27 October 2015: The first flight of the Sikorsky CH-53K King Stallion Engineering Development Model–1, Bu. No. 169019, at West Palm Beach, Florida. In the cockpit was Stephen McCulley, Chief Experimental Test Pilot for Sikorsky. During the 30 minute flight, the new helicopter demonstrated sideward, rearward and forward flight while remaining in in-ground-effect hover.
Up to this point, the helicopter had completed about 200 hours of “turn-time,” or ground testing, with engines running..
Three more aircraft will join the test fleet for a planned 2,000 hour flight test program.
The fuselage of the CH-53K King Stallion is 73 feet, 1.5 inches (22.289 meters) long and its width is 9 feet, 10 inches (2.997 meters). The maximum width, across the sponsons, is 17 feet, 6 inches (5.334 meters). The seven-bladed main rotor has a diameter of 79 feet (24.079 meters). The four-blade tail rotor is 20 feet (6.096 meters) in diameter. The tail rotor is tilted 20° to the left. With rotors turning, the helicopter has an overall length of 99 feet (30.175 meters), and height of 28 feet, 4.9 inches (8.659 meters). The helicopter’s maximum gross weight is 88,000 pounds (39,916 kilograms).
Power is supplied by three General Electric T408-GE-400 engines which produce 7,500 shaft horsepower, each. The engine has digital electronic controls. The T408 has a 6-stage compressor section (5 axial-flow stages, 1 centrifugal-flow stage) and – stage turbine section (2 high- and 3 low-pressure stages). The engine is 57.5 inches (1.461 meters) long and 27 inches (0.686 meters) in diameters.
At Sea Level with maximum continuous power, the CH-53K cruises at 158 knots (182 miles per hour/293 kilometers per hour). It can hover out of ground effect at Sea Level at its maximum gross weight. The helicopter’s service ceiling is 16,000 feet (4,877 meters).
The first production CH-53K was delivered to the U.S. Marine Corps on 16 May 2018, at West Palm Beach, Florida.
17 October 1974: Sikorsky Chief Pilot James R. (Dick) Wright and project chief test pilot John Dixson made the first flight of the prototype YUH-60A, 73-21650, at the company’s Stratford, Connecticut, facility. This helicopter was the first of three prototypes.
Early flight testing revealed excessive vertical vibrations associated with the main rotor. Extensive engineering and flight testing determined that this was caused by air flow upward through the rotor system and around the transmission and engine cowlings. The purpose of the low-mounted main rotor was to aid in fitting inside transport aircraft with minimal disassembly. It was necessary to increase the height of the mast and reshape the cowlings to achieve an acceptable level of vibration.
After eight months of testing, the U.S. Army selected the YUH-60A for production over its competitor, the Boeing Vertol YUH-61A. In keeping with the Army’s tradition of naming helicopters after Native Americans, the new helicopter was named Black Hawk, who was a 17th Century leader of the Sauk (or Sac) people.
The Sikorsky Model S-70 (YUH-60A) was designed to meet the requirements of the U.S. Army Utility Tactical Transport Aircraft System (UTTAS). It had a 3-man crew and could carry an 11-man rifle squad. The helicopter could be transported by a Lockheed C-130 Hercules.
The three UTTAS prototypes were 63 feet, 6 inches (19.355 meters) long, with rotors turning. The span of the horizontal stabilizer was 15 feet, 0 inches (4.572 meters). The prototypes’ overall height was 16 feet, 10 inches (5.131 meters).
The YUH-60A had an empty weight of 11,182 pounds (5,072 kilograms) and gross weight of 16,750 pounds (7,598 kilograms). The helicopter had a structural load factor of 3.5 Gs. With 1,829 pounds (830 kilograms) of fuel, it had an endurance of 2 hours, 18 minutes.
The YUH-60A had a four-blade fully-articulated main rotor with elastomeric bearings. It had a diameter of 52 feet, 0 inches (15.850 meters). During flight testing, the diameter was increased to 52 feet, 4 inches (15.951 meters), and finally to 52 feet, 8 inches (16.053 meters). The blades were built with titanium spars and used two different airfoils and a non-linear twist (resulting in a net -16.4°). The outer 20 inches (0.508 meters) were swept aft 20°. These characteristics improved the helicopter’s maximum speed and hover performance. The main rotor turned counterclockwise, as seen from above (the advancing blade is on the right) at 258 r.p.m. The blade tip speed was 728 feet per second (222 meters per second). During flight testing it was decided to change the main transmission gear reduction ratio in order to operate the engines at a slightly increased r.p.m. At the higher r.p.m., the engines produced an additional 50 horsepower, each.
The four-bladed bearingless tail rotor was positioned on the right side of the tail rotor pylon in a tractor configuration. The tail rotor diameter was 11 feet (3.353 meters), and turned 1,214 r.p.m., rotating clockwise as seen from the helicopter’s left (the advancing was blade below the axis of rotation). The blade tip speed was 699 feet per second (213 meters per second). The tail rotor blades had -18° of twist. Because the Black Hawk’s engines are behind the transmission, the aircraft’s center of gravity (c.g.) is also aft. The tail rotor plane is inclined 20° to the left to provide approximately 400 pounds of lift (1.78 kilonewtons) to offset the rearward c.g.
Power was supplied by two General Electric T700-GE-700 modular turboshaft engines, rated at 1,622 shaft horsepower at 20,900 r.p.m. Np, at Sea Level under standard atmospheric conditions. The T700 has a 5-stage axial-flow, 1-stage centrifugal-flow compressor, with a 2-stage axial-flow gas producer and 2-stage axial-flow power turbine. The T700 is 3 feet, 11 inches (1.194 meters) long, 2 feet, 1 inch (0.635 meters) in diameter and weighs 437 pounds (198 kilograms). The helicopter’s main transmission was designed for 2,828 horsepower. The engines are derated to the transmission limit.
The YUH-60A had a cruise speed of 147 knots (169 miles per hour/272 kilometers per hour) at 4,000 feet (1,219 meters) and 95 °F. (35 °C.). It could climb at 450 feet per minute (2.29 meters per second) at the same altitude and air temperature.
While operating with an Army crew on the night of 9 August 1976, YUH-60A 73-21650 developed a significant vibration. An emergency landing was made. Because of darkness and mist, the pilots thought they were landing in a corn field, but it was actually a pine tree plantation. The helicopter’s rotors cut down more than 40 trees with trunk diameters up to 5 inches (12.7 centimeters).
Close inspection by Army and Sikorsky personnel found that the only visible damage was to the four main and four tail-rotor blades other than nicks and dents to the airframe that were of no structural concern. All gearboxes and engines turned freely, and all flight controls responded properly. ¹ The blades were replaced on-site and the helicopter was flown out the following day.
73-21650 crashed into the Housatonic River near the Stratford plant at 9:10 a.m., Friday, 19 May 1978, killing all three Sikorsky employees on board, pilots Albert M. King, Jr., John J. Pasquarello, and flight engineer John Marshall.
During routine maintenance an airspeed sensor for the all-flying tailplane had been disconnected. As the Black Hawk transitioned from hover to forward flight, the all-flying tailplane remained in the hover position and forced the helicopter’s nose to pitch down to the point that recovery was impossible.
The Black Hawk has been in production since 1978. More than 4,000 of the helicopters have been built and the type has been continuously improved. The current production model is the UH-60M.
Sikorsky is a Lockheed Martin Company.
¹ Black Hawk: The Story of a World Class Helicopter, by Ray D. Leoni, American Institute of Aeronautics and Astronautics, Reston, Virginia, 2007, Chapter 8 at Page 173.
14 October 1964: The first prototype Sikorsky YCH-53A Sea Stallion, Bu. No. 151613, made its first flight at the Sikorsky plant at Stratford, Connecticut. (Sikorsky Model S-65, serial number 65001.)
The fuselage of the YCH-53A was similar in configuration to the smaller CH-3C (S-61R). It used the dynamic components from the CH-37 Mojave (S-56) and CH-54A Tarhe (S-64).
The Sikorsky CH-53A Sea Stallion is a twin-engine heavy-lift transport helicopter operated by two pilots. It is 88 feet, 2.4 inches (26.883 meters) with rotors turning. The fuselage is 67 feet, 2.4 inches (20.483 meters) long and 8 feet, 10 inches (2.692 meters) wide. The six-blade fully articulated main rotor is 72 feet, 2.7 inches (22.014 meters) in diameter and turns counterclockwise as seen from above. (The advancing blade is on the helicopter’s right.) Main rotor speed is 185 r.pm. The four-blade semi-articulated tail rotor has a diameter of 16 feet (4.877 meters) and is placed on the left side of the tail rotor pylon in a pusher configuration. It turns clockwise as seen from the helicopters left. (The advancing blade is below the axis of rotation.) Overall height (rotors turning) of the Sea Stallion is 24 feet, 10.8 inches (7.599 meters). The tail rotor speed is 792 r.p.m.
The CH-53A is powered by two General Electric T64-GE-6 turboshaft engines rated at 2,850 shaft horsepower, each. Performance of the CH-53D (T64-GE-413, 3,925 s.h.p) has a maximum speed (Vne) of 130 knots (241 kilometers per hour) service ceiling of 16,750 feet (5,105 meters) and range with maximum payload of 540 miles (870 kilometers)
Two YCH-53A prototypes were built, followed by 139 CH-53A Sea Stallion production models.
The CH-53 was developed into the three-engine CH-53E Super Stallion. The current production variant is the CH-53K King Stallion.
12 October 1976: The Sikorsky S-72 Rotor Systems Research Aircraft (RSRA) made its first flight at Stratford, Connecticut. The S-72 was a hybrid aircraft built for the United States Army and the National Aeronautics and Space Administration. Its purpose was to serve as a flight test vehicle for various helicopter rotor configurations.
The S-72 was three-place, four-engine, single main rotor/tail rotor compound helicopter with retractable main landing gear. The flight crew consisted of two test pilots in a side-by-side cockpit, and a flight test engineer in the cabin. The left pilot’s position was equipped with “fly-by-wire” flight controls, while the right seat used conventional mechanical controls as a safety back up. The S-72 had a crew escape system, which blew the main rotor blades off, allowing the crew to land the aircraft in its airplane mode, or to be extracted by rockets.
The aircraft was built with a low-drag fuselage capable of reaching 340 knots (391 miles per hour/630 kilometers per hour) and used the rotors and drive train of the S-61 Sea King. A wing and two turbofan engines allowed the aircraft to fly as an airplane.
The S-72 had an overall length with rotors turning, of 75 feet, 11 inches (23.139 meters). The fuselage had a length of 63 feet, 8 inches (19.406 meters), and maximum width of 8 feet, 4 inches (2.642 meters). The RSRA had an overall height of 15 feet, 6 inches (4.724 meters). The variable incidence wing has a span of 45 feet, 1.2 inches (13.746 meters). The angle of incidence could be varied in flight from +15° to -9°. The span of the horizontal stabilizer is 20 feet, 10 inches (6.350 meters). The S-72 compound helicopter had an empty weight of 20,812 pounds (9,440 kilograms) and gross weight of 26,392 pounds (11,971 kilograms). When stripped to a pure helicopter configuration, the empty weight was reduced to 14,490 pounds (6.573 kilograms).
The S-72 was first flown using the rotors from the S-61. These were later to be replaced with experimental rotor systems. The S-61 main rotor has five blades and a diameter of 62 feet, 0 inches (18.898 meters). Each blade has a chord of 1 foot, 6.25 inches (0.464 meters). The main rotor turns at 203 r.p.m., counter-clockwise, as seen from above. (The advancing blade is on the right.) The S-72’s tail rotor also has five blades and has a diameter of 10 feet, 7.25 inches (3.232 meters). The blades have a chord of 7–11/32 inches (0.187 meters). The tail rotor turns clockwise as seen from the helicopter’s left. (The advancing blade is below the axis of rotation.) The tail rotor turns 1,244 r.p.m.
The S-72 was powered by two General Electric T58-GE-5 turboshaft engines, driving the rotor system, and two General Electric TF34-GE-2 turbofan engines providing thrust for flight in the airplane or compound helicopter configuration.
The T58-GE-5 turboshaft engines are the same engines that powered the HH-3E Jolly Green Giant combat search and rescue helicopters. They are a free-turbine turboshaft with a 10-stage axial-flow compressor section a 2-stage gas generator turbine (N1) and 1-stage free power turbine (N2). The T58-GE-5 has a Maximum Continuous Power rating of 1,400 shaft horsepower, each, and Military Power rating of 1,500 shaft horsepower. The engine is 59.0 inches (1.499 meters) long, 20.9 inches (0.531 meters) in diameter, and weighs 335 pounds (152 kilograms).
The TF34-GE-2 turbofan was developed for the U.S. Navy’s Lockheed S-3A Viking anti-submarine aircraft. It was a two-spool axial-flow jet engine with a single-stage fan section, 14-stage compressor, and 6-stage turbine section (2 high- and 4 low-pressure stages). The TF34-GE-2 was rated at 9,275 pounds of thrust (41.26 kilonewtons).
The S-72 had a maximum speed in level flight of 300 knots (345 miles per hour/556 kilometers per hour), and 340 knots (391 miles per hour/630 kilometers per hour) in a dive.
Two RSRAs were built. After Sikorsky’s flight test program was completed in 1979, the two RSRA aircraft were delivered to NASA Ames. The Aircraft received civil registrations N740NA (72001) and N741NA (72002).
The stripped airframe of the first Sikorsky S-72, 72001, sits behind a chain link fence at Fort Rucker, Alabama.
1 October 1947: Los Angeles Airways began regularly scheduled air mail service in Los Angeles, using the Sikorsky S-51 helicopter.
“. . . the U.S. Civil Aeronautics Board awarded LAA the route authorities to operate local air mail services in Southern California using the Sikorsky S-51. Before long, LAA was operating a twice-a-day mail service between the main downtown post office and Los Angeles International Airport along with a small package air express service.
“With a fleet of five S-51s, LAA’s first year of operations resulted in 700 tons of mail being carried with approximately 40,000 landings throughout the Los Angeles metropolitan area. The small operation maintained a 95% reliability rate and by the time it began its small package air express service in 1953, it was annually moving nearly 4,000 tons of mail a year.
“In July 1951 the CAB awarded LAA’s reliable helicopter operation the rights for passenger services which started in November 1954 with larger Sikorsky S-55 helicopters while the smaller S-51s continued the mail and small package services. . . .”
The S-51 was a commercial version of the Sikorsky R-5 series of military helicopters. It was a four-place, single-engine helicopter, operated by one pilot. The cabin was built of aluminum with Plexiglas windows. The fuselage was built of plastic-impregnated plywood, and the tail boom was wood monocoque construction. The main rotor consisted of three fully-articulated blades built of metal spars and plywood ribs and covered with two layers of fabric. (All metal blades soon became available.) The three bladed semi-articulated tail rotor was built of laminated wood. The main rotor turned counter-clockwise, as seen from above. (The advancing blade is on the helicopter’s right.) The tail rotor was mounted on the helicopter’s left side in a pusher configuration. It turned clockwise as seen from the helicopter’s left.
The helicopter’s fuselage was 41 feet, 7.5 inches (12.687 meters) long. The main rotor had a diameter of 48 feet (14.630 meters) and tail rotor diameter was 8 feet, 5 inches (2.565 meters), giving the helicopter an overall length of 57 feet, 1 inch (17.399 meters). It was 13 feet, 1.5 inches (4.001 meters) high. The landing gear tread was 12 feet (3.7 meters). The S-51 had an empty weight of 4,050 pounds (1,837 kilograms) and maximum takeoff weight of 5,500 pounds (2,495 kilograms). Fuel capacity was 100 gallons (378.5 liters).
The helicopter was powered by an air-cooled, supercharged, 986.749-cubic-inch-displacement (16.170 liter) Pratt & Whitney Wasp Jr. T1B4 (R-985 AN-5) direct-drive, nine-cylinder radial engine which was placed vertically in the fuselage behind the crew compartment. This engine was rated at 450 horsepower at 2,300 r.p.m., Standard Day at Sea Level. The R-985 AN-5 was 48.00 inches (1.219 meters) long, 46.25 inches (1.175 meters) in diameter and weighed 684 pounds (310.3 kilograms) with a magnesium crankcase.
The S-51 had a maximum speed (Vne) of 107 knots (123.1 miles per hour/198.2 kilometers per hour). Range was 275 miles (442.6 kilometers). The service ceiling was 14,800 feet (4,511 meters). The absolute hover ceiling was 3,000 feet (914.4 meters).
Of 220 helicopters in the S-51 series built by Sikorsky, 55 were commercial models.