Bc12d info

[PA1195]

Re: Bc12d info

I wonder in lieu of welding a brace tubing if a clamp-on brace could be fabricated? Maybe fit between the rear round gear leg and diagonal leg like in #11 above. The diagonal is tapered so something not round might be required over that. To make it work under side loads a triangle shaped brace might have to be formed from two pieces of cross tubing and three clamps. Just an idea in case welding isn't an option.

Maybe mechanics here could come up with something that clamps on to support that weak area.

Gary

[Robert Lees]

Re: Bc12d info

... might block the drain hole....

Drain holes are good for inspecting periodically, to ensure they're clear!

Rob

[PA1195]

Re: Bc12d info

Drain holes are good for inspecting periodically, to ensure they're clear!

Rob

Something 100# of air pressure blown through a nozzle would insure! Any crap that gets blown out at the top would be worth an exam.

Gary

[Robert Lees]

Re: Bc12d info

Something 100# of air pressure blown through a nozzle would insure! Any crap that gets blown out at the top would be worth an exam.

Gary

I meant ALL drain holes (including those in fabric surfaces!)

[PA1195]

Re: Bc12d info

Yes all drains should be clear, but the topic here is specific to landing gear. This issue won't go away by only monitoring a gear leg drain hole. Aircraft owners and their A&P's need to take positive action to monitor gear leg airworthiness. That includes potential internal and external corrosion in addition to Taylorcraft SB 78-001 noted here on CAP's Blog: http://dc65stc.blogspot.com/2010/07/...ern-sheet.html

Gary

[Scott]

Re: Bc12d info

ACF50 is for aluminum only

Huh??

[STEVE KUNKLE]

Re: Bc12d info

I have a left & right, but the strut braces are bent, I'm going to make a jigs, right 1st, looking for usable or unusable gear


Steve
484-256-8066

[LostnSpace]

Re: Bc12d info

I have a left & right, but the strut braces are bent, I'm going to make a jigs, right 1st, looking for usable or unusable gear


Steve
484-256-8066

I've got an extra left, serviceable, spliced about 5 inches from the top, rosette welds, so there is a tube or something on the inside, it came off a flying T, BC12-D, welds look good and don't see anything wrong with it, gary

[PA1195]

Re: Bc12d info

Please note there are at least two failure modes I can envision for the diagonal strut. One would be excessive compression from periodic side loads forcing the lower gear left inwards causing metal fatigue and then bending....and the other would be excessive tension from the lower gear leg being forced outwards after or during stress events.

Any compromise in the diagonal strut in either event could cause failure. Once the safety cable near the shock cords reaches a limit something may fail under tension or torque at the lower gear leg.

Keeping the diagonal strut in good uncorroded shape will help. A welded brace between the diagonal and rear gear leg offers support as noted above. So would a safety cable installed along the diagonal under tension.

Gary

Gary

[Scott]

Re: Bc12d info

ACF50 is for aluminum only

For clarity, specs on acf50:
MIL SPEC 81309 TYPE II AND III APPROVALS which means ACF-50 is approved for ferrous and nonferrous metals, electrical systems and electronic components.

[Hank Jarrett]

Re: Bc12d info

Please note there are at least two failure modes I can envision for the diagonal strut. One would be excessive compression from periodic side loads forcing the lower gear left inwards causing metal fatigue and then bending....and the other would be excessive tension from the lower gear leg being forced outwards after or during stress events.

Any compromise in the diagonal strut in either event could cause failure. Once the safety cable near the shock cords reaches a limit something may fail under tension or torque at the lower gear leg.

Keeping the diagonal strut in good uncorroded shape will help. A welded brace between the diagonal and rear gear leg offers support as noted above. So would a safety cable installed along the diagonal under tension.

Gary

Gary

Slight correction. It isn't actually a "compression" failure or a "bending" failure. When a tube is put into compression it is almost impossible for it to actually fail in compression. There is almost always a slight flaw somewhere that causes the first bend to be introduced that causes sudden collapse in crippling (like when you stand on an empty soda can and someone touches the side with a stick (DON'T TOUCH IT WITH YOUR FINGER!!!! You CAN NOT get your finger out fast enough!) It doesn't last long enough to fail in bending in one place. The reason for jury struts is to make the struts on the wing effectively shorter which dramatically increases resistance to crippling failure. Same would be true for the gear diagonal.
It is probably really just a matter of semantics, but you guys know I can get kind of anal. ;-)
We do need to get in front of the gear corrosion problem. If WE solve it, the FAA won't try to use THEIR solution, which will probably ground ALL of us while they try to figure it out. We don't need another wing strut fiasco! If the FAA does "do their thing" they will probably just ground us all and say to replace all of our landing gears. We DO NOT WANT THAT!!!!!! We need a gear fixture in the group to do repairs and a good way to inspect our gear, OURSELVES so they don't jump in and do something stupid. I have a welder who was interested in taking the strut fixture we lost. There are also a few good gears around to build a new fixture. We need a small group who wants to do a project. Anyone up for it?

Hank

[PA1195]

Re: Bc12d info

Interesting discussion Hank and thanks for the thoughtful correction. I guess the question is: Does that strut most frequently fail in tension - strut separates causing gear to fold out and then up - but possibly weakened due to prior side loads and compression? If that's the typical failure mode (does anyone actually know?) then a safety cable along the strut may delay or prevent a final failure event.

Adding a welded cross tube gear diagonal should prevent prior bending and weakening as Hank notes. Same for a clamp on support like I suggested. But...and here's a question for the engineers...what's the best way to support that tube? That assumes it's not just a corrosion issue to begin with that's exacerbated by extreme loads.

The only gear I've seen up close that failed I believe did so finally under tension. The diagonal strut appeared to separate which allowed the rest of the gear to fold out until the bungee safety cable reached its limit. At that point the upper "A" cross tubing going to the bungee near the gear attach ears failed (bent and separated) which allowed the rest of the gear leg to fold further out past the safety cable's limit.

Comments?

Gary

[Scott]

Re: Bc12d info

Someone mentioned the gear braces are open at the top. This is apparently not always the case (see pic).

Would be interesting to know if there is any coloration between open or closed struts and corrosion/failure. One reality is; if there is no way for moisture/oxygen to get in, corrosion is much less likely to happen.

Question; how large is the opening on the assemblies with open struts? It only needs to be about .25" to fit a USB camera which would enable very good (and inexpensive) inspection of the interior of the strut.

It also may be possible to drill a 1/4" access hole somewhere none-critical (like the center of the attach plate at the bungee end) to inspect a strut that exhibits signs of corrosion (red dust from the lower drain hole).

Before I sent my wing struts to Wag Aero, I did this type of inspection on each strut. The baseline from Wag was that if I found ANY signs of corrosion inside, the strut could not be sealed. So I did the USB inspection so as to not waste money on shipping! see video:

https://www.youtube.com/watch?v=IHBZNLrGwEw

[PA1195]

Re: Bc12d info

Hi Scott. I, and perhaps others (?), have noted the opening(s) at the location in your picture in Post #28. I discovered that by spraying Corrosion-X in the lower drain hole drilled though the TAC A-530 strap located at the lower diagonal strut. I tipped both gears upside down to let it distribute. The next day oil had exited the area near the upper cluster on each...probably from the open tubing at the upper right and lower left of your picture but I didn't look further as I assumed it was normal.

To test while on the plane apply air pressure at the lower drain hole and see if it maintains pressure or exits the upper cluster. It may be that not all gear is open at that location.

Maybe it's time for some discovery and then deal with the situation.

Gary

[Scott]

Re: Bc12d info

Ok now I think I understand.

I suspect the bottom (upper in my photo) of the short "open" tube which butts up to the the end cap (forms the side of the bungee boss) is not welded, because it ends up inside the strut tube. This would be consistent with assembling all the parts before welding, as opposed to welding in two steps.

Anyway that answers the question about access for camera.


I looked over some unrelated accident results and there have been some considerable impacts, enough to cause deformation of the fuselage, without failure of the gear diagonal strut. And have not yet found a failure of a non-corroded strut. So I remain of the believe that there is nothing inherently wrong with the design from a structural/strength perspective.

Likely typically over-built, with the exception of the potential for internal corrosion.
This is also consistent with the bulletins, that indicate no further action unless corrosion residue is detected.