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Elevator Pitch Servo Failure

 
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Jim Combs



Joined: 24 Jan 2010
Posts: 129
Location: Lexington, Ky

PostPosted: Sun Apr 14, 2019 10:33 am    Post subject: Elevator Pitch Servo Failure Reply with quote

Had an elevator pitch servo fail on a flight yesterday. The cable
pulled out of a hole that uses a set screw to hold the cable in place.
It's a TruTrak pitch servo. It uses a cable that wraps around a drum.
Each end of the cable is attached to an aluminum channel.

1200 hours on the airplane with no prior issues. The pilot said the
elevator felt funny on any up travel past neutral. He also heard a
clicking noise as it passed the neutral point.

An engineering EC would be to leave the cable slightly long and crimp
a sleeve onto the cable as a a failsafe for the set screw(s).

I will call TruTrak tomorrow to see if this should be replaced or
repaired. I will be adding this to my inspection checklist. I
noticed nothing during the last condition inspection.

Not sure exactly when it failed. It was noticed prior to a return
flight from another airport. Removal of the bulkhead and removing the
control arm of the servo from the elevator bellcrank was done to allow
the flight home.

N312F - 1200 hours

Jim Combs


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bill.peyton



Joined: 19 Sep 2010
Posts: 191
Location: St. Louis, MO

PostPosted: Sun Apr 14, 2019 3:12 pm    Post subject: Re: Elevator Pitch Servo Failure Reply with quote

Hi Jim,
I was always concerned with this design of the pitch servo. I spoke with TT about it 8 years ago and they assured me they had redesigned the force multiplier to remedy this issue. Yours is not the first time this has happened. Just consider yourself extremely fortunate that the arm did not jam the entire elevator operation.
I designed a fail-safe retainer to prevent this from happening should the cable come loose. I also shared this with TT. Here are a few photos of my modification.


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PostPosted: Mon Apr 15, 2019 5:45 am    Post subject: Elevator Pitch Servo Failure Reply with quote

Thanks for sharing.

I'm at 1100 hours and the trim servo has done more flying than I...

Bill "in the middle of a series of minor 1,000 hour failures" Watson

On 4/14/2019 1:59 PM, Jim Combs wrote:
Quote:
Had an elevator pitch servo fail on a flight yesterday. The cable
pulled out of a hole that uses a set screw to hold the cable in place.
It's a TruTrak pitch servo. It uses a cable that wraps around a drum.
Each end of the cable is attached to an aluminum channel.

1200 hours on the airplane with no prior issues. The pilot said the
elevator felt funny on any up travel past neutral. He also heard a
clicking noise as it passed the neutral point.

An engineering EC would be to leave the cable slightly long and crimp
a sleeve onto the cable as a a failsafe for the set screw(s).

I will call TruTrak tomorrow to see if this should be replaced or
repaired. I will be adding this to my inspection checklist. I
noticed nothing during the last condition inspection.

Not sure exactly when it failed. It was noticed prior to a return
flight from another airport. Removal of the bulkhead and removing the
control arm of the servo from the elevator bellcrank was done to allow
the flight home.

N312F - 1200 hours

Jim Combs

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PostPosted: Mon Apr 15, 2019 5:52 am    Post subject: Elevator Pitch Servo Failure Reply with quote

Seems like an elegant, easy to implement fail safe mod.

I take it that there may not be an easily identifiable failure mode
where the elevator does jam, but the fact that a stiff control arm could
be flopping about is enough to justify a fail safe mod.

Thanks for sharing!

On 4/14/2019 7:12 PM, bill.peyton wrote:
Quote:


Hi Jim,
I was always concerned with this design of the pitch servo. I spoke with TT about it 8 years ago and they assured me they had redesigned the force multiplier to remedy this issue. Yours is not the first time this has happened. Just consider yourself extremely fortunate that the arm did not jam the entire elevator operation.
I designed a fail-safe retainer to prevent this from happening should the cable come loose. I also shared this with TT. Here are a few photos of my modification.

--------
Bill
WA0SYV
Aviation Partners, LLC


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PostPosted: Mon Apr 15, 2019 3:16 pm    Post subject: Elevator Pitch Servo Failure Reply with quote

I have a two axis TruTrak DigiTrak autopilot with an AlTrak altitude hold and did NOT install the torque multiplier. When the elevator trim is set for light stick pressure the pitch servo has no problem(in 140 hours) keeping the altitude correct. Does anyone else use the stock servo without the enhancer?

PH
On Apr 15, 2019, at 12:44 AM, RV10-List Digest Server <rv10-list(at)matronics.com> wrote:
______________________________Message 2 _____________________________________
Time: 11:33:03 AM PST US
From: Jim Combs <jiminlexky(at)gmail.com>
Subject: Elevator Pitch Servo Failure

Had an elevator pitch servo fail on a flight yesterday. The cable
pulled out of a hole that uses a set screw to hold the cable in place.
It's a TruTrak pitch servo. It uses a cable that wraps around a drum.
Each end of the cable is attached to an aluminum channel.

1200 hours on the airplane with no prior issues. The pilot said the
elevator felt funny on any up travel past neutral. He also heard a
clicking noise as it passed the neutral point.

An engineering EC would be to leave the cable slightly long and crimp
a sleeve onto the cable as a a failsafe for the set screw(s).

I will call TruTrak tomorrow to see if this should be replaced or
repaired. I will be adding this to my inspection checklist. I
noticed nothing during the last condition inspection.

Not sure exactly when it failed. It was noticed prior to a return
flight from another airport. Removal of the bulkhead and removing the
control arm of the servo from the elevator bellcrank was done to allow
the flight home.

N312F - 1200 hours

Jim Combs


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PostPosted: Mon Apr 15, 2019 3:48 pm    Post subject: Elevator Pitch Servo Failure Reply with quote

We had the standard Servo in the beginning. It worked ok, but the torque enhancer was much better.

Jesse Saint
Saint Aviation, Inc.
jesse(at)saintaviation.com
C: 352-427-0285
F: 815-377-3694

Sent from my iPhone

Quote:
On Apr 15, 2019, at 7:15 PM, Eagerlee6 <eagerlee6(at)gmail.com> wrote:



I have a two axis TruTrak DigiTrak autopilot with an AlTrak altitude hold and did NOT install the torque multiplier. When the elevator trim is set for light stick pressure the pitch servo has no problem(in 140 hours) keeping the altitude correct. Does anyone else use the stock servo without the enhancer?

PH


On Apr 15, 2019, at 12:44 AM, RV10-List Digest Server <rv10-list(at)matronics.com> wrote:
______________________________Message 2 _____________________________________


Time: 11:33:03 AM PST US
From: Jim Combs <jiminlexky(at)gmail.com>
Subject: Elevator Pitch Servo Failure

Had an elevator pitch servo fail on a flight yesterday. The cable
pulled out of a hole that uses a set screw to hold the cable in place.
It's a TruTrak pitch servo. It uses a cable that wraps around a drum.
Each end of the cable is attached to an aluminum channel.

1200 hours on the airplane with no prior issues. The pilot said the
elevator felt funny on any up travel past neutral. He also heard a
clicking noise as it passed the neutral point.

An engineering EC would be to leave the cable slightly long and crimp
a sleeve onto the cable as a a failsafe for the set screw(s).

I will call TruTrak tomorrow to see if this should be replaced or
repaired. I will be adding this to my inspection checklist. I
noticed nothing during the last condition inspection.

Not sure exactly when it failed. It was noticed prior to a return
flight from another airport. Removal of the bulkhead and removing the
control arm of the servo from the elevator bellcrank was done to allow
the flight home.

N312F - 1200 hours

Jim Combs






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PostPosted: Tue Apr 16, 2019 4:56 am    Post subject: Elevator Pitch Servo Failure Reply with quote

Didn't know that was an option.

Just  FYI, I have the 2 axis controller with the torque multiplier and
TT Autotrim.  It trims the elevator automatically well enough that I
more often use the AP to set pitch trim than doing it myself.  I also
have safety trim.

Bill "if I could just get the occasional wing wag out of my AP thru GRT
HXr connection hands free flight would be perfect" Watson

On 4/15/2019 7:15 PM, Eagerlee6 wrote:
Quote:


I have a two axis TruTrak DigiTrak autopilot with an AlTrak altitude hold and did NOT install the torque multiplier. When the elevator trim is set for light stick pressure the pitch servo has no problem(in 140 hours) keeping the altitude correct. Does anyone else use the stock servo without the enhancer?

PH
On Apr 15, 2019, at 12:44 AM, RV10-List Digest Server <rv10-list(at)matronics.com> wrote:
______________________________Message 2 _____________________________________
Time: 11:33:03 AM PST US
From: Jim Combs <jiminlexky(at)gmail.com>
Subject: Elevator Pitch Servo Failure

Had an elevator pitch servo fail on a flight yesterday. The cable
pulled out of a hole that uses a set screw to hold the cable in place.
It's a TruTrak pitch servo. It uses a cable that wraps around a drum.
Each end of the cable is attached to an aluminum channel.

1200 hours on the airplane with no prior issues. The pilot said the
elevator felt funny on any up travel past neutral. He also heard a
clicking noise as it passed the neutral point.

An engineering EC would be to leave the cable slightly long and crimp
a sleeve onto the cable as a a failsafe for the set screw(s).

I will call TruTrak tomorrow to see if this should be replaced or
repaired. I will be adding this to my inspection checklist. I
noticed nothing during the last condition inspection.

Not sure exactly when it failed. It was noticed prior to a return
flight from another airport. Removal of the bulkhead and removing the
control arm of the servo from the elevator bellcrank was done to allow
the flight home.

N312F - 1200 hours

Jim Combs



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PostPosted: Tue Apr 16, 2019 6:18 am    Post subject: Elevator Pitch Servo Failure Reply with quote

Has whatever y'all are talking about ever happened with a Dynon SV-42T servo?  If not, I won't worry about it, but if it has, I want to understand the failure mode and its prevention. 

On Tue, Apr 16, 2019 at 9:01 AM Bill Watson <Mauledriver(at)nc.rr.com (Mauledriver(at)nc.rr.com)> wrote:

Quote:
--> RV10-List message posted by: Bill Watson <Mauledriver(at)nc.rr.com (Mauledriver(at)nc.rr.com)>

Didn't know that was an option.

Just  FYI, I have the 2 axis controller with the torque multiplier and
TT Autotrim.  It trims the elevator automatically well enough that I
more often use the AP to set pitch trim than doing it myself.  I also
have safety trim.

Bill "if I could just get the occasional wing wag out of my AP thru GRT
HXr connection hands free flight would be perfect" Watson

On 4/15/2019 7:15 PM, Eagerlee6 wrote:
> --> RV10-List message posted by: Eagerlee6 <eagerlee6(at)gmail.com (eagerlee6(at)gmail.com)>
>
> I have a two axis TruTrak DigiTrak autopilot with an AlTrak altitude hold and did NOT install the torque multiplier. When the elevator trim is set for light stick pressure the pitch servo has no problem(in 140 hours) keeping the altitude correct. Does anyone else use the stock servo without the enhancer?
>
> PH
>
>
> On Apr 15, 2019, at 12:44 AM, RV10-List Digest Server <rv10-list(at)matronics.com (rv10-list(at)matronics.com)> wrote:
> ______________________________Message 2  _____________________________________
>
>
> Time: 11:33:03 AM PST US
> From: Jim Combs <jiminlexky(at)gmail.com (jiminlexky(at)gmail.com)>
> Subject: Elevator Pitch Servo Failure
>
> Had an elevator pitch servo fail on a flight yesterday.  The cable
> pulled out of a hole that uses a set screw to hold the cable in place.
> It's a TruTrak pitch servo.  It uses a cable that wraps around a drum.
> Each end of the cable is attached to an aluminum channel.
>
> 1200 hours on the airplane with no prior issues.  The pilot said the
> elevator felt funny on any up travel past neutral.  He also heard a
> clicking noise as it passed the neutral point.
>
> An engineering EC would be to leave the cable slightly long and crimp
> a sleeve onto the cable as a a failsafe for the set screw(s).
>
> I will call TruTrak tomorrow to see if this should be replaced or
> repaired.  I will be adding this to my inspection checklist.  I
> noticed nothing during the last condition inspection.
>
> Not sure exactly when it failed.  It was noticed prior to a return
> flight from another airport.  Removal of the bulkhead and removing the
> control arm of the servo from the elevator bellcrank was done to allow
> the flight home.
>
> N312F - 1200 hours
>
> Jim Combs
>
>
>
>
>


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