flianbrian

I'm curious about the f/g fuses especially popular with pattern planes. What weight/style of cloth, how many plies, what resin? (And any other tid bits you may think of).

Thanks
flianbrian

Mike James

The short answer is that you have to make them to suit the purpose, but...

A typical layup for a .60 to 1.20-size pattern fuselage could be made with two layers of fiberglass cloth, say 2 oz. or 4 oz. cloth for the surface, and perhaps 5 oz. or 6 oz. cloth on the inside. Many variations are possible, with combinations of different types and weights of cloth, the use of Kevlar, carbon fiber, Nomex, etc..

We've just had an extensive discussion on this over on the "Design, 3D/CAD" page, which included comments and photos by the designer of the "PTX Vector" pattern plane. It's at http://rcuniverse.com/showthread.php...893&forumid=58

There's also info on my web site, (Click the "www" button, below) including tutorials on how to make plugs and molds, a description of the "J-45" pattern plane I've designed, accurately predicting structural weights, and more. (free, non-commercial site)

The best bet, as with most aspects of fiberglass construction, is to talk to everyone you can, to see what they do, read all the articles and web sites you can, make some small test samples, then go for it!

Good luck.

flianbrian

Mike,
Great stuff to mull over. Thanks. Some of my work involves working with various composite materials, so it occurred to me I might look into this to see if I'n crazy enough to want to try :bananahea

flianbrian

Mike James

flianbrian,

Just do it! It's a lot of fun after the first one.

ptxman

My Feedback: (2)

Composite pattern/aerobatic models have unique & challenging requirements. The layup sequence is usually a compromise of many (& sometimes conflicting) parameters: cost, manual effort, target weight, rigidity, vibration dampening, aesthetic finish, service life, material availability… the list goes on. Basically you have to get in there, try a layup, fly the hell out of it, observe the results & iterate from there. Start by examining successful analogous models but also recognize what works for model A may not be quite right for model B.

Here are some pictures of my PTX Vector (2mx2m F3A model) to get you going as an example. The ordinary all-glass fuse was 3 oz outer + 6 oz inner reinforcement, both cloth layers run continuous through the mold, laminating epoxy used. The removable canopy & belly pan was reduced slightly to a 3 + 4 oz sequence. Removable sections are desirable features for functionality, but they also take big chunks out of the structure. You can reduce them to a point - if they are good fitting, they become part of the structure. If you make them too flimsy, the fuse has to compensate. Belly pans in particular must withstand a lot of heat & usually get cut up to accommodate inlet cooling, exhaust & engine accessories. I used simple CF tow stringers in the aft fuse section because this is a tall slabby section requiring reinforcement for the torsional rigidity. I’m also a big believer in interconnected lightened cross bracing cleverly disguised as servo trays, tank plates hold downs etc.

From the plain-Jane glass layups it basically turns into how much effort & dollars you want to put into the project. The glass models were coming in acceptably within the target weight range (at the time) of 9.50-9.75 lb with component weights: canopy = 66g (2.3 oz), b/pan = 134g (4.7 oz), fuse = 580g (20.4 oz), total = 780g (27.5 oz). Later on, I replaced the 6 oz glass with 4 oz carbon on the fuse resulting in about 15% weight saving & better than expected rigidity. The next step would be cut back on the 3 oz glass & replace it with lighter/different material. Like most things it becomes one of those diminishing return type deals: 40$ worth of carbon fiber buys you 2 oz. Or, a 1000$ paint booth, 30$ of Kevlar, 40$ of carbon + 60$ of bagging consumables buys you 5 oz. Fictional numbers but you get the idea. Fortunately, there are lots of glass styles and weights to choose from. Unfortunately, the same cannot be said about carbon & Kevlar. Try and find a 2 oz plain weave carbon cloth or a 3 oz satin weave Kevlar cloth. They might be perfect for our models but they don’t exist from weavers or at a price you are willing to pay. Happy layups!

ptxman

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plain jane glass layup

ptxman

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glass version with gear install

ptxman

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partial carbon variation

ptxman

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Latest version (my molds, not my layup). Full color scheme painted in the molds thereby allowing RSR (resin sucking rampage).

ptxman

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PS - surface curves & bumps like cheek cowls increase rigidity with low weight penalty & also helps increase drag. Guess that explains why they never caught on with glider guys

teleplayr

OK, I'll bite, what the heck is resin sucking rampage?

-Joe

ptxman

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Sounds sexy doesnt it? All I mean is, by having the presence of a paint coat against the mold, the subsequent cloth layup can be very lean in terms of resin saturation because there is no concern of exposed pinholes. This can be accomplished by aggressive squeegee action, or by vacuum bagging through a perforated film like peel ply and a bleeder. This is desirable for the lowest weight layup without compromising strength. If pull excess resin out with just cloth against the mold, you risk exposed pinholes as an end result since the resin is not contained between the cloth strands.

js3

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ptxman,

I've been thinking of starting a new thread for this topic but since it has been mentioned here, I'll take this opportunity...

When painting inside the mold, what precisely is your procedure? Specifically, do you shoot a clear coat in the mold first, then mask and add color/trim, then add the layup or do you apply only the color coats inside the mold before the layup and clear coat the piece after it is 'born'? What about joining seams? What is the procedure for dressing the seams when the part is prepainted in the mold.

My next question is about plugs. What is the best (adequate) surface preparation before the layup of the mold? What will produce that glass-smooth surface?

Fascinating stuff. Good forum and great topics!

JS3

ptxman

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I can’t speak for this particular paint-in-mold job because it was done by Harold Sattler of H&M Racing for the individual who purchased my PTX Vector molds. Harold does this work full time making world class Q40 & FAI pylon racing models of his own design. They also have pre-painted, vacuum bagged composite shell (coreless) wings. Check out his website at http://www.superminnow.com/hmracing/racing/about.html

I can tell you a few things from my own related experience, but I leave the finer details of pre-painting to those who do it a lot & who’s results ‘do the talking’. The most important trick is the releasing agent itself. Without the right system, it is very difficult to obtain good results, trust me on that. We desire 2 properties that normally oppose each other in most releasing agents: we want to lay down a thin coat of paint without it beading away until cured & then we want the release agent to readily let go of the whole layup when we part the molds. You can blow a lot of $ and time pursuing what doesn’t work, or.. I understand Harold is now selling his releasing wax in modelers quantities. Trying to mimic the techniques used by boat-builders & others with variations of gel results in shiny but heavier parts. That application relies on the thicker gel viscosity, thicker spray application & faster cure time to hang on the surface to get these results. That might be Ok for a boat, unacceptable for a competition model.

The subsequent cloth layup process is pretty much the same in both cases although the presence of pre-paint allows more options in terms of tuning the cloth weights & lean resin concentrations because there is no concern for pinholes.

The seaming operation is pretty much the same, usually the overlap or tape method. Remember the paint is sprayed in both the mold cavity and on the parting flange, so when the molds are parted, a small paint flashing will exist which is gently removed. A crisp, aesthetically pleasing, near-zero seaming line is basically a function of very accurate mold edges & skill.

Re: plugs, on mine I chose a shell coating of laminating epoxy, followed by catalysed auto primer & paint. I then use polishing compounds. This procedure is where the real work is if you are trying to achieve a perfect surface finish. The resulting plug has to be dimensionally stable.

winship

For ptxman;

I noticed the carbon tow formers placed in your fuselage for rigidity. Do they eventually print through the sides of your fiberglass fuselage after time?

Dan Winship

ptxman

My Feedback: (2)

Over a couple years maybe. It guess its not much different than other internal formers like a firewall or servo tray on edge against the fuse lamination. What helps is the CF tow bands dont see direct force applied to them & they are comprised of more alike materials to the fuse itself. Personally Ive found dark paint schemes + hot sun = accelerated print through of most composites over time, even the finer cloth weave.