Rod/rail sizes

[Jimbooregon]

Hi all,
Is there some guidelines on how long a rail or rod leave should be for a given motor range? A through D is pretty straight forward, but through the mid power range I'm not sure. Thanks.

 

[cls]

The guide should be long enough that the fins are working aerodynamically when the rocket leaves the guide. Most folks guesstimate that happens at 50fps, 35mph.

If you have a heavy fat rocket with a low thrust motor, use a longer rod. Longer rods can whip with smaller lighter rockets under high thrust motors.

Rule of thumb, SWAG:

I use 3 foot lengths for 1/8", 3/16", and 1/4" rod. Sometimes 4' lengths for 1/4". Rails come in 6 foot lengths and that's great for MPR.

Sometimes 8 foot lengths for level 2 rockets.

Enjoy!