Just how important is it to use the suggested engine for the first flight?
What could happen if I don't use the A8-3 and instead used a much higher one on the list such as a C6-5?
Does the lowest suggested engine break in the rocket?
Also, is it OK to use other engines that are not on the list?
If I use a C6-3 in a rocket even though it's not listed.
Thank you for any replies.
Using the "suggested engine for the first flight" is not a requirement (there are no "first engine police") but can be very helpful for you to understand the flight characteristics, and to make sure you will be able to recover the rocket for subsequent flights (assuming you are confident your launch site is big enough for the first flight engine).
You could always start out using a larger suggested engine, but again, you may not be familiar with how high the rocket may go, may lose sight of it, and then not know what to expect...
Regarding "Is it OK to use other engines not on the list," it is possible, but you should be aware that they may not be suggested for a reason...for example, a rocket that has suggested engines of A8-3 & C6-5 sounds like a lighter rocket, and the C6-3 would likely set the ejection charge off much too early, and possibly shred the parachute when it deploys while still going up at a high rate of speed (and nowhere near the apogee).
Have you ever tried the OpenRocket 14.11 software? It is free flight simulation software that will calculate things for you, like max altitude, best delay time, speed of rocket at deployment, etc., for all known commercially produced engines/motors. All you have to do is download (or create) the file for the rocket you have, most commercial rockets (like the Estes models) already have pre-existing files you can download. Read the Wiki, or Google "OpenRocket tutorial", or ask for help on this forum if you need it...
Download OpenRocket at:
https://openrocket.sourceforge.net/download.html