What would happen if the trim actuator failed?

The trim system to me seems to be a potential single point failure. I am sure that I am not the first person to have this thought but I have search the forum and can't find this possibility disscussed.
I have recently been talking with a man who is finishing a series 5. He switched the trim system from horizontal stabilizer to making tabs on the elevator. His reason was the possibility of the actuator failing.

If it failed and just stoped in a certain position the plane would be hard to fly but still landable. The problem that I could see is if it fails doesn't freeze but instead just floated uncontrolably, or if it runs to an extreme positon. (I think we would all agree this would be bad)

Are there good ways to use the trim system while also making a backup or are these actuators just that good that they can be trusted in this fasion?
(by the way I have the kf SS)
Tyler

airlina tested this scenario and found the aircraft was flyable, no worries. Here is the post...
http://www.teamkitfox.com/Forums/sho...3&postcount=18

Tyler, When I was building my Series 5 several years ago this was a concern to me as well because there was a Kitfox accident that was thought to be caused by a failed lower attach point of the trim actuator. (An example of this can be found at the following website-Sportflight.com then go to the "share photos and files section" then -"damage/incidents" section and find the trim actuator photos.) To prevent this from happening on mine I fabricated a backup attach system for the lower trim attach point as seen in the photos. I was not smart enough to design this myself and readily admit that I copied this from another builder. Also Skystar changed trim actuators to a different manufacturer after these failures and I have not heard of any other failures since. To see some other ideas on how to reinforce this attach point click on the "add on mods" and "improvements" sections on the Sportflight site. In fact there is a ton of great Kitfox information on this site that builders will find useful so all you builders check it out.
As Randy mentioned , flying with a stuck trim actuator is not a problem on my airplane as I have tested this stop to stop during my flight test period.This is not something you would want to do for very long as the stick pressures can be very heavy , but if you adjust speed and use flaperons to offset the control force a safe landing can be made. As a matter of fact I went flying last week and my trim quit working after takeoff. I kept the speed back and returned for landing with no problem. It turned out that the contact points on my trim rocker switch had carboned up a bit and needed a cleaning. Bruce Lina N199CL

Tyler,
As Bruce said having the actuator fail in any of the possible trim positions and stick in that position would not be dangerous as you could still land the aircraft in an out of trim condition.
The problem with the old actuators was the casting around the motor itself would break allowing the H.S.(horizontal stabilizer) to move up and down from stop to stop rapidly during flight causing some real problems for the pilot to control pitch.
After this happened many builders went back and reinforced the casting area on the actuator with add on brackets or used aircraft cable to at least maintain the actuator in it's original position thus reducing the stop to stop travel allowing for safe landings. There may be some old actuators still working perfectly and not reinforced but it would be a good idea to double check and add the bracket if not reinforced already. Model 5's and probably Model 6's used this system. I'm not sure of the early model 7's but I believe they went to a manual trim system on all the 7's.
The photo that Bruce posted (bottom photo) shows one of the brackets someone made to encapsulate the motor casting area to prevent this from happening.

There has been discussions regarding this issue for some time... Here are some of the facts:

There has been one reported failure at the base of the trim actuator... This was reported from the pilot and did end up with a bent aircraft after landing. Without getting into too much detail it was determined -BY THE PILOT- that the actuator base broke and caused pitch oscillations during landing.

Looking back at the installation of the actuators.. originally, the base hole is to be reamed to .313 then a bushing was press installed with locktite. A bearing was then installed inside the bushing during installation. While this installation worked well, it offered some oportunity to invite cracking if not reamed correctly or put on a bind during the bushing installation.
The Super Sport installation is different. It does not require the reaming at all and we have sized the bearing correctly for the install.

I have seen several ideas on capturing the base.. main concern with some of the ideas was inspection.. the base could possibly crack without knowledge and the capturing device is not allowing for a good inspection during condition inspections. Therefore if the capturing device fails you have the same result.

This is a little premature in the offering as we have not developed the installation instructions but it is pretty straight forward and simple to install. It allows for inspection of the base while also keeping the actuator in place should the base fail during an extremely hard arrival...

To the original Kitfox Super Sport customers $10 US and $20 Outside the US.
Kit cost is $45

Just got my bracket. Painted it and mounted it. I found the bolt supplied with it, a AN3-12A, was too short and replaced it with a -13A. Cheap insurance, worth the price of admission.

A footnote: The kit came with the nut, bolt, metal and plastic washers. I originally put one metal washer and one plastic washer between the bracket and the mounting tab on the fuse. I found that after everything was tightened, now the trim motor would not pivot around the bolt, instead the bolt was turning inside the mounting tabs. This may create wear. I added another plastic washer which I had in my washer collection, to the outside of the bracket and a metal washer on top of this one. Now the the motor pivots on the bolt again with only a slight movement of the bolt when it first moves. Whew!

Well, no joy. This morning I went out and happened to move the motor and once again it's the bolt rotating. I sent John an email and am awaiting a response.