Trim went to full up during run-up?

[Neal@F14]

I've experienced nose-up excess trim, ostensibly happening during runup, while flying my friend's RV-8 a few times. Turned out that I was inadvertently fat-fingering the buttons on top of the stick (Ray Allen #205 stick grip with 4 trim buttons, the rear one for nose up is quite touchy) while holding the stick back, when I could've sworn that I wasn't touching any of the buttons... but it turned out that I was. I changed my technique of how I held the stick back during runup and never had the problem again. Taking off with too much nose-up trim can really get your attention when the plane suddenly jumps off the runway and the nose points skyward way before you're expecting it to

[RV7A Flyer]

Just to add to this newly updated thread that I started...I have not seen this problem since I reported it here, which would be about 60-70 hours of flight since that time.

I can only conclude that I must have inadvertently been hitting and holding the button during taxi with the stick held full aft. Being attentive to how I'm holding the stick grip during taxi seems to have "fixed" the problem.

[turbo]

i hope your problem is just because of of a fat finger.

for what its worth,when my servo finally bit the dust the trim went to full up or down position. dont remember which way though.

[Clarkie]

We had this happen on our -6 as well. We figured we must've fat fingered it while holding the stick back during the landing roll out. Since this has happened, we added "trim to neutral" on the After Start Checklist and again on the Line up/Final Items Checklist.

[GeneL]

Any chance you have an auto pilot with auto trim?

[RV7A Flyer]

Originally Posted by GeneL

Any chance you have an auto pilot with auto trim?

Nope, sure don't.

[RV10inOz]

I will have a Safety Trim system for sale shortly as the new avionics panel going in has it integrated.

[apatti]

Well, I am going with the "fat finger" theory. I played with the trim on the ground for about 20 minutes including taxing around and doing a run up or two. Never could repeat the problem.

About a month ago I had not flown in a while and knew that it would be even longer before I got a chance to go out. So, I decided to take the plane out and taxi it around and do a couple of run ups. The winds were blowing way beyond my personal limits that day. So much so, in fact, I felt the need to position the ailerons and elevator accordingly; in this case I held the stick in the 4:30 position. I remember my arm getting tired and that I moved my hand around on the stick quite a lot; including placing it on top of the stick at times. My theory is that when I did this I was unknowingly activating the hat switch. If you think about holding the stick in the 4:30 position, if you did hit the hat switch you would be calling for nose up trim and right aileron. That is exactly where I found the trims set. So, I think all is fine; but I will keep a close eye on this. As part of my preflight, I always take specific note of where the autopilot and trim circuit breakers are. I'll pay even more attention to this part of the checklist in the future; even practice reaching quickly to pull the trim CB.

I appreciate all of the replies and suggestions!

[60av8tor]

Late to the party, Tony, but I had the exact same issue when I first began flying my 7A. Cruising along and all of a sudden a huge nose pitch up. I swore my trim was running away. Low and behold, it hasn't happened in the last year - once I trained my hand to grip the stick as not to interfere with the hat switch. Checking trim is one of my last before take-off checklist items, as on the ground I hold the stick from the top and have a tendecy to bump the switch.

[Wayne Gillispie]

One reason my pitch trim rocker is on the panel beside throttle, right beside a push to enable button. No power goes to trim servo with switch failure or accidentally pressing rocker switch. I think I adjust trim on takeoff, after level off, descent and landing. PTT and AP disc on the stick, 4 wires. Simple.