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TRIM Disconnect Switch

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richard(at)talbots.net.au
Guest

Posted: Tue Nov 06, 2007 12:20 pm Post subject: TRIM Disconnect Switch

G’day Everyone,  

   

First let me start this discussion with how I would install manual trim systems in my RV 7 next time.  The servos, wiring, relays, stick grips and other associated issues are just not worth the trouble and cost IMO.  However, I have the things now so I am going to finish putting them in.  

   

I am fairly unhappy having an electric trim system in my aircraft without any manual system as I believe it is at risk of running away and cannot be manually returned to an in trim position.  My expectation is that it may be possible to catch it in the act and disable the trim system before it manages to get itself to full travel.  I believe this is virtually a requirement in the certified world, and I have lost count of the number of aircraft I have flown over the years with electric trim disabled.  I want the disconnect on the stick as I feel it may be difficult to find in a hurry if it is elsewhere.  

   

In order to alleviate this issue I propose to fit a “trim disconnect” switch to my Ray Allen G207 switch.  To date I have the four momentary push buttons for trim, another button for PTT, another for AP disconnect and a spare momentary switch.  I propose to use this for the Trim Disconnect.  

   

The momentary switch is not ideal, as I guess I am going to need to use it to trigger a CB to pop or similar.  This adds expense for the cct breaker and the wires running to my stick grip are pretty small (around 24 AWG or smaller) so I am not sure it will work.  



 My other option is to replace the momentary switch with a miniature toggle from Ray Allen rated at 2A.  I could use this to switch the power supply to both motors.  I can see this adds failure points.  



 Has anyone satisfactorily done this previously?  What is recommended in this area?  



 Thanks/Regards  

Richard  

       [quote][b]

Dale Ensing

Joined: 11 Jan 2006
Posts: 571
Location: Aero Plantation Weddington NC

Posted: Tue Nov 06, 2007 2:57 pm Post subject: TRIM Disconnect Switch

Richard,

 I have the miniature toggle switch for trim  disconnect on my stick grip. Works fine other than occasionally hitting the  switch unintentionally and turning off power to servo. Have Ray Allen trim  servos on two homebuilt airplanes with no run away problems.

 Dale Ensing

 [quote]   ---

_________________
Dale Ensing
RV-6A
Aero Plantation
Weddington NC

rhdudley1(at)bellsouth.ne
Guest

Posted: Tue Nov 06, 2007 3:44 pm Post subject: TRIM Disconnect Switch

Hi Richard,

 I resonate with your comments about the value of electric trim and switches on the stick grip. I had a couple of Cherokee 235s a couple of decades ago, one with a manual elevator trim by overhead crank, the other with electric elevator trim on the yoke. Both had manual flaps. When I flew the second one with the electric elevator trim, though it worked perfectly well, I found myself using the overhead manual crank for elevator trim. I never found the electric trim useful. The manual flaps were never a problem. When I built my RV-6A, I decided that I would go with manual elevator trim, manual aileron trim and manual flaps. Part of the rationale was the experience with the Cherokees and the rest was independence from the electrical system. At the time, I did not even think of runaway trim. Though I believe that runaway trim is a fairly remote failure in a simple system, I would now make it a consideration. The chance of detecting it in time to hit another switch before it went full throw seems poor. The real benefit of a trim access on the grip versus reaching for a manual trim knob doesn't strike me as worth the complications of multiple speed trim and concern about runaway and its solutions. I find my manual trim to allow delicate adjustment at all airspeeds. Perhaps, those who spend a lot of time at formation flying might find convenience with electric trim. However, in Navy flight training in SNJs in the 50s, we did a lot of formation flying with manual elevator and rudder trim without any related problems.

 I have a similar rationale for my manual flaps. They are not electrically dependent and are only used for landing and occasionally for takeoffs.

 My only switch on the stick grip is my push-to-talk. I consider that to be essential.

 I have read  lots of e-mails on this list by folks who want to not only have push-to-talk and trim on the grip, but starter button and ident. That is a lot of stuff to wire, for parts count and reliability concerns.

 

 Best regards,

 

 Richard Dudley

 richard(at)talbots.net.au (richard(at)talbots.net.au) wrote:

 [quote]                   

G’day Everyone,   

    

First let me start this discussion with how I would install manual trim systems in my RV 7 next time.  The servos, wiring, relays, stick grips and other associated issues are just not worth the trouble and cost IMO.  However, I have the things now so I am going to finish putting them in.   

    

I am fairly unhappy having an electric trim system in my aircraft without any manual system as I believe it is at risk of running away and cannot be manually returned to an in trim position.  My expectation is that it may be possible to catch it in the act and disable the trim system before it manages to get itself to full travel.  I believe this is virtually a requirement in the certified world, and I have lost count of the number of aircraft I have flown over the years with electric trim disabled.  I want the disconnect on the stick as I feel it may be difficult to find in a hurry if it is elsewhere.   

    

In order to alleviate this issue I propose to fit a “trim disconnect” switch to my Ray Allen G207 switch.  To date I have the four momentary push buttons for trim, another button for PTT, another for AP disconnect and a spare momentary switch.  I propose to use this for the Trim Disconnect.   

    

The momentary switch is not ideal, as I guess I am going to need to use it to trigger a CB to pop or similar.  This adds expense for the cct breaker and the wires running to my stick grip are pretty small (around 24 AWG or smaller) so I am not sure it will work.   



 My other option is to replace the momentary switch with a miniature toggle from Ray Allen rated at 2A.  I could use this to switch the power supply to both motors.  I can see this adds failure points.   



 Has anyone satisfactorily done this previously?  What is recommended in this area?   



 Thanks/Regards   

Richard   

    	  Quote: 	
		  



 href="http://www.matronics.com/Navigator?AeroElectric-List">http://www.matronics.com/Navigator?AeroElectric-List



	
 [b]

Dave(at)AirCraftersLLC.co
Guest

Posted: Tue Nov 06, 2007 4:02 pm Post subject: TRIM Disconnect Switch

I usually recommend a  master trim switch.  On my plane I used a toggle CB between the flap switch  and autopilot master.

  

 Another approach is to  use a momentary pushbutton in the ground from the trim switch.  Then it  takes two fingers to activate trim, and runaway trim is pretty much eliminated  since both switches would have to fail simultaneously.

  

  Dave Saylor

 AirCrafters LLC

 140 Aviation Way

 Watsonville, CA 

 831-722-9141

 831-750-0284 CL

 www.AirCraftersLLC.com



  

  



   From:  owner-aeroelectric-list-server(at)matronics.com  [mailto:owner-aeroelectric-list-server(at)matronics.com] On Behalf Of Dale  Ensing

Sent: Tuesday, November 06, 2007 2:54 PM

To:  aeroelectric-list(at)matronics.com

Subject: Re: TRIM  Disconnect Switch

 

 Richard,

 I have the miniature toggle switch for trim  disconnect on my stick grip. Works fine other than occasionally hitting the  switch unintentionally and turning off power to servo. Have Ray Allen trim  servos on two homebuilt airplanes with no run away problems.

 Dale Ensing

 [quote]   ---

khorton01(at)rogers.com
Guest

Posted: Tue Nov 06, 2007 4:36 pm Post subject: TRIM Disconnect Switch

On 6-Nov-07, at 3:18 PM, <richard(at)talbots.net.au> <richard(at)talbots.net.au 

 > wrote:



 	  Quote: 	
		   I am fairly unhappy having an electric trim system in my aircraft  

 without any manual system as I believe it is at risk of running away  

 and cannot be manually returned to an in trim position.  My  

 expectation is that it may be possible to catch it in the act and  

 disable the trim system before it manages to get itself to full  

 travel.  I believe this is virtually a requirement in the certified  

 world, and I have lost count of the number of aircraft I have flown  

 over the years with electric trim disabled.  I want the disconnect  

 on the stick as I feel it may be difficult to find in a hurry if it  

 is elsewhere.



 In order to alleviate this issue I propose to fit a “trim  

 disconnect” switch to my Ray Allen G207 switch.  To date I have the  

 four momentary push buttons for trim, another button for PTT,  

 another for AP disconnect and a spare momentary switch.  I propose  

 to use this for the Trim Disconnect.



 The momentary switch is not ideal, as I guess I am going to need to  

 use it to trigger a CB to pop or similar.  This adds expense for the  

 cct breaker and the wires running to my stick grip are pretty small  

 (around 24 AWG or smaller) so I am not sure it will work.


	


My RV-8 electric trim is wired through a master switch on the side  

console, and a momentary disconnect switch on the stick.  The trim  

power is removed while the momentary switch on the stick is pressed.   

If I had a trim runaway, I would press and hold the trim disconnect  

switch on the stick, then turn off the master switch on the side  

console, then release the momentary switch on the stick.



I also plan to do flight testing to check the stick forces with the  

trim at full travel in either direction.  If the stick forces were too  

high, I would reduce the travel of the trim tab.



--

Kevin Horton         RV-8 (finishing kit)

Ottawa, Canada

http://www.kilohotel.com/rv8

mprather(at)spro.net
Guest

Posted: Tue Nov 06, 2007 5:13 pm Post subject: TRIM Disconnect Switch

Does anyone use a visual or audible indicator for when the trim motor is

running?  A steady tone when the motor running wouldn't be too annoying, I

think, and might make it easy to identify a problem.  You could use a hall

effect sensor to drive the indicator.  I know it's counter to the goal of

making systems simpler, but might be worth it for installations where a

mechanical backup is impractical..

Matt-

 	  Quote: 	
		   

 <khorton01(at)rogers.com>



 On 6-Nov-07, at 3:18 PM, <richard(at)talbots.net.au> <richard(at)talbots.net.au

  > wrote:



> I am fairly unhappy having an electric trim system in my aircraft

> without any manual system as I believe it is at risk of running away

> and cannot be manually returned to an in trim position.  My

> expectation is that it may be possible to catch it in the act and

> disable the trim system before it manages to get itself to full

> travel.  I believe this is virtually a requirement in the certified

> world, and I have lost count of the number of aircraft I have flown

> over the years with electric trim disabled.  I want the disconnect

> on the stick as I feel it may be difficult to find in a hurry if it

> is elsewhere.

>

> In order to alleviate this issue I propose to fit a “trim

> disconnect” switch to my Ray Allen G207 switch.  To date I have the

> four momentary push buttons for trim, another button for PTT,

> another for AP disconnect and a spare momentary switch.  I propose

> to use this for the Trim Disconnect.

>

> The momentary switch is not ideal, as I guess I am going to need to

> use it to trigger a CB to pop or similar.  This adds expense for the

> cct breaker and the wires running to my stick grip are pretty small

> (around 24 AWG or smaller) so I am not sure it will work.



 My RV-8 electric trim is wired through a master switch on the side

 console, and a momentary disconnect switch on the stick.  The trim

 power is removed while the momentary switch on the stick is pressed.

 If I had a trim runaway, I would press and hold the trim disconnect

 switch on the stick, then turn off the master switch on the side

 console, then release the momentary switch on the stick.



 I also plan to do flight testing to check the stick forces with the

 trim at full travel in either direction.  If the stick forces were too

 high, I would reduce the travel of the trim tab.



 --

 Kevin Horton         RV-8 (finishing kit)

 Ottawa, Canada

 http://www.kilohotel.com/rv8

Bob McC

Joined: 09 Jan 2006
Posts: 258
Location: Toronto, ON

Posted: Tue Nov 06, 2007 6:07 pm Post subject: TRIM Disconnect Switch

Trim runaway should hopefully be of  minor concern for several reasons.

  

 1; The likelihood of it happening is very low.  (probably not worth worrying about)

  

 2; Full trim travel in the types of aircraft we  are building is generally liveable. i.e. although it may increase the stick  forces somewhat the aircraft is still controllable (if it isn't  then the trim effectiveness should perhaps be reduced until it  is)

  

 3; If you are really paranoid about the  possibility, then it is a simple matter to install a DPDT centre off  toggle switch in the wiring to the motor (after all the relays, control  devices etc) so that in the event the trim does run away, the relays weld  etc, you simply reverse this switch to run the trim back to neutral then select  the centre off position to totally disconnect and isolate the motor. (this  switch, if it becomes your choice, should be spring return to off from the  reverse position to make it impossible to leave in the reverse  position)

  

 4; Manual trim eliminates even the remotest  possibility if you're not otherwise comfortable.

  

 Bob McC

  

 [b]---

_________________
Bob McC
Falco #908
(just starting)

rtitsworth

Joined: 16 Jan 2006
Posts: 76
Location: Detroit, Mi

Posted: Tue Nov 06, 2007 7:41 pm Post subject: TRIM Disconnect Switch

Richard,  

   

If you’re referring to the typical Ray Allen (RAC) electric trim, you’ll note that the only time there is power to the trim servo is when your wiring is commanding a trim movement.  So, first off, it is virtually impossible for the servo itself to run-away.  Rather, a “run-away” has to be caused by the up-stream wiring.  Keep this in mind when designing and constructing your trim circuits.  Also therefore, there are several potential approaches to mitigate potential run-away scenarios.      Limit      the overall trim such that the plane is still manually controllable at      full time.  
Think      about having two independent trim feeds/buttons (with isolated      disconnects).  One on each stick, or 1 stick and 1 panel, etc.  That      way, if one feed fails and causes a runaway, you can disconnect it and      then take corrective action with the other.  
Some      folks have even put a momentary power feed line reversal circuit (button)      in the system.  Push it and whatever is causing the trim to run one      way will automatically cause it to run back the other way.  Let go (and      disconnect) when it’s in the middle (neutral).  
etc   

The RAC system’s safety is in it’s inherent simplicity.  

   

   

From: owner-aeroelectric-list-server(at)matronics.com [mailto:owner-aeroelectric-list-server(at)matronics.com] On Behalf Of richard(at)talbots.net.au

 Sent: Tuesday, November 06, 2007 3:19 PM

 

   

G’day Everyone,  

   

….I am fairly unhappy having an electric trim system in my aircraft without any manual system as I believe it is at risk of running away and cannot be manually returned to an in trim position….    

        [quote][b]

nuckolls.bob(at)cox.net
Guest

Posted: Tue Nov 06, 2007 7:43 pm Post subject: TRIM Disconnect Switch

At 07:18 AM 11/7/2007 +1100, you wrote:



 	  Quote: 	
		  G day Everyone,



First let me start this discussion with how I would install manual trim 

systems in my RV 7 next time.  The servos, wiring, relays, stick grips and 

other associated issues are just not worth the trouble and cost 

IMO.  However, I have the things now so I am going to finish putting them in.



I am fairly unhappy having an electric trim system in my aircraft without 

any manual system as I believe it is at risk of running away and cannot be 

manually returned to an in trim position.  My expectation is that it may 

be possible to catch it in the act and disable the trim system before it 

manages to get itself to full travel.  I believe this is virtually a 

requirement in the certified world, and I have lost count of the number of 

aircraft I have flown over the years with electric trim disabled.  I want 

the disconnect on the stick as I feel it may be difficult to find in a 

hurry if it is elsewhere.



In order to alleviate this issue I propose to fit a trim disconnect switch 

to my Ray Allen G207 switch.  To date I have the four momentary push 

buttons for trim, another button for PTT, another for AP disconnect and a 

spare momentary switch.  I propose to use this for the Trim Disconnect.



The momentary switch is not ideal, as I guess I am going to need to use it 

to trigger a CB to pop or similar.  This adds expense for the cct breaker 

and the wires running to my stick grip are pretty small (around 24 AWG or 

smaller) so I am not sure it will work.

My other option is to replace the momentary switch with a miniature toggle 

from Ray Allen rated at 2A.  I could use this to switch the power supply 

to both motors.  I can see this adds failure points.

Has anyone satisfactorily done this previously?  What is recommended in 

this area?


	


   See:



http://www.aeroelectric.com/PPS/Flight/Trim/AP_Disconnect_B.pdf



        Bob . . .



        ----------------------------------------

        ( "Problems are the price of progress. )

        ( Don't bring me anything but trouble. )

        ( Good news weakens me."               )

        (              -Charles F. Kettering-  )

        ----------------------------------------

Eric M. Jones

Joined: 10 Jan 2006
Posts: 565
Location: Massachusetts

Posted: Wed Nov 07, 2007 6:53 am Post subject: Re: TRIM Disconnect Switch

Runaway trim....I agree with those who point out that the aircraft's maximum trim should still be flyable. But the problem still needs fixing.



I would also like to point out that one should use environmentally-sealed switches for stick-grip trim switches. A sweaty hand on non-sealed switches leads to early failure.



I have worked on a system that used the "watchdog" idea from computers where the trim system has to get a periodic signal from the controller, otherwise the trim actuator resets to some "safe" position. This is trivial to do.



I have also sold plenty of my "True Servo Conversion for MAC/RAC". These seem to be a great way to make the MAC/RAC trim box work like the Cessna trim wheel. 



But recently I have doubted the utility of the elevator trim at all. Why bother?



Well...so the pilot won't have to push on the stick constantly. This leads to fatigue. So how about putting a strain gauge on the elevator cable (perhaps near the trim box) and auto-trimming the elevator to remove the force on the stick? Easy to do, and one more pilot distraction eliminated. Anybody want a patent?



"When the Oakies left Oklahoma and moved to California, 

 it raised the I.Q. of both states." 

   --Will Rogers

_________________
Eric M. Jones
www.PerihelionDesign.com
113 Brentwood Drive
Southbridge, MA 01550
(508) 764-2072
emjones(at)charter.net

frank.hinde(at)hp.com
Guest

Posted: Wed Nov 07, 2007 7:05 am Post subject: TRIM Disconnect Switch

And if you have a fast airplane like an RV or Glassair and  the stick forces get too high then simply slow down.

  

 I certainly would not bother with another  switch.

  

 Frank

 RV 7a



   From:  owner-aeroelectric-list-server(at)matronics.com  [mailto:owner-aeroelectric-list-server(at)matronics.com] On Behalf Of Robert  McCallum

Sent: Tuesday, November 06, 2007 6:06 PM

To:  aeroelectric-list(at)matronics.com

Subject: Re: TRIM  Disconnect Switch

 

 Trim runaway should hopefully be of  minor concern for several reasons.

  

 1; The likelihood of it happening is very low.  (probably not worth worrying about)

  

 [b][b] 

[/b][/b]  [quote][b]

marcausman

Joined: 08 Feb 2007
Posts: 70

Posted: Wed Nov 07, 2007 8:17 am Post subject: Re: TRIM Disconnect Switch

The electric trim on my RV-7 is run by the Vertical Power system. The trim motors are controlled with solid-state switches - no mechanical relays. It provides runaway trim protection (stops the motor) by simply holding down the opposite trim switch, then after 3 seconds it disconnects the trim switches.  You can then use the backup switches on the display to return the trim back to a neutral position. There is also a visual indicator when the trim is running, and soon audio as well. And it's all simpler to wire than a conventional system with mechanical relays. Of course it's part of a broader system - you can't buy just the trim alone - but the whole point is to make overall wiring a lot simpler.

_________________
Marc Ausman
http://www.verticalpower.com "Move up to a modern electrical system"
RV-7 IO-390 Flying

DanFM01(at)butter.toast.n
Guest

Posted: Wed Nov 07, 2007 8:56 am Post subject: TRIM Disconnect Switch

 	  Quote: 	
		  From my reading of aviation magazines,  I gather the BIG airplanes often 

come with auto-trim systems.  It's a good idea but probably already patented 
	


or covered by "prior art".



---

Melvinke(at)coho.net
Guest

Posted: Wed Nov 07, 2007 9:36 am Post subject: TRIM Disconnect Switch

The Tru-Trak autopilots already offer such an auto-trim function. Works

magnificently.

Kenneth Melvin

RV9A

nuckolls.bob(at)cox.net
Guest

Posted: Wed Nov 07, 2007 4:12 pm Post subject: TRIM Disconnect Switch

 	  Quote: 	
		  

But recently I have doubted the utility of the elevator trim at all. Why 

bother?



Well...so the pilot won't have to push on the stick constantly. This leads 

to fatigue. So how about putting a strain gauge on the elevator cable 

(perhaps near the trim box) and auto-trimming the elevator to remove the 

force on the stick? Easy to do, and one more pilot distraction eliminated. 

Anybody want a patent?


	


   Demonstrated this for Lear about 30 years ago.

   They had a flight test aircraft fitted with

   a pilot pitch effort strain gage. We closed the

   loop on stick force and used the servoed trim

   system I'd already certified. The pilot held an

   AUTO TRIM button on the stick. He would hand-fly

   to desired pitch condition and the trim system would

   be constantly driving to take force out of the

   stick. Worked great, marketing couldn't see enough

   demand to justify developing it into a product.



   But that was on Lears and 30 years ago, we're working

   a whole new market now.



   Bob . . .

list(at)toddheffley.com
Guest

Posted: Sun Nov 11, 2007 7:11 pm Post subject: TRIM Disconnect Switch

Way off topic here..



Any time I hear the "patent" word in the midst of real innovators I cringe.



PLEASE look at



"Case Against Patents" on Don Lancaster's WWW.tinaja.com



Then if you want to know how real innovators make money from ideas,  

read "Riskdown" on the same site.



todd



Do not archive

nuckolls.bob(at)cox.net
Guest

Posted: Mon Nov 12, 2007 6:07 am Post subject: TRIM Disconnect Switch

At 10:09 PM 11/11/2007 -0500, you wrote:



 	  Quote: 	
		  



Way off topic here..



Any time I hear the "patent" word in the midst of real innovators I cringe.



PLEASE look at



"Case Against Patents" on Don Lancaster's WWW.tinaja.com



Then if you want to know how real innovators make money from ideas,

read "Riskdown" on the same site.


	


    Agreed. I've had numerous clients bring up the

    topic of seeking formalized "protections" of one

    kind or another, including patents. I refer them

    to the biographies of individuals like Edwin

    Armstrong . . .



http://en.wikipedia.org/wiki/Edwin_Howard_Armstrong



    who had a "great idea" but not the resources to

    exploit it . . . in particular a high-demand

    marketplace. His patent battles ultimately consumed

    both his material and spiritual existence.



    I always tell my customers that the best way

    to "protect their investment" is to vigorously

    and skillfully exploit it while working diligently

    to be the first to obsolete the present incarnation

    of the idea before competition does it for them.



    Nowhere has this philosophy been more successfully

    practiced than in the computer accessories business.

    Had a client in KC seek my help some years ago

    on a product that would be manufactured for a total

    of perhaps 18 months but 9-12 months more typical.

    Many of their products ran their market life

    in two or three batches of production only to be

    replaced by the next greatest thing.



    Return on investment peaks when the agile

    supplier of goods figures out how to optimize

    their product in ways most attractive to

    consumers. These folks are always successful

    and probably much more successful than those

    who spend $time$ arguing the finer points

    of their patents before a jury educated in

    American public schools.



    There is probably no feature of an RV that

    is worthy of patenting or even copyrighting

    but Mr. V has demonstrated his ability

    to offer an attractive product that is constantly

    evolving into the next greatest thing.



    Bob . . .



        ----------------------------------------

        ( "Problems are the price of progress. )

        ( Don't bring me anything but trouble. )

        ( Good news weakens me."               )

        (              -Charles F. Kettering-  )

        ----------------------------------------

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