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Aileron Squeeze Question

Toobuilder

Well Known Member
I have read penty here concerning the often dramatic difference the radius of the folded TE makes. But what I cant seem to find through a search is what the nature of the change is, aerodynamically. For example, a "fat" TE will produce a slightly convex skin profile, while a very sharp fold will produce a slightly concave profile. In the RV world, will a sharper TE tend to "fly" that aileron to a higher TE (creating a roll into that side) or will it fly the TE lower (rolling away).

I built a new left aileron (to eliminate the roll servo and tab) and flight test shows an aerodynamic servo action on the ailerons creating a right roll. If I center the ailerons visually lining up the TE of the flap and tip the airplane flies true. As soon as I let go, the aileron TE's jump to a pro right roll position of about 1/2 inch displacement. The airplane is mechanically rigged straight and the lined up TE's confirm. So I'm concluding that one aileron is flying the system off center like an aerodynamic trim tab.

Considering that premise is correct, to fix my right roll, do I need to sharpen the left TE or blunt the right?

My thanks
 
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Considering that premise is correct, to fix my right roll, do I need to sharpen the left TE or blunt the right?

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I think it's easier to sharpen the trailing edge gently and of course it will probably look better.

I have the folded trailing edges which were built by the quickbuild factory and they kindly left them a bit "fat" in case I needed to do any adjustments. If you still have a bit of fatness then I'd squeeze rather than smash.

As you have read, it takes very little to make this happen, and I too would like to understand the aerodynamics of this better.
 
Clearly its easier to squeeze than UN squeeze, but the basic question remains: does a sharper TE fly higher or lower? If the sharper TE flies lower, its going to make my right roll condition worse.

Bottom line is that one of my ailerons is a bad actor here and is introducing an unwanted servo movement into both. I dont want to start arbitrarily working to make one look like the other without understanding the effects of the change.
 
Clearly its easier to squeeze than UN squeeze,

My experience and uneducated conclusion is that the aileron simply need to be the same. I think the larger radius allows the pressure side to wrap around the edge a little reduce its "lift".

Overall the larger radius seems to make the aileron a bit more sensitive to AOA. Just reading the history and listening to guys like Scott. i.e. lighter feel.

And -it is amazingly easy to undo the squeeze if measuring as a convex vs concave shape from spar to tip with a straight edge. Just don't be doing much of anything and it is easily reversed. You know - the hammer on stick on the TE will undo it.

My AP seems very sensitive to imbalance and the stick will twitch to the left or right indicating a tick of trim is needed. Mine lingers on the heavy side and ticks to the light side. tick tick tick.

YMMV
 
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I don't have it in front of me, but I believe Van's covered this in the RVator (and I of course don't remember which way it works!). They may have a link on the website - or email customer support ;)
 
can't help on the aerodynamics, but I found that the TE shape didn't influence my heavy wing much. I had to move the Aileron up and down at the hinge for a meaningful change in behavior. I did, however, find that the TE shape, or more likely the concave or convex shape it imparts on the aileron skin in front of it, had a profound impact on the sensitivity of the aileron and the elevator. Controls were best when that skin was dead flat like it is supposed to be.

Because manipulating the TE shape prevents the skin from being flat in all but the designed shape, I recommend that the TE be shaped according to the section 5 recommendations and other methods be used to remediate heavy wing issues - hinge slotting or tabs. Moving the hinge up or down even a very small amount makes a large difference. It seems even the pre-puched stuff isn't perfect and often requires a slight adjustment. I believe it is the shape of the skin hanging over the rear spar that generates minor change from aircraft to aircraft, but have no data to back that up. However, with pre-punched kits, it has to be something that is being done differently across builders.

I was struggling with maintaining precise altitudes during early IFR training. manipulating the Elevator TE's to get the skins perfectly flat made a significant difference in reducing the excessive sensitivity and made training easier.

Larry
 
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Please keep in mind squeezing the aileron trailing edge is in the bucket of “very fine adjustment” and assumes everything else associated with rigging is correct.

I have worked many heavy wings and squeezing the trailing edge was never the first tool. Fix the aileron rigging (up, down, in, out, same on both sides) after you make sure both flaps are fully up and at the same height. After that, then squeeze.

Carl
 
Higher. Van's says to squeeze the light wing, which means that reducing the radius will move the aileron up, pushing the wing down.

Thats some good news right there. At least it will take things in the right direction if it doesn't wash it all out.

Thanks for the insight everyone. Will report back when this is resolved.
 
Trailing Edge

Barnaby Wainfan covered this in great detail in Kitplanes Magazine several years ago. My experience with fabric covered ailerons on a Pitts is that a convex trailing edge strip 1" wide chordwise completely removed the centering force and significantly lightened control force.
On my Tailwind with all metal ailerons the convex shape lightens stick force but still has good centering. I corrected a very slight wing heaviness by raising the flap on the opposite wing by less than 1/16" at the trailing edge.
 
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