Warren is the guy to learn from here. I've been exceedingly happy with the v-bagging Warren and I have done. I basically ran the scissors and the scale and talked Warren into doing everything else 😯

Given the amount of interest in this the last year or so, I should probably do another class.

I have a vacuum pump I bought reconditioned from Aircraft Spruce for $150 that will pull 25-28" of Mercury - depending on the ambient air pressure. (I live at altitude so the maximum vacuum pressure is a function of ambient air pressure). This is effectively the gold standard shy of having a pressurized autoclave. Venturi-style vacuum generators work OK, but don't have the efficiency or capability of pulling a vacuum like a pump does. If you don't plan on doing it often and can be satisfied with lesser vacuum, this is definitely a cheaper route although not by as much as you think.

Think of vacuum bagging as applying uniform pressure on all parts of the layup - the amount of pressure determined by the ambient atmospheric pressure. At sea-level with a perfect vacuum, you'd pull something on the order of 29"+ of mercury. Here in Colorado, you can be happy with anything 24"-26" or thereabouts - the higher your altitude the lower the number. At sea-level, that would result in about 14.3 pounds per square inch forcing your layup tighter and closer to the substrate and squeezing out the excess epoxy into the breather fabric.

In an ideal layup, epoxy comprises about 45% by weight of the layup, however just try to thoroughly wet out a piece of fabric with that little epoxy and you'll find a lot of dry spots or it won't properly wet out all of the fibers. The reality in the home workshop is that you'll find you have to use something on the order of 55% by weight of epoxy to get a good thorough wet-out of the fabric. V-bagging with a permeable release fabric like peel ply will allow you to get a full wet-out while at the same time removing most of the excess epoxy through the release into the breather.

In addition to the pump, you'll also need a vacuum gauge, hose(s), vacuum fittings, a bagging fitting, bag material, bag sealer tape, breather fabric, and peel-ply or mylar release film and of course the materials you'll need for the actual lay-up - fiberglass, Kevlar, carbon, and epoxy, etc. By the time I was set up to do my first big layup, I probably had $350 invested.

One big issue to address is the epoxy you plan on using. I'm a died in the wool West Systems guy - I know it and have used it for far longer than I have been building rockets. There are other good epoxies as well - some of the layups I've done for JW have been done with Pro-set and I've also used Aeropoxy. Personally I like Aeropoxy, but in my laziness I generally stick with the West Systems because of the pump dispensers. I don't like to weigh the epoxy components out when I'm mixing. There are certainly better epoxies out there but the best of them all require heat during cure and/or post-cure to get to full strength and a curing oven, particularly one that can be used while pulling a vacuum is just a bit more tooling than I care to deal with. That said, the gold-standard for high-strength, high temp resistance are heat-cured epoxies and if you have the space for or access to a curing oven that is definitely the way to go.

I'm about to do a 4" MD project sometime in the next month or so and I'll be doing one of my unitary v-bagged fin cans on a PF convolute-wound airframe. I can always use extra hands while I'm doing the layup so if you want to see the process in action, let me know and I'll be happy to have you over to help and learn.

I'd love to lend you a hand Warren, and learn some more techniques. Steve, I use a medical pump, which is capable of about 25, I still haven't put a valve on mine and I've let it run for hours, motor never gets to hot.
I wish i would have had someone to watch in person, my first couple attempts were pretty rough. Its a lot like painting its all about the prep in my opinion.

I bet you get a few takers Warren, name the date and time.

Right now I'm waiting on some Nomex honeycomb fin cores from Giant Leap. When those turn up and I get the airframe slotted, and then post a Saturday date for doing a v-bagged layup. I'll be happy to have a couple folks over to watch and lend a hand. Given the likely schedule, think sometime in mid or late March. Unfortunately, I can't fit more than 3 or 4 into my shop while still having space to work. Also, somewhere along the line I'll be doing another project with Scott Evans and perhaps yet a third project so there will be other opportunities - all in the March/April timeframe. I'll make a forum posting on this soon so please don't post here to indicate interest.

A couple of tips:

Paper towels make pretty good breather material.
Sealing vacuum bags with bag sealer tape is sometimes necessary, but almost always a pain. Whenever I can make it fit, I just use a lawn&leaf bag and put a knot in the open end. Perfect seal the first time, every time, and it doesn't get any cheaper. Use a bag fitting of a 2-part type that pokes through a hole in the bag and clamps together.

When making fin stock, use 2 granite floor tiles sandwiching the layup (including release ply, paper towels and peel ply on both sides) and put the whole thing in the lawn&leaf bag. The tiles only cost about $2 each, and they make a great flat surface for all kinds of uses.

Dry carbon is usually no more expensive, for the same strength, as fiberglass. Sometimes it's actually cheaper, and always thinner/lighter for the same strength. I always use carbon except for applications that need RF or optical transparency, electical insulation or when I want a very thin/conformable cloth for some really tight corners.

I might add that Adrian's comments are good - particularly for smaller jobs. My first v-bag project was a 24mm altitude bird and was done with a shop vac, plastic garbage bag and duct tape with a kludged vacuum fitting and it turned out great. You CAN make a very nice start at v-bagging without spending a lot of money and by creatively using various work-arounds. If you have no plans to get into large or complex projects, you can save some money and buy motors instead.

The granite tile idea is something I still do (in concept if not fact) for making plate stock. My rig is actually 4 layers of 3/4" finish plywood covered with melamine board and the actual layup surface is 1/4" tempered glass. Best way to do it is to just drive a tire of your car up onto it to compress the lay-up. You can get far more than 14.2 psi on the layup that way so it is even better than v-bagging. Only thing better would be a multi-ton hydraulic press and a made for the purpose mold.

Paper towels are excellent for smaller projects and even larger projects if you're only laying up a single layer at a time. The big issue is how much excess epoxy needs to be soaked up while the layup is compressed. I have a tendency to lay-up multiple layers at a time and even 4 or 5 layers of paper towels won't wick it all up and if it does, it doesn't allow enough airflow through the layup. Real breather fabric is 3/16" to 3/8" thick and will provide air flow even with a heavy load of epoxy soaked into it. For larger lay-ups, it is indispensable.

Once you get into 3", 4" or larger birds or complex multi-layer lay-ups you really need to use real v-bagging material - a plastic garbage bag and paper towels just won't cut it. Non-stretch mylar or stretchable poly v-bag material and a tightly cut, conformal v-bag is necessary to get a wrinkle free layup on larger projects.

Unless you're really pushing the envelope, carbon is overkill. Fortunately though, carbon fabric has gotten a LOT cheaper. Several years ago standard weave 5.6oz fabric was up over $75/yard. Now it is price-competitive with fiberglass. My problem with it is that it doesn't wet-out as easily as glass and it is much harder to get it to conform to tight radius curves like fin fillets. It is also quite brittle and doesn't handle impact damage as well as fiberglass. Unless you have significant weight restrictions, it makes sense to use multiple fabrics in a layup to take advantage of the differing characteristics of various fabrics. I tend to layup Kevlar close to the substrate for impact resistance and alternating layers of glass for flexibility and carbon for stiffness and then cover the top layer with glass as a sanding veil so I don't sand down into the carbon.

Actually, most of what I do in terms of lay-up design and multiple fabrics and v-bagging is overkill for sport rocketry. The fin can on my L3 bird could probably impact from 10K and survive to fly again. The place where these techniques and carbon fabric can really shine is making truly minimum-weight, just-strong-enough-to-survive projects for smaller altitude attempts. Once you get up into bigger motors, optimal weight is frequently higher than what you would get from just a normal build.

I will add one thing here. Making plate stock for fins or building integral fin cans isn't difficult. Both can be done without v-bagging or other fancy techniques of any kind. For most sport rocketry purposes, v-bagging is overkill and good hand-layup techniques are more than good enough. I do what I do because I'm more interested in building things than in flying them to be honest about it. Tubing, nose cones and such are a whole different matter.

Unless you're really pushing the envelope or want to overbuild to a fault, you don't really need to do this stuff for sport rockets - paper or phenolic tubing and plywood fins and bulkheads suffice for almost any project most rocketeers build. Lots of successful L3's have flown on no more and that without any composite work whatsoever. Certainly the commercial composite nosecones, airframe tubing and G10 plate stock that you can buy are all better quality than you can make yourself without investing in expensive tools and tooling so it really is a waste of time and energy, not to mention money, to make component parts yourself.

The primary place where it becomes worthwhile and cost effective to get into v-bagging is in the area of fin cans. While I've made various components, commercial suppliers can all do it better and cheaper than I can for the most part.

Warren, I'd love to lend a hand and watch. I've read all our threads and a few referenced materials. However, nothing beats experience. I envision using this technique on fin cans initially. (I do have a Kestrel...)

I'd be interested in a class too and can get the materials, if you give me a shopping list and a few weeks lead time.

I travel for work (too much), so if you could give me a heads up sometimes I can reschedule.

Steve

Thanks David too!

I agree with both Warren and Adrian. Carbon fiber is lighter, thinner, stronger then fiber glass. Fiber glass can handle some extreme flights. I did a 5" min dia P motor rocket. It was a fiber glass hand laid. It did have a single layer of carbon fiber on the outside of the layup. Why? Because it looks cool and chicks dig it!. I used .125 G-10 fins with 1/3 -2/3-1 layup. The rocket was 'misplaced', but it did not rain down parts on the way up. To me that was a pretty extreme flight for a hand laid (mostly) fiber glass rocket.

Tony

Just to add clarity to Tony's post - that long section in the upper photo above is the MOTOR.

The "up" part of that boost was very cool. Unfortunately, at about T+30 someone on the flight line fired up a transmitter that was the same frequency as Tony's... and the party was over. Hence the reason this rocket is being stored outdoors in the Nevada desert instead of in Tony's shop.

That was an epic boost. I watched it from a few miles out. It sure held together nicely. You know Tony, it may have never come down 😀 Perhaps it burned up during re-entry?

Tony,

😯 , very impressive sir. I mean holy #$%@ WOW!

I still think about that flight. I would love to know how high it went, the thrust curve of the motor and how my constructtion held up.

Is that to much to ask? Hopefully some day it will turn up.

Tony