Maarten Labordus

For all flat parts, you basically need nothing else then a flat plate like a sheet of steel. I find it very convenient to use a glass plate. First: it's perfectly flat and absolutely airtight, but second: you'll have the possibility of a visual control of the resin flow at the bottom side of your laminate. But the point is: investment in tooling is very low for flat parts. For double curved parts, it get's slightly more complicated. But since most curved parts on a aircraft will probably have something to do with aerodynamics, I would rather spent some more time on getting the right geometry. And it does not really matter so much whether you spend your time on sanding and filling a tooling surface or on working on actual part. O, but adding filler on the actual part also increases the weight.... But as soon as you have the tooling finished, making the actual part is peanuts! It seems to me all of you are more or less building the same aircraft. Why not use one finished aircraft and use that as a master mould for getting a complete set of tooling? And have that tooling circulate among all the builders. There might even be some business in doing that! That will probably safe all of you a lot of time! You will be able to infuse a complete wing structure in a couple of hours, rather than spending weeks shaping your wing. Or to take it to the next level, would the regulations for kit-aircraft allow complex parts being build by one company which supplies them to all the home builders who'll perform the assembly? In that case, I'll build (and vacuum infuse!) the parts for you!

Vacuum bagging will not automatically improve your laminate quality. If you've done a poor job hand laminating your part, vacuum bagging will only make it worse. You're decreasing the pressure causing air bubbles to increase in size (the well-known Gass law: P*V=constant). So the first thing is to remove all air during lay-up with proper de-air rollers or similar. If your pressure in your vacuum bag is too low (=too deep vacuum), dissolved air from your epoxy can come out of solution. Similar to a beer bottle where the CO2 comes out of solution when you open it. Degassing resin before you use it will solve the problem. Bagging at higher pressures (=less vacuum) will reduce the problem. The next thing that can go wrong is if you use a very low pressure (=too deep vacuum), is that you have squeeze out so much resin that the laminate is resin starved. During curing, the epoxy will shrink (up to 7% by volume) and that will cause shrink voids. If done properly, vacuum bagging will give a far more consisted laminate quality than laminates cured at astmospheric conditions. Even beter would be to vacuum infuse your parts!

Vacuum infusion will give you a better quality laminate than hand lay-up with respect to void content and fibre volume content. But only when performed correctly. It all depends on the details and a basic knowledge of what you are doing. That's why I always start by giving my students or new clients a bit of theory (Darcy's law, some fundamentals on vacuum vs. pressure infusion etc) before I show them the process. My personal experience is that is far easier to have inexperienced people achieve good laminate qualities by vacuum infusion than by hand lay-up. Yes, there are some requirements to tooling (airtight). No, the process does not need to be expensive. Most stuff can be bought in simple hardware stores. Determining infusion strategies can be done by sophisticated simulation software, but common sense and maybe some simple lab tests will get you there aswell. Some papers on infusion projects can be downloaded from our website: www.lightweight-structures.com