Bipe aileron setup?!
 

I've finished building my first bipe...a Lanier SE5a EP...


My question is on the aileron setup: This plane has dual aileron servos connected by a Y harness and ailerons on the upper and lower wings connected by a pushrod.

No matter what I do, I can't get the ailerons on the upper and lower wings to have equal throw. If I set up the lower ailerons for the correct throw, the upper has near the correct throw when going up and much more when going down. I have expiremented with different holes on the control arms, etc etc.

I have a few questions:

1st: Is it normal for bipes with dual ailerons to have different throw from upper to lower ?
(just due to the arcs that the control arms travel through)

2nd: if this isn't normal, what can I do to fix it?

3rd: if it is normal, which ailerons to I set the throws off of, upper or lower?

4th: do any bipe flyers recommend expo on the aileron servos? I've never flown with expo before but these ailerons look pretty snappy...I'm not sure what to expect. I've flown bipes on Real Flight briefly and I'm not sure how those are set up.

Thanks for any replies, this is a nice little plane and I don't want to pack it in on the maiden because of a screwy setup.

RE: Bipe aileron setup?!
 

OK, I'm your man. I've been fighting this dragon for a couple of years now.

What you are probably experiencing is a problem with the rigging design that is being used to connect the ailerons together top to bottom. When they have horns bolted to the inside of the ailerons, pointing at each other, they screw up the way the paired ailerons deflect by destroying any chance they will move in unison. I'm going to go find my pictures. be right back

RE: Bipe aileron setup?!
 

Here is a picture that shows what happens with the rigging that is very often used with smaller biplanes.

You wind up with the uniform movement completely screwed up, a real mess. When the servo moves the aileron it drives directly a certain amount, the paired one will move a very different amount. When the same servo moves it's aileron in the other direction, the paired will move a DIFFERENT amount than it did the other way!

What you wind up with are 4 ailerons moving, with the two that are being driven by the servos moving the same deflection as each other. No problem. But on one side of the airplane, the paired aileron moves a different amount than the one it's connected to. So you got one side somewhat screwed up a certain amount. Now, on the other side of the airplane, the paired aileron moves an entirely different amount than any of the other 3 ailerons.

It's really screwed up and hard to put into words.

But here's a picture of the side of the biplane that has the downgoing ailerons. Let's pretend the servos drive the lower aileron. And the servo on one side is driving down. The servo commands a 20degree deflection and what the rigging does is change that deflection to the paired aileron to 26degrees down. So on one side there is a 6degree difference in deflections. OK, that's just on that side of the airplane.

On the other side, that rigging design doesn't screw up the same when the ailerons are being deflected upwards. Over there, the servo also commands 20degrees and whichever aileron is directly driven will do it. But when that rigging design moves in the up direction, the amount of difference is different. You don't even get the same screwup side to side. On the up side you get 23degrees from the driven one.

Talk about lack of uniformity. You have two ailerons going 20degrees, a third aileron going 23, and the fourth one going 26.

OK, why is this? And what can you do to fix it.

RE: Bipe aileron setup?!
 

OK, you remember the advice about pushrod connections that goes something like, "always connect your pushrods to servos and horns to give a 90degree angle".

There is a really good reason for this. It's why everyone with any building experience has heard that rule more than once, and heard it said in a number of diffrerent ways.

If the pushrod doesn't make a right angle to the servo with the servo arm or to the hingeline with the horn, the deflection at one end of the pushrod won't be the same deflection at the other end. It's been proven over and over and over. And the people who designed your biplane didn't seem to get it.

Here is a sort of useful picture to show conceptually where the pushrod ought to go and where the connection points should be. The green dotted line is what would give uniform deflection top to bottom. The black dotted shows an often used layout that really won't give you uniform deflection.

RE: Bipe aileron setup?!
 

Here is how I've got my Skybolt's ailerons rigged.

You will notice that the connections for that pushrod are above both ailerons. If you were to draw a line like the green one in the post above, it would match up with the picture in this post.

I gotta go fix something in the house. Be right back in awhile. In the meantime, I've bumped an old thread that goes over this same ground.

RE: Bipe aileron setup?!
 

daRock , How much difference did this make , in the way your SkyBolt flies ?

RE: Bipe aileron setup?!
 

Yes and no. You will NOT see any biplanes have such screwed up throws except the ones with paired ailerons, where one aileron drives the other. It simply does not happen with any biplane that drives each aileron with it's own servo. And it is not something that would be copied on purpose. There are no positive benefits of it. So the bigger bipes that use 4 servos are not going to have the problem and you can bet your house and car their designers won't be showing how you can adjust your radio to get f'd-up deflections.

See the above posts and the other thread.


It's not which ailerons drive and which are driven, it's the design of the rigging.

The expo or not decision isn't really related to biplanes versus monoplanes. Expo is really useful for most people on elevators. It's slightly less useful on ailerons. And that depends on the airplane, not the number of wings the airplane has.

When landing, you know how delicate you have to use the elevator. Well, that's what expo helps with. Think about the maneuvers where aileron control needs to be delicate like that. People flying very precisely do correct with fine precision with the ailerons. That's what expo would help with on the ailerons. Do you want some help there? Go for it. But it's not going to make the airplane less prone to yaw variably like this aileron problem causes. And it's not going to make the bipe with these almost random deflections less apt to suddenly lose a wing in the turns or during hard pitching.

This deflection problem probably most often manifests itself as an airplane that unexpectedly does things. Is apt to snap out of a maneuver without warning. Has to be watched closely on landing if you're a bit slow because it just might drop a wing if you're curling it in instead of bringing it straight and level. Things like that.

RE: Bipe aileron setup?!
 

So is what you've found going to ruin the airplane.

Probably not.
Thousands of people don't even know it's a problem. And most couldn't care less even if it's explained to them so they understand it.

A bunch of them simply put it down to, "that airplane is a bit tricky to fly, but it flies great otherwise, what's the problem" or say "it's a little touchy to land and you need to keep the turns a bit open but it's just a snappy airplane"

They don't have to be. And knowing a bit more about what you've got and what you're doing often helps make your airplanes just a bit better than everybody else's. Heck, there are people who think "it's good enough" is good enough.

RE: Bipe aileron setup?!
 

I wish it was that easy.
There are thousands of Skybolts flying with that ARF factory rigging. I don't know a Skybolt owner who doesn't like his model.

I've never had mine surprise me. And I do know one guy who offered to let me fly his and followed that offer in the same breath with a few "warnings". I put it down to the rigging. I flew his and definitely felt it wasn't going where I expected it to in the quick stick maneuvers. That could have been the CG or the different TX setup or throws or a bunch of things. Snaps came out different places and such. When I was landing his, he kept telling me to keep the speed up. So I landed a bit hotter than I would have with mine. He flew mine and immediately wanted to know what servos I had because he wanted to get some like must be in the plane. He assumed right away I had digitals. He said he liked the way mine flew. I don't have digitals in the sucker, btw.

It's really not something that anybody with my skills is going to know for certain. I'm not a precision aerobatics kind of flyer (in R/C ;) that is).

No way to prove something like this. Or even predict with any assurance how it'll show up in the air.

BTW........... The first time I saw this rigging design on an airplane I was building, I corrected it. So I've never flown my own biplanes with the lash-up setup. I've maidened a couple of other guys bipes and flown the Skybolt mentioned above a bit, but that's all. So I won't ever fly the "wrong way" setup enough to get a firm basis of comparison.

RE: Bipe aileron setup?!
 

OK, here is a picture that shows the lower aileron driven. The painted picture above with the 20/22 deflections was with different wing stagger and was figured with geometry, not just modeled as in this picture. Modeling simply shows what happens without any possibility of errors in arithmetic.

RE: Bipe aileron setup?!
 

The last picture, if I remember correctly, was a setup I made using the dimensions of a 46size Ultimate biplane. The "paperdolls" are basically templates laid out where they'd be on the plans of that model. It's a dead accurate way to see and measure what would happen on the airplane.

What causes the problem are two things.

The wings stagger. One is appreciably farther forward than the other. This moves the axis of the pushrod off perpendicular. But that's not any worse than the other problem.

When you place one horn above the hingeline (the lower horn) and the other one below the hingelin (the upper horn) you wind up ruining the 90degree angle even more.

You always want a pushrod to create a 90degree angle with the servo arm and with the horn. If you don't........................ ;)

RE: Bipe aileron setup?!
 

BTW, with my Skybolt, I used the hardware that came in the ARF kit to do the installation pictured. No kidding. The better setup didn't cost me a penny more.

And it actually took me less time to do and was easier to do accurately.

I cut the horns provided and threw away the bases. (Kept the screws however. ;)
I used a razor saw and slotted the ailerons to take the tops of the horns. Epoxied them in and went to supper. Done...........

Do you find that lining up the screw holes of the horn's top with the bottom to be a real pain in the ass, and it takes a bunch of time and never works out worth spit. I didn't have to do that exercise in frustration FOUR times worth. That alone makes me look forward to my next biplane. If this rigging arrangement didn't do anything else, just not having to screw on 4 bloody horns is worth doing linked ailerons this way. To heck that it flies better. I DON'T HAVE TO do 4 horns. The better flying is hard to prove to skeptical people anyway. Tell everyone you did it that way to save time and frustration. And let 'em fly their "tricky" biplanes in ignorance.

RE: Bipe aileron setup?!
 

Thanks for the info . I have 2 SkyBolts {arfs} 1 still in the box and one with a Saito 1.00 . I`ve got about 30 flights on it, and having trouble getting comfortable with this plane. I think I`m just afraid to smuck it ,as it gives butterfliys in the stomach every time I fly it.

Your right , sometimes good is not good enough , time to get the throw gauge out and do some checking.
Thanks again for the info. Did`nt even think about it when I set the plane up.

RE: Bipe aileron setup?!
 

WOW! Thanks da Rock... That's awesome information. I will take a look at the plane and see if I can make your modification with some confidence (I'm sometimes unsure of my modeling skills...more confident in flying skills at this point. )

RE: Bipe aileron setup?!
 

It's actually pretty easy to do. And if the airplane is already setup, all you have to replace are the top aileron horns.

What the job amounts to is cutting a slot into the aileron the width of the top part of the aileron horn. You cut the base off and use just the top part. Epoxy that part in and it's done for the bottom aileron. Almost done for the top. For the top, you have to remove some aileron TE so the pushrod doesn't hit.

Pretty simple.

RE: Bipe aileron setup?!
 

Da Rock,

THANK YOU for helping me out with this! I flipped the upper aileron control horn around and put it on top of the aileron instead of the bottom and, presto! perfect synchronized travel from all 4 ailerons. I didn't even have to notch the TE. I did have to debond the CA holding the control horn in (it's an electric plane...no screws in the horns) and that's the part I was concerned about but things are perfect now.

Since this is such an obvious problem and an easy fix, I wonder why these model engineers don't address this when designing these ARFs.

I guess it's all about the $$.

I have a CG Pitts P-12 Monster waiting to be built and I will once again be modifying the aileron linkage on that too.

Thanks again.

RE: Bipe aileron setup?!
 

da Rock - I was pondering this as being a problem on the Herr Pitts with upper ailerons I am building due to the staggered connection points for the horns... Herr Pitts Bipe Thread Figured I'll just go with the horns on the inner sides of the ailerons after I pondered this a bit. Nice to see your guy's dialogue here... sanity check for me. :)

somegeek

RE: Bipe aileron setup?!
 

da Rock, good information. I built my 1/3 scale Gary Allen Bucker Jungmeister by the plans. As you can see from the photo the horn on the top wing is on the top. The aerobatics that the plane does are really good. I have flown many other bipes with the horn on the bottom of the top wing and I thought that they flew very well.

RE: Bipe aileron setup?!
 

Unfortunately, it's not about money. You just used the hardware that came with the airplane. So what you did correctly cost nothing additional. And was done with what came in the ARF.

What they prove with almost every ARF is that the people assembling them don't understand the things they're putting together. The flaws in design prove pretty much the same thing only they prove the correctness of the term "engineer".

Today, the experience we need to have is what to look for in our next ARF that need reinforcing or re-glueing. And we need to learn enough about flying models that we catch design screwups. For an example of design things, there are a number of tricycle gear ARFs that have the main gear coming straight down from the CG. Dumb. It's dumb because a couple could work perfectly if the struts had been bent back instead of straight down.

ARFs are wonderful things. Convenience and beauty you can't beat. But we have to keep in mind that they're being built by people who won't come close to every owning radio equipment or flying models. And they're being passed through a design process that allows things like firewalls made out of liteply.

RE: Bipe aileron setup?!
 

Great thread, but I have a question: If the ailerons are connected at the trailing edge (or just aft), will the throw be the same for the upper and lower? I'm thinking that what matters is that each aileron is connected at the same location relative to each aileron, so whether it is above, below, or in the middle (at the TE), it should work fine as long as both ailerons are done the same way.
thanks
Steve

RE: Bipe aileron setup?!
 

Don't worry about it.
The rigging police aren't going to check.
What's the big deal about having differing throws, upper and lower wing?
The plane responds no matter what.
Could it respond better?
Who could tell?

RE: Bipe aileron setup?!
 

Hi Steve,

Yes it really does matter if you want the best performance from your plane. I built a 1/4 scale Waco YMF-5 and originally rigged the ailerons as shown in the first photo. The top aileron moved a greater distance than the bottom aileron. When the top aileron came down it was hitting the wing before the bottom aileron came close to hitting therefore the rolls were very slow because I didn't have enough total aileron travel.

To correct this I made a tab that attached to the bottom wing to cause the two ailerons to move the same amount. See second photo. The plane roll rate was much better after this.