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what if? elevator trim tab runaway

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chris Sinfield

Joined: 28 Nov 2006
Posts: 270
Location: Sydney Australia

Posted: Thu Feb 28, 2008 2:30 am Post subject: what if? elevator trim tab runaway

Q. for those out flying their XL's. 



With the large elevator trim tab, if it was deflected full one way up or down, is it still controllable? I am fitting the Ray Allen Trim system and thinking about if one switches sticks. 



I may fit a CB to the trim power line and pull it to stop the trim run away  if required, rather than hide it with a fuse. What do others think?

Chris

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DaveG601XL

Joined: 27 Oct 2006
Posts: 351
Location: Cincinnati, Oh

Posted: Thu Feb 28, 2008 3:39 am Post subject: Re: what if? elevator trim tab runaway

Chris,



That is what I did.  I have few CB's and trim is one of them for the very reason that I could pull it if desired.



Good luck,

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_________________
David Gallagher
Cincinnati, OH area

davgray(at)sbcglobal.net
Guest

Posted: Thu Feb 28, 2008 4:22 am Post subject: what if? elevator trim tab runaway

Chris



I have the full span left side elevator trim tab.  When I get ham handed I

sometimes inadvertently activate the trim switches on the top of the control

stick.  It will get your attention but it is still controllable.  Same for

the aileron trim.

I have been at full deflection.  The first time it happened it took 10

seconds to diagnose what was causing it.

At normal flight speed it has the most authority.  At pattern speeds I need

to increase the trim setting on the aileron.



Time for full deflection is about 3 seconds.  By the time you notice it, it

will be at full deployment so pulling a fuse wouldn't help.  It will take

power to reverse the setting.  I think if it happened it would be an

irritation.  The controls are normally very light.



Gary Ray 601XL, 64 hrs TT

davgray(at)sbcglobal.net

---

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Al Hays

Joined: 01 Oct 2007
Posts: 42
Location: Gore, VA

Posted: Thu Feb 28, 2008 5:14 am Post subject: what if? elevator trim tab runaway

Listers,

FWTW, it seems to me that what might be no more than an irritation  

under most conditions could easily become one distraction too many in  

a busy airport environment or when dealing with other more  

challenging situations.  I'm putting in an order for the "Safety- 

Trim" system from TCW to use with Ray Allen servos in my ZenVair  

601XL (unfinished). Still haven't heard about anyone else having used  

it other than  Tim Olson's RV-10.   TCW's website is:   www.tcwtech.com

Al



On Feb 28, 2008, at 7:11 AM, Gary Ray wrote:



[quote] 



 Chris



 I have the full span left side elevator trim tab.  When I get ham  

 handed I

 sometimes inadvertently activate the trim switches on the top of  

 the control

 stick.  It will get your attention but it is still controllable.   

 Same for

 the aileron trim.

 I have been at full deflection.  The first time it happened it took 10

 seconds to diagnose what was causing it.

 At normal flight speed it has the most authority.  At pattern  

 speeds I need

 to increase the trim setting on the aileron.



 Time for full deflection is about 3 seconds.  By the time you  

 notice it, it

 will be at full deployment so pulling a fuse wouldn't help.  It  

 will take

 power to reverse the setting.  I think if it happened it would be an

 irritation.  The controls are normally very light.



 Gary Ray 601XL, 64 hrs TT

 davgray(at)sbcglobal.net

 ---

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dredmoody(at)cox.net
Guest

Posted: Fri Feb 29, 2008 4:24 pm Post subject: what if? elevator trim tab runaway

I second Dave Gallagher's advice regarding a CB for  the trim. The RAC instructions advise a 2amp fuse or breaker so buy a breaker  that can be shut off if the problem arises. That's what I did as  well.

  

 Dred

   [quote][b]

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psm(at)att.net
Guest

Posted: Sat Mar 01, 2008 10:32 pm Post subject: what if? elevator trim tab runaway

I don't see how a circuit breaker or fuse would help at all if you have run-away trim.  By the time you turn off the power to the trim servo, the trim will already be crashed into one end of the travel or the other.  Turning off the power just guarantees it will stay there.



 Fortunately, I have heard reports that it doesn't take super-human strength to overcome full limit trim.



 Paul

 XL fuselage



 

 At 10:59 AM 2/29/2008, you wrote:

 [quote]I second Dave Gallagher's advice regarding a CB for the trim. The RAC instructions advise a 2amp fuse or breaker so buy a breaker that can be shut off if the problem arises. That's what I did as well.

  

 Dred

 

 [b]

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tski0403(at)yahoo.com
Guest

Posted: Sun Mar 02, 2008 5:52 am Post subject: what if? elevator trim tab runaway

I have talked with some of the guys in my EAA group. most are RV's, and they said that a runaway does not happen that often, but they do run it to the limit and fly. They say it is not that difficult to control, just slow down and fly the plane. A breaker would be good to stop the servo from driving and burning out. Good luck Tom, saving for wings.



Paul Mulwitz <psm(at)att.net> wrote:   [quote]I don't see how a circuit breaker or fuse would help at all if you have run-away trim.  By the time you turn off the power to the trim servo, the trim will already be crashed into one end of the travel or the other.  Turning off the power just guarantees it will stay there.



Fortunately, I have heard reports that it doesn't take super-human strength to overcome full limit trim.



Paul

XL fuselage

At 10:59 AM 2/29/2008, you wrote:

     [quote][b]

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ifly4fun2(at)sbcglobal.ne
Guest

Posted: Mon Mar 03, 2008 6:41 pm Post subject: what if? elevator trim tab runaway

On some of the larger airplanes a "trim clacker" aural alert is sounded if the pitch trim is

manually or automatically activated for more then say three seconds to make the crew member aware

of this potential failure mode.  Time to install the aural warning box and an EICAS.  Just kidding

about the last part...



do not archive

Art

--- Paul Mulwitz <psm(at)att.net> wrote:



 	  Quote: 	
		   I don't see how a circuit breaker or fuse would help at all if you 

 have run-away trim.  By the time you turn off the power to the trim 

 servo, the trim will already be crashed into one end of the travel or 

 the other.  Turning off the power just guarantees it will stay there.

 

 Fortunately, I have heard reports that it doesn't take super-human 

 strength to overcome full limit trim.

 

 Paul

 XL fuselage

 

 

 At 10:59 AM 2/29/2008, you wrote:

 >I second Dave Gallagher's advice regarding a CB for the trim. The 

 >RAC instructions advise a 2amp fuse or breaker so buy a breaker that 

 >can be shut off if the problem arises. That's what I did as well.

 >

 >Dred

 >

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