ArmedZagi

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Hey all,

I'm thinking about trying a build from mostly fiberglass. The subject is an old Nazi design that never made it into the air. Span, 80" Length 86" 50cc
[link=http://www.luft46.com/henschel/hsp75big.gif]4 view (link)[/link]

Correct me if any of what I say sounds like a bad idea, but heres what I was planning... First, carve down pieces of foam into the shape of the airframe, cover the foam with spackling and sand smooth. wrap the styrofoam forms in saran wrap and lay the wetted out fiberglass over 1/2 the form. Then after its cured, do the same for the other 1/2 of the form. After both are cured, I'll glue a very minimal balsa and ply structure inside the forms. Then join the halves together. The pics should explain it a little better. To vacuum bag the parts I plan to build a box with a pegboard top and hook a Shop Vac up to it... Something like an air hockey table in reverse.

Ok, questions, what weights of cloth and how many layers of each should I use? Will a Shop-Vac be strong enough to vacuum bag? Or should I forget about bagging the parts? And it theres anything thats sounds wrong please let me know.

Thanks

dreadnaut

My Feedback: (5)

Carve the thing out of polyurethane foam. This is not the white stuff used for wing cores. It is the grey stuff used as the base for flower arraqingements. It is not good for flying modes, but is a lot easier to carve.

Get the shape right, then glass it with a couple of layers of 4-6 oz cloth. Polyester resin is OK. It will melt the white foam, but does not attack polyurethane. Use Bondo to patch irregularities. Paint it with catalysed automotive primer paint and wet sand until it is SMOOTH. Give it a finish coat of automotive paint, polish and wax it. The make a mold.

This is the tutorial I used for my first mold;

http://www.cstsales.com/fiberglass_mold.html

I suggest you start small, like wheel pants or a cowl. Something as large as you propose is a potential bummer if you get is wrong. It is a lot les painful if you have to redo a small part.

The way you suggest doing it will make it very difficult, if not imposible, to get a good finish that is also light. With a mold, you can make lighter partS (plural)

ArmedZagi

My Feedback: (1)

I priced the florist foam when I first started thinking about this. Way out of my range. White foam however, I can get for free. I know white foam is harder to carve.. I've done it before for small things using knives heated over a candle.

For something this large I was planning on building something like a small hand held hotwire cutter and carve the rough shape from it. Then clean it up with a heated knife before spackling.

Epoxy wont attack white foam will it?

dreadnaut

My Feedback: (5)

Epoxy will not eat the white foam. Get good stuff, like the West System. It seems a little pricey, but compare the price per ounce of West System to the 30-45 minute stuff you get at the LHS, you will find them comparable. It seems expensive because it comes in quart and gallon sizes. For what you plan to do, the 30-45 minute stuff is not realy appropriate, and a plug and mold that size will take over a half gallon.

Be careful when working with WS, or other Aircraft grade epoxies. The fumes are not very noxious (bad smelling), but you should still work with resperatory protection, and gloves. Also mix small batches at a time, one or two ounces. Large volumes in containers with too small a surface area to dissapate the heat of reaction can get real hot. Hot enough to melt the mixing cup. I know this from experience. I have heard that it can actualy burst into flames, but have not seen this.

ArmedZagi

My Feedback: (1)

I've melted a solo cup with too much epoxy before...but an fire sounds like one for the Mythbusters to test

smoothy840

Dont carve! to get a good shape use a hot wire (a shorted wire with dc power) it will give you a good even shape but be carefull the wrong type of fome will make toxic fumes and kill you [sm=what_smile.gif] then smoth starting with 250 grit sande paper working your way up to 400 grit. after that you can use a kevlar carbin mix to cover it 2-3 ply on fus. and 5-6 ply on wings. Then smooth with a thin coat if micro ballons sand to smooth with 400-1000 grite paper. Acitone will eat most fomes so you can fill with acitone to make it holow. hope this helps.

TeamSeacats

I believe the "florist" foam is a PVC foam - not polyurethane. Still, though, it carves just great.

ByLoudDesign

How is it to glass, the "Green" stuff!

dreadnaut

My Feedback: (5)

Green (sometimes pink and gray) foam is not reactive with polyester resin. If using white foam you will neet to use Epoxy. This stuff is used a lot by sculpture artists because thay can sculpt it then spray it with a ''chopper gun''. This is a tool that spray a stream of polyester resin with chopped glass fibers entrained in the flow. Too heavy for RC work.

Flower shop foam is MUCH easier to carve than trying to get a good shape witha hot wire on white foam. If the carbon/kevlar he is talking about is the stuff I am thinking about, it is 5oz/yd, so he sugesting a 15-30oz/yd layup! WOW. Bullet proof, but not light. (That stuff is about 6-8 times the cost of fiberglass too.)

2 meter pattern planes are usualy 6oz/yd total layup. The high end stuff uses two 1-2/oz layups over a foam or Nomex honeycomb core. l would suggesst the extra work of a female mold, and a 6-8oz/yd layup for this project. The lighter the layup, the more internal structure (bulkheads and stringers) you will need. If you are going to go with composite wings, they should br done with the foam core method.

This is a VERY ambitious project for a first timer. Like I said before, consider starting small, and working your way up. My first FG part was a cowl that I used the ''lost foam'' method for. Never did it again. Female molds are the way to go.

wc524

I'm encouraged to see someone else trying to scratch build a composite plane. I'm currently working on a composite Yak 54 Design pictured below. It's been two months in the making and it has taken a lot longer due to other projects in the way. I am going to use 6oz glass and carbon reinforcement for strength. It should be done before next spring. Ha Ha.

TeamSeacats

I profess to not know much about composite r/c planes, but 6oz glass is pretty heavy for what you are doing there. (6oz is roughly the "bondo" brand glass you can find at walmart). I think you would be much better off with a 3 or 3.5oz fabric.

dreadnaut

My Feedback: (5)

6 oz layup is pretty typical for a .60 sized sport airplane, though it is usualy not a single layer of 6 oz cloth. For laying up in a female mold, a layer of .5 oz is layed in first to reduse the unsightly print through of the weave. High performance pattern planes often use a sandwich of .5 oz - structural foam - and 2 oz fabric. This is a time consuming and expensive process, and involves vacuum bagging.

I have had good results laying up 1/3 scale Extra wheel pants using 3.2 oz ''harness'' weave s-glass. This stuff has a higher thread count than the e-glass used in most applications. Because of this it requres less resin to completely wet out, and is therefore lighter. I use 1'' squares of 5 oz carbon fiber for the hard points where the axle goes, and some CF tow to re-enforce the wheel opening.

smoothy840

I was thinking about wings when i said to use a hot wire. I like a hevy layup do to the tipes of feilds i fly at and it can take punishment well. also i save on wight do to the fact i dont have internel strucsher. the skin is the strucsher.