need the rudder to overcome inertial forces and yaw the aircraft into the turn and then again out of the turn. The combination of wing dihedral and wing sweepback couple to induce dutch rolls that can be dangerous to the stability of large aircraft.So perhaps an alternative might be to make the wing-tips telescopic, with one moving in as the other moves out.Cheers,- jahman.