At Oshkosh I was told that the aileron trim tab, shown in the construction manual was inadaquate. Is that true? If so, what type of trim tab is recommended for a non turbo LIV?

Carl,
When building my IV-P, I cut out a section of the aileron and made this into a trim tab, hinged at the bottom. As the effective moment was shorter than the original metal tab, I made the tab 10” long and 1.5” wide—more than three times the surface area of the original tab, and increased the deflection to +/- 25 degrees.

This has been sufficient in my 750 flight hours to date, but I use very little aileron trim. In fact, if I see the aileron trim deflected more than 5 degrees or so, I know it’s time to switch fuel tanks. Most of the time I fly on autopilot with the aileron trim neutral. The TruTrak DGSV autopilot does an excellent job of keeping the airplane on a steady and constant track.

The only time I’ve felt a need for more trim was when I was doing fuel system testing. I ran each wing tank empty one at a time, with 20-25 gallons of fuel in the other tank. At cruise speed, the trim is more than adequate to hold the wings level, but as I slowed the airplane down, I had to run the trim all the way to the limit to do so. I did not test this, but I suspect that with more than a 20-25 gallon fuel imbalance, I’d not have adequate roll trim. On the other hand, I couldn’t envision a situation that would get me in that position during flight…

Last thought: The aileron and pitch trim are not balanced at all. That is, during normal cruise, a quick click of the pitch trim will noticeably change the stick force required to hold the pitch steady. The aileron trim will require a couple of seconds of run time…or more…to achieve a comparable roll force on the stick. One might think this should be better balanced, but the reason it’s done this way is that a substantially larger pitch trim movement is required to maintain neutral stick forces as the airplane is slowed down and configured for landing. This also varies substantially with loading and CG location…a couple of heavy passengers in the back seat really change the pitch characteristics of the airplane from 2-person, or single pilot operation.

My advice…increase the area of the aileron trim tab to double the Lancair-provided tab. If you recess it in the aileron, make it about three times the area of the original. Consider the position of the existing ribs in the aileron and fit the tab between them.

Good luck; call me if questions.

Bob Pastusek

757-286-4802