Daily Archives: July 16, 2017

16 July 1983

British Airways’ Sikorsky S-61N Mark II, G-BEON, at Newquay Cornwall Airport, 21 July 1982. (Carl Ford)

16 July 1983: At 11:10 a.m., a British Airways Sikorsky S-61N-69 helicopter, c/n 61-770, registration G-BEON, departed Penzance Heliport enroute across the Celtic Sea to St. Mary’s Airport, Isles of Scilly. On board were a crew of 3 and 23 passengers. Visibility was poor due to fog. Flying under visual flight rules, the helicopter was at 250 feet (76 meters) while the pilots tried to maintain visual contact with the surface of the calm sea.

Because of the limited visual cues, the crew did not recognize that they were in a slight descent. At approximately 11:35 a.m., the Sikorsky slammed into the ocean at cruise speed. It sank almost immediately. Only six persons survived, including the pilots, Dominic Lawlor and Neil Charleton. The helicopter sank to the sea bed 200 feet (61 meters) below. It was later recovered by the salvage vessel RMAS Seaforth Clansman, along with the bodies of 17 victims.

The official investigation determined that the cause of the accident was pilot error by their failure to recognize and correct the unintentional descent while attempting to fly in conditions not suitable for visual flight. This was the worst helicopter accident in terms of fatalities up to that time.

The Sikorsky S-61N is a civil variant of the United States Navy HSS-2 Sea King. The first S-61N, s/n 61143, first flew 7 August 1962. It is a large twin-engine helicopter with a single main rotor/tail rotor configuration. The S-61N fuselage is 4 feet, 2 inches (1.270 meters) longer than that of the HSS-2. The S-61N is 72 feet, 7 inches (22.123 meters) long and 16 feet, 10 inches (5.131 meters) high, with rotors turning.

The main rotor has five blades and a diameter of 62 feet (18.898 meters). Each blade has a chord of 1 foot, 6.25 inches (0.464 meters). The tail rotor also has five blades and a diameter of 10 feet, 4 inches (3.149 meters). They each have a chord of 7–11/32 inches (0.187 meters). At 100% r.p.m., the main rotor turns 203 r.p.m. and the tail rotor, 1,244 r.p.m. The main rotor turns counter-clockwise, as seen from above. (The advancing blade is on the helicopter’s right side.) The tail rotor turns clockwise, as seen from the left side. (The advancing blade is below.)

G-BEON was powered by two General Electric CT58-140-1 turboshaft engines, each of which had maximum power rating of 1,400 shaft horsepower for takeoff and 1,500 SHP for 2½ minutes. The main transmission was rated for 2,300 horsepower, maximum.

The S-61 has a cruise speed of  166 miles per hour (267 kilometers per hour).  The service ceiling is 12,500 feet (3,810 meters). The maximum takeoff weight is 20,500 pounds (9,298.6 kilograms).

Between 1958 and 1980, Sikorsky built 794 S-61 series helicopters. 123 were S-61Ns.

© 2016, Bryan R. Swopes

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16 July 1969, 16:16:16 UTC, T + 02:44:16.2

This 1966 illustration depicts the J-2 engine of the S-IVB third stage firing to send the Apollo spacecraft to the Moon. (NASA)
This 1966 illustration depicts the J-2 engine of the S-IVB third stage firing to send the Apollo spacecraft to the Moon. (NASA)

16 July 1969: At 16:16:16 UTC, T+02:44:16.2, the Apollo 11 S-IVB third stage engine reignited for the Trans Lunar Injection maneuver.

One of the necessary features of the Rocketdyne J-2 engine was its ability to restart a second time. The third stage was first used to place the Apollo 11 spacecraft into Earth orbit and was then shutdown. When the mission was ready to proceed toward the Moon, the J-2 was re-started. Using liquid hydrogen and liquid oxygen for propellant, Apollo 11′s S-IVB burned for 5 minutes, 41.01 seconds, with the spacecraft reaching a maximum 1.45 Gs just before engine cut off. The engine was shut down at T+02:50:03.03. Trans Lunar Injection was at 16:22:13 UTC.

© 2015, Bryan R. Swopes

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16 July 1969, 13:34:42.30 UTC, T + 2:42.30

Apollo 11 S-1C first stage separation at 2 minutes, 41 seconds, altitude 42 miles, speed 6,164 mph, has burned 4,700,000 pounds of propellant. (NASA)
Apollo 11 S-1C first stage separation at 2 minutes, 41 seconds, altitude 42 miles (67.6 kilometers), speed 6,164 mph (9,920 kph), has burned 4,700,000 pounds (2,131,884 kilograms) of propellant. (NASA)

16 July 1969: At 13:34:42.30 UTC, 2 minutes, 42.30 seconds after launch, the S-IC first stage of the Apollo 11/Saturn V has burned out and is jettisoned. Apollo 11 has reached an altitude of 42 miles (68 kilometers) and a speed of 6,164 miles per hour (9,920 kilometers per hour). The five Rocketdyne F-1 engines have burned 4,700,000 pounds (2,132,000 kilograms) of liquid oxygen and RP-1 propellant.

After separation, the S-IC first stage continued upward on a ballistic trajectory to approximately 68 miles (109.4 kilometers) altitude, reaching its apex at T+4:29.1, then fell back to Earth. It landed in the Atlantic Ocean approximately 350 miles (563.3 kilometers) downrange.

© 2015, Bryan R. Swopes

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16 July 1969, 13:34:30 UTC, T + 2:30

Apollo 11 gains altitude while the first stage Rocketdyne F-1 engines increase thrust. (NASA)
Apollo 11 gains altitude while the first stage Rocketdyne F-1 engines increase thrust. (NASA)

16 July 1969: Apollo 11/Saturn V AS-506 accelerates with all five Rocketdyne F-1 engines burning. As the rocket climbs through thinner atmosphere, the engines become more efficient and the total thrust for the S-IC first stage increases from 7,648,000 pounds of thrust to 9,180,000 pounds of thrust at about T+1:23.0.

In order to limit acceleration, a pre-planned signal to cut off the center engine is sent at T+2:15.2 (Center Engine Cut-Off, “CECO”). As the first stage burns fuel at a rate of 13 tons per second, the rapidly deceasing weight of the Saturn V and the increasing efficiency of the F-1 engines could cause the limits of vehicle acceleration to be exceeded.

By T+2:30, the Saturn V has reached an altitude of 39 miles (62.8 kilometers) and is 55 miles (88.5 kilometers) downrange.

This photograph was taken by a 70mm telescopic camera aboard a USAF/Boeing EC-135N A/RIA (Apollo Range Instrumentation Aircraft) serial number 60-374. The airplane is in the collection of the National Museum of the United States Air Force.

© 2015, Bryan R. Swopes

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16 July 1969, 13:33:06 UTC, T + 1:06.3

Apollo 11 goes supersonic at T+1:06.3 (NASA)
Apollo 11 goes supersonic at T+1:06.3 (NASA)

16 July 1969:  At 1333 UTC (9:33 a.m. EDT) one minute, six seconds after liftoff, the Apollo 11/Saturn V reached Mach 1 at an altitude of 4 miles (6.4 kilometers). As it goes supersonic, condensation clouds, called “shock collars,” form around the S-II second stage.

© 2015, Bryan R. Swopes

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