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:
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.