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Internal aileron linkage

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Scheny

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I am interested in what internal aileron linkage methods you know of. I am only aware of how it is done in the Cirrus SR22, but I don't like the way they are using cables.

Is there any good solution to do it push/pull tubes? The easiest solution would be to "shorten" the lever arm in the aileron horn until it is within the aileron.

What method are the glider guys using? Please feel free to add some pictures.

BR, Andreas
 

wsimpso1

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Scheny,

I designed my wings with essentially the same thing as used in RV's. Long lateral pushrod, bellcrank anchored to a rib, short pushrod running chordwise and connecting near the upper skin of the aileron directly above the hinge line. Hinge line on my ship is below the foil profile. Forces give large FOS for the fasteners, control surface hinge bearings, and spherical rod end bearings. I wanted the portion of the aileron forward of the hinge for both mass balance and aerobalance, so the external hinges were worth the trade, while the linkage is entirely internal.

Once you have done a system like this, you can configure the aileron leading edge with a radius swung from the hinge line, so the slot is always small (and you can brush seal it) or you can configure the slot to open up as the aileron trailing edge moves down, increasing slot effect. You could even try one, and if you do not like it, make another set of ailerons to try the other...

Billski
 
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pictsidhe

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Mine will be a mostly if not entirely cable system. Probably a short pushrod from the aileron to a bellcrank/pulley, then cables. The more throw you have, the lighter the cables/pushrods can be. Double the throw, you can use stuff with 1/2 the strength and 1/4 the stiffness. To get the same performance. Internal aileron linkages don't give much mechanical advantage. But if you hook them up to a nearby bellcrank, you can gear them up there. I did consider direct cable operation, but then I'd need much heavier cables. Stiffness is the most critical design parameter for mine.
 

Hot Wings

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Here are some ideas for a hidden/internal hinge. The thumbnails are of a glider hinge - make forgotten - and a model version of the same thing to see how it works.
Edit: Hinge from a Libelle


Edit: There is also the method used by the Fauvel AV-36 rudder with the hinge on one surface and the imbeded push/pull tube just under the skin on the other side.
 

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Dan Thomas

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Whatever method you use, it will have its disadvantages. If there was a clear-cut winning method, all the certificated airplanes would use it.

Cessna used cables in everything except the Corvalis, which used pushpull tubes. The tubes run in guides that are small nylon wheels attached to a frame. There has to be some clearance between the wheels and tube, to prevent any grit getting pressed into the wheel and abrading the tube, and that clearance results in vibration wearing both the wheels and tube. Cessna wants the aileron control tubes inspected closely every so often because of this, and they want the tubes taken out to do it. That is no small job. Lake aircraft used pivoting swings along long runs of the tube, with separate tubes running from the control to a swing to another swing to the surface. Lots of hardware there. Lots of weight.

The push-pull tube system has a nice feel to it, with low system friction, but cable systems properly designed and rigged work every bit as well in flight and the flight loads completely mask any system friction unless the airplane has been poorly maintained and pulleys and bellcranks are all stiff and half-seized. I sometimes found pulleys totally seized. I ran into a disappointing proportion of airplanes like that in my career. I would free everything up, lube it all, rig the system exactly per manual, and the owner would wonder what sort of magic I had done to his airplane. It flew so nice after that.

Cessna used cables to operate bellcranks to operate the ailerons (all internal), and direct cables to the rudder and elevator except for the 170 and the 180/182/185/206/210 airplanes where a cable-operated bellcrank operated the elevator via pushrod.

Cable is inexpensive and can be run through some difficult routing with little trouble. It's very strong. It does need pulleys and brackets and terminal hardware, and it suffers wherever it passes over or through any fairlead or rub strip, which should be avoided as much as possible. Grit gets embedded in those things and it eats the cable. I found plenty of worn cables in airplanes that had been tied down outside for many years, with the wind wiggling the surfaces just a little and wearing the cables at those fairleads and rub strips. A push-pull tube system would get its tube guides and rod ends worn out in that situation, too. An owner needs external control surface locks to prevent ALL movement. The control column lock is totally insufficient.
 

BoKu

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Pretty much all modern sailplanes use push-pull tubes for wing control surfaces and elevator, with cables for the rudder. I'm using 5/8" OD 0.035" wall aluminum for all P-P tubes.

For the flaperon drive I use a skew drive similar to that of the Libelle ailerons (see photos in an earlier post in this thread), but I use it internally to drive a mass balance weight, with an external pushrod to a horn on the flaperon:


The guides are all linear ball bearings that I make myself. They're based on ones I saw in a wrecked LS6, but you can buy them from Aircraft Spruce as well:

 

Jay Kempf

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Pretty much all modern sailplanes use push-pull tubes for wing control surfaces and elevator, with cables for the rudder. I'm using 5/8" OD 0.035" wall aluminum for all P-P tubes.

For the flaperon drive I use a skew drive similar to that of the Libelle ailerons (see photos in an earlier post in this thread), but I use it internally to drive a mass balance weight, with an external pushrod to a horn on the flaperon:


The guides are all linear ball bearings that I make myself. They're based on ones I saw in a wrecked LS6, but you can buy them from Aircraft Spruce as well:

That's a fascinating picture. I like the term skew drive and haven't heard it before although I have seen plenty of them. Can you tell me what the grey tube is actually doing? You said mass balance. Is the rod coming from the right just reacting the weight of the tube around it's bellcrank axis somehow? Just curious.
 

BoKu

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That's a fascinating picture. I like the term skew drive and haven't heard it before although I have seen plenty of them. Can you tell me what the grey tube is actually doing? You said mass balance. Is the rod coming from the right just reacting the weight of the tube around it's bellcrank axis somehow? Just curious.
The gray tube is a chunk of steel tube containing 4 lbs of lead. It mass-balances the flaperon that later gets connected to the remaining arm of the carbon fiber bellcrank.
 

Will Aldridge

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Pretty much all modern sailplanes use push-pull tubes for wing control surfaces and elevator, with cables for the rudder. I'm using 5/8" OD 0.035" wall aluminum for all P-P tubes.

For the flaperon drive I use a skew drive similar to that of the Libelle ailerons (see photos in an earlier post in this thread), but I use it internally to drive a mass balance weight, with an external pushrod to a horn on the flaperon:


The guides are all linear ball bearings that I make myself. They're based on ones I saw in a wrecked LS6, but you can buy them from Aircraft Spruce as well:

So I have 2 questions;
1. So how would you go about mounting the ball roller guide?

2. I'm having trouble visualizing exactly how it works. I can understand how a tube would slide/ rotate through it but i can't see how it would restrict travel to 3.5"?
 

cblink.007

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I am interested in what internal aileron linkage methods you know of. I am only aware of how it is done in the Cirrus SR22, but I don't like the way they are using cables.

Is there any good solution to do it push/pull tubes? The easiest solution would be to "shorten" the lever arm in the aileron horn until it is within the aileron.

What method are the glider guys using? Please feel free to add some pictures.

BR, Andreas
Servus! My design uses push-pull tubes and bellcranks all throughout, including a mechanical mixing unit. Not sure of your layout, but if you want to see how I did mine, drop me a PM!
 

BoKu

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So I have 2 questions;
1. So how would you go about mounting the ball roller guide?
I generally tape them in with a few plies of fiberglass. In one or two cases where that's difficult, I wrap them with a couple plies of fiberglass tape, then pot them onto a surface with a bit of flox.

2. I'm having trouble visualizing exactly how it works. I can understand how a tube would slide/ rotate through it but i can't see how it would restrict travel to
Here's a sectional view. The balls and cage travel half the distance of the push pull tube. At the end of travel, the stop (a common pop rivet) prevents the cage and balls from escaping the body tube.

pp linear bearing.png
 

Will Aldridge

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I generally tape them in with a few plies of fiberglass. In one or two cases where that's difficult, I wrap them with a couple plies of fiberglass tape, then pot them onto a surface with a bit of flox.



Here's a sectional view. The balls and cage travel half the distance of the push pull tube. At the end of travel, the stop (a common pop rivet) prevents the cage and balls from escaping the body tube.

View attachment 103524
Thanks, that makes sense. I guess the balls and cage are loose enough that you can slide the pushrod in but tight enough that normal actuation of the pushrod doesn't cause it to slide inside the cage? Or is there some kind of adhesive to secure the pushrod in the cage?
 

BoKu

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Thanks, that makes sense. I guess the balls and cage are loose enough that you can slide the pushrod in but tight enough that normal actuation of the pushrod doesn't cause it to slide inside the cage? Or is there some kind of adhesive to secure the pushrod in the cage?
No, the push-pull tube is loose in the cage. If you ever watch an open ball bearing, you see that the balls and cage rotate at half the speed of the inner race. This is just like that; the balls and cage go half the travel of the push-pull tube. The inner race is the push-pull tube, and the outer race is the body tube, and the balls separate them just like in any ball bearing. The cage just keeps the balls in plane and prevents the balls from getting loose when you withdraw the push-pull tube.
 

Jay Kempf

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The gray tube is a chunk of steel tube containing 4 lbs of lead. It mass-balances the flaperon that later gets connected to the remaining arm of the carbon fiber bellcrank.
OK, can I ask another context question that I cannot see in your vid. The motion of the lead filled rod is circumferential at the farthest pinned joint at the rib. This seems to be generally moving vertically up and down along the shear web. How is that balancing out the flap? I can't visualize how you are transferring the moment of one to the other to balance across the rotation axis.
 
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