The S-TEC 20 responded very gently, and almost unnoticeably, to the scalloping, even close to the VOR.
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Unlike GPS tracks, VOR needles tend to scallop - wag back and forth - and an autopilot that overreacts to that will soon make the passengers (and pilot) seasick with all the rocking. We were able to try all of these during the test flight northwest of Waterloo (except for the LOC tracking, due to a miscommunication with Waterloo tower). Track a localizer on a LOC or ILS approach.Track a VOR radial inbound or outbound.Track a heading set on my heading indicator.Keep the wings level, and allow simple, stable turns using a knob (without risk of overbanking).
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While the S-TEC 20 can’t hold an altitude, here’s what it can do: Kitchener Aero sent me up on a test flight with one of its people, ready to adjust the autopilot, but it was absolutely perfectly tuned. Barry warned me that I’d wish I’d paid a few thousand extra for the S-TEC 30 with altitude hold, but I was already close to my spending limit, and knew I’d end up asking for extra maintenance work on my existing avionics (and a new 406 MHz ELT, since the plane was there anyway …). The S-TEC 20 is a single-axis autopilot - that means that it controls roll (and heading), but not pitch (and altitude) or yaw. I decided on the S-TEC System 20, a rate-based autopilot (much smoother and more reliable than old APs) that is built into a turn coordinator, and replaces that instrument on my panel without needing any extra space. I called a few places for quotes, but the only one that answered my calls and questions consistently was Kitchener Aero, where owner Barry Aylward went out of his way to carry on a friendly e-mail and phone correspondence for half a year while I hemmed and hawed, then fit me right in as soon as I made up my mind, as if I were one of his bizjet customers rather than a tight-fisted Cherokee owner. I knew it was time to improve rather than just maintain my plane, and I also considered an IFR GPS and a new paint job (both about the same cost), but the autopilot gave me the biggest safety and operational benefits for the money. Even 4 hours in good VFR weather can be tiring, because of the constant attention needed to keep the plane straight, level, and on course. I’m proud that I can do that, but at the same time, it’s tiring: after 8 hours bumping around in cumulus clouds and dodging storms on the Stormscope, I’m exhausted beyond anything I’d ever imagined. I’ve flown over 850 hours, about 120 of them in actual instrument conditions, and all by hand.
STEC 50 AUTOPILOT BACK AND FORTH UPGRADE
It's a great upgrade though over the Stec regardless.Today I flew my plane home from Waterloo to Ottawa with a brand-new autopilot installed. I didn't have WAAS, but got to fly one with and you could definitely tell the difference. With WAAS, it's rock solid and truly on rails. It is a much better autopilot than the Stec 55X, but still tends to wander a little in windy conditions. The only recommendation I would suggest is to do WAAS (G430W or GTN650) since it significantly improves the preciseness of the autopilot. I didn't have any service issues at all and it just works. If you are rapidly climbing the e-protection will catch it if you are in busy airspace and IMC and aren't watching, but setting the IAS for climbs is just easier and safer IMO. The later I learned to use a lot on climbs since it just works so well and you don't have to fiddle with anything to keep from getting too slow. Once we got it all configured it works awesome! I especially like the envelope protection, level button, and the IAS settings.
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Philip, I flew it for over a year and about 230 hours. When this takes place, a voice will sound off in the headsets stating “Speed Protection Active.” The same applies on the over speed side if you command a vertical decent that would result in exceeding Vne, the DFC90 will intervene and not allow an over speed to occur. If you command a climb that the aircraft is not capable of, the autopilot will allow the climb until the airspeed bleeds off and then the autopilot will hold a safe speed, not allowing a stall. The envelope protection of the DFC90 eliminates this issue. The end result is that the autopilot flies the plane into an autopilot induced stall. There have been several accidents in the Cirrus fleet alone, where pilots get busy and aren’t monitoring the aircraft and the aircraft is set up to climb at a rate in which it cannot keep up with. In addition to the increase preciseness of the DFC90, Avidyne incorporated its “Envelope Protection.” One of the major safety issues using the S-Tec, is that you could stall the aircraft with the autopilot.