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  #16  
Old 08-16-2004, 02:24 PM
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Quote:
Originally Posted by mplafleur
Hey, I'm a real engineer! Just electrical, not mechanical.
I know, I know, i meant structural/mechanical. Mr lafleur, i loved your solution to reinforce the area with ultra low temperature super magnets made from arsenic. I just couldn't find a properly shaped thermos bottle to keep it in at 2 degrees Kelvin, but I really think it would work better than the stupid glass and plywood solution we came up with.

Oh yeah, this is my website.
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  #17  
Old 09-20-2004, 10:47 PM
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Any day now the pics mp took A FEW WEEKS AGO should show up on how i solved the percieved problem with the nose gear
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  #18  
Old 09-21-2004, 12:08 AM
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Quote:
Originally Posted by Dust
Any day now the pics mp took A FEW WEEKS AGO should show up on how i solved the percieved problem with the nose gear
Ok, ok. Sheeesh.

In fact, I just downloaded these yesterday.

These are some snaps of our reinforcements. We dug out an inch of foam and filled with flox. The rest is self-explanatory I hope. dust can always chime in...
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  #19  
Old 09-21-2004, 12:00 PM
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Thanks mike, I owe you one.

pic 1 just shows where we removed 1" of foam on the entire ng30 and filled with flox, the plywood idea was scrapped as not needed and in the way.

pic 2 show the extension box dave added to make room for an extra ujoint to put the handle for the manual gear controll rod to be moved down on the panel and the two 2.5 x 9 inch plywood ribs added

pic 3 shows the 6x4 4 ply bid angle added to the floor and ng30 on each side

pic 4 shows the layup that goes from the ng30 around the ply rib on both sides and ends up accros the bulkhead butting the other rib

pic 5 shows 4 ply bid layup the extends from front of box down bulkhead to canard hard point layup area.

pic 6, not shown, shows layup from bottom of box down the bulkhead, between ply ribs

pic 7, not shown, shows layup from inside box bottom and down 4 inches on the other side of bulkhead

pic 8, not shown, shows layup from top of plywood rib outside to bottom of rib outside

all layups 4 layers of random BID

All work approved by an electrical engineer

OH, yeah and a structural one too
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  #20  
Old 09-21-2004, 01:55 PM
Marc Zeitlin Marc Zeitlin is offline
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Since my nose gear failure was the genesis of this thought process, and since I am an aeronautical/mechanical engineer, I'll comment on what I see here based on my experience and my desire not to have folks copy stuff that may be extra work without any clear benefit.

Quote:
Originally Posted by Dust
pic 1 just shows where we removed 1" of foam on the entire ng30 and filled with flox, the plywood idea was scrapped as not needed and in the way.
Since the 4 plies of BID on each side of each NG-30 is what provides almost ALL of the strength/stiffness in the layup, even if the center is solid flox, substituting flox for foam will accomplish nothing other than adding a few ounces of weight to the structure. A much more useful change, assuming that ANYTHING is warranted (which I'm NOT at all sure of), is Nat's recommendation of raising the front section of the NG-30's a couple inches, and then having a generous radius at the intersection of the flat front section and the angled rear section.

Quote:
Originally Posted by Dust
pic 2 show the extension box dave added to make room for an extra ujoint to put the handle for the manual gear controll rod to be moved down on the panel....
I was wondering what that was for. Not a bad idea (although Nick Ugolini says to eliminate the manual extension altogether - just use a direct override line from the battery). I've got the manual extension, with the double u-joint.

Quote:
Originally Posted by Dust
and the two 2.5 x 9 inch plywood ribs added ....pic 4 shows the layup that goes from the ng30 around the ply rib on both sides and ends up accros the bulkhead butting the other rib....pic 5 shows 4 ply bid layup the extends from front of box down bulkhead to canard hard point layup area.....
OK - I'm not at all sure what the point of these plywood ribs on F-22 is - in my case, the whole NG-30/F-22 section ripped off the fuselage floor, and punched out the top of F-22 and the flat area on top of F-22. You could make F-22 infinitely strong and stiff, and all that would happen was that you'd rip out a larger section of F-22 and the flat top area.

In this case, I think all you've done is move the failure point further out, closer to the canard attach points, so that IF you have a failure, you're more likely to destroy something important.

Quote:
Originally Posted by Dust
pic 3 shows the 6x4 4 ply bid angle added to the floor and ng30 on each side
This is marginally useful - probalby all it will do is move the break line slightly further forward on the inner floor, ensuring that you rip a larger section of the inner floor off the foam when it fails.

Quote:
Originally Posted by Dust
pic 6, etc.
These are all related to the plywood box on the rear of F-22 - same comments apply as above. Extra weight, no utility - possibly harmful in an actual failure due to movement of failed area further toward structurally important areas.

Maybe I'm misinterpreting what you've done here, and how it work or how it was intended to work, but that's my $0.02 based on what I see. Sorry.
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  #21  
Old 09-21-2004, 08:54 PM
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Quote:
Originally Posted by Marc Zeitlin
Maybe I'm misinterpreting what you've done here, and how it work or how it was intended to work, but that's my $0.02 based on what I see. Sorry.
OK the failure appears to be one of lateral movement opposite the nose wheel, at the top rear of ng30's going side to side, when that failed everything else went kablooie and probably doesn't need to be strengthen. upward force from the landing did not rip it out, but the shimmy did.

now, look at what there is to stop the shimmy and it aint much, ng30's stop too low and are barely tied into the structure. we have just made a structure to absorb the lateral stresses from severe shimmy.

My analysis procedure was quite simple, retired engineer looked at structure of our planes(fortunatly he has also built quite a bit of them), told me where it was week and what forces caused the problem. then i showed him the pics of your problem and they agreed with his cold analysis. bottom and the front of ng30's ripped out AFTER rear of ng30 broke out due to lateral force of shimmy I was going to reinforce other parts, but i think his analysis is correct, the shimmy gotcha and we have put 80% of our work in that area

I'm not saying i am right, this is what we did and in 30 years i can tell you the result.

if i were to build them today, i would go 1/4 inch wider, so motor would fit in, and have the ng30 go all the way up to the top of that area and tie the whole thing together with glass. more glass from inside ng30's to bulkhead both inside and out.
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  #22  
Old 09-22-2004, 10:02 AM
Marc Zeitlin Marc Zeitlin is offline
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Quote:
Originally Posted by Dust
OK the failure appears to be one of lateral movement opposite the nose wheel, at the top rear of ng30's going side to side, when that failed everything else went kablooie and probably doesn't need to be strengthen. upward force from the landing did not rip it out, but the shimmy did.
I completely disagree - there was (and can be) no lateral motion at the top rear of the NG-30's - there's nothing attached there that could drive such a motion. Hard side to side motion of the nose strut would twist the box that NG-6 is mounted in, which would then stress the front lower section of the NG-30's. There is NO doubt in my mind that the NG-30's ripped at the battery cutout sharp corner FIRST, and then the whole structure rotated up and back around the NG-30/F22 bottom joint.

Quote:
Originally Posted by Dust
now, look at what there is to stop the shimmy and it aint much, ng30's stop too low and are barely tied into the structure. we have just made a structure to absorb the lateral stresses from severe shimmy.
No you haven't, because you're addressing an issue that doesn't exist and not addressing one that does. You've stiffened an area that doesn't need it. If you take a look at my failure pictures, you'll see that the NG-30/F-22 box didn't fail at all - it held together completely after the front of the NG-30's failed.

Quote:
Originally Posted by Dust
My analysis procedure was quite simple, retired engineer looked at structure of our planes (fortunatly he has also built quite a bit of them), told me where it was week and what forces caused the problem. then i showed him the pics of your problem and they agreed with his cold analysis. bottom and the front of ng30's ripped out AFTER rear of ng30 broke out due to lateral force of shimmy I was going to reinforce other parts, but i think his analysis is correct, the shimmy gotcha and we have put 80% of our work in that area
Well, I'm going to disagree with your engineer's analysis 100%. I think he's got it backwards, as I said above, and I think that looking at the way the stress cracks progressed in the NG-30's and fuselage floor proves the sequence of events.

Here's the sequence:
1) Shimmy causes NG-6 rocking, causing FRONT LOWER section of NG-30's to move side to side and rotate.
2) NG-30's crack at tension stress concentration corner (battery cutout corner)
3) crack propagates at 45 degree angle down to the rear of NG-30's and at 45 degrees back along fuselage floor
4) as crack gets large enough, NG-30/F22 box rotates up and back due to upward force from nose gear mechanism, allowing nose gear mechanism to punch backwards through top of F-22 and bending rudder pedal tubing

This is the only sequence of events that matches the damage history and the damage as examined.

Sorry to say, but your engineer's judgment is just incorrect, that's all there is to it. By following his advice, you've wasted a bunch of time and effort and added some unneccesary weight to the planes. You haven't done any damage, mind you - the plane will work just fine.

Quote:
Originally Posted by Dust
I'm not saying i am right, this is what we did and in 30 years i can tell you the result.
Not really. You won't have any clue WHY you haven't had a nose gear failure, if you never have one. The only way you'll be able to tell anything is if it DOES fail.
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  #23  
Old 09-22-2004, 10:39 AM
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Quote:
Originally Posted by Marc Zeitlin
You haven't done any damage, mind you - the plane will work just fine.

Not really. You won't have any clue WHY you haven't had a nose gear failure, if you never have one. The only way you'll be able to tell anything is if it DOES fail.
Well, we also added 3 layers of bid to the nose bottom and wrapped them around the flange for the landing gear.

Tom looked at the gear as acting as a fulcrum. A close look at all of the reinforcements we made, i believe will show that the specific areas of concern have been strengthened.

As this is a RARE occurrence, i won't pay any more attention to it, but i must thank you for you very polite disagreement,

The fun thing about failure analysis, unless you have a high speed camera to record it for analysis, its all conjecture.
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  #24  
Old 12-27-2004, 07:31 PM
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Having spent the last two days goggling over and pawing at my plans I started going over the newsletters last night, and the first thing I notice is the beef-up of the NG30's discussed above. Am I right in assuming the increase in the depth of the NG30 means a corresponding decrease in the height of F5 with a "radiused" bottom edge? I realise I'll be building for months/years before I get to this bit, but it would be nice to get some confidence in my first pencil marks on the plans...
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  #25  
Old 12-27-2004, 09:04 PM
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did you see the pic i posted elsewhere and i suggest you increase the space between the ng30 by 1/4 inch to make room for the wilhemsons gear to pivot inside the rear where I suggest you take the ng30's up to the bottom of a future cross brace and tape them in.
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  #26  
Old 12-27-2004, 10:06 PM
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Default cuting out ng 30's

ok there out out of here....just ordered more h100 pvc(?) for the retrofit.
dont have the top on yet,but if i do i think i can still get to them.
so now thet i have so time waiting for ups...i can type

Get this, i called genal plactic to beg for a small order of the foam,but he said he was bissy for at lest a week filling orders for all you wanabe builders who ordered from assc, so i called assc to get the foam and they were out,so they back ordered it and had it shiped from gorgia for a extra charge to me
the funny part is that genarals plactic is the one sending them my foam
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  #27  
Old 12-27-2004, 10:09 PM
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Marc talks in a language I understand and being a generalist (50% electronics and 50% structural) I concur. Looking at the basic design though it does not follow basic box beam construction principals. If you have an open bottom you can not have an open top. It must be at least C shaped.

I failed to mention that this would require gear installable from the gear door opening which is doable.
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