Rocket Ratios

[Juxt]

I belong to an organization named Science Olympiads. One event is named Bottle Rockets. The object is to shoot a 1L soda bottle into the air and put as much time as you can between launch and touchdown. My question is this, what is the best ratio of length for the nosecone on a rocket? It seems that rockets are alike enough that there would be some ratio like 1m of nosecone to 20m of rocket. Anyone have any ideas about this?

[enigma]

The shape of the nose cone will depend greatly on the parameters of the rocket.

Mach number profile, velocity vs. atmospheric density profiles, payload sizes, etc. all play a part.

[Michael D. Sewell]

What sort of flight times are typical? Do the bottles have to be empty? Can you alter their shape, or do you have to use "stock" bottles? What do you use for fuel? Sounds like a lot of fun.
-Mike