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Old 01-13-2014, 01:57 PM   #1
drummaker
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Default Flaperon Epiphany

I had an epiphany I wanted to share.

I have come to some conclusions so. let me know if you KNOW if I am wrong, but I have been studying fluid dynamics, and I believe strongly that I am right here. I believe this info to be invaluable to many people

Have you even noticed that so many ailerons which cover the full length of the wing are wider at the inside than they are on the outside? They are this way for a great reason, and if you are scratch building, or contemplating flaperons or spoilerons you should be aware of why, and what.

When you are moving the trailing edge of a wing down you are actually doing 3 things.
1. Adding Camber. Camber is a description of an airfoil that his concave on the bottom, and is known for a LOT of LIFT per Square inch of wing. so you are adding lift to the wing, thus adding the ability reduce your minimum stall spead.
2. Cambered wings add drag, so the model slows down.
3. This is the important part for Spoilerons V Flaperons.
When you lower the trailing edge of the wing, you are also changing the incidence, or angle of attack of the wing. This is important because of several things, and is the reason you must add down elevator to compensate, but mainly when you have a straight non beveled aileron, you are changing the incidence of the whole wing, and therefore when you slow down enough, if there is no wash out in the wing, you will tip because the entire wing looses lift at the same time. OK now pay attention. When you have an aileron tapered wide toward the fuselage and narrow toward the tip.. YOU ARE ADDING washout by lowering the ailerons. This is because you are adding more incidence on the inside than outside of the wing because the aileron has more actual down deflection here.

It follows that if you move the ailerons up, you are actually adding Wash In which causes tipping again but usually pushes the model down so fast it doesn't matter.

Using Real flaps works so well because it causes washout ..


There are some smart people out there aren"t there? Every time I figure something like this out it gives me renewed respect for those who came before us. It took me a lot of pondering to figure out why full length ailerons were so often shaped that way.

Hope this helps!
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Old 01-13-2014, 03:23 PM   #2
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This is only true if wing is not tapered. A constant chord wing will do as you say.

If a wing is tapered from root to tip - then this will generally have greater effect than a tapered aileron and create washin. It's pure geometry.

It's one of the reasons full size do not use full span for flaps and keep them to inner section of wing.

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Old 01-13-2014, 03:33 PM   #3
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Thanks Nigel. I will try to wrap my head around this. I guess I will have to just do some measuring.

Wow I am impressed

So thinking about it on a tapered wing it is really just a matter of how much taper on the aileron compared to the taper of the wing. Hmmm Linear... think not I will have to do some math.
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Old 01-13-2014, 03:59 PM   #4
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I am still trying to wrap my head around this stuff. Things I have learned or have been told...
Flaps are at the root of a wing because if you stall a wing it is better to stall it at the root than the tip.
And, when I apply flaparons to my slow stick (only because I can) I have to add a ton of UP elevator! Not reccommended it just makes the plane a mess to fly.

I'm either going to get good at flying em, or get good at fixin em!
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Old 01-13-2014, 04:04 PM   #5
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Originally Posted by BroncoSquid View Post
I am still trying to wrap my head around this stuff. Things I have learned or have been told...
Flaps are at the root of a wing because if you stall a wing it is better to stall it at the root than the tip.
And, when I apply flaparons to my slow stick (only because I can) I have to add a ton of UP elevator! Not reccommended it just makes the plane a mess to fly.
ya I am thinking up or down elevator is decided by how far you move things but

good to see you here broncosquid.

I am thinking my son Jordan stationed in Hawaii is on his way home in a month or so. Really excited to fly with him. He has been playing real flite is his main video game since about June
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Old 01-13-2014, 05:00 PM   #6
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For RC planes that don't have flaps, programming flapperons is an okay option. I did this with the ole T-28 just to try it. I have other planes with flaps, split and drop types.

What I want to do on the Deuces Wild is deploy flaps in two stages on the downwind prior to base leg. As soon as touchdown occurs with throttle cut, I want to deploy spoilers using the ailerons and elevator in unison. It's a big plane and known to come in hot.
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Old 01-13-2014, 05:01 PM   #7
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Up or down elevator being needed when applying flaps is dependant on CG, the geometry of the wing and the geometry of the flaps.

The normal tendency of an untapered wing with untapered flaps of about 10% to 15% chord (any % of span) and the CG forward of 35% MAC is to nose down when you apply flaps. Start changing stuff and you can get different results.

Note that just as you apply the flaps you might see the plane balloon even though it will push the nose down. This generally means you applied the flaps at too high an angle for the airspeed.
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Old 01-13-2014, 05:03 PM   #8
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Originally Posted by fhhuber View Post
Up or down elevator being needed when applying flaps is dependant on CG. the geometry of the wing and the geometry of the flaps.

The normal tendency of an untapered wing with untapered flaps of about 10% to 15% chord (any % of span) and the CG forward of 35% MAC is to nose down when you apply flaps. Start changing stuff and you can get different results.
I can always count on you guys
Thanks for the Info FHhuber



Funny isn't it how I thought I had made a giant leap and all it did was have to consider even more complexity? That's the way the world goes. I am thankful to have resources like you guys available to me.
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Old 01-13-2014, 06:13 PM   #9
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I always assumed the aleroins and wing were longer against the fuse to make up for wing area taken by the fuse and because it was in the prop wash.

slow stock prop reversal. it flies! easily! 543 watt dual motor bipe slow stick. push-me-pull-you. 242 watt 3 channel slow stick. 365 watt mini ultra stick. 415 watt mini contender. 810 watt ultra stick .25e. 220 watt alpha 450 sport (retired).
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Old 01-13-2014, 06:53 PM   #10
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Nope... we use the strip ailerons because its simple. The in-board 1/3 of full span strip ailerons has very little effect on roll.

For "3D" aerobatics the inboard portion can become important in hovering maneuvers where there is inadequate airflow over the rest of the wing. But you'd do as much good programming "tailerons" for a split elevator.
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Old 01-13-2014, 07:32 PM   #11
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Originally Posted by fhhuber View Post
Nope... we use the strip ailerons because its simple. The in-board 1/3 of full span strip ailerons has very little effect on roll.

For "3D" aerobatics the inboard portion can become important in hovering maneuvers where there is inadequate airflow over the rest of the wing. But you'd do as much good programming "tailerons" for a split elevator.
Not sure what you are refering to here... Are you saying they are there just for looks unless you are dealing with 3d? I would have a tendancy to concur but not sure why you said it.
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Old 01-13-2014, 07:38 PM   #12
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There's no prop wash on a sailplane, so there goes that theory.

"Give a man a plane and he'll fly for a day.
Teach a man to build a plane and he'll fly for a lifetime"
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Old 01-13-2014, 07:53 PM   #13
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Originally Posted by drummaker View Post
Not sure what you are refering to here... Are you saying they are there just for looks unless you are dealing with 3d? I would have a tendancy to concur but not sure why you said it.
Strip ailerons are usually just for simplicity, especially when driving the ailerons from a central servo via torque rods.
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Old 01-13-2014, 11:00 PM   #14
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Originally Posted by JetPlaneFlyer View Post
Strip ailerons are usually just for simplicity, especially when driving the ailerons from a central servo via torque rods.
I do sometimes wonder how much of the central servo movement is actually maintained down a narrow strip aileron to the tip where it is really required!

Even a 1/4 span aileron at the wing tip and directly connected to a wing mounted servo is remarkably effective but of course is completely out of the prop wash.
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Old 01-13-2014, 11:08 PM   #15
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Originally Posted by BroncoSquid View Post
And, when I apply flaparons to my slow stick (only because I can) I have to add a ton of UP elevator! Not reccommended it just makes the plane a mess to fly.
Yeah
I've tried flapperons on several of my models, but didn't like them much. One thing that showed up on my models is the tendency to snap out if you fly a little to slow during a landing.

Pure flaps are much better. I've got them on several models.

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Old 01-14-2014, 02:03 AM   #16
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With strip ailerons and no taper or sweep to the wing (or taper to the aileron) yo are usually better off with spoileron than flaperon. the ailerons moving up forces you to pull the nose up presenting the belly of the wing as a big airbrake. And they act to "washout" the wing letting you bring the nose higher without stalling.

This can be MUCH better to get a slow landing speed than by using flaperon.... for some airplanes, such as a Stick.
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Old 01-14-2014, 01:16 PM   #17
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Originally Posted by fhhuber View Post
With strip ailerons and no taper or sweep to the wing (or taper to the aileron) yo are usually better off with spoileron than flaperon. the ailerons moving up forces you to pull the nose up presenting the belly of the wing as a big airbrake. And they act to "washout" the wing letting you bring the nose higher without stalling.

This can be MUCH better to get a slow landing speed than by using flaperon.... for some airplanes, such as a Stick.
So after beating this thing to death..

Although it wouldn't be that complicated to calculate it looks like this and only applies to Strip Ailerons.

A straight wing with a tapered aileron... Flaperons should work fine as long as you aren't too severe.

A straight wing wing with no taper on the aileron.... Hmmm could go either way but assuming their is washout in the wing already. Then most likely Flaperons.

Strip aileron no taper on tapered wing.... Spoilerons for sure.


Now I am speculating.

Strip Aileron Tapered on tapered wing... Could go either way but most likely spoilerons.
it would be pretty simple to tell if this creates wash out or in, by using a string or ruler from the bottom edge of the aileron to the bottom of the front of the wing parallel with the fuselage at 2 places on the wing, one close to the fuselage and one close to the wing tip.

Determine which one causes a steeper angle in relationship to the bottom or the fuselage or table or whatever. The steeper angle one will stall 1st so you want this to be towards the Fuselage. If it is... Flaperon if it is not... Spoileron. Note although incidence is really measured at the center of the leading edge of the wing. in most cases this ruler method should work...


OK all this said. I have found that any model which is designed without flaps generally doesn't need any of this so... In my mind this is kind of an exersize to work our brains.

This was fun.

I had never thought about spoilerons actually forcing the belly up.. Interesting
but I am not sure I would do it that way. I will have to give it some thought. My spoilerons (on glider only) have just made the plane drop.do to very little lift, but I have always used them at the last minute. I guess the thought of using them to change the incidence and slow the plane down had never occurred to me.
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Old 01-14-2014, 04:16 PM   #18
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All this talk of Flaperons, Spoilerons and the like make me want to build a Storch wing for my Slow stick that much more. It will be fun to play with the different combos on the DX8. Now I am thinking run each of the 4 servos to different channels.....hmmmmmm.

I'm either going to get good at flying em, or get good at fixin em!
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Old 01-14-2014, 06:22 PM   #19
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You can play with all sorts of things having flaps, ailerons and one channel per servo.

Mix the ailerons to the flaps for full span aileron effect and a switch to turn that on/off, You can see the actual difference between full span aileron vs the tip only.

Ailerons up as flaps go down... very effective air-braking. Virtually impossible to stall the tip before the root.

Both ailerons and flaps going up together for for the spoileron effect or down for the flap effect of full span "flaperon/spoilerons"

And the conventional separate flaps and ailerons as if you just used 2 channels and a Y

I use all of these on a 50cc low wing stick. (AMR kit)

Use the right setup for the plane you are flying... The stick with separate flaps and ailerons is an ideal testbed to see the assorted effects possible.
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Old 01-14-2014, 07:29 PM   #20
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Originally Posted by fhhuber View Post
You can play with all sorts of things having flaps, ailerons and one channel per servo.

Mix the ailerons to the flaps for full span aileron effect and a switch to turn that on/off, You can see the actual difference between full span aileron vs the tip only.

Ailerons up as flaps go down... very effective air-braking. Virtually impossible to stall the tip before the root.

Both ailerons and flaps going up together for for the spoileron effect or down for the flap effect of full span "flaperon/spoilerons"

And the conventional separate flaps and ailerons as if you just used 2 channels and a Y

I use all of these on a 50cc low wing stick. (AMR kit)

Use the right setup for the plane you are flying... The stick with separate flaps and ailerons is an ideal testbed to see the assorted effects possible.

Thus my wanting a Taranis
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