Aileron Trim Quality
 

Has anyone experienced a failure of the spring and safety wire connection to the manual trim handle arm? I could imagine that sending you for an interesting ride:eek:.

Reason I ask is that this design doesn't seem too robust. There is barely any edge distance on the holes In the arm and I could envision this, or the safety wire eventually wearing through.

Definitely something to inspect periodically or make better, or add a safety.

Thoughts?

I didn't like the safety wire suggested by the plans either, so I went to my local Hobby Shop and bought some steel clevis with rods (similiar to the pic below).

You can cut them roughly to legnth then put a Z bend in the end that attaches to the Trim servo. The type I bought are locking, but I put an extra zip-tie to make sure they stay closed.... seemed like a much more robust solution to me.

I've been flying ~70 hours now without any issues.

Jason

The safety wire per the plans has worked fine. It is simple and easy. 170hrs

Yep - until I hear of anyone having a failure I'm not worried. And even if it failed the spring force isn't that great.

What kevinh said. Nearly 400 hr on mine and no issues. But for those who want something a little more elegant, and if it helps with sleeping at night, Jason's hobby shop setup looks like a perfectly good option too. :)

Several hundred hours on mine (safety wire).

I almost went with the hobby shop solution (I have the unused parts in my hangar), but after playing with the setup, I wasn't sure that the probability of failure wouldn't actually be a little higher with the substitute (just couldn't get comfortable with how the clevis worked and the material it was made from). Also, I think I recall that I would have had to enlarge the holes in the arm and that would have further reduced the edge distance.

The sudden loss of one spring should be manageable in flight. I don't think the autopilot would have a chance at the task, but it seems like it wouldn't take that much to safely get the plane on the ground. (It would be a little more of a challenge IFR if you had to juggle an iPad or fish out an approach plate.)

Dan

I left it disconnected so I could do the intial test flying without any bias, 8 years later I've never bother to re-install it, just not necessary IMO.

Another Option
 

I went to the local Bait and Tackle store and bought some stainless steel leaders with clip ends. They come in various lengths and I found ones that fit perfectly.

I like an airplane in trim, always.

The spring bias system is flawed in my opinion. The fundamental flaw with it is that the two springs are always working against each other, so the system is marginally effective. And if there's no friction in how the shaft fits in the plastic block, the trim is mostly useless because it wont stay. The last couple of RVs I've flown have had this condition and its annoying.

I had a very nice electric trim system in my RV-6 that was cobbled together out of manual trim parts and a Ray Allen servo.

The other day during my commute home I designed a spring cartridge electric aileron trim mechanism, but its still just in my head. :)

What you look at as a flaw, I see as a positive. The system is designed to have two springs working against each other to reduce the spring gradient. If the force gradient was "stiffer" or if you had a stronger spring, then the trim would interfere with the full movement of the stick.

And you just make sure there is enough friction to hold the lever still throughout the full motion of both the stick and the trim lever. The system is essentially infinitely adjustable by lengthening and shortening the springs, making sure they oppose each other in the right manner. At neutral, both springs should be stretched out to some extent, opposing each other.

Better would be an aerodynamic tab, but the springs, if set up properly, are excellent, IMHO. Mine works without a hitch.