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Trim Failure

FL Flier

Active Member
My -8A?s Ray Allen trim failed. The relay clicks, but the servo doesn?t run. My A&P checked everything (I?m not much good with electrical stuff) and said it was definitely the relay. So I bought a new relay, replaced it, and same same.

He?s made it clear that he doesn?t like working on electrics and avionics. What do I need to do next to figure out what the problem is? I?m fine with just hiring someone who knows what he?s doing.

I?m near Ft. Pierce, Florida. Frustrated with all the squawks that keep popping up. Total hangar queen and waste of money so far.
 
Check output of relay with it activated to see if you are getting voltage.
If not you have a power issue (wiring to relay or relay itself).

If you do have output voltage it's a wiring or servo issue.
 
Jump a 9 volt battery right at the servo. If my memory is correct, its the 2 white wires, no stripes. Reverse polarity to make it run the other way. That will tell you if its the servo or to keep looking.
 
Often folks add one or more resistors to slow down the swervo travel rate so that trim is not overly sensitive. Is your failure just on teh ground with the master on, or when your engine and alternator are running? THe lower voltage without the engine running could be the difference in whether the swervo operates or not. If thats not it, you may need to track down where you are losing voltage.

Erich
 
The trim failed in flight - nose up on climbout. It stuck in that position - 30 mile flight home pushing the stick forward.

I?m stepping over to the hangar to try these suggestions. Then it?s just fixing the empennage gap fairing (stripped screw threads - Van?s says put in nutplates, but I see folks here used pulled rivets) and a couple other things.
 
Relay output is good, and the servo is working just fine. Now I just need to figure out where the wiring is broken.

So many lessons being learned here. #1 is hire a recognized expert in the type, spend more on a deep inside-out prebuy and say no if it?s not darned close to perfect.
 
Everything seems to be good up to the tail. I found a loose pin on a small computer-type connector (Dsub or Molex maybe) between the wire bundle coming from the cockpit and the servo. Is there any functional or regulatory reason to not use butt connectors? I don?t have the tools to crimp and set pins in the other connectors. Looks to me like these are wires that won?t ever need to be disconnected, so regular crimped connectors should work.
 
Butt connectors should be fine. The servo wires are very thin so after they are stripped, you can fold the wire over the insulation and crimp that. It will stabilize the hair thin wires.
 
Everything seems to be good up to the tail. I found a loose pin on a small computer-type connector (Dsub or Molex maybe) between the wire bundle coming from the cockpit and the servo. Is there any functional or regulatory reason to not use butt connectors? I don?t have the tools to crimp and set pins in the other connectors. Looks to me like these are wires that won?t ever need to be disconnected, so regular crimped connectors should work.

Those small connectors used on the servo have proven to be hard to work but now that you own the plane, think long term and with maintenance in mind. There are other type molex connectors that are much easier to work with and more reliable. Perhaps investing in a set of tools will pay in the long run for not having to pay an A&P that you might end up not happy with.
 
....it?s just fixing the empennage gap fairing (stripped screw threads - Van?s says put in nutplates, but I see folks here used pulled rivets) and a couple other things.


If you use pulled rivets, you'll have to remove them to do the condition inspection, if I understand what you're planning. Over time, that'll mess up the holes. Go with Van's advice.

Dave
 
If you use pulled rivets, you'll have to remove them to do the condition inspection, if I understand what you're planning. Over time, that'll mess up the holes. Go with Van's advice.

Dave
This is the small gap fairing below the horizontal stab, not the horse collar above. I?m still a bit hesitant to drill more holes in the longeron because the existing ones are not all in a perfectly straight line with each other (not all equidistant from the edges), and I don?t want to add holes and weaken it.

I read a few posts on here saying that it doesn?t need to be removed for the CI. I certainly won?t change how the upper fairing attaches, though.

Still learning a lot every day, a long way to go until I feel like I?m starting to get a handle on owning something other than Brand C.
 
Val,

I'm at 64FA, once this rain stops I can hop on over and check it out for you.

Lenny
Thanks!

Starting to think that ?once? might be changing to ?if? the rain stops. Came home yesterday and a pair of catfish were swimming in the swale in our front yard next to the street!
 
Echo to the Check switch comment

We had the same issue, run away trim but happened when adjusting trim after adding flaps. Turned out to the be the switch in the handle grip that failed in the closed position.
 
you can fold the wire over the insulation and crimp that.

Woahh. That's a bad idea! You're crimping against the soft insulation. Yeah it will stabilize it, but then eventually it will get loose.

Put a heatshrink on it instead. That will get you the same result without compromising the connection itself.
 
the solution i use is to use sub d pins for connectors. they are made for the smaller wires, male on one side, female on the other a bit of heat shrink over the two. nice and neat and if you ever need to unplug them just slice the heat shrink and slide them apart.

bob burns

RV-4 N82RB
 
the solution i use is to use sub d pins for connectors. they are made for the smaller wires, male on one side, female on the other a bit of heat shrink over the two. nice and neat and if you ever need to unplug them just slice the heat shrink and slide them apart.

bob burns

RV-4 N82RB

a friend of mine used this method but the heat shrink wore away and the pins came into contact and shorted. so, if you use this method rather than a purpose built connector be aware of the failure mode.
 
Pin Splices

a friend of mine used this method but the heat shrink wore away and the pins came into contact and shorted. so, if you use this method rather than a purpose built connector be aware of the failure mode.

The pin-splice method is actually used on spacecraft. However: 1. The splices of adjacent wires are required to be offset from each other. 2. The splices are covered with 2 layers of heat shrink tubing. 3. The wire bundle must be tied securely on both sides of the pin-splice joints.

Skylor
 
Trim failure

My pitch trim also failed recently.
I?ve been trying to find the problem for longer than I?d care to admit. With some help, we finally found it today. It was a broken solder joint at a connecter in the tail. It was located under the empennage fairing. I can only assume it was placed there in the event the horizontal stab needed to be removed. I removed the connector, and shrink soldered everything back up. Everything works.
It?s really frustrating cleaning up someone else?s sloppy work. I hope you?re able to find the issue.
 
The pin-splice method is actually used on spacecraft. However: 1. The splices of adjacent wires are required to be offset from each other. 2. The splices are covered with 2 layers of heat shrink tubing. 3. The wire bundle must be tied securely on both sides of the pin-splice joints.

Skylor

it's a light weight solution and I like that, but if it's not done properly then problems can arise. do you really want to gamble with the trim connection?
 
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Solved. Broken wire somewhere between the cockpit and servo. A&P ran new wiring to the servo - working properly.
 
I had a similar problem. The avionics guy was stumped. Ended up replacing the servo and indicator and grip. Found a broken soldered connection in the Ray Allen grip. I was not impressed with the soldering quality in the grip. Installed an Infinity grip. Fortunately the cost of auxiliaries for experimentals is not very high.

Take heart. I had similar issues during the first year after buying my plane. If I ever do it again, especially for a plane with over 1000 hrs on it, I would probably replace all the older/original auxiliaries in one go at the outset...e.g. mags, fuel pump, trim system, master solenoid, cheap tires. I also got rid of the vacuum system. Auxiliaries wear out. Cheaper and quicker that way rather than one at a time. Do not cheap out on the quality of any new auxilliaries you install (e.g. no “overhauled” mags). Nowadays I just hop in it, fire it up and go. You’ll get there too. But the maintenance learning curve is also a highly instructional...and necessary experience, though maybe a bit frustrating at times. Ive had my plane professionally maintained from the outset, but even that isnt always a walk in the park. It’ll never be as cheap or easy as maintaining an automobile. :)
 
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Ray Allen Grip soldering

I had a similar problem. The avionics guy was stumped. Ended up replacing the servo and indicator and grip. Found a broken soldered connection in the Ray Allen grip. I was not impressed with the soldering quality in the grip. Installed an Infinity grip. Fortunately the cost of auxiliaries for experimentals is not very high.
...
Just throwing this out there - the Ray Allen grips are soldered by the builder, at least mine were. They come "naked", then the builder gets to solder the wires on.

http://www.rv8.ch/ray-allen-company-stick-grips/

20041120212301548_5_original-1024x768.jpg
 
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