What was found
WHILE IN THE TRAFFIC PATTERN, EXPERIENCED ENGINE FAILURE WHILE DEMONSTRATING A NORMAL TAKEOFF. BEGAN TO ACCELERATE FWD AND PASSED THROUGH 40 KNTS AND BEGAN TO CLIMB, THERE WAS A LOUD BANG AND A LEFT YAW OF ACFT, ACFT IS APPROX 20 FT AND 50 KNOTS. TRIMED HELICOPTER AND COMPLETED AUTOROTATION TO TOUCHDOWN WITH FWD AIRSPEED. NO FURTHER DAMAGE TO AIRCRAFT.