Jump to content

Main Gear Attachment Failure


cozy1bh
 Share

Recommended Posts

Canard Zone Members,

 

I discovered I have a gear attachment failure like the one described by Bill Oertel in the latest CSA newsletter.

 

The failure is made up of three items: 1) the steel tube between the two attach brackets that mount on the fuselage sides is broken at the point where the steel bushing ends, 2) the AN6 bolt is bent, and 3) there is a de-lamination in one of the four heavy glass tabs.

 

In my case, the de-lamination is in the tab only and does not extend into where the lay-ups attach to the strut. Does anyone know if it is best to repace the whole lay-up or can I repair the de-laminated portion by injecting wet flox?

 

For the other two items, I am replacing the thin wall steel tube and bushing arrangement with a thick wall 4130 tube that has the same outside diameter but is reamed out on the inside to perfectly accept new AN6 bolts.

 

Also, since only the Cozy Mark IV has an access panel under the gear strut so that it can be inspected or removed, I had to cut out a portion of the bottom of the fuselage to get the gear out! Big and messy job! I talked to Nat Puffer and he said it is O.K. for me to make a removable access panel out of the part I cut out. This will make future inspections and repairs easier.

 

As always, I'm open to any suggestions on completing this project any of you may have. Any cautions I am not thinking of??? Bill Oertel has been very helpful so far. Thanks Bill!

 

Brian....

Link to comment
Share on other sites

Brian, how are you doing with this? I saw the CSA article as well, but ignorantly thought it only applied to 30 year-old Long-EZs.

 

Does anyone know if it is best to repace the whole lay-up or can I repair the de-laminated portion by injecting wet flox?

Any specific feedback on this particular question? My first reaction would be to replace the layup, but maybe you might be able to do as you suggest -- inject thoroughly with wet flox and clamp. Still, as I write that, I think I'd be more inclined to rebuild the tab.

 

For the other two items, I am replacing the thin wall steel tube and bushing arrangement with a thick wall 4130 tube that has the same outside diameter but is reamed out on the inside to perfectly accept new AN6 bolts.

I was dumbstruck, when visiting John DiStefano this past weekend, that the bushings alone (2 each pin) cost upwards of $40/ea from Brock. A fair price compared to making a one-off, but rather steep if you make a couple per month, IMO. Are you machining your own?

 

Do you have any pictures? I can post them here if you'd like -- just send them my way.

Jon Matcho :busy:
Builder & Canard Zone Admin
Now:  Rebuilding Quickie Tri-Q200 N479E
Next:  Resume building a Cozy Mark IV

Link to comment
Share on other sites

I am still working on the "fix" on my Cozy III as I go. When I am done with this project, I'll post a full article with pictures for others to learn from.

 

I don't have all the answers yet. But for now, here is what I can say in answer to your questions:

 

First, the delamination in the composite tab I discovered was as a result of me trying to remove the old steel tube. It was not from landing loads or the failure of the AN6-80A bolt and tube. The delamination is rather small and minor and does not extend to the strut itself. Local builders have looked at this and have come to the same conclusion. Therefore, I do believe I can fix the delaminated area with an injection of wet flox. The problem is that in the plans, you build up half of the tab, let it cure, then build the other half. Between lay-ups, you must rough the first lay-up to ensure a good bond. But this will never be as good a bond as you get if you lay-up over wet glass. This is where the delamination occured. It happened when I had to pound out the old tube, right at the point where the two lay-up schedules come together.

 

This is not just a "30-year old EZ" problem. In fact, I believe that there are builders out there right now flying on damaged gear who don't even know it. I believe I had been flying on mine with the damage for about 18 months to two years. I say this because I noticed some alignment problems. On some flights, the airplane would pull to the left while taxiing. Then on others to the right. Sometimes it would taxi strait. I kept thinking that maybe it was a crosswind with the open canopy, or a sloping taxiway, or uneven tire pressure, or the new set of tires I just installed, or a dragging brake.... You see, there was always a variable that coused me to think that something other than a gear problem was the cause. Know I know that as the gear moved on the tube - back and forth - both sides did not always move evenly. Sometimes the right side of the strut would move back; other times the left. In any case, the shifting gear caused alignment problems. In 1986, when there were no 30 year-old EZs, RAF issued a recommendation that spacers be installed on the tube between the saddle and the extrusions to keep the gear from moving in its attachment. Unfortunately, word did not get to a lot of builders. I never knew about it. And, although I am not a structural engineer, I can't help but think that the combination of the shifting strut problem, the thin wall tube, and the foam instead fo flox in the void between the tube and the strut all work together to result in broken tubes and bent bolts. And, if the condition continues, in delamination of the tab lay-ups.

 

Finally, I'm not using the bushings. Instead, I'm following the Bill Oertel recommendation to replace the thin wall tube and bussing design with a solid tube. But, instead of using 4130, which can rust, I'm using 304 stainless. It has the same outside diameter of 5/8" to fit the current installation but I need to have a machine shop ream up the center to match the 3/8 inch AN6 bolt.

 

Pictures to come later with the full article.

Link to comment
Share on other sites

I was dumbstruck, when visiting John DiStefano this past weekend, that the bushings alone (2 each pin) cost upwards of $40/ea from Brock. A fair price compared to making a one-off, but rather steep if you make a couple per month, IMO. Are you machining your own?

 

The mating bushings (MKMG-4 in a COZY IV) run about $18 each. The two in the MKMGA tube are included in the price when one buys the tube. The price is worth it, based on my experience making my own and some for another builder.

 

The bushings take some fair attention - or some darned expensive CNC equipment - to stay within the spec. Plus the reamer for the hole (they need to be that smooth, just boring them won't cut it) has a limited life ... at least it *should* have a limited life in a responsible shop, where it would be replaced as soon as the taper approached .0005"/in. (Reamers wear in a taper - front end first.) A decent reamer for this is $20. With a good coolant /lubricant [such as "Edge" ®] it should be good for at least 100 bushings.

 

Regards,

Dale R. (___

COZY MkIV-R13B #1254 |----==(___)==----|

Ch's 4, 5, 9, 16 & 23 in progress o/ | \o

Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

 Share

×
×
  • Create New...

Important Information