337 autopilots

Rick Gardner · #1 04-04-10, 01:05 AM

I have an STEC 55X in our 76 model and it reallly does not work well at all. I have spent thousands to have the computer, transducer etc. sent to STEC. We had a King KAP140 in out Cessna206 and it worked really well. Now, I am not trying to promote one versus the other but my impression after having both is that the STEC does very poorly capturing laterally and vertically. As usual, the avionics shop says it the autopilot, STEC says its the installation and I say......

Now STEC admits there may be an issue wih the servos and that there is a procedure to clean out the servos.....

Anyone else have this issue?

Roger · #2 04-04-10, 08:47 AM

The only problem I have with my plane is my piece of crap stec 60-2. It is like riding a porpoise at cruise, plus I can't get my altitude pre-select to capture any input data. I typically don't use altitude hold. It works great on the Bug, needle and GPS tracking (GPSS Roll Stearing) and if trimmed corrrectly the plane itself holds altitude, bit the minuite I click on Altitude Hold it start to porpoise. Any help would be appreciated.

tropical · #3 04-04-10, 10:25 AM

Quote:

Originally Posted by Roger

The only problem I have with my plane is my piece of crap stec 60-2. It is like riding a porpoise at cruise, plus I can't get my altitude pre-select to capture any input data. I typically don't use altitude hold. It works great on the Bug, needle and GPS tracking (GPSS Roll Stearing) and if trimmed corrrectly the plane itself holds altitude, bit the minuite I click on Altitude Hold it start to porpoise. Any help would be appreciated.

Sounds like you have moisture in the static line to the autopilot computer. Dry that out and the problem will go away.

skymstr02 · #4 04-04-10, 05:02 PM

Quote:

Originally Posted by Roger

The only problem I have with my plane is my piece of crap stec 60-2. It is like riding a porpoise at cruise, plus I can't get my altitude pre-select to capture any input data. I typically don't use altitude hold. It works great on the Bug, needle and GPS tracking (GPSS Roll Stearing) and if trimmed corrrectly the plane itself holds altitude, bit the minuite I click on Altitude Hold it start to porpoise. Any help would be appreciated.

Is the bridle cable tension on the pitch servo tight enough? Sometimes low cable tension will create the porpose effect.

Rick Gardner · #5 04-05-10, 11:50 AM

Static lines checked, servo motor removed and set to factory torque settings, rigging checked for proper tensions.

Roger · #6 04-05-10, 07:42 PM

My IA advised me to try flying the autopilot with the interior standby static open. I flew first with it closed and the 60-2 hunted 100' +/-, then I closed it and after re-establishing a set altitude, it tracked +/- 20'. Much, much better. So I guess the problem is in the static system, water, etc..

Rick Gardner · #7 04-05-10, 10:09 PM

OK Thanks, that's a new one. I will try it tomorrow. We are in Cabo San Lucas right now headed fo Puerto Vallarta tomorrow morning and then back to Cancun so there are plenty of miles to try it out (or to continue cursing under my breath about STEC).
Thanks!

SteveG · #8 04-06-10, 08:59 AM

I'm quite surprised to read of so many unhappy S-Tec users. I have the older Model 50 and it holds heading and altitude +/- virtually nothing. Occasionally, in turbulence, you'll want to "help" it dampen the initial jolt but it then recovers nicely. I have never seen any tendency to porpoise or hunt. My only negative comment would be that its approach mode is insufficiently sensitive to accurately track a localizer, wandering +/- a half dot or so. I just fly the approach on the heading bug with no problem so it's not any real concern. Assuming the guts of the system are essentially the same across the differing models being discussed, I would have to conclude that precision problems are installation problems or rigging problems based on my experience with the make.