For the Science Olympiad being held in my district, I am in the
bottle rocket competition.
The rockets are ranked in LONGEST TIME FROM LIFT OFF TILL
IT TOUCHES THE GROUND!
We are to use a 2 liter bottle, and the propulsion system is
air. (compressed into the bottle.). No pyrotecnics allowed
Anyway, the difficulty is that this year, unlike when my brother
did it a few years ago, parachutes are not allowed. A parachute
is defined as anything that traps air or USES AIR TO OPEN to slow
down the rocket.
We are having trouble finding a recovery system that does
not create drag when it is launched. I need some brainstorming
ideas before the competition.
-PK
(Fortunately I construct things better than I spell…)
If it can’t use air drag to slow descent (parachute, autogyro), what else is there? Helium? I think they want you to just let it fall, with no recovery system, so that the winner is based on the best propulsion system, not the best recovery system.
no for some reason they allow like fins and wings and stuff to “glide” down, like last years winners’. how that doesnt fall in the parachute category is beyond me, but i think they just wanted to go away from the cloth and strings approach
Fear Itself is right. There’s only one force available to you to slow descent of the rocket, and that’s wind resistance. Unless;
You hang a hunk of tar, or something like that, from a helium balloon, shoot the rocket into it…
Peace,
mangeorge
Propulsion is easy. All you need is either some Mentos ,alkaseltzer or dry ice mixed with fresh soda. All 3 will cause the soda to “fizz like a bastard” and provide thrust. For a parachute you can use fins that are hinged near the nose of the rocket. They will open up when the rocket starts to fall.Think of a car door. If you open it when the car is going forward wind will push it closed, but if you are going in reverse then the wind will hold it open. The only real problem will be decideing how big to make the fins. I would use 2 rows that overlap, kind of like this pattern ***** and attatch then with duct tape to cut down on weight and drag. The other 2 things to consider is the nozzle and how big it needs to be so that there is sufficient thrust to get it moveing, but no so much that it runs out of fuel too quickly. The other would be fins for stability. Depending on the angle and size they can be used to spin the rocket like a bullet to provide better stability.
If they allow fins and wings, then they should allow an autogyro, which is like an unpowered helicopter blade that spins to slow descent. An autogyro blade is nothing more than two wings on a pivot point. You would have to rig some kind of deployment mechanism (spring or rubber band) to unfold the blades after apogee, then they will start spinning on their own. If each blade was close to 2 meters in length, that would give you a pretty big span that would keep you up for a long time.
Here are some plans for this type of recovery system for a conventional pyrotechnic model rocket, you should be able to adapt them for your bottle rocket. For more ideas on this type of recovery system, try this Google search on Helicopter Recovery Rocket, which has lots more variations on this design.
**
There is obviously only one course of action open to you: cheat.
You need a recovery system, but one that uses something besides air to open. I’d suggest some sort of helicopter recovery system that is released either mechanically or via an electromagnet, if you can afford the weight.
Your rocket would have the rotors pinned to its side. Once the thrust stops and the rocket pitches over, release the rotors and let autogyration take over.
