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Long EZ Mold Construction - Question

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Nims11

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I read much of the very informative sticky on composites, still more I need to read. But I have a question about why one can't use molds to construct a Long EZ. It was pointed out to me by a friend that a significant portion of the time it takes to build an ez is in the finishing of the fiberglass, the sand and fill process. But by using a mold and vacuum bag technique you do not have all that finish work. Firstly is that correct? And given that it is said an ez takes about 4000 hours for the average builder to complete then what percent of that time is the finish work? Would it be a significant savings in time if you did not have to do it?

My thought was that you could use a CNC router, or 3D printer to make the mold very easily.

Could the reason be that this process in not used is that it is more difficult to bond the glass skin to the foam?

Thanks.
 

Turd Ferguson

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Moldless composite construction methods were used as an expedient. "Quick and dirty" were Burt's words. Certainly no reason why you couldn't build it with molds but without some structure redesign, it wouldn't be the most efficient building methodology. At any rate, the time saved during finishing will be used elsewhere.

Burt built the prototype VariEze's in 7-9 months. 4000 hrs to build a EZ? First, I'd like to question the validity of that claim. But beyond that, maybe some people simply enjoy the building process and are not concerned with how long it takes. There are some builders that want a finish with zero imperfections. That takes a long time. Having built a couple of moldless composite airframes, I don't find the process all that time consuming.
 

cheapracer

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I read much of the very informative sticky on composites, still more I need to read. But I have a question about why one can't use molds to construct a Long EZ. It was pointed out to me by a friend that a significant portion of the time it takes to build an ez is in the finishing of the fiberglass, the sand and fill process. But by using a mold and vacuum bag technique you do not have all that finish work. Firstly is that correct? And given that it is said an ez takes about 4000 hours for the average builder to complete then what percent of that time is the finish work? Would it be a significant savings in time if you did not have to do it?

My thought was that you could use a CNC router, or 3D printer to make the mold very easily.

If you can't afford it and keeping within the "Homebuilt" theme that to me implies you can't, you don't need CNC router, nor 3D printer, you don't need to vac bag, and your assumptions are correct, you most certainly can make a simple plug out of anything and everything, take a mold and go from there, I find it that easy.

I'll find a picture that will help you ...
 

autoreply

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Using molds, it'd be hard to impossible to use the same structural layout (foam-cored, skinned). That yield a completely different structural layout, which means you're designing a new plane. Can certainly be done (see the Berkut), but doesn't seems to be what you're after.
 

Nims11

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OK, I did not guess the strucural layout could not be reproduced with a mold. Is that because the finish part, sanding and filling, adds strength that cannot be made in a mold? Or is it something with the relationship of the glass skin to the foam?
 

autoreply

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OK, I did not guess the strucural layout could not be reproduced with a mold. Is that because the finish part, sanding and filling, adds strength that cannot be made in a mold? Or is it something with the relationship of the glass skin to the foam?
The latter. If you use molds for the wing, the foam core has to have a very exact shape and thickness, too little and you don't have proper (if any) adhesion, too much and you're crushing the foam or can't close the mold. Very hard to do closed molding right, even after a few tries, not to mention that quality control is terribly hard if possible at all.

A technique that's discussed on several places here on HBA is; do the classic foam core on which you layup, but using thick foil (paper-thick) over the laminate and vacuum-bag everything together, to get a nice smooth top finish. Sanding still required, but it's way less work. Only works for simple tapered surfaces though.
 

Turd Ferguson

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OK, I did not guess the strucural layout could not be reproduced with a mold. Is that because the finish part, sanding and filling, adds strength that cannot be made in a mold? Or is it something with the relationship of the glass skin to the foam?
Fill and finish of the fiberglass weave adds nothing to structural strength. I think what's being said is you can't put a solid foam core structure into a mold. Think about it. It will have to be redesigned so the "molded" part is a shell which means the internals have to be redesigned.

I think you are making too much out of fill and finish of the fiberglass cloth weave. I've seen planes in the field where it appears very little fill was used as the cloth was quite visible and those planes flew just fine.
 

kent Ashton

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This chap is using molds for a Varieze variant:
Photos

It is massively more work to use molds. First make a plug and finish it to the quality of a finished Long-ez. Then use the plug to make your molds. Then use the molds to make the actual skins. Along the way add foam or honeycomb to the skins in the mold.
 

Nims11

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The latter. If you use molds for the wing, the foam core has to have a very exact shape and thickness, too little and you don't have proper (if any) adhesion, too much and you're crushing the foam or can't close the mold. Very hard to do closed molding right, even after a few tries, not to mention that quality control is terribly hard if possible at all.

A technique that's discussed on several places here on HBA is; do the classic foam core on which you layup, but using thick foil (paper-thick) over the laminate and vacuum-bag everything together, to get a nice smooth top finish. Sanding still required, but it's way less work. Only works for simple tapered surfaces though.
Thanks. Sorry but I'm still not understanding, if you could indulge one more question please. In the regular moldless way, you take a peice of solid foam and cut it to the exact dimension for the wing, then you lay the glass cloth and resin over it such that the glass adheres directly to it and is enmeshed with it, such that the glass skin is the same shape as the original foam, correct? Could you not CNC cut a mold that is the exact shape of the foam plus the required thickness of the glass skin, using half mold of the wing. Then layup the glass in the mold, take the two halves and bond them together so you have a complete wing that is hollow inside. Then inject liquid foam into the wing and it would adhere to the inside of the glass. Isn't the Divinycell solid foam a liquid in its original state anyway?
 

Nims11

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Fill and finish of the fiberglass weave adds nothing to structural strength. I think what's being said is you can't put a solid foam core structure into a mold. Think about it. It will have to be redesigned so the "molded" part is a shell which means the internals have to be redesigned.

I think you are making too much out of fill and finish of the fiberglass cloth weave. I've seen planes in the field where it appears very little fill was used as the cloth was quite visible and those planes flew just fine.
Ok, well maybe the person who told me the sand and fill part was a significant portion of the total build time was incorrect, he is not built one yet so he is not an expert on the process.

It is massively more work to use molds. First make a plug and finish it to the quality of a finished Long-ez. Then use the plug to make your molds. Then use the molds to make the actual skins. Along the way add foam or honeycomb to the skins in the mold.
Can't you just use a CNC router to make the mold directly?
 

autoreply

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Thanks. Sorry but I'm still not understanding, if you could indulge one more question please. In the regular moldless way, you take a peice of solid foam and cut it to the exact dimension for the wing, then you lay the glass cloth and resin over it such that the glass adheres directly to it and is enmeshed with it, such that the glass skin is the same shape as the original foam, correct? Could you not CNC cut a mold that is the exact shape of the foam plus the required thickness of the glass skin, using half mold of the wing. Then layup the glass in the mold, take the two halves and bond them together so you have a complete wing that is hollow inside.
You could. In theory.
In reality, the inaccuracies make it totally unfeasible. Mold and foam deformation, tolerances etc.
Then inject liquid foam into the wing and it would adhere to the inside of the glass. Isn't the Divinycell solid foam a liquid in its original state anyway?
It takes millions US$ of investment to make a controlled environment where you can produce PVC foam in a given shape.

High temperatures (beyond the reach of vinylester or epoxy), controlled blowing of foam won't work with a temperature gradient, the problems are virtually endless.

Note that the Long-Ez uses Polystyrene. Lower blow temperature compared to PVC, but the same problems, not to mention that bonding of a blowing foam isn't exactly great.
 

bmcj

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I don't doubt that Burt built the EZ in 4,000. In fact I'd expect about half that time. He had the process down well. If you recall Scaled's ATTT transport. It seemed like just overnight between it flying with a single tail and flying with twin tail booms.
 

Turd Ferguson

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Then layup the glass in the mold, take the two halves and bond them together so you have a complete wing that is hollow inside. Then inject liquid foam into the wing and it would adhere to the inside of the glass. Isn't the Divinycell solid foam a liquid in its original state anyway?

If you have a hollow wing, it won't carry the required loads. Injecting liquid foam into the void won't suffice. You need the proper load carrying structure. With the moldless method, the foam cores are cut apart so structural layups can be added. Then they are glued back together and a "skin" is glassed all over the outside. A Glassair has molded skins but inside the hollow wing is a spar and ribs like a conventional airplane.

Filling and sanding a moldless composite airplane may consume a large portion of the build time but the overall build time is not that much. Remember moldless composite popularity is based on the fact it was a fast way build a plane. That's how Scaled composites got started. They could build a prototype in a few months using moldless composite vs. yrs using conventional methods. So unless you just don't like sanding.......and if that's the case, get a couple of migrant workers from an auto body shop. Teach them what to do, buy them a few tacos and you won't have to get dirty.
 

Turd Ferguson

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I don't doubt that Burt built the EZ in 4,000. In fact I'd expect about half that time. He had the process down well. If you recall Scaled's ATTT transport. It seemed like just overnight between it flying with a single tail and flying with twin tail booms.
He built one of the prototype vari ezes in 7 months with one part time helper. Of course he didn't go for the grand champion finish either.
 

Nims11

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You could. In theory.
In reality, the inaccuracies make it totally unfeasible. Mold and foam deformation, tolerances etc.

It takes millions US$ of investment to make a controlled environment where you can produce PVC foam in a given shape.

High temperatures (beyond the reach of vinylester or epoxy), controlled blowing of foam won't work with a temperature gradient, the problems are virtually endless.

Note that the Long-Ez uses Polystyrene. Lower blow temperature compared to PVC, but the same problems, not to mention that bonding of a blowing foam isn't exactly great.
I see, thanks.

Filling and sanding a moldless composite airplane may consume a large portion of the build time but the overall build time is not that much. Remember moldless composite popularity is based on the fact it was a fast way build a plane. That's how Scaled composites got started. They could build a prototype in a few months using moldless composite vs. yrs using conventional methods. So unless you just don't like sanding.......and if that's the case, get a couple of migrant workers from an auto body shop. Teach them what to do, buy them a few tacos and you won't have to get dirty.
Wow, this goes against everything I've been researching. Over at the Canard forums they are saying that the biggest single reason the EZ is not more popular is the build time. One person said that you can build 3 RV-7s in the time it takes to build one EZ, I'm sure that is an exaggeration to make his point. You hear of people that have been working on theirs for 8+ years, and many build projects for sale have been handed down through several builders. Many have said that 4 years of steady part-work, like 20 hours a weeks is necessary. That seems like a long time building to me.
 

Turd Ferguson

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Wow, this goes against everything I've been researching. Over at the Canard forums they are saying that the biggest single reason the EZ is not more popular is the build time. One person said that you can build 3 RV-7s in the time it takes to build one EZ, I'm sure that is an exaggeration to make his point. You hear of people that have been working on theirs for 8+ years, and many build projects for sale have been handed down through several builders. Many have said that 4 years of steady part-work, like 20 hours a weeks is necessary. That seems like a long time building to me.
Apples to oranges comparison.

Back up a few decades. Vari-EZ's and Long-EZ's dominated the flight line at EAA. Compared to other options of that era, they could be built quickly (2 yrs was a common gestation period) and they were easy to build. In fact, that's how the Vari-EZ got it's name, it was described as Very-Easy to build.

Now you can build a RV very quickly due to the completeness of the kit. Van was business smart. He knew the more complete the kit, the better the sales. It doesn't hurt that he included excellent flying qualities which boosted popularity. Imagine had he sold plans only. Builders would have to cut aluminum sheet, form ribs over wood blocks, etc. Wouldn't be nearly as many RV's built. EZ's would be much, much faster to build. Even with the RV kits, it's not unusual to see 7 and 9 yr projects. Though EZ's could be built in 2 yrs, some people took decades to build theirs. Not a fault of the plane.

There's other reasons why EZ's are not more popular today. The mission they are designed for is somewhat limited by today's standards. Vari-EZ and Long-EZ are improved surface airplanes more suited for speeding cross country than hamburger runs or airport bumming. Other designs can do that and much more. A recent survey indicated many builders today want a weekend flyer they can land off airport and/or in remote areas. Hence the popularity of some of the super STOL birds.

Quite frankly, if I wanted to build a canard airplane, I'd try to build a Vari-Viggen. They are just plain cool even though they are not fast or easy to build.
 

bmcj

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He built one of the prototype vari ezes in 7 months with one part time helper. Of course he didn't go for the grand champion finish either.
Nor did he believe in the grand champion finish. He finished the wing's upper surface enough to get smooth airflow with good lift, but left the bottom unfilled. He reasoned that it was unnecessary weight that was only for show.
 

BJC

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Wow, this goes against everything I've been researching. Over at the Canard forums they are saying that the biggest single reason the EZ is not more popular is the build time. One person said that you can build 3 RV-7s in the time it takes to build one EZ, I'm sure that is an exaggeration to make his point. You hear of people that have been working on theirs for 8+ years, and many build projects for sale have been handed down through several builders. Many have said that 4 years of steady part-work, like 20 hours a weeks is necessary. That seems like a long time building to me.

A friend who built four or five scratch-built airplanes, including a Cassutt from first tube cut to first flight in four months, while working a full-time day job, had this response when he was asked how long it would take to build an airplane.

"Well, how long does it take to drink a beer? Some people sip on one all night, and some people guzzle it down all at once." I know guzzlers, and I know sippers. Apparently, I'm a sipper when it comes to building airplanes.

He also said that it takes engineers ten times as long to build an airplane, because engineers think about changes and design too much, when they should "just build the thing."


BJC
 
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