new name need for plastic peel ply

[Rui]

OK, back to the thread. I actually like plastic peel ply. Maybe shorten it to plastic ply.

 

I'm not too fond of pressure bagging because you don't use a bag. Seems to me that this is even more misleading then plastic peel ply.

[Aaron]

Originally posted by Rui

I find that I really learn only by making mistakes. I can read all I want, but until I actually screw up and see the consequences I don't really know it. I know others are much better at reading something and "getting" it. Unfortunately I'm not one of those.

 

Rui you are officially NOT invited to come skydiving with me

 

 

But I know how you feel I find I never fully understand it until I can teach it to a 5 year old.

[dust]

Jon you got it, a new simple explainitory name

 

plastic pressure laminate peel ply bagging

 

in aviation speak that would simply be pplppb

 

But i didn't know you were an attorney

 

great job

 

enjoy the build

 

dust

[crashdog]

Hmm, Pressure Bagging.

 

OK, so I havn't started building aeroplanes yet, but I do have some experience in boats, model boats, bike frames, which may or may not come in handy...

 

I developed a technique some time ago which I called "poor man's pressure bagging" to mimic vaccuum bagging. It was particularly applicable when doing a composite repair to a boat where bringing in vacuum apparatus was not practical. I have used it since in building a couple of marblehead model boats, an aerohydrofoil (!?!), and a carbon fibre bicycle frame. Seems to work.

 

I use shrink wrap vinyl to provide the positive pressure in place of a vacuum bag. Essentially, I start with a wet pre-preg of laminate, either like John Slade has done (laid up on sacrificial .4 mm plastic and squeegied) or put through the nifty old-fashioned-laundry-roller-mangle-turned-into-pre-preg-roller-press. The laminate is then put onto the mould (or foam core, in the case of the aeroplane in question). A release fabric (peel ply) is layered on, then I use a bleeder/absorber (loosely spun polyester blanket), which is doubled up. On top of all of this, I put heat shrink vinyl, which I seal to the edges of the mold or wrap entirely around the part. Apply a little heat, to take up some of the vinyl's slack, then let the cure do the rest. Note that the polyester blanket's double layer tends to insulate the vinyl from a lot of the laminate's cure heat. When it is set, pull the vinyl off, and peel away the consumables, no worries at all. Works very much like a vacuum bag technique.

 

A comment. If the parts were being manufactured in a female mould, this technique would be much more expensive of the course of an aeroplane build than would be the investment in vacuum bag technology. Vinyl heat shrink is not as cheap as all that. However, in the kind of construction which is employed in the Cozy, building up over foam cores, this technique has a lot going for it. The heat shrink allows for uniform pressures over compound curves, the bleeder/absorber tending to smooth out the application of pressure from the bag. The parts can be completely wrapped in the heat-shrink, and there is no need for an air-tight seal.

 

This is a real pressure bag technique. In fact, so is vacuum bagging, since the weight of the ENTIRE ATMOSPHERE (!) is supplying the pressure, and all we are doing is getting rid of a little of that pesky air...

 

cheers

 

blue

[Jon Matcho]

I use shrink wrap vinyl to provide the positive pressure in place of a vacuum bag.

Awesome. I didn't know the stuff was available beyond tube-sized electrical coverings. Given the uniqueness of this technique, I would tend to think of this as shrink wrap bagging. The only concern I have for this is whether the majority of the pressure exists at the edges as opposed to the surface, similar to how a rubber band would apply its pressure if wrapped around a wing. I think the perfect use for this would be with parts that are approximately cylindrical.

 

There's yet one more technique that may or may not be applicable. As a RC modeler, we hot-wire foam core wings as well. We would save the "throw-away" portions of the foam so that when we skinned the wings later, we would wrap in ply or wax paper, and place back together in the shape that the foam was initially. You then put weights on the foam block, which applies distributed pressure on the assembly. This may or may not work for hot-wired Cozy parts.

 

I offer the new and improved list to the group for discussion:

 

1) Vacuum Bagging

2) Pressure Bagging

3) Shrink Wrap Bagging (crashdog's technique)

4) Box Bagging (the "keep the throw-away foam" technique)

 

It's not important which names to use, as long as we all use the same names.

 

 

...carbon fibre bicycle frame.

Wow, another expensive hobby of mine. Would it be possible that you have a Web page out there showing the result of this project? I recall finding an example a while ago. Regardless, I might be interested in making my own $3,000 bike frame if you have any pointers.