Question about Low-Vac and weight

[JLKnolla]

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?

[TMann]

Why not just commit to vacuum bagging?

 

There are other advantages other than weight. The pressure on the part combined with the vacuum does a real good job of erradicating any missed air bubbles between the glass and the foam.

 

I put my parts that are flat on a piece of 3/4 MDF and put the works in the bag. Result is no warping.

 

If you plan on using CF for anything then vacuum bagging is a must to get quality results.

 

Take the plunge.

 

....... now vacuum infusion is even more exciting.

[Lynn Erickson]

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?

to answer the question. no there is no hard data. for there to be hard data to prove that, it would have to be true. I believe it is not. I have seen some parts made that way that are heavier. in general there is not much difference in weight but it is more complicated to do, requires more expense, and is a very wasteful process. All the extra materials used for the process end up in a land fill.

[TMann]

.... it is more complicated to do, requires more expense, and is a very wasteful process. All the extra materials used for the process end up in a land fill.

As someone who does vacuum bag all parts possible, It is not hard to do, the parts are of a very high quality and you can SEE the amount of epoxy you failed to remove everytime you pull off the bleeder/breather material.

 

I do have to admit though ........ I spend a lot of sleepless nights thinking about the landfill.

[Cozy Girrrl]

My guess is they are not following the very simple instructions then. It has to be done with the right pump as well.

 

Waste over and above straight plans technique plus peel ply?

-cheapest paper towels available

-pallet wrap

 

 

The instructions are explicit to do a layup same as you would normally.

The technique is intended to produce "highly conformal layups without bubbles or voids" Though parts will not come out resin rich it was not intended to be "Vacuum Bagging" to produce lightweight parts.

I'd say they are typically lighter.

 

...Chrissi & Randi

[Cozy1200]

I've followed the girls instructions as close as possible, but still haven't had a lot of success. I do have the exact same pump. The few times I've tried it the layup comes out dry. To the extent you can see the weave and actually suck air through it. The parts to turn out to be very conformed. I haven't figured out what I've been doing wrong, but I really haven't tried it that much.

[TMann]

The few times I've tried it the layup comes out dry. To the extent you can see the weave and actually suck air through it.

There's the key. If you don't get a good seal, air will find it's way in and travel through the layup on it's way out. The same can happen with vacuum bags. If you detect a leak, you must find the source and seal it.

[Cozy Girrrl]

There's the key. If you don't get a good seal, air will find it's way in and travel through the layup on it's way out. The same can happen with vacuum bags. If you detect a leak, you must find the source and seal it.

Okay, this does not make sense to me. It would be another thing if you tried this by taping a bag to one side of a structure and were sucking air through it but in a bag it wil all be at the same pressure (eventually) everywhere inside the bag. You could hypothisize that you are sucking trapped air within the foam through the epoxy/glass matrix but the LoVac concept voids this on to levels, first not enough suction in the first place, second as soon as the slowly saturating paper towels get wet, since it also acts as the bleeder layer it shuts off that area, no more vacuum, no more migration.

...C&R

[TMann]

C & R

Agree completely .......... provided the bag is good.

I had one part where a small leak developed on the under side and the air found it's way through seam in the foam where it was joined. It came through the layup resulting in a dry spot. Even the micro slurry migrated to this point.

 

That is the only way I think you could end up with a dry layup provided everything was wetted out properly from the start.

 

As far as evedence that it (Low-Vac or standard vacuum bagging) saves weight, when you have a part complete per a standard layup procedure, put it in the bag ......... that extra weight you are saving is what you have in the paper towels (or bleeder/breather material.)

 

It's evidence you can weigh.

[chasingmars]

TMann,

 

Are you sure you vac bagged *all* parts?

 

To be fair (as someone who's vac bagged pretty much everything through to the outside of the fuselage), given that the plans don't account for needing to seal things up, vac bagging some things is very tricky...

 

Vac bagging the flat stuff is quite doable, if expensive. My take is that given the amount of epoxy used on these planes, you're not going to save a huge amount of weight (maybe a couple tens of pounds at best), and probably not even. The cost is substantial to do it right, and if you're not doing it right, you shouldn't be doing it.

 

Anyhow, TMann, by now your bird (if you're keeping your early pace) should be looking pretty nice... how did you skin the outside of the fuse, and if you vac bagged it, any tips on procedure?

[mak790]

My take is that given the amount of epoxy used on these planes, you're not going to save a huge amount of weight (maybe a couple tens of pounds at best), and probably not even.

Isn't it also about glass, resin ratio?

 

Seb

[TMann]

TMann,

 

Are you sure you vac bagged *all* parts?

Not every part but many more than I thought was possible.

As someone who does vacuum bag all parts possible,

 

No I did not bag the outside of the fuselage but I did bag all bulkheads, sides, floor, canard, the nose forward of FS 0.0, nose strut cover, hatches, portions of the center section spar, landing brake, gear doors .......

 

Mostly it has taken a little imagination and creativity but most parts can be bagged. I just finished my inside layup of my landing brake. I started out by casting the area where the door goes, bagged the outer skin, microed the side where the foam meets the CF and bagged it again to get a good bond, added two ribs to stiffen it up, more CF and just popped it in the bag 20 minutes ago. The form will keep it all true to shape.

 

I think I could have done 90% of the CS spar by bagging it. Still may go back and do that.

 

....... but other than that, I think it's just a waste of time.

[RGlos]

I went to one of the original glassing forums at Oshkosh in the mid 80's.

 

The stipling/squegee technique was developed to get the lowest weight possible.

 

1) Spread the micro on the foam.

2) Stipple the glass into the micro

3) Scrape off the excess with the squeege

 

The amount of epoxy was only enough to fill the glass. After repeated squeegeing, I found the proper blend of micro/epoxy to make the technique consistant. This left the glass with almost a dry look. I would not have learned this easily without the forum. I knew what to look for.

 

It is now 30 years later. How does this knowledge get down to new builders.

 

Vacuum bagging. I guess that replaces number 2 above. But if you don't know know what how much to do #3 or if the micro is too wet in #1 where does that leave you. It leaves you with a 950+ lbs Long EZ or 1300 lb Cozy MK IV. even with the vacuum bagging and you won't know how badly you've done it until you put it on the scales for the first time.

 

I guess what I'm saying is that don't count on Bagging alone to save weight. You must insure that you have amply used the squeege.

 

Idealy, find one of the original builders to pass his knowledge along.

[Lynn Erickson]

I went to one of the original glassing forums at Oshkosh in the mid 80's.

 

The stipling/squegee technique was developed to get the lowest weight possible.

 

1) Spread the micro on the foam.

2) Stipple the glass into the micro

3) Scrape off the excess with the squeege

 

The amount of epoxy was only enough to fill the glass. After repeated squeegeing, I found the proper blend of micro/epoxy to make the technique consistant. This left the glass with almost a dry look. I would not have learned this easily without the forum. I knew what to look for.

 

It is now 30 years later. How does this knowledge get down to new builders.

 

Vacuum bagging. I guess that replaces number 2 above. But if you don't know know what how much to do #3 or if the micro is too wet in #1 where does that leave you. It leaves you with a 950+ lbs Long EZ or 1300 lb Cozy MK IV. even with the vacuum bagging and you won't know how badly you've done it until you put it on the scales for the first time.

 

I guess what I'm saying is that don't count on Bagging alone to save weight. You must insure that you have amply used the squeege.

 

Idealy, find one of the original builders to pass his knowledge along.

if that is what they told you it is not correct. you do not want to stipple the glass and pull up the resin with the micro in it. you do not want the micro to get into the glass. the micro should be put on as dry as possible (peanut butter) it should not be runny at all ( runny is heavy ). the dry micro is to fill the foam pores with a lightweight compound of the resin so it will stick to the foam but not weigh as much as pure resin. when the micro is mixed correctly there is not any extra resin in it to stipple up into the glass. the glass should be wet out with resin from the top . this keeps the micro in the foam and from coming up into the glass. squeegeeing is to remove any air and get off the excess resin. micro in the glass weakens the layup. it is the same as air in the layup. this is another reason to hard shell before vacuum bagging, the micro in the foam can not be pulled up into the glass layup. vacuum bagging compresses the glass to a smaller volume so it can't hold as much volume of resin but does leave the weave filled with pure resin. On thin layups like 2 or 3 plys it does not really save any weight. what you gain by compressing the fibers is lost buy filling the weave with heavy pure resin instead of a light weight filler. when used on the uni that is used on our canards it will add weight.

[brainfart]

Vacuum bagging isn't expensive. You don't need those super expensive bagging supplies, many everyday items can substitute.

Some plastics are permeable to air though. It doesn't need a real leak in the bag, if the whole bag is leaking on its whole surface resin starved parts will be the result.

 

There are electronic devices which can detect leaks (since leaks cause ultrasonic noise). These devices are expensive though. Someone I met on another forum built a bat detector (plans and kits available online) to detect leaks, and it seems to work great (and costs much less).

[mak790]

Someone I met on another forum built a bat detector (plans and kits available online) to detect leaks, and it seems to work great (and costs much less).

Could you give a link to that forum?

 

Seb

[TMann]

The stipling/squegee technique was developed to get the lowest weight possible.

 

I would venture to say that if you used all of the techniques you described, I could take that same part when you were finished with it, stick it in a vacuum bag and get even more additional epoxy out of it without creating a dry layup.

if that is what they told you it is not correct. you do not want to stipple the glass and pull up the resin with the micro in it.

...... which is another reason I typically hardshell my parts.

 

Vacuum Bagging, Low Vac, etc are not difficult. It's just second nature for me. A different technique to perform the same function.

 

Like fishing ...... spinning rod >>>>>> bait caster >>>>>> fly rod.

Same objective.

[Phil Kriley]

the micro should be put on as dry as possible (peanut butter) it should not be runny at all ( runny is heavy ).

Well, that sure as heck isn't what Burt and Mike demonstrate in their video...and what is described in the plans, chapter 3.

 

The micro slurry is RUNNY - more like molasses than peanut butter. The thicker stuff is called dry micro, and is used to fill holes, dings and areas such as the trailing edge over the peel-ply.

 

My completed center spar weighs 44 lbs - that seems comparable to other builders who have a reputation for excellent construction technique.

 

I'm working on my wings now, and if I tried to spread dry micro on the wing, I'm sure I would damage it because of the hollow portions and the need to press hard with the squeegee to move dry micro around.

 

Mike Melville's demonstration in the video shows him POURING the micro slurry on the foam, moving it around with light passes of the squeegee, then using firmer strokes to remove most of it. Then he lays down the glass cloth, pours on pure epoxy, moves it around the part until it is wet out, then squeegees off the excess.

 

I sure hope I'm doing this right! I had a couple of inspectors check my work a couple of weeks ago and got a "thumbs up" from them. They are both A&P's and one does fiberglass work for the airlines as his day job.

[longezdave]

I'm with Lynn on this. You want to use micro on the foam that is as thick as practical to spread and work with. I think that the Rutan video used thinner slurry to show how quick and easy the composite construction is.

[Lynn Erickson]

Well, that sure as heck isn't what Burt and Mike demonstrate in their video...and what is described in the plans, chapter 3.

 

The micro slurry is RUNNY - more like molasses than peanut butter. The thicker stuff is called dry micro, and is used to fill holes, dings and areas such as the trailing edge over the peel-ply.

 

My completed center spar weighs 44 lbs - that seems comparable to other builders who have a reputation for excellent construction technique.

 

I'm working on my wings now, and if I tried to spread dry micro on the wing, I'm sure I would damage it because of the hollow portions and the need to press hard with the squeegee to move dry micro around.

 

Mike Melville's demonstration in the video shows him POURING the micro slurry on the foam, moving it around with light passes of the squeegee, then using firmer strokes to remove most of it. Then he lays down the glass cloth, pours on pure epoxy, moves it around the part until it is wet out, then squeegees off the excess.

 

I sure hope I'm doing this right! I had a couple of inspectors check my work a couple of weeks ago and got a "thumbs up" from them. They are both A&P's and one does fiberglass work for the airlines as his day job.

how long ago was that video made. now a days we have peanut butter that will spread on the bread without tearing it. micro is light , resin is heavy, buy adding the most micro possible and still being able to apply the stuff on a given surface the lighter the part.

[Phil Kriley]

how long ago was that video made. now a days we have peanut butter that will spread on the bread without tearing it. micro is light , resin is heavy, buy adding the most micro possible and still being able to apply the stuff on a given surface the lighter the part.

I have version 3 of the plans, and micro slurry is not described as peanut butter texture.

[Lynn Erickson]

I have version 3 of the plans, and micro slurry is not described as peanut butter texture.

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.

[RGlos]

The puspose hear was to bring attention to the whole process and not just vacuumn bagging. Don't think your going to come out light without paying attention to the micro, stipling and squeege.. Lynn I purposely did not go into detail. Who said anything about banging the brush againist the glass.

 

The forum showed this tecnique quite nicely, thank you. And the micro was not exactly peanut butter but a tad wetter.

 

No one is against bagging here. Tman, I sure you can pull more epoxy out but then what . How much do you squeege? I was shown that you can draw the squeege over the glass with enough force to create a small ridge. When the ridge was gone you were done. This force can very, it took practice.

 

Fortunately, I and three others who were building at the same time came in at under 860 lbs. Ten years later when I repainted and got rid of the feather fill (nightmare filler) and switched to suprafill and imron, I lost anther 15lbs

 

The micro is wetter than peanut butter as Phil Krily has said. Dry micro may not get down into the voids properly and thus reduce bonding strength. The micro is not to serve as a skin but an interface between the foam and the glass all while keeping it light. Rutan's were quoting less than 800lbs on a Long EZ as a target. I did not make it but I sure tried and paid attention.

 

Then I see Long EZ empty weights of 950 to 1050 (adjusting for engine differences) and I wounder what the hell went wrong. These planes lost a great deal of utility.

[TMann]

No one is against bagging here. Tman, I sure you can pull more epoxy out but then what . How much do you squeege? I was shown that you can draw the squeege over the glass with enough force to create a small ridge. When the ridge was gone you were done. This force can very, it took practice.

 

My point was to address whether or not low-vac or vacuum bagging will save you some weight, and the answer is yes. It is not a substitute to good technique, but an enhancement of good technique.

 

If I weigh the peel ply/ perf ply/ bleeder material prior to bagging a part that had been prepared as you stated, that waterial would weigh more afterward due to some additional epoxy being drawn out of the layup.

 

Can you build a light airplane without these techniques? A definite yes. I believe CP25 or 26 (can't remember which) has some weights from a Long-EZ project Mike & Dick did and VB was not used. They had some very impressive numbers to aim for (not to mention an excellent timeline.)

 

So ...... yes & yes.

[brainfart]

mak790, sent you a PM.