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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?

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A smaller engine means a lower peak altitude and a smaller recovery area. You wouldn't want your first flight to involve losing sight of it as it passes 1000 ft AGL and letting it drift a mile away, never to be seen again, would you?

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    $\begingroup$ Is it really bad of me that the first thing I thought of is Right, but it's OK on the second flight? So what you're saying is model rocketry is a bit like dating? :D $\endgroup$ – TildalWave Aug 20 '14 at 21:11
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    $\begingroup$ I suppose, in a sense it is. Don't do too much on the first flight until you know how it reacts. Afterward, well, that's up to you. $\endgroup$ – Tristan Aug 20 '14 at 21:14
  • $\begingroup$ My cousin used max-sized rockets for the maiden voyage of a two-stage rocket. Lost sight of it with binoculars, and never saw it again. $\endgroup$ – supercat Jun 11 '17 at 17:54
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The issue is if something's wrong with your rocket. The smaller the engine the slower it will be going if things go badly.

I've seen one case where the motor mounting broke free on second stage ignition. I don't know exactly what went wrong but the rocket hesitated in flight and pretty much fell over before the second stage was producing any substantial thrust. (I suspect the engine might have been defective.) Fortunately it was still heading slightly into the sky at that point so there was no danger to any of us on the ground. (The rocket headed far from the launch site and did a belly landing. The ejection charged fired after it had come to a stop--the nose had been blown forward and the still-furled chute was laying there. Reglue the mount, touch up the paint and it was good to fly.)

I've also seen a fin come off on liftoff. The rocket headed up on an arcing trajectory and was never found--the smoke trail suggested it was spinning rapidly, the chute probably tied itself up and it was heading far from the vertical, way beyond our outer trackers.

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