Aileron Trim Tabs

[Sonerai13]

At the risk of sounding foolish, I thought that once I fly my plane, simply adjusting the length of the combination of aileron push tubes would eventually 'balance' any roll tendency (if present)?

Adjusting the aileron pushrods will not correct a roll problem. The ailerons will always seek an aerodynamic equilibrim. Adjusting the pushrods will change where they trail in relation to the wing, but not where they trail in relation to each other. In other words, after an aileron pushrod adjustment you might find both aileron trailing edges trailing a little higher or lower in relation to the wing tip (or flap trailing edge), and you will find a lateral displacement of the control stick (as compared to where its neutral location was before the adjustment), but the roll tendency will still be there.

There are many ways to correct a roll problem. The problem likely is a result of slight rigging issues. These issues may or may not have to do with the wings. Some (more than what you may think) rigging issues have to do with the tail rather than the wings. I always start any rigging investigation with the tail, and then move to the wings. Now, on a Sonex there won't be much you can do about the tail rigging, or the wing for that matter, without remaking parts. Thus, we end up with either a trim tab on an aileron or a balance spring under the seat, as these are the least expensive (in terms of time and money) ways to fix the issue.

Another thing to remember is that, in an aircraft as light as a Sonex, lateral trim will be affected by loading. An airplane that might roll slightly one way or another with one person aboard will have a different roll tendency with two aboard. Depending on which way it wants to roll, adding a passenger may either fix the problem or make it worse. This being the case, it's important to trim the airplane for the flight regime it will most often be operated in, and then live with out-of-trim situations in other loading configurations. (Or put in an adjustable aileron trim system as one builder has described previously in this thread.)

[achesos]

Yep - sounded foolish then - the ailerons balance each other, so I stand corrected.
But what about the drag and lift created by each flap that are not equal but opposite? Can a slight adjustment in retracted position alter roll as well as yaw? Or is this more drag then benefit compared with a small trim tab?

[Rynoth]

But what about the drag and lift created by each flap that are not equal but opposite? Can a slight adjustment in retracted position alter roll as well as yaw?

What you describe is exactly how the plans say to initially trim the roll tendencies of the plane in the first test flights (adjusting retracted flap position.) Apparently for some people/planes this adjustment alone isn't quite enough.

[peter anson]

The problem with adjusting retracted flap position to change the roll trim is that unless you have the flap stop angles fitted, and you probably don't because you don't know where to fit them yet, the flap drive linkage on the right is so much more flexible than on the left that the wing is effectively changing shape as you fly. I have written an explanationhttp://www.ansoneng.com/sample-page/adjustable-flap-stops/ of this on my web site. (Warning: sales pitch involved). It's possibly the reason Mike Smith's trim tab on his flap works - its springing the whole flap.
If you fit a flap stop of some type you at least know where the flap is during flight - it's up against the flap stop. You can then adjust the flap drive linkage (and the flap stop too) to get a consistent change in trim. BUT, if you started with the trailing edges of the flaps level and you have to adjust the drive linkage rod end by 3 or 4 turns, I reckon you might have a rigging problem.
Joe's comments about pilot and passenger weight rings true with me too. My Sonex flies straight with me in it but a heavy passenger upsets the balance.

I am thinking of readjusting the overall wing rigging by redrilling/reaming one rear wing tab attachment bolt hole in a vertical direction and moving it slightly to get a the wing rigged back to near perfect.
Has anyone tried this, any bright ideas to get the ideal drag free solution?

I can think of a few ways, but none are easy.
1. You could "drag" the hole and use an oversize fastener. You need a drill guide - for one-off use ordinary mild steel would do but something a bit harder would be better, and you need everything clamped firmly in the new position. I doubt if there's room in the Sonex to do that.
2. You could clamp the parts in the new position and then use stepped drills to enlarge the hole in stages. You risk damaging both parts and getting a clamp in there might still be a problem.
3. Make a new rear spar attachment plate SNX-W12. You could use the existing plate as a drilling guide.

Peter Anson
Sonex 894
226 hours

[merle reppert]

If you have wheel pants on --make sure they are straight ----After I got them straight I didn't need a Roll trim---
They are just like Ailerons---------
Merle Reppert---

[pfhoeycfi]

Check out my video on trimming an airplane on the EAA Hints for Homebuilders site. It contains quite a few photos of trim tabs on the factory Sonex aircraft. Here' the link: http://bcove.me/pa2hjbxk

Cheers!

Does anyone know if this vid is still available online? I couldn't find it.

Peter

[XenosN42]

Check out my video on trimming an airplane on the EAA Hints for Homebuilders site. It contains quite a few photos of trim tabs on the factory Sonex aircraft. Here' the link: http://bcove.me/pa2hjbxk

Cheers!

Does anyone know if this vid is still available online? I couldn't find it.

Peter

I guess the URL has changed. This is the new one: https://www.eaa.org/videos/3521049103001 I think you need to be an EAA member to view it.

[Skippydiesel]

I started with a right role tendency - adjusted left flap up to correct.

Flaps at Left 0.9 degrees Right 0.4 degrees (relative to trailing edge of each wing skin, using digital level)

Now have to use right rudder and left stick to get ball centred.

Yet to test but have adjusted right flap down 1/2 turn Right flap now 0.1 degrees.

Also - with no baggage have run out of aft (elevator up) trim ie at cruise (130 + knots) pilot must hold continual back pressure to prevent nose drop. Have tried adjusting trim spring positions with limited benefit. Just about to go out and see if I can find a heavier (front, pilot adjustable) spring.

[Skippydiesel]

Test flight showed some improvement at 1/2 turn down of right flap.
Re tested with an additional 1/2 turn (making a full turn from origional setting).
Success! Aircraft shows no tendency to roll (wings level) however a very small amount of right rudder is still required to centre the ball.
I think a small fixed trim tab on the rudder will address the slight ball out of balance .

[Skippydiesel]

My Sonex flies straight & level, with just me on board

Wing tank level still effects tendency to yaw - this can be managed by fuel transfer, to centre header, or just switching consumption to the heavy tank.

I am now at the stage where I am flying with a dummy load (ballast)/passenger and have a right wing down/yaw that I correct with aileron. This is okay for the short test flight but my plan is to do long X countries.

My last aircraft had a simple bungee set up that worked on the aileron linkage, to lift the right wing, when I had a heavy passenger - I would like to fit something similar but as yet haven't worked out the details.

If others have been down this path, perhaps they would post photo's/sketch of how they have done it (no point in reinventing the wheel).