Question about Low-Vac and weight

[brainfart]

mak790, sent you a PM.

[mak790]

Got it thanks.

 

Seb

[Tyson]

For those interested in "conventional" type bagging with a regular vacuum pump...

 

Look into the type of system that ACP sells...specifically the nylon vacuum bag tubes with "quick lock" seals. ACP sells bags that are 18" or 36" across. Essentially you create your layup as usual, apply a breather, batting, then slip into the bag. Apply the quick locks to each end of the bag. The quick locks don't leak. Attach the vacuum to the adapter nipple and turn on the vac. The bag is re-usable a few times (depending on how you take care of it).

 

-This system doesn't leak, except maybe around the adapter into the bag (the nipple that goes through the bag). Easy enough to locate and deal with.

 

-This system is easy to do on small flat pieces, adds negligible time, and just a little bit of consumables.

 

-This system is impractical except for those hell bent on weight savings. And if so inclined, seems easier/less messy/more reliable than low vac.

[Phil Kriley]

I would say then follow the plans. what I should have said is what you were told is not correct for LOW-VAC, or any composite parts being made in this century, the plans method, I am sure did not talk about LOW- VAC. the discussion here is about low vac and weight, which is a mod to the plans and many that have used that method do not pore on their micro, they use it more like peanut butter.

Fair enough - but just to be clear, my plane IS being made in this century and I am using the most current plans available. They are pretty clear on the subject of preparing the foam for glassing. The micro slurry is made by mixing micro spheres 1-1 by volume with pure epoxy. This is POURED onto the foam and moved around with a squeegee, then the excess removed. The plans state that the slurry is almost as runny as pure epoxy.

 

The plans go on to explain that making the slurry too dry will not give a good bond between the glass and the foam. If low-vac or vacuum bagging fixes this, then that's great.

 

I do believe I will continue to follow the plans to the best of my ability.

[TMann]

For those interested in "conventional" type bagging with a regular vacuum pump...

 

Look into the type of system that ACP sells...specifically the nylon vacuum bag tubes with "quick lock" seals. ACP sells bags that are 18" or 36" across. Essentially you create your layup as usual, apply a breather, batting, then slip into the bag. Apply the quick locks to each end of the bag. The quick locks don't leak. Attach the vacuum to the adapter nipple and turn on the vac. The bag is re-usable a few times (depending on how you take care of it).

 

I use the bag/system from ACP and have been real happy with the results.

They also make a 50" wide version. It's really nice. You can have a bag of any size in short order. Just cut to length.

 

I usually save my old perf ply and put it on top of the bleeder breather layer to prevent the epoxy in that layer from sticking to the inside of the bag thus extending the life of the bag.

 

ACP also puts out a video that is good for those just starting up.

[Edge 513]

It would be kinda interesting to have a poll listed for those BUILDING a LEZ or Cozy or Velo to list what style of layup they are USING to build their actual plane...or DID BUILD their Rutan derivative from.

 

I havent seen a post for a very very long time by John Matcho, so if you are here in the shadows and think it might be useful, maybe you could set it up.

 

I think it would be most appropriate for Builders to list what they are DOING, not guys just favoring one or the other.

Building one of these planes is a big task, and maybe it would make a difference to somebody. Reflecting on my personal patience level, if I had thought I had to Vac-bag to build, I dont know if I wouldve felt I could commit.

YMMV.

[SAF_Zoom]

Is there a builder that indicate the weight of every parts he is making. I know many indicate the time it took them to make the part, but I wonder if any indicate the weight...

[RGlos]

In case you missed it the first time around I asked volunteers awhile ago to help compile a canard empty weight spread sheet. I have attached it for convenience.

 

I am #3 on the list. If you have not particpated yet send me your data and I will ad you to the list

 

Rglos721@comcast.net

 

You will note for each plane there is a wide difference (more than can be made up from equipment ad-ons) for each make of plane.

 

You can make a light plane the old way and from what vacuum bagging claims, even lighter. But if you don't have a clue what the difference is betweeen wet and dry layups you could be in for a big surprise when your done.

Canard Weights II.xls

[TMann]

Reflecting on my personal patience level, if I had thought I had to Vac-bag to build, I dont know if I wouldve felt I could commit.

YMMV.

Fair enough..... but there are those who want to take it to the next level.

I've listened to some folks talk about filling air pockets after the cure. Sometimes that just happens and you have to live with fixing it. So when you're fixing that problem, is it still easier than vacuum bagging?

Is there a builder that indicate the weight of every parts he is making. I know many indicate the time it took them to make the part, but I wonder if any indicate the weight...

As posted earlier, Mike Melville and Dick Rutan did this in CP 25-26 (might be off by an issu number but pretty close) in which they weighed parts and posted the timeline (I believe it was around 6 months.)

[Phil Kriley]

In case you missed it the first time around I asked volunteers awhile ago to help compile a canard empty weight spread sheet. I have attached it for convenience.

 

I am #3 on the list. If you have not particpated yet send me your data and I will ad you to the list

 

Rglos721@comcast.net

 

You will note for each plane there is a wide difference (more than can be made up from equipment ad-ons) for each make of plane.

 

You can make a light plane the old way and from what vacuum bagging claims, even lighter. But if you don't have a clue what the difference is betweeen wet and dry layups you could be in for a big surprise when your done.

That's a good spreadsheet, but what I'd like to see are weights of the components before final assembly. This would help us who are still building to assess whether we are making a heavy mess or are on the right track.

 

Wayne Hicks, IIRC, posted on his web site that his center spar weighed 44 lbs. Since mine came out the same, I figure I must be doing something right.

 

It would be nice to be able to compare the weight of my canard to other builders, and the weight of my wings, fuselage as of chapter 6, etc.

[TMann]

In CP#26 M&Ds CS Spar was 27 lb 5 oz.

Compared to that, I'm heavy

[Phil Kriley]

In CP#26 M&Ds CS Spar was 27 lb 5 oz.

Compared to that, I'm heavy

How does the Long EZ CS compare in size to the Cozy Center section spar? I hope the Cozy's is bigger!

[TMann]

How does the Long EZ CS compare in size to the Cozy Center section spar? I hope the Cozy's is bigger!

It is by 24 inches

[brainfart]

I've briefly worked in an aircraft composite repair shop and have visited several commercial aircraft manufacturers. You might be surprised to hear that they all regularly used plain cheap TRASH BAG plastic from the grocery store for vacuum bagging. You really don't need all those high-priced supplies. $20 per roll bag sealant tape? Forget it, for most parts a cheap caulk gun (?) and some cheap acrylic caulking compound (? that stuff you use in your bathroom) will work just as well. Same is true for batting, release film etc.

[TMann]

for most parts a cheap caulk gun (?) and some cheap acrylic caulking compound (? that stuff you use in your bathroom) will work just as well. Same is true for batting, release film etc.

I would not want silicone calk anywhere close to a layup.

As for the other materials, I believe you can get bleeder/breather material (quilt batting) locally, say at a Walmart or the like. There is a criteria to meet though. I can't remember off the top of my head but some of these batting materials are not compatable.

I bought a roll of 30 yds @ 1.70 yd plus $30 for shipping. It sounds like a bad deal until you realize a competitor was selling it @ 3.20 / yd.

 

I don't use the sealant tapes. As stated, too much $ for what you get.

The bags (tubes actually) from ACP work great and are reasonable.

[brainfart]

> I would not want silicone calk anywhere close to a layup.

 

That's why I said acrylic. Not all of them are made of silicone.

[ColinB]

I have a better way to seal the bags (and it even works on the hightemp bags used for prepreg and claving)

 

the heat sealers you use for packaging (and infact the clear packaging tubes also work well as vac bags and are ultra cheap)

 

 

seal one end a few times

 

place part and valve inside

 

then use heat sealer to seal the end up

 

creates one of the best vac bags iv used, iv never had a leak to find as with bag tapes and other than the cost of the sealer it costs next to nothing

 

you can get the hand held sealers that are best as they dont have anything at the sides limiting the width of the bag so you can even seal the really big bags by moving it along and zapping it

 

 

something like this

 

[Bruce]

That's a good spreadsheet, but what I'd like to see are weights of the components before final assembly. This would help us who are still building to assess whether we are making a heavy mess or are on the right track.

 

Wayne Hicks, IIRC, posted on his web site that his center spar weighed 44 lbs. Since mine came out the same, I figure I must be doing something right.

 

It would be nice to be able to compare the weight of my canard to other builders, and the weight of my wings, fuselage as of chapter 6, etc.

Very good point Phil, proper weights of the components would be extremely helpful for the new guys(actually all of us). Doing the small test in the plans is helpful as a starting point, however, when you step up to the much larger parts, it'd be really nice to see if you're transferring your beginning skills along correctly.

 

Many years ago I helped a guy build a Vision aircraft and he would weigh his fiberglass and mix up an amount (by weight) of epoxy for that glass. I don't remember what that ratio was, or where he obtained it. Does anyone know what the ratio by weight of glass to epoxy is or should be for that perfect combination? This is obviously for hand lay-ups. Weigh the foam and fiberglass, add the epoxy and you'll know if the part is to heavy or light. I think this would be a good way for the beginner to keep track and see if he's at least getting the right amount of epoxy on the part. I'll send an email to Pro Composites (they sell the Vision kits) next week and see if they have any information on that.

 

Bruce

[Marc Zeitlin]

.... Does anyone know what the ratio by weight of glass to epoxy is or should be for that perfect combination?...

Well, there are hand layups and there are hand layups. For NON vacuum bagged wet layups, you should be happy with 50% epoxy, 50% glass by weight. Most builders are probably closer to 60% epoxy by weight. So if you have a layup that should weigh 10 lb. with the 50/50 ratio, it'll weigh 12.5 lb with a 60/40 ratio - 25% more. Sounds pretty crappy. And it is, but not quite as bad as it might seem:

 

Remember that out of the 1050 lb. that the perfect COZY MKIV should weigh empty (or the 1150 lb. that the reasonably built ones actually do, but not the 1300 lb. behemoths out there), about 450 lb. is behind the firewall, another 100 or so is landing gear and wheels, and another 75 lb. or so is foam. Throw in 25 lb. for batteries and another 150 lb. for random other stuff (like electric landing gear extension and instrument panel and wiring, etc.), and you've got 675 lb for stuff that isn't glass and epoxy. This is a lot of handwaving, but we're trying to get an order of magnitude estimate of what difference going from 50% to 60% means.

 

So, for an 1150 lb. COZY, you've got 350 lb. of fiberglass and epoxy, or 175 lb. of epoxy. That estimate lines up pretty well with the 17 gallons that Nat says you'll need in the kit with a 75% utilization rate (25% scrap). Now, going back to the 60/40 difference, 25% of 350 is 88 lb, and you'll have 438 lb. of fiberglass and epoxy - pretty big difference - clearly it's worthwhile to do a good job of stippling and squeegeeing, and being careful not to have really wet layups (except on the tank inside surfaces). None of this requires different equipment or techniques. Maybe this is where 1200 - 1300 lb. COZY's come from.

 

Now lets say that you can somehow vacuum bag everything (which you can't, but let's say it). That might get your epoxy percentage down to 40%, which is about as good as you can expect with vacuum bagging a wet layup. You'll save 17% of your 350 lb - 58 lb - getting it down to 292 lb.

 

BUT, you CAN'T bag everything, or get to 40% on everything. I'd guess that without major redesigns, you might be able to save 1/2 of that, for about 25-30 lb. Well, that's not nothing, but at least for me, it's not nearly worth the effort to bag in order to save that kind of weight.

 

But those are the types of numbers you're talking about. Worth it for some, not for most.

[Bruce]

Thanks Marc, I also found some info from the EAA, here's a partial quote about the proper ratio, and this is from 1988.

 

Sport Aviation - 5/88

 

By Ben Owen

 

If you will check some of the advanced articles on fiberglass components, you will see that many of the early articles and textbooks on fiberglass show . . . "a good ratio by weight of epoxy to fiberglass cloth to be about 50/50." However, with today's material the best for strength is approximately 40% epoxy and 60% cloth. This is very hard to do with a hand lay-up procedure without vacuum bagging.

 

I'll have to try a piece at the 50/50 weight ratio and see how close I am with my usual approach of applying epoxy. My guess is, I'm above that ratio, sometimes the application of epoxy does not always go as planned. At least we have a way of ball parking where our weight should be on any given part, if we take the time to weigh the glass and epoxy, and since I use a scale to measure my epoxy, I'm half way there.

 

 

Bruce

[ColinB]

That might get your epoxy percentage down to 40%

 

I think the 40% figure is an optimistic one just using the lowvac approach

 

your getting into the realms of prepreg ratios at 35-40% and i doubt people are getting that close with wetlay in most circumstances

[Marc Zeitlin]

I think the 40% figure is an optimistic one just using the lowvac approach

I did not mention "lowvac". I explicitly said "vacuum bagging".

 

your getting into the realms of prepreg ratios at 35-40% and i doubt people are getting that close with wetlay in most circumstances

I can guarantee that they're not. It's not trivial to get to 40% even with vac. bagged wet layups. To get to 35% - 40%, there is no choice but to go to pre-pregs.

[trans4md]

Is there any hard data on whether or not using the low-vac technique produces truly lighter parts when combined with the moldless foam core process on the EZ family?

I'm new to these discussions and also to the topic of low-vac. Since I may soon be diving into my own Cozy project, I'm also interested the answer to JLKnolla's question. The discussion in this thread is educational for me and the various bits of embedded discussions are also valuable However, since I haven't seen an affirmative response to JLKnolla's question, is it accurate to conclude that there is no known hard data reflecting weight comparisons between parts completed using low-vac techniques against those without?

 

Since I also understand that there are other benefits of low-vac, I'm also curious whether there's objective data regarding strength improvements, time-savings, etc.

 

I understand that the technique may be somewhat controversial, but objective comparison data of the various attributes would help me make a determination about the techniques that I may use in my own construction.

[JLKnolla]

Trans4md, it appears that there may be some anecdotal evidence but no one has yet set out to simply build some representative coupons (samples) to show what, if any, weight savings there are, nor whether or not there are structural benefits (although we know epoxy rich layups are undesirable).

 

Like so many other things, there is no shortage of opinion (both informed and otherwise) but hard data seems hard to come by (or is something those in the know are not willing to share).

 

The appeal, and undeniable reason for the success of the Rutan Moldless Foam Core methodology is that it is exceedingly tolerant of the kind of variations in technique, environment and results that the average builder will accept as 'airworthy', and of course it creates large shapes and structure in a relatively short period of time with a minimum of tooling.

 

My question centered on the low-vac approach as an improvement to the Rutan method, specifically in terms of weight - it is logical that 'some' weight would be saved, but how much is not quantifiable based on the responses and like (IMO) too many discussions here, it degraded into areas not part of the question (e.g., setup time, consumables cost, and the ever present heresy of varying from the plans, etc.).

 

The lesson I have learned is be prepared to sort a lot of chaff to get to the wheat or ask private questions of folks whose opinion and experience you respect.

[Cozy Girrrl]

Back to the beginning bluntly, if you want low weight, go search and study vacuum bagging, we know nothing about it, if you want highly conformal parts where conformal of layups to parts may be dificult, then LoVac -may- be helpful provided you use the same techniques, materials and tools. It is not for use everywhere, it will not work properly with other epoxies, materials or pumps. Thats our experience, there are others with similar results as well, there are those who have had difficulty reproducing our results though this is rare, there ore those who have used other pumps and they have all failed to do this successfully following the LoVac instructions.

Hope that helps a little bit?

Now all the experts can weigh in again about vacuum bagging...

...Chrissi