Elevator trim-tab rod failure

[Ted Waltman]

Folks,

My elevator trim-tab was connected to the trim servo using about a 7"
long 8x32 threaded rod (that's 1/4" diameter for non-technical types
like me <grin>). I recently took a cross country where I had the plane
loaded to within 250 lbs of gross (1250 lbs of fuel, people and camping
gear). During the initial flight I found myself having to hold perhaps
10 lbs of forward pressure on the stick even with full down elevator
trim.

Upon investigating, I found the threaded rod was bending into a slight
"U" shape. With just a little bit of pressure to bend it straight, the
rod snapped. I'm glad this happened on the ground rather than flying or
things would have been very interesting indeed. It's clear the rod size
is inadequate for the elevator incidence and gross-weight flying
characteristics of the Moose.

Needing to make a field repair, I found the same size rod at a local
hardware store. I however, slid a thin steel tube on the outside of the
rod to provide more strength. Thus far, after 7 hours of flight, the
updated rod seems to be holding well.

Clearly the weak point now is where the rod attaches on each end to the
elevator tab and the servo. I thought about getting a larger stock rod
and having it's ends machined down to fit the existing elevator trim tab
attach point and the servo attach point. However, this would
essentially leave me with the same weak point as I have now with the
sleeve and existing rod. Without having an expensive end-to-end custom
part made, does anyone have any other idea other than leaving things as
I've repaired them and inspecting them regularly?

I'll try to remember to take a digital picture of the updated rod with
sleeve in the next day or two and post it to the site.

Thanks,

Ted Waltman
Moose N142SR




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[Scott Aldrich]

That sounds like the standard rod that comes with the MAC or Ray Allen
servo.

Where did it snap? Near the clevis?

The instructions mention not using a longer threaded rod.

I am thinking maybe changing to a solid, no thread, stainless steel rod with
slots cut in each end. Just use the threaded rod for measurement.

Scott
Moose 174

-----Original Message-----
From: mike.davis@dcsol.com [mailto:mike.davis@dcsol.com] On Behalf Of Ted
Waltman
Sent: Monday, July 12, 2004 3:26 PM
To: rebel-builders@dcsol.com
Cc: murtech@murphyair.com; rdyck@murphyair.com
Subject: Elevator trim-tab rod failure

Folks,

My elevator trim-tab was connected to the trim servo using about a 7"
long 8x32 threaded rod (that's 1/4" diameter for non-technical types
like me <grin>). I recently took a cross country where I had the plane
loaded to within 250 lbs of gross (1250 lbs of fuel, people and camping
gear). During the initial flight I found myself having to hold perhaps
10 lbs of forward pressure on the stick even with full down elevator
trim.

Upon investigating, I found the threaded rod was bending into a slight
"U" shape. With just a little bit of pressure to bend it straight, the
rod snapped. I'm glad this happened on the ground rather than flying or
things would have been very interesting indeed. It's clear the rod size
is inadequate for the elevator incidence and gross-weight flying
characteristics of the Moose.

Needing to make a field repair, I found the same size rod at a local
hardware store. I however, slid a thin steel tube on the outside of the
rod to provide more strength. Thus far, after 7 hours of flight, the
updated rod seems to be holding well.

Clearly the weak point now is where the rod attaches on each end to the
elevator tab and the servo. I thought about getting a larger stock rod
and having it's ends machined down to fit the existing elevator trim tab
attach point and the servo attach point. However, this would
essentially leave me with the same weak point as I have now with the
sleeve and existing rod. Without having an expensive end-to-end custom
part made, does anyone have any other idea other than leaving things as
I've repaired them and inspecting them regularly?

I'll try to remember to take a digital picture of the updated rod with
sleeve in the next day or two and post it to the site.

Thanks,

Ted Waltman
Moose N142SR




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[Ted Waltman]

That would be the way to go I guess--that being the solid rod with slots
in each end. It snapped close to the middle. The rod is about 7" long
total with 5.25" in the 'open' between the two threaded/slotted plastic
ends.

Ted

-----Original Message-----
From: mike.davis@dcsol.com [mailto:mike.davis@dcsol.com] On Behalf Of
Scott Aldrich
Sent: Monday, July 12, 2004 3:39 PM
To: rebel-builders@dcsol.com
Subject: RE: Elevator trim-tab rod failure


That sounds like the standard rod that comes with the MAC or Ray Allen
servo.

Where did it snap? Near the clevis?

The instructions mention not using a longer threaded rod.

I am thinking maybe changing to a solid, no thread, stainless steel rod
with slots cut in each end. Just use the threaded rod for measurement.

Scott
Moose 174

-----Original Message-----
From: mike.davis@dcsol.com [mailto:mike.davis@dcsol.com] On Behalf Of
Ted Waltman
Sent: Monday, July 12, 2004 3:26 PM
To: rebel-builders@dcsol.com
Cc: murtech@murphyair.com; rdyck@murphyair.com
Subject: Elevator trim-tab rod failure

Folks,

My elevator trim-tab was connected to the trim servo using about a 7"
long 8x32 threaded rod (that's 1/4" diameter for non-technical types
like me <grin>). I recently took a cross country where I had the plane
loaded to within 250 lbs of gross (1250 lbs of fuel, people and camping
gear). During the initial flight I found myself having to hold perhaps
10 lbs of forward pressure on the stick even with full down elevator
trim.

Upon investigating, I found the threaded rod was bending into a slight
"U" shape. With just a little bit of pressure to bend it straight, the
rod snapped. I'm glad this happened on the ground rather than flying or
things would have been very interesting indeed. It's clear the rod size
is inadequate for the elevator incidence and gross-weight flying
characteristics of the Moose.

Needing to make a field repair, I found the same size rod at a local
hardware store. I however, slid a thin steel tube on the outside of the
rod to provide more strength. Thus far, after 7 hours of flight, the
updated rod seems to be holding well.

Clearly the weak point now is where the rod attaches on each end to the
elevator tab and the servo. I thought about getting a larger stock rod
and having it's ends machined down to fit the existing elevator trim tab
attach point and the servo attach point. However, this would
essentially leave me with the same weak point as I have now with the
sleeve and existing rod. Without having an expensive end-to-end custom
part made, does anyone have any other idea other than leaving things as
I've repaired them and inspecting them regularly?

I'll try to remember to take a digital picture of the updated rod with
sleeve in the next day or two and post it to the site.

Thanks,

Ted Waltman
Moose N142SR




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[Mnleber]

Try getting a plain rod and only threading portion you need. the thread roots in middle of rod provide areas of potential fatigue stress and effectively make the rod "thinner" throughout its length providing an easier means of bending.

I liked your sleeve idea!!

Mike LeBer R683


In a message dated Jul/12/2004 4:26:15 PM Eastern Standard Time, "Ted Waltman" <tedwaltman@i1ci.com> writes:

[quote]Folks,

My elevator trim-tab was connected to the trim servo using about a 7"
long 8x32 threaded rod (that's 1/4" diameter for non-technical types
like me <grin>).

[Ken]

Hi Ted

This is a classic "buckling mode" failure. The rod is being compressed
and it bends or buckles. So the ends are not the problem. The problem is
that the center section of the rod needs to be thicker. You did exactly
the right thing to slip a tube over top of the threaded rod. Gluing that
on might be an acceptable permanent fix. For all
intents and purposes the ends are free to swivel and the center of the
rod has to be strong enough to resist buckling. The rod accepts load
until it becomes unstable and bends/buckles. Mike and you are correct
that the rod being threaded full length greatly reduces it's strength
and I would guess that a non threaded rod of the same diameter would
resist at least 3 times the load before failing in this application.
Your suggestion of threading the ends of a solid rod would also make the
rod several times stronger for this application. Taper the diameter down
to the threads gradually (not abruptly) if you can to reduce multiplying
the stresses at the diameter change.
_____
\/\/\/\/\
OK !
!
_____/\/\/\/\/

____
\__/\/\/\/\
Best !
__ !
____/ \/\/\/\/

A 3/16" (0.187") solid or hollow rod will be many times stronger than a
#8 threaded rod which is about 0.15" outer diameter but much smaller at
the narrowest point across the bottom of the threads. And that narrowest
point is further weakened by stress concentration due to the sudden
diameter change caused by the threads. That is why the second diagram
here is preferable as well as easier to machine..

As an aside, this case is the same reason why a hollow push pull tube is
almost as strong as a solid shaft. It is only the outside
diameter material that is efficiently loaded to resist bending.

Ken

Ted Waltman wrote:

Folks,

My elevator trim-tab was connected to the trim servo using about a 7"
long 8x32 threaded rod (that's 1/4" diameter for non-technical types
like me <grin>). I recently took a cross country where I had the plane
loaded to within 250 lbs of gross (1250 lbs of fuel, people and camping
gear). During the initial flight I found myself having to hold perhaps
10 lbs of forward pressure on the stick even with full down elevator
trim.

Upon investigating, I found the threaded rod was bending into a slight
"U" shape. With just a little bit of pressure to bend it straight, the
rod snapped. I'm glad this happened on the ground rather than flying or
things would have been very interesting indeed. It's clear the rod size
is inadequate for the elevator incidence and gross-weight flying
characteristics of the Moose.

Needing to make a field repair, I found the same size rod at a local
hardware store. I however, slid a thin steel tube on the outside of the
rod to provide more strength. Thus far, after 7 hours of flight, the
updated rod seems to be holding well.

Clearly the weak point now is where the rod attaches on each end to the
elevator tab and the servo. I thought about getting a larger stock rod
and having it's ends machined down to fit the existing elevator trim tab
attach point and the servo attach point. However, this would
essentially leave me with the same weak point as I have now with the
sleeve and existing rod. Without having an expensive end-to-end custom
part made, does anyone have any other idea other than leaving things as
I've repaired them and inspecting them regularly?

I'll try to remember to take a digital picture of the updated rod with
sleeve in the next day or two and post it to the site.

Thanks,

Ted Waltman
Moose N142SR

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[steveh]

Checked out my trim tab that we received with our Moose kit and found that a
piece of Alu. tubing came with the kit. The tube is to slipped over the rod
after you have adjusted the tab to the correct possision, than mark the rod
and remove from one end turn buckle, insert the tube and reconnect the turn
buckle to the correct possision. This will hopefully keep ti from bending in
the future.

Steve H
Moose 213



On 7/13/2004 4:32 AM, KLEHMAN@ALBEDO.NET wrote to REBEL-BUILDERS:

-> Received: by dcsol.com (Wildcat! SMTP Router v6.0.451.1)
-> for rebel-builders@dcsol.com; Tue, 13 Jul 2004 04:30:57 -0800
-> Received: from juliet.albedo.net ([206.51.22.2]) EHLO=juliet.albedo.net
-> by dcsol.com (Wildcat! SMTP v6.0.451.1) with SMTP
-> id 332935796; Tue, 13 Jul 2004 04:30:56 -0800
-> Received-SPF: neutral (dcsol.com: 206.51.22.2 is neither
-> permitted nor denied by domain of klehman@albedo.net)
-> Received: from albedo.net (ppp147.albedo.net [206.51.22.147])
-> (authenticated bits=0)
-> by juliet.albedo.net (8.12.11/8.12.3) with ESMTP id i6DCUnDH010726
-> for <rebel-builders@dcsol.com>; Tue, 13 Jul 2004 08:30:50 -0400
-> Message-ID: <40F3D658.50000@albedo.net>
-> Date: Tue, 13 Jul 2004 08:32:24 -0400
-> From: Ken <klehman@albedo.net>
-> User-Agent: Mozilla/5.0 (Windows; U; Win98; en-US; rv:1.0.2) Gecko/20021120
Netscape/7.01
-> X-Accept-Language: en-us, en
-> X-Orig-MIME-Version: 1.0
-> To: rebel-builders@dcsol.com
-> Subject: Re: Elevator trim-tab rod failure
-> References: <002301c46856$dd624e60$6b7ba8c0@trader>
-> X-Orig-Content-Type: text/plain; charset=us-ascii; format=flowed
-> X-Orig-Content-Transfer-Encoding: 7bit
-> X-Virus-Scanned: clamd / ClamAV version 0.74, clamav-milter version 0.74a
-> on juliet
-> X-Virus-Status: Clean
->
-> Hi Ted
->
-> This is a classic "buckling mode" failure. The rod is being compressed
-> and it bends or buckles. So the ends are not the problem. The problem is
-> that the center section of the rod needs to be thicker. You did exactly
-> the right thing to slip a tube over top of the threaded rod. Gluing that
-> on might be an acceptable permanent fix. For all
-> intents and purposes the ends are free to swivel and the center of the
-> rod has to be strong enough to resist buckling. The rod accepts load
-> until it becomes unstable and bends/buckles. Mike and you are correct
-> that the rod being threaded full length greatly reduces it's strength
-> and I would guess that a non threaded rod of the same diameter would
-> resist at least 3 times the load before failing in this application.
-> Your suggestion of threading the ends of a solid rod would also make the
-> rod several times stronger for this application. Taper the diameter down
-> to the threads gradually (not abruptly) if you can to reduce multiplying
-> the stresses at the diameter change.
-> _____
-> \/\/\/\/\
-> OK !
-> !
-> _____/\/\/\/\/
->
-> ____
-> \__/\/\/\/\
-> Best !
-> __ !
-> ____/ \/\/\/\/
->
-> A 3/16" (0.187") solid or hollow rod will be many times stronger than a
-> #8 threaded rod which is about 0.15" outer diameter but much smaller at
-> the narrowest point across the bottom of the threads. And that narrowest
-> point is further weakened by stress concentration due to the sudden
-> diameter change caused by the threads. That is why the second diagram
-> here is preferable as well as easier to machine..
->
-> As an aside, this case is the same reason why a hollow push pull tube is
-> almost as strong as a solid shaft. It is only the outside
-> diameter material that is efficiently loaded to resist bending.
->
-> Ken
->
-> Ted Waltman wrote:
->
-> >Folks,
-> >
-> >My elevator trim-tab was connected to the trim servo using about a 7"
-> >long 8x32 threaded rod (that's 1/4" diameter for non-technical types
-> >like me <grin>). I recently took a cross country where I had the plane
-> >loaded to within 250 lbs of gross (1250 lbs of fuel, people and camping
-> >gear). During the initial flight I found myself having to hold perhaps
-> >10 lbs of forward pressure on the stick even with full down elevator
-> >trim.
-> >
-> >Upon investigating, I found the threaded rod was bending into a slight
-> >"U" shape. With just a little bit of pressure to bend it straight, the
-> >rod snapped. I'm glad this happened on the ground rather than flying or
-> >things would have been very interesting indeed. It's clear the rod size
-> >is inadequate for the elevator incidence and gross-weight flying
-> >characteristics of the Moose.
-> >
-> >Needing to make a field repair, I found the same size rod at a local
-> >hardware store. I however, slid a thin steel tube on the outside of the
-> >rod to provide more strength. Thus far, after 7 hours of flight, the
-> >updated rod seems to be holding well.
-> >
-> >Clearly the weak point now is where the rod attaches on each end to the
-> >elevator tab and the servo. I thought about getting a larger stock rod
-> >and having it's ends machined down to fit the existing elevator trim tab
-> >attach point and the servo attach point. However, this would
-> >essentially leave me with the same weak point as I have now with the
-> >sleeve and existing rod. Without having an expensive end-to-end custom
-> >part made, does anyone have any other idea other than leaving things as
-> >I've repaired them and inspecting them regularly?
-> >
-> >I'll try to remember to take a digital picture of the updated rod with
-> >sleeve in the next day or two and post it to the site.
-> >
-> >Thanks,
-> >
-> >Ted Waltman
-> >Moose N142SR
->
->
->





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[Scott Aldrich]

Interesting. The aluminum tube was in the servo box? I just checked the
Ray Allen site and there is no mention there of anything other than the
standard SS threaded rod.

If someone at MAM knows enough about it to put a tube in the box you'd think
they would mention it to the rest of us. Maybe I just missed it on the very
"up to date" tech support page...

Scott
Moose 174

-----Original Message-----
From: mike.davis@dcsol.com [mailto:mike.davis@dcsol.com] On Behalf Of
steveh@dcsol.com
Sent: Sunday, July 18, 2004 8:38 PM
To: rebel-builders@dcsol.com
Subject: Re: Elevator trim-tab rod failure

Checked out my trim tab that we received with our Moose kit and found that a

piece of Alu. tubing came with the kit. The tube is to slipped over the rod

after you have adjusted the tab to the correct possision, than mark the rod
and remove from one end turn buckle, insert the tube and reconnect the turn
buckle to the correct possision. This will hopefully keep ti from bending
in
the future.

Steve H
Moose 213



On 7/13/2004 4:32 AM, KLEHMAN@ALBEDO.NET wrote to REBEL-BUILDERS:

-> Received: by dcsol.com (Wildcat! SMTP Router v6.0.451.1)
-> for rebel-builders@dcsol.com; Tue, 13 Jul 2004 04:30:57 -0800
-> Received: from juliet.albedo.net ([206.51.22.2]) EHLO=juliet.albedo.net
-> by dcsol.com (Wildcat! SMTP v6.0.451.1) with SMTP
-> id 332935796; Tue, 13 Jul 2004 04:30:56 -0800
-> Received-SPF: neutral (dcsol.com: 206.51.22.2 is neither
-> permitted nor denied by domain of
klehman@albedo.net)
-> Received: from albedo.net (ppp147.albedo.net [206.51.22.147])
-> (authenticated bits=0)
-> by juliet.albedo.net (8.12.11/8.12.3) with ESMTP id i6DCUnDH010726
-> for <rebel-builders@dcsol.com>; Tue, 13 Jul 2004 08:30:50 -0400
-> Message-ID: <40F3D658.50000@albedo.net>
-> Date: Tue, 13 Jul 2004 08:32:24 -0400
-> From: Ken <klehman@albedo.net>
-> User-Agent: Mozilla/5.0 (Windows; U; Win98; en-US; rv:1.0.2)
Gecko/20021120
Netscape/7.01
-> X-Accept-Language: en-us, en
-> X-Orig-MIME-Version: 1.0
-> To: rebel-builders@dcsol.com
-> Subject: Re: Elevator trim-tab rod failure
-> References: <002301c46856$dd624e60$6b7ba8c0@trader>
-> X-Orig-Content-Type: text/plain; charset=us-ascii; format=flowed
-> X-Orig-Content-Transfer-Encoding: 7bit
-> X-Virus-Scanned: clamd / ClamAV version 0.74, clamav-milter version 0.74a
-> on juliet
-> X-Virus-Status: Clean
->
-> Hi Ted
->
-> This is a classic "buckling mode" failure. The rod is being compressed
-> and it bends or buckles. So the ends are not the problem. The problem is
-> that the center section of the rod needs to be thicker. You did exactly
-> the right thing to slip a tube over top of the threaded rod. Gluing that
-> on might be an acceptable permanent fix. For all
-> intents and purposes the ends are free to swivel and the center of the
-> rod has to be strong enough to resist buckling. The rod accepts load
-> until it becomes unstable and bends/buckles. Mike and you are correct
-> that the rod being threaded full length greatly reduces it's strength
-> and I would guess that a non threaded rod of the same diameter would
-> resist at least 3 times the load before failing in this application.
-> Your suggestion of threading the ends of a solid rod would also make the
-> rod several times stronger for this application. Taper the diameter down
-> to the threads gradually (not abruptly) if you can to reduce multiplying
-> the stresses at the diameter change.
-> _____
-> \/\/\/\/\
-> OK !
-> !
-> _____/\/\/\/\/
->
-> ____
-> \__/\/\/\/\
-> Best !
-> __ !
-> ____/ \/\/\/\/
->
-> A 3/16" (0.187") solid or hollow rod will be many times stronger than a
-> #8 threaded rod which is about 0.15" outer diameter but much smaller at
-> the narrowest point across the bottom of the threads. And that narrowest
-> point is further weakened by stress concentration due to the sudden
-> diameter change caused by the threads. That is why the second diagram
-> here is preferable as well as easier to machine..
->
-> As an aside, this case is the same reason why a hollow push pull tube is
-> almost as strong as a solid shaft. It is only the outside
-> diameter material that is efficiently loaded to resist bending.
->
-> Ken
->
-> Ted Waltman wrote:
->
-> >Folks,
-> >
-> >My elevator trim-tab was connected to the trim servo using about a 7"
-> >long 8x32 threaded rod (that's 1/4" diameter for non-technical types
-> >like me <grin>). I recently took a cross country where I had the
plane
-> >loaded to within 250 lbs of gross (1250 lbs of fuel, people and
camping
-> >gear). During the initial flight I found myself having to hold
perhaps
-> >10 lbs of forward pressure on the stick even with full down elevator
-> >trim.
-> >
-> >Upon investigating, I found the threaded rod was bending into a
slight
-> >"U" shape. With just a little bit of pressure to bend it straight,
the
-> >rod snapped. I'm glad this happened on the ground rather than flying
or
-> >things would have been very interesting indeed. It's clear the rod
size
-> >is inadequate for the elevator incidence and gross-weight flying
-> >characteristics of the Moose.
-> >
-> >Needing to make a field repair, I found the same size rod at a local
-> >hardware store. I however, slid a thin steel tube on the outside of
the
-> >rod to provide more strength. Thus far, after 7 hours of flight, the
-> >updated rod seems to be holding well.
-> >
-> >Clearly the weak point now is where the rod attaches on each end to
the
-> >elevator tab and the servo. I thought about getting a larger stock
rod
-> >and having it's ends machined down to fit the existing elevator trim
tab
-> >attach point and the servo attach point. However, this would
-> >essentially leave me with the same weak point as I have now with the
-> >sleeve and existing rod. Without having an expensive end-to-end
custom
-> >part made, does anyone have any other idea other than leaving things
as
-> >I've repaired them and inspecting them regularly?
-> >
-> >I'll try to remember to take a digital picture of the updated rod
with
-> >sleeve in the next day or two and post it to the site.
-> >
-> >Thanks,
-> >
-> >Ted Waltman
-> >Moose N142SR
->
->
->





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[steveh]

The tube came packed in the "Ray Allen" box with the servo and indicator.
I thought that it was part of the kit! ! !

Steve H
Moose 213


On 7/18/2004 8:17 PM, SA@MWUTAH.COM wrote to REBEL-BUILDERS:

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-> for rebel-builders@dcsol.com; Sun, 18 Jul 2004 20:19:02 -0800
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-> by dcsol.com (Wildcat! SMTP v6.0.451.1) with SMTP
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-> Received: from localhost (localhost [127.0.0.1])
-> by mail.mwutah.com (mwutah.com) with ESMTP id 1A95914004D
-> for <rebel-builders@dcsol.com>; Sun, 18 Jul 2004 22:17:35 -0600 (MDT)
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-> by localhost (brother [127.0.0.1]) (amavisd-new, port 10024)
-> with ESMTP id 03557-05 for <rebel-builders@dcsol.com>;
-> Sun, 18 Jul 2004 22:17:34 -0600 (MDT)
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-> by mail.mwutah.com (mwutah.com) with ESMTP id 431BF14003D
-> for <rebel-builders@dcsol.com>; Sun, 18 Jul 2004 22:17:34 -0600 (MDT)
-> From: "Scott Aldrich" <sa@mwutah.com>
-> To: <rebel-builders@dcsol.com>
-> Subject: RE: Elevator trim-tab rod failure
-> Date: Sun, 18 Jul 2004 22:17:59 -0600
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->
-> Interesting. The aluminum tube was in the servo box? I just checked the
-> Ray Allen site and there is no mention there of anything other than the
-> standard SS threaded rod.
->
-> If someone at MAM knows enough about it to put a tube in the box you'd think
-> they would mention it to the rest of us. Maybe I just missed it on the very
-> "up to date" tech support page...
->
-> Scott
-> Moose 174
->
-> -----Original Message-----
-> From: mike.davis@dcsol.com [mailto:mike.davis@dcsol.com] On Behalf Of
-> steveh@dcsol.com
-> Sent: Sunday, July 18, 2004 8:38 PM
-> To: rebel-builders@dcsol.com
-> Subject: Re: Elevator trim-tab rod failure
->
-> Checked out my trim tab that we received with our Moose kit and found that a
->
-> piece of Alu. tubing came with the kit. The tube is to slipped over the rod
->
-> after you have adjusted the tab to the correct possision, than mark the rod
-> and remove from one end turn buckle, insert the tube and reconnect the turn
-> buckle to the correct possision. This will hopefully keep ti from bending
-> in
-> the future.
->
-> Steve H
-> Moose 213
->
->
->
-> On 7/13/2004 4:32 AM, KLEHMAN@ALBEDO.NET wrote to REBEL-BUILDERS:
->
-> -> Received: by dcsol.com (Wildcat! SMTP Router v6.0.451.1)
-> -> for rebel-builders@dcsol.com; Tue, 13 Jul 2004 04:30:57 -0800
-> -> Received: from juliet.albedo.net ([206.51.22.2]) EHLO=juliet.albedo.net
-> -> by dcsol.com (Wildcat! SMTP v6.0.451.1) with SMTP
-> -> id 332935796; Tue, 13 Jul 2004 04:30:56 -0800
-> -> Received-SPF: neutral (dcsol.com: 206.51.22.2 is neither
-> -> permitted nor denied by domain of
-> klehman@albedo.net)
-> -> Received: from albedo.net (ppp147.albedo.net [206.51.22.147])
-> -> (authenticated bits=0)
-> -> by juliet.albedo.net (8.12.11/8.12.3) with ESMTP id i6DCUnDH010726
-> -> for <rebel-builders@dcsol.com>; Tue, 13 Jul 2004 08:30:50 -0400
-> -> Message-ID: <40F3D658.50000@albedo.net>
-> -> Date: Tue, 13 Jul 2004 08:32:24 -0400
-> -> From: Ken <klehman@albedo.net>
-> -> User-Agent: Mozilla/5.0 (Windows; U; Win98; en-US; rv:1.0.2)
-> Gecko/20021120
-> Netscape/7.01
-> -> X-Accept-Language: en-us, en
-> -> X-Orig-MIME-Version: 1.0
-> -> To: rebel-builders@dcsol.com
-> -> Subject: Re: Elevator trim-tab rod failure
-> -> References: <002301c46856$dd624e60$6b7ba8c0@trader>
-> -> X-Orig-Content-Type: text/plain; charset=us-ascii; format=flowed
-> -> X-Orig-Content-Transfer-Encoding: 7bit
-> -> X-Virus-Scanned: clamd / ClamAV version 0.74, clamav-milter version 0.74a
-> -> on juliet
-> -> X-Virus-Status: Clean
-> ->
-> -> Hi Ted
-> ->
-> -> This is a classic "buckling mode" failure. The rod is being compressed
-> -> and it bends or buckles. So the ends are not the problem. The problem is
-> -> that the center section of the rod needs to be thicker. You did exactly
-> -> the right thing to slip a tube over top of the threaded rod. Gluing that
-> -> on might be an acceptable permanent fix. For all
-> -> intents and purposes the ends are free to swivel and the center of the
-> -> rod has to be strong enough to resist buckling. The rod accepts load
-> -> until it becomes unstable and bends/buckles. Mike and you are correct
-> -> that the rod being threaded full length greatly reduces it's strength
-> -> and I would guess that a non threaded rod of the same diameter would
-> -> resist at least 3 times the load before failing in this application.
-> -> Your suggestion of threading the ends of a solid rod would also make the
-> -> rod several times stronger for this application. Taper the diameter down
-> -> to the threads gradually (not abruptly) if you can to reduce multiplying
-> -> the stresses at the diameter change.
-> -> _____
-> -> \/\/\/\/\
-> -> OK !
-> -> !
-> -> _____/\/\/\/\/
-> ->
-> -> ____
-> -> \__/\/\/\/\
-> -> Best !
-> -> __ !
-> -> ____/ \/\/\/\/
-> ->
-> -> A 3/16" (0.187") solid or hollow rod will be many times stronger than a
-> -> #8 threaded rod which is about 0.15" outer diameter but much smaller at
-> -> the narrowest point across the bottom of the threads. And that narrowest
-> -> point is further weakened by stress concentration due to the sudden
-> -> diameter change caused by the threads. That is why the second diagram
-> -> here is preferable as well as easier to machine..
-> ->
-> -> As an aside, this case is the same reason why a hollow push pull tube is
-> -> almost as strong as a solid shaft. It is only the outside
-> -> diameter material that is efficiently loaded to resist bending.
-> ->
-> -> Ken
-> ->
-> -> Ted Waltman wrote:
-> ->
-> -> >Folks,
-> -> >
-> -> >My elevator trim-tab was connected to the trim servo using about a 7"
-> -> >long 8x32 threaded rod (that's 1/4" diameter for non-technical types
-> -> >like me <grin>). I recently took a cross country where I had the
-> plane
-> -> >loaded to within 250 lbs of gross (1250 lbs of fuel, people and
-> camping
-> -> >gear). During the initial flight I found myself having to hold
-> perhaps
-> -> >10 lbs of forward pressure on the stick even with full down elevator
-> -> >trim.
-> -> >
-> -> >Upon investigating, I found the threaded rod was bending into a
-> slight
-> -> >"U" shape. With just a little bit of pressure to bend it straight,
-> the
-> -> >rod snapped. I'm glad this happened on the ground rather than flying
-> or
-> -> >things would have been very interesting indeed. It's clear the rod
-> size
-> -> >is inadequate for the elevator incidence and gross-weight flying
-> -> >characteristics of the Moose.
-> -> >
-> -> >Needing to make a field repair, I found the same size rod at a local
-> -> >hardware store. I however, slid a thin steel tube on the outside of
-> the
-> -> >rod to provide more strength. Thus far, after 7 hours of flight, the
-> -> >updated rod seems to be holding well.
-> -> >
-> -> >Clearly the weak point now is where the rod attaches on each end to
-> the
-> -> >elevator tab and the servo. I thought about getting a larger stock
-> rod
-> -> >and having it's ends machined down to fit the existing elevator trim
-> tab
-> -> >attach point and the servo attach point. However, this would
-> -> >essentially leave me with the same weak point as I have now with the
-> -> >sleeve and existing rod. Without having an expensive end-to-end
-> custom
-> -> >part made, does anyone have any other idea other than leaving things
-> as
-> -> >I've repaired them and inspecting them regularly?
-> -> >
-> -> >I'll try to remember to take a digital picture of the updated rod
-> with
-> -> >sleeve in the next day or two and post it to the site.
-> -> >
-> -> >Thanks,
-> -> >
-> -> >Ted Waltman
-> -> >Moose N142SR
-> ->
-> ->
-> ->
->
->
->
->
->
-> -----------------------------------------------------
-> List archives located at:
-> https://www.dcsol.com/default.htm
-> username "rebel" password "builder"
-> Subscription services located at:
-> https://www.dcsol.com/public/code/html-subscribe.htm
-> List administrator: mike.davis@dcsol.com
-> -----------------------------------------------------
->
->
->





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[Scott Aldrich]

It must be now, even though no mention of it on their site. Just talked
with another builder only one serial number from my kit and he has the
sleeve also.

Scott

-----Original Message-----
From: mike.davis@dcsol.com [mailto:mike.davis@dcsol.com] On Behalf Of
steveh@dcsol.com
Sent: Monday, July 19, 2004 9:17 AM
To: rebel-builders@dcsol.com
Subject: RE: Elevator trim-tab rod failure

The tube came packed in the "Ray Allen" box with the servo and indicator.
I thought that it was part of the kit! ! !

Steve H
Moose 213


On 7/18/2004 8:17 PM, SA@MWUTAH.COM wrote to REBEL-BUILDERS:

-> Received: by dcsol.com (Wildcat! SMTP Router v6.0.451.1)
-> for rebel-builders@dcsol.com; Sun, 18 Jul 2004 20:19:02 -0800
-> Received: from mail.mwutah.com ([208.186.255.2]) EHLO=mail.mwutah.com
-> by dcsol.com (Wildcat! SMTP v6.0.451.1) with SMTP
-> id 217019953; Sun, 18 Jul 2004 20:19:01 -0800
-> Received: from localhost (localhost [127.0.0.1])
-> by mail.mwutah.com (mwutah.com) with ESMTP id 1A95914004D
-> for <rebel-builders@dcsol.com>; Sun, 18 Jul 2004 22:17:35 -0600 (MDT)
-> Received: from mail.mwutah.com ([127.0.0.1])
-> by localhost (brother [127.0.0.1]) (amavisd-new, port 10024)
-> with ESMTP id 03557-05 for <rebel-builders@dcsol.com>;
-> Sun, 18 Jul 2004 22:17:34 -0600 (MDT)
-> Received: from LEERE (unknown [208.186.255.7])
-> by mail.mwutah.com (mwutah.com) with ESMTP id 431BF14003D
-> for <rebel-builders@dcsol.com>; Sun, 18 Jul 2004 22:17:34 -0600 (MDT)
-> From: "Scott Aldrich" <sa@mwutah.com>
-> To: <rebel-builders@dcsol.com>
-> Subject: RE: Elevator trim-tab rod failure
-> Date: Sun, 18 Jul 2004 22:17:59 -0600
-> X-Orig-MIME-Version: 1.0
-> X-Orig-Content-Type: text/plain; charset="us-ascii"
-> X-Orig-Content-Transfer-Encoding: 7bit
-> X-Mailer: Microsoft Office Outlook, Build 11.0.5510
-> Thread-Index: AcRtOXZjOQw6ZsStQO+Iim6jLwr00gADJRTA
-> In-Reply-To: <1090204700@dcsol.com>
-> X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2800.1441
-> Message-Id: <20040719041734.431BF14003D@mail.mwutah.com>
-> X-Virus-Scanned: by amavisd-new-20030616-p9 (Debian) at example.com
->
-> Interesting. The aluminum tube was in the servo box? I just checked the
-> Ray Allen site and there is no mention there of anything other than the
-> standard SS threaded rod.
->
-> If someone at MAM knows enough about it to put a tube in the box you'd
think
-> they would mention it to the rest of us. Maybe I just missed it on the
very
-> "up to date" tech support page...
->
-> Scott
-> Moose 174
->
-> -----Original Message-----
-> From: mike.davis@dcsol.com [mailto:mike.davis@dcsol.com] On Behalf Of
-> steveh@dcsol.com
-> Sent: Sunday, July 18, 2004 8:38 PM
-> To: rebel-builders@dcsol.com
-> Subject: Re: Elevator trim-tab rod failure
->
-> Checked out my trim tab that we received with our Moose kit and found
that a
->
-> piece of Alu. tubing came with the kit. The tube is to slipped over the
rod
->
-> after you have adjusted the tab to the correct possision, than mark the
rod
-> and remove from one end turn buckle, insert the tube and reconnect the
turn
-> buckle to the correct possision. This will hopefully keep ti from
bending
-> in
-> the future.
->
-> Steve H
-> Moose 213
->
->
->
-> On 7/13/2004 4:32 AM, KLEHMAN@ALBEDO.NET wrote to REBEL-BUILDERS:
->
-> -> Received: by dcsol.com (Wildcat! SMTP Router v6.0.451.1)
-> -> for rebel-builders@dcsol.com; Tue, 13 Jul 2004 04:30:57
-0800
-> -> Received: from juliet.albedo.net ([206.51.22.2])
EHLO=juliet.albedo.net
-> -> by dcsol.com (Wildcat! SMTP v6.0.451.1) with SMTP
-> -> id 332935796; Tue, 13 Jul 2004 04:30:56 -0800
-> -> Received-SPF: neutral (dcsol.com: 206.51.22.2 is neither
-> -> permitted nor denied by domain of
-> klehman@albedo.net)
-> -> Received: from albedo.net (ppp147.albedo.net [206.51.22.147])
-> -> (authenticated bits=0)
-> -> by juliet.albedo.net (8.12.11/8.12.3) with ESMTP id i6DCUnDH010726
-> -> for <rebel-builders@dcsol.com>; Tue, 13 Jul 2004 08:30:50 -0400
-> -> Message-ID: <40F3D658.50000@albedo.net>
-> -> Date: Tue, 13 Jul 2004 08:32:24 -0400
-> -> From: Ken <klehman@albedo.net>
-> -> User-Agent: Mozilla/5.0 (Windows; U; Win98; en-US; rv:1.0.2)
-> Gecko/20021120
-> Netscape/7.01
-> -> X-Accept-Language: en-us, en
-> -> X-Orig-MIME-Version: 1.0
-> -> To: rebel-builders@dcsol.com
-> -> Subject: Re: Elevator trim-tab rod failure
-> -> References: <002301c46856$dd624e60$6b7ba8c0@trader>
-> -> X-Orig-Content-Type: text/plain; charset=us-ascii; format=flowed
-> -> X-Orig-Content-Transfer-Encoding: 7bit
-> -> X-Virus-Scanned: clamd / ClamAV version 0.74, clamav-milter version
0.74a
-> -> on juliet
-> -> X-Virus-Status: Clean
-> ->
-> -> Hi Ted
-> ->
-> -> This is a classic "buckling mode" failure. The rod is being compressed
-> -> and it bends or buckles. So the ends are not the problem. The problem
is
-> -> that the center section of the rod needs to be thicker. You did
exactly
-> -> the right thing to slip a tube over top of the threaded rod. Gluing
that
-> -> on might be an acceptable permanent fix. For all
-> -> intents and purposes the ends are free to swivel and the center of the
-> -> rod has to be strong enough to resist buckling. The rod accepts load
-> -> until it becomes unstable and bends/buckles. Mike and you are correct
-> -> that the rod being threaded full length greatly reduces it's strength
-> -> and I would guess that a non threaded rod of the same diameter would
-> -> resist at least 3 times the load before failing in this application.
-> -> Your suggestion of threading the ends of a solid rod would also make
the
-> -> rod several times stronger for this application. Taper the diameter
down
-> -> to the threads gradually (not abruptly) if you can to reduce
multiplying
-> -> the stresses at the diameter change.
-> -> _____
-> -> \/\/\/\/\
-> -> OK !
-> -> !
-> -> _____/\/\/\/\/
-> ->
-> -> ____
-> -> \__/\/\/\/\
-> -> Best !
-> -> __ !
-> -> ____/ \/\/\/\/
-> ->
-> -> A 3/16" (0.187") solid or hollow rod will be many times stronger than
a
-> -> #8 threaded rod which is about 0.15" outer diameter but much smaller
at
-> -> the narrowest point across the bottom of the threads. And that
narrowest
-> -> point is further weakened by stress concentration due to the sudden
-> -> diameter change caused by the threads. That is why the second diagram
-> -> here is preferable as well as easier to machine..
-> ->
-> -> As an aside, this case is the same reason why a hollow push pull tube
is
-> -> almost as strong as a solid shaft. It is only the outside
-> -> diameter material that is efficiently loaded to resist bending.
-> ->
-> -> Ken
-> ->
-> -> Ted Waltman wrote:
-> ->
-> -> >Folks,
-> -> >
-> -> >My elevator trim-tab was connected to the trim servo using about a
7"
-> -> >long 8x32 threaded rod (that's 1/4" diameter for non-technical
types
-> -> >like me <grin>). I recently took a cross country where I had the
-> plane
-> -> >loaded to within 250 lbs of gross (1250 lbs of fuel, people and
-> camping
-> -> >gear). During the initial flight I found myself having to hold
-> perhaps
-> -> >10 lbs of forward pressure on the stick even with full down
elevator
-> -> >trim.
-> -> >
-> -> >Upon investigating, I found the threaded rod was bending into a
-> slight
-> -> >"U" shape. With just a little bit of pressure to bend it
straight,
-> the
-> -> >rod snapped. I'm glad this happened on the ground rather than
flying
-> or
-> -> >things would have been very interesting indeed. It's clear the
rod
-> size
-> -> >is inadequate for the elevator incidence and gross-weight flying
-> -> >characteristics of the Moose.
-> -> >
-> -> >Needing to make a field repair, I found the same size rod at a
local
-> -> >hardware store. I however, slid a thin steel tube on the outside
of
-> the
-> -> >rod to provide more strength. Thus far, after 7 hours of flight,
the
-> -> >updated rod seems to be holding well.
-> -> >
-> -> >Clearly the weak point now is where the rod attaches on each end
to
-> the
-> -> >elevator tab and the servo. I thought about getting a larger
stock
-> rod
-> -> >and having it's ends machined down to fit the existing elevator
trim
-> tab
-> -> >attach point and the servo attach point. However, this would
-> -> >essentially leave me with the same weak point as I have now with
the
-> -> >sleeve and existing rod. Without having an expensive end-to-end
-> custom
-> -> >part made, does anyone have any other idea other than leaving
things
-> as
-> -> >I've repaired them and inspecting them regularly?
-> -> >
-> -> >I'll try to remember to take a digital picture of the updated rod
-> with
-> -> >sleeve in the next day or two and post it to the site.
-> -> >
-> -> >Thanks,
-> -> >
-> -> >Ted Waltman
-> -> >Moose N142SR
-> ->
-> ->
-> ->
->
->
->
->
->
-> -----------------------------------------------------
-> List archives located at:
-> https://www.dcsol.com/default.htm
-> username "rebel" password "builder"
-> Subscription services located at:
-> https://www.dcsol.com/public/code/html-subscribe.htm
-> List administrator: mike.davis@dcsol.com
-> -----------------------------------------------------
->
->
->





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List administrator: mike.davis@dcsol.com
-----------------------------------------------------






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