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Rudder Trim - Spring Bias

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jkreidler

Joined: 13 Feb 2008
Posts: 151
Location: Sheboygan Falls WI

Posted: Fri Feb 22, 2008 10:03 am Post subject: Rudder Trim - Spring Bias

I have 'developed' a spring bias rudder trim system for the RV-10.  After sharing this idea with Deems he encouraged me to do the same with the rest of the group.  So here goes, but before I get into any details let me preface this whole conversation with a few thoughts.  This is all in theory, I have absolutely no actual flight testing to back up any of the 'claims', or assumptions.  Just good old common sense and a tiny bit of engineering.  Our airplane is not in the air yet, I had hoped to get in the air, prove out the system, then share with the world.  To prevent anyone else for possibly needlessly cutting into their rudder to add a trim tab, I have decided to bear the scrutiny of an unproven, theoretical system.  Please be gentle... 

 

I will attempt to verbalize the system.  I used two torsion springs, one mounted / wrapped around, each rudder bar (the bar that connects the rudder pedals).  One of the springs is fixed on both ends providing a torsional force on the rudder bar.  The other springs free end is hooked to a servo motor that allows approximately 30 degrees deflection.  The theory is that the two springs will seek equilibrium (OK, that's not much theory, that's more fact), here is where the testing needs to happen.  If I deflect the one springs free arm 30 degrees, will it create enough force to put the airplane in trim.  The springs apply about an 8 pound force to the rudder cables (pre-load if you will), assuming they will want to maintain in equilibrium a 30 degree deflection should be more than enough to trim the airplane.  The servo will act as sort of a fine tuning mechanism, the course adjustment will be accomplished by winding more or less tension in one spring or the other during flight testing. 

 

I like a few things about this method. 

1) It can be installed to any flying airplane with no modifications required other than wiring. 

2) There is a chance that this system could be made manual and eliminate the RAC servo if desired. 

3) This system provides tension to both rudder cables, no more 'flopping rudder'. 

4) Keeps the rudder 'clean'. 

5) Doesn't add much extra rudder input force. 

 

I sent pictures of this system to Deems, I will 'attempt' to post some pictures to this forum if there is interest.  Comments welcome, I apologize for the extremely long post, but I have added Deems questions below, I figured if he asked, many more will have the same questions.... 

 

 

1. How did you determine which spring type/size/strength to use? 

OK, you busted me!!  I didn't do the math, I feel extremely guilty about this, as an engineer, I should probably go back and figure the forces here.  Here is what I did; since I grew up in the business of garage doors (my Dad owned his own company doing this), I went to Fleet Farm (one of our local supply houses, similar to most lumbar yards) and found a garage door spring that had an ID that would slide over the rudder bar with room to spare, and would fit between the two rudder bars (I will measure this for you).  I then cut lengths of the spring until I got what I 'thought' was a reasonable amount of force with two turns of pre-load, and bent some custom ends on them.  With torsion springs you have two options to increase the reaction force.  You can add turns of pre-load, or you can shorten the spring with the same number of turns.  I just went until I reached what I 'felt' was a happy medium.  Remember that as you wind a torsion spring more and more the inside diameter decreases, until it eventually binds on the shaft (rudder bar).  What mostly drove me not to do the math, was I had absolutely no idea what sort of corrective rudder pressure was required to put the ball in the middle.  My plan all along has been to get it in the air and do some experimenting, I installed the system so that modification of the spring force should be simple.  I just need to start dating a contortionist  



 2. I assume that you can 'adjust the torsional load somewhat by moving 

 the collar/s, Is that true? 

Correct, I started out with each spring wound an equal amount.  If I find that I need additional trim to one side or the other I will wind one of the springs to compensate.  The servo will just provide the 'fine tuning'. 



 3. One of the pictures shows the center support brace minus the delrin 

 bushings, I'm assuming that leaving those out is not a requirement of 

 your approach and was just the result of taking the picture before they 

 were installed? 

Correct, in fact there isn't a single modification to the airframe, if I remove the system no one could ever tell it was installed.  I built the mount so that it could be used in either the forward or aft rudder mounting positions, my pedals are mounted in the aft position.  But I drilled and prepped the airframe to mount the rudder pedals in either position. 



 4. What about the mount for the RAC servo, do you have a picture of it 

 before the servo is mounted. 

See attached....  The angle was determined by something, I just don't recall what anymore.  I know it has to be at an angle to work though.  I can measure if you decide to attempt this. 



 5. Also it' looks like you used a small section of SS cable to connect 

 the servo arm to the spring coil, correct? Picture? 

Correct, see attached.  One end is run through the servo arm, the other gets hooked by the spring.  The spring on the pilot side is hooked over the opposite rudder bar. 

 

I gave some thought to your desire to have a manually operated system, I think this system could be done manually with very little pain.  You may be able to add a knob that would come out of the sub panel, really anywhere along its length.  What would have to happen is a bracket would need to be made that slid over the rudder bar with a nut in it.  Then a threaded shaft running from the rudder bar to the sub panel would be used to adjust the free arm of the spring.  It may be best if the spring were pushed by the shaft instead of pulled, as this would make the mechanism a bit simpler.  I could do a drawing of what I am thinking if you are not following. 

 

While it was not my intention to begin producing kits, if there is enough interest, I could be persuaded to fabricate a few. 



 Thanks, Jason

 

 Jason Kreidler - 40617 Finishing 

(4 Partner Build) 

 [quote][b]

_________________
Jason Kreidler
4 Partner Build - Sheboygan Falls, WI
Tony Kolar, Kyle Hokel, Wayne Elser, Jason Kreidler
N44YH - Flying - #40617

recapen(at)earthlink.net
Guest

Posted: Fri Feb 22, 2008 10:44 am Post subject: Rudder Trim - Spring Bias

When do we get to see some pictures?

--

jkreidler

Joined: 13 Feb 2008
Posts: 151
Location: Sheboygan Falls WI

Posted: Fri Feb 22, 2008 11:18 am Post subject: Re: Rudder Trim - Spring Bias

Enclosed are a few photographs....



Thanks, Jason



Jason Kreidler - 40617 Finishing

(4 Partner Build)

CoPilotSide.JPG

Description:

Filesize:

53.17 KB

Viewed:

676 Time(s)

Overview.JPG

Description:

Filesize:

66.12 KB

Viewed:

682 Time(s)

PilotSide.JPG

Description:

Filesize:

52.45 KB

Viewed:

671 Time(s)

ServoMtg1.JPG

Description:

Filesize:

55.19 KB

Viewed:

626 Time(s)

_________________
Jason Kreidler
4 Partner Build - Sheboygan Falls, WI
Tony Kolar, Kyle Hokel, Wayne Elser, Jason Kreidler
N44YH - Flying - #40617

capsteve

Joined: 09 Jan 2006
Posts: 111
Location: NIAGARA FALLS NY

Posted: Fri Feb 22, 2008 11:20 am Post subject: Rudder Trim - Spring Bias

Jason, its sounds like a very elegant solution i can't  wait to see some pics. 

 

[Steven  DiNieri] 

  

  rom:  owner-rv10-list-server(at)matronics.com  [mailto:owner-rv10-list-server(at)matronics.com] On Behalf Of  jason.kreidler(at)regalbeloit.com

Sent: Friday, February 22, 2008  12:55 PM

To: rv10-list(at)matronics.com

Subject: RV10-List:  Rudder Trim - Spring Bias

 [quote]   



I have 'developed' a spring bias    rudder trim system for the RV-10.  After sharing this idea with Deems he    encouraged me to do the same with the rest of the group.  So here goes,    but before I get into any details let me preface this whole conversation with    a few thoughts.  This is all in theory, I have absolutely no actual    flight testing to back up any of the 'claims', or assumptions.  Just good    old common sense and a tiny bit of engineering.  Our airplane is not in    the air yet, I had hoped to get in the air, prove out the system, then share    with the world.  To prevent anyone else for possibly needlessly cutting    into their rudder to add a trim tab, I have decided to bear the scrutiny of an    unproven, theoretical system.  Please be gentle... 



I will attempt to verbalize the system.  I used    two torsion springs, one mounted / wrapped around, each rudder bar (the bar    that connects the rudder pedals).  One of the springs is fixed on both    ends providing a torsional force on the rudder bar.  The other springs    free end is hooked to a servo motor that allows approximately 30 degrees    deflection.  The theory is that the two springs will seek equilibrium    (OK, that's not much theory, that's more fact), here is where the testing    needs to happen.  If I deflect the one springs free arm 30 degrees, will    it create enough force to put the airplane in trim.  The springs apply    about an 8 pound force to the rudder cables (pre-load if you will), assuming    they will want to maintain in equilibrium a 30 degree deflection should be    more than enough to trim the airplane.  The servo will act as sort of a    fine tuning mechanism, the course adjustment will be accomplished by winding    more or less tension in one spring or the other during flight testing.    



I like a few things about this    method. 

1) It can be installed to any    flying airplane with no modifications required other than wiring.    

2) There is a chance that this system could    be made manual and eliminate the RAC servo if desired. 

3) This system provides tension to both rudder cables,    no more 'flopping rudder'. 

4) Keeps    the rudder 'clean'. 

5) Doesn't add    much extra rudder input force. 



I    sent pictures of this system to Deems, I will 'attempt' to post some pictures    to this forum if there is interest.  Comments welcome, I apologize for    the extremely long post, but I have added Deems questions below, I figured if    he asked, many more will have the same questions.... 

1. How did you determine which spring    type/size/strength to use? 

OK,    you busted me!!  I didn't do the math, I feel extremely guilty about    this, as an engineer, I should probably go back and figure the forces here.     Here is what I did; since I grew up in the business of garage doors (my    Dad owned his own company doing this), I went to Fleet Farm (one of our local    supply houses, similar to most lumbar yards) and found a garage door spring    that had an ID that would slide over the rudder bar with room to spare, and    would fit between the two rudder bars (I will measure this for you).  I    then cut lengths of the spring until I got what I 'thought' was a reasonable    amount of force with two turns of pre-load, and bent some custom ends on them.     With torsion springs you have two options to increase the reaction    force.  You can add turns of pre-load, or you can shorten the spring with    the same number of turns.  I just went until I reached what I 'felt' was    a happy medium.  Remember that as you wind a torsion spring more and more    the inside diameter decreases, until it eventually binds on the shaft (rudder    bar).  What mostly drove me not to do the math, was I had absolutely no    idea what sort of corrective rudder pressure was required to put the ball in    the middle.  My plan all along has been to get it in the air and do some    experimenting, I installed the system so that modification of the spring force    should be simple.  I just need to start dating a contortionist     



2. I assume that you can    'adjust the torsional load somewhat by moving 

the collar/s, Is that    true? 

Correct, I started out    with each spring wound an equal amount.  If I find that I need additional    trim to one side or the other I will wind one of the springs to compensate.     The servo will just provide the 'fine tuning'. 



3. One of the pictures shows the center support    brace minus the delrin 

bushings, I'm assuming that leaving those out is    not a requirement of 

your approach and was just the result of taking the    picture before they 

were installed? 

Correct, in fact there isn't a single modification to the airframe,    if I remove the system no one could ever tell it was installed.  I built    the mount so that it could be used in either the forward or aft rudder    mounting positions, my pedals are mounted in the aft position.  But I    drilled and prepped the airframe to mount the rudder pedals in either    position. 



4. What about the    mount for the RAC servo, do you have a picture of it 

before the servo is    mounted. 

See attached....     The angle was determined by something, I just don't recall what anymore.     I know it has to be at an angle to work though.  I can measure if    you decide to attempt this. 



5. Also it' looks like you used a small section of SS cable to    connect 

the servo arm to the spring coil, correct? Picture?    

Correct, see attached.  One end is    run through the servo arm, the other gets hooked by the spring.  The    spring on the pilot side is hooked over the opposite rudder bar.    



I gave some thought to your desire to    have a manually operated system, I think this system could be done manually    with very little pain.  You may be able to add a knob that would come out    of the sub panel, really anywhere along its length.  What would have to    happen is a bracket would need to be made that slid over the rudder bar with a    nut in it.  Then a threaded shaft running from the rudder bar to the sub    panel would be used to adjust the free arm of the spring.  It may be best    if the spring were pushed by the shaft instead of pulled, as this would make    the mechanism a bit simpler.  I could do a drawing of what I am thinking    if you are not following. 



While it was not my intention to begin producing kits, if there is    enough interest, I could be persuaded to fabricate a few. 



Thanks, Jason



Jason Kreidler - 40617    Finishing 

(4 Partner Build)  

 	  Quote: 	
		  

	
[b]

carlosh(at)structuralaz.c
Guest

Posted: Fri Feb 22, 2008 12:07 pm Post subject: Rudder Trim - Spring Bias

First I must admit I'm building a 7A. Second - you guys are an awesome 

resource for ideas! Do any of you repeat offenders know if the rudder 

tubes are the same size in the 10 and 7? I like this idea very much and, 

with your permission Jason, I'd like to use it if it works.



Carlos in Arizona

(Watching this development with great interest.)



jkreidler wrote:

 	  Quote: 	
		   



 Enclosed are a few photographs....



 Thanks, Jason



 Jason Kreidler - 40617 Finishing

 (4 Partner Build)



 --------

 RV-10 Quick Build

 4 Partner Build - Finishing





 Read this topic online here:



 http://forums.matronics.com/viewtopic.php?p=165593#165593





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 http://forums.matronics.com//files/copilotside_947.jpg

 http://forums.matronics.com//files/overview_610.jpg

 http://forums.matronics.com//files/pilotside_821.jpg

 http://forums.matronics.com//files/servomtg1_720.jpg



   


	


-- 

Carlos Hernandez <carlosh(at)sec-engr.com>

Structural Engineers Company

2963 W. Elliot Rd. - Suite 3

Chandler, AZ 85224

Phone: 480.968.8600

Fax: 480.968.8608

www.sec-engr.com

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rv10builder(at)verizon.ne
Guest

Posted: Fri Feb 22, 2008 12:23 pm Post subject: Rudder Trim - Spring Bias

Jason;

 you mentioned "While it was not my intention to  begin producing kits, if there is enough interest, I could be persuaded to  fabricate a few. "

  

 I may be  interested after hearing how well it works and you feel that the "engineering"  is complete.

 Thanks!

  

 Pascal

 



 [quote]   ---

KiloPapa

Joined: 24 May 2006
Posts: 142
Location: Pearblossom, CA

Posted: Fri Feb 22, 2008 3:48 pm Post subject: Rudder Trim - Spring Bias

Jason,

Thanks for taking the time to share your work on a Rudder

Trim system.  I look forward to the pictures.  This is one

of the prime attributes of the experimental community.



Kevin

40494

do not archive



----- Original Message Follows -----

From: jason.kreidler(at)regalbeloit.com

To: rv10-list(at)matronics.com

Subject: Rudder Trim - Spring Bias

Date: Fri, 22 Feb 2008 11:55:17 -0600



 	  Quote: 	
		  I have 'developed' a spring bias rudder trim system for the

RV-10.  After  sharing this idea with Deems he encouraged

me to do the same with the rest  of the group.  So here

goes, but before I get into any details let me  preface

this whole conversation with a few thoughts.  This is all

in  theory, I have absolutely no actual flight testing to

back up any of the  'claims', or assumptions.  Just good

old common sense and a tiny bit of  engineering.  


	


---snipped---



 	  Quote: 	
		  While it was not my intention to begin producing kits, if

there is enough  interest, I could be persuaded to

fabricate a few.



Thanks, Jason



Jason Kreidler - 40617 Finishing

(4 Partner Build)

_________________
Kevin
40494

do not archive

ricksked(at)embarqmail.co
Guest

Posted: Fri Feb 22, 2008 5:07 pm Post subject: Rudder Trim - Spring Bias

Very Cool!!! Like the torsion springs in a garage door....good thinking. But alas...I ain't crawling under that panel one more time.  

Rick S. 

40185

---

johngoodman

Joined: 18 Sep 2006
Posts: 530
Location: GA

Posted: Sat Feb 23, 2008 7:36 am Post subject: Re: Rudder Trim - Spring Bias

Jason,

I love it! Simple, clean, and easy to install or remove. You've sold me on it. If you decide to make a few, sign me up.

John



 	  jkreidler wrote: 	
		  Enclosed are a few photographs....



Thanks, Jason



Jason Kreidler - 40617 Finishing

(4 Partner Build)

_________________
#40572 Phase One complete in 2011

bob.kaufmann(at)cox.net
Guest

Posted: Sat Feb 23, 2008 7:54 am Post subject: Rudder Trim - Spring Bias

Somehow I seem to not have the pictures, where can I see them.



Bob K



--

jkreidler

Joined: 13 Feb 2008
Posts: 151
Location: Sheboygan Falls WI

Posted: Sat Feb 23, 2008 3:42 pm Post subject: Re: Rudder Trim - Spring Bias

All, thanks for the encouraging comments both on-line and off.  I really didn't expect this sort of interest.  With that being said, I would really like to find a willing participant to test this on a flying RV-10.  We are several months away from our fist flight, I don't think everyone has that sort of time available.  If anyone would be interested in helping out with this sort of testing please let me know.



I am really surprised at the number of people who expressed interest in installing a kit (once the system is working).  I have decided to create a kit of parts once the concept is reality.



As far as using this kit on an RV-7, I have a friend building a 7 not far from where I live, I will stop by his house and measure it all up and see if it will work.



If you are still unable to view the pictures please send me an e-mail, I would be happy to e-mail copies.



Thanks again everyone!!



Jason - 40617 Finishing

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