I am always looking for an advantage in regards to speed in my racing planes.

I have a way of setting up my racers (with a single aileron servo) so that the ailerons ONLY move up and not down.

My question is? Is it cleaner (faster) having one aileron move up quite a bit, rather than having one move up, and the other moving down?

Or, is the gain so minimal as to not be worth pursueing.

I know from my glider flying that ANY control surface movement sucks up energy from the model's motion. From this I'd say that it's the roll rate that eat's up the energy rather than deflecting one or two surfaces. So I would say it's best to roll into a turn slowly using as small an amount of throw as you can live with. But then one surface has less hinge line length.....

It's all a compromise, isn't it........

But I would think you'd be more at risk of stalling or causing draggy flow separation using one surface deflected farther than two surfaces deflected less. And a fairly clean and well sealed hinge line has very little drag.

The answer depends on a lot of things. If you typically use more than 5 degrees of aileron deflection in a turn then you can expect to have flow seperation on the bottom surface of the up-going aileron and a sharp increase in profile drag. Also, the up-going aileron reduces the average lift coefficient of the wing making high G turns wider for a given angle of bank than with two ailerons or one down-going aileron.

My guess is that if you normally turn with less than five degrees of aileron deflection, you shuld stick with your present arrangement. If you normally use more than about 5 degrees of deflection, you would be better off with two ailerons and less deflection.

The 5 degree criterion is based on a thin airfoil with very smooth and slightly rounded contour to the hinge line with a seal and minimum gap. If your hinge line isn't very smooth and virtually gap free, then about 3 degrees of deflection will probably produce flow seperation and a sharp increase in profile drag. Obviously, the up-going aileron should be hinged on the bottom surface and the down-going aileron on the top surface to minimize flow seperation in high speed turns. From a flow seperation point of view, skin hinges are best, tape hinges next best and pinned hinges are worst.

If we are talking about speed, we are talking about drag. If you move one aileron 20 degres, the "wet" surface should be about the same than moving 2 ailerons 10 degres. What is cleaner is to have a deeper (in chord) aileron, so that you can get the same result by moving it 5 degres instead of 10.

The benefits of having ailerons moving only up, from my point of view, are not about drag, but about adverse yaw (Should not have any), and the ability to have ailerons AND full wingspan flaps (as you can have up-aileron-only forward the trailing edge), but I doubt that those results are of any interest in your search for speed.

Bernard

Perhaps not so obvious as you think Ollie. This is a brilliant idea for a racing model that only has to turn in one direction. I'm a two way turning kinda guy and found this to be a lovely and logical solution for a specific situation.

Or is this just an old racing model trick? If it's original then a big ol' :thumbup: to ya.

BMatthews,
I must confess that I've never even witnessed a pylon race much less flown in one. I'm a glider kind of guy and have one interest in common with the pylon racers: DRAG REDUCTION.

daven,

I have no quantitative basis for this, but I would guess that you are better off using both ailerons, with less deflection. Since you always turn one way, and don't care about inverted flight, you could optimize by using aileron differential, perhaps. If you do want to use only one aileron, I would be tempted to only build one aileron, and use it up and down. This way you get one wing which is perfectly clean all the time. Of course, you now get a little bit of yaw input from the higher drag on the aileron wing, which will add some drag. Hard to say how you come out ahead. I definitely think that ailerons with more chord and less deflection would give less drag, as was suggested. Probably the most critical is how clean you get the hinge line.

I am in Minnesota as well, south of Minneapolis. Do you race at Grassfield? I am hoping to get up there this coming spring to check out the furious pylon action.

Good luck,

banktoturn

Currently, all of my new racers use a fiberglassed skin hinge on the top which is extremely clean.

Using two ailerons, typical movement is about a 1/8" inch. Translated into degrees I would guess that it would be about 5-10 degrees??

I would anticipate that I would need nearly 1/4" movement if I went with just one aileron.

Even though we only make left turns, you still level the plane back off after the turn. So you end up using right aileron just as much as left.

Not to confuse the original question, but would it make more sense to hinge on the bottom of the wing?

Banktoturn,

Yes I fly at Grassfield, and am the current V.P. of the club. We would love to have you up next year to check out our racing (and joining us). Our club racing really took off this year, and we were routinely getting 20-25 racers.

Your comments about a longer chord aileron at less deflection brings about other thoughts. We kinda went away from the longer ailerons a few years back due to flutter issues, but with the stiffer skinned hinges this may no longer be an issue. I think I may give this a try also. Maybe I can go with a relatively long aileron on just the left wing. The added weight would help laterally balance the plane.

[QUOTE]Originally posted by daven
[B]
Not to confuse the original question, but would it make more sense to hinge on the bottom of the wing?

Hinge the ailerons on top.

Has anyone ever given a thought to using servo driven variable wing warping, or moving the entire wing halves on both sides of the plane, to effect roll instead of ailerons? It could be engineered into a wing at the root. It seems to me the amount of deflection necessary would be miniscule, considering that we would be working with the entire wing surface. It would have the effect of altering the entire angle of attack of each wing independently. Laminar flow over the wing would be least disturbed because the effective camber of the wing would remain unchanged during the deflection, as is not the case with ailerons.

New term. We could call this "wingerons".

I have a feeling that "Wingerons" although a neat idea, would not meet the racing rules and regulations that I am required to follow.

You need "stealth" wingerons! Ailerons that look pretty but do nothing, meanwhile the entire wing secretly moves!!!!!

Just kidding.

You could even put this on a mixing switch..... "disable regular ailerons and enable secret wingerons"!!

It has been done. At some point, there was a quite famous slope soaring aerobatic all molded sailplane made in France, named "Axel", using this technic. Problem is, you don't really gain anything (beside cleaner wings for straight and level flight), because the change in AOA on wings trigger increasing drag of the WHOLE wing.

For a racer, which need to absorb a lot of Gs, it might be difficult to built such a system as light as the normal ailerons, and not have the potentail slight aerodynamic gain erased by the greater weigth.

Bernard

Seems like with only one control moving up, you will get yaw along with roll. DO you really want this?

Yaw is always a consequence of roll control that produces the roll torque by changing the lift distribution of the wing when there is a net lift involved as in horizontal flight. When the lift distribution on one side of the wing is greater than the lift distribution on the other side, the side with the greater lift also has the greater induced drag. The unbalance in induced drag from one side to the other is what produces adverse yaw. Of course, if the wing is producing no net lift as in vertical flight then the two sides of the wing can produce equal and opposite lift distributions and the induced drag will be balanced for no adverse yaw.

In the case of speed models like pylon racers in horizontal flight, the net coefficient of lift is small enough that the difference in coefficient of lift is also small. Since the induced drag is proportional to the square of the coefficient of lift the incuced drag will only produce a very small yaw. For example: if the Net coefficient of lift is 0.05 with one side of the wing producing zero coefficient of lift and the other side producing a coefficient of lift of 0.1. the first side will produce no induced drag and the other side will produce induced drag proportional to 0.1 squared or 0.01. That is, the coefficient of induced drag will be aproximately 0.01/(pi x AR). If the aspect ratio of one side of the wing is three then the induced drag unbalance will be roughly 0.00107/2= 0.000535. That's why speed models often get away without compensating for adverse yaw.

OK now, don't everybody jump my case! I like differential in my ailerons. I believe the reason real planes have differential is to minimize the adverse yaw caused by the drag of the "down" aileron...........what ever the reason for using differential is, I seem to be able to retain the maneuverability at max deflection with less travel. Thats has to be good. Less deflection, more speed.

As Bernie said it's been done before. Wingerons, while not normal, are far from unique with slope soaring gliders. The Sig Samurai had them. And there's been a couple of them that not only use the differential wing rotation to replace ailerons but also pitch the wings up and down together to replace the normal stab operation. And you are right about the reduced throw. A guy in my club made a thermal sailplane using wingerons and started with plus and minus 1/4 inch at the trailing edge for a 1/2 inch totoal difference between trailing edges and it was all but uncontrollable until he redid the linkages and reduced the throw to plus or minus 1/8 inch. That's only 1/4 inch total difference between the trailing edges at full throw. Even then it was VERY aerobatic.

A lot of 1/4 midget class models and a few formula one models used single ailerons. I know they have to straighten up but I think they would do this slower than the turn in so perhaps the adverse yaw wasn't so bad. Not sure as I don't pylon race.

With aileron differential the extra profile drag of the up-going aileron partly off sets the induced drag of the down going aileron (in order that adverse yaw is reduced) for a net increase in wing drag. The question remains as to which is greater, the increase in wing drag due to aileron differential or the decrease in fuselage drag due to reduced yaw. My intuition is that there is very little net benefit or detriment in speed models where the net wing lift coefficient is small, the induced drag is very small and the fuselage drag due to yaw is very small. Also, this drag analysis only applies very briefly when the plane is rolling into or out of a turn.