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  #1  
Old 02-04-2021, 12:29 PM
Ender Ender is offline
 
Join Date: Dec 2017
Location: Marion, IA
Posts: 78
Default Wind Skin Lap Joint (Inbrd/Outbrd)

Hello! I did ask this on the FB group, so anyone who answered, please feel free to ignore this question! (And thanks for your answer as well!).

The plans have us sand down the forward corner of the Inboard and Outboard wing skins where they overlap. This is to make the part that overlaps the same thickness as the fuel tank skins.

In order to do this, you really need to take off quite a bit of material.

I am not keen on doing this as I'm worried about future cracks. I have seen at least one place on here where a crack developed on a QB wing around a rivet.

An alternative is not doing any sanding and having a 2 inch area of skin 0.025inches above the fuel tank skin.

Normally having the skin drop away (fwd to aft), vs having it stick up is worse from an airflow separation standpoint - but I don't want to pretend I'd have any quantitative data to back this up.

So my question is: Have any of you forgone this step? Or have any of you sanded significantly less than the plans asked? If yes to either of the above, have you seen any issues with stall speeds/characteristics or if you got caught where you shouldn't be ... icing.

Thanks a bunch in advance!
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  #2  
Old 02-04-2021, 01:11 PM
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Bsquared Bsquared is offline
 
Join Date: Mar 2018
Location: Valencia CA
Posts: 105
Default

I initially stressed over doing this task but in the end I took a deep breath, grabbed a dremel tool with a drum sander attachment and went for it. 5 minutes later I had the desired result and once assembled with the tank the joint looked great. Bottom line..... trust the plans. The processes are based on 40+ years of experience and thousands of aircraft flying.
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  #3  
Old 02-09-2021, 08:56 AM
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Just wanted to leave this here for future search's.

Vans confirmed this is only a cosmetic step and could be skipped or reduced, it won't have an impact on aero.
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  #4  
Old 02-09-2021, 02:08 PM
avatty avatty is offline
 
Join Date: Sep 2015
Location: Walnut Creek, CA
Posts: 47
Default

A 2-inch Roloc wheel works great for the scarf joint.
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  #5  
Old 02-11-2021, 07:13 AM
Ender Ender is offline
 
Join Date: Dec 2017
Location: Marion, IA
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Thanks! I had also considered my 2inch sanding drum that I can chuck into my drill.

When I experimented with a oscillating tool (which had a little give on the sanding pad) I found that the "edges" were more sanded than the middle. I'm thinking the sanding drum doesn't have any give, so the material will be more uniformly removed. (I'm saying across the joint, I know that from the corner to the interior there is a slope to how much material is removed).

I think I will end up taking a little bit off the inboard (bottom) thicker skin. But for the most part will leave the top skin alone.
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  #6  
Old 02-11-2021, 09:29 AM
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nzrv8 nzrv8 is offline
 
Join Date: Jun 2009
Location: Australia and NZ
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I made the (apparently common!) mistake of dimpling the skins before scarfing, meaning I couldn't remove as much material as normal. I ended up only scarfing 1" or so, and tweaking the front edge of the outboard skin so it tucked down behind the tank skin. It looks fine.
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