Surprise Pitch Trim Excursion

Last Thursday, Thanksgiving, I was cruising at 6500 feet in my RV-10 with the A/P on and everything dialed in. Headed west, VFR on top with better air confirmed ahead.

I asked my 14 year old son, sitting in the copilot seat, to hand me something from the pocket, which he does.

About 4 seconds later, the airplane pitches up so quickly that we squish into our seats and enter a very high angle climb (>45 deg maybe).

We went from 160kt to 90kt (gained a lot of altitude...not sure how much) by the time I pushed the nose over and turned off everything that I thought could be related.

Then, I saw it.

He has the large iPad (the 12 inch) and it had been laying on the pitch trim since he had reached into the pocket for me.

Eventually the A/P reached its torque limit and disengaged, sending us into a sudden extreme pitch up.

I was holding the stick nose down against the trim while crushing the trim button back to neutral.

All of this takes place in about 15 seconds.

No one barfed...that's the good part. Besides my 12 year old daughter in the back seat thinking it was awesome.

This is one reason I installed the Dynon AP panel. It will disable the trim button after 5 seconds. It also slows the trim motor at higher speeds (configurable). I also installed a panel switch that disables all the CP buttons except for PTT.

You are not the first to have this issue. Some builders have put trim selector switches on the panel that disable the selected stick buttons. I chose to not install a right stick trim button - instead, there's a rocker switch on the panel, within reach. I also put the pullable CBs for the autopilot and trim side by side, directly in front of the left seat. With an uncommanded pitch change, these get pulled; then pushed back in after figuring out the problem.

Not sure if this trim was on the copilot stick but I have a copilot stick disable switch on my panel to prevent similar events.

I installed the Safety-Trim module by TCW Technologies when I built my RV-10. Worked as advertised. http://www.tcwtech.com/Safety-Trim-Page.htm

teenagers can kill you

Old is new

This is a classic case of what is old is new. This issue has been dealt with so effectively that folks have forgotten about it. A search of posts 6 years ago or so should show one Tim OLSON posted about his runaway trim. TCW solved the problem with a neat little unit

Gary Specketer

Pilot/Co-Pilot trim/flap selector switch

I installed a DPDT locking toggle switch on the panel to give either the pilot or co-pilot trim and flap control. The DPDT switch provides the common ground for trim and flap control to either the pilot or co-pilot Infinity Grips.

My objective:
- Assume that you will fly with someone that has no clue not to touch stuff and will play with the stick. In addition to messing up the trim, the person could put out flaps while you are in cruise - and they will quickly depart the airplane.
- If I end up breaking off the trim top hat on the pilot stick with my iPad or such, I can select Co-pilot for control and just reach over to trim.

Two other things:
- Either install the Safety Trim product or the Dynon AP module for the trim switch functions. Both provide a 3 second cut out for run away trim.
- I added another "Flap Permissive" switch on the panel to further protect from mistakenly putting out flaps at speed. In the cutout position, the switch allows for "flaps up" but not "flaps down". So the take off checklist has the switch in cutout after you put out half flaps if using them, and the landing checklist moves the switch to flaps permissive for normal flap operation.

Carl

switch

I have a switch to enable or disable all the fonction of the co-pilot stick.
Also have another switch with elevator trim ON-OFF-REVERSE in case of a stuck switch. This one is cover with a switch gard.
Also did the upset recovery training but hope i will never need it. : )

I personally think Safety-Trim should be something everyone puts on their RV-10/RV-14. Here's the write-up I did back in 2007 when I first installed it.
It addresses your sudden excursion. The same thing happened to me during my flyoff with a clipboard. The RV-10 and RV-14 are far too pitch sensitive in cruise to allow the system to have complete full-speed trim and no limit if it runs on. This system will fix it perfectly. I now have 1200+ hours on the RV-10 and closing in on 100 on the RV-14 and it's a great system.

Here's that link...
http://www.myrv10.com/N104CD/upgrades/20071027/index.html

G3X autopilot has these protection features built in

If you install the G3X autopilot and wire the trim system per the installation manual, the autopilot will disconnect immediately if you touch the trim switch (just like certified autopilot systems). G3X also allows you to configure trim speed vs airspeed (so it runs slower at higher airspeeds) and you can configure a trim run time limit as an additional safety feature.

Yes. I am aware of the long standing and much discussed solutions proposed. Both the trim protection and the co-pilot disconnect switch.

I looked at three different -10s when selecting this one, and two of them had copilot disconnect.

This one didn't, but man was it absolutely loaded with everything else I could have wanted.

I have not been at all concerned about it. My wife and I have been flying together for 22 years and she knows what to do and what not to do.

But, by son has only been in the front seat three times...my fault for not thoroughly briefing him.

Besides that lesson, the other lesson is that the RV-10 can indeed withstand an auto-pilot disconnect with full pitch up trim. It really didn't seem to stress the plane, but it did the stress the passengers.

Shouldn't trim disconnect the auto pilot? it does on my G3X setup, then again, my servos are commanding trim

I have a G900X with a TruTrak Sorcerer.

The Sorcerer does not have an auto-trim function, at least its not set up on this plane if it does.

The Sorcerer provides on-screen feedback directing you to trim neutral in one direction or the other while the AP is engaged.

It would make sense to mount the copilot/pax trim switches (and PTTs) on the panel (side by side) or bulkhead (tandem). It's very easy for a pax to accidentally active the trim switch in a stick.

In the G3X system, this disconnects the autopilot, which is annoying.

I developed an autotrim system for SkyView systems that allows trim inputs without autopilot disconnect. I think it should always be the pilot's decision on when the autopilot disconnects and that automatic disconnects can lead to unexpected behavior, even with audio alerts. [Note, there was a bug in the old Garmin 296 that could cause DigiTrak autopilots to silently switch from ground track to heading mode, leading you off course without alerts!]

My autotrim controller also includes a trim fault system that detects and corrects stuck switches or conflicting copilot switch input without 3-second time-outs on the trim input. If you ever have done a touch and go in a Harmon Rocket, you'll quickly see that you need several seconds of trim down or the climb rate will be very uncomfortable/dangerous. To have a trim controller shut off by making a wrong assumption is IMHO wrong. Again, I don't like the aircraft making assumptions/decisions for the pilot. Much better to detect and alert on fault rather than autonomously take action.

In the same vein, auto-flap systems that retract flaps when above Vfe are making decisions best left to the pilot. During a forced landing, I just may want to put my flaps out at >Vne if my life depended on it.

These are just opinions FWIW.

vlittle said:

It would make sense to mount the copilot/pax trim switches (and PTTs) on the panel (side by side) or bulkhead (tandem). It's very easy for a pax to accidentally active the trim switch in a stick.

In the G3X system, this disconnects the autopilot, which is annoying.

Click to expand...

If you don't want autopilot disconnects due to inadvertent trim activation by the passenger you can locate the trim switch where it's less likely to be bumped (as you suggested) or add a switch that de-activates the passenger switch functions when not needed. The latter is pretty easy to do since most of the functions typically located on the stick are activated via a path to ground, so if you simply open the ground path you've accomplished the objective.

vlittle said:

I developed an autotrim system for SkyView systems that allows trim inputs without autopilot disconnect.

Click to expand...

Autotrim by definition means the autopilot is automatically trimming the aircraft. No autopilot will disconnect itself when it is commanding the trim to run.

vlittle said:

I think it should always be the pilot's decision on when the autopilot disconnects and that automatic disconnects can lead to unexpected behavior

Click to expand...

The whole point of disconnecting as soon as an external trim input is detected is to avoid the unexpected behavior experienced by the original poster in this thread.