Turnigy specs now rate their motors at 6000w max. from 7000w previously. If you use 3 motors that would be 18Kw (24HP) usage max at 4C for takeoff and hover. This would equate to 4.5/18x60 = 15 min. of flight time. However, 18Kw may be marginal power as the props probably won't be able to achieve 10lbs thrust per HP. That then requires 4 motors and a bigger battery pack (say 6.5Kwh). The law of diminishing returns!