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Re. mono gear collapse

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jonsmitheuropa(at)tiscali
Guest

Posted: Wed Feb 28, 2007 12:53 am Post subject: Re. mono gear collapse

Hi all, having been following this discussion here's my random thoughts!  

ASSUMING THE MECHANISM IS CONSTRUCTED AND ADJUSTED CORRECTLY then with the  gear down and locked the over centre lock cannot possibly "unlock" itself (ie  travel back undercentre) UNLESS SOMETHING BREAKS OR BENDS. An overcentre lock is  exactly that - a lock. 

With the gear down the LG8 arms will be tight against the stops and will be  held there in place by the retraction lever which will be tight against the  FORWARD face of the DOWN gate. (That's important - any gap here and the lever  could travel forward a small amount in the gate thus moving the LG8's back off  the stops slightly and critically REMOVING the overcentre). 

With the LG8's correctly locked against the stops as above, then the  overcentre lock cannot possibly "collapse" undercentre. It doesn't need much  overcentre. Even a tiny amount will be enough to create a "safe" lock. As long  as there is "some overcentre" present it will stay overcentre. 

However, studying the diagrams again I then started to worry - and the  following is pure speculation! If due to a very unfortunate series of  oscillations (bounces!) in conjunction with undulationg ground, could a freak  occurance happen such that the rubber block compresses so much that the swinging  arm would then be "fired" downwards again with such force that (as the shock  absorber became extended again) the arm would continue down with such force that  it pulled on the LG8 arms enough to actually pull them back a little off their  stops? (Of course, something would have to bend or break - probably the  retraction lever - for this LG8 movement to happen). It wouldn't need something  to bend much, just enough for the LG8's to move back to a small undercentre  geometry. The next ground contact would then finish the job. (One thing is sure,  if there is any "undercenter" present for any reason then nothing will hold the  plane up - the gear will collapse immediately). Sadly, any "evidence" of damage  caused by the first event would be completely lost by the continuing damage  caused during the subsequent gear collapse. 

Could this scenario happen? I don't know but I feel it is most unlikely. It  needs someone with much more engineering knowledge (and knowledge of energy  stored in rubber blocks!) than myself to speculate, but I feel that compared to  the whole gear assembly the rubber block is tiny and the swinging arm will have  a lot of inertia. (The wheel at the end is very heavy though.) Also the angles  involved, even with correct overcentre geometry are very small. Any "pull"  downwards from the shock absorber will be almost straight down and not much in  the direction required to pull the LG8's off their stops! Ironically, too much  overcentre could make this scenario worse?? - the angle will then be increased  and any pull downwards by the shock absorber will have a greater pull on the  LG8's in a rearward direction thus straining the retraction lever. (Zero  overcentre and the pull would be straight downwards so no risk - but no safety  margin either!). During development one presumes that Ivan, Andy or Nev will  have swung and bounced up and down at great length to prove this can't  happen! 

A while ago in the UK the PFA issued a document detailing mandatory  undercarriage inspections at each annual which includes a check of the geometry  amongst other things. Compliance with this should be good for peace of mind! If  owners from outside the UK don't have this then it may be worth getting a copy  as it's good reading. 

I love my monowheel and it's flying characteristics and think it's a great  design! I will continue with the (completely unproven) thought that in the small  number of uncommanded retraction occurances that have happened (with the  greatest respect and sympathy to the owners) something must have been wrong  somewhere. However I will be checking my geometry carefully and will be trying  not to bounce too much!! 

Regards, 

Jon Smith 

G-TERN

    [quote][b]

davidjoyce(at)doctors.org
Guest

Posted: Wed Feb 28, 2007 1:47 am Post subject: Re. mono gear collapse

Jon, I think you are on the right lines here. Although a lock is a lock it

is clearly capable of being unlocked!  If the plane takes off abruptly

having gone over a significant bump the unloading of compression will

encourage the swinging arm to continue downwards, putting tension on the

overcentre elements thus tending to bring them back into a straight line and

indeed travel on into an 'undercentre' unlocked position if the movement is

violent enough, and if the gear lever set up is loose enough.

      From this point of view it might be argued that being further over

centre in the downlocked position might increase the hazard as more momentum

(of the overcentre locking elements) will be developed when the swinging arm

unloads downwards, increasing the likelihood of forcing itself undercentre.

If it starts significantly overcentre it effectively (like a good back row

forward) takes a run at it and gets up a fine head of steam by the time it

reaches the neutral centre position, and is inclined to carry on taking

anything in its path with it!

      The fragility of the joint between the gear selector lever and the

rest of the system was brought home to me when I found after flying through

some fairly severe  turbulence in rotor, that the gear lever stopped 1/4

inch short of the detent on putting the gear down. The inertial effects on

the swinging arm and wheel had been enough to shift the alignment of the

joint where the gear lever joins LG08S with three bolts. Others of course

have reported similar things after trailing the plane with the gear locked

in an up position.

       My conclusions are:

 (1) that the system is best set up being only just overcentre

 (2) that the Gear lever/ LG08S joint has to be as solid as possible, ie

holes precisely to size and    faces bonded, and the reinforcing mod added)

  (3) that the detents for the gear lever should allow no significant

movement

              Regards, David Joyce, G-XSDJ

---

william(at)wrmills.plus.c
Guest

Posted: Wed Feb 28, 2007 8:15 am Post subject: Re. mono gear collapse

To all flying monos,

Has anyone decided to renew the U/C shock cord as a timed maintenance issue? 

Mine is 10 years old and 1,000 plus hours, flying off rought grass strips, 

but still seems to function well, albeit probably a little tired by now. 

(like me!)  Someone has suggested that if the shock cord is not sufficiently 

tight, it may contribute towards a gear collapse.  If that were the case, it 

would be nice to know what others think and what maintenance they have done, 

or intending to do, to the U/C mechanism over the years.  All I have done so 

far, is to replace the two bronze bushes, when they appeared to be a bit 

sloppy at approx 600 hours, but I am not sure if that was absolutely 

necessary.

Regards,

William

rparigor(at)suffolk.lib.n
Guest

Posted: Wed Feb 28, 2007 9:33 am Post subject: Re. mono gear collapse

Hello Jon



I read your post, and:

"the following is pure speculation!" I am not sure that will really

happen.



As far as my speculation, I believe that a rammed and jammed LG08 against

its stop that is 1/16" to 1/8" overcentre can be brought undercentre!



How???



Lets say you hit a ski jump on take off, the plane will get light, and

lets say it is not ready to fly, then when it comes back down, one wing is

slight low (matters not which one), then a outrigger latch decides to be

defeated at that very moment. Can the rearward force on the outrigger, be

applied to the flap, which will be applied to the cross tube, then the

connecting rod and ultimate to the starboard LG08 forcing it

undercentre???



My wings are not rigged yet, can someone next time when doing a gear swing

test, defeat a outrigger latch and push aft on gear leg and have a look at

starboard LG08 to see if it can be lifted off its stop?

Thx.

Ron Parigoris

william(at)wrmills.plus.c
Guest

Posted: Wed Feb 28, 2007 10:15 pm Post subject: Re. mono gear collapse

Ron,

I know of at least two monos that have ground away the front of the 

outrigger spat right through to the front face of the wheel fork tube and 

removed the head of the retaining bolt.  This happens during a ground loop 

owing to strong crosswinds on a hard runway.  The leg is bent horizontal 

when this happens, but it does not cause it to collapse.  The U/C will also 

withstand an A/C drop after hitting a bump on landing below flying speed, 

sufficient to break the prop, but the U/C does not collapse.  Hope this give 

mono builders confidence, that if the over-centre is correct, the system 

should not collapse owing to heavy treatment.

Regards,

William

---

gcrowder2

Joined: 09 Jan 2006
Posts: 136
Location: Golden, Colorado USA

Posted: Wed Feb 28, 2007 10:59 pm Post subject: Re. mono gear collapse

I sure bounced the hell out of some early landings with my mono till I 

figured

it out (just get the tail down first - duh!) to the point I thought I was 

going

to prop strike but no u/c collapse.  I have the mod to stiffen the u/c lever 

but

still have not installed it.  The lever is still very tight with no play 

after 400 hrs.

  My flaps can be left in any position in slow flight and they will not move 

up

or down.   I only fly off of pavement tho.  I plan to tighten the u/c bungee

this spring as raising the gear that last inch into the detent can be 

difficult.



                                          Glenn



[quote]From: "William Mills" <william(at)wrmills.plus.com>

Reply-To: europa-list(at)matronics.com

To: <europa-list(at)matronics.com>

Subject: Re: Re. mono gear collapse

Date: Thu, 1 Mar 2007 06:13:45 -0000




<william(at)wrmills.plus.com>



Ron,

I know of at least two monos that have ground away the front of the 

outrigger spat right through to the front face of the wheel fork tube and 

removed the head of the retaining bolt.  This happens during a ground loop 

owing to strong crosswinds on a hard runway.  The leg is bent horizontal 

when this happens, but it does not cause it to collapse.  The U/C will also 

withstand an A/C drop after hitting a bump on landing below flying speed, 

sufficient to break the prop, but the U/C does not collapse.  Hope this 

give mono builders confidence, that if the over-centre is correct, the 

system should not collapse owing to heavy treatment.

Regards,

William

---

grahamsingleton(at)btinte
Guest

Posted: Sat Mar 03, 2007 2:50 am Post subject: Re. mono gear collapse

David

My conclusions are the same.

The snap effect on the overcentre is dependant on the amount of 

overcentre, IOW if there is no overcentre there will be no tendency for 

it to flick undercentre when the load comes off the gear, the more the 

O'centre the more the tendancy to flick under.

I think the strut reinforcement is almost essential too, it reduces the 

flexibility of the locking mechanism.



Graham



David Joyce wrote:



 	  Quote: 	
		          My conclusions are:

  (1) that the system is best set up being only just overcentre

  (2) that the Gear lever/ LG08S joint has to be as solid as possible, ie

 holes precisely to size and    faces bonded, and the reinforcing mod added)

   (3) that the detents for the gear lever should allow no significant

 movement

               Regards, David Joyce, G-XSDJ

-- 
	


Graham Singleton



Tel: +441629820187

Mob: +447739582005

hurstkr(at)redzone.com.au
Guest

Posted: Mon Mar 05, 2007 3:16 am Post subject: Re. mono gear collapse

Fellow Europaphiles  (Mono believers only)

  

 I think I made the list aware of this some  time back but just in case I didn't . . .

  

 Take a look at the attached photos which  are self explanatory and note the packing which was necessary on one of the  stops.

  

 Of three undercarriage frames I have  checked, all have had this problem.  I therefore suspect that YOURS might  be like it too.

  

 IOW, one stop is shorter than the other and  when the LG08's are pinned to the shaft, although they both touch their  respective stops at the same time, they (the LG08's) are not in the same  plane.  One is more over-centre than the other.  I'll leave it as an  exercise to work out what this could cause!

  

 Cheers

 Kingsley in Oz

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jodel(at)nildram.co.uk
Guest

Posted: Mon Mar 05, 2007 9:30 am Post subject: Re. mono gear collapse

Kingsley,  

   

In those photos the mount is resting on the engine mounting points.  These are offset toward the starboard side of the aircraft.  I suspect that the “error” that you found is supposed to be there.  

   

Simon  

   

G-BZTN  

         

  

From: owner-europa-list-server(at)matronics.com [mailto:owner-europa-list-server(at)matronics.com] On Behalf Of Kingsley Hurst

 Sent: 05 March 2007 11:13

 To: europa-list(at)matronics.com

 Subject: Re. mono gear collapse  

  

     

Fellow Europaphiles (Mono believers only)  

    

   

    

I think I made the list aware of this some time back but just in case I didn't . . .  

    

   

    

Take a look at the attached photos which are self explanatory and note the packing which was necessary on one of the stops.  

    

   

    

Of three undercarriage frames I have checked, all have had this problem.  I therefore suspect that YOURS might be like it too.  

    

   

    

IOW, one stop is shorter than the other and when the LG08's are pinned to the shaft, although they both touch their respective stops at the same time, they (the LG08's) are not in the same plane.  One is more over-centre than the other.  I'll leave it as an exercise to work out what this could cause!  

    

   

    

Cheers  

    

Kingsley in Oz  

  

        [quote][b]

hurstkr(at)redzone.com.au
Guest

Posted: Mon Mar 05, 2007 4:51 pm Post subject: Re. mono gear collapse

Simon,

  

 You must compare BOTH photos.  The frame was in  the same position on the bench when both were taken.

  

 The frame was resting on the engine mounts but the  purpose of photos was to show the relationship between the stops and the housing  for the shaft that ties the LG08 's.  A line drawn between the two stops  was not parallel to the axis of the shaft.  Believe me, the stops were NOT  correct.

  

 Anyway, my frame is a Classic one and as such does not  have offset engine mounts AFAIK.

  

 Regards

 Kingsley

  

 [quote]   

   --

jodel(at)nildram.co.uk
Guest

Posted: Tue Mar 06, 2007 10:34 am Post subject: Re. mono gear collapse

Sorry!  I see what you are getting at now.  

   

Simon  

         

  

From: owner-europa-list-server(at)matronics.com [mailto:owner-europa-list-server(at)matronics.com] On Behalf Of Kingsley Hurst

 Sent: 06 March 2007 00:54

 To: europa-list(at)matronics.com

 Subject: RE: Re. mono gear collapse  

  

     

Simon,  

    

   

    

You must compare BOTH photos.  The frame was in the same position on the bench when both were taken.  

    

   

    

The frame was resting on the engine mounts but the purpose of photos was to show the relationship between the stops and the housing for the shaft that ties the LG08 's.  A line drawn between the two stops was not parallel to the axis of the shaft.  Believe me, the stops were NOT correct.  

    

   

    

Anyway, my frame is a Classic one and as such does not have offset engine mounts AFAIK.  

    

   

    

Regards  

    

Kingsley  

    

   

  [quote]  

--

raimo.toivio(at)rwm-syste
Guest

Posted: Tue Mar 06, 2007 12:06 pm Post subject: Re. mono gear collapse

All,

  

 Is there any mono flying with fixed main  gear

 but adjustable /moveable flaps  /outriggers?

  

 If so, what is the penalty (speed,  handling)?

  

 Just a thought. Personally I will definetely  not try it.

 Retractable main gear was one of my main  

 reason to build  Europa MW - I like it.

  

 Geometrical lock is safe - if it is there and w/o  play.

  

 Regards, Raimo

 ============

 Raimo M W  Toivio

37500  Lempaala

Finland

  

 tel +358 3 3753 777

fax +358 3 3753 100

gsm +  358 40 590 1450

  

 OH-CVK

OH-BLL

OH-XRT  #417

    [quote][b]

karelvranken(at)hotmail.c
Guest

Posted: Tue Mar 06, 2007 3:43 pm Post subject: Re. mono gear collapse

Hi Kingsley and all,

                  I made the same measurements as you did  with the same results.

                  In my logbook I entered the "optional" mod  51 strut application on februari 2001 two years after publication. But I did it  my way.

                  Page two of the mod begins: The strut will  not be absolutely straight but its sideways flexibility will allow this. I  thought not to allow any                      flexibility at all.  Neither the bending of the lower part of the landing gear lever could ever  receive my green to go. Last but not  least                              the moment arm to tranfer the moving forces to the three AN4 bolts seemed  to me to long even with the proposed strut. The mecanism                      has  also to work when the supporting bungee eventualy fails; and then  friction forces are great. 

                  In attachment a raw outline of my strut  mod. Of the same alloy I made it in one flat plane. The problems that further  occured were                               easily solved. a) The shaft moved 1,5 cm outwards to accept the lever  without bending. In the cockpit module this was a problem for the                       incurved swell for big thighs. But since I never had  them big, at my age I could easily make the choice and modified the cockpit  module,                      not yet installed. By  eliminating the curve I had a beautifull flat surface as well horizontal as  vertical and believe me certainly as strong as it                  was before,  because the way it was made was for people who never will look how it was  done. 

                  b) I remarked by visiting other builders  and Cranfield and Kemble that for those  building like the book; the handle to operate the lever                           was only at the left side (sorry trikers, whe are mono's). In  my mod I have sufficient space left to operate the landing gear lever in the  same                  vertical plane without forcing a torsion on the lever and without amputating my  little finger.

                  c) At the lowest end I changed the pivot  pin by one 4 mm longer  without  problem.

                  d) Finally I was lucky to notice that by  fixing the three bolts, the lever gave a light pressure inside to facilitate the  locking in the gates of                      the guide plate.

                  By trial and error I made the stuts equal  to stop the overcenter and avoided hammersledge from metal to metal. I remeber  that I was laying                  under my beauty pushing up and down the gear many, many  times. Believe me there was no sexual meaning at all but I got a real                               satisfaction when  I knew it would perform when I would be the pilot. Meanwhile I have only 25  hours self done from the beginning ( I am                      flying since 1959)  and now waiting for the mod 72 and inspection at the same  time.

                  Kingsley, I much appreciate your  observations,and forgive me if I did violence to your beautiful language, I am  Flemish.

                  Since my pics for the modified cockpit module are not available at the moment,  I will send them when I am able to do, you will                                    receive them later on your personal e-mail adres.

                 Greatings  to down under,

                  Karel Vranken, # 447   F-PKRL

 [quote]   [quote]     

     --

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karelvranken(at)hotmail.c
Guest

Posted: Tue Mar 06, 2007 4:04 pm Post subject: Re. mono gear collapse

Dear raimo,

 Don't think you are the first of thinking that it  would be better. You know that for the trikes there is an operational mode for  flap setting. But we as mono's, we need our outriggers, so we can't separate the  setting for half or full or less. But remember we made perhaps the choice to be  faster.

 I really think the best Europa flyers are the  mono's. The trikes are apron exhibition and not without success.

 Best regards,

 Karel Vranken  #447  F-PKRL

 [quote]   From:    Raimo Toivio (raimo.toivio(at)rwm-systems.fi) 

   To: europa-list(at)matronics.com (europa-list(at)matronics.com) 

   Sent: Tuesday, March 06, 2007 9:05    PM

   Subject: Re: Re. mono gear    collapse

   



   All,

    

   Is there any mono flying with fixed main    gear

   but adjustable /moveable flaps    /outriggers?

    

   If so, what is the penalty (speed,    handling)?

    

   Just a thought. Personally I will definetely    not try it.

   Retractable main gear was one of my main    

   reason to build    Europa MW - I like it.

    

   Geometrical lock is safe - if it is there and w/o    play.

    

   Regards, Raimo

   ============

   Raimo M W    Toivio

37500  Lempaala

Finland

    

   tel +358 3 3753 777

fax +358 3 3753 100

gsm    + 358 40 590 1450

    

   OH-CVK

OH-BLL

OH-XRT #417

 	  Quote: 	
		  



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[b]

raimo.toivio(at)rwm.fi
Guest

Posted: Wed Mar 07, 2007 3:02 am Post subject: Re. mono gear collapse

Dear Karel,

  

 You can be sure I do understand we need 

 outriggers (and full flaps)  when on the ground! 

  

 I meant the moment before landing,

  it could be possible to have graduated 

 flaps. Let is say 10 degrees during downwind,

 20 degrees during basic and finally all 27  degrees

 when landing...that was my point. 

  

 I do like my Cessna´s adjustable flaps.

  

 Raimo

 =====

  

 [quote]   ---

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