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Mono tail wheel spring mounting bolt break

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tennant

Joined: 19 Apr 2011
Posts: 121

Posted: Fri Sep 07, 2018 5:37 am Post subject: Mono tail wheel spring mounting bolt break

Just a heads up for Mono flyers.

My AN5-21A Bolt that mounts the tail wheel spring to its mounting has broken. Thank goodness during movement in the hanger.

The bolt shows a classical Fatigue fracture through the shank that must have taken some time to break.

I am getting the plane back this evening into my workshop.

Perhaps mono drivers would like to check the tightness of this bolt or if there is sideways movement on the spring.



Happy Days!!



Barry

_________________
Barry Tennant
D-EHBT
At EDLM - Germany

ward.t(at)xtra.co.nz
Guest

Posted: Sun Sep 09, 2018 6:21 pm Post subject: Mono tail wheel spring mounting bolt break

Thanks Barry,

Just replaced the bolt. Old one was ok to the naked eye however you never know.

Cheers,

Tim

Sent from my iPhone



Tim Ward

12 Waiwetu Street

Fendalton 

CHRISTCHURCH 8052

Hom 03315166



 	  Quote: 	
		   On 8/09/2018, at 1:37 AM, tennant <barrington.tennant(at)gmail.com> wrote:

 

 

 

 Just a heads up for Mono flyers.

 My AN5-21A Bolt that mounts the tail wheel spring to its mounting has broken. Thank goodness during movement in the hanger.

 The bolt shows a classical Fatigue fracture through the shank that must have taken some time to break.

 I am getting the plane back this evening into my workshop.

 Perhaps mono drivers would like to check the tightness of this bolt or if there is sideways movement on the spring.

 

 Happy Days!!

 

 Barry

 

 --------

 Barry Tennant

 D-EHBT

 At EDLM  -  Germany

 

 

 

 

 Read this topic online here:

 

 http://forums.matronics.com/viewtopic.php?p=482946#482946

roddyeuropa(at)aol.com
Guest

Posted: Sun Sep 09, 2018 10:16 pm Post subject: Mono tail wheel spring mounting bolt break

I had a similar failure of the tailwheel bolt about 3 years ago. Broke on

the ground after some stormy weather (tied down outside).  Bolt broke near

the head, classic fatigue crack marks. I now check every annual.

Roddy Kesterton

G-IKRK



--

tennant

Joined: 19 Apr 2011
Posts: 121

Posted: Mon Sep 10, 2018 5:01 am Post subject: Re: Mono tail wheel spring mounting bolt break

Hi Roddy,

It would have been quite an adventure if it had broken on landing as the rudder jams firmly to one side!!

I am thinking of a bit better security for the tailwheel spring and will float it by the forum when I have worked it out.



Barry

_________________
Barry Tennant
D-EHBT
At EDLM - Germany

erichdtrombley(at)juno.co
Guest

Posted: Tue Sep 11, 2018 12:46 pm Post subject: Mono tail wheel spring mounting bolt break

Hi Barry,

 

   

 

  Glad to hear you didn't sustain any damage to your plane.  Typical of other Mono folks I too bent my tail wheel bolt which led me to creating the following mod I performed over 10 years ago.  Never had a problem since.  The original design relies on the AN5-21A bolt to counter the torsional load of the tail spring which isn't ideal as you can attest too.  I created a simple mod that takes the torsional load from the tail spring and transfers it to the XTW15 steel support plate rather than the AN5 bolt in bending.  I installed an aluminum block with a channel milled down the middle (the width and height of the mounting end of the tail spring) with a through hole in the center to pass the AN5 bolt.  As shown in the attached drawing the block captivates the end of the tail spring and transfers the load as described above.  The AN5 bolt is now in double shear instead of single shear and bending.  A longer bolt is required to replace the existing AN5-21A which is too short to pass through the block.  That's it. And it works a treat.  You may not even require approval of the mod as it could be considered a really thick washer of sorts.   The mod also prevents the through hole in the bottom of the fuselage in which the AN5 bolt passes from wallowing out.

 

   

 

  Also, regarding bonding of the tail spring to the rear stern post I deviated slightly from the instructions.  When I originally installed the tail spring I was giving consideration to serviceability and realized if the spring were bonded to the stern post I would need to deal with the Redux.  Realizing the benefit of having the additional bearing surface of the Redux I installed the tail spring per the manual, however, I applied a release to the tail spring such that the Redux wouldn't adhere.  This allows the tail spring to be easily removed without compromising the design.  

 

   

 

  Glad to answer any questions you may have.

 

   

 

  Regards,

 

  Erich

 

  N28ET Classic Mono 914

 

  



____________________________________________________________

Unbelievable German World War 2 Photo Shocks Americans

pro.healthresponses.org

http://thirdpartyoffers.juno.com/TGL3132/5b9829569b4262956084ast02vuc

MonoTailwheelSpringMod.pdf

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peterz(at)zutrasoft.com
Guest

Posted: Tue Sep 11, 2018 1:47 pm Post subject: Mono tail wheel spring mounting bolt break

Awesome solution. Thx!



On Sep 11, 2018, at 4:45 PM, Erich Trombley <erichdtrombley(at)juno.com (erichdtrombley(at)juno.com)> wrote:

 	  Quote: 	
		   Hi Barry,

 

   

 

  Glad to hear you didn't sustain any damage to your plane.  Typical of other Mono folks I too bent my tail wheel bolt which led me to creating the following mod I performed over 10 years ago.  Never had a problem since.  The original design relies on the AN5-21A bolt to counter the torsional load of the tail spring which isn't ideal as you can attest too.  I created a simple mod that takes the torsional load from the tail spring and transfers it to the XTW15 steel support plate rather than the AN5 bolt in bending.  I installed an aluminum block with a channel milled down the middle (the width and height of the mounting end of the tail spring) with a through hole in the center to pass the AN5 bolt.  As shown in the attached drawing the block captivates the end of the tail spring and transfers the load as described above.  The AN5 bolt is now in double shear instead of single shear and bending.  A longer bolt is required to replace the existing AN5-21A which is too short to pass through the block.  That's it. And it works a treat.  You may not even require approval of the mod as it could be considered a really thick washer of sorts.   The mod also prevents the through hole in the bottom of the fuselage in which the AN5 bolt passes from wallowing out.

 

   

 

  Also, regarding bonding of the tail spring to the rear stern post I deviated slightly from the instructions.  When I originally installed the tail spring I was giving consideration to serviceability and realized if the spring were bonded to the stern post I would need to deal with the Redux.  Realizing the benefit of having the additional bearing surface of the Redux I installed the tail spring per the manual, however, I applied a release to the tail spring such that the Redux wouldn't adhere.  This allows the tail spring to be easily removed without compromising the design.  

 

   

 

  Glad to answer any questions you may have.

 

   

 

  Regards,

 

  Erich

 

  N28ET Classic Mono 914

 

  



____________________________________________________________

Unbelievable German World War 2 Photo Shocks Americans

pro.healthresponses.org

http://thirdpartyoffers.juno.com/TGL3132/5b9829569b4262956084ast02vuc



<MonoTailwheelSpringMod.pdf>

JonSmith

Joined: 21 May 2010
Posts: 110

Posted: Tue Sep 11, 2018 11:45 pm Post subject: Re: Mono tail wheel spring mounting bolt break

This is my slightly modified tailwheel spring front mounting bolt arrangement.   An extra piece of aluminium across the top with redux/ flox built up either side of the spring to support it.   The extra top piece of aluminium is permanently fixed in place and the spring just slots snugly in place under it.   Easy to remove the spring, once the bolt is removed it just slides out backwards.    Been good for many years now.

4684CD1E-54B1-4A6C-972C-DCE48BC2C524.jpeg

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_________________
G-TERN
Classic Mono

tennant

Joined: 19 Apr 2011
Posts: 121

Posted: Wed Sep 12, 2018 2:55 am Post subject: Re: Mono tail wheel spring mounting bolt break

Hi Eric & John,

It looks as if you both came to the same solution with differing ways to do it. Both good and a great improvement on the standard design.



Barry

_________________
Barry Tennant
D-EHBT
At EDLM - Germany

roddyeuropa(at)aol.com
Guest

Posted: Thu Sep 13, 2018 11:14 pm Post subject: Mono tail wheel spring mounting bolt break

I agree that these are really good solutions, so thank you Eric and John.

They address the issue that the bolt no longer has bending mode, but also

the issue that both Barry and I had in that the bolt seems to have sheered

due to fatigue, and on the ground. The bolt is not in compression on

landing, or when stable on the ground, as the tailwheel arm is pivoted at

the sternpost,. I think that most of the tension stresses causing the

fatigue will come from weight on the bolt during flight, and mine actually

broke after being bounced around on the ground during stormy weather. (I now

also tied down the tailwheel when parked.)

Roddy



--

Nigel Graham

Joined: 23 Mar 2017
Posts: 36
Location: Winchester - UK

Posted: Fri Sep 14, 2018 2:32 am Post subject: Re: Mono tail wheel spring mounting bolt break

The bolt failures are the symptom of the problem â€“ not the cause!

The problem is the plywood stack that the tail spring sits on. During the build, the plywood is sheathed in waterproof epoxy, but then you have to drill the hole for the bolt to pass through, exposing the wood to the atmosphere â€“ and THAT is the problem. 

In service, moisture wicks up the bolt and into the plywood end grain, where it sits unseen. Eventually the wood begins to rot and the structural rigidity is lost. 

At this point, the clamping force of the bolt is lost and the spring begins to rock from side to side during taxying. 

This allows the bolt shank to fret and eventually the fatigued bold will fail. 

I have attached a picture of a tail spring bolt that was replaced just in time (the ground handler noticed the tailwheel flopping from side to side during taxying).

This shows everything; the deep pitted rust indicates that the plywood stack was wet, the fretting has worn away the blot shaft where is passes through the end of the tail spring, and you can see the fatigue crack developing nicely.

Simply replacing the bolt will cure the symptoms, but it will eventually fail again in exactly the same way.

To affect a lasting repair, the plywood should be thoroughly dried out and then impregnated with a thinned epoxy resin to restore the structural rigidity. 

To keep the bolt shank away from the wood, I over bored the mounting hole to accept a 5/16â€ bore 4041 sleeve, which was bonded permanently in place. The new bolt was then greased and inserted through the sleeve.

I also made up a steel saddle bar that sits on top of the tail spring mount to prevent it from rocking (just like Jonâ€™s).

Nigel

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jeanphilippeneel(at)yahoo
Guest

Posted: Fri Sep 14, 2018 9:02 pm Post subject: Mono tail wheel spring mounting bolt break

Bonjour Erich

Could  you please send me a drawing with cotation of your interesting solution?

Merci

Jean-Philippe NEEL

NÂ° 273 F-PSLH

France

 

    Le Mardi 11 septembre 2018 22h54, Erich Trombley <erichdtrombley(at)juno.com> a Ã©crit :



  



  Hi Barry,

 

   

 

  Glad to hear you didn't sustain any damage to your plane.  Typical of other Mono folks I too bent my tail wheel bolt which led me to creating the following mod I performed over 10 years ago.  Never had a problem since.  The original design relies on the AN5-21A bolt to counter the torsional load of the tail spring which isn't ideal as you can attest too.  I created a simple mod that takes the torsional load from the tail spring and transfers it to the XTW15 steel support plate rather than the AN5 bolt in bending.  I installed an aluminum block with a channel milled down the middle (the width and height of the mounting end of the tail spring) with a through hole in the center to pass the AN5 bolt.  As shown in the attached drawing the block captivates the end of the tail spring and transfers the load as described above.  The AN5 bolt is now in double shear instead of single shear and bending.  A longer bolt is required to replace the existing AN5-21A which is too short to pass through the block.  That's it. And it works a treat.  You may not even require approval of the mod as it could be considered a really thick washer of sorts.   The mod also prevents the through hole in the bottom of the fuselage in which the AN5 bolt passes from wallowing out.

 

   

 

  Also, regarding bonding of the tail spring to the rear stern post I deviated slightly from the instructions.  When I originally installed the tail spring I was giving consideration to serviceability and realized if the spring were bonded to the stern post I would need to deal with the Redux.  Realizing the benefit of having the additional bearing surface of the Redux I installed the tail spring per the manual, however, I applied a release to the tail spring such that the Redux wouldn't adhere.  This allows the tail spring to be easily removed without compromising the design.  

 

   

 

  Glad to answer any questions you may have.

 

   

 

  Regards,

 

  Erich

 

  N28ET Classic Mono 914

 

  



____________________________________________________________

Unbelievable German World War 2 Photo Shocks Americans

pro.healthresponses.org

http://thirdpartyoffers.juno.com/TGL3132/5b9829569b4262956084ast02vuc

John Wighton

Joined: 18 May 2010
Posts: 241

Posted: Fri Sep 14, 2018 11:12 pm Post subject: Re: Mono tail wheel spring mounting bolt break

A nice description of the cause and effect.



 The actual root cause is poor design.  A Design which takes rolling loads as differential bending would be so much better.  This could be achieved with 2 bolts although it would need a T shaped end.  



A fully bushed insert would also relieve bending in the bolt.



Design is so much easier with hindsight.

_________________
John Wighton
Europa XS trigear G-IPOD

JonSmith

Joined: 21 May 2010
Posts: 110

Posted: Sat Sep 15, 2018 1:05 am Post subject: Re: Mono tail wheel spring mounting bolt break

 	  John Wighton wrote: 	
		  The actual root cause is poor design.  A Design which takes rolling loads as differential bending would be so much better.  This could be achieved with 2 bolts although it would need a T shaped end.  



Design is so much easier with hindsight. 	


A â€œT shaped endâ€ might be a bit tricky to get through the â€˜ole in the fin close out when fitting the arm.....

_________________
G-TERN
Classic Mono

tennant

Joined: 19 Apr 2011
Posts: 121

Posted: Mon Sep 17, 2018 4:38 am Post subject: Re: Mono tail wheel spring mounting bolt break

A good synopsis Nigel. My bolt was nowhere as rusty as yours, just showing a light surface corrosion, but the root cause is certainly the ability of water to ingress into the wood allowing bending of the bolt.

I have 2 Kg of lead in my tail to compensate for the weight of my MT prop. so I can build a solution that will last forever!!



Barry

_________________
Barry Tennant
D-EHBT
At EDLM - Germany

rparigoris

Joined: 24 Nov 2009
Posts: 796

Posted: Tue Sep 18, 2018 10:59 am Post subject: Re: Mono tail wheel spring mounting bolt break

Hi Group



I was in contact with Nev on this subject and he warned against making the tailwheel spring too "STUCK" to the fuse. He said it's OK to make things a little stronger, but if yo make things "TOO" strong, instead of bending the bolt (EZ to replace) you can trash the aft fuse.



You can see my resolution on page #1:

http://www.europaowners.org/main.php?g2_itemId=27732



Note: If you replace the recommended factory cable adjusters with turn-buckles, you can easily defeat that simple solution and shoot yourself in the foot. See page #2 of above link. If you pull rudder pedals just slightly forward  with turn-buckles installed, the cable can easily twist and jam that side shorter. For a Mono especially, that could be a real bad thing. Some shrink wrap can easily fix that potential problem.



Ron P.

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