Female Plug/Mold

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AVI

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Just curious: the accepted method of construction appears to be to first build a male plug, pull female 'glass molds off the plug, and then to layup the fuselage in the female molds.

Male bucks have been constructed from various materials, including foam covered with 'glass, as with Tony's Corsair 82, and from wood, as evidenced in the Algie website.

What are the possibilities, advantages, and disadvantages of fabricating a female plug out of foam and 'glass or out of wood for each half of the fuselage and finishing it to a high enough standard to be used as the female mold itself, thus eliminating the necessity of pulling female molds?

Now, I realize that a female plug would be more difficult to finish to a high standard than a male plug, and that in the construction of the plug, allowance would have to be made for the skin thickness, but has anybody tried this?

There are examples of the Cozy turtle deck formed in a crude female mold consisting of wood formers with thin wood strips, and the Vision fuselage formed in a similar male mold consisting of wood formers and lathe strips but I'm talking about a fully finished female plug that would be used as a female mold.
 

orion

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Female tools can be made directly but due to the difficulties of getting a precise geometry and finish on a concave surface, I don't know anyone who is doing this on a regular basis outside of those who machine their tools using CNC mills.

Another caution with wood - keep in mind that the wood changes shape with every change in temprature or air humidity. All of these changes will end up visible in your part. Also, just the exotherm generated by the laminate may be enough to imprint the underlying structure.

The whole reason behind molding a part, and all the associated work, is the quality of the finish and the control of the geometry (dimensions, symmetry, fairness, etc.). This is very difficult to achieve with a concave tool, especially made from wood.
 

PTAirco

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Female molds

For a fuselage, I agree, it would be very hard to make a female mold. However for wing surfaces/skins I would think it is quite feasable.
We're dealing with large, fairly flat surfaces without compound curves (except for tips maybe, which could be made seperately).

My idea would be to cut a large number of ply/mdf formers these being the 'negative' of the airfoil section required, mount them on a flat surface and then skin the inside with either ply or perhaps a flat glass fibre panel, pre-made on a flat, smooth surface such as plate glass or formica.
 

wsimpso1

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+1 on male plugs and female molds for compound shapes. An EAA Technical Counselor that I know had run the composites shop for GM for a time, and he concluded through experience that male plugs are where you make them perfect, then pull the female mold. If it has to have better surfaces, then pull another male from your first female, and then pull yet another female off of the second male...

On simple prismatic shapes (straight or simple tapered sections of wings, tails, and control surfaces) I have made female molds directly, but the key is to skin with a solid so as to avoid finishing the mold surface. I made mine by hotwiring blue foam and bonding a skin inside with a vacuum bag.

Alan Shaw presented the same method during a forum at Sun 'n Fun in 1998 or 1999, so it was nice to see someone else validate my method. His company, Dynamic Wing, made wings, canards, and other large components for Velocity aircraft, so he has a little credibility.

I used plywood templates of the desired female mold sections including a horizontal shelf around the entire periphery of the tool. For wing skin molds, there were three sections that then had to be aligned and bonded together. A fiberglass tape was then applied wet around the periphery and sealed with wet micro for application of mastic and sealing.

I used coated roof flashing to skin my molds. Alan Shaw stated that he used Formica type plastic laminate. Either way, the skin is pretty stiff, has continuity of curve for following a smooth curved shape, and really only wants to follow a simple curvature. It makes for a pretty nice looking mold in little time.

Roof flashing is available from construction supply firms by the roll. Mine was 36" wide and coated on both sides in white. I sanded the back side prior to bonding for adhesion. For bonding, I used a toothed spatula to spread a uniform layer of wet micro on the mold, and vacuum bagged the skin to the mold. I did not piece the skins because that will produce a groove and interrupts the continuity of the curves that this method gives.

They took about 10 hours of total effort to make each one (once you have your templates) and worked well, but there is no fixing them if they are flawed. Best to start over again. Precision in jigging is important. I have eight molds in my shop with beautiful skins resting in them.

Billski
 

orion

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Good points. Personally, I had only two successes with female direct tools which, as both of you alluded to, were wing skins. The first was for a project many years ago where I made an enclosed box for rigidity (2 x 4s with 3/8" ACX ply), on top of which I mounted a series of rib patterns, which were also enclosed on the sides. The skin surface was formed of .050" thick 6061-T6 aluminum, which was bonded and screwed to the wood formers. The thick aluminum was used because it formed a very smooth surface with no distortions.

The second success was similar except here we made a 22' long mold of welded aluminum, which we used to form the graphite component (2.75" thick at the thickest point) of the hydrofoil wing. Despite the 265 deg. cure required for the graphite, the tool proved very stable - the part came in within .050" over the 22' span.
 

AVI

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Female Plug/Jig

In my initial post I should have stated that my curiosity was peaked when I discovered a method of construction that promises simplicity and a smooth outer surface that requires less finishing than the Rutan moldless while surfing the web.

The first site is Kelsall Marine, a designer of Catamarans. Their KSS or Kelsall Swiftbuild Sandwich promises extreme simplicity. The initial sandwich construction is made on a smooth-surface table where the core and ply are vacuum formed. Then the sandwich is shaped in a jig.

http://www.fortunecity.com/marina/fishing/917/kss1/2WhatisKss.htm

The second site is a Vision site, Shafer's Vision construction using Steve Rahm's "Fold-A-Plane" method of construction which is very similar to the Kelsall method.

http:www.shaferintl.com/Vision/fuse

The third site is Mark Langford's KR 2 site, a wealth of information. Here, Mark forms wing skins by sanding foam to shape in a jig.

http://home.hiwaay.net~langford/owings.htm

So, why not combine these methods and use a simple female mold/jig to shape the sandwich and vacuum form the inner ply? The fuselage "boat" could be formed in two halves, and the turtle deck in a third mold/jig, or the fuselage in two halves, right down the center. I'm talking about a relatively simple design with few compound curves, much like a regular metal fuselage.
 

orion

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For a simple one-off, either process is applicable. Keep in mind though that this only works with very simple surfaces that curve only in one direction. Compound curves are virtually impossible.

And of course that brings up the next question: If you're only doing simple surfaces, why not consider aluminum? Don't get me wrong, I'm a fan of composites but if working with that material, presonally I'd prefer to go a bit further and design a more optimal and/or pleasing shape. Seems to me to still be an extensive process for making just simple flat-wrapped shapes - despite what the pictures present, this is still quite a bit of work.
 
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jumpinjan

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Orion is correct on simple flat shapes only. On the compound, one-off shell, I would suggest making the fuselage like a soapbox derby car body. Look at this building guide:
http://ctl.ncsc.dni.us/derbtech/Construction_Manual.pdf
Look on page 29, and there is a keel that holds plywood body formers. The body is a sandwich (very ridged) of sugar pine (I used cedar) or white pine 1/4" thick x 1" wide strips, with a coat of glass cloth & epoxy on the outside (and a coat on the inside, once the shell is removed). The strips provide a natural lofting to make the shape true without adverse waves between the formers (something impossible with free standing foam sheets). The result is very light ridged structure without a mold (and plug to make).
Jan
This is a method that I want to try to build a WWI German, Roland fighter replica.
 
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AVI

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Bead & Cove

Jumpinjan, thanks for the soapbox derby manual. It's very much like model airplane construction with balsa planking.

Why don't you check out:

http://www.cyberstreet.com/andre ?

This is Andre Bilodeau's website which advertises his book, "Building Your Hull with the Bead & Cove System Using Core Cell Foam". This is probably the way you might want to go.

I had considered the use of roof flashing and Formica as mentioned by PTAirco and wsimso1 but wondered about filling in the seams if multiple pieces of Formica or flashing are used. The boat builders cut "darts" in the skin to better shape it around areas of compound curves. Why couldn't the Formica or flashing be formed by cutting darts to allow it to follow the shape of the jig/mold provided the compound shape were not overly severe? If this is done, what's the best way to fill the grooves to create a smooth skin?

Orion, aluminum, of course, is an alternate choice for construction material, but after so many years of research, I'm loathe to start all over with additional research. There's also additional metal working equipment to consider as well. Think I'll stick to composites.

My personal belief is that creating curves and wasp-waisted fuselage shapes simply because the use of composites allows the freedom of expression does not necessarily produce a pleasing fuselage shape.
There are some downright ugly composite airframes flying around. On the other hand, there are also some beautiful aluminum airplanes. No fancy compound curves, but still lots of good looks.

It's often been stated that if an airplane looks good, it usually performs well. Take the Spitfire and Mustang for example.

Now, getting back to the subject, it seems possible to create a pleasing fuselage shape using simple female molds, especially if the fuselage is broken down into three or four separate longitudinal molds, two for the port and starboard portions of the boat and either on or two molds for the turtle deck, as long as compound curves are gentle in nature. I'm convinced that it can be done by shaping foam and either glassing it under vacuum or skinning it with a hard surface, flashing or formica.

The Canard guys are doing this in female jigs rather than molds but I'm searching for a method that also provides the benefit of the smooth surface that the female mold provides.

Guess I was looking for a shortcut but maybe it is better to build a buck and pull female molds after all. When you come down to it, the only extra step is in pulling the molds off the male plug. There is no disputing that it's easier to create a perfect plug by building a male buck than trying to shape a female one.

One additional benefit is that after a male plug is completed, it's easy to visualize the finished fuselage. Thanks for the help, guys.
 

orion

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The bead/cove material from ATC is great - I've used in on two customer projects now, as well as on a 17' graphite rowboat I built for my wife. I ordered a whole shipping case of the stuff and even though I did three rather sizeable projects out of it, I still have a whole bunch of it up on a shelf.

The customer projects were plugs which were used to produce molds. The rowboat initially started as a one-off that I was going to pull off and glass on the inside however, after all that work I decided just to go ahead and pull off a mold.

The bead/cove material is great at forming even relatively complex shapes. There are really only two drawbacks - one is that the formers supporting the structure have to be relatively close together so as to allow the foam to form the curve but do so without forming any "flats" between the frames. That results in a bit of extra work in lofting and cutting out the bulkheads.

The second drawback is that it's not all that cheap, although given the time it saves in forming the basic shape, the higher cost might be justifiable.
 

wsimpso1

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Farrier designed sailboats are built by forming foam and glassing it. http://www.f-boat.com/. There is a guy in the Netherlands who went all of the way to vacuum infusion. Here is his site http://www.fram.nl/

It is possible to build using vacuum and foam, without plugs and molds. My tail and control surfaces are all built of hotwired foam and vacuum bagging directly. My fuselage parts are made on a male mold with vacuum bagging.

But this is not pulling a female mold directly, which is where you started... In the end, you are really only limited by your imagination.

Billski
 

AVI

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Orion, when you say that the formers had to be placed "relatively close together" when using the bead & cove method, what kind of distance are you talking about? Five inches, a foot, etc.?

Thanks, wsimpso1, the Farrier website and the Dutch one with vacuum infusion are both extremely interesting. I did note that the Dutchman used a great deal of filler in the finish of the hulls so it appears that much elbow grease is required in the final finish. The Farrier method is almost identical to the method used in Steve's Vision aircraft. Doesn't appear that we're the only ones surfing sailboat/catamaran websites.

Tony's used vacuum infusion in the construction of his Corsair82 but he has not updated his site for over a year - maybe he's too busy working on the other project he started. Tony, are you reading this? How about an update?

BTW, wsimpso1, do you have a website or can you post photos of your project?

One of my favorite sites is the HP -24 sailplane website:

http://www.hpaircraft.com

It's a wonderful place to gain an education in composite construction, with tremendous detail of the process from the construction of the plug through the fabrication of molds to forming the fuselage shell and wing skins.
 

orion

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Relatively flat sections or section with a minor amount of compound curving were able to have the bulkheads spaced at 18 to 24 inches. In areas where a significant shape change was occuring over a finite distance, the frames had to be placed at about 6 to 10 inches. For the latter though it is very important to have a very accurate loft since any inaccuracy in the loft will make the cross sections inaccurate also, which will leave you with quite a bit of filling and fairing. That becomes a real pain on a concave compound surface.
 

wsimpso1

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Sorry, no website, not even any digital pictures yet. I suppose that I should start. The wife offered to digitize my construction album, and then i could set up a site, log, etc. I am really out at the unsophisticated end of this process.

The guy behind Corsair 82 (Tony Pileggi) actually gave a forum with a demo of his vacuum infusion process at AirVenture. There is a thread on the topic that Tony participated in. It is currently the next one down in the Composites forum.

https://www.homebuiltairplanes.com/forums/showthread.php?threadid=2357

Billski
 

Bart

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For wing skins and similar basically two dimensional skins, look into Alex Strojnik's method as reported in his Laminar Lightplane books. He laid up fiberglass on smooth flat plexiglass, to impart such smoothness to the layup. After the resin started to set but before it had completely hardened (~45 minutes of cure), he peeled it off the plexiglass table, then draped it over the foam wing core, then held it down to shape with vacuum. Got laminar flow. Works. Cheap and easy. Vastly better than Rutan method, which winds up using too much of everything, then sanding to smooth, often with consequence of sanding into the fiberglass, which weakens it.
 
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