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Lost Foam Fuselages - Jart fiberglass fuselage build thread

thenated0g

Drinker of coffee, Maker of things
Mentor
#1
In researching vacuum bagging a Jart slope soarer i came across a lot of people doing a lost foam fuselage, as the designer of the jart does this in his original build.

What is lost foam? It is exactly what it sounds like. You "lose" the foam in some way. If you search youtube for lost foam you will get a lot of metal casting videos in your search. This is where you make a perfect example of the object you want. It could be wax or foam. Anything that will melt and burn away quickly when you pour metal into it. The material melts and the metal fills in that cavity perfectly matching the original shape you put in. So in a lost foam fuselage you are doing basically the same thing. You are creating the shape you want out of a material that you can easily remove later.

In the case of a fuselage though you do not need to fill the entire shape. You just use the foam to hold your laminates in place until the glue dries. Than you use something like acetone to eat away all the foam and leave you with a nice empty space for electronics.

Most people make these lost foam fuselages out of several layers of fiberglass with some support materials inside if desired. Such as carbon fiber, kevlar, or even s-gass. These flat cloths are used similar to the spars we would put in our wings, just think of them as sliced open and laid flat rods.

Here is a great video on the differences of materials:


Based off my research at the moment i am going to be using S-glass with some 24k carbon tow in stress areas. Nose to tail and in the vertical stabilizer for example.
In talking to knowledgeable guys over in rcgroups it seems a good starting point on a layup for the JART is going to be 12-20oz of cloth. By that i mean total layers equalling 12-20oz. So if you have 4oz cloth, than 3 layers is 12oz. Or 4x layers of 5oz cloth for 20oz total. Now that recommendation was for E-glass which is the standard fiberglass. S-glass is like 20% stronger so you don't need as much. Now this 12-20oz is specific to the JART as it doesnt mind being "heavy". That just makes it go faster.

The basic steps as i understand it at the moment:
  • Shape foam
  • Wrap entire foam plug in packing tape. **This seals the foam from the epoxy and easily pulls out later.
  • Wax packing tape or use some other release agent like pva
  • Use spray adhesive lightly on fiberglass and carbon to keep threads together and temp hold on foam
  • Apply first layer of fiberglass and wet with epoxy
  • Apply reinforcements if needed and wet with epoxy
  • Apply next layer of fiberglass and wet with epoxy
  • Repeat previous until weight achieved.
  • Optional: Wrap fuselage in tape or vacuum bag to achieve a nicer surface and save some time on sanding
  • After curing:
  • Epoxy in wood blocks for hold downs screw points and cutout wing saddles and tail feather hard points.
  • Sand, fill, sand, fill, sand
  • Paint as desired.
 

PsyBorg

Wake up! Time to fly!
#4
Hrmmmm...

I wonder if that carbon tow would work well with the white gorilla wood glue for non fiberglassed foamie repairs.
 

thenated0g

Drinker of coffee, Maker of things
Mentor
#5
I know some people apply it with ca glue. I have also seen a guy do an entire fuselage fiberglass job with gorilla glue instead of epoxy.
 

thenated0g

Drinker of coffee, Maker of things
Mentor
#6
Got some pink foam ready for the hot wire. Then, lots of sanding and shaping.
The aluminum templates get the wire bow and the paper template will be done on my scroll saw with hot wire blade.
IMG_20181009_063139.jpg IMG_20181009_063149.jpg
 

thenated0g

Drinker of coffee, Maker of things
Mentor
#7
IMG_20181002_181949.jpg
Here's a picture of my scroll saw. I removed the blade took little pieces of control rod and wrapped fishing wire around it and then use the tension spring in the back to make it tight.
 

thenated0g

Drinker of coffee, Maker of things
Mentor
#9
Ohh... I like that scroll saw idea. Enjoying the progress on this!
Thanks man! I have appreciated watching your builds and videos over the years. They are definitely some of the building blocks that eventually gave me confidence to start moving to more advanced build techniques.
 

Fluburtur

Cardboard Boy
#10
Lost foam is a technique that I would clearly want to try, by chance I have many projects that would suit it and and I have the materials needed so maybe one day when im done with my other stuff. I will clearly follow where this is going!
 

thenated0g

Drinker of coffee, Maker of things
Mentor
#12
Recieved my 24k carbon tow yesterday and had a person on facebook share the following picture with me of a Jart fuselage pre painting. Nice example of the tow in place to fight the different stress's it would receive in flight.

1539277084647.png


Also somewhat related is this nice video a guys shared in the composites section of rcgroups. Mold making is another way to create a fuselage and i will be trying that at some point as well:
 

thenated0g

Drinker of coffee, Maker of things
Mentor
#13
Epoxy and S-glass acquired. Now i just need to figure out the best way to cut it out. One large piece draped over the top? 4 profile pieces with overlaps?

IMG_20181015_194532.jpg IMG_20181015_194549.jpg
 

wilmracer

I build things that fly (sometimes)
Mentor
#15
Epoxy and S-glass acquired. Now i just need to figure out the best way to cut it out. One large piece draped over the top? 4 profile pieces with overlaps?
What is the weight of the glass again? And how many layers are you planning? I like the idea of pieces with overlaps and depending on weight multiple layers with the bias in the ply in running at 45* to each other with the CF tow between the layers.
 

thenated0g

Drinker of coffee, Maker of things
Mentor
#16
I have some 6oz S-2 Volan glass and some carbon tow. Im going to do it in two pieces, one side than the other, with an overlap on the top and bottom.

My plan right now is to do one layer, add tow, do a second layer (2x 6oz layers). Wait for that to harden and see how stiff it feels just so i know. From what guys have been telling me in the composites section on rcgroups i will probably want 3 layers with maybe a 4th in the nose/wing area.
 

thenated0g

Drinker of coffee, Maker of things
Mentor
#18
Fuselage was shaped last night. Sanded it down with around a 400 grit paper and than filled in the major low spots with spackle. I didnt worry about getting a perfect surface as the entire fuselage will be covered in packing tape. Just some light sanding and it should be ready for tape.
IMG_20181023_202353.jpg


After wrapping the entire thing in tape i will do a couple coats of Wax and than a couple coats of pva. This will give a physical and chemical barrier between the tape and the epoxy and "should" allow it to come out easily.
1540397971516.png
1540397951774.png
 

thenated0g

Drinker of coffee, Maker of things
Mentor
#19
Last night i finished sanding down the spackle and applied clear packing tape to the entire fuselage. Having wrapped several planes in iron on laminate it wasn't too difficult, just takes about 20 minutes.
IMG_20181024_200202.jpg
 

thenated0g

Drinker of coffee, Maker of things
Mentor
#20
Also, if you wanted to leave the foam in, this would increase the strength and you could get away with less fiberglass. The foam weighed 78 grams before tape. But the epoxy would soak into the foam so its not a straight 78 increase to leave the foam in.