JohnW

My Feedback: (6)

This isn't anything all that spectacular, but it is my first composite project of any size. Up to now my largest project was a rocket powered flying wing which was a one piece composite wing/lifting body about 3' in span. But mainly I have only made canopies, cowls, landing gear, stuff like that. So I'm not totally green, but I still consider myself a novice on this stuff. So I'm looking for any tips, suggestions, etc. anyone might have as I progress.

This is a 2M pattern fuse of my own design. It is loosely based on a blend between a PL Prod Excellence, PL Prod Smaragd, and Oxai Pinnacle. Designed in Autodesk AutoCAD 2004. Fuse without canopy and chin cowl is shown.

I printed out formers at certain stations on a large format laser printer. I then spray tacked these to 1/4" aircraft ply. These were cut out to shape. Holes drilled in the formers to accept 1/2" conduit. Formers were then assembled on the conduit, squared and aligned, and bonded to the conduit with CA. Nose ring was bonded at a 2.5 degree right thrust offset.

I decided on the conduit as opposed to other tubes because it is only $1.79 for a 10 foot stick. It isn't exactly the straightest stuff on earth, but I managed to find a few good sticks at Home Depot (I think the help thought I was nuts as I was checking dozens of tubes to find the really straight ones.) To help ensure I didn't get a twist, I made guides that I bolted to my building table to force all five tubes parallel to each other when bonding the formers.

Formers are cut 1/4" undersize. I plan on sheeting this skeleton with 1/4" balsa, then glass, prime and sand, hence my plug.

Others that have made plugs this way, look OK so far? Thanks in advance. -John

Magne

Hello John.
Yes, making a fuselage plug the way you describe it is quite feasible.
I only made the front part of my plug with planked formers, the rear part was made with sections of hot wire cut foam blocks sheeted with balsa. (In principle the same method as you use to make foam wings. Most of my plug was made in two halves, i.e. left and right hand side, and glued together before glassing. The whole plug was glassed with one layer 6 oz cloth and one layer of 2 oz cloth, applied to one side at the time, overlapping at the top and bottom.
I have enclosed a few pictures of my process.

Regards,
Magne

tschmidt

My Feedback: (1)

Hey John,

Your project is looking good! Have any updated pics? Keep us posted on your progress.

Todd Schmidt

TT2

My Feedback: (13)

Very nice work guys!

I like to use polystyrene foam sheets (trimmed to EXACTLY 1 3/8" thick) then use the 3D CAD model to create 'slices' every 1 1/2". I plot the section of the slices, 3M77 them to 1/8" lite ply then cut to size. I use copper pipe or conduit for alignment (usually 2 pipes minimum so I can keep everything straight) much like JohnW did. I cut the foam sheets slightly oversize (at the 'large' end) then I sandwich the lite ply and foam sheets together through the pipes using 3M77 to hold everything together. I throw this into the vacuum bag for a few minutes so that everything sticks together well. I sand the foam down until I hit lite ply, then fill any mistakes, sand, then glass with 3 layers of 3.2 oz crowsfoot cloth. After curing it's prime, final sand, polish, mold release, DONE! I wish it went as fast as it sounds!

IMO this method is pretty fast and you end up with a rigid (well, rigid enough) plug.

-Tom

JohnW

My Feedback: (6)

OK, I have the fuse (less canopy and chin cowl) 95% sheeted. Just have a bit by the spinner area to finish. My building room is a total balsa dust disaster at the moment, but I’ll get a new pic up this week sometime.

Following is what I have learned and will pass on. The method of plug building I selected seems to create a very ridged and accurate plug, which I am pleased with. Attaching the sheeting wasn’t too terribly difficult for the most part. I used poly glue in the sheeting seams and the sheeting is attached to formers with CA. There is basically no sheeting flexing between the formers as everything is bonded as one unit. Simple curves were fairly easy to cope with, such as the belly pan and turtle deck areas. However, the compound curves around the nose area and a bit on the tail have caused me to lose sleep. They will come out OK after sanding, but I don’t think I will do a plug of this type this way again. I fear the canopy and turtle deck will be even worse as they are basically 100% compound curves.

I like TT2 and Magne’s ideas. I have made glassed foam plugs before, but never with the lite-ply formers as guides. In the past, I have run into alignment issues and I have damaged the foam shape in handling. Even after glassing I’ve had the foam plugs deform. I saw this ply/balsa method on some web page for a giant SU-27? I think. I figured with the problems I’ve had dealing with foam plug, I’d try the ply/balsa method. Hind sight, If I had it to do all again, I think I’d try the lite ply formers and internal tubes mentioned by TT2. Would there be any benefit in sheeting a foam/lit-ply plug with 1/16 balsa like what Magne did? I.E., to help stiffen and/or produce a better surface for glassing?

It’s too late now for me to switch gears on the fuse part of the plug. But I may try the foam/former method for the canopy and chin cowl. I already have the formers cut and I have some high density building (pink) poly-styrene foam laying around.

Cheers.

TT2

My Feedback: (13)

Check [link=http://www.rcuniverse.com/forum/m_2830021/anchors_2910460/mpage_1/key_/anchor/tm.htm#2910460]THIS[/link] thread out. It contains details of the cowling plug construction for the fiber-lite 30% Edge 540. Some deviations from what I preached then to what I practice now:

1. I don't use aluminum templates between the layers of foam. The thermal expansion properties seem to be nowhere near foam, glass, or plywood. This creates a 'ghosting' effect...not noticeable on the final parts, but it will drive you insane when you see it on your finished plug. The slight (0.00005" or so) 'dip' that is created by the aluminum contracting is visible. You can sand it out, then it appears again. I'm pretty sure it's caused by the delta in the thermal expansion but I'm not 100% sure. Use lite ply...or even better (I JUST thought of this!!!) use 1/32" aircraft ply for the templates. The 1/32" aircraft ply cuts GREAT with scissors and would still serve as a decent sanding guide.

2. The 8.9 oz satin weave FG has fallen out of favor with me. The weave is very tight and does not release air very well. I use 3 layers of 3.2 crowsfoot cloth in it's place. Still a tight weave (no pinholes), but unbeatable conformability and great air release.

3. I tend to use wipe-on liquid mold releases (Frekote, Chemlease, Zyvax) instead of wax and the dreaded PVA. It took me years and $$$ in different sprayguns to get my PVA spraying technique down...what a waste. I don't use any 'sacrificial' releases now unless I absolutely have to.

-Tom

TT2

My Feedback: (13)

Possibly...depends on the situation. IMO, foam sands easier than balsa, and I can lay down glass over a 'difficult' surface much easier than balsa. If you need more surface strenght, just add more glass.

-Tom

JohnW

My Feedback: (6)

I must be doing something wrong when I'm working on foam without sheeting. I have made plugs without sheeting, i.e. just glassed foam, but I seem to fight them. My main problem is that they seem to deform too easily. I was hoping the balsa sheeting method I'm using now, while possibly more time consuming, would ultimately work better for me. I do want to try the former/foam/tube method on my next plug. Maybe all I need is a bit more experience to get the hang of plug making from foam.

Anyway, here is a pic of my progress to date. The fuse, less canopy and chin cowl, is sheeted. I splattered some spray paint on the whole thing as a sanding depth guide. First sanding is mostly done, less some areas around the nose. If this doesn't work out, I can always use this plug as a bongo. When you give it a thunk, it rings with a really nice tone.

Cheers

tschmidt

My Feedback: (1)

Looking good John,

How wide is the widest part of the nose?

Just a suggestion on foam. The best foam I've found for making plugs is polyurathane foam. Its rigid, doesn't dent easy and sands like real soft balsa. When making my plugs, I make formers out of 1/8" balsa, fill in between with foam and shape. On my canopy and chin plug, inorder to get a good fit to the main fuselage, I ironed monocoat on the main fuse plug in the canopy and chin area, waxed and PVA it, then layed a couple of layers of 7.5oz cloth down. When that dries, trim the glass base to fuselage then glue formers and center crutch on that. Fill in the structure with foam and shape it down while on the main fuselage. After its shaped you can pop it off and it will fit perfect. The monocoat will give somewhat of a gap to leave room for painting.

Todd

JohnW

My Feedback: (6)

Todd, 7.9" wide at the nose. The trailing edge of the cheek vents stick out a smidge more, about 8.25" wide at the cheek vents. Still wide, but this is over 2" more narrow than the fat pig I'm flying now. Pic looks pretty blocky in the nose, but I plan on sanding that out. The nose is basically an Excellence nose, but more narrow and a bit more sweep on the cheeks.

Do you cast your poly foam, or do you have a source for blocks? What densisty do you suggest?

tschmidt

My Feedback: (1)

John,

You can get the foam at www.fibreglast.com in sheets or mix it yourself. I buy the 24"x48"x2" sheets.
Sorry, I can't tell you the density of it, but it has served my purpose well.

Good Luck and keep us posted!

Todd

miniCAP

My Feedback: (3)

John,

How's the plug coming? Flying taking up all your time? I'm just really excited to see how this thing turns out, I know you do great work!

JohnW

My Feedback: (6)

Made some more progress in the last several weeks.

In the last photo, I had the entire frame sheeted. I've done a lot since then. I trued the plug with t-bar sanders loaded with 80 grit and a lot of bondo. I kept sanding until guide coats indicated no more low spots, etc. I used about 2/3 gallon of bondo and 15 sheets of sandpaper in that process.

I then glassed the plug with 8oz plain weave glass. Epoxy was post cured at 150F for 4 hours. Weave was filled with Evercoat Easy sand (polyester filler) and wet sanded with 120 grit until my guide coats indicated everything was true.

There were a lot of fiddly bits in the above process, everything from symmetrical verification to getting hard 90 degree corners where required. Lots of apply more filler, sand and repeat about a zillion times.

I primed 4 coats with PPG Omni 282 high build urethane primer. This was wet sanded with 180 grit on t-bars until the guide coat was gone.

For the final finish, I shot 6 coats of PPG Deltron 3057 over reduced for better laydown, and 10 coats on outside corners. Then I wet sanded starting at 320, then 400, 600, 1000 and 1500 grit. Then buffed with polishing compound.

Still have a few minor issues to attend too before I can wax, such as rudder exit guides and I want to mark reference dimples for wing tubes, adjustors, etc., but basically the plug is 99% done.

miniCAP

My Feedback: (3)

John,

Dude that thing looks sweeeeeet! You do very nice work, I must say. How much does the plug weigh? I bet it's pertty heavy. So, I'm still on the first production recipient list right

JohnW

My Feedback: (6)

Alex, thanks for the complements, but are you sure you want to be the first one? I don't even know if it will fly yet. OK, it will fly fine as I didn't reinvent the wheel, very standard pattern moments, etc. It is almost a copy of my Excellence, but much narrower, a bit taller, and I moved side area forward a bit as you can see in the canopy.

Never weighed the plug, but it is very heavy, maybe 20 lbs. Would make an excellent cat beater.

Finished my new "larger" post cure oven last night. It is 2' by 2' by 8'. Indirect infra-red forced air, 1000 watts. Not sure exactly what it will hit, but as Justin will verify is easily obtains and can hold 170F and will ramp up from 60F to the 170F real quick, like about 5 minutes, so I have power to spare. My guess is it could reach low 200's. But not sure if I want it much hotter than 170F anyway as it is literally 2 feet away from 50 gallons of 30% nitro.

Finished my mold test strips, verified on the samples I'm getting clean releases and polished finish. Hope that carries to the real molds. Will be starting on the molds this week. I should be producing parts in June. I want to have mine airborne by late summer if possible. You'll have to stop by and check it out if you come back for the fun fly.

Later...

troyhm

Hi

I currently have to models that I want to make plugs from, what process did you use for finishing the model ? did you use epoxy or polyetser based resin ? what wieght cloth did you use for the final surface. I already have the tooling gelcoat and the resin for making the mold and the two halves of the wood to hold the model ready to make the two halves . I have made smaller parts before just nothing this big

Thanks

Troy

hoofty

Forgive me for jumping in but this caught my attention.

Just a note on your ramp rate. Check with your resin manufacturer for specifics, but most epoxy and poly resins don't do well with rapid thermal variation. You should try for a 5-6 degree/min ramp up and down. NEVER take a composite part out of the oven until it's temperature is within 20-30 degrees of ambiant air temp. (Think; hot glass touching cold water) A rapid thermal change can crystalise and weaken the resin matrix and the part becomes very brittle, thus producing a weaker part. I know this isn't as critical on a plug but keep it in mind anytime you are curing resin in an oven.


Hoofty


P.S. project looks great.

JohnW

My Feedback: (6)

Hoofty, thanks for the reminder. I wasn't planning on shocking the parts, was just commenting on power. I will ramp up/down the temp at a much more reasonable rate, such as what you suggested. I wasn't aware I had to go as slow as 5F/min, so that is nice to know. Better safe than sorry, eh? My epoxy suggest a very high post cure temp, close to 200F for two hours. I called the reseller and they said 150F at 4 hours is almost as good, so I figured if I split the diff, say 170F at 3 hours, I'd be close to spec and after all, this isn't a people carrying plane, so I have some fudge factor. My initial concern was I wouldn't hit a high temp in the new oven. My previous oven, much smaller, only would reach about 140F. I had to guess "seat of the pants" on how much power I needed on the larger oven to obtain 170F. I think I guessed pretty close. I also took care to be sure the IR is indirect, so no hot spots. Heat exchange is done via forced air that blows thru the IR setup. Any other tips you might have, I'm all ears.

Troy, not sure if you are asking about the plug, the molds, or the final part. First, consider I am very new to parts this large too. I’m using all epoxy resins, with the only exception is polyester resins for filler when I made the plug. I finished the plug with one layer of 8oz glass, then applied urethane automotive primer for the finish. Haven't started the molds, only test samples. What I plan, based on my tests, is wax only for release (8 coats), then a epoxy tooling coat, then one layer of 10oz glass, probably 5 or more layers of heavy glass mat (random fiber), then one layer of 10oz glass to finish. Done this before, worked fine, get a decent mold thickness and stiffness. Not sure yet what I'm going to do for part schedule. Probably prime or paint in the mold, then 3.5oz crows foot with a foam sandwich on the fuse sides. Don't know if that will be stiff enough or not, but should know after the first part.

troyhm

HI

I was more curious about your plug finishing ways. I have two models already to make plugs from at the moment but just need to fiberglass and finish them off.

Thanks

Troy

JohnW

My Feedback: (6)

Troy, the plug was finished with 8oz glass/epoxy. After the glass, minor imperfections were filled with a finishing automotive polyester resin that had the viscosity of warm honey. I used a product called EverCoat Easysand. Might not be available down under, but I'm sure there is an identical product under another name. I wet sanded with 180 grit or maybe 220, can't remember. Cleand the plug really well and then shot 6+ coats of a good automotive urethane primer. I used PPG Deltron 3057 if I remember correctly. I then wet sanded the primer up to 1500 grit, and used two fine cut automotive polishing compounds, the last one being super fine. You'll start to get a shine with the 1500, but haze when looking head on. After the polishing compounds, I had a mirror finish no matter how you look at it. Pics I posted, are after the first polishing compound and before the super fine polishing compound. While this seemed to work for me, I'd still like to throw out the disclaimer that I am fairly new to this, and by no means an expert.

gluedoc

Hoofty, hate to jump on you for this, but you are right for the wrong reason. Thermal shock is a problem in composites because the coefficients of thermal expansion are often very different for the fiber (e.g. glass, carbon, kevlar) and the resin. When you take a part out of a hot (or cold for that matter) environment and expose it to a large thermal shock, you make the fiber and resin want to grow at different rates, which creates large internal stresses and can crack the part.

Here is the caveat. The reason we do this in full size composites processing is more for operator safety (I don't want a part at 350F sitting around the shop).

Yes, epoxies can crystallize, but not after they are cured.

Matt