I powered mine with a HB .61 and it flew at a SCALE speed. My friend said it looked just like the RENO air races. Don't forget, the full size String went about 200 mph MAX. At 1/4 scale that would be about 50 MPH. Shoestrings do not go 600 mph. PS it had plenty of power to do aerobatics and that is at 5000 feet altitude.