Tag Archives: Prototype

17 October 1974

First flight, Sikorsky YUH-60A 73-21650 at Stratford, Connecticut, 17 October 1974. (Sikorsky, a Lockheed Martin Company)

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.

Sikorsky YUH-60A 73-21650 at roll-out, 28 June 1974, with low main rotor, large-area tail rotor pylon and swept stabilator. (Sikorsky, a Lockheed Martin Company)

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 three Sikorsky YUH-60A UTTAS prototypes. A fourth prototype, an S-70, was built and retained by Sikorsky for internal research and development and demonstrations. (Vertical Flight Society)

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.

Sikorsy YUH-60A 73-21650 (c/n 70-001), right profile. In this photograph, the prototype has been modified closer to teh production variant. The rotor mast is taller, the vertical fin has been decreased in size, the crew side window is the two-piece version. (U.S. Army Aviation Museum)
Sikorsky YUH-60A 73-21650 (c/n 70-001), right profile. In this photograph, the prototype has been modified closer to the production variant. The rotor mast is taller, the vertical fin has been decreased in size, a variable-pitch stabilator has replaced the fixed horizontal stabilizer, the engine cowlings have been redesigned, and the crew side window is the two-piece version. (U.S. Army Aviation Museum)

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.

Cutaway illustration of the T700-GE-700 turboshaft engine. (Global Security)

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.

Sikorsky YUH-60A prototype, 73-21650, late configuration. (Vertical Flight Society)

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.

A Sikorsky YUH-60A and Boeing Vertol YUH-61A hover for the camera. (U.S. Army)
A Sikorsky YUH-60A and Boeing Vertol YUH-61A hover for the camera. (U.S. Army)

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.

A Sikorsky UH-60M Black Hawk in flight. (Sikorsky, a Lockheed Martin Company)
Sikorsky's UH-60M Black Hawk for the U.S. Army, seen here in the Military Hangar at Sikorsky Aircraft in Stratford, Conn. Feb. 20, 2008.
Sikorsky’s UH-60M Black Hawk for the U.S. Army, seen here in the Military Hangar at Sikorsky Aircraft in Stratford, Connecticut, 20 February 2008. (Sikorsky, 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.

© 2019, Bryan R. Swopes

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14 October 1964

Prototype Sikorsky YCH-53A Sea Stallion, Bu. No. 151613, 14 october 1964. (Sikorsky Archives)
Prototype Sikorsky YCH-53A Sea Stallion, Bu. No. 151613, 14 October 1964. (Sikorsky Archives)

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).

U.S. Marine Corps Sikorsky CH-53A Sea Stallion (Wikimedia)

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.

Sikorsky HH-53B 66-14428, Super Jolly Green Giant, first flight at Stratford, Connecticut, 15 March 1967. (Sikorsky Historical Archives)
Sikorsky CH-53E Super Stallion at Mojave, California, 9 September 2007. (Alan Redecki/Wikipedia)
This photograph by Alan Radecki of a Sikorsky CH-53E Super Stallion taking off at Mojave, California, 20 September 2007, is too exciting not to include. (Akradecki/Wikipedia)
Sikorsky CH-53K King Stallion at West Palm Beach, Florida, 2 March 2017. (Lance Corporal Molly Hampton, United States Marine Corps)

© 2017 Bryan R. Swopes

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14 October 1938

The Curtiss-Wright XP-40 prototype, 38-10, on its first flight, 14 October 1938. Test pilot Ed Elliot is in the cockpit. (San Diego Air and Space Museum Archives) 16_008532

14 October 1938: At Buffalo, New York, test pilot Everett Edward Elliot made the first flight in the new Curtiss-Wright Corporation’s Model 75P, a prototype for a single-engine pursuit plane which had been designated XP-40 by the U.S. Army Air Corps.

Curtiss-Wright’s Chief Engineer, Donovan Reese Berlin, had taken the tenth production P-36A Hawk, Air Corps serial number 38-10, and had its air-cooled radial engine replaced with the Harold Caminez-designed, liquid-cooled, supercharged, 1,710.597-cubic-inch-displacement (28.032 liter) Allison Engineering Co. V-1710-C13 (V-1710-19).

Donovan Reese Berlin. (Niagara Aerospace Museum)

The V-1710-19 was a single overhead cam (SOHC) 60° V-12 engine with four valves per cylinder and a compression ration of 6.65:1. It had a Normal Power rating of 910 horsepower at 2,600 r.p.m. at Sea Level, and 1,060 horsepower at 2,950 r.p.m. for Takeoff. At 10,000 feet (3,048 meters), the V-1710-19 had Maximum Continuous Power rating of 1,000 horsepower at 2,600 r.p.m., and Military Power rating of 1,150 horsepower at 2,950 r.p.m. The engine required 100/130-octane aviation gasoline. It drove a three-bladed Curtiss Electric constant-speed propeller through a 2:1 gear reduction. The V-1710-19 was 8 feet, 1.75 inches (2.483 meters) long, 3 feet, 4.75 inches (1.035 meters) high and 2 feet, 4.94 inches (0.735 meters) wide. It weighed 1,320 pounds (599 kilograms).

Curtiss-Wright XP-40 38-10 (SDASM 16_008531)

At 1,829.39-cubic-inches (29.978 liters), the original Pratt & Whitney Twin Wasp S1C1-G (R-1830-17) 14-cylinder radial engine had greater displacement and produced 80 horsepower more for takeoff than the Allison V-12. The long, narrow V-12, though, allowed for a much more streamlined engine cowling for higher speed and greater efficiency.

XP-40 16_008533
Curtiss-Wright XP-40 prototype. (SDASM 16_008534)
The Curtiss XP-40 prototype at Langley Field in the original configuration. (NASA)
The Curtiss-Wright XP-40 in the original configuration at Langley Field. (NASA)
Everett Edward Elliot (1907–1981).

In the early testing, the XP-40 was much slower than expected, reaching only 315 miles per hour (507 kilometers per hour). (The P-36A Hawk had a maximum speed of  313 miles per hour). Engineers experimented with different placement for the coolant radiator, oil coolers and the engine air intake. The Air Corps project officer, Lieutenant Benjamin Scovill Kelsey, had the prototype sent to the National Advisory Committee for Aeronautics (NACA) Research Center at Langley Field, Virginia, where the full-size airplane was placed inside a wind tunnel.

Over a two-month period, NACA engineers made a number of improvements. The radiator was moved forward under the engine and the oil coolers utilized the same air scoop. The exhaust manifolds were improved as were the landing gear doors.

When they had finished, Lieutenant Kelsey flew the modified XP-40 back to Curtiss. Its speed had been increased to 354 miles per hour (570 kilometers per hour), a 12% improvement.

By December 1939 the airplane had been further improved and was capable of 366 miles per hour (589 kilometers per hour).

The Curtiss-Wright XP-40 prototype in a wind tunnel at Langley Field, 24 April 1939. (NASA)
Curtiss XP-40 in the NACA Full Scale Wind Tunnel at Langley Field, Virginia, April 1939. (NASA)
Curtiss-Wright XP-40 in the NACA Full Scale Wind Tunnel at Langley Field, Virginia, 24 April 1939. (NASA)

The Curtiss Hawk 75P, XP-40 38-10, was 31 feet, 1 inch (9.574 meters) long with a wingspan of 37 feet, 4 inches (11.354 meters) and overall height of 12 feet, 4 inches (3.734 meters). It had an empty weight of 5,417 pounds (2,457.1 kilograms) and maximum gross weight of 6,870 pounds (3,116.2 kilograms).

The prototype had a maximum speed of 342 miles per hour (550 kilometers per hour) at 12,200 feet (3,719 meters) with a gross weight of 6,260 pounds (2,839.5 kilograms). Its range was 460 miles (740 kilometers) flying at 299 miles per hour (481 kilometers per hour) with 100 gallons (378.5 liters) of fuel. With 159 gallons (601.9 liters) and with speed reduced to 200 miles per hour (322 kilometers per hour), the XP-40 had a maximum range of 1,180 miles (1,899 kilometers).

The prototype was armed with two air-cooled Browning AN-M2 .50-caliber machine guns mounted above the engine and synchronized to fire forward through the propeller arc.

The Air Corps placed an initial order for 524 P-40s. This was the largest single order for airplanes by the U.S. military up to that time. The first production model was the P-40 Warhawk, armed with two .50-caliber machine guns. There was only one P-40A variant which was a P-40 modified as a camera aircraft. The definitive pursuit model was the P-40B Warhawk, which retained the two .50-caliber guns of the P-40 and added two Browning M2 .30-caliber machine guns to each of the wings.

A Curtiss-Wright P-40B Warhawk, 79th Pursuit Squadron, 20th Pursuit Group, Hamilton Field, California, 1940. (U.S. Air Force)

The P-40B was best known as the airplane flown by the American Volunteer Group fighting for China against the Japanese. They were called the “Flying Tigers”. Between 1939 and 1945, Curtiss built 13,738 P-40s in many configurations. They flew in combat in every theater of operations during World War II.

A Curtiss-Wright Hawk 81-A3 (Tomahawk IIb) of the American Volunteer Group, Kunming, China, 1942. (U.S. Air Force)

© 2018, Bryan R. Swopes

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9 October 1987

PP1, the first prototype of the EH101, ZF 641. (Paul Thallon)
PP1, the first prototype of the EH101, ZF 641. (Paul Thallon)

9 October 1987: Westland Helicopters Ltd. Chief Test Pilot John Trevor Eggington and Deputy Chief Test Pilot Colin W. Hague take PP1, the first EH 101 prototype, for its first flight at Yeovil, Somerset, United Kingdom. The helicopter had been completed 7 April 1987 and underwent months of ground testing.

A medium-lift helicopter, the EH 101 was a joint venture of Westland and Costruzioni Aeronautiche Giovanni Agusta S.p.A. of Italy, known then as European Helicopter Industries, or EHI, to produce a replacement for the Sikorsky S-61 Sea King, which both companies built under license. The Italian and British companies merged in July 2000 and are now known as AgustaWestland NV, with corporate headquarters in the Netherlands. After the merger of the two helicopter manufacturers, the EH 101 was redesignated AW101. It is also known as the Merlin.

Canadian Forces CH-149 Cormorant, a search and rescue variant of the AgustaWestland AW101. (Korona4Reaal via Wikipedia)
Canadian Forces CH-149 Cormorant 149902, a search and rescue variant of the AgustaWestland AW101. (Korona4Reel via Wikipedia)

Nine prototypes were built, four by Agusta at Vergiate, Italy, and five by Westland at Yeovil. During testing, Agusta-built PP2 and Westland’s PP4 were destroyed.

PP1, the first prototype, was powered by three General Electric CT7-2A turboshaft engines which were rated at 1,625 shaft horsepower, each. In production, Rolls-Royce/Turbomeca RTM322 engines are optional, as are the more powerful CT7-8s. Produced in both military and civil variants, the Merlin is used in search-and-rescue, anti-submarine warfare, mine countermeasures, airborne early warning and utility configurations. Production began in 1995 and continues today.

The AgustaWestland AW101 Merlin is a single main rotor/tail rotor medium helicopter powered by three turboshaft engines. It is equipped with retractable tricycle landing gear. The helicopter may be flown by a single pilot and uses a digital flight control system. The actual flight crew is dependent on aircraft configuration and mission.

The five blade composite main rotor has a diameter of 61 feet, 0 inches (18.593 meters) and turns counterclockwise as seen from above. (The advancing blade is on the helicopter’s right side.) The blades use a BERP feature that was pioneered on the Westland Lynx AH.1 Lynx, G-LYNX, which Trevor Eddington flew to a world speed record, 11 August 1986. This allows higher speeds, greater gross weight and is quieter than a standard blade. A four blade tail rotor with a diameter of 13 feet, 1 inch (3.962 meters) is positioned on the left side of the tail boom in pusher configuration. It rotates clockwise as seen from the helicopter’s left. The tail rotor pylon is inclined to the left.

PP.5 parked aboard HMS iron Duke. (Royal Navy)
PP5, the prototype  ASW variant parked aboard HMS Iron Duke (F234). (Royal Navy)

Overall length of the AW101 is 74 feet, 10 inches (22.809 meters) with rotors turning. The fuselage is 64 feet, 1 inch (19.533 meters) long. Overall height of the helicopter is 18 feet, 7 inches (5.664 meters). Its empty weight is 20,018 pounds (9,080 kilograms) and the maximum takeoff weight (MTOW) is 34,392 pounds (15,600 kilograms).

The RTM322 engine was developed as a joint venture between Rolls-Royce and Turboméca, but is now a Safran Helicopter Engines product. The RTM322 02/8 is a modular reverse-flow turboshaft engine with a 3-stage axial-flow, 1 stage centrifugal-flow compressor and 2-stage high-pressure, 2-stage power turbine. The output drive shaft turns 20,900 r.p.m. The RTM322 02/08 is rated at 2,000 shaft horsepower, and 2,270 shaft horsepower for takeoff. It has a One Engine Inoperative (OEI) rating of 2,472 shaft horsepower (30 minute limit). The engine is 3 feet, 10.1 inches (1.171 meters) long, 2 feet, 1.5 inches (0.648 meters) in diameter and weighs 503 pounds (228.2 kilograms).

The AW101’s cruise speed is 278 kilometers per hour (150 knots). The hover ceiling in ground effect (HIGE) is 3,307 meters (10,850 feet). In utility configuration, the Merlin carries fuel for 6 hours, 30 minutes of flight and has a maximum range of 1,363 kilometers (735 nautical miles).

John Trevor Egginton, Chief Test Pilot, Westland Helicopters. (Photograph courtesy of Neil Corbett, Test and Research Pilots, Flight Test Engineers)
John Trevor Eggington, Chief Test Pilot, Westland Helicopters. (Photograph courtesy of Neil Corbett, Test and Research Pilots, Flight Test Engineers)

Trevor Eggington retired from Westland in 1988 and Colin Hague became the company’s chief test pilot. In 2003, Hague was appointed an Officer of the Most Excellent (OBE) Order of the British Empire for his contributions to aviation.

Deputy Chief Test Pilot Colin W.Hague, with the first prototype EH101, PP1. (Photograph courtesy of Neil Corbett, Test and Research Pilots, Flight Test Engineers)
Deputy Chief Test Pilot Colin W. Hague, with the first prototype EH101, PP1. (Photograph courtesy of Neil Corbett, Test and Research Pilots, Flight Test Engineers)

Since 2010, PP1 has been used as an instructional airframe for maintenance personnel at RNAS Culdrose, Cornwall, UK.

ZF641, the first prototype of the EH101 (AW101) Merlin, at RNAS Culdrose, 2010. (dyvroeth)
ZF 641, the first prototype of the EH 101 (AW101) Merlin, at RNAS Culdrose, 2010. (dyvroeth)

© 2016, Bryan R. Swopes

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7 October 1963

Prototype Learjet 23 N801L, first flight, 7 October 1963. (Lear)
Prototype Learjet 23, N801L, first flight, 7 October 1963. (Lear Jet Corporation)

7 October 1963: The first of two Learjet 23 prototypes, N801L, makes its first flight at Wichita, Kansas, with test pilots Henry Grady (“Hank”) Beaird, Jr., and Robert S. Hagan. A light twin-engine business jet, the Learjet 23 is considered a “first” because it was designed from the start as a civil aircraft.

The Learjet 23 is operated by two pilots and can carry six passengers. It is 43 feet, 3 inches (13.183 meters) long with a wingspan of 35 feet, 7 inches (10.846 meters) and overall height of 12 feet, 7 inches (3.835 meters). It has an empty weight of 6,150 pounds (2,790 kilograms) and maximum takeoff weight of 12,499 pounds (5,670 kilograms).

A characteristic of all Learjets is the 13° sweep of their wings’ leading edges, and the straight trailing edge.

Learjet 23 N802L was the second prototype. This airplane is in the collection of the Smithsonian Instititution National Air and Space museum. (NASM 9A11735)

The airplane was powered by two General Electric CJ610-4 turbojet engines. The CJ610 is a single-shaft axial-flow turbojet with an 8-stage compressor and 2-stage turbine. The CJ610-4 has a maximum continuous power rating of 2,700 pounds (12.010 kilonewtons) at 16,500 r.p.m. at Sea Level, and 2,850 pounds of thrust (12.677 kilonewtons) at 16,700 r.p.m., for takeoff (5 minute limit). The engine is 3 feet, 4.50 inches (1.029 meters) long, 1 foot, 5.56 inches (0.446 meters) in diameter, and weighs 403 pounds (183 kilograms).

The Learjet 23 has a cruise speed of 518 miles per hour (834 kilometers per hour) at 40,000 feet (12,192 meters) and a maximum speed of 561 miles per hour (903 kilometers per hour), 0.82 Mach, at 24,000 feet (7,315 meters). The service ceiling is 45,000 feet (13,716 meters) and its maximum range is 1,830 miles (2,945 kilometers).

Lear Jet Corporation built approximately 100 Learjet 23s.

The first prototype was damaged beyond economical repair while simulating an engine failure on takeoff during flight testing, 4 June 1964. The accident was attributed to pilot error. N801L had accumulated just 194 flight hours.

© 2018, Bryan R. Swopes

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