What Motor Size Should I Use For My
Rocket?
For safety, use a 5:1 Thrust to Weight Ratio.
The following formula is used to make sure you have
selected a motor that will provide enough thrust to lift your rocket quick
enough so the fins will stabilize the rocket after it leaves the launch
rod.
Example:
 A G80 motor produces an average thrust of
80 newton seconds. This is a metric measurement, to convert to english
divide by 4.5, you get 18, or 18 pound seconds.
 So now we know a motor with an average thrust of
80 newton seconds will produce 18 pound seconds of thrust. Now divide 18
by 5 to get the 5:1 ratio required.
 After dividing 18 by 5 you get 3.6. Therefore 3.6
pounds is the maximum weight a rocket should be , using a motor with an
average thrust of 80 newton seconds.
 Yes, it's the same for an F80, G80 or H80, these
motors will all have the same average thrust but performance will differ
due to their burn times. A 5:1 ratio is used by many RSO's to determine
if a rocket could be launched safely. Although the formula will give you
a safe starting point, it will not select the perfect motor for your rocket.
