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1st June 2010, 01:01 AM
I know there is an optimal mass for altitude, ie. a Tennis ball goes farther than a bowling ball or feather with the same force, but is this applicable for maximum speed? :confused:

SD

blackjack2564
2nd June 2010, 08:07 AM
Optimal mass for speed = glue fins & nose cone to a motor.

Or.... as light as you can make it and have it fly SAFELY....

For altitude you must deal with the coast phase.

For speed..... it's over at motor burnout. From there downhill.

bobkrech
2nd June 2010, 01:21 PM
Look at the basic law of acceleration:

F = ma and rearrange to a = F/m

v = at and by substitution v = (F/m)*t

F is the thrust of the motor in newtons, m is the mass of the rocket in kilograms, and t is the burn time of the motor in seconds.

You want the highest thrust motor burning for the longest time in the lightest weight rocket you can build.

To be more generic in terms of thrust to weight ratio, T/W.

a = g(T/W-1) so v = g(T/W-1)t where g is the acceleration of gravity, 9.81 M/s^2, T/W) is the thrust of the motor in newtons and the weight of the rocket in newton (mg), and t is the burntime of the motor.

Drag is proportional to V^2 so the faster the rocket velocity, the more thrust is required to overcome drag, but if the rocket diameter doesn't change the the higher the thrust to weight the faster the rocket goes.

Bob