A little more on this topic:
From a "Wind Caused Instability" report on Apogee's Website:
"High thrust/short burn time motors are preferred in windy conditions.
Divide the average thrust of a typical Aerotech motor (in Newtons) by 3.42 to get a rough estimate of the initial thrust in pounds. In windy conditions, divide by 30, or divide by 100 and then multiply by 3 for a rough, usually conservative estimate of maximum rocket gross weight for a thrust/weight ratio of about 10 or 11 to 1 at launch. (Based on initial thrust 1.3 times average thrust.) Just remember that not all Aerotech motors are typical. It's always more accurate to look at the thrust curve.
On a calm day, you can divide the average thrust by 20, which gives the launch weight for a thrust/weight ratio around 5.85:1. As always, the rocket's liftoff weight should never exceed the maximum liftoff weight specified for the particular motor by its manufacturer."
BUT, consider this:
"The average initial thrust is usually not the same as the average thrust (which is averaged over the entire burn time of the motor). The difference is most pronounced with thrust profiles like those of the Estes A10 and C5, the Aerotech/Apogee F10, and the Aerotech K125W. With thrust profiles like these, the average initial thrust is several times higher than the average thrust, to give the rocket good acceleration off the launcher.
There are some motors with initial thrust lower than their average thrust, such as the Aerotech K185W, the Rocketflite Silver Streaks, and the Plasmajet I102.
Most Aerotech rocket motors have an initial thrust somewhere between 1.1 and 2.0 times their average thrust."
SO, what I am I trying to say. Well, I have yet to see the thrust curve on the E9, however, if it is a high initial thrust curve like the Apogee E6 or F12 then you might get away with a little heavier rocket than the ol' 5:1 method.
- Nick
(Geez, get a room.) Anyway, Dave is into bigger, louder toys. He just bought a fully restored 1969 Dodge Charger.
