CG strakes: Separate or single panel?

[rnbraud]

Hello All,

 

I am preparing to build the CG extended strakes and am curious as to the best way to handle the multi-segment issue.

 

I have seen on some websites that the first juncture at R33 causes some separation issues when bending the top and/or bottom

skins.

 

I also saw on one website where someone utilized separate panels; one between R33 and the fuse, and another between R33 and the end of the strake.

 

This seems easier to fabricate, however, I don't see how to make the T-Hats ontop of the ribs with separate panels.

 

I can see that if I leave off the bottom strake skin and first build the T-Hats from the bottom, that separate panels would work.

 

What is the conventional wisdom for building the CG Strakes: separate top skins or one whose piece?

 

How does one make the T-Hats with the CG Strakes?

 

Thanks.

[steve]

i did mine this way...first i filled the first foot of all ribs with blue foam(le-back to the flat top) and filled in the cg strake. it was all shaped like R-33.

you can segment or do and one long bend.

i then took 3'? long 3/4?" wide strips and pinned them to the Le and one at a time i micored and pinned all the way back to the flat spot on the top(fuel lid). there i was able to use flat sheets of foam and fitted them in place all the way back to the spar. the trick was filling the cracks with micro, so i just pulled out 2 or 3 staples,microed,put the staples back, and so on. let the hole thing dry till morning and pulled out all the staples and lightly sanded and glassed as per plans. after cure i removed it(top skin) and placed it on a table glass down and microed and glassed the inside (do this 4 times)

now place it back on and trace where it touches all the ribs. remove, invert, duck tape 2" over the tracings and place the skin back on the ribs.

now wet out 10 yards of 2" bids and foil-ply them up from underneath.(2 times) and wala, you now have one top skin/with mated T-caps.

the bottom is the same but no tracing and no duck tape.

[TMann]

Just wondering if anyone uses divinycell pvc foam for the strake skins?

 

It's fuel resistant and can be vacuum or heat shaped to get your leading edge curve.

 

Is it viable?

[Marc Zeitlin]

Just wondering if anyone uses divinycell pvc foam for the strake skins?

Well, at least in the COZY MKIV, that's what the plans call for, so I'd guess that a whole lot of folks use it. I'd venture a guess that that's what the Long-EZ plans call for as well - the H45 foam.

[TMann]

Well, at least in the COZY MKIV, that's what the plans call for, so I'd guess that a whole lot of folks use it. I'd venture a guess that that's what the Long-EZ plans call for as well - the H45 foam.

So I'm a little confused. I hear where some builders are scoring the foam, cutting it into strips. It's only a 1/4 thick, it seems as though a heat gun and a little skill would get you there as far as reaching the contour desired. I haven't done my strakes yet so maybe there's more to it than I suspect.

[Jack Morrison]

Actually the foam is 3/8 thick. The E Racer plans call for scoring for the leading edge, no big deal, works great.

 

Jack

[Cozy Girrrl]

Rock, too complex to do the whole thing in print without pics and diagrams and we don't have that chapter ready to post to the web site yet, so call Randi for questions.

BIG HINT: do not skin the bottom first. Add an R45 Rib. Spline sand the tops of the ribs and bulkheads with a long spline only to knock off the offending high spots, no need to make it perfect. Fit top skin(s) on and put external witness marks on everything so that it always goes back the same place. From underside mark rib and bulkhead positions on underside of skin(s) then remove and mask with packing tape, then replace and apply 2X BID 1" on bulkheads 2" on underside of skin(s), let it go off, remove skin(s) and trim your new perfect hat sections to 1" each side of the ribs and bulkheads.

Then you can bond in the bottom skin.

Oh, theres a lot more stuff like that involved, they may look like they were borrowed from a LE, has nothing to do with why we did it but also they are not built anything like to plans of LE or Cozy.

...Chrissi & Randi

[Jerry Schneider]

Sorry my site doesn't go into better detail.

 

I have the CG strakes. I made the skins in one piece, (I got the foam from a boat supply store.) I glassed the entire under-side of the top skins first.

 

The dip/gap that forms at the CG Strakes is no big deal because it's a dry area. Just make sure the foam/glass is right at the wet area of R-33 (or is it R-38? I'm going from memory here.) You can easily fix those areas later.

 

After you glass the bottom side of the top skin, (and it has cured.), place the skin, mark the ribs with a pen, and put box tape to the places where the ribs ride. Epoxy wide peel ply to the box tape, (this makes the top skins pop off the flanges easily.). Then place the skin on, weight it down, layup the t-flanges, and let cure.

Pop the skins off, remove the peel-ply and tape, and you're good to go.

 

Put the bottom skins on. Then the top skins.

 

HTH

[rnbraud]

Thanks to all for your responses and advice.

 

I see now that it is ok to NOT install the bottom skin. The ribs, when joined, are strong enough to allow the formation of the T-Hats by placing the top skin on with release tape, and so on. This will allow the use of two-panels per skin.

 

I will try to make the skins in two panels, one between the fuse and R-33 and one between R-33 and the wing.

 

Since we bond the bottom skin to the ribs with 2" tapes, and the top skins will have a generous T-Hat along R-33, I think there won't be any lost bonding strength in using two panels vs one single skin.

 

I have also seen the use of thin strips along the leading edge curve. While that process does look interesting, I think it may be more work than just using two panels.

 

My main concern here is in that juncture at R-33 at the leading edge and the compound curve there. Using two panels should make this spot easier to form.

 

Thanks for all the info, it is much appreciated.