[NSRCA-discussion] Mo'CF gear talk from AeroSlave

[Gray E Fowler]

Gear mount plate failure is independent of the gear itself, although it is 
safe to say that a too stiff gear will put more stress on the plate. So 
needs to flex so reduce stress, but not a spring.

Your failure across the fibers is strange, but not unheard of. Composites 
weak link is compression, because it is the duty of the resin to transfer 
compression load from one fiber to the next, and resin is orders of 
magnitude weaker than fibers. A genereal rule of thumb is for every 2% 
void volume in the laminate equals about a 20% drop in compression 
strength. It sounds as if your failure was a compression initated failure, 
as what you describe sounds like a compression failure. 
Every RC gear I have looked at, I can visually see voids. Normally a void 
volume greater than 15% is required to be able to be seen without a 
microscope. When I first posted that AeroSlave gear would be Autoclave 
processed, that is to keep the void volume below 2%, and industry 
standard. Your failure was most ikely as you described..a hidden flaw in 
the laminate. In the real world we ultrasonically scan composites for 
voids-not feasible($$$)  for RC models.




Gray Fowler
Senior Principal Chemical Engineer
Radomes and Specialty Apertures
Technical Staff Composites Engineering
Raytheon



<glmiller3 at suddenlink.net> 
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01/19/2009 09:34 AM
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Re: [NSRCA-discussion] Mo'CF gear talk from AeroSlave






I had an ES gear failure in Crowley two years ago- grass field and the 
landing was a 9 before the broken gear leg zeroed it.  The gear strut 
broke straight across  perpendicular to the long axis about half way 
between the fuse and wheel.  In a human bone, I would call this a 
"pathologic fracture" ie, implying an underlying pathologic defect.  I 
actually patched this gear by splinting it with a piece of carbon plate, 
wrapping it with carbon cloth, soaking the whole thing with epoxy and 
wrapping it up tight with celophane and tape.  It isn't pretty, but it is 
quite funtional.  Since it was one of my last long ES gears I'm still 
using it. 

No manufacturing process is perfect, and I think somehow there was a 
structural weakness that failed here.  However, not all the preceding 
landings were 10's, so I might have cracked it on an earlier landing and 
it failed later.

Interestingly enough I had a gear plate failure on that same airplane (E 
Pinnacle- Oxai).  the gear plate was made with carbon reinforcing the 
bottom of a light ply plate.  I had drilled it and put screws with large 
washers through from above and locknuts below.  As I flew, the gear would 
loosen as the washers were pulled into the light ply.  After several 
rounds of tightening, I noticed fatigue around the washers and upsized 
them, but eventually, (again in Crowley on a grass field) the screw and 
washers pulled through the plate...leaving nice holes in the plate which 
stayed attached to the fuse sides.  The carbon cloth pulled off the bottom 
and added no significant strength.    I repaired it with a hardply top 
surface and it never was a problem again. 

George
---- aeroslave at tx.rr.com wrote: 

=============
Dave

Concerning your earlier email

"I am not a fan of the typical 2 piece gear – where each half stops short 
of the middle, and a nasty bending load is created in the center of the 
gear plate (unless a spreader plate/joiner is attached between the two 
legs). "
--

Here's how I see the stress...

On a landing, hard or soft when the gear impact, the load will be tension 
on the bolt closest to the edge of the "Half gear". Bolts work really good 
in tension. The other load is the bending back of the bolts-a load at 
which bolts suck. So a rough landing using a two piece gear wants to 
either pull the bolt through its mounting  in the plane (cuz 11lbs ain't 
gonna tension fail the bolt) or its gonna bend the bolt heads ...resulting 
in a semi tension on the plane bolt mount, wanting to once again pull it 
through. What happens in reality is the bolts do not break, but the entire 
mounting plate is stress tension up front, compression in the rear until 
it find sthat weak "terminated area" and rips out at that point. My whole 
thinking here is that regardless of a 1 piece or two piece design, the 
weak link to failure lay elsewhere-so 1 or 2 piece does not matter. 
Speaking of failures.......

Anyone who has had a gear failure...please let me hear it. Describe the 
landing (wasn't a 10 now was it???? be honest)  describe the 
failure...bolts,  plane mount, fuse sides, gear break..whatever.

My landing are always scored about 9.24-9.56, which is why Lance is 
testing the prototype gear.

Gray 

AeroSlave Dude #2 (Lance is #1-I default to him) 

AeroSlave
4408 Elmhurst Dr
Plano, TX  75093
www.aeroslave.com
PayPal: aeroslave at tx.rr.com
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