Aileron trim

[utawl]

Good Day,

I am sure this query has been placed before, I will appreciate any advice on how to install a trim for the ailerons on the RV7, I have the Ray Allen servo for the elevator trim, this is fitted, I just need to figure out how to fit the aileron trim, I have the Ray Allen trim servo.

Regards and thank you,

Kevern Brown

[islandmonkey]

Use the manual trim available from Vans here:

Manual Trim

It works, is light and is simple to install. You do not have to rework the aileron.

[L.Adamson]

There are two methods of installing electric trim for the ailerons. One is to use the servo to operate the bias spring lever. The other is to install the servo in the aileron, which operates a short 1"*6"piano hinge trim tab. The bias method is usually preferred these days for "simplicity". However, I much prefer the tab method for "feel & perfection". I'm not a fan of bias springs...... anywhere. Van's still sells both kits (on their web page), and I believe some pics are still included. Haven't checked lately.

L.Adamson

[Bill Wightman]

Kevern, I installed a Ray Allen trim servo inside the right aileron in my RV4. I wanted a true aerodynamic tab, not spring bias. I also wanted the tab installed integral to the trailing edge of the aileron; not mounted as a protrusion to the trailing edge.

- Inboard end of right aileron -


To accomplish this, I made a few extra internal parts. The servo mounts between the inboard aileron end-rib and an internal stub rib that rivets to the aileron spar. As you can see in the pic, the servo mount flanges lie on top of the rib flanges, and I installed nutplates in the servo flanges for flush screws that also secure an access plate on the bottom of the aileron.

The little stub-spar is inset forward in the aileron, and carries a piano hinge on the upper flange. The aileron tab itself was made of .025 skin, bent trailing edge, and also had a little spar inside its front edge that carried the mating hinge piece.

I calculated the required hinge moment and mass balance issues for the aileron, which sized the tab as well as its deflection limits. I sold the plane back in 2000, but IIRC the tab was about 6x2" in size with about +/- 20 deg of deflection.

It worked absolutely perfectly with superb feel and authority for a trim tab. I'll do it again when I build the new wings for my 8.

[jjconstant]

When I was chasing a heavy wing problem, one of the things that bothered me about it was that even though I could trim out the heaviness easily, the lateral trim changed considerably with airspeed. It was explained to me that this was a characteristic of the spring biased method of trim. Once I got the heavy wing corrected the plane remains in trim laterally throughout the airspeed range. I don't know the characteristics of the trim tab approach. I kept the spring biased trim.

The trim motor is installed with a bracket on a central rib (I can't remember if it spans the 2 central ribs), with the servo arm extending forward and mid way between the bottom of the sticks. It is mounted so that when the servo arm moves it moves left and right and springs are attached, with one end connected to the servo arm and the other connected to the bottom of the joy sticks. As you move the servo arm it pulls on the bottom of the sticks. I would recommend getting the drawing of the installation as my description is probably way lacking, but hopefully it's enough to give you a feel for it.

All Best

Jeremy Constant

[jjconstant]

As I mentioned in my first post, I kept the bias spring lateral trim, which doesn't require any change to the aileron. I have the normal elevator trim tab. With the elevator, changes in trim are accomplished with very quick "bumps" on the stick trim button. Holding it for any length of time will overshoot the desired trim except at low speeds. With the bias spring on the ailerons, you hold the button for much longer.

With the trim tab approach to lateral trim, do you have to use the "bump" technique or is it less sensitive than the elevator? I'm keeping my system, I'm just interested in an education...

All best

Jeremy

P.S. I know about the speed controllers

[Buggsy2]

Kevern--I have the plans for the electric servo+ bias spring method; could scan them and email them. The only problem might be the plans are reduced and somewhat fuzzy already, a scanned version might be unreadable.

Or, you could have Vans send you just the parts for the bias spring trim kit, though I guess that would be expensive to South Africa.

[utawl]

Hi All,

Thank you for all the replies, I have lots to think about. I have the manual spring bias trim, I think I will fit it and see how it works. I have the kit without any plans, hopefully there is a scanned set on the way.

Regards,

Kevern

[Homie]

Speaking of the heavy wing and trim control.....I have a slightly heavy right wing in my 9-A, it trims out with my electric trim but I'm still in Phase I testing and am thinking that when I get someone in the right seat I may not be able to trim it all out. What about cranking the right flap down a half turn, would that have the desired effect to lift the wing?? My autopilot servo is in that wing, otherwise can't figure as to why it is heavier. Thoughts??

[Pat Hatch]

I don't think it's a good idea to make your flaps asymmetrical to correct a heavy wing. It is too dependent on airspeed and could give you some unintended consequences. Unfortunately in your -9 you don't have the "squeeze the trailing edge" option.

I went the aileron trim tab route and absolutely love it. I think 99% of folks will not be interested, but for the other 1%, it is the cat's meow. It takes a lot of extra work, but if you like doing this kind of stuff, go for it. I can have one tank full and the other empty and trim it out with my trim tab. Besides, it's so cool to watch the little tab go up and down in flight!

Here are a couple of photos. You have to add the little stiffener spar and I just made the tab to fit between stiffeners. Worked out to be just right.