It would be MUCH more impressive on a cluster of four SU 18mm D21-4T or D10-4W motors though.
Four C6-3's is slightly less power than ONE E28 reload or E30 single use motor that is much less hassle. That single reload or SU motor costs significantly less as well.
If I was to cluster the composites I would use D21's as blue thunder is a much more "instant" ignition propellant than white lightning unless using very hot igniters.
A full 80n-sec in a 1/70 S1B is a GREAT flight.

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When in doubt, WHACK the GAS and DITCH the brake !!!

Yes, there is such a thing as NORMAL, if you have to ask what is "NORMAL" , you probably aren't !
Failure may not be an OPTION, but it is ALWAYS a POSSIBILITY.
ALL systems are GO for MAYHEM, CHAOS, TURMOIL, FIASCOS, and HAVOC !