You won’t see a skydiver jump from a plane holding his parachute bundled loosely in his arms. Well, probably not the same guy twice anyway. Serious parachute users, whether dropping people or cargo, put their parachutes in special deployment bags.
A smaller drogue chute is deployed. When it catches air it pulls the folded main chute out of the deployment bag, allowing it to open safely.
When can you use them in water rockets?
You must use a drogue chute, attached to a reliably separating nose cone, as well as the main chute which is in the pocket. The pocket is attached by a cord to the drogue, which opens first and pulls the pocket off of the main chute.
Why use them?
You can deploy a much smaller drogue chute easier than a larger main chute.
It keeps the main chute neatly folded while you load it into the rocket.
There is less chance for tangles if lines tend to unwrap from folded parachutes.
It can pull a main chute farther away from the rocket before it opens.
A main chute doesn’t expand as much inside a rocket compartment, making deployment less difficult.
There is possibly less shock to a main chute if it is accidentally deployed before a rocket slows down completely. In this case, the drogue chute should also be made strong enough to withstand a high-speed deployment.
Making the pockets
The material that I used to make the pockets is a thin and very supple upholstery fabric. One side has a very thin coating of vinyl and that side is the inside lining of the pocket so that the chute slides out easily.
Make patterns from thin cardboard. Mine range from 3″ x 4″ to 4″ x 5″. Just create a square, then add an inch to one side and round off that side so that there are no corners to snag. Cut two pieces of material with this pattern, along with about an inch wide piece that matches the rounded end. Line up the two pieces, smooth sides in, with the small rounded piece between them, and stitch them together as shown in the photo. Install a grommet, or make some other reinforced hole, in the rounded end for attaching a cord.
How to use them
The tightly folded chute should fit loose enough inside the pocket to fall out or at least be easily tugged out by the drogue. Wrap the lines around the folded chute (from edge to center) and place the narrowest end in the pocket first. Place the closed end of the pocket, with drogue cord attached, in the rocket first so that the main chute is sure to be pulled out of the rocket, not just the pocket pulled off leaving the chute behind.