While building model rockets with my son, I figured I would ask a question that had been bothering me for a while. When you look at the packaging of the Estes rockets, regardless of complexity level (I tried a level 3, and that was WAY more effort than I wanted to put in), it recommends a different engine for first launch.
Usually B class. Then, for later launches, you can do higher powered engines.
Why the lower power for the first flight?