27 March 1966

Test pilot Jack L. Zimmerman with the record-setting Hughes YOH-6A Light Observation Helicopter, 62-4213. (FAI)

27 March 1966: At Edwards Air Force Base in the high desert of southern California, Hughes Aircraft Company test pilot Jack Louis Zimmerman flew the third prototype YOH-6A Light Observation Helicopter, 62-4213, to set six Fédération Aéronautique Internationale (FAI) World Record for Altitude and Time-to-Climb. The records were set in two sub-classes, based on the helicopter’s take-off weight. Fifty-one years later, one of these records still stands.

Hughes YOH-6A 62-4213 at Edwards Air Force Base, 1966. (FAI)

Zimmerman took the YOH-6A from the surface to a height of 3,000 meters (9,843 feet) in 4 minutes, 1.5 seconds (FAI Record File Number 9922); and to 6,000 meters (19,685 feet) in 7 minutes, 12 seconds (FAI Record File Number 9923). The helicopter reached an altitude in level flight of 8,061 meters (26,447 feet). (FAI Record File Numbers 9920 and 9921). 9921 remains the current record for helicopters in Sub-Class E-1b, with a takeoff weight of 500–1,000 kilograms (1,102–2,205pounds).

Beginning with a takeoff weight between 1,000–1,750 kilograms (2,205–3,858 pounds) (Sub-Class E-1c), Zimmerman took the “loach” to a height 3,000 meters (9,843 feet) in 5 minutes, 37 seconds. (FAI Record File Number 771). The helicopter reached an altitude of 5,503 meters (16,578 feet), without payload. (FAI Record File Number 772)

[The field elevation of Edwards Air Force Base (EDW) is 2,210 feet (704 meters) above Sea Level. If the time-to-altitude flights had been made at nearby NAS Point Mugu (NTD) on the southern California coast, which has a field elevation 13 feet (4 meters), the times might have been significantly reduced. The air temperature at Edwards, though, was much colder.]

One day earlier, 26 March, Allison Engine Company test pilot Jack Schweibold flew the same YOH-6A  to set three Fédération Aéronautique Internationale (FAI) World Records for Distance Over a Closed Circuit Without Landing of 2,800.20 kilometers (1,739.96 miles).¹ One week earlier, 20 March, Jack Zimmerman had set a Fédération Aéronautique Internationale (FAI) World Record for Distance Over a Closed Circuit Without Landing of 1,700.12 kilometers (1,056.41 miles).² Fifty-one years later, these four World Records still stand.

The Hughes Model 369 was built in response to a U.S. Army requirement for a Light Observation Helicopter (“L.O.H.”). It was designated YOH-6A, and the first aircraft received U.S. Army serial number 62-4211. It competed with prototypes from Bell Helicopter Company (YOH-4) and Fairchild-Hiller (YOH-5). All three aircraft were powered by a lightweight Allison Engine Company turboshaft engine. The YOH-6A won the three-way competition and was ordered into production as the OH-6A Cayuse. It was nicknamed “loach,” an acronym for L.O.H.

The third prototype YOH-6A, 62-4213, testing the XM-7 twin M60 7.62 weapons system. (U.S. Army)

The YOH-6A was a two-place light helicopter, flown by a single pilot. It had a four-bladed, articulated main rotor which turned counter-clockwise, as seen from above. (The advancing blade is on the helicopter’s right.) Stacks of thin stainless steel “straps” fastened the rotor blades to the hub and were flexible enough to allow for flapping and feathering. Hydraulic dampers controlled lead-lag. Originally, there were blade cuffs around the main rotor blade roots in an attempt to reduce aerodynamic drag, but these were soon discarded. A two-bladed semi-rigid tail rotor was mounted on the left side of the tail boom. Seen from the left, the tail-rotor rotates counter-clockwise. (The advancing blade is above the axis of rotation.)

The YOH-6A was powered by a T63-A-5 turboshaft engine (Allison Model 250-C10) mounted behind the cabin at a 45° angle. The engine was rated at 212 shaft horsepower at 52,142 r.p.m. (102% N1) and 693 °C. turbine outlet temperature for maximum continuous power, and 250 shaft horsepower at 738 °C., 5-minute limit, for takeoff. Production OH-6A helicopters used the slightly more powerful T63-A-5A (250-C10A) engine.

The Hughes Tool Company Aircraft Division built 1,420 OH-6A Cayuse helicopters for the U.S. Army. The helicopter remains in production as AH-6C and MH-6 military helicopters, and the MD500E and MD530F civil aircraft.

Hughes YOH-6A 62-4213 is in the collection of the United States Army Aviation Museum, Fort Rucker, Alabama.

U.S. Army Hughes YOH-6A prototype 62-4213 at Le Bourget, circa 1965.

¹ FAI Record File Numbers 786, 787 and 11656.

² FAI Record File Number 762.

© 2017 Bryan R. Swopes

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27 March 1942

North American Aviation B-25B Mitchell 40-2291 at Eglin Field, Florida, March 1942. (U.S. Air Force)

27 March 1942: After three weeks of intensive training at Eglin Field, Florida, twenty-two North American Aviation B-25B Mitchell twin-engine medium bombers of the 34th Bombardment Squadron (Medium), 17th Bombardment Group (Medium), U.S. Army Air Force, under the command of Lieutenant Colonel James Harold Doolittle, completed a two-day, low-level, transcontinental flight, and arrived at the Sacramento Air Depot, McClellan Field, California, for final modifications, repairs and maintenance before an upcoming secret mission: The Halsey-Doolittle Raid.

The B-25 had made its first flight 19 October 1940 with test pilot Vance Breese and engineer Roy Ferren in the cockpit. It was a mid-wing airplane with twin vertical tails and retractable tricycle landing gear. The first 8–10 production airplanes were built with a constant dihedral wing. Testing at Wright Field showed that the airplane had a slight tendency to “Dutch roll” so all B-25s after those were built with a “cranked” wing, using diehdral for the inner wing and anhedral in the wing outboard of the engines. This gave it the bomber’s characteristic “gull wing” appearance. The two vertical stabilizers were also increased in size.

A 34th Bombardment Squadron B-25B Mitchell bomber at Mid-Continent Airlines, Minneapolis, Minnesota, for modifications, January–February 1942. (U.S. Air Force)

The B-25B Mitchell was operated by a crew of five: two pilots, a navigator, bombardier and radio operator/gunner.  It was 53 feet, 0 inch (16.154 meters) long with a wingspan of 67 feet, 7.7 inches (20.617 meters) and overall height of 15 feet, 9 inches (4.801 meters). The The B-25B had an empty weight of 20,000 pounds (9,072 kilograms) and the maximum gross weight was 28,460 pounds (12,909 kilograms).

The B-25B was powered by two air-cooled, supercharged, 2,603.737-cubic-inch-displacement (42.668 liter) Wright Aeronautical Division Cyclone 14 GR2600B665 (R-2600-9) two-row 14-cylinder radial engines with a compression ratio of 6.9:1. The engines had a Normal Power rating of 1,500 horsepower at 2,400 r.p.m., and 1,700 horsepower at 2,600 r.p.m. for takeoff, burning 100-octane gasoline. These engines (also commonly called “Twin Cyclone”) drove three-bladed Hamilton Standard Hydromatic variable-pitch propellers through 16:9 gear reduction. The R-2600-9 was 5 feet, 3.1 inches (1.603 meters) long and 4 feet, 6.26 inches (1.378 meters) in diameter. It weighed 1,980 pounds (898 kilograms).

“On a low level training mission early in 1942 B-25 40-2297 would be airplane number 14 for the Doolittle Raid on Tokyo — This image was taken before the modification to the troublesome ventral turret. Pilot Major J.A. Hilger, Co-Pilot 2nd Lt. Jack A. Sims, Navigator 2nd Lt. James H. Macie, Jr., Bombardier S/Sgt. Jacob Eierman, Engineer/Gunner S/Sgt. Edwin V. Bain” —HISTORYNET

The medium bomber had a maximum speed of 322 miles per hour (518 kilometers per hour) at 15,000 feet (4,572 meters) and a service ceiling of 30,000 feet (9,144 meters).

It could carry a 3,000 pound (1,361 kilograms) bomb load 2,000 miles (3,219 kilometers). Defensive armament consisted of a single Browning M2 .30-caliber machine gun mounted in the nose, two Browning M2 .50-caliber machine guns in a power dorsal turret, and two more .50s in a retractable ventral turret. (The lower turrets were removed from all of the Doolittle B-25s.)

North American Aviation, Inc., built 9,816 B-25s at Inglewood, California, and Kansas City, Kansas. 120 of these were B-25Bs.

North American Aviation B-25 Mitchell medium bombers being assembled at the Kansas City bomber plant, October 1942. (Alfred T. Palmer, Office of War Information)

© 2017, Bryan R. Swopes

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26 March 1967

Republic F-105D-6-RE Thunderchief 59-1772, parked in a revetment. Colonel Scott flew this airplane 26 March 1967 when he shot down a MiG-17. (U.S. Air Force)
Republic F-105D-6-RE Thunderchief 59-1772, parked in a revetment. Colonel Scott flew this airplane 26 March 1967 when he shot down a MiG 17. (U.S. Air Force)

26 March 1967: Colonel Robert Ray Scott, United States Air Force, commanding the 355th Tactical Fighter Wing, was leading 20 Republic F-105 Thunderchief fighter bombers from Takhli Royal Thai Air Force Base, Thailand, on an attack against an enemy military barracks near Hanoi, North Vietnam. Colonel Scott’s airplane was Republic F-105D-6-RE, serial number 59-1772, and his call sign was “Leech 01.” As he came off the target, he shot down an enemy Mikoyan-Gurevich MiG 17 fighter with the 20 mm M61A1 Vulcan cannon of his fighter bomber.

Colonel Robert R. Scott, U.S. Air Force
Colonel Robert R. Scott, U.S. Air Force

The third MiG-17 destroyed during the month was credited to the 355th TFW, Colonel Scott, who was leading an F-105 flight on a strike mission not far from Hoa Lac airfield on 26 March. His account follows:

“I had acquired the target and executed a dive-bomb run, while heading approximately 250°, altitude approximately 4,000 feet, I observed a MiG taking off from Hoa Loc airfield. I began a left turn to approximately 150° to follow the MiG for possible engagement. At this time I observed three more MiG-17s orbiting the airfield at approximately 3,000 feet, in single ship trail with 3,000 to 5,000 feet spacing. MiGs were silver with red star. I then concentrated my attention on the nearest MiG-17 and pressed the attack. As I closed in on the MiG it began turning to the right. I followed the MiG, turning inside, and began firing. I observed ordnance impacting on the left wing and pieces of material tearing off. At this time the MiG began a hard left-descending turn. I began to overshoot and pulled off high and to the right. The last time I saw the MiG it was extremely low, approximately 500 feet, and rolling nose down.”

Aces and Aerial Victories: The United States Air Force in Southeast Asia 1965–1973, by R. Frank Futrell, William H. Greenhalgh, Carl Grubb, Gerard E. Hasselwander, Robert F. Jakob and Charles A. Ravenstein, Office of Air Force History, Headquarters USAF, 1976, Chapter II at Page 45.

This former Egyptian Air Force Mikoyan-Gurevivch MiG-17F in the collection of the National Museum of the United States Air Force is painted in the colors of the Vietnam Peoples' Air Force. (U.S. Air Force)
This former Egyptian Air Force Mikoyan-Gurevivch MiG 17F in the collection of the National Museum of the United States Air Force is painted in the colors of the Vietnam Peoples’ Air Force. (U.S. Air Force)

The pilot of the MiG 17, Second Lieutenant Vũ Huy Lượng, 923rd Fighter Regiment, Vietnam Peoples’ Air Force, was killed.

As a Northrop P-61 Black Widow pilot with the 426th Night Fighter Squadron during World War II, Colonel Scott had shot down two enemy airplanes. By destroying the MiG-17, he became only the second U.S. Air Force pilot, after Colonel Robin Olds, to achieve aerial victories during World War II and the Vietnam War.

Mikoyan Gurevich MiG-17F in Vietnam Peoples' Air Force markings at the National Museum of the United States Air Force, Wright-Patterson Air Force Base, Ohio. (U.S. Air Force).
Mikoyan-Gurevich MiG 17F in Vietnam Peoples’ Air Force markings at NMUSAF, Wright-Patterson AFB. (U.S. Air Force).

Robert Ray Scott was born at Des Moines, Iowa, 1 November 1920. He was the first of two children of Ray Scott, a railroad worker, and Elva M. Scott. He graduated from North High School in Des Moines, January 1939. He studied aeronautical engineering at the University of Iowa for two years before he enlisted as an Aviation Cadet in the U.S. Army Air Corps, 15 August 1941. Scott was 5 feet, 7 inches (1.70 meters) tall and weighed 144 pounds (65.3 kilograms). He was trained as a pilot and and was commissioned as a Second Lieutenant, 16 March 1942. He was assigned as an instructor pilot in California, and was promoted to 1st Lieutenant 15 December 1942.

Scott was transferred to the 426th Night Fighter Squadron, 14th Air Force, flying the Northrop P-61 Black Widow in India and China. He was promoted to captain, 3 May 1944, and to major, 16 August 1945. Major Scott was credited with shooting down two enemy aircraft. He was awarded the Distinguished Flying Cross and the Air Medal.

Captain Robert Ray Scott (back row, second from left) with the 426th Night Fighter Squadron, 1944. The airplane is a Northrop P-61 Black Widow. (U.S. Air Force)

Following World War II, Major Scott returned to the University of Iowa to complete his bachelor’s degree. He also earned two master’s degrees.

In 1952 he graduated from the Air Force test pilot school at Edwards Air Force Base, then served as a project pilot on the North American F-86D all-weather interceptor. Later he was a project officer at Edwards AFB on the Republic F-105 Thunderchief Mach 2 fighter-bomber.

Scott flew the North American Aviation F-86F Sabre during the Korean War. From January to July 1953, he flew 117 combat missions. From 1953 to 1956, Lieutenant Colonel Scott commanded the 405th Fighter Bomber Wing, Tactical Air Command, at Langley Air Force base, Virginia.

Lieutenant Richard Hill and Lieutenant Colonel Robert R. Scott (in cockpit) after their record-breaking transcontinental flight. (Unattributed)

On 9 October 1955, Scott set a transcontinental speed record by flying a Republic F-84F Thunderstreak fighter bomber from Los Angeles International Airport, California, to Floyd Bennett Field, New York, in 3 hours, 46 minutes, 33.6 seconds. Later he was a project officer at Edwards AFB on the Republic F-105 Thunderchief Mach 2 fighter-bomber.

Scott was promoted the rank of Colonel in 1960.

During the Vietnam War, Colonel Scott commanded the 355th Tactical Fighter Wing, flying 134 combat missions in the Republic F-105 Thunderchief.

Colonel Scott’s final commanding was the 832nd Air Division, 12th Air Force, at Cannon Air Force Base, New Mexico. He retired 1 September 1970 after 29 years of military service.

Colonel Robert Ray Scott flew 305 combat missions in three wars. During his Air Force career, Colonel Scott was awarded four Silver Star medals, three Legion of Merit medals, six Distinguished Flying Crosses and 16 Air Medals. He died at Tehachapi, California, 3 October 2006 at the age of 86 years. He is buried at the Arlington National Cemetery.

Republic F-105D 59-1772 is credited with another air-to-air victory. Just over a month after Colonel Scott’s Mig-17 shoot-down, on 28 April 1967 Major Harry E. Higgins, 357th Tactical Fighter Squadron, shot down another MiG-17 with the fighter bomber’s cannon, for which Major Higgins was awarded the Silver Star.

The Thunderchief, though, met its own end when it was shot down by 37 mm anti-aircraft gunfire 10 miles (16 kilometers) west of Ko Hinh, Laos, 27 January 1970. The pilot was rescued.

Colonel Robert R. Scott, commander, 355th Tactical Fighter Wing, checks the bombs loaded on a multiple ejector rack while preflighting his Republic F-105 Thunderchief. (U.S. Air Force)
Colonel Robert R. Scott, commander, 355th Tactical Fighter Wing, checks the bombs loaded on a multiple ejector rack while preflighting his Republic F-105 Thunderchief. (U.S. Air Force)

Republic Aviation Corporation built 833 F-105 Thunderchief fighter bombers at its Farmingdale, New York factory. 610 of those were single-seat F-105Ds. The F-105D Thunderchief is 64 feet, 3 inches (19.583 meters) long with a wingspan of 34 feet, 11 inches (10.643 meters) and overall height of 19 feet, 8 inches (5.994 meters). It has an empty weight of 27,500 pounds (12,473.79 kilograms) and a maximum takeoff weight of 52,546 pounds (23,834.47 kilograms).

The Thunderchief  was powered by one Pratt & Whitney J75-P-19W engine. The J75 is a two-spool axial-flow afterburning turbojet with water injection. It has a 15-stage compressor section (8 low- and and 7 high-pressure stages) and 3-stage turbine section (1 high- and 2 low-pressure stages.) The J75-P-19W is rated at 17,200 pounds of thrust (76.51 kilonewtons), and 26,500 pounds (117.88 kilonewtons) with afterburner. It is 20 feet (6.1 meters) long, 3 feet, 7.0 inches (1.092 meters) in diameter, and weighs 5,960 pounds (2,703 kilograms).

The maximum speed of the F-105D is 836 miles per hour (1,345 kilometers per hour) at Sea level and 1,420 miles per hour (2,285 kilometers per hour) at 38,000 feet (11,582 meters). The combat ceiling is 48,500 feet (14,783 meters) and combat range is 778 miles (1,252 kilometers).

The F-105D is armed with one 20 mm M61A1 Vulcan rotary cannon and 1,028 rounds of ammunition. It has an internal bomb bay and can carry bombs, missiles or fuel tanks on under wing and centerline hardpoints. The maximum bomb load consisted of 16 750-pound (340 kilogram) bombs.

The F-105 Thunderchief was a supersonic tactical fighter bomber rather than an air superiority fighter. Still, during the Vietnam War, F-105s shot down 27 enemy MiG fighters. 24 of those were shot down with the Thunderchief’s Vulcan cannon.

Of the 833 F-105s, 395 were lost during the Vietnam War. 334 were shot down, mostly by antiaircraft guns or missiles, and 17 by enemy fighters. Another 61 were lost due to accidents. The 40% combat loss is indicative of the extreme danger of the missions these airplanes were engaged in.

This Republic F-105D-10-RE Thunderchief, 60-0504, served with the 355th TFW at Takhli AB, Thailand. It shot down two enemy fighters. Similar the the F-105D flown by Colonel Scott, 26 March 1967, it is in the collection of the National Museum of the United States Air Force, Wright-Patterson AFB, Ohio. (U.S. Air Force)
This Republic F-105D-10-RE Thunderchief, 60-0504, served with the 355th TFW at Takhli AB, Thailand. It shot down two enemy fighters. Similar the the F-105D flown by Colonel Scott, 26 March 1967, it is in the collection of the National Museum of the United States Air Force, Wright-Patterson AFB, Ohio. (U.S. Air Force)

© 2016, Bryan R. Swopes

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26 March 1966

Allison Engine Co. test pilot Jack l. Schweibold with teh record-setting prototype Hughes YOH-6A, 62-4213, at Edwards Air Force Base, California, 1966. (FAI)
Allison Engine Co. test pilot Jack Schweibold with the record-setting number three prototype Hughes YOH-6A Light Observation Helicopter, 62-4213, at Edwards Air Force Base, California, 1966. (FAI)

26 March 1926: Allison Engine Company test pilot Jack Schweibold flew the third prototype Hughes Aircraft Company YOH-6A Light Observation Helicopter, 62-4213, to set three Fédération Aéronautique Internationale (FAI) World Records for Distance Over a Closed Circuit Without Landing of 2,800.20 kilometers (1,739.96 miles), including an Absolute Record for Class E (Rotorcraft).¹ These records still stand.

Hughes YOH-6A 62-4213 at Edwards Air Force Base, 1966. (FAI)
Hughes YOH-6A 62-4213 at Edwards Air Force Base, 1966. (FAI)

One week earlier, 20 March 1966, Hughes Aircraft Company test pilot Jack L. Zimmerman flew the same helicopter to set another distance record of of 1,700.12 kilometers (1,056.41 miles).² One 27 March, Zimmerman would set six more world records with 62-4213.³

Jack Schweibold wrote about the record flight in his autobiography, In the Safety of His Wings (Holy Fire Publishing, DeLand, Florida, 2005). He was one of a group of military and civilian test pilots selected to attempt a series of world record flights, using the number three prototype Hughes YOH-6A, 62-4213, from 20 March to 7 April 1966.

The record attempt began at midnight to take advantage of the cold desert air. The cold-soaked YOH-6A had been fueled with pre-cooled JP-5 in order to get the maximum amount of fuel on board. In addition to the standard fuel tank, two auxiliary tanks were placed in the cabin. The helicopter was so heavy from the overload that it could not hover. Jack made a running take-off, sliding the skids across the concrete until the increasing translational lift allowed the aircraft to break free. He began a very shallow climb.

Schweibold was flying a 60 kilometer (37.28 miles) closed course, but because of the near total darkness, he flew on instruments and was guided from the ground by Air Force test range radar controllers (Spatial Positioning and Orientation Radar Tracking, call sign SPORT). Accuracy was critical. The attempt would be disqualified if the helicopter cut inside of a pylon—which Jack could not see—but if he flew too far outside, the extra distance flown would not be counted and time would be lost. The maximum range would be controlled by the amount of fuel carried in the three tanks, and by the endurance of the pilot.

Throughout the flight, Jack gradually increased the altitude, as the T-63-A-5 turboshaft would be more efficient in thinner, colder air. He was flying a precisely calculated profile, taking into consideration aerodynamic drag, the efficiency of the helicopter’s rotor system, and the performance characteristics of the engine. He had been airborne for four hours before he climbed through 10,000 feet (3,048 meters).

At 14,000 feet (4,267 meters), Schweibold was on oxygen. He continued through 20,000 feet (6,096 meters) but was having trouble staying alert. (It would later be discovered that there was a malfunction in his oxygen mask.)

On the final lap, at 22,000 feet (6,706 meters) Jack had to fly around a towering cumulus cloud and radar contact was lost. He dived to lose altitude and popped out from under the cloud about a half-mile short of the runway.

When he shut down the engine, Jack Schweibold had flown the prototype YOH-6A 2800.20 kilometers (1,739.96 statute miles), non-stop. His record still stands.

Jack set 30 FAI World Records between 1966 and 1986. 26 of these remain current.

Frederick Jack Schweibold was born at Toledo, Ohio, 8 November 1935, the son of Henry E. and Jeanette Schweibold. He attended Ohio State University and majored engineering. He had enlisted in the United States Navy Reserve in 1952 and the joined the United States Air Force in 1954 as an Aviation Cadet. Schweibold went through pilot training at Randolph Air Force Base, San Antonio, Texas, flying the T-34 and T-28. He went on to train in the B-25 at Reese Air Force Base, Lubbock, Texas. Schweibold was commissioned as a second lieutenant and received his pilot’s wings in July 1957. In  momentary decision, he selected helicopter training.

Lieutenant Schweibold flew the Sikorsky H-19B for the Air Rescue Service, assigned to Oxnard Air Force Base, California. (The airfield is now Camarillo Airport, CMA, where I first soloed, and is about ten miles away from my desk.)

After leaving the Air Force, Jack flew Sikorsky S-55s for Chicago Helicopter Service, then Bell 47s for Butler Aviation. In 1960, he was hired by the Allison Division of General Motors as a test pilot and engineer for the new 250-series turboshaft engine.

I had the good fortune to have known Jack Schweibold. I first met him through his involvement in the Helicopter Association International biennial flight instructor recertification seminars, held during the HAI’s annual convention. He kept the seminar classes on track, and in between, was always available for questions. He was the authority on Allison’s 250-series turboshaft engines, and over the years I often called him for technical information and operational advice. On top of that, Jack Schweibold was just an all-around nice guy.

U.S. Army Hughes YOH-6A prototype 62-4213 at Le Bourget, circa 1965.
U.S. Army Hughes YOH-6A prototype 62-4213 at Le Bourget, circa 1965. (R.A. Scholefield Collection)

The Hughes Model 369 was built in response to a U.S. Army requirement for a Light Observation Helicopter (“L.O.H.”). It was designated YOH-6A, and the first aircraft received U.S. Army serial number 62-4211. It competed with prototypes from Bell Helicopter Company (YOH-4) and Fairchild-Hiller (YOH-5). All three aircraft were powered by a lightweight Allison Engine Company turboshaft engine. The YOH-6A won the three-way competition and was ordered into production as the OH-6A Cayuse. It was nicknamed “loach,” an acronym for L.O.H.

The YOH-6A was a two-place light helicopter, flown by a single pilot. It had a four-bladed, articulated main rotor which turned counter-clockwise, as seen from above. (The advancing blade is on the helicopter’s right.) Stacks of thin stainless steel “straps” fastened the rotor blades to the mast and also allowed for flapping and feathering. Hydraulic dampers controlled lead-lag. Originally, there were blade cuffs around the main rotor blade roots in an attempt to reduce aerodynamic drag, but these were soon discarded. A two-bladed semi-rigid tail rotor was mounted on the left side of the tail boom. Seen from the left, the tail-rotor rotates counter-clockwise. (The advancing blade is on top.)

Overhead photograph of a Hughes YOH-6. Note the blade cuffs. (U.S. Army)
Overhead photograph of a Hughes YOH-6A. Note the blade cuffs. (U.S. Army)

The YOH-6A was powered by a T63-A-5 turboshaft engine (Allison Model 250-C10) mounted behind the cabin at a 45° angle. The engine was rated at 212 shaft horsepower at 52,142 r.p.m. (102% N1) and 693 °C. turbine outlet temperature for maximum continuous power, and 250 shaft horsepower at 738 °C., 5-minute limit, for takeoff. Production OH-6A helicopters used the slightly more powerful T63-A-5A (250-C10A) engine.

The Hughes Tool Company Aircraft Division built 1,420 OH-6A Cayuse helicopters for the U.S. Army.  The helicopter remains in production as AH-6C and MH-6 military helicopters, and the MD500E and MD530F civil aircraft.

Hughes YOH-6A 62-4213 is in the collection of the United States Army Aviation Museum, Fort Rucker, Alabama.

The third prototype YOH-6A, 62-4213, testing the XM-7 twin M60 7.62 weapons system. (U.S. Army)
The third prototype YOH-6A, 62-4213, testing the XM-7 twin M60 7.62 weapons system. (U.S. Army)

¹ FAI Record File Numbers 786, 787 and 11656

² FAI Record File Number 762

³ FAI Record File Numbers 771, 772, 9920, 9921, 9922, and 9923

© 2017, Bryan R. Swopes

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26 March 1955

Pan American World Airways' Boeing 377-10-26 Stratocruiser serial number 15932, N1032V.
Clipper Unites States, Pan American World Airways’ Boeing 377-10-26 Stratocruiser serial number 15932, N1032V. (Unattributed)

26 March 1955: At 8:15 a.m., Pan Am Flight 845/26, a Boeing 377 Stratocruiser, N1032V, named Clipper United States, departed Seattle-Tacoma Airport (SEA, or “SeaTac”) on a flight to Sydney, Australia, with an intermediate stop at Portland, Oregon and Honolulu, Hawaii. The airliner departed Portland (PDX) at 10:21 a.m., with a crew of 8 and 15 passengers on board.

Captain Herman S. Joslyn was in command, with First Officer Angus Gustavus Hendrick, Jr., Second Officer Michael F. Kerwick, Flight Engineer Donald Read Fowler and Assistant Flight Engineer Stuart Bachman. The cabin crew were Purser Natalie R. Parker, Stewardess Elizabeth M. Thompson, and Steward James D. Peppin.

Clipper United States was cruising at 10,000 feet (3,048 meters) when a severe vibration began, lasting 5–8 seconds. The Number 3 engine (inboard, right) was violently torn off of the starboard wing. The damage to the airplane resulted in severe buffeting. The nose pitched down and airspeed increased. Captain Joslyn reduced engine power to limit airspeed. The Stratocruiser quickly lost 5,000 feet (1,524 meters). Because of damage to the engines’ electrical system, the flight engineer was not able to increase power on the remaining three engines. The Boeing 377 was too heavy at this early stage in the flight to maintain its altitude.

At 11:12 a.m. (19:12 UTC) the flight crew ditched the Stratocruiser into the north Pacific Ocean. approximately 35 miles (56 kilometers) west of the Oregon coastline. [N. 43° 48′ 15″, W. 125° 12′ 40″] The conditions were ideal for ditching, but the impact was hard. Seats were torn loose, and several occupants were injured. Evacuation began and all three life rafts were inflated. The water temperature was 47 °F. (8.3  °C.).

Screen Shot 2016-03-26 at 22.15.47
Miss Natalie R. Parker (Medford Mail Tribune)

The Stratocruiser floated for about 20 minutes before sinking. Of the 23 persons on board, four, passengers John Peterson, David Darrow,  First Officer Hendrick, and Flight Engineer Fowler, died of injuries and exposure.

The actions of one of Flight 845/26’s crewmembers was particularly mentioned in the Civil Aeronautics Board accident investigation report:

“The purser, a woman, [Natalie R. Parker¹] although suffering from shock swam and towed the only seriously injured passenger to the nearest raft, some 200 feet [61 meters] distant.”

—Civil Aeronautics Board Accident Investigation Report SA-304 File No. 1-0039, 15 November 1955, History of the Flight

A North American Aviation F-86F Sabre flown by Captain W. L. Parks, 142nd Fighter Interceptor Group, Oregon Air National Guard, located the scene of the ditching and observed smoke flares which led to two life rafts tied together. A Lockheed Constellation was also inbound to the scene from the south. After confirming that Air Force rescue aircraft were on the way, Captain Parks returned to Portland, very low on fuel.

The survivors were rescued after two hours by the crew of USS Bayfield (APA-33), a U.S. Navy attack transport.

The U.S. Navy attack transport USS Bayfield (APA-33) during the rescue of the survivors of Pan Am Flight 845/26, 26 March 1955. A civilian tanker stands by to assist. Two of the airliner's life rafts are visible at the right edge of this photograph. One is at the end of the smoke trail crossing the center of the image. The other is a bright object at the right lower corner. (U.S. Navy)
The U.S. Navy attack transport USS Bayfield (APA-33) during the rescue of the survivors of Pan Am Flight 845/26, 26 March 1955. A Standard Oil Co. tanker, SS Idaho Falls, stands by to assist. Two of the airliner’s life rafts are visible at the right edge of this photograph. One is at the end of the smoke trail crossing the center of the image. The other is a bright object at the right lower corner. (U.S. Coast Guard)

During the Civil Aeronautics Board hearings into the accident, Vice Chairman Joseph P. Adams commended the flight’s purser, Miss Parker:

“. . . all of us feel inspired that a fellow citizen, or just a fellow human being, can rise to such an occasion in the manner in which you did. It is most commendable, Miss Parker.”

—Civil Aeronautics Board Accident Investigation Report SA-304 File No. 1-0039, 15 November 1955, Footnote 3

Because the engine and propeller were not recovered, the exact nature of the failure could not be determined, but the most likely cause was considered to be a fracture of a propeller blade resulting in a severely unbalanced condition, followed by the violent separation of the engine from the wing. This was the fifth time that a Boeing 377 Stratocruiser had lost an engine following the failure of a hollow-steel Hamilton Standard 2J17 propeller blade.

When the flight engineer attempted to increase the propeller r.p.m. on the three engines simultaneously, an electrical overload occurred which opened the master circuit breaker. This prevented any power increase.

Clipper United States was a Boeing Model 377-10-26, serial number 15932, registered N1032V. It was one of twenty of a specific variant built for Pan American World Airways. The airliner had been delivered to Pan Am on 21 May 1949. At the time of its loss, it had flown a total of 13,655 hours.

A color photograph of a Pan American World Airways Boeing 377 Stratocruiser in flight. (Pan Am)
A color photograph of a Pan American World Airways Boeing 377 Stratocruiser in flight. (Pan Am)

The Model 377 was a large, four-engine civil transport which had been developed, along with the military C-97 Stratofreighter, from the World War II B-29 Superfortress long-range heavy bomber. It utilized the wings and engines of the improved B-50 Superfortress. The airplane was operated by a flight crew of four. It was a double-deck aircraft, with the flight deck, passenger cabin and galley on the upper deck and a lounge and cargo compartments on the lower. The airliner was pressurized and could maintain Sea Level atmospheric pressure while flying at 15,500 feet (4,724 meters). The Model 377 could be configured to carry up to 100 passengers, or 28 in sleeping births.

The Stratocruiser was 110 feet, 4 inches (33.630 meters) long with a wingspan of 141 feet, 3 inches (43.053 meters) and overall height of 38 feet, 3 inches (11.659 meters). The airliner had an empty weight of 83,500 pounds (37,875 kilograms) and the maximum takeoff weight was 148,000 pounds (67,132 kilograms).

N1032V was powered by four air-cooled, supercharged, 4,362.49-cubic-inch-displacement (71.488 liter) Pratt & Whitney Wasp Major B6 engines. These were four-row, 28-cylinder, radial engines with a compression ratio of 6.7:1. The B6 had a Normal Power rating of 2,650 horsepower at 2,550 r.p.m., at 5,500 feet (1,676 meters), and Maximum Continuous Power rating of 2,800 horsepower at 2,550 r.p.m. at 3,500 feet (1,067 meters). The Takeoff Power rating was 3,500 horsepower at 2,700 r.p.m. with water/alcohol injection.² The engines drove four-bladed Hamilton Standard Hydromatic 24260 constant-speed propellers with a diameter of 17 feet (5.182 meters) through a 0.375:1 gear reduction. The Wasp Major B6 was 4 feet, 7.00 inches (1.397 meters) in diameter and 8 feet, 0.50 inches (2.451 meters) long. It weighed 3,584 pounds (1,626 kilograms), dry. The propeller assembly weighed 761 pounds (345 kilograms).

Clipper America, a Pan American World Airways Boeing Model 377 Stratocruiser. (Boeing)
Clipper America, a Pan American World Airways Boeing Model 377 Stratocruiser. (Boeing)

The 377 had a cruise speed of 301 miles per hour (484 kilometers per hour) and a maximum speed of 375 miles per hour (604 kilometers per hour). During testing by Boeing, a 377 reached 409 miles per hour (658 kilometers per hour). Its service ceiling was 32,000 feet (9,754 meters) and the range was 4,200 miles (6,759 kilometers).

Boeing built 56 Model 377 Stratocruisers, with Pan American as the primary user, and another 888 military C-97 Stratofreighter and KC-97 Stratotankers.

 

¹ Miss Natalie R. Parker was born 2 June 1925, the first child of Carold J. Parker, a potato chip manufacturer, and Ruth A. Parker, of Portland, Oregon. She was a 1944 graduate of Medford High School, and she then attended Reed College at Portland.

Miss Parker enlisted in the United States Cadet Nurse Corps, U.S. Public Health Service, in 1945 and trained as a nurse at the Johns Hopkins Hospital School of Nursing, Baltimore, Maryland, graduating 13 June 1948.

She joined Pan American World Airways in 1951.

 

² During a demonstration of the Pratt & Whitney Wasp Major engine (military designation, R-4360) a regular production engine was taken from the assembly line and run for 22 continuous hours at 4,400 horsepower, then checked and run for another hour at 4,850 horsepower. It was then run for 100 hours at 3,000 horsepower, and 50 hours at 3,500 horsepower. When the engine was disassembled for inspection., it remained in serviceable condition.

© 2017, Bryan R. Swopes

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