I’m working on my first build and I’ve but off quite a lot. It’s a scratch build and I’m having trouble designing the fuselage. How do you shape round parts that taper? How do you calculate the radius for a cone that doesn’t come to a point when you’re cutting it out of foam board? Thanks in advance
Help! First scratch build.
- Thread starter Tophat
- Start date
mastermalpass
Master member
The only curved fuselages I have built were pretty cylindrical. Making it quite easy to wrap pieces of foam around circular formers then pinch the end of the fuselage around the vertical stab.
For forming them into a cone, there are two ways: cuts go down the fuselage longitudinally, so the flat piece ends with a set of triangles. This is easiest to do with prism fuselages that have hexagonal or octagonal cross sections. I have tried to bend the pieces of a fuselage to make the finished piece more round, but it's hard to get a piece foam to bend along the long and lateral axis.
So, here's the other way: you connect a series of curved pieces of foam to bend into conical cylinders or half-pipes.
(These shapes are for the sloping curved front, underneath the motor)
For forming them into a cone, there are two ways: cuts go down the fuselage longitudinally, so the flat piece ends with a set of triangles. This is easiest to do with prism fuselages that have hexagonal or octagonal cross sections. I have tried to bend the pieces of a fuselage to make the finished piece more round, but it's hard to get a piece foam to bend along the long and lateral axis.
So, here's the other way: you connect a series of curved pieces of foam to bend into conical cylinders or half-pipes.
Right, but how do calculate the radius of the curved pieces to get the ends to come out straight? So that the cones stack with flat sides.
mastermalpass
Master member
I've not really put this theory into action yet. But I've measured out formers to set the cross-section of the fuselage at different points. With the skin pieces intended to join on the formers, you measure the perimiters of the two formers you want the piece to go between to get the length of the foreward and aft edges. The distance between the formers will give you the measurement for the depth of the piece.
If you want a cylindrical piece to curve down on one end, I guess you can cut wedges from the piece and bend it around, or make seperate curved pieces like in my earlier examples. Just kinda eye-balling it with my plans atm.
If you want a cylindrical piece to curve down on one end, I guess you can cut wedges from the piece and bend it around, or make seperate curved pieces like in my earlier examples. Just kinda eye-balling it with my plans atm.
TheFlyingBrit
Legendary member
You have made that look easier than it is in reality I speak from experience, excellent job by the way looks impressive
TheFlyingBrit
Legendary member
I would probably take an easy option and use card to make a rough template, then transfer the card template to the foamboard and trim where necessary to get a good fit.
However, having had limited success bending my foam board, I would also remove both paper surfaces to give myself a fighting chance of getting a smooth curve. After forming to the required shape, I would probably need to cover the foam in a protective layer as the paper is now omitted, maybe this is where my new acrylic sealant may come in handy
b-29er
Well-known member
There was a gent on one of the model airplane publications about a year ago who built a super connie using 1/4" and 1/2" pink foam. He built the fuselage out of circular sections, and mounted it all to a frame, he used a couple of electrical conduits, you can use more foam to create a box fuselage. Then he used weights to press the skin down on the aircraft. May be a way of doing things, a tad heavier, but it doesn't require complex geometry. Could also just do a boxy fuselage like @mastermalpass , see if its worth the investment to add the detail in a v2, or if it flies like a dog, and move on from there.