Is there a string to parachute ratio?

Question

im building a bottle rocket for science, is there a good way to figure out how long my string should be for my parachute?

Answer 1

I don't know of a formula, but you want to get the string at a proper angle to deploy the entire chute.

For example if you use a very long set of strings then the chute should catch air and work properly. If you use too short of a set then the chute can't deploy properly. The best way is to make sure you have close to a 60 degree angle between the ground and the chute lines with the deployed chute parallel to the ground. OR you can have less than a 45 degree angle between the chute lines and the axis of fall.

The old Estes rocket motors were solid fuel rockets and had a small charge on top of the motor to deploy the chute. As the fuel burned upward inside the rocket it would reach the end and ignite this small charge that would give a puff of gas to knock the chute out of the rocket tube. The rocket would be designed to have a nose cone or the middle of the body fly off and then it would be tied to the bottom. The Chute would deploy and the rocket would safely fall to the ground. Put the string inside of the tube to not interfere with the aerodynamics of flight during launch. The top tube should be slightly larger than the bottom tube to prevent turbulence from deploying the chute early.

On common method used is to tie a single short string to the rocket and then tie the parachute lines to a knot on that string. This keeps the chute further away from the rocket and it is how dragsters and jets deploy their deceleration parachutes.

I have included some web sites that might help:
http://www.pcprg.com/rocketre.htm
http://www.rocketparachutes.com/
http://www.performancehobbies.com/paindex.htm
http://van.physics.uiuc.edu/qa/listing.php?id=2131
http://store.heavenlyhobbies.com/tarc.html

Answer 2

Yes, you can use a sheet as a parachute but you have to attach cords to the corners, length about twice the long side of the sheet, and make a small hole in the centre - about head size! - to give some stability. A double bed sheet and a baby bouncer harness will slow the average two year old to a survivable speed, but in the event of a fifth floor fire the time to construct might be unavailable. Personally, I always stay with the aircraft. It is worth noting that a porous fabric or mesh will give very good results, but totally impervious fabrics require several shaped apertures for best results. Your bog standard bedsheet works best if four limbs are available, so jump with a friend! :-)