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Lower Forward Longerons

M

mquam99

Well Known Member
Today I started reassembly of the fuselage after parts prep. When I attached the lower left longeron to the firewall I had a gap between the firewall mount and the longeron.

I fabricated a spacer and assembled with AN-6A bolts instead of 5A to accomodate for the spacer. I still have clearance to the bottom skin, but need to know if this fix is OK. I can replace the lower longeron since it is not riveted to anything yet, but wanted to get additional opinions. I will call Van's on Monday if need be. Please let me know what you think

thanks

DSC00740.jpg
 
Edge distance?

Mike,

I'm building a -7A, but IIRC the edge distance was tricky to get right on the weldment ears. I'd check if it's still OK since you went with a larger bolt.

Good luck.
 
My first thought would be NO - by introducing the spacer you are changing the thrust line of the engine and this will affect the way the airplane will fly. Unless you've got reason to believe that the longeron itself is not in the position it needs to be (bent or something) then I would be inclined to simply bolt it up without the spacer, let it pull itself together with the bolts, and start measuring very carefully to see what moved where as you did that.

There are many parts of the airplane that don't naturally fall into place when we first assemble them, they have to be pulled or pushed or prodded to conform to their desired shape or position. The firewall assembly in this case (I was there just a couple weeks ago) is heavy enough, and the supporting structure weak enough at this point (especially if you've still got the fuse supported at the 904 bulkhead right now, as you should before rolling the canoe) that there will be some sag downward (up on the aircraft) resulting in that gap. I had some slight gap on mine as well, about 1/8" on one side and 1/16" on the other - but by putting only a slight pull, maybe 10 pounds, on the firewall it closed up completely and mated perfectly. I was surprised how easy it was to move the firewall in relation to the fuse frame at this point - it's not out of the question at all for weight sag to produce this much gap on yours.

A call to Vans on Monday is a good idea.
 
I think you should get some new angles from Van's. It'll only cost 10 or 20 and you'll have piece of mind which is priceless. Those lower longerons are a PSE (primary structural element) and you don't want them compromised in any way. I fitted mine a couple months back and they fit well with no shims and no preload.
 
update

airguy said:
There are many parts of the airplane that don't naturally fall into place when we first assemble them, they have to be pulled or pushed or prodded to conform to their desired shape or position. The firewall assembly in this case (I was there just a couple weeks ago) is heavy enough, and the supporting structure weak enough at this point (especially if you've still got the fuse supported at the 904 bulkhead right now, as you should before rolling the canoe) that there will be some sag downward (up on the aircraft) resulting in that gap. I had some slight gap on mine as well, about 1/8" on one side and 1/16" on the other - but by putting only a slight pull, maybe 10 pounds, on the firewall it closed up completely and mated perfectly. I was surprised how easy it was to move the firewall in relation to the fuse frame at this point - it's not out of the question at all for weight sag to produce this much gap on yours.
Click to expand...



So I pulled the spacers out and then attached the angle using the correct bolts and indeed the whole assembly came together. the one thing I noticed when it came together is the the ears of the weldment spread a little.

my first inclination is that is ok since the wledment ears are not solid at that point.

ignore the loose bolts in the middle

any ideas??



DSC00744.jpg
 
Wow - that's quite a gap, I'm not sure I like that at all. Here's a pic I just took of mine, there is a slight separation but nothing like what you're seeing. I think a call to Vans is definitely in order for Monday morning. I would recommend taking some careful measurements of lengths on various parts so you have that data ready when you call them, I'm sure they'll be asking those questions.

It *could* just be the difference in placement of the rivet holes in the angle, if you look at the difference between yours and mine, when I backdrilled mine through that plate I put the plate where it would live, and drilled the holes in the angles accordingly. Your holes are more centered than mine, which will result in a larger spread of those tabs. This might be entirely normal and could be the reason those tabs aren't welded full-length. That would be a question for the boys in Oregon...

Also - I notice you've only got the one cleco in the longeron holes, and it seems that it has shifted a little, looking at all the side holes - they don't all line up. Put clecos in every hole and see how much it draws the part back into position.

1002468.jpg
 
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I am with Greg, I don't like the looks of that. Mine looks just like his picture. I think where you might see a problem is on the aft end of the longeron. You may end up with edge distance issues there.
 
thanks

Thanks for the comments.. I will call vans tomorrow and see what they say. I think what happened is the longeron may have moved when I drilled everything. FWIW the other side is good. gaps look "normal". I will probably replace the longeron and re-drill (peace of mind is good), but I will verify with Van's

thanks again
 
mquam99 said:
So I pulled the spacers out and then attached the

any ideas??

DSC00744.jpg
Click to expand...




Mike in the photo it looks like the holes are not lined up , both for the firewall side of the solo cleco you have in the longeron series and also for the (in the photo) lower weldment line of rivet holes.

what does it look like if you cleco every hole?
 
Update

Thanks for all the input this weekend. I called Van's today regarding my issue and talked to Joe. Basically he said that the gap in those ears or the shims are ok.

He recommended that using the shims is probably the best option and won't sacrifice any stength in the location.. I mentioned the use of longer bolts, AN3-6A instead of AN3-5A and he said there is no issue with that either

thanks for all the input
 
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