The military tactics of vertical envelopment require the transport of 8000 pounds of payload to a radius of 100 nautical miles at a speed of 150 knots. The aircraft should be able to hover at 6000 feet on a standard day and with one engine inoperative maintain level flight in turbulent air. The helicopter should be readily convertible to carry cargo or troops.

The CH-53A meets these requirements. Additional design constraints, including emergency water landing, rear loading, self-contained navigation system and weight and dimensions compatible with aircraft carriers have been imposed.

With special attention having been given to the vibrational environment two General Electric T-64 engines have been installed. The 72-foot diameter main rotor is equipped with six blades with 26 inch chord and a NACA 0012 aerofoil modified to improve the characteristics at high Mach number. To achieve low drag and interference the fuselage and rotors have been developed in the wind tunnel. Tail surfaces have been especially developed to provide good handling qualities. An automatic stabilisation system was provided to relieve the pilot of various flight duties and to permit him to give more attention to the military situation.

Special design procedures have been followed to control weight, drag, reliability and vibration. The final helicopter is within 3-7 per cent of the desired weight and the performance is in substantial accord with predictions. The vibration level is generally about ±0-10 g throughout the cockpit and cabin.

During the flight development phase the control system was modified to provide appropriate coupling to relieve the pilot and automatic flight control system of any unnecessary compensating control motions. The structural integrity tests revealed the need for improvement of the main rotor blade attachment spindle. The engine-to-transmission shafting required a damped support.

The finally developed version of the CH-53A meets the mission requirements already stated. The hovering ceiling on a standard day Is over 5000 feet. The maximum level flight speed is 170 kt. The handling qualities and vibration are superior to any helicopter previously built by Sikorsky Aircraft. The reliability and maintenance features have been demonstrated by extensive testing. The overhaul periods will be 1200 hours in early service operation; 5-5 direct maintenance man-hours per flight hour are required to accomplish all maintenance except overhaul of repairable components. The dynamic components have been developed to such a high degree of reliability that they will be overhauled “on condition” only and continued in service throughout the normal military usage.

In terms of commercial service, the CH-53A (S-65) will have a direct operating cost of approximately 4c per seat mile.