Elevator Trim over-ride

Mike Kimball · Post by **Mike Kimball** » Sat Feb 18, 2012 2:45 pm

Has anyone with a flying Super Rebel / Moose ever ran the elevator trim
servo to it's limits in flight to see how hard it would be to over-ride a
runaway or broken trim servo? A conversation with Scott at Ray Allen got me
thinkin'. He wants me to trade in my MAC-8A servo for the newer, and
supposedly better constructed T3-12A servo. He also thinks that my plan to
use a T2-7A servo to move the aileron pivot block on the roof for aileron
droop is ambitious. He's afraid that the servo will be working too hard to
overcome aerodynamic forces on the block and will fail. Any opinions on the
aerodynamic forces acting on the block? Operationally, I will most likely
be in level flight whenever I am making changes to the droop. I.e., I'll be
deciding and setting the droop based on conditions while on downwind. That
also made me think about the fact that I have separated the aileron droop
function from the flaps. There has been some concern that it will be a
muscle man pull on the flap lever with my roof mounted system. At least I
have removed any force on the block that the ailerons might induce. Food
for thought.

Mike

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Brian Godden · Post by **Brian Godden** » Sat Feb 18, 2012 2:45 pm

Mike....it is impossible to override a full nose down position of the trim
in a Moose. Tried it during testing...very scary. Bob is absolutely correct
when he says fit a breaker and highlight it in red.
Brian

From: Mike Kimball <mkimball@gci.net>
Reply-To: <rebel-builders@dcsol.com>
To: Rebel Builder's List <rebel-builders@dcsol.com>
Subject: Elevator Trim over-ride
Date: Thu, 19 Jan 2006 20:08:35 -0900

Has anyone with a flying Super Rebel / Moose ever ran the elevator trim
servo to it's limits in flight to see how hard it would be to over-ride a
runaway or broken trim servo? A conversation with Scott at Ray Allen got
me
thinkin'. He wants me to trade in my MAC-8A servo for the newer, and
supposedly better constructed T3-12A servo. He also thinks that my plan to
use a T2-7A servo to move the aileron pivot block on the roof for aileron
droop is ambitious. He's afraid that the servo will be working too hard to
overcome aerodynamic forces on the block and will fail. Any opinions on
the
aerodynamic forces acting on the block? Operationally, I will most likely
be in level flight whenever I am making changes to the droop. I.e., I'll
be
deciding and setting the droop based on conditions while on downwind. That
also made me think about the fact that I have separated the aileron droop
function from the flaps. There has been some concern that it will be a
muscle man pull on the flap lever with my roof mounted system. At least I
have removed any force on the block that the ailerons might induce. Food
for thought.

Mike

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Dale Fultz · Post by **Dale Fultz** » Sat Feb 18, 2012 2:45 pm

Thanks for stepping in here finally and giving us some good feedback that we
all need. Thanks again Brian. Dale SR-033 Back to riveting

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Wayne G. O'Shea · Post by **Wayne G. O'Shea** » Sat Feb 18, 2012 2:45 pm

Then the question begs to be answered...does anyone use the full travel of
that HUGE trim tab in normal flight envelopes? The trim tab on my 4200lb
gross UTVA's is about 1/2 that size if that.......and I'd have a hard time
shoving the stick forward in that if it got stuck at even 1/2 travel nose up
and I wasn't coming into land immediately.

Cheers,
Wayne

----- Original Message -----
From: "Dale Fultz" <dfultz17086@earthlink.net>
To: <rebel-builders@dcsol.com>
Sent: Friday, January 20, 2006 10:07 PM
Subject: Re: Elevator Trim over-ride

Thanks for stepping in here finally and giving us some good feedback that

we

all need. Thanks again Brian. Dale SR-033 Back to riveting

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Robert and Olga Johnson · Post by **Robert and Olga Johnson** » Sat Feb 18, 2012 2:45 pm

I was really surprised to see this response and find it hard to believe if
this condition exists, that Murphy would not caution builders and/ or build
in a limiting stop. When I first flew my Rebel I checked full travel of the
trim in both directions to make sure I could still maintain control should a
trim runaway occur. - No problem with the Rebel, although I would be landing
as soon as possible.Thank God ( I mean Mike) that this site exists so we may
all learn and hopefully avoid this potensionally disastrous condition. Just
my $0.02 Cdn worth. Bob J

----- Original Message -----
From: "Brian Godden" <brian_godden@hotmail.com>
To: <rebel-builders@dcsol.com>
Sent: Friday, January 20, 2006 9:37 PM
Subject: RE: Elevator Trim over-ride

Mike....it is impossible to override a full nose down position of the trim
in a Moose. Tried it during testing...very scary. Bob is absolutely
correct
when he says fit a breaker and highlight it in red.
Brian

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Brian Godden · Post by **Brian Godden** » Sat Feb 18, 2012 2:45 pm

Good question Wayne...compare the Elite elevator (identical, just smaller)
and it's trim tab. The Elite's trim is much smaller in chord, and no problem
to override. Trouble is the spades are too big!! You do need almost full
nose up trim in a radial Moose during approach, but builders should limit
the nose down travel....from memory I just set it at 6 degrees.

From: "Wayne G. O'Shea" <oifa@irishfield.on.ca>
Reply-To: <rebel-builders@dcsol.com>
To: <rebel-builders@dcsol.com>
Subject: Re: Elevator Trim over-ride
Date: Sat, 21 Jan 2006 00:35:13 -0500

Then the question begs to be answered...does anyone use the full travel of
that HUGE trim tab in normal flight envelopes? The trim tab on my 4200lb
gross UTVA's is about 1/2 that size if that.......and I'd have a hard time
shoving the stick forward in that if it got stuck at even 1/2 travel nose
up
and I wasn't coming into land immediately.

Cheers,
Wayne

----- Original Message -----
From: "Dale Fultz" <dfultz17086@earthlink.net>
To: <rebel-builders@dcsol.com>
Sent: Friday, January 20, 2006 10:07 PM
Subject: Re: Elevator Trim over-ride

Thanks for stepping in here finally and giving us some good feedback
that
we
all need. Thanks again Brian. Dale SR-033 Back to riveting

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CWS1932 · Post by **CWS1932** » Sat Feb 18, 2012 2:45 pm

To prevent a runaway trim (elevator and rudder) I installed red-guarded
cut-off switches to disable trim system in event of a runaway (removes power from
the trim system). Same type systems used on 727's, etc.
Charlie Starr SR-2500

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Wayne G. O'Shea · Post by **Wayne G. O'Shea** » Sat Feb 18, 2012 2:45 pm

I don't mean to "rain"...but I doubt anyone will get a breaker pulled or
switch shut off in the time period it takes to go full travel on the trim
and you've figured out WTF is going on.

Flight test..find trim limits you can man handle...and then set the servo
limits to match.

Cheers,
Wayne

----- Original Message -----
From: <CWS1932@aol.com>
To: <rebel-builders@dcsol.com>
Sent: Saturday, January 21, 2006 10:40 AM
Subject: Re: Elevator Trim over-ride

To prevent a runaway trim (elevator and rudder) I installed red-guarded
cut-off switches to disable trim system in event of a runaway (removes

power from

the trim system). Same type systems used on 727's, etc.
Charlie Starr SR-2500

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Bill Delcambre · Post by **Bill Delcambre** » Sat Feb 18, 2012 2:45 pm

It happened to me during climbout in a 210. It just kept winding up...
You'd be amazed how fast you can think!

I like Wayne's idea a lot better, though.

Bill

On 1/21/06, Wayne G. O'Shea <oifa@irishfield.on.ca> wrote:

I don't mean to "rain"...but I doubt anyone will get a breaker pulled or
switch shut off in the time period it takes to go full travel on the trim
and you've figured out WTF is going on.

Flight test..find trim limits you can man handle...and then set the servo
limits to match.

Cheers,
Wayne

----- Original Message -----
From: <CWS1932@aol.com>
To: <rebel-builders@dcsol.com>
Sent: Saturday, January 21, 2006 10:40 AM
Subject: Re: Elevator Trim over-ride

To prevent a runaway trim (elevator and rudder) I installed red-guarded
cut-off switches to disable trim system in event of a runaway (removes
power from
the trim system). Same type systems used on 727's, etc.
Charlie Starr SR-2500

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Keith Kinden · Post by **Keith Kinden** » Sat Feb 18, 2012 2:45 pm

One simple answer to the trim problem is a double switch. I saw this done on
a customers airplane.
instead of the Mac rocker switch he used 2 toggle
switchs. one to run the Mac servo and one to power power the Mac switch.
pertty simple and quite fail safe, the chances of both switchs failing at
the same time are nill. For those who want the trim switch on the stick, you
could get a double rocker switch in place of your transmit switch, use the
down side for the radio and the upper for energizing the trim switch.
to operate the trim depress the power switch then move the trim switch.
Keith

-----Original Message-----
From: mike.davis@dcsol.com [mailto:mike.davis@dcsol.com]On Behalf Of
CWS1932@aol.com
Sent: Saturday, January 21, 2006 8:41 AM
To: rebel-builders@dcsol.com
Subject: Re: Elevator Trim over-ride

To prevent a runaway trim (elevator and rudder) I installed red-guarded
cut-off switches to disable trim system in event of a runaway (removes
power from
the trim system). Same type systems used on 727's, etc.
Charlie Starr SR-2500

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N.Smith · Post by **N.Smith** » Sat Feb 18, 2012 2:45 pm

For what it's worth, I plan to add a small audio source fed by the voltage
that feeds the servo, it will sound when ever the servo runs. If it runs
when I don't expect it I've got a red collar on the CB to trip it ASAP
Nig
745E

-----Original Message-----
From: mike.davis@dcsol.com [mailto:mike.davis@dcsol.com]On Behalf Of
Bill Delcambre
Sent: 21 January 2006 17:00
To: rebel-builders@dcsol.com
Subject: Re: Elevator Trim over-ride

It happened to me during climbout in a 210. It just kept winding up...
You'd be amazed how fast you can think!

I like Wayne's idea a lot better, though.

Bill

On 1/21/06, Wayne G. O'Shea <oifa@irishfield.on.ca> wrote:

I don't mean to "rain"...but I doubt anyone will get a breaker pulled or
switch shut off in the time period it takes to go full travel on the trim
and you've figured out WTF is going on.

Flight test..find trim limits you can man handle...and then set the servo
limits to match.

Cheers,
Wayne

----- Original Message -----
From: <CWS1932@aol.com>
To: <rebel-builders@dcsol.com>
Sent: Saturday, January 21, 2006 10:40 AM
Subject: Re: Elevator Trim over-ride

To prevent a runaway trim (elevator and rudder) I installed red-guarded
cut-off switches to disable trim system in event of a runaway (removes
power from
the trim system). Same type systems used on 727's, etc.
Charlie Starr SR-2500

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Mike Kimball · Post by **Mike Kimball** » Sat Feb 18, 2012 2:45 pm

I'll have to have another look at the servo. I didn't realize that the
limits are adjustable. Problem is, the servo is attached to the elevator
which is at my unheated hangar at the airport and it's 20 below during the
day. I don't wanna go look right now.

Mike

-----Original Message-----
From: mike.davis@dcsol.com [mailto:mike.davis@dcsol.com] On Behalf Of Wayne
G. O'Shea
Sent: Saturday, January 21, 2006 7:33 AM
To: rebel-builders@dcsol.com
Subject: Re: Elevator Trim over-ride

I don't mean to "rain"...but I doubt anyone will get a breaker pulled or
switch shut off in the time period it takes to go full travel on the trim
and you've figured out WTF is going on.

Flight test..find trim limits you can man handle...and then set the servo
limits to match.

Cheers,
Wayne

----- Original Message -----
From: <CWS1932@aol.com>
To: <rebel-builders@dcsol.com>
Sent: Saturday, January 21, 2006 10:40 AM
Subject: Re: Elevator Trim over-ride

To prevent a runaway trim (elevator and rudder) I installed red-guarded
cut-off switches to disable trim system in event of a runaway (removes

power from

the trim system). Same type systems used on 727's, etc.
Charlie Starr SR-2500

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Wayne G. O'Shea · Post by **Wayne G. O'Shea** » Sat Feb 18, 2012 2:45 pm

Pretty darn sure if you open the cover you can adjust the stops that hit the
limit switches.

----- Original Message -----
From: "Mike Kimball" <mkimball@gci.net>
To: <rebel-builders@dcsol.com>
Sent: Saturday, January 21, 2006 8:56 PM
Subject: RE: Elevator Trim over-ride

I'll have to have another look at the servo. I didn't realize that the
limits are adjustable. Problem is, the servo is attached to the elevator
which is at my unheated hangar at the airport and it's 20 below during the
day. I don't wanna go look right now.

Mike

-----Original Message-----
From: mike.davis@dcsol.com [mailto:mike.davis@dcsol.com] On Behalf Of

Wayne

G. O'Shea
Sent: Saturday, January 21, 2006 7:33 AM
To: rebel-builders@dcsol.com
Subject: Re: Elevator Trim over-ride

I don't mean to "rain"...but I doubt anyone will get a breaker pulled or
switch shut off in the time period it takes to go full travel on the trim
and you've figured out WTF is going on.

Flight test..find trim limits you can man handle...and then set the servo
limits to match.

Cheers,
Wayne

----- Original Message -----
From: <CWS1932@aol.com>
To: <rebel-builders@dcsol.com>
Sent: Saturday, January 21, 2006 10:40 AM
Subject: Re: Elevator Trim over-ride

To prevent a runaway trim (elevator and rudder) I installed red-guarded
cut-off switches to disable trim system in event of a runaway (removes
power from
the trim system). Same type systems used on 727's, etc.
Charlie Starr SR-2500

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