Reworking a B model cowling

[C5Engineer 1170]

The curve and uneven edges is proving challenging. I am going to switch gears and lay in a dam with carboard on the inside and then use some 2-part expanding foam and then shape that for a layer of glass. I will then smooth out the foam on the back and build it up with several more layers. Whatever foam is left should act as a core. 

[wypaul 448]

Sounds like a plan that will work.  I suggest that you use West epoxy and Rutan cloth for your layup.  It only cost a little more than the polyester crap and is so much easier to work and finish. Having built a 24' sailboat using polyester and an airplane with epoxy, epoxy is the material for me, also built a couple of cowls from scratch with epoxy.  I have some good references for finishing epoxy parts the easy way if you chose to go that route. PM me, if you are interested in talking about it, with your number and I will give you a call.

[Geoffrey Thorpe 31]

Not a Avid, but...

 

Used to be:

 

Is now (new glass from a few inches behind the exhaust pipe and up around the bottom corners):

I didn't get the radius from the side to the bottom to exactly match - but yours should turn out fine.

(I used the West System epoxy because that's what I use for purd near everything)

[C5Engineer 1170]

Getting ready to pour some foam today so I can start shaping.

[C5Engineer 1170]

Foam is in. I had a little bit of a low spot so I chipped out a square and added some more. Stuff is really easy to work with and is extremely sandable. Now for the fun part....trying to make that blob look like a cowl.

[Av8r3400 1178]

Fun = mess

So, your plan is to sand the foam down smooth to the surface, then make a female mold to the face of the cowl?

[EDMO 1078]

Joey,  I don't know what you are planning to use to cut that foam down to where you start sanding,  but I would think that if you could get your hands on your wife's electric carving knife like you use on a turkey, it should cut it fast.  I think that there may be an electric hacksaw that has about the same kind of handle - Sawsalls are just too big for that job.

 EDMO

Edited 28 Jan 2016 by EDMO

[C5Engineer 1170]

Fun = mess

So, your plan is to sand the foam down smooth to the surface, then make a female mold to the face of the cowl?

Yes with just one or two layers and then I will remove most of the foam and build it up from the backside. Ed one pass of a rasp knocks a significant chunk off. It's going pretty quickly. 

Edited 28 Jan 2016 by C5Engineer

[EDMO 1078]

Fun = mess

So, your plan is to sand the foam down smooth to the surface, then make a female mold to the face of the cowl?

Yes with just one or two layers and then I will remove most of the foam and build it up from the backside. Ed one pass of a rasp knocks a significant chunk off. It's going pretty quickly. 

I didn't think of a rasp or one of those Styrofoam cutter thingys - guess I need another cup of coffee to wake up on!

EDMO

[TJay 1041]

watch you'll Get the hang of it and you will be able to make your fairings to go from your wing struts to your spars and clean that bird up a bit.

[Luked 71]

Composites are fun! You'll soon be addicted 

[Av8r3400 1178]

[EDMO 1078]

That photo reminded me to make a comment in "Droop Tips"...Look at those tips sticking UP...All 4 of them!

EDMO

Edited 29 Jan 2016 by EDMO

[C5Engineer 1170]

I was on my lunch break today letting my dogs out and grabbed the rasp and saw. Knocked it down to this in 20 mins. Should have it fully shaped tonight. 

 

[Luked 71]

Hey Joey, not to tell you how to do things, but just some thoughts. When you get down to final shaping, I've found that a paint stir stick (from HD or paint store) or something similar with sand paper glued to it works good for mild curves like that. You want something that will flex around the curves, and not make waves. You can sand across it in multiple directions to avoid waves. You also want to get a balance between how stiff your sanding board is, how course your sanding paper is, and how easily your foam sands. A stir stick might be too stiff for sanding the foam. It may put too much pressure down. Finer sand paper may help too if that's the case. Looking good.

Edit, also moving the sanding stick 45 degrees to the stick itself (in both directions) helps avoid waves.

Edited 29 Jan 2016 by Luked

[C5Engineer 1170]

Thanks for the advice. I've done quite a bit of work with balsa wood building RC models and it behaves very similar to this. It still needs a little more touching up but pretty much ready for glass. I used the US composites foam and was very impressed at how nice it sanded. I'd say I had maybe an hour into it from the time it was a giant blob to this. oh and look what's on the new CPS cover 

[lostman 198]

Looking good Joey!

[wypaul 448]

If you are just going with one layer of glass on the outside it may be to flexable to hold its shape with the foam removed from the back side. So one thing you can do is put the micro slurry on the outside a good 1/4" thick as per the article and then wait to finish it after the inside layers are in place.

[Luked 71]

If you are just going with one layer of glass on the outside it may be to flexable to hold its shape with the foam removed from the back side. So one thing you can do is put the micro slurry on the outside a good 1/4" thick as per the article and then wait to finish it after the inside layers are in place.

Excellent idea. I'll have to go back and read through that whole article.

[C5Engineer 1170]

Put in 2 layers today using the West System and Rutan Bid glass. Came out really smooth. I will pull the foam and start on the back tomorrow then onto finishing.

[TJay 1041]

Nice work.

[1avidflyer 1983]

Knew you could do it!  The sanding will be the worst part of the whole job.  And then remember, if you can feel a bump or ridge with your fingertips, you will sure see it when you paint.  Looks good!  Jim Chuk

[wypaul 448]

Looking good!

[C5Engineer 1170]

Thanks everyone. I pulled the foam last night and should be able to lay up the rest today.

[C5Engineer 1170]

Ready for fill and finishing.