you can get a really clean roll in an aerobatic plane with a more simmetrical airfoil. Normally the configuration of a plane like the citabria and its airfoil its more like to do barrels than rolls. the barrels use rudder.

Da Rock is right.
Symmetrical wing means nothing and still does not negate the excessive drag and lift and in general messing up the roll that an aileron in "FLAP DOWN" position causes. There is a reason for differential.

Jim

Here is a link to a Super Decathlon test flight that shows the aileron at deflection and the rather lazy roll that results. The time is between 1:43 and 2:06 that shows the deflection. Barndoor ailerons just don't produce high rates of roll on scale type high wing models.

http://www.youtube.com/watch?v=oDRxXi02y4o

I don't even need to look at it to know that I didn't set that one up. Because if I had, I can assure you the roll rate would have been higher than that.

I'll let you believe what you want to. I've had several Decathlons and Citabrias, and they are GREAT flying planes, and they are aerobatic, which is of course how Citabria got its name. Spell Citabria backwards sometime if you don't believe me. The Decathlon is just a Citabria with a bigger engine and a few more advancements.

Jim

Thanks for all the advice and tips.
Like I said earlier, I had the same exact kit 15 yrs ago that rolled fine for a Citabria but alas, not the present one.
I'll be cutting some access hatches into my wings to get at them bellcranks in order to give myself some differential.

I am still reading this thread and will post updates of my results....

What happens is that this stuff isn't simple.

One problem is that "the same model" isn't guaranteed to be. The people who made the kit years ago aren't making it now, or making the ARF of it now. Or two guys who put together what actually are similar models do things differently. Or two workers in the ARF plant do things differently.

A year ago we were looking closely at two identical ARFs from the same retailer. One was at least a couple of years old, the other brand new. It was amazing how many things were different from the factory. And darned if the two CGs were amazingly different considering both guys claimed to have balanced his plane exactly where the factory recommended but with "just a bit of nose down to be safer".

[ If an aileron is moving 10 degrees not 30 degrees then it does not have the full effectiveness that it could have. I was referring to the effectiveness it does not have from reduced deflection not the aerodynamic effectiveness it already lost. Besides the roll rate is reduced mostly because of the side loads from the yaw and the interaction of a wing with dihedral. Wings with no dihedral do not seem to significantly slow down their roll rate, even if the yaw is enough to see the tail wobble.

Adding in yaw does add drag, but not enough to matter. I am flying a model already getting very poor efficiency due to its nitro engine, I couldn't give a flip. Besides, as anyone who has flown a full scale plane would know it actually flies very well that way. In fact you may flunk your flight exam if you don't add rudder in the turns, even on aircraft such as a Cessna 150 which has differential. The fact is my planes have a slightly faster roll rate with no differential and rudder than with differential and no rudder.

Uh-HUH.

I wanna SEE you roll that Cessna.

I'm not talking about flunking flight exams here, I know all about two-minute turns and a hundred other Full-scale things an RC pilot wouldn't bother with. They want you to add rudder to pass your test. That means nothing here.

YAW is a BIG deal, and the DRAG from Yaw is IMMENSE, it matters. I can slow a plane down from a rocket to a crawl just from crabbing it on approach. It doesn't fly well that way, every other aspect of that plane's flight is FIGHTING the Yaw. Throw that into a roll and you've got a problem, and a very inefficient roll. It slows the roll and makes it sloppy.

Jim

I have done it, it takes a while.

Yes, but you correct the yaw with rudder, there is no longer drag from the wind hitting the side of the fuse. The drag from the rudder is very minor. In fact reducing the drag is part of the reason it turns better with rudder. The other part is that the wing is no longer trying to roll the opposite dirction from the side load on a dihedral wing.

Adverse yaw has a simple cause.

One wing has more drag than the other.

Moreover, with cambered wings, the up-going aileron momentarily reduces the drag on that side. In reality, one wing has less drag than the other.

In fact, in order to get "full power" from ailerons on cambered wings, if you want the most power from the combination of both ailerons, the ailerons must move at different rates. Full scale airliners have been making more efficient turns for years by using spoilers. Or more correctly, they've been doing single spoiler turns. The spoiler on the wing that'll be inside the turn comes up, and that's it. The wing gets a bit of drag, a little less lift, and the sucker banks a bit and yaws a tad, and less fuel is burned while it makes the desired turn. You wanted to turn, and by golly you ain't going to change directions without changine directions and they all gotta yaw to do that.

Adverse yaw has a simple cause; the wrong wing has more drag than the other.

BTW, full deflection is what caused this mess in the first place.

And you're not going to lose total deflection because with the rigging change proposed, the up deflection is being increased quite a bit, more than the down deflection is being decreased.

With the rigging changes, you get roughly the same total deflection, only it's balanced to the needs of the aircraft, not just slapped on the sucker. There is nothing magic about 50% up with 50% down. But there is magic in getting equal lift and equal drag. What you get is a change in the roll axis that doesn't affect the yaw or pitch axis. Balance the aerodynamic results to the desired needs.

You're not just reducing the down deflection. You're increasing the up quite a bit and best of all, you're reducing not just the down deflection, but the wasted excess of lift and drag on one side.

Wrong, for full power you have full deflection for both ailerons and correct the yaw with the rudder. I know for a fact that many full scale planes do not completly correct with differantial ailerons. The same C 150 I mentioned did not because the roll rate was too slow. Fighters almost never use this though moderen computer controlled ones do during the landing configuration.

Nothing wrong with this. But it doesn't change the fact you will have a faster roll rate with 100% up and down aileron and rudder to correct yaw.

Sorry, it's not wrong. Adequate, appropriate deflection works perfectly. Yes, when the design of a plane makes that impossible, you've proven that airplane doesn't fit the basic requirement, not that all others can't. And proven that design hasn't got adequate aileron sizing/shape/movement.

Yeah, I should have said, "in order to get as much power available from the ailerons your plane has"....

The reason those full scale planes that can't completely correct isn't a fault of differential. It's just that those planes have stronger reasons for needing it than their ailerons as designed can provide. And what did the designers decide the C150 needed? Differential, not just more rudder. Unfortunately, the C150 ailerons or their linkages weren't modifiable enough. Or it being a real world airplane, the designers didn't have the time or money or desire to go that route to fix it.

Don't confuse "efficiency" with fuel consumption.

The reason designers rig differential into their airplane's ailerons is to make the sucker fly better and safer. Better can be a synonym for efficient. Matter of fact, in this case it is.

An airplane coming in for a landing that has the ailerons cranked into the cross wind and then needs rudder to kill the adverse yaw and resulting slip/skid has a number of things going against it. Roughly speaking, it's envelope has been reduced in a number of things by all that's wrong with it. It's not a very efficient design in certain areas and is generate excessive drag to fly the pilot's chosen course. Solve some of those problems and the airplane flies more efficiently.

For example, move the CG from an overly safe forward location, and the elevator needs less deflection to give you the pitch you want from it AND the pitch stability isn't affected. That elevator works more efficiently. If you understand what you've done by moving that CG to a "better" location you'll know to use less stick or re-rig the elevator connection, and the airplane will fly more efficiently. It'll actually be able to fly a little slower and do it with better control. It'll also lose less speed from pitch changes. Why, because of the increased efficiency. What happens to the gas mileage? Who cares. And make the ailerons roll the plane with more efficiency and you'll need less rudder to make your turn more efficiently. Efficiency just washes over everything from everywhere when you tune just one thing to suit the plane better.

Always looking for good suggestions on set up. What would you do on this one to improve the roll rate?

Actually the reason for differential instead of mixing rudder with the controls is mostly for simplicity. And the reason they do it at all instead of not bothering as with older planes is to reduce spin accidents.

There is no problem with using rudder to kill the adverse yaw. The problem is that many pilots do not do it correctly at all times. You seem to think there is a lot of drag when the rudder is cranked over a few degrees, but actually it is fairly small. The large drag you are thinking of is uncorrected yaw, from the side of the fuse facing th wing. Yes it is better to use differantial aileron for several reasons. But for our models they really don't exist. And with a high wing high life surface with dihedral you will get improved roll rate with rudder correction than with differantial aileron.

Full scale Citabria? You can't do anyting except make sure the stock rigging is correctly adjusted. Against the law to do otherwise.

We are talking about the model in the link.
Having instructed in a Citabria, I know how to get the maximum roll rate out of it. Use free weights on your right arm and build it up to where you can do 3 one armed pushups in 10 seconds.[8D]

I cannot see the video, and somehow thought that you were talking about full scale. IMO the aileron stick pressure is not nearly that great on a Citabria, elivator is a lot worse.. Don't know about the Decathalon though.

I guess I'm getting in on this one a little late but I have to think the topic of this thread has gone off what the original poster asked. He wanted a faster roll rate. To me that means angular speed (degrees/second improvement). Aileron differential is great for improving tracking in turns but I don't think it will improve roll rate much. In fact I lean toward SportPilots opinion that it may even reduce rate.

One thing thats fun to do is take a large wing out in the backyard and twist it around in front of you like a batton to simulate the rolling wing on an airplane. You'll see that as you try to increase the angular speed the air resistence builds up rapidly. It's because the wing's plan area must displace a very large amount of air. Biplanes and delta's tend to have a much higher roll rate because the wing is not having to dig that big screwthread through the atmosphere.

After checking for underperforming servo and properly sealed aileron gaps, the only way I can see to dramatically increase roll rate is to increase aileron area (displacement angle from neutral) or shorten the wing. Fifteen years is a long time and it's likely there have been better planes flown since then to increase the OP's expectations. I loved the game Fallout back in 1998. I installed it recently for a playthrough on the PC and couldn't believe what a piece of crap it was!

Some great info guys!
I really like the fact that I can post on here and get such a wealth of info/experience quickly.....

I haven't started surgery on the Citabria yet.
There is a bit of slop in the bellcrank linkage setup, though I'm sure it's no more than the original.
Right now I'm back to thinking how to cut the one piece servo to bellcrank linkage into two, then mount a round servo arm....

Aileron movement that causes excessive drag is going to slow down the airplane. Instead of pulling the nose off line, if the ailerons only cause a rotation on the roll axis, that energy they create is going to go into causing the airplane to roll.

And that's a good idea.

You can get whatever differential you need right at the servo. No need to futz with the bellcranks at all.

You can also get differential by leaning the aileron horns, btw.

I'd describe how to do this, but I don't think the audience is interested.

BINGO!!!!!!!!!
Very interested!!!!!!
Wow! The light bulb that you just switched-on is soo bright that I'm still blinking my eyes!! LOL.........
The control horns are built into the airelons, not just bolted on top......hmmmm....