Question about 201 trim switch

[NotarPilot]

Does anyone happen to know if the original early 201s came with trim from the factory or were they aftermarket? Looking at different 201s on Controller it seems there's more than one trim switch on the yokes. I have a 1978 and wanted to replace to trim switch with a newer one (since I got the Aero Comfort wrapped yokes) I wanted a newer look. Cygnet makes a great trim switch but it doesn't have a PMA. 

That makes me wonder if you even need a PMA for a trim switch, especially if it functions similarly to the existing one. As far as I know the PPT and AP disengage push buttons are not PMA'd nor do they require it. So does a trim switch need to be PMA'd or TSO'd? Thoughts?

[NotarPilot]

I should also mention that this switch, although not PMA'd, is standard in the newer Piper GA aircraft. Not sure if that counts for something.

[N201MKTurbo]

The switch on my 77 201 is hooked to a Centuary electric trim and IIB autopilot. They all work together. The switch is trim and autopilot disconnect all in one. Does your plane have a separate autopilot disconnect switch? Does it have a CIIB autopilot?

[bradp]

Odd that my 77 also has electric trim and a Ciib autopilot.  The AP is single axis, so it's convenient not to have the AP disconnect every time I want to make a trim adjustment.  The disconnect is the rocker switch on the pedestal.   

I can't speak to the legality of a switch.  

B

[carusoam]

The BK system also has a specific switch that came with it. A good electronics shop should be able tell if a substitution can be made.  I would expect that there is one switch that is legal and expensive and other switches that look nice and do the same thing but may not be legal....

That switch gets a real work-out during a go around...  Your thumb is pushing down on the switch.  Your arms are pushing down on the yoke.  Your brain is paying attention to everything outside.  That switch gets pressed pretty hard sometimes... 

As for the dual switch buttons... They are required to tell the AP that the pilot intends to move the trim. They are a Protection from trim runaway because of a single stuck switch.

Best regards,

-a-

[Marauder]

7 hours ago, NotarPilot said:

Does anyone happen to know if the original early 201s came with trim from the factory or were they aftermarket? Looking at different 201s on Controller it seems there's more than one trim switch on the yokes. I have a 1978 and wanted to replace to trim switch with a newer one (since I got the Aero Comfort wrapped yokes) I wanted a newer look. Cygnet makes a great trim switch but it doesn't have a PMA. 

That makes me wonder if you even need a PMA for a trim switch, especially if it functions similarly to the existing one. As far as I know the PPT and AP disengage push buttons are not PMA'd nor do they require it. So does a trim switch need to be PMA'd or TSO'd? Thoughts?

I have been following the Cygnet switch for a couple of years now hoping that it would be approved. The original STEC replacement is really expensive. Since we are talking about the electric trim, I'm sure it is different than the AP disengage because you don't want something that could command up and down doing so. I would love to replace mine as well for the same reason, its looking old -- like me.

[carusoam]

Something to consider....

What are our yoke forces when we are pushing down with flaps down and throttle all the way in?  10 to 20 pounds? We are doing a bench press type exercise.  It may be more...

Expect that much of the force may be applied through the thumb switch. The BK switch is a stout industrial strength metal device that takes the beating pretty well.

Looking at the plastic switch consider how it will handle your bench press exercise?

Just an idea to consider...

Best regards,

-a-

[N201MKTurbo]

FWIW

My switch has three switches. The outside ones are for the electric trim and the center is for the autopilot disconnect. I have priced out the individual switches and they are very expensive mil spec mini-microswitches. Much higher quality then the switches shown in the Cygnet switch. There is a mechanical arrangement for the levers that is separate from the switches. The whole assembly can be disassembled, cleaned and re-painted. Just don't lose any of the tiny parts while doing it.

[flyboy0681]

2 hours ago, carusoam said:

 

As for the dual switch buttons... They are required to tell the AP that the pilot intends to move the trim. They are a Protection from trim runaway because of a single stuck switch.

Best regards,

-a-

A couple if years ago I had a few cases of runaway down trim on the KAP 150 (I wrote about that harrowing experience here) that couldn't be explained until one day while adjusting the trim on the ground I noticed the wheel continued to turn until it reached the stops. It was then that I realized that when pressing the trim switch forward in a certain way that it was sticking and I was finally able to recreate it every time. But that was after shipping the A/P head to Autopilot Central for inspection. Then came installation of a new switch from King..

[NotarPilot]

6 hours ago, N201MKTurbo said:

The switch on my 77 201 is hooked to a Centuary electric trim and IIB autopilot. They all work together. The switch is trim and autopilot disconnect all in one. Does your plane have a separate autopilot disconnect switch? Does it have a CIIB autopilot?

Yes I have a separate AP disconnect button which looks like a standard switch you buy from Radio Shack. Does anyone know if the AP disconnect or PTT switches have any kind of approval? I don't think they do. But I could be wrong.

[N201MKTurbo]

Just now, NotarPilot said:

Yes I have a separate AP disconnect button which looks like a standard switch you buy from Radio Shack. Does anyone know if the AP disconnect or PTT switches have any kind of approval? I don't think they do. But I could be wrong.

Do you have a Century IIB autopilot?

[NotarPilot]

No, I have an S-tec 30.

[Rwsavory]

We looked into the same issue a couple years ago and consulted with our avionics guy on it.  For the STEC trim in a certified plane your only legal options right now are replacement with a new or used STEC switch assembly, or repair the existing one with parts salvaged from a used one.  Our guy was able to repair ours using salvaged parts.  

[NotarPilot]

23 hours ago, carusoam said:

Something to consider....

What are our yoke forces when we are pushing down with flaps down and throttle all the way in?  10 to 20 pounds? We are doing a bench press type exercise.  It may be more...

Expect that much of the force may be applied through the thumb switch. The BK switch is a stout industrial strength metal device that takes the beating pretty well.

Looking at the plastic switch consider how it will handle your bench press exercise?

Just an idea to consider...

Best regards,

-a-

I spoke to a guy at Cygnet and he said the switch is not plastic but machined aluminum. Also, this switch is already in certificated aircraft like newer Piper and Kodiaks.

[N201MKTurbo]

Talk to your FSDO guy and see if he would approve it. You better show up with at least mechanical and electrical sketches that prove it will fit and function. You may need to prove that the switches can handle the current they are required to carry. They almost certainly will, but that doesn't prove anything. You could find the specs of the current switch and show equivalency or contact S-TEC and see if they will supply you with the requirements.

 

Or just have the hangar fairies put it in and don't tell anybody how it got there...

[Piloto]

Switches, knobs, connectors, bolts, rivets and other parts are not individually FAA approved. What is approved is the collective of these parts that perform a function. To insure proper part replacement it must come from the original part manufacturer or an approved supplier. Part equivalency would need to be demonstrated if a different part is to be used.

José

Edited May 7, 2016 by Piloto

[Marauder]

Where does "owner supplied" fit in all this? If the switch is commercially available but pricey, are you expected to buy it instead of a cheaper alternative? In other words, if STEC no longer produced or acquired the switch, is that the only time "owner supplied" can be used?

[Rwsavory]

42 minutes ago, Marauder said:

Where does "owner supplied" fit in all this? If the switch is commercially available but pricey, are you expected to buy it instead of a cheaper alternative? In other words, if STEC no longer produced or acquired the switch, is that the only time "owner supplied" can be used?

I don't think it's required that the part be unavailable from the manufacturer. Here's a good article that covers the topic: http://www.avweb.com/news/savvyaviator/savvy_aviator_54_is_repair_a_lost_art_197316-1.html

 By the time you write the specifications and demonstrate airworthiness, you've probably already paid double the cost of a replacement.

BTW, Our avionics tech told me that the microswitches in the Stec trim switch are specially made for them and configured  differently from off-the-shelf components. I don't know if that's correct, of course. 

 

[Andy95W]

One thing about the STEC disconnect switch is that it is a NC (normally closed) switch.  This is different from PTT switches that are normally open.

[dooleypster]

I have a 1988 J model with the Century 2000 autopilot.  I have replaced the trim switch several times as they are really flimsy inside (very thin metal contacts) and they are very pricey ($750-800).  I also have separate buttons for autopilot disconnect, CWS, etc.  My avionics tech said there are 62 different versions of the switch depending on your individual equipment.

[231MJ]

I have the Century trim system and it will only trim down so I suspect the switch is bad.  Does anyone know if this switch from Spruce will work with the Century system?  http://www.aircraftspruce.com/catalog/elpages/trimSwitches2.php?clickkey=5126

Does anyone have a wiring diagram for the Century trim system?

Thanks

231MJ

[OR75]

Century has the schematic for the trim available on their website 

[N201MKTurbo]

15 hours ago, aochabauer said:

I have the Century trim system and it will only trim down so I suspect the switch is bad.  Does anyone know if this switch from Spruce will work with the Century system?  http://www.aircraftspruce.com/catalog/elpages/trimSwitches2.php?clickkey=5126

Does anyone have a wiring diagram for the Century trim system?

Thanks

231MJ

With the engine off, operate the trim switch in both directions, if you hear the relay click in both directions then it is probably not the switch. 

In either case I would trouble shoot it with a meter before changing any parts.

Edited December 11, 2016 by N201MKTurbo

[231MJ]

Thanks MKTurbo.  I only hear the relay click when trimming down so I changed the relay but no change after the new relay.  I'll meter the switch next to see if I can learn more.   Darn thing...

I'm hoping someone has insight regarding the switch from Spruce - it would get great if the switch had the same functions.

 

  

[cnoe]

With the older Century trim switches I believe the correct answer is to either replace the "assembly" with new from Century or "repair" your existing one by replacing the 3 individual micro-switches (which is a delicate and somewhat difficult procedure). The switches used in my '78J are Honeywell 21SX39-T units available at Mouser for $10.51 each + shipping.

Again, replacing these is not a job for most hangar elves/fairies. It requires more skill than simply soldering the wires and bolting it in place; delicate adjustments may also be necessary. The consequences of screwing up the job are serious. I'd suggest just ponying up the money for the whole assembly from Century. But... if you have a qualified repair-person (a somewhat lost art) then the switches are not expensive nor hard to source.