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  #1  
Old 04-11-2010, 10:05 AM
fred gassit fred gassit is offline
 
Join Date: Nov 2008
Location: Perth western Australia
Posts: 26
Default Tank skin alignment and baffling baffle asymmetry

Hi all, I have just placed the fuel tank skin (no ribs yet as per instructions) onto the tank baffle that is clecoed to the main spar.

All holes line up fine but I have 2 queries.

The holes in the baffle web are not pre-punched dead centre, I am certain this is intentional but my main spar doubler bars are not aligned perfectly with the C section part of my spar either. (less intentional I think but only 3/64 wider from one side to the other)

I realise this is difficult to explain but what it means is the flange on the tank baffle when it is clecoed in place rests up against the main spar doubler bar on one side (underside) and has about 3/32 clearance on the other side,(It is however centred on the spar C channel to which it is attached) has anyone else had this happen?

It doesn't seem to cause any problems but it isn't exactly how the drawings portray.

The other slightly more pressing issue is that tank skin/leading edge fit is less than "perfect".

Where the tank skin and leading edge skins meet at the leading edge there is a gap of maybe 1/16", as the join moves rearward toward the spar they come together tightly and ever so slightly overlap in the region of the spar. All other joins are tight and consistent along their length.

The book says to slot the baffle to achieve a better fit but at this stage I think deburring the skin edges would just about do it given how little overlap there is. Where people have "slotted" the baffle hole could you simply drill a number or 2 oversize? This is tiny adjustment for the most part.

Doing a search on this revealed most alignment challenges after the tanks are built, do I wait until then to address my issues or go for perfect alignment now? (I have checked the usual suspects such as wing sag as suggested in the other threads)

Any suggestions on these 2 issues would be appreciated.
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  #2  
Old 04-11-2010, 05:55 PM
RV7ator RV7ator is offline
 
Join Date: Jan 2005
Location: Boise, ID
Posts: 1,007
Default

Fred, being blunt, you've got some major builder-induced problems. Don't go removing any metal anywhere (deburring, slotting, trimming, etc.) until you talk with Van's. (Perth is what, 20 hrs and a day off the US west coast?) There are techniques superior to Van's instructions for fitting up these fussy bits, that's how much it's worth getting it right during the fit-up. But stick with the book for now. You'll know what to change on your next project!

My quick guesses are that you've got the baffles interchanged L/R, or the flanges facing forward, not aft. The baffles are not symmetrical. The tapered gap between leading edge and tank skins likely means the spar wasn't/isn't straight. You checked sag, but cleco on the top skins all around the skeleton, ribs too, for self-jigging verification. Temporarily cleco the bottoms, also, for verification.

The fit should be "perfect", that is line-to-line on the seams, maybe needed nothing more than smoothing the edges (deburring) to prevent any overlap. Slot, don't drill the bracket holes oversize and ask so much of a rivet's capacity to swell up. If you don't already have a fine point tapered round file suitable for slotting 3/32 holes, get one. There's a lot of airplane to go and it will come in handy.

John Siebold

Last edited by RV7ator : 04-11-2010 at 06:05 PM.
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  #3  
Old 04-11-2010, 06:59 PM
fred gassit fred gassit is offline
 
Join Date: Nov 2008
Location: Perth western Australia
Posts: 26
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Thanks for the quick reply again John, the previous fix was great too thanks.

I have gone and had another look this morning, the gap at the top of the skins is 1/64 or 1/32" at the most and the overlap at the bottom can be pushed out with finger pressure or changing the clecoing sequence so maybe not so significant (Rechecked spar is level and no twist.) and all skins are on.

I think the baffle is all ok but I did put the other baffle on the right spar and it really doesn't have the same amount of room to move from side to side (correct as per drawings).

This seemingly reinforces my belief that the reinforcement bar on this spar is slightly misaligned, and I have verified by measurement as such (an hour or more with vernier!) I'm going to have to learn how to attach pictures.

I was hoping others may have seen this before, would you slot to centre the baffle over the bars or leave it centred over the C channel? The skin is attached to both hence the conundrum.

I will contact Vans for an opinion and post what they suggest.

Thanks again

Last edited by fred gassit : 04-11-2010 at 10:29 PM.
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  #4  
Old 04-11-2010, 10:31 PM
fred gassit fred gassit is offline
 
Join Date: Nov 2008
Location: Perth western Australia
Posts: 26
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Post Script: After inserting the ribs into the tank the fitup is mostly perfect, the baffle is still off centre in relation to the spar bars but I'm not concerned about that.

Why do the instructions get you to check fitup without the ribs in? The pre bent shape of the tank is not the easiest thing to check alignment on when it is bulging out all over the place.

Did anyone else check skin fit with the ribs already installed in the tanks?

Thanks again
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