I would forget the brushless route and look at car starter motors. Play around with the voltage and spool size.to get the acceleration and speed you need. They will tolerate 30 volts for a few seconds.

If you need more oomph use a starter motor to spin up a large flywheel and clutch the spool to it when you are up to speed. At one point we were getting 9 lb gliders to 600 700 ft on zoom launches BUT BE VERY CAREFUL IF YOU GO DOWN THIS ROUTE. You need a burst cage around the flywheel and a weak link as a minimum.