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  #1  
Old 11-22-2008, 11:28 AM
Ironflight's Avatar
Ironflight Ironflight is offline
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Location: Dayton, NV
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Default TruTrak Servo Shear Pin...sheared!

Rather than take this very important thread on Pat's incident with a jammed elevator linkage in a tangential direction, I'll start a new one with a coincidental failure we had on Louise's roll servo yesterday.

Louise was off on a trip and called to tell me that her roll autopilot wasn't working. All the lights came on as if it were engaged, but there was no resistance to moving the stick in that axis. Pitch worked normally. Since we were going to inspect for the problem noted in Pat's thread anyway, I had her fly it home (recommending no loops or rolls!), and we took it apart last night. Sure enough, you could hear the servo trying to control, but nothing happened with the stick, and sure enough, when we got it out, the shear pin (a screw actually) had failed. The servo appears to be operating completely normally, the center screw was tight - the shear pin had simply failed after time.

I'm curious if anyone else has had these fail, and if they might be a life-limited item? I haven't had a problem with either servo in the -8, and plan to simply put a new pin in this servo. (BTW, anyone in Houston have a spare? I'm sure TT will send me a few next week, but then I have time to install one this weekend!)

The center screw did it's job of keeping the servo arm captured in this case, so it failed exactly as it was supposed to.

Paul
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  #2  
Old 11-22-2008, 02:25 PM
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frankh frankh is offline
 
Join Date: Jul 2006
Location: Corvallis Oregon
Posts: 3,547
Default YUP me too

Mine failed in IMC on a bumpy Xcountry flight...No big deal but it does wake you up..

replace screw all well for a year and a half.

Frank

Last edited by Mike S : 11-22-2008 at 05:17 PM.
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  #3  
Old 10-23-2011, 10:40 PM
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Rosie Rosie is offline
 
Join Date: Dec 2004
Location: I live in on the Rosamond Skypark (CA) and am married to Victoria (Tuppergal).
Posts: 981
Default

Quote:
Originally Posted by Ironflight View Post
Rather than take this very important thread on Pat's incident with a jammed elevator linkage in a tangential direction, I'll start a new one with a coincidental failure we had on Louise's roll servo yesterday.

Louise was off on a trip and called to tell me that her roll autopilot wasn't working. All the lights came on as if it were engaged, but there was no resistance to moving the stick in that axis. Pitch worked normally. Since we were going to inspect for the problem noted in Pat's thread anyway, I had her fly it home (recommending no loops or rolls!), and we took it apart last night. Sure enough, you could hear the servo trying to control, but nothing happened with the stick, and sure enough, when we got it out, the shear pin (a screw actually) had failed. The servo appears to be operating completely normally, the center screw was tight - the shear pin had simply failed after time.

I'm curious if anyone else has had these fail, and if they might be a life-limited item? I haven't had a problem with either servo in the -8, and plan to simply put a new pin in this servo. (BTW, anyone in Houston have a spare? I'm sure TT will send me a few next week, but then I have time to install one this weekend!)

The center screw did it's job of keeping the servo arm captured in this case, so it failed exactly as it was supposed to.

Paul
My TruTrak roll A/P servo stopped working on the way home (yesterday) from Copperstate 2011. The plane started wandering off course, and after a few power cycles I just left if off. Got it apart and found that the shear pin (not a screw but a pin) had broken. Same as Ironflight said: "The center screw did it's job of keeping the servo arm captured in this case, so it failed exactly as it was supposed to."

It was a simple fix (new shear pin) and am back to normal ops. I checked the aircraft log and see that I have ~500 hobbs hours since servo installation, and I only use the A/P on long trips. A quick look through the pilot log book shows I have maybe ~220-ish hours on the servo.

No complaints here: Just a data point. I LOVE my TruTrak A/P system Rosie
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  #4  
Old 10-24-2011, 09:02 AM
TrutrakTech TrutrakTech is offline
 
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I know where you can get spares. They're on the way!
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  #5  
Old 10-24-2011, 03:41 PM
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Fred.Stucklen Fred.Stucklen is offline
 
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Location: Brooksville, FL
Posts: 428
Default Servo Shear pin

Quote:
Originally Posted by Ironflight View Post
Rather than take this very important thread on Pat's incident with a jammed elevator linkage in a tangential direction, I'll start a new one with a coincidental failure we had on Louise's roll servo yesterday.

Louise was off on a trip and called to tell me that her roll autopilot wasn't working. All the lights came on as if it were engaged, but there was no resistance to moving the stick in that axis. Pitch worked normally. Since we were going to inspect for the problem noted in Pat's thread anyway, I had her fly it home (recommending no loops or rolls!), and we took it apart last night. Sure enough, you could hear the servo trying to control, but nothing happened with the stick, and sure enough, when we got it out, the shear pin (a screw actually) had failed. The servo appears to be operating completely normally, the center screw was tight - the shear pin had simply failed after time.

I'm curious if anyone else has had these fail, and if they might be a life-limited item? I haven't had a problem with either servo in the -8, and plan to simply put a new pin in this servo. (BTW, anyone in Houston have a spare? I'm sure TT will send me a few next week, but then I have time to install one this weekend!)

The center screw did it's job of keeping the servo arm captured in this case, so it failed exactly as it was supposed to.

Paul
Mine failed about 1.5 years ago. Replaced it, and now also carry a spare in the tool bag. Hasn't failed since!
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  #6  
Old 10-25-2011, 08:13 AM
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gvouga gvouga is offline
 
Join Date: Aug 2005
Location: Raleigh, NC
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I had a shear pin fail a few years ago. At the time, I estimate the servo had less than 50hrs of operational time. Lucas sent me a new one and I have almost 800hrs (maybe 300hrs servo time) on the plane now without another shear pin failure.

I'm not 100% sure what caused the failure, but it is possible that I kicked the stick climbing in and out of the plane while working on the interior stuff. A sharp force on the stick could possibly add enough force to the pin to cause it to snap.

Greg
RV-7
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  #7  
Old 10-25-2011, 09:22 AM
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Geico266 Geico266 is offline
 
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Location: Huskerland, USA
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I had a roll servo go bad and TT repaired it and I'm back up and flying again, no problem with the shear pin in 500 hours.
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Last edited by Geico266 : 12-09-2012 at 10:04 PM.
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  #8  
Old 10-25-2011, 08:04 PM
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Location: Stuart, FL /Hartford, CT/Virgin Gorda,BVI
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after 2,200 TT AP hrs i have had no shear pins fail. numerous servos replaced at no charge. one thing that may prove helpful........ if a servo goes bad, you can go into the settings and 'turn' it off and continue on using the other servo. this has been helpful for me on a prior trip. also, a rebuild of the DG at a slight cost of $200. amazing company and product. love it. coupled to the 430 it does everything i need.
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  #9  
Old 12-09-2012, 09:21 PM
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Toobuilder Toobuilder is offline
 
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Looks like I have a failed shear pin on the roll servo as well. Was working fine one minute, gone the next. Probably about 250 airframe hours since install.
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WARNING! Incorrect design and/or fabrication of aircraft and/or components may result in injury or death. Information presented in this post is based on my own experience - Reader has sole responsibility for determining accuracy or suitability for use.

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  #10  
Old 12-09-2012, 09:29 PM
molson309 molson309 is offline
 
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Location: Longmont, CO
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Had one shear in the RV7A, put in the replacement and 200 hours later it is still going strong. I'd rather have one shear once in a while than be too strong and not shear with jammed controls as a result...
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