Construction of Parts - How To Make A Parachute

A parachute helps cushion the fall of whatever it's attached to, providing it's big enough. Though they have many hobby uses, parachutes are perhaps most commonly used to return hobby rockets safely to the ground or plastic figures released from kites or merely thrown into the air. A car might also have a mechanism to deploy one at the end of a race to slow it down.

If the parachute is used in the open where wind can affect it, thought must be given to reducing the size of the parachute. One suitable in calm conditions may be blown far down range in a breeze. Reducing its size will allow a faster fall without as much drift. Unfortunately, a faster fall is harder on landing.

Steps

1. Determine the diameter of the parachute appropriate for the weight of the suspended object (see the table). The parachute diameter is the diameter of the shroud (the material forming the disk), not the diameter of its opening size (aperture) when deployed. Its aperture is about 4/7ths of the shroud diameter.
2. Cut eight heavy threads or cotton strings about one and a half times the radius of the parachute. Nylon or fishing line tend to be too stiff.
3. Cut a disk from a large plastic bag (grocery bags are good to about 14 inches). You may be able to trace around a large pot lid, an other object or using a compass as a guide.
4. Fold the thin disk in eighths and attach a string to the middle of each of the eight folds with a small piece of packing tape or dot stickers. It really doesn't matter that much, but you may want to figure out which side of the chute the tape will be on.
5. Gather the loose ends of the strings and tie them together. (When you get good at it, you will see how to use only four strings of twice the length)
6. Attach to the object by tying or with a small screw eye (from a hardware store) or carefully cut a paper clip and glue one of the "U" pointed ends first into the object.
7. Push the strings through the eye and loop over the parachute. When the parachute is pulled the strings synch up on the screw eye securely. Better yet, attach your parachute to a swivel snap (from a hardware store) so you can clip it to your load object and remove it easily. This works well when swapping for a smaller parachute on a breezy day.

How A Parachute Works

A parachute is a rather flexible "wing" anchored from its edges to a weight that freely dangles below it. The chute creates pressure drag. This drag pushes on the chute as if it were all concentrated in one spot at the center of the chute's volume. This point is called the center of pressure (CP). It is the point at which air pressure is balanced inside the chute.

What makes a parachute work is that the air filling the chute always pushes the center of pressure to move above the center of mass (CM). The center of mass is usually in the middle of the weight (chutes can be very light). The weight may swing a bit, but never enough to rise above the center of pressure on its own.

You could force such a situation by swinging the weight hard so it rises above the center of pressure, but it always drops down again. If it passes over the middle of the chute, it may collapse it and cause the whole thing to come crashing down!