Internal aileron linkage

[BoKu]

@BoKu there are good linear slide bearings available from IGUS...

In small airplanes and especially sailplanes, having the elevator circuit free of slop and friction is extremely important for good feel and handling. When you spend a lot of time circling, and also when you need to smoothly transition along a wide range of speeds, it's very important that you can feel what's going on and react to it easily. A very low-friction elevator circuit is one of the things that makes the Vans RV airplanes so much fun to fly. The aileron circuit is important too, but not to the same degree as the elevator. Rudder is much less important, as are secondary systems like flaps and airbrakes.

The issue with sailplanes is that there are rarely just one or two slide bearings. For the 5/8" push-pull tube that drives my elevator, there are seven guides along its length between the cockpit and the vertical fin--five in the aft fuselage, one under the drag crossmember, and one more where the push-pull tube goes through the seat back bulkhead. In the wings there are three guides for the tube that connects the inboard and outboard flaperon bellcranks. With just straight bushings, the accumulated friction would be quite noticeable and unpleasant. With the linear ball bearings, my elevator push-pull tube will move downhill under its own weight with a slope of only 2 degrees.

The V-tailed Schreder HP-gliders are especially prone to suboptimal handling due to friction from the hardening of the nylon slide bushings in the aft fuselage. Each ruddervator tube has six nylon guides, and in order to make a pitch input you have to move both tubes--that's a dozen guides worth of friction to overcome.

 

[pictsidhe]

Click on the video. It shows how the CH701 uses push rods and ball cranks for it's aileron control

Yes, yours was relevant. The following post was not.

 

[Scheny]

Thanks for the video, I already knew this channel and how ailerons are done in general. I am especially interested of how it is done without having external horns which protrude into the airflow. As my cruise speed is 230kt and 300kt Vne, it is of importance to have everything optimized.

After looking at these solutions, I would like to build something somewhere between BoKu and the Cirrus, where a pushrod acts on an aileron horn at an 45° angle.

@BoKu , how did you estimate the skew drive?

For linear bearing, I thought about using these IGUS for the ailerons inside the wing. For the elevator (and the rudder which uses the same pushrods as the elevator), I will only need two bearings and I will use a solution like in the Diamonds, where they have 3 POM rollers at 120° holding the rod.

BR, Andreas

 

[BJC]

As my cruise speed is 230kt and 300kt Vne, it is of importance to have everything optimized.

For a Vd of 333 knots, I would try to avoid linkages between the aileron and the balance mass, because of the potential in three or more connections for enough play to permit flutter.


BJC

 

[Scheny]

My plan was to build the ailerons from two carbon half shells and add a stripe of steel to the 1 inch leading edge seam. This would also distribute the weight in 3 dimensions, rather than having it balanced only in one point.

The high Vd is also my main concern why I wanted to get more info on available internal aileron techniques. The good thing is, that with a span of only 5.8m (~16ft) the minimum carbon layup is already very stiff and I will overdo it (use the layup for a plane twice the size). Aileron and flaps are the main concerns in terms of flutter. Another hard sleep will be that the flaps need to endure up to at least 150kt!!! This is one of the main problems for the JSX-2 and BD-5, that you cannot slow down until you are already slowed down. Gear/flaps only available below ~110kt, but the aircraft will not slow down below 150kt in clean configuration.

Would you guys (and girls if there are any around) go for an aileron with a piano hinge at the bottom and a pushrod attached to the top, or rather for the skew drive if the requirement is that everything needs to be inside the wing?

 

[Scheny]

Here a video of the P-47 flaps, where all links are internal when retracted. When extended, they are protruded, but this is also the time when you are happy about the extra drag.

 

[pictsidhe]

My plan was to build the ailerons from two carbon half shells and add a stripe of steel to the 1 inch leading edge seam. This would also distribute the weight in 3 dimensions, rather than having it balanced only in one point.

The high Vd is also my main concern why I wanted to get more info on available internal aileron techniques. The good thing is, that with a span of only 5.8m (~16ft) the minimum carbon layup is already very stiff and I will overdo it (use the layup for a plane twice the size). Aileron and flaps are the main concerns in terms of flutter. Another hard sleep will be that the flaps need to endure up to at least 150kt!!! This is one of the main problems for the JSX-2 and BD-5, that you cannot slow down until you are already slowed down. Gear/flaps only available below ~110kt, but the aircraft will not slow down below 150kt in clean configuration.

Would you guys (and girls if there are any around) go for an aileron with a piano hinge at the bottom and a pushrod attached to the top, or rather for the skew drive if the requirement is that everything needs to be inside the wing?

Do the aero design of your ailerons first. Frise ailerons are popular for good reason, but won't work with piano hinges. Something else to consider is binding with wing flex. That may need addressing. I need to use non binding hinges as my ailerons are huge and my wings somewhat flexible. Boku only uses +/- 45 plies for his ailerons. Torsionaly very stiff, but floppy in bending. There are many ways to skin a cat, just make sure you do a good job of it!

 

[BJC]

Would you guys (and girls if there are any around) go for an aileron with a piano hinge at the bottom and a pushrod attached to the top, or rather for the skew drive if the requirement is that everything needs to be inside the wing?

For reference, several Glasair III’s have routinely flown over 350 knots with no flutter. The wing has more span than your’s, at 23.3’. The ailerons attach with two piano hinges, each about 9” long at each end of the aileron. The actuator rod is entirely inclosed. The mass balance extends forward from the tip, and is flush with the lower wing tip when not deflected.

Wrt flaps, I would consider slotted flaps with well-streamlined brackets and a good seal when retracted to lower the landing speed with the small wing. The actuator will likely have to be electric (or other power) because of the high forces involved, especially if they are cusped. (I don’t recall your airfoil.) They can be designed for partial deployment at 150 knots.


BJC

 

[Jay Kempf]

Thanks for the video, I already knew this channel and how ailerons are done in general. I am especially interested of how it is done without having external horns which protrude into the airflow. As my cruise speed is 230kt and 300kt Vne, it is of importance to have everything optimized.

After looking at these solutions, I would like to build something somewhere between BoKu and the Cirrus, where a pushrod acts on an aileron horn at an 45° angle.

@BoKu , how did you estimate the skew drive?

For linear bearing, I thought about using these IGUS for the ailerons inside the wing. For the elevator (and the rudder which uses the same pushrods as the elevator), I will only need two bearings and I will use a solution like in the Diamonds, where they have 3 POM rollers at 120° holding the rod.

BR, Andreas

Scheny,

Flap drive housings on most modern jets don't seem to limit cruise speed. No reason you couldn't use a similar approach limited to size scaled to your span. You are planning speeds that don't benefit from sweep so you shouldn't be limited by such concerns.

Your wing is going to have a fairly thin trailing edge and rear spar cove so you have pretty limited real estate to house the mechanisms within the wing thickness. Moving the aileron pushrod forward into the fatter portion of the wing makes a lot of sense at the risk of having to close them inside the composite wing. Probably they can be inserted from the root opening anyway depending on whether you are doing a one piece wing or not. Assembly of the controls in composite structures is always a puzzle of minimizing hatches and allowing everything proper access for maintenance.

 

[Norman]

 

[speedracer]

Do the aero design of your ailerons first. Frise ailerons are popular for good reason, but won't work with piano hinges. Something else to consider is binding with wing flex. That may need addressing. I need to use non binding hinges as my ailerons are huge and my wings somewhat flexible. Boku only uses +/- 45 plies for his ailerons. Torsionaly very stiff, but floppy in bending. There are many ways to skin a cat, just make sure you do a good job of it!

All EZ's have frise ailerons..... with piano hinges.

 

[Dan Thomas]

The Bellanca Viking uses that mechanism for its ailerons.

 

[Dan Thomas]

My plan was to build the ailerons from two carbon half shells and add a stripe of steel to the 1 inch leading edge seam. This would also distribute the weight in 3 dimensions, rather than having it balanced only in one point.

There's a good reason why aileron mass balance weights are at or near the tip. Flutter of an aileron is linked to the flex of the wing, both vertically and in torsion. The tip of the wing and aileron move the most, so the weight out at the tip can be smaller, lighter and more effective than if spread along the control surface.

 

[BJC]

There's a good reason why aileron mass balance weights are at or near the tip. Flutter of an aileron is linked to the flex of the wing, both vertically and in torsion. The tip of the wing and aileron move the most, so the weight out at the tip can be smaller, lighter and more effective than if spread along the control surface.

... most of the time.


BJC

 

[Steve C]

They got that Cirrus idea from the P-51 I bet. It has cables turning the pulley that the control link follows.

 

[Jay Kempf]

There's a good reason why aileron mass balance weights are at or near the tip. Flutter of an aileron is linked to the flex of the wing, both vertically and in torsion. The tip of the wing and aileron move the most, so the weight out at the tip can be smaller, lighter and more effective than if spread along the control surface.

Raises a question. What is the optimum way to control an aileron? multiple horns to multiple bellcranks off of a single pushrod to keep it from twisting and then a weight attached to the tip? You never see that... One horn and bellcrank in the middle or at the AC of the aileron, weight at the tip? One horn inboard weight at the tip? Agreed on the tip being the source of perturbation. So flex has to play into it. If the weight is at the tip and control input at the root then there is certainly a built in twist just due to aero loads. Weight, parts count, aero loads, buckling of the pushrod, size of the horn, actuation method, all play into it.

 

[Dan Thomas]

Raises a question. What is the optimum way to control an aileron? multiple horns to multiple bellcranks off of a single pushrod to keep it from twisting and then a weight attached to the tip? You never see that... One horn and bellcrank in the middle or at the AC of the aileron, weight at the tip? One horn inboard weight at the tip? Agreed on the tip being the source of perturbation. So flex has to play into it. If the weight is at the tip and control input at the root then there is certainly a built in twist just due to aero loads. Weight, parts count, aero loads, buckling of the pushrod, size of the horn, actuation method, all play into it.

Ever tried to twist an aileron? They're made very light and fantastically stiff. Even fabric-covered ailerons are really stiff. The fabric-covered aileron is made with diagonal ribs attached to the spar and trailing edge adjacent to the next rib, creating a structure that resists twisting far more than it would appear. Metal or composite or plywood-covered ailerons form a box, or tube, that is naturally torsionally stiff.

Cessna actuates their ailerons at the center. Champs, Citabrias actuate at the inboard end, and if it has the spade that also acts as a mass balance, it's at the tip. There are numerous variations on this theme all through the fleet. Mass balances are typically as far outboard as practical.

 

[tallank]

OK, I just got it. This translates the linear movement of the pushrod into rotation and the weight rotates around an offset axis that has an identical moment to the flap. The up and down was confusing me without seeing the flap. Is the flaperon horn or horns conventional, as in non skewed actuation?

I will use this in the future for a bunch of things. Sort of like a lot of the little universal joints in a lot of landing gear legs to rotate the leg while retracting. You can never have a large enough library of solutions available.

If I followed what you are saying here, this is how my 1930 Fleet works.

 

[Marc Zeitlin]

Frise ailerons are popular for good reason, but won't work with piano hinges.

Tell that to every Varieze, Long-EZ, COZY, Berkut, E-Racer, Velocity, etc. airplane owner. Put the piano hinge on the top surface and voila' - Frise aileron, no problem. These planes use three piano hinges for each aileron, but obviously it could be more, or one continuous hinge, and work exactly the same.

Existence proof...

 

[Yellowhammer]

@BoKu there are good linear slide bearings available from IGUS that I am planning on using. This one is for 5/8 (16mm) and can be clipped onto 3mm strong carbon panels:

I used the IGUS products for the steering of my boat, where I have a sidestick acting on a torque tube which is supported by two of these bearings. Slides almost without any noticeable resistance and needs no service at all. I heard that a lot of aircraft already use these products.

Nice, I just make my own..