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Trio Avionics / Trutrak autopilot - possible STC

I know there have been autopilots for many years which just do wings-level and altitude hold, for example, but I would disagree that for any kind of “serious” IFR this is a useful box.

Also it seems clear, from the marketing, that most people who buy these will not discover this missing functionality until they fly it.

Shoreham EGKA, United Kingdom

wigglyamp wrote:

The S-Tec 30 and 50 autopilots have always been like this. We have the 30 in our PA28 and the lack of autotrim is no problem at all.

I was surprised to learn at the AERO that the GFC500 can be installed without pitch trim — it will then give trim up/down annunciations just like the S-Tec. Of course, if the elevator forces become too large, it will disconnect.

You could save a noticeable amount of money by not installing pitch trim. I wouldn’t mind retrimming at the beginning/end of a climb/descent, but I wouldn’t like having to do it when flying through thermals – or “waves” in an inversion layer.

@wigglyamp, what is your experience with flying though thermals with the S-Tec? Do you have to retrim? If you don’t, will the A/P disconnect?

ESKC (Uppsala/Sundbro), Sweden

I have often flown aircraft (Grumman Cheetah, Cessna Cardinal) with an STEC-50 and no electric pitch trim.
Well, it does create some additional workload in critical phases (levelling off from a climb/descent). Is it manageable? Yes. Is it a nuisance/shortcoming? Well, sort of. But some aircraft don’t have electric pitch trim to start with, so in these cases, it makes the AP installation a bit more simple.

Frankfurt (EDFZ, EDFE), Germany

You could save a noticeable amount of money by not installing pitch trim

You could save even more by not installing an autopilot

How much you save depends on the metalwork layout. On the TB for example you would save only the pitch trim servo plus its mounting, so basically 1/3 of the installation cost of the three servos which is not a lot when you look at the overall installation cost, which is not trivial. And I suspect the same will be true for any plane which has (or can have as an option) an electric trim, or can have as an option an autopilot which does trim.

For serious use I would not even dream of installing an autopilot which doesn’t trim and doesn’t fly an ILS.

If you don’t trim, then eventually the pitch servo will not be able to create enough torque, so will current limit. If it disconnects the autopilot at this point, that would be really great (not)…

Shoreham EGKA, United Kingdom

The STec 30/50 doesn’t have a torque-limit disconnect system. It’s not really the lack of auto-trim that’s the problem in turbulence (other than the loud beeping and flashing trim command lights), but being a rate-based system rather than attitude based, it can make some significant pitch changes as it attempts to maintain altitude, so consequently speed can go drop significantly or go well up into the yellow arc. In this sort of weather I prefer to disconnect the pitch channel. By comparison, the G3X autopilot (essentially a GFC500) in my RV12 is absolutely brilliant (and does have auto-trim).

Avionics geek.
Fairoaks. EGTF

I’m sure it won’t meet your needs Peter, but it might well meet mine.

As you know I fly a group-owned TB10. It has no autopilot at all, but otherwise is a good solid aircraft which is quite good for trips of a reasonable length.

I have an IR(R) rather than a full IR, and although I’m fully confident hand-flying in prolonged IMC (I don’t go near anything convective or icy) it can be very tiring and isn’t much fun. Something just to hold the wings level and maintain altitude would be a very nice addition indeed. I can certainly live with adjusting the heading bug rather than having full nav integration and would probably want to fly my approaches by hand anyway, for currency if nothing else ~ I don’t fly as often as some.

At the price suggested it might well be an option. Our group pays higher-than-necessary monthly contributions on the basis that every now and then the treasurer can announce we have a pot of money to spend on something nice.

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