Fibreglass cowling

[Marty_d]

Hey folks,

 

Anyone built a cowling from scratch?

 

I was talking to someone at the Fibreglass Shop about it the other day. He suggested a very thin (3mm) semi-flexible foam board which, with heat, can be curved. Couple of layers of matting and resin over inside and out to form the cowling. (Very light too).

 

He also thought that aluminium strips built into all edges that get screwed together was a good idea.

 

Sounds to me like a more attractive option than building a male plug, doing a female mould, then using that to do the cowling. I'm only making 1, not 10.

 

Any thoughts, experiences, suggestions?

 

Cheers, Marty

[Kyle Communications]

Look at some of the later Mike Patey "Scrappy" videos on how he does glassing and molds...bloody amazing how much work he shortcuts....by using tape and alu sheet and stuff. This super cub hotchpotch he is building is something on steroids. The carbon skin and dash and pretty much all of the parts he makes is outstanding. The guy is a obsessive compulsive but he is unbelievable. I have never seen how he applies the sheets already loaded with resin..he has a plastic backing on it.

I think he isnt far from doing the cowl either so subscribe to his channel if you havent already and make sure you tick the bell for notifications.

[Kyle Communications]

Mike already has the cowl..I was just looking for something for you but still watch a few of them and you will get the idea

 

[Old Koreelah]

Marty your mate's technique is pretty much what I did to build my wheel spats and cowls for two different engines.

I achieved a pleasing shape and greatly enjoyed the shaping process. Bypassing the whole plug-mould thing also made it fairly easy for me to make several modifications to my cowl since I first built it

 

After building mounting points with dzuss fasteners I covered the whole engine area with glad wrap, then built up the cowl with "planks" of 10mm Klegecell PVC rigid foam, glued together with epoxy. After achieving the approx. shape, it's easy to rasp it into a streamlined shape. I made up a long wooden shaping tool on which to mount one-metre strips of sandpaper. A few layers of fibreglass cloth each side gave me a good strong result.

 

What I learned:

A reasonable finish requires lots of work at night with a strong light to show up imperfections. There are some very light fillers available.

Mine is rigid and quickly-removable because it has few mounting points, but weighs more than one with lots of attachement points.

As your mate says, you can mould piano hinge into the joins. I had to form air-tight overlaps to all joints to stop pressure leaks.

I used some vinyl-esters resin in the areas above the engine where, after shut-down, it gets cooked.

[M61A1]

sheets already loaded with resin..he has a plastic backing on it.

That's the best and cleanest way to get the resin through the fabric. A 2M roll of plastic comes folded in half. Just put the fabric between the fold spread the resin over it, fold the top over and work the resin through the fabric.

Great for patches too, or anything where you need to cut out shapes as you can mark out your patterns with correct clock orientation before you mix you resin and just cut them out and peel them like stickers.

[Kyle Communications]

I hadnt seen it done that way before...certainly makes life a lot easier

[Raytol]

I find plastic sheeting a pain with vinylester as it will curl up. I use baking paper which is less slippery, can be folded and stays in shape for ages while wet.

If doing repairs, I draw the shape of the repair patches on the baking paper back-to-front and then turn it over before wetting out, so that the drawn lines

don't show up on the repair glass!

The PVC foam comes in segmented and mini segmented sheets which have a glass scrim on one side to hold the blocks together. A touch of car bog holds

things together quickly.

[Bruce Tuncks]

There is an aerodynamic consideration... you want the front lower cowl to bulge maybe more than simply clearing all the engine bits needs. This turned out to be so for the Jabiru SK I built.

[Old Koreelah]

There is an aerodynamic consideration... you want the front lower cowl to bulge maybe more than simply clearing all the engine bits needs...

Good point, Bruce. Another role for the cowl is to protect the engine from damage in a minor bingle.

 

I learned this the hard way: I was packing up my camping gear before leaving a fly-in and wanted to access my belly door to stow my sleeping bag. Normally that involves grovelling under the plane, but this morning the grass was damp so I lifted the fuselage to chest height and asked a mate to hold it while I opened the hatch. He didn't realise that it was already balancing on the main wheels and gave it an almighty lift.

It tipped forward, crushing the cowl against the engine sump.

 

That's when Dave became the first (and only) person to prang my aeroplane.

[Marty_d]

That's when Dave became the first (and only) person to prang my aeroplane.

May that always remain the case!

 

There's a Tasmanian member who said that he may be able to lay hands on 701 cowl moulds - really hoping this happens because it'll take the pressure off trying to design and construct my own moulds or formwork.

 

Anyway will let you know! The problem at the moment will be everywhere shutting down so even if I end up with the time to do this, I won't be able to source materials.