21. All cleaned out, nothing left but the edge of the original base and the glass.
22. Weighs 5/8 oz.  It is fuel proof too.  It will get clear inside as well.
23. The PA 75 is hiding.
24. Trimmed away the front for proper cooling.
25. The front mounts are completed. 

I still have a little ways to go on it.  Rear mounts and some filler wood around the front to give it some thickness at the edges.  I hope to get that done today.

Very cool approach.
I might try it soon....

Marcus

Same way I do my cowls too, I use Urethane foam, it will not melt with solvents either,, you have to dig it out, but it works much easier,,
the blue , pink or white foam will melt,,
That green foam looks like Urethane florists foam for doing plant arrangments

So how much smaller do you make the base and rest of plug to allow for the wall thickness of finished cowl. 
Sounds like you normally make the glass layup from multiple layers of .75oz,  how many layers is sufficient ?

Hello Allan,

The glass is actually pretty thin. If you make the base smaller by 1/64-1/32 it should be enough to compensate for the layer of glass.  If you can manage just 1/64 it should be right on the money.  This one initially came out too small. The base only needs to be smaller by just a tad but has to be uniform all the way around.

I normally use 1 layer of 6oz for the strength, then a layer of 2 oz, then a layer of .75 oz for the finish.  I also add multiple strips around the mouth area on the corners and all over the nose ring area.  But I always had some thin areas and had to be careful of sanding through it at the edges.  In the future I will probably go with 3 layers of 2 oz, let it cure then come back with 3 layers of .75 oz.  I liked how it came out doing it in two stages. After the initial setup had dried I was able to insert some balsa around the mouth area in those corners and the second layup really added some overall strength in those areas and on the whole part.

6. Trim away any excess balsa and add more epoxy with milled fiberglass to the dowel/mount joint.  
7. Side view.  Round the dowel ends just a tad as the cowl will need to lift up just a tiny bit to go over the needle as it slides off the model.
8. Inside view once it is in place on the model.  
9. Mounts are complete and hidden for the most part.  The scale still says 5/8 oz.  I will come back and add in a piece of 3/32 balsa in the mouth of the cowl to give it a nice uniform thickness across that front edge.  Since that is an exposed edge it looks nicer, to me anyways, to have a little thickness there like you would see if it were a balsa cowl. I like this method because the cowl is held in place from two different angles.  The part slides in place from the front, spinner has to be off to get it on the model.  Then the screws go in vertical.  
10. Almost a complete model.  

I will come back and add in a ½” wide piece of 1/64 ply flush with the front of the bottom block where it meets the cowl. Not on the edge but actually inside the block.  This helps it keep shape and give it strength.  I will add a small drain hole, lined with an aluminum tube, at the front of the bottom block and the rear of the cowl as well. I had a leaky tank in my 2009 model and I didn’t know it right away, PA still ran flawless, and several flights was all it took to soak that front lip of the bottom block. Raw 15% nitro sitting inside the fuse for a few days can do some serious damage. I will come back in and seal the engine bay and pipe tunnel again with thinned epoxy.  

 I have only the fin between the rudder and the turtle deck and it will be done.  I can see light at the end of the build tunnel.  I add the fillets after I cover the wood so I count them in the finish.  What you see here weighs 29.75 oz.  That puts me about 1.75 oz over my target.  I plan to fill mostly with dope so I am hoping to make some of that back.  Just for reference from the tip of the rudder to the nose ring it is 46.75” long.  The stab span is 29” and the wing span is 63”.

That is more or less what I do. I usually use carbon dowel and aluminum tubing but the same idea.

Nice work.

The cowl is complete.

I added in some balsa to the front edge and put in the Nicad hole.

I added a 1/64 ply stip inside the front of the bottom block.  I also glassed the joint at the opening of the pipe tunnel.

Lookin' real good Doug! 

Been following this from the first piece of wood cut, and I've definitely learned some good stuff to incorporate on my next plane whenever that may be.

How does that compare to the other one at this stage ?

If I remember correctly the other one was 29oz at this stage.  Then there was a big problem with the spray gun and I had to reprimer it and ended up adding a bunch of weight to it.

I am going to be using alot of dope filler this time and less primer to see if I can keep the weight down.