Draw a circle about 1’ in diameter. The measurement doesn’t need to be precise, as you can make adjustments later. The simplest way to do this is to find a bowl of about the right size, place it upside down on the piece of paper, and trace it. Cut out the circle, and cut a straight line from the outside to the approximate center of the circle. Again, precision isn’t particularly important, just estimate where you think the center is. Slide the cut edges over each other to create a cone shape. Hold it over the cone to figure out the right size, and then tape or glue the paper together so it holds that cone shape.
It’s up to you to decide the exact dimensions of your fins. Start by cutting a triangle out of cardboard, and holding it up to the side of the rocket to see how it looks. Adjust the shape until you’re satisfied, then trace it onto the cardboard twice and cut two more identical triangles.
Artificial corks work best for this, as real ones tend to crumble. [4] X Research source The cork will likely be too long, and need to be trimmed down a bit to allow the needle to go all the way through. [5] X Research source
If the rocket does not launch, it is probably because it is not airtight. Make sure there are not any holes in the bottle. If there are, patch them up with duct tape. If not, the cork is probably not sealing the bottle tightly enough. Try applying hot glue or industrial strength glue around the lip of the bottle. You may also have drilled too wide a hole in the cork, in which case you will need to try again with another cork and a narrower drill bit.
