21 September 1961: Boeing Vertol YCH-1B-BV, serial number 59-4983, a twin-turboshaft, tandem-rotor heavy lift helicopter, flown by test pilot Leonard Joseph (“Len”) LaVassar, made its first flight at Morton Grove, Pennsylvania. This aircraft was the number two prototype. (The first aircraft, 52-4982, had been damaged 12 July 1961 when the rotors went out of phase during ground testing. It was repaired but never flew.) In 1962, the YCH-1B was was redesignated YCH-47A.
The YCH-1B fuselage was 51 feet, 0 inches (15.545 meters) long and had a maximum width of 12 feet, 5 inches (3.785 meters). The helicopter’s overall length, with rotors turning, was 98 feet, 3.25 inches (29.953 meters), and its maximum height (to the tip of the uppermost blade) was 18 feet, 6.6 inches (5.654 meters). Empty weight of the production CH-47A is approximately 25,500 pounds.
The counter-rotating fully-articulated three-bladed rotors each had a diameter of 59 feet, 1.25 inches (18.015 meters). The forward rotor turned counter-clockwise, as seen from above. (The advancing blade is on the helicopter’s right side.) The rear rotor turns the opposite direction. They rotate at 215 r.p.m.
The prototypes were powered by two Lycoming LTC4B-3 (T55-L-5) turboshaft engines. These were free-turbine engines using a 7-stage axial-flow, 1-stage centrifugal-flow compressor section with a single-stage high-pressure turbine and two-stage low-pressure power turbine. The T55-L-5 was rated at 1,870 shaft horsepower at 14,430 r.p.m. N2. It was 3 feet, 8.1 inches (1.120 meters) long and weighed 560 pounds (254 kilograms).
The helicopter had a maximum speed of 153 knots (176 miles per hour/283 kilometers per hour) at Sea Level. Its hover ceiling, out of ground effect (HOGE), was 11,650 feet (3,551 meters), and in ground effect (HIGE), 14,500 feet (4,420 meters). The helicopter’s service ceiling was 18,600 feet (5,669 meters).
The Chinook remains in production as the CH-47F Block I and MH-47G, and is used by the military services of several nations. Boeing is continuing development of the Block II variant.
© 2023, Bryan R. Swopes