Aileron Formula?

[Crabjuice]

Is there a general rule of thumb for calculating the size and configuration of ailerons?

I would like to apply it to a situation where I'm going to put a 48" wing with a chord of 6" on a Beaver (plane, not mammal :D ).

Any help would be appreciated.

[Ollie]

The most important thing is to put the ailerons at the wing tips where they have the most leverage. Any aileron span from 30 to 50% of the wing semispan should work. An aileron chord of 20 to 25% of the wing chord is practical. I'll bet, without looking, that the scale ailerons fall within that range. Smaller ailerons will just result in a slower roll rate than large ailerons. If you want the plane to fly in a scale like way keep the wing tips light and the wing loading light.

[Crabjuice]

Ollie,
Thank you. That was exactly the sort of answer I was hoping for.

[Sail 'n Soar]

Is there a general rule of thumb for calculating the size and configuration of ailerons?

I would like to apply it to a situation where I'm going to put a 48" wing with a chord of 6" on a Beaver (plane, not mammal :D ).

Any help would be appreciated.

Crabjuice,

The 20% to 25% cord is good advice for conventional ailerons, i.e., toward the tips and length's something like 50% of the wing span. I've had the same question as you in the past. Seems common design practice whether you are dealing with conventional or strip ailerons is that the total aileron area be something like 10% of the wing area. With your ~8:1 aspect ratio, the conventional aileron configuration is probably adviseable. However, if your model had something like an AR of 6 or lower, there are offsetting ease of installation and construction arguments suggesting the strip aileron approach. In terms of full scale practice, numerous Goodyear, later named Formula 1, racing planes used strip or near strip ailerons. I seem to recall some ultralights with strip ailerons as well.

Gerry

[Antonsoarer]

If you want the plane to fly in a scale like way keep the wing tips light and the wing loading light.

Interesting, I have found that light wings and wingtips make a model look and behave more like a model, sort of twitchy and easily blown about. This has (in this case) less to do with CG or control throws I have set.

I have some large models with deliberately heavy wings including heavier than usual tips. They move about in a very scale like manner with smooth transitions and a more graceful flight pattern than their light wing contemporaries. They draw comments like, 'that's a smooth flyer' and 'thought it was bigger than that the way it flew!'

Tony.

[Ollie]

I suppose we have different ideas of what "scale like" means.

If the model is 1/12 scale and the full scale plane stalled at 48MPH then the model should have a stall at about 4MPH. That requires a light wing loading indeed.

If the model is flown in 10 MPH winds that would be like the full scale flying in 120 MPH winds. I dare say the full scale would bounce around a bit under those conditions.

I admit that not many people share my point of view on "scale like" flight.

[Antonsoarer]

Ollie,

I see what you mean, I thought about scale-speed but that seems to only make an impression on me when I do the calculations, not while actually watching the model. When I watch a scale model I tend to compare it to moving images of full-size aircraft and then notice the model like characteristics as a distraction, the scale-speed of the model and wind never really figure in that perspective.

Maybe we all see things differently depending on how we visualise and what experiences we have had. I see the scale-factor as an after the event thought based on conscious math.

Tony.

[Ollie]

Here is a thought experiment that defines what I mean by "scale like." Lets compare a 1/12 scale model with the full size counter part. When the full scale plane is 12 times farther away than the model and in the same orientation to the observer, the two will have the same aparent size. Starting with the model in visual line with the full scale and both flying in the same direction, when the full scale is flying 12 times faster than the model, their images will remain superimposed and of the same aparent size. If the model were of scale fidelity, the only way you could tell which was the model would be the fact that it blotted out the image of the full scale because it was closer. You couldn't even estimate what the scale factor was unless you could see the two shadows on the ground.

[Antonsoarer]

Ollie,

Makes sense, I suppose your thought experiment takes care of most parameters but the wind and turbulence would be similar on both airframes even given any height difference (maybe more turbulence on the model nearer the ground). The type of movement of the aircraft might be similar for a given disturbance but for the model I would expect to see less inertia or lock-in-place effects and indications of smaller disturbances that the full-size wouldn’t respond to. My son and I can always spot a model in a film and what gives it away is usually the twitchy appearance.

I was once flying formation with another sloper, both 64” 40oz models. I was inverted flying above his model and we had made a couple of good close circuits. I tended to dive slightly off turns and he climbed a little. We collided very gently; my inverted fin just lightly contacted his wing near the root, we laughed and carried on doing circuits and improving or technique. When we landed we were both shocked by the damage to both planes, it was amazing that they still flew! My fin was cracked and his basswood spar was broken and the whole wing was about to come off! :eek:

I also recall standing on a big slope with a 100” racer in a strong wind, holding it just behind the wings as I was moving ailerons to check them and noticed that I couldn’t resist the plane twisting my arm/wrist, and I couldn’t easily twist the model with my arm, it felt locked in place by the 40mph wind.

Those two incidents left quite an impression on me; models aren't really floating round they are locked in place or on a course by some surprisingly powerful forces.

In conclusion; aerodynamic forces acting on the model seem to give increased inertia or mass effects if a model is heavier (or its full-size) and flying faster and generating larger forces that will resist external disturbances. I think our models fly through many minor disturbances that in the same period a full-size or heavier model wouldn't react to.

The problem with scale flight is that no one tells the boiling cauldron of air to scale itself to match our models. So my approach is to make them heavier if I want to carve more like the real thing.

So is my intuitive perspective flawed? :) It's based on a lot of flying.

Tony.

[vintage1]

I suppose we have different ideas of what "scale like" means.

If the model is 1/12 scale and the full scale plane stalled at 48MPH then the model should have a stall at about 4MPH. That requires a light wing loading indeed.

If the model is flown in 10 MPH winds that would be like the full scale flying in 120 MPH winds. I dare say the full scale would bounce around a bit under those conditions.

I admit that not many people share my point of view on "scale like" flight.

I do, but there is a problem. For scale like motion in a straight line, sure, speed needs to come down with the scale factor, but for similar sized loops etc, it comes down as the square root.


so what you need to do is scale time by the square root of the scale factor as well, and fly the models at the square root of scale speed :)

This presents us with insuperable problems - we can get it right for scale speed, or make the loops and turns look right (similar bank angle for scale turns etc) but not BOTH at the SAME TIME.

Basically gravity doesn't scale down and neither does air viscosity....

In practice we tend to build models somewhat between. I am expecting a 1/12 scale WWI biplane to have a top speed of maybe 30mph, and stall at 12, the full size was about 120mph top speed and stalled at maybe 48, so the speed is down by a factor of 4, whereas it should be 12, or root 12 - about 3.1.....

It gets you worst on airliners where scale factors are huge. I have held off doing a DC3 until I can find a way to build a 60" span twin IPS model weighing in at 12 oz or so :)

[Antonsoarer]

So Vinatge1, it comes down to which compromise you decide on or are limited to? :)

Scale flight attributes, like beauty, is in the eye of the beholder.

[vintage1]

I think my aim is to get scake models to fly as SLOW as I can, and then overpower them so they will pull big lazy loops. Thats wwI fighters.

Airlinres - well as slow as possible, because they don't do much except waft around looking airlinerish.

WWII warbirds...Mmm. here its fairly important that they do go round in vertical banks pulling huge radius circles, so its probably best to have much higher wing loading. And fly much faster than 'scale speed'...

But the answer is giant scale. The closer to the full size you get, the less the effects are noticeable. I built a gash plane to practice on before completing a 30" BF109, and frankly, I may never complete it. The speed of the little plane is so high that its almost unflyable. I mean its probably about 1/16 scale and flies at 60mph plus? Scale speed of comfortably over Mach 1 :D

[HELModels]

Ollie,




I think our models fly through many minor disturbances that in the same period a full-size or heavier model wouldn't react to.

The problem with scale flight is that no one tells the boiling cauldron of air to scale itself to match our models. So my approach is to make them heavier if I want to carve more like the real thing.

.



You see the same thing in old movies where ship models are used. difference is the fluid is water and you can actually see the fluid in the "cauldron". I wonder if filming in slow motion would dampen the effect.

[jofo1]

http://www.csd.net/~cgadd/eflight/calcs_servo.htm

Try this link, for sizing servos, may help out with your aileron sizing as it identifies what the torque requirements will be.

jofo