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.
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?
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.
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)…
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).
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.
reviving the old thread.
Lately I’ve been talking to EASA to get the FAA STC for trio autopilot approved.
I had already done the “basic approval” process for my shoulder harnesses. This time however the whole process got stuck in a dead end because the Trio does not come with TSO parts.
The funny thing is EASA did the exact same one off approval for Trio on a EASA Grumman about 2 years ago. When I wrote them about my case and told them they had already approved Trio before, they admitted they screwed up back in 2019 and should not have approved trio.
so anyway, has anyone found any other alternative way to resolve this?
The only option EASA gave me was a “non basic” standard STC approval process which of course I am not going to pay for.
the Trio does not come with TSO parts ….
The funny thing is EASA did the exact same one off approval for Trio on a EASA Grumman about 2 years ago. When I wrote them about my case and told them they had already approved Trio before, they admitted they screwed up back in 2019 and should not have approved trio.
That’s totally hilarious – I thought 100% of EASA was reading EuroGA but evidently only 50% of it does 
So Trio or Trutrak cannot ever have a “normal” EASA STC?
Depending on the aircraft in question, I would carefully examine the inability to fly an ILS or even a heading, on these autopilots.
Peter wrote:
So Trio or Trutrak cannot ever have a “normal” EASA STC?
to be more clear, I was referring to the “single, one off validation”. that is impossible for trio, trutrak etc.
If the want however they can apply themselves to EASA for the “proper” EASA STC. This is still possible. But then without TSO, they have to work a lot and getting EASA to approve. It is just about whether they would be interested in this investment. Like Garmin did for their nonTSO GFC-500.
Peter wrote:
Depending on the aircraft in question, I would carefully examine the inability to fly an ILS or even a heading, on these autopilots.
Trio is one of those with no heading hold. But I don’t think it is that much of an issue flying it with a gps track.
In the end it is far better option than not having one. Has all altitude hold, preselect, gpss and even 3D gps approach capability (down to 500feet).
There is currently a group buy on Trio for PA24.. there are more than 33 orders placed and the purchase price dropped to $5795. Just ridiculous compared to what an STEC costs.
