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Old May 01, 2012, 11:18 AM
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Aileron Differential

OK so I'm having this discussion about aileron differential with SDR and I thought I had it right in my mind but he's questioning me. So I go back into the RCG archives and I see a lot of people are just as confused as I am because they answer it both ways. Don't you set the differential with more down than up or do I have it backwards?
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Old May 01, 2012, 11:20 AM
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I am not sure if it is right but I have mine setup with more down than up and it works great. That is the setup that GMo recommended to me last year and I have used it since.

this subject is like so many others in this hobby everyone will have their opinion......
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Old May 01, 2012, 11:23 AM
Duane
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Differential is usually more up, less down. Typically, the downward-deflected aileron creates more drag than the upward-deflected one, which causes adverse yaw (that is, the nose moves opposite the intended direction of turn). Aileron differential can help with this, but proper use of the rudder is more effective. Aileron differential is also used in hand launch (which most often uses full-span flaperons) to eliminate pitch changes with roll input. A lot of pilots flying rudderless airplanes are using reverse differential (more down, less up).
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Old May 01, 2012, 11:27 AM
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Quote:
Originally Posted by Alan C View Post
I am not sure if it is right but I have mine setup with more down than up and it works great. That is the setup that GMo recommended to me last year and I have used it since.

this subject is like so many others in this hobby everyone will have their opinion......
OK. I've got mine set up the same way and that's the way I've always done it Of course, it's done to varying degrees, depending on the plane. At least now I know I'm not the odd man out. Right now, I have my B3 set up with twice as much down as up. It seems to turn nicely like that.
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Old May 01, 2012, 11:32 AM
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Quote:
Originally Posted by Wazmo View Post
Differential is usually more up, less down. Typically, the downward-deflected aileron creates more drag than the upward-deflected one, which causes adverse yaw (that is, the nose moves opposite the intended direction of turn). Aileron differential can help with this, but proper use of the rudder is more effective. Aileron differential is also used in hand launch (which most often uses full-span flaperons) to eliminate pitch changes with roll input. A lot of pilots flying rudderless airplanes are using reverse differential (more down, less up).
Geez... and now the controversy starts. Id like to see someone like Gerald answer the question so that I can once and for all get an answer I know is proper. Not that I don't trust you guys but as you can see, the answers I'm getting are inconsistent.

Way back when, I built a kit that called for more down than up. That's where I got my idea of how it was suppose to be.
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Old May 01, 2012, 11:33 AM
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The way I set mine up is to fly the ship at a moderate speed and roll the wing back (pure ailerons, no rudder) and forth and see if the nose drops or raises. Adjust the differential until the nose stays level when you rock the wings. This is the starting point. Now when you initiate a turn with rudder and ailerons the nose should stay level. When you are in a thermal and need opposite aileron to hold the turn you should not need additional elevator to hold the turn.
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Old May 01, 2012, 11:43 AM
Duane
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G_T wrote a fair bit about aileron differential in the Initial programming of a DLG thread, particularly this post.
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Old May 01, 2012, 11:55 AM
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Ah-ha.... good info. There is no right or wrong answer. Each plane is or could be different and the pilot must choose for themselves. Seems like no aileron differential on a rudder equipped DLG is the best way to go.
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Old May 01, 2012, 11:57 AM
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Quote:
Originally Posted by Mr. Wiz View Post
Seems like no aileron differential on a rudder equipped DLG is the best way to go.
I believe G_T advocates using whatever aileron differential yields no pitch change with roll-only input, and use the rudder to control adverse yaw.
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Old May 01, 2012, 12:30 PM
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I think after reading that Id rather just fly the minor rudder adjustments myself.
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Old May 01, 2012, 12:33 PM
G_T
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Yes, particularly if a pilot is not already expert at reading the air from the plane response. If someone is still having difficulty or questions about that (in other words, if it is not an automatic skill) then I recommend setting differential for no pitch response for small quick rocking motions of the wing.

This makes it easier to read the air when flying along in straight line flight. Finding the lift and getting into it quicker is worth more than whatever perceived benefit one might get for various settings for turns.

Beginners and intermediate pilots have issues with finding and centering lift. Make that job as easy as possible.

Experts generally don't have issues with finding and centering lift, except when the air is tricky. Experts are also often quite good at the sticks. They can set differential however they want and it is up to them to deal with it. But IMO novices/beginners in particular should really avoid pitch-inducing differential settings, and intermediate pilots would be better served by avoiding it as well.

Slightly OT warning ...

Many pilots really can't fly their planes. By this I mean that if they try to do anything beyond the simple flight motions they routinely do in a flight, they can't. They don't have the skill at the sticks.

Many have even developed mental blocks against certain maneuvers.

You see this in the pilots who only ever turn to the right (or is it the left - I forget). They have to always have a straight line approach to landing. They have to always land straight upwind. They can't dodge people on landing approach. They can't do a turn-and-burn of the various flavors.

Loops? Fly inverted? Inverted thermalling? Fancier stuff?

If this description fits you, then you need to do some flying.

But first, tighten up the springs on your transmitter sticks. If the sticks are anywhere near their factory settings, then they are too loose for you to feel where the sticks are located. If you can't feel it, you can't fly it. So fix that first. IF you have been using differential and/or dual rates, then remove or disable those settings at the same time. You'll very likely find you don't need them any more. Often DLG pilots use them essentially as a correction for not being able to feel where they are holding the sticks. But our planes really have a small speed range so differential doesn't make as much sense, not for thermal flying. And expo results in having less control of pitch/roll during banked turns so it is harder to fly them smoothly. Life is easier if the response during turns is the same as the response in level flight and you will not get that with expo.

Get out there and fly. Get some altitude, and bang the sticks around. Do rolls. Notice that wacky pitch response when inverted? I bet your CG setting isn't anywhere as close to neutral as you think it is!

Do loops. See how the plane rolls off some as one continues loops? That means the plane is actually flying in a small sideslip. Adjust the aileron and rudder trims to eliminate it - or fix the warps in your wings/flaperons! Or if you have slop in your flaperon setup, set your camber positions when holding the plane upside-down. Then the loading on the flaperons is the same direction it is in upright flight. Or better, get rid of the slop.

Get comfortable turning both directions. Fly figure-8 turns. This is where you'll learn if you really know how to fly turns. You should be able to do them keeping the fuselage horizontal - at least if you have a rudder. You should be able to do them in the same horizontal plane, regardless of rudder or not.

Landing approaches. Start doing some catches while the plane is in a turn. When I used to fly by myself - when I had time and a convenient field - I'd often be practicing low level thermalling close by. Too close and too low to really set up approaches. I'd often catch the plane literally out of a turn without leveling the wings. Rather fun actually.

Practice flying turns close to the ground. Practically scrape the grass (if you have any) with a wingtip. Of course, don't hit, or you'll be doing a fair bit of repairs. But get comfortable flying lower so that attempting to thermal out from ground level no longer seems like a big deal.

Practice some ballistic flying. Launch, leave it in speed mode and push over way early. Or dive down to get speed. Fly around fast, doing smooth graceful turns and other maneuvers. Learn to make microscopic smooth corrections to the sticks.

Get some music, grab the sticks, and make that plane dance!

Go out as the sun is setting, trim for float, and see how smoothly you can persuade the plane to go where you want. This is persuade, not drive. Move the sticks no more than perhaps 5mm, and never in a jerky fashion. The plane may take several seconds to respond. That is all right. Really focus on the plane and fly it super smooth. Watch for any signs of improvements to air in one area or another. Any signs of drift in the air, or any motion of the plane at all that wasn't directed by you. Repeat - really focus on the plane. Study its flight and how it reads even the tiniest change in the air.

When you feel comfortable flying the plane in any attitude at any speed, then you are becoming an expert on the sticks.

If you have to think about what to do, then you aren't doing it yet. Practice will help! This is flying, not thermalling. But being good at flying helps with all the rest.

Then, go out on an active air day, and practice reading the plane while blistering along in speed mode. It is good for scouting before a round and it is good practice.

Also go out on some low wind day and pick some random direction (but not downwind as you know too much about what is going on there). Launch and head out until you've lost half your launch height (hint, don't launch super high or you may be testing your vision as much as your flying). Now you have to find some lift to get back. Get comfortable doing it, and knowing you can do it. You are not going where you have a read based on ground signs. All your reads will come from what your plane is telling you out there. Get good at reading it.

Do some practice flying your plane while looking elsewhere. Put it in a turn, not too far away and not overhead. Feel where you are holding the sticks, and freeze the position. Look away for a second, spot and notice something else. Then look back. Work on that until you are still nicely in your turn. Then look away longer. Look over your shoulder. Look at someone elses plane. Study their plane and read their air. Get good at this, and you won't be relying on your timer nearly as much for reads.

Gerald

PS - I'm remembering all the things I'm getting lousy at by not getting out to practice these last several years.
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Old May 01, 2012, 01:37 PM
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First off, I'm not one that has any difficulty banging the sticks. I'm coming from pattern flying to DLG flying. Inverted flying, no big deal... Inverted thermaling? I've never even considered it. My camber settings go the wrong way but now that you mention it I'll have to give it a try.

For me, stiff springs on the sticks are a must. Ive switched my SD-10G to the stiffest springs I can buy and dialed in about half of the tension. That's plenty stiff for me to feel the centers but not so stiff as to cause fatigue. Each person is different in this regard but the mushy stock spring settings just don't get it. Most people never adjust this so they never know what what I'm talking about even when I hand them my TX to feel it. You really have to try it to see the difference it makes.

As for your comments about dual rates and expo. I don't agree. I use dual rates to set up my servo travel limits and not the servo travel functions themselves. If you dial down the travel with that function your servo steps become coarse. At least that's how it's been explained to me. So I crank my servo throws up to 150% and then tame them down with dual rates. That's the method the pattern guys use. Now I also like a lot of throw for getting out of trouble or doing aerobatics so I don't tame the throws down too far. Doing that can get you into trouble when you need to make swift corrections.

Expo is something I absolutely love. Why? For several reasons but here is #1. Smooth flying is what we all want. Ever see a guy that can bang the sticks like mad but cant fly a nice straight and level line to save his butt? His throws are set up for wild stuff but at those settings, just the pulse through his fingertips gets translated to his plane. This is particularly true with elevator and many times with aileron input too. But when I need full throws to whip the plane around fast or make a correction in tough conditions I want that authority there. With expo, you can have the best of both worlds. Just don't over it. I generally run 20%-30% on ailerons and elevator. Only 10%-15% on rudder. Play with it to see what works best for you. Also, we were talking about stiff springs on the sticks. The stiffer you like them, the more you're likely to shake a little as you hold the sticks deflected. Even if you like a twitchy plane 10% expo on everything can smooth out your flying.

Now any and all of this discussed is personal taste. I like a plane that is very easy to fly smoothly because for me, being smooth is the hard part. Just a little example here, one day several years ago I attended a local pattern contest and there was this old guy that told me he built Andrew Jesky's pattern planes. To look at the quality of the fit and finish of his own plane, I believed him. As I recall, he was flying in Advanced and I was flying Sportsman (Novice). He looked like he was experiencing the beginnings of Parkinson's disease and his hands shook all over the place but his plane tracked like it was on rails. He had beautiful execution, cross wind corrections and all. I couldn't see any flaws in the old guys routine. So I asked him. He said, said he has a ton of expo dialed in to counteract the shaking. He went on to tell me that most people set up their planes to be too touchy around center. They do it for that time when they need a lot of throw to perform a maneuver. The trick he said, is to set it up with just the right amount of throw to perform the needed maneuver and nothing more. Then set in a little expo to really put the icing on the cake. That's what I've done ever since and the minute I did it people thought I'd really improved my flying skills. Nobody will ever convince me that setting up a touchy plane is the right way to go... unless you happen to be wanting to fly torque rolls down on the deck and even then there is such thing as too much.

So now you have my secret to smooth flying. I'm still not as smooth as I'd like to be at times with the DLG but I'm learning and I'm improving every time I go out.... cept when I crash on the first flight cause I forgot to connect the radio. Dont ask.
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Old May 01, 2012, 01:44 PM
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Oh... and remember, touchy on the controls does not mean that plane signals lift any better. You're not suppose to be hard on the controls when looking for lift, right? You just want smooth inputs when you make them. That's all expo and dual rates does. Well anyway, there is one man's opinion on the subject but like everything in this hobby, your mileage may vary.
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Old May 01, 2012, 02:11 PM
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With the non linier servo horns we use, expo does have a place in all RC flying. Usually an expo rate of about 25 (JR) gives you a linier movement of the control surface. This of course can vary with the type of control setup. Dual rates can help when you switch between flight modes. Thermal mode does not need lots of aileron movement so why not tone it down with dual rates? I agree that when trimming out a new ship, zeroing out the expo and dual rates is the way to go but after you have it trim I use these option to make the ship feel the way I want for the mode I’m in. With the huge ailerons on DLG's having expo will smoothout the center of the stick throw. This is a good thing. When I roll my ships I want half roll rate at half stick deflection and full roll rate at full deflection. I adjust the expo to get this. Same goes with elevator. I have flown many ships that have 70% of the roll rate (or loop diameter) in the first 1/4 of stick deflection. This is not taking full advantage of the radio's capabilities.
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Old May 01, 2012, 02:31 PM
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I don't play with different expo or dual rate settings on my DLGs between flight modes. I want the same control response regardless of where my camber settings may be. But again, that's just me. If it works for you, who is to say its wrong?

I start with a zeroed out model when I first start programming but I don't have zero rates for the first flight. For me the rates are nothing more than a servo travel tool. I set up the max throw I want right in the beginning. Expo is usually started out at 10% on everything but usually adjusted up a little from there. The only planes that I don't start out with like that are ones that are so docile to begin with that I'm afraid I might not have enough control response to get me out of trouble. DLGs so far aren't that docile. I did however over do it a little on my B3. I initially had the elevator max set too low. I cranked up the throw and dialed in a little more expo and then I got a smooth flying plane that can turn on a dime if I want it to. Keep this in mind as well. Our planes indicate thermals better with a rearward CG, right? A rearward CG also causes a sensitive elevator. Move the CG back to get a good thermal indicating plane and then dial in some expo to counter act that elevator sensitivity around center on the stick.
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