Making a tube from 2mm foam sheets

7 February 2017

Idea for hollow and round fuselage with a 8.5mm direct drive hubsan prop. It is a lot of work.

Former

1. Those prop are about 55mm, so choose plastic bottles that is slightly larger.
2. If length of plastic bottle is too short, use 2 plastic bottles that are hot-glued bottom to bottom.

Rolling 2mm foam sheet

1. Cut an oversized rectangular piece, the width will be the circumference plus 1", the foam grain running fore & aft.
2. Draw in panel lines to one side. The panel lines should be centred on the foam sheet. This will be the outside of the fuselage. If packing tape will be used, then this is also the time to put in as much colour and decoration.
3. Apply clear packing tape to the panel drawn foam sheet.
4. Roll the foam sheet gradually, using the bottle former. The foam sheet will open up and un-curl.
5. Roll the pre-curled foam sheet with a smaller diameter rolling pin until the sides of the foam sheet just about overlap by 1".
6. Tape one edge to the bottle former, let the other foam side overlap the taped end and temporary tape the free side in it's position.

Trimming the basic tube

1. Place a steel edge in the middle of the overlap and slice.
2. Slip off the curled sheet, remove the taped foam pieces from the bottle former and the curled sheet.
3. Secure a piece of clear tape, sticky side out with pieces of tape onto the bottle former.
4. Apply UHU Por to the edges of the curled foam but do not let the edges touch each other.
5. Position carefully one edge of the curled foam so that it is at the middle of the clear tape. Rub it down so that the clear tape sticks to this edge.
6. Bring the other edge and butt it against the first edge. Rub it down so that the clear tape sticks to this edge as well.
7. Run a piece of clear tape over the butt joint.
8. Slit the clear tape loose of the bottle former and slip the foam tube out. Remove waste tape from the bottle former.

Embellishing the tube

1. For tapered ends of a tube, calculate how much foam needs to be trimmed away. Apportion this to the ends of the tube. The more segments, the better the taper will be but much more work is required. Mark the centre of V-cuts, cut away and join the exposed edges, one at a time.
2. If a compound slit is desired, start with a narrow slit throughout, then progress to the wider slits.
3. The tube will now resemble the fuselage.
4. Immerse the fuselage in hot water to relieve the stress so that its shape can be retained easier. If the tape will wrinkle because of water, then substitute with some hot air from hot-air gun or hair-dryer.

Access hatch and gear installment

1. Mark all openings for the wings/tail/battery access/equipment installation using the drawn panel lines as reference.
2. Some areas will be glued together and some made removable.

Idea for a larger hollow and round fuselage with a propeller inside like the Caproni Stipa.

Former

Same bottle former of the size for the 8.5mm direct drive, but in this case, it is not a former but a temporary support for cutting and gluing the tube.

Rolling 2mm foam sheet

1. After cutting an oversized rectangular piece like the previous example, there is no panel lines for the Caproni Stipa, but mark where the width lines are so you will know how much to overlap (1/2" from the oversized edges).
2. Decorate the foam sheet and apply clear packing tape (for strength) as before.
3. Roll the foam sheet gradually, using the bottle former until the sides of the foam sheet just about overlap by 1".

Trimming the basic tube

1. After curling, cut the curled sheet to exact width and lay one edge to the sticky tape on the bottle former like the previous example. Then bring together the other edge and tape it on the outside.
2. Release the tape (inside) from the bottle former and slip off the curled sheet.

Embellishing the tube

1. Follow the same procedure as previous for tapering and stress-relieving.

Access hatch and gear installment

1. There is no panel lines for reference, but the tube can be marked on the outside with a pen on a fixed height stand. When cutting openings, use the bottle former to support the tube against the straight edge.