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Jerry and Steve,
You may be interested in my article "The Quest for Trimmed Flight in N92EX, a Lancair 320" in the Lancair Network News #29 (Oct/Nov 1997), pg 377. Since you focused on aileron trim, I have included the part of the article which petains to that:
Lateral Trim: Spring has Sprung
As work progressed on the wings (seemingly decades ago), I was reluctant to install the standard aileron trailing edge electric tab because it stuck out and required too much balance weight to be added to the control surface. After all, I was building a "light" plane. Instead, I built a 3.5" by 5" servo controlled tab into the pilot's wing tip. Many years later, during flight-testing with the tab at neutral, a left wing heavy condition was noted during single pilot operations, requiring about 2 pounds of stick pressure to correct. The airplane flew reasonably level if two equally weighted people were present or, in the pilot-only case, if there were 4 gallons less fuel in the left wing. Computation shows 24 pounds less of left wing fuel has a roll moment similar to that induced by a 180-pound co-pilot.
Let it be forever noted that any position of the tab made no difference in roll. When tufted with yarns, the tufts lifted off the upper surface of the tab when it was lowered beyond 10 degrees. Egad, I had created a left wing tip drag device adding to all the other left turning tendencies!
Brooding about tearing up the aileron, I began complaining to my neighbors (Bonanza and Cozy people) and they responded with "Think spring." Thus was born the servo controlled, spring-biased, aileron trim system. Such systems are utilized in Bonanzas, Cozys (Cozies?), the Cirrus SR20 and others. My implementation uses a small servo, mounted at the aft center of the main spar web, that moves a pivot arm through a 3" arc. Attached cables pass thru the phenolic stick mounting pads to two independent springs per side for redundancy. Each spring is separately attached to the large area washer securing the backside of the rod ends that connect the aileron control rods to the stick. The bolt securing each rod end is changed to use a cotter pinned castle nut instead of a lock nut. The springs are under tension and they add a small amount to the stick force required to displace the ailerons. However, anyone that has rolled a Lancair into a steep turn knows that plenty of stick force is required to initiate such a turn. The system is easily overpowered if trimmed to the maximum in one direction and a full aileron deflection is required in the opposite direction. Trim is actuated thru a rocker switch (left side down, left wing down, etc.) with the servo indicator seldom out of the green "servo-centered" indication. The switch, indicator, servo and electrical harness were recycled from the wing-tip system. The difference is that this trim system works, meeting my requirements of KISS, no undue additional weight and no unsightly tab on the aileron. Life is better.
Scott Krueger
N92EX
PS: Spring biased aileron trim also dampens the effect of winds on the control surfaces when you airplane is parked outside.
[Scott... would you describe the springs that you used (ie, overall length
and diameter, wire diameter), and maybe send along a sketch of your system?
Thanx.... <Marv> ]
LML homepage: http://www.olsusa.com/Users/Mkaye/maillist.html
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