REFLECTOR: Lay up c question

[Andrew Ellzey]

Everyone has to decide which direction that they prefer on this issue. Neither method is wrong. Since I chose the cave method, it the one I am most familiar with. The reason that everyone keeps asking what they should do is that the manual is unclear on this issue. One of the main reasons that I like about the cave method is that you have a completely sealed compartment for the rudder horn to operate in. See the attached photo's of my almost completed winglet and rudder. Even if you don't do the cave method, you will still wind up with a cave when you add your bottom to your winglets. Your cave wouldn't have a bottom other than the bottom of the winglet. I also added the two closeout bulkheads that are bonded into place with velocipoxy and milled fiber. Since the vertical bulkhead is bonded to my cave opening (C layups) and the lower winglet, it should add strength in compression of the C layups. The exposed foam that is seen in my photo will be
 covered with one ply bid when I get around to it. I also left more length on my rudders than the manual called for, my personal choice.
 
Andy Ellzey
 
 

- Original Message ----
From: Steve Goldman <steve at fatcatair.com>
To: Velocity Aircraft Owners and Builders list <reflector at tvbf.org>
Sent: Monday, June 16, 2008 8:52:41 PM
Subject: Re: REFLECTOR: Lay up c question

Andrew Ellzey wrote:
> 
> I made the rudder horn pocket on my wings also and I like the way it 
> turned out. I don't agree that the glass over the pocket doesn't add any 
> strength. If I ever build another pair of wings, I'll do it the same way 
> again.

I'd like an explanation as to how it adds strength to the 
winglet/attachement. Here's a simple thought experiment. Imagine layup 
D is simply a hinge and there is no layup C at all. Then obviously you 
can move the winglet towards the fuselage with no effort at all. Now 
imagine that all you have for layup C is the portion of glass over the 
bellhorn area. That piece of glass (except for maybe a very tiny 
amount just aft of the foam, i.e. the most forward piece of glass) has 
a bend in it so that the bellhorn can fit in the cave. So what happens 
now when you apply force to the winglet trying to move it toward the 
fuselage? It moves fairly easily (a short distance) until the glass is 
stretched out straight and is finally in tension. So at that point it 
does add strength. However in order for the winglet to be moved to 
that position all the glass of layup C "forward of the rudder 
bellcrank cutout" would have to tear. That's 15 or 16 inches of glass. 
If it has torn so that the aft section of glass can load you are 
already in serious trouble.

I think there is a reason why older manuals (and the video) describe 
the cave and the current manual says "Keep layups forward of the 
rudder bellcrank cutout". I did check with the factory and they said 
you don't need the cave. Building the cave doesn't hurt although it 
does seem to make accessing the connection of the cable to the 
bellhorn less convenient.

So I guess that means Andy says digital and I say analog and Matt has 
to make his own decision. :-)

-- 
Steve Goldman
'77 Tiger N28531
Velocity XL5-RG (T-2762 hrs) N758SG (reserved)
Pittsboro, NC (9NC8)
http://fatcatair.com
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