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Gee Whiz Questions

Auburntsts

Auburntsts

Well Known Member
So I'm match drilling my wing top skins last night; a mundane task, and yet exceedingly boring. With my body on autopliot my mind begins wandering and I begin to ponder things for which I had no readily available answers such as the meaning of life, why they picked Ellen Degeneres to be a judge on American Idol, and why the heck I didn't buy a pneumatic cleco puller? Anyway, I ended the session with 2 questions that I'm still at a loss as to the answers:

1. Why the spar extensions? Couldn't have Van's just made the spars 6 inches longer?

2. Why the two-piece top and bottom skins? Seems Van could have easily just went with a one-piece skin (I believe fellow builder William Curtis did just that).

Can anyone help put these burning, but pointless questions, to rest?
 
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Answers

I think Ellen Degeneres is doing a great job on American Idol. Better than Paula. I REALLY like Kara.

As far as the airplane questions, NFC!!!!!
 
Let me see if I can help. Without looking at the plans, I can make an educated guess.

My guess on the spar extensions is that it probably has something to do with "standard" lengths of material and the fact that loads are lighter at the tips. It would probably be much more expensive to buy longer material than to add extensions. Van works extensively at keeping costs down.

As far as the 2 skins, I believe that the 2 skins are different thicknesses. This saves both weight and cost. The thicker skin is not needed for strength toward the tips.
 
I'll take a shot at answering them. Not sure if I'm right but I've given it a bit of thought also.

For question 1, I think it is because the 12 foot length (without the additional 6 inches) of the spar is a standard length by aluminum manufacturers. Tooling is probably set up for these standard lengths. For Van's to include a 150" length of spar cap, cost of this part would probably be dramatically higher. Much more cost effective to just add the extension.

For question 2, I think it is because as you get further out on the wing less strength is required. So aside for the aesthetic value of a seamless one piece top skin, reducing outboard top skin thickness is a more effective engineering wise.
 
Hmmm.

The answers to #1 make perfect sense.

As for # 2, the only problems with the theories presented are A. both the inboard and outboard skins are the same thickness: .032 (at least for the top skins) and B. the outboard skin is the wider (span wise) of the two: approx 44 inches for the inboard and 101 inches for the outboard.
 
Inner 0.032" outer 0.025"

Actually, no inboard are 0.032" and outboard are 0.025". Trust me, I know as when I butted my 0.032" top skin up against the 0.025 outboard leading edge skins, I had to come up with a solution to get them to sit flush.
 
I trust ya! Sounds like my questions are answered.

I just finished drilling the left wing, now on to the right. So I'm sure I'm think of something else that I just have to have gthe answer to.
 
w1curtis said:
When I attached the outboard leading edge to the spar, a layer of aluminum tape was added underneath the top skin. This allowed the 0.025" outboard leading edge skin to sit flush with the 0.032" top skin. This was not needed at the fuel tank portion since the fuel tank skin is also 0.032".

http://wcurtis.nerv10.com/07Wings/wings90a.html
Click to expand...

I think most builders find that after a paint job has flowed over the surface, the difference in thickness of .007 is virtually undetectable, not to mention all of the other bumps on the airplane caused by skin lap joints... just kind of goes with the territory on metal skinned light airplanes.

To each his own I guess.
 
Hot!

That Ellen Degenerate is HOT! Almost as good looking as a Tri-pacer (AKA flying milkstool).
 
press-brake length?

Another possible reason why Van's uses a short extension for the spars is that their press-brake may not be long enough to handle the full span. Just a guess, though.
 
I understand it was a combination of the length of the break and the material. Fun discussion last weekend of who would be the first to say the heck with the extension and build a clipped wing RV-10:D
I tapered the skins as per the plans and a swipe of filler prior to paint hid the seam pretty well. I know of one builder who bought new skin material large enough and made them one piece. Not sure if it's worth the effort though. IIRC, the inboard skin is thicker than the outboard, this may also be a reason for the two pieces.
 
I was always under the impression that they used two skins for weith savings and to reduce the size of the crate for shipping.

If I were to build another RV-6, I would consider going with a one-piece top skin...
 
It's been said already, the inboard skin is heavier duty - 32thou against 25.

Building with aluminium, you have to have laps so live with it. I can't see any issue. If you want a beautifully smooth skin then build a Lancair or something.

As for drag, forget it if that is what anyone worries about. Even with an immaculate wing, the flow becomes turbulent rather than laminar behind the max camber (about 1/3 chord). So blending a 32thou fuel tank to a 25 thou skin achieves nothing other than making you feel better.

Worry about the big picture....... I wish I had a $ for every time I had said that to one of my trainees :eek:
 
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