Infinity Gear Pins

[Larry Wiechman]

Could the pin flex at the failure point if the bore was not deformed?

[TMann]

Good question Larry.

I think a lot on unanswered questions exits on this one.

 

I would really would like to know why the pattern exists on the break at a 45 degree angle to the drilled hole.

[Lynn Erickson]

I am NOT an engineer.

I would question the timing of the deformation of the bore that the pin is pressed into.

Was it the deformation of the bore that caused the pin to fail?

Or, was it the failure of the pin that caused the deformation of the bore?

there is no timing, they have to happen at the same time. in order for the pin to flex the aluminum bore had to deform. and in order for the bore to deform the pin had to flex. unless it was not built to the proper standards, loose hole or undersize shaft. may be just not engineered to take the stress imposed on the parts. I still say the tube is being twisted back and forth by the wheel loads imposed on the outer tube which waiter said was loose and the twist in the inner aluminum alignment tube. the whole system has to work together to prevent twisting which it is clearly not. its not like this is the first one of these to fail. I was there when the same part failed only two flights after the set of gear was overhauled by the factory where it had the new updated aluminum tubes installed. the pin was bent at a 45 degree angle to the gear leg and the tubes on both gear were cracked, one all the way through and one about 3/4 through. when the inner tube cracked through it allowed the tube to twist and the resultant forces of the twisting and the weight on the over center strut ( which is mounted at 45 degrees to the gear leg ) caused the pin to be overloaded and bend. we also found the outer bolts loose after the mishap. after the tubes were replaced with the steel ones these problems seem to be resolved.

[Lynn Erickson]

I rigged up a pin puller and was able to "mostly" remove the lower pivot pin. Pressed in is an understatement! Even with the pin puller, it required an awful lot of force to move the pin. I was able extract the pin until it was flush on the forward portion where it protrudes inside the side brace Mount's angle bracket.

 

After seeing how tight and exacting that fit is, I can't imagine how Waiter's pin failed in the way it did AND if even if it had, I'm surprised it came out on its own considering how much force is required to pull that pin versus the type of retention hardware is installed on the aft end. It's nothing but a simple retaining ring and a washer.

 

That method tells me that it's virtually all shear loads and almost no tension loads.

 

I'm curious about elongation of the hole where Waiter's lower pivot pin was.

 

Elongation and a shimmy.. yea... I can see the failure in that case.

Frank, I don't believe the pin is the problem. Because of recent failure and past failures of the inner alignment tube I would recommend that you also check these tubes for cracking and twisting and maybe install a set of steel tubes if it has not already been done.

[plmjohnson]

Good question Larry.

I think a lot on unanswered questions exits on this one.

 

I would really would like to know why the pattern exists on the break at a 45 degree angle to the drilled hole.

The side brace is connected at 45 degrees (approx) so the load on the pin runs directly down the the line of the sidebrace. If you look at the pictures that Waiter presented the failed pin matches the line of force from the side brace. This suggests that the roll pin is no longer on the neutral axis and represents a significant part of the strength direction.

 

Regarding the timing of the events: It may be that the aluminium deformed elasticly alowing the steel to pass through the yield point and fail. As the failed pin started to move out of the press fit hole it further deformed the aluminium. If my hypothesis is correct then the pin failed on a landing and it took some taxi time before the remaining ping finally came out.

 

Regards

 

Phillip Johnson

[TMann]

The side brace is connected at 45 degrees (approx) so the load on the pin runs directly down the the line of the sidebrace. If you look at the pictures that Waiter presented the failed pin matches the line of force from the side brace. This suggests that the roll pin is no longer on the neutral axis and represents a significant part of the strength direction.

 

Regarding the timing of the events: It may be that the aluminium deformed elasticly alowing the steel to pass through the yield point and fail. As the failed pin started to move out of the press fit hole it further deformed the aluminium. If my hypothesis is correct then the pin failed on a landing and it took some taxi time before the remaining ping finally came out.

 

Regards

 

Phillip Johnson

That makes the most sense. I have a set of the gear here and a new set on order. I'm using this set for building while I wait for my new set.

 

I'll talk with the manufacturer and get an engineered solution in case I opt to keep this set. I know the new set are done differently.

 

As far as any other changes, I think I would prefer an engineers opinion/evaluation vs. other opinions ...... but that's just me. I would not want to post a change to the gear that ended up getting someone hurt (or worse) especially with the litigious society we live in today.

[Steve Innova]

That makes the most sense. I have a set of the gear here and a new set on order. I'm using this set for building while I wait for my new set..

Might as well modify your 1st generation set, once the solution is known. I'd trust a 1st Gen with the correct axles and modified steel guide tubes over a (delivery date TBD) Xgeneration set w/the wrong axles and AL guide tubes.

 

I'll talk with the manufacturer and get an engineered solution in case I opt to keep this set. I know the new set are done differently. .

How are they different? What's improved?

 

As far as any other changes, I think I would prefer an engineers opinion/evaluation vs. other opinions

Good choice!

[Waiter]

Just got off the phone with JD;

 

A quick review:

 

JD reiterated that he has never seen this pin fail like this, He's seen them bent, but never broken.

 

This agrees with everyone who has looked at the pin, this failure should not have happened.

 

It appears as if the pin may have had a defect in it. There is a small nick /notch at about 45 degree from the original roll pin hole. This appears the be where the pin started to fail. a close examination reviels the fracture line starting at this nick, extending through the roll pin hole, and continuing. As Phil observed, this line is perpenducular to the angle of the side brace and the stress it would induce.

 

Add a couple "Very Hard" landings that may have started the fracture, then it was just a matter of time before the pin completely failed.

 

The Hard landing happened very early on, just as I was returning the plane to service. I told JD that if I had landed the plane this hard with the standard bow gear, I know I would have hit the prop. :eek:

 

I discussed my repair strategy with JD, I told him that I have complete trust and confidence in the gear and will continue to support him.

 

However, I didn't have confidence in the pin, as long as it used a roll pin for retention. We discussed the repair procedure, simply clean the existing hole and ream it oversize, then make and press fit a new pin in place. The roll pin will be relocated to the end of the pin, rather than go through the middle.

 

JD offered several other repair options, but ultimately agreed that a new "Custom Pressed in" pin was a viable repair.

 

I'll apply this repair procedure to both gear legs.

 

 

Waiter

[philc1]

Two more "non-engineer" thoughts/questions to add to the fray - probably worth what I paid for my engineering education. ($0.00)

 

1) If the solution is to machine a new, slightly oversized press fit pin, would it make sense to add a shoulder to the inboard end of the pin for retention? (Similar to the artwork in post #32 with the shoulder moved to the inboard end. and sized to fit in the available space at the peak "Infinity" triangle) The pin would then be pressed outward through the press fit hole. The pin geometry progression from inboard (forward) to outboard (aft) would be shoulder, radius, five thou oversized body (for the length of the oversized press fit hole), transition to the standard diameter needed for the ID of the bearing, and finally the retention mechanism which in the case of the original is a slot for a retention ring (and brings me to my next question/thought.)

 

2) The current retention mechanism (which keeps the brace assembly from sliding off the pin) is a special retaining clip. The current clip seems superior to the standard retaiing clip used in years past. If we make the effort to create a new pin, is there another retention mechanism that may offer additional reliability? (e.g. a castle nut and a short threaded section outboard (aft) of the bearing and retaining washer/bushing.)

 

There seems to be great progress here toward a small design change that may prevent future failures. I don't want to take things off course with naive ideas, but thought I'd put these out there just in case eithier made sense to more educated and experienced minds.

 

Phil - LEZ RG project Milwaukee.

[Lynn Erickson]

Two more "non-engineer" thoughts/questions to add to the fray - probably worth what I paid for my engineering education. ($0.00)

 

1) If the solution is to machine a new, slightly oversized press fit pin, would it make sense to add a shoulder to the inboard end of the pin for retention? (Similar to the artwork in post #32 with the shoulder moved to the inboard end. and sized to fit in the available space at the peak "Infinity" triangle) The pin would then be pressed outward through the press fit hole. The pin geometry progression from inboard (forward) to outboard (aft) would be shoulder, radius, five thou oversized body (for the length of the oversized press fit hole), transition to the standard diameter needed for the ID of the bearing, and finally the retention mechanism which in the case of the original is a slot for a retention ring (and brings me to my next question/thought.)

 

2) The current retention mechanism (which keeps the brace assembly from sliding off the pin) is a special retaining clip. The current clip seems superior to the standard retaiing clip used in years past. If we make the effort to create a new pin, is there another retention mechanism that may offer additional reliability? (e.g. a castle nut and a short threaded section outboard (aft) of the bearing and retaining washer/bushing.)

 

There seems to be great progress here toward a small design change that may prevent future failures. I don't want to take things off course with naive ideas, but thought I'd put these out there just in case eithier made sense to more educated and experienced minds.

 

Phil - LEZ RG project Milwaukee.

some good thoughts but the pin can not be inserted from the inside to the outside because of the angle of the part. see post 5 second picture. the retaining clip used on the sets that I have worked on were both spiral retaining clips. they seemed to be very secure and never had a problem with the clip. I like Waiters idea of putting in a new pin with the retaining pin on the inside of the opening. but I might use a bolt and lock nut instead of a pin just like the retaining bolts used in the control stick system. you could also use a spiral clip just like the outer end

[Richard]

I know this doesn't relate to the pin itself but I looking for information on the related bracket (drag brace?) where it is "bonded" to the strut body.  It looks like it was soldered or brazed rather than welded maybe "Alumaloy" or similar.  I have heard that these have come loose.

Does anyone have any experience welding these; removal of anodizing, contamination of weld due to aluminum brazing, etc?

Why did JD chose to not weld the assembly?  Are they made from 2024 or 7075 (not weldable)?

Yes I have tried to get a hold of JD, no he has not responded.

[Kent Ashton]

There was a discussion not long ago here and it sounded like a PIA to fix.

https://groups.google.com/forum/?utm_medium=email&utm_source=footer#!searchin/cozy_builders/infinity|sort:date/cozy_builders/Nhv-zVchpD4/kO40H86qAAAJ

I had heard JD was sick and commented that he might be out of business but he replied a bit bruskly that he had not.  So who knows?