MGS285 and VIP

General Composites Discussions Composites Talk
#1

Hi all,

I’m new to this forum. I’m starting to build a Cozy MKIV canard aircraft (based on Burt Rutan’s Long EZ & Varieze). http://www.cozyaircraft.com/

The technique usually used is hand layups. Now more and more poeple are vacuum bagging their hand layup, but some want to try VIP, I’m one of those.

Among all the approved epoxy systems, MGS285 as the lowest mixed CP (300-500). We used foam core (except for the firewall which is balsa). Bulkheads are roughly 42"x36", with open areas. Like this: http://cozy.caf.org/chapter-04/index.shtml

So my question is how would I go about VIPing these bulkheads. And can it be done.

Regards,

#2

I do not know much about aircraft, or what/how exactly your bulkheads are being done…but.
If they are just the panels, solid and cut out, shown in that website…and the intent is to just cover them with fiberglass. THen yes, it can be done. If the steps are normally to wet out fiberglass, lay it on the bulkhead, and let it cure (or vacuum bag), then all you have to do is standard VIP/VARTM methodology of production. Lay up dry fiber, peelply, inlet and outlet tubes, bag it, and infuse with the resin. Even with the cutouts, you can just let those open in the bag, or you can seal off each one (as long as you are GOOD with your bagging technique :slight_smile:
Even if you use one large bag over the bulkhead with cutouts, as long as you bag it well, any excess resin that would seep into the holes, would just need to be sanded out.
The problem is, depending on the thickness andyour technique of bagging, you can easily bridge the bag, thereby leaving a large open void that resin will pool, and you would have to recut out the holes. (and use tons of extra resin)
I hope that made sense.

#3

Thanks Riff,

Just one thing I forgot. The plans methology is to :

1 : Apply a thin coat of micro slurry to the foam core (a mixture of pure epoxy and glass micro sphere (about 50:50 by vol.)). This is to fill the voids;

2: Apply the fiber glass/carbon/etc. over the core and wet it out; and

3: Let it all cure.

Now poeple are very vocal about the “micrfo slurry” part of the methodoly. But my understanding is that this is done to cut down on weight. I beleive that using only pure epoxy should not have any negative impact on the structural integraty of the part (no less chance of delamination). Am I right assuming this.

#4

Why not buy pre-made sandwich panels for the bulkheads?

#5

SAF: Yeah, that sounds like a normal layup and method, minus the micro balloons. I Do not see the need to smooth the surface of the foam, unless it is REAAAAAALY chunky, but at that point, I would just cut new foam correctly! Else, the epoxy and fabric will smooth out the surface well enough. Even if you are going to vacuum bag wet, or infuse it.

Capt: Then what is the fun of building an airplane yourself? :slight_smile:

#6

So what would be a good pump to purchase for VIP. And would this pump also be suitable for vaccum bagging? Like I said, I’m new to this (I only do hand layups). What should I buy? A list would be very appreciated.

#7

You probably have a good point there:o

#8

The ideal pump will pump down to 29.7" Hg. Most can get away with 27-28". For an aircraft, I wouldn’t do anything less (then again, if you can get away with hand layup, 10" would be good too!)
Some people swear by old fridge/AC unit compressors. They compress air on one side, and suck it on the other. They are cheap, if not free, more or less trouble free (maybe require some oil once and awhile) and can get down a good vacuum.
If you are to buy one with a good vacuum, even used, they might run a few hundred $. Might find a good used one for cheaper. You won’t need much CFM, since once you vacuum the part down, you aren’t really pulling much air through. Even with infusion, you won’t need over 2cfm I would think.
Gast and Welsh are good pump companies.

Don’t forget the resin trap. It’s basicly a bucket with 2 fittings, maybe a ball valve and a vacuum gauge. It will collect the excess resin you suck through the lines, and will catch it before you suck it into the pump. They can range from a paint pressure bucket, or glass jar with a nice lid.