Tag Archives: Helicopter

6–7 May 1943

Colonel Frank Gregory lands the Vought-Sikorsky XR-4, 41-18864, aboard SS Bunker Hill, 6-7 May 1943. (Sikorsky Historical Archives)
Colonel Frank Gregory lands the Vought-Sikorsky XR-4, 41-18874, aboard SS Bunker Hill, 6-7 May 1943. (Sikorsky Historical Archives)

6–7 May 1943: To determine the feasibility of operating helicopters from the decks of merchant ships for antisubmarine patrols, Colonel Hollingsworth Franklin (“Frank”) Gregory, U.S. Army Air Corps, made 23 landings and takeoffs from the tanker SS Bunker Hill in Long Island Sound, flying the Army’s Vought-Sikorsky XR-4, 41-18874.

According to an official U.S. Coast Guard history of the tests,

The tanker BUNKER HILL was made available for the tests and a deck 78 feet [23.8 meters] long, with obstructions at both ends, was put in place. An eight foot [2.4 meters] bullseye in the center of a square was painted in the middle of the platform. Colonel Frank Gregory arrived on 6 May to fly the Army XR-4 provided for the tests. The entire helicopter project rested on the XR-4’s ability to land on a ship. Gregory was concerned at first. His “shipboard” experience was limited to a 20 foot [6.1 meters] platform at Wright Field. He immediately set about getting “additional experience.” Gregory noted with reference to his first attempt:

Igor Sikorsky and Colonel Frank Gregory with the Vought-Sikorsky XR-4. (Sikorsky Historical Archives)
Igor Sikorsky and Colonel Frank Gregory with the Vought-Sikorsky XR-4. (Sikorsky Historical Archives)

“The space on the deck looked even smaller—it didn’t look like the helicopter would fit. The cabin superstructure towered up like a two story building, and the people on it had that “it can’t be done” look on their faces—yet the big white bullseye stuck out like a target—the XR-4 came true to the white marker as though being pulled by a powerful magnet, and a minute later the floats touched the deck.”

He continued to practice landings and takeoffs that afternoon with the ship at anchor, then underway at five, seven and one-half, ten and fifteen knots. As the speed increased the landings became more difficult because of increased turbulence over the superstructure but the helicopter proved to be completely controllable.

The next morning guests were ferried out to the BUNKER HILL . . . A total of 97 names were on the guest list. Gregory put on an impressive and flawless performance as the ship cruised at various speeds up to 15 knots and on various headings with relation to the wind which was blowing at 12 knots. . . .

—”The Helicopter as an Anti-Submarine Weapon,” A History of Coast Guard Aviation, The Growth Years (1939–1956).

SS Bunker Hill, a Type T2 tanker, with a tugboat alongside. (Unattributed)
SS Bunker Hill, a Type T-2 tanker, with a tugboat alongside. (Unattributed)

SS Bunker Hill was a 10,590 gross ton Type T-2 tanker owned by the Keystone Tankship Corporation. It was  504 feet (153.6 meters) long, with a beam of 68.2 feet (20.8 meters) and drawing 39.2 feet (12 meters). Its engine developed 7,000 horsepower.

On 6 March 1964, Bunker Hill was enroute from Tacoma to Anacortes, Washington when it suffered a vapor explosion in the Number 9 cargo tank which broke the ship in half. It sank in Rosario Strait in less than one hour. Five members of the crew of thirty-one, including the captain, chief mate, third mate, quartermaster and steward, were lost.

The Vought-Sikorsky VS-316A (which was designated XR-4 by the U.S. Army Air Corps and assigned serial number 41-18874), established the single main rotor/anti-torque tail rotor configuration. It was a two-place helicopter with side-by-side seating and dual flight controls. The fabric-covered three-blade main rotor was 38 feet (11.582 meters) in diameter and turned counter-clockwise as seen from above. (The advancing blade is on the helicopter’s right). The three-blade tail rotor was mounted to the right of the tail boom in a tractor configuration, and rotated clockwise when seen from the helicopter’s left side. (The advancing blade was below the axis of rotation.)

The XR-4 was 33 feet, 11.5 inches (10.351 meters) long and 12 feet, 5 inches (3.785 meters) high. It weighed 2,010 pounds (911.7 kilograms) empty and the maximum gross weight was 2,540 pounds (1,152.1 kilograms).

The VS-316A had originally been powered by a 499.8-cubic-inch-displacement (8.19 liter) air-cooled Warner Scarab SS-50 (R-500-1) seven-cylinder radial engine, rated at 145 horsepower at 2,050 r.p.m. In the XR-4 configuration, the engine was upgraded to an air-cooled, direct-drive 555.298-cubic-inch-displacement (9.100 liter) Warner Super Scarab SS185 (R-550-3) seven-cylinder radial engine with a compression ration of 6.20:1. The R-550-3 was rated at 185 horsepower at 2,175 r.p.m. at Sea Level, and 200 horsepower at 2,475 r.p.m (five minute limit) for takeoff. The engine was placed backwards in the aircraft with the propeller shaft driving a short driveshaft through a clutch to a 90° gear box and the transmission. The R-550-3 weighed 344 pounds (156 kilograms).

The XR-4 was redesignated XR-4C. This would be the world’s first production helicopter. It is at the Steven F. Udvar-Hazy Center of the Smithsonian National Air and Space Museum.

Vought-Sikorsky XR-4 41-18874 during shipboard testing, June 1943. (Sikorsky Historical Archives)
Vought-Sikorsky XR-4 41-18874 during shipboard testing, June 1943. (Sikorsky Historical Archives)

© 2019, Bryan R. Swopes

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6 May 1941

Igor Sikorsky with his VS-300A, Stratford, Connecticut, 6 May 1941. (Sikorsky Archives)

6 May 1941: At Stratford, Connecticut, Igor Sikorsky piloted his Vought-Sikorsky VS-300 helicopter to a new world’s record for endurance. He flew for 1 hour, 32 minutes, 26 seconds. ¹ The previous record—1 hour, 20 minutes, 49 seconds—had been set by Ewald Rohlfs with the Focke-Wulf Fw 61 tandem-rotor helicopter, 25 June 1937. ²

During its development, the VS-300 went through at least 18 changes in its rotor configuration. This photograph, taken after the record-setting flight, shows an intermediate version, with one main rotor for lift and three auxiliary rotors for anti-torque and directional control.

Igor Ivanovich Sikorsky 1888–1970. Sikorsky Archives)

In the final configuration, Sikorsky arrived at what we now recognize as a helicopter, with the main rotor providing lift, thrust and roll control through variable collective and cyclic pitch, and a single tail rotor for anti-torque and yaw control.

The VS-300 had a welded tubular steel airframe and used a 28-foot (5.34 meters) diameter, fully-articulated, three-bladed main rotor, which turned clockwise (as seen from above) at 260 r.p.m. (The advancing blade was on the left. This would later be reversed.) The main rotor had collective pitch control for vertical control, but cyclic pitch (Sikorsky referred to this as “sectional control”) for directional control would not be developed for another several months.

The tail “propellers” (what we now consider to be rotors—one vertical and two horizontal) each had two blades with a diameter of 7 feet, 8 inches (2.337 meters) and turned approximately 1,300 r.p.m. The vertical rotor provided “torque compensation” (anti-torque) and the blade pitch was fully reversible. The horizontal rotors were mounted on 10-foot (3.048 meters) outriggers at the aft end of the fuselage. For lateral control, the pitch on one rotor was increased and the other decreased. For longitudinal control, the pitch of both rotors was increased or decreased together.

The VS-300 was originally equipped with an air-cooled, normally-aspirated 144.489-cubic-inch-displacement (2.368 liter) Lycoming O-145C-3 four-cylinder horizontally-opposed engine which was rated at 75 horsepower at 3,100 r.p.m. According to Mr. Sikorsky, “early in 1941,” the Lycoming engine was replaced by an air-cooled, normally-aspirated 198.608 cubic inch (3.255 liter) Franklin 4AC-199-E, a four-cylinder horizontally-opposed overhead valve (OHV) direct-drive engine with a compression ratio of 7:1, rated at 90 horsepower at 2,500 r.p.m. It is not known if this change was made prior to 6 May.

¹ During World War II, only a very few ballooning and gliding world records were certified by the Fédération Aéronautique Internationale. Although Sikorsky’s flight duration exceeded that of Rohlfs, it is not listed as an official world record.

² FAI Record File Number 13147

© 2019, Bryan R. Swopes

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4 May 1924

Étienne Edmond Oehmichen, France, 1924
Étienne Edmond Oehmichen, France, 1924

4 May 1924: At 7:30 a.m., Étienne Edmond Oehmichen (1884–1955), an engineer for Société Anonyme des Automobiles et Cycles Peugeot, flew his four-rotor L’Hélicoptère Nº2 around a triangular closed circuit of approximately 1 kilometer (0.62 mile) at Valentigney, France. The flight took 7 minutes, 40 seconds. It was observed by the public, members of the press and officials of the Service Technique de l’ Aéronautique (S.T.Aé, the French air ministry). For his accomplishment, Oehmichen was awarded a prize of ₣90,000 by the government of France.

FLIGHT reported:

A Fresh Helicopter Record

     M. Oemichen has been continuing his experiments at Valentigny with his helicopter, and on Sunday, May 4, established a record for helicopters by accomplished a flight of more than one kilometre—1,100 yards—in a closed circuit. The flight lasted 7 mins. 40 secs. and during most of the time the machine maintained a height of about 3 feet, but sometimes rose to 10 feet. The flight was officially observed by a representative of the Department of Military Aeronautics. By this performance M. Oemichen wins an award of 90,000 francs given by the French Government.

FLIGHT, The Aircraft Engineer & Airships, No. 802 (No. 19, Vol. XVI.) May 8, 1924, Page 267, Column 1

Helicopter No. 2
Oehmichen’s helicopter. (Collection Phillipe Boulay)

The previous month, Oehmichen had set two FAI world rotorcraft records for distance in a straight line. On 14 April 1924, he flew 360 meters (1,181 feet)¹, and on 17 April, 525 meters (1,722 feet).²

On 14 September 1924, he would set two records for altitude, 1 meter (3.28 feet) with a 100 kilogram (220 pounds) and a 200 kilogram (441 pounds) payload.³

L'hélicoptère No. 2
One of the configurations of Oemichen’s helicopter.

Oehmichen’s helicopter (also referred to by some sources as the Peugeot Nº2) was a cross-shaped structure built of metal tubing. Lift was generated by four two-bladed, counter-rotating, main rotors. Two rotors had a diameter of 6.5 meters (21 feet, 4 inches), and the other two, 7.5 meters (24 feet, 7 inches). They all turned at 145 r.p.m. Blade pitch was controlled by warping.

The helicopter had another five rotors positioned in the horizontal plane. Three had a diameter of 1.45 meters (4 feet, 9 inches), and two, 1.55 meters (5 feet, 1 inch). These had reversible pitch were used to provide lateral control. Two variable-pitch pusher propellers with a diameter of 1.40 meters (4 feet, 7 inches) were positioned on each side of the lateral structure, and were driven by belts. The helicopter was steered by another small rotor at the front.

“Ensemble perspectif sçhématique des sustentateurs, propulseurs et évoluers de l’hélicoptère Oemichen-Peogeot Nº 2.”  (L’Aéronautique, 6me Année. Nº 61, Juin 1924, at Page 138)

With the helicopter having an operating weight of approximately 1,000 kilograms (2,205 pounds), the rotors had a load factor of 33 kilograms per square meter (6.8 pounds per square foot).

L’hélicoptère Nº2 was powered by a single Société des Moteurs Gnome et Rhône Type R nine-cylinder rotary engine placed vertically near the center of the structure.

The Le Rhône Type R, introduced in 1917, was an air-cooled, normally-aspirated, 15.892 liter (969.786 cubic inches) nine-cylinder overhead valve rotary engine with two valves per cylinder. The Type R produced 170 cheval vapeur (167.7 horsepower) at 1,360 r.p.m. The engine was 0.990 meters (3 feet, 2.9 inches) long, 0.995 meters (3 feet, 3.2 inches) in diameter, and weighed 166 kilograms (366 pounds).

Étienne Oehmichen's Helicopter No. 2
Étienne Oehmichen’s Helicopter No. 2, 4 May 1924.

¹ FAI Record File Number 13093

² FAI Record File Number 13095

³ FAI Record Files 13091 (100 kilograms) and 13092 (200 kilograms)

© 2019, Bryan R. Swopes

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17 April 1941

Igor Sikorsky piloting his pontoon-equipped VS-300, 17 April 1941. (Sikorsky Historical Archives)
Igor Sikorsky piloting his pontoon-equipped VS-300, 17 April 1941. (Sikorsky Historical Archives)

17 April 1941: Igor Sikorsky’s Vought-Sikorsky VS-300 helicopter went through various rotor configurations during development as he searched for a combination that would give stability, anti-torque control, as well as lateral and yaw control. By April 1941, the VS-300 was configured with a single main rotor for lift and three smaller tail rotors to provide anti-torque and directional control.

This was not the ultimate solution, but on 17 April, he had the aircraft fitted with three inflatable pontoons and made a successful water landing, demonstrating that the helicopter could be a practical amphibious aircraft. During a lecture to the Rotating Wing Section of the Tenth Annual Meeting of the Institute of Aeronautical Sciences, Igor Sikorsky gave a brief description of the flight:

Igor Ivanovich Sikorsky 1888–1970. Sikorsky Archives)
Igor Ivanovich Sikorsky (Sikorsky Archives)

“On April 17 the helicopter, mounted on rubber floats, was repeatedly taken off from water and landed on water and then landed on ground, demonstrating for the first time a direct lift aircraft with excellent amphibian characteristics on which no adjustments whatsoever are needed when going from water to land and vice versa.”

The VS-300 had a welded tubular steel airframe and used a 28-foot (5.34 meters) diameter, fully-articulated, three-bladed main rotor, which turned clockwise (as seen from above) at 260 r.p.m. (The advancing blade was on the left. This would later be reversed.) The main rotor had collective pitch control for vertical control, but cyclic pitch (Sikorsky referred to this as “sectional control”) for directional control would not be developed for another several months.

The tail “propellers” (what we now consider to be rotors—one vertical and two horizontal) each had two blades with a diameter of 7 feet, 8 inches (2.337 meters) and turned approximately 1,300 r.p.m. The vertical rotor provided “torque compensation” (anti-torque) and the blade pitch was fully reversible. The horizontal rotors were mounted on 10-foot (3.048 meters) outriggers at the aft end of the fuselage. For lateral control, the pitch on one rotor was increased and the other decreased. For longitudinal control, the pitch of both rotors was increased or decreased together.

Igor Sikorsky banks the VS-300 through assymetric pitch of the horizontal tail rotors. (Sikorsky Historical Archives)
Igor Sikorsky banks the VS-300 through assymetric pitch of the horizontal tail rotors. (Sikorsky Historical Archives)

The VS-300 was originally equipped with an air-cooled, normally-aspirated 144.489-cubic-inch-displacement (2.368 liter) Lycoming O-145C-3 four-cylinder horizontally-opposed engine which was rated at 75 horsepower at 3,100 r.p.m. According to Mr. Sikorsky, “early in 1941,” the Lycoming engine was replaced by an air-cooled, normally-aspirated 198.608 cubic inch (3.255 liter) Franklin 4AC-199-E, a four-cylinder horizontally-opposed overhead valve (OHV) direct-drive engine with a compression ratio of 7:1, rated at 90 horsepower at 2,500 r.p.m. It is not known if this change was made prior to 17 April.

© 2019, Bryan R. Swopes

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11 April 1952

Piasecki YH-21-PH Work-Horse 50-1231, first flight at Morton Grove, PA. (San Diego Air and Space Museum Archives)
Piasecki YH-21-PH Work-Horse 50-1231, first flight at Morton Grove, PA. (San Diego Air and Space Museum Archives)

11 April 1952: At the Piasecki Helicopter Corporation factory at Morton Grove, Pennsylvania, the first YH-21 tandem-rotor helicopter, serial number 50-1231, made it’s first flight. The test pilots were Leonard Joseph (“Len”) LaVassar and Martin P. (“Marty”) Johnson, both former U.S. Navy aviators.

The Piasecki Helicopter Corporation built 18 pre-production YH-21-PH helicopters, followed by three production variants, the H-21A, H-21B and H-21C.

The U.S. Air Force immediately ordered 32 H-21A helicopters for Search and Rescue operations. The Workhorse was well suited to cold weather operations and it was widely used in Alaska, Canada, and the Antarctic. Another 163 H-21B models were ordered as a troop transports. The U.S. Army ordered a similar H-21C variant.

Piasecki YH-21, left profile.
Piasecki YH-21 Work Horse 50-1231, with rotors turning.

The YH-21 was a single-engine, tandem-rotor transport helicopter. It was normally operated by two pilots, with a flight mechanic (crew chief), and could carry up to 20 soldiers under ideal conditions.

With rotors turning, the YH-21’s overall length was 86 feet, 5 inches (26.340 meters). The fuselage was 52 feet, 6 inches (16.002 meters) long, and the helicopter had an overall height of 16 feet, 0 inches (4.877 meters). The rotors were 44 feet, 0 inches (13.411 meters) in diameter. The YH-21’s empty weight was approximately 8,117 pounds (3,682 kilograms) and maximum gross weight was 14,500 pounds (6,577 kilograms).

Piasecki H-21B Workhorse 51-3433 at Elmendorf Air Force Base, Alaska, circa 1960. (U.S. Air Force)

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. Normal operating speed for the main rotors was 233 to 258 r.p.m. (233–270 r.p.m. in autorotation.) The counter-rotating rotors cancelled out engine torque, eliminating any need for a tail rotor. The angle in the fuselage was intended to provide adequate vertical clearance between the intermeshing fore and aft rotor assemblies. (Later tandem rotor helicopters use raised pylons.)

Piasecki HH-21B 51-15855 supported X-15 flight operations at Edwards Air Force Base. (NASA)

The H-21 was powered by a single air-cooled, supercharged, 1,823.129-cubic-inch-displacement (29.875 liter) Wright Aeronautical Division Cyclone 9 863C9WD1 (R-1820-103) nine-cylinder radial, mounted inside the fuselage at midship, and drove the front and rear rotors in opposite directions through drive shafts and gear boxes. The Wright R-1820-103 engine was rated at 1,275 horsepower at 2,500 r.p.m., and 1,425 horsepower at 2,700 r.p.m., for takeoff. This direct-drive engine had a compression ratio of 6.80:1 and required 100/130 aviation gasoline. The engine was 4 feet, 0.50 inches (1.232 meters) long, 4 feet, 6.95 inches (1.396 meters) in diameter, and weighed 1,350 pounds (612 kilograms). Wright built 971 R-1820-103s from November 1950 through 1957.

The YH-21 could reach a maximum speed in level flight of 131 knots (151 miles per hour/243 kilometers per hour). Its Never Exceed limit (VNE) was 151 knots (174 miles per hour /280 kilometers per hour) (diving). The maximum Sea Level range was 397 nautical miles (457 statute miles/735 kilometers) at 125 knots (144 miles per hour/232 kilometers per hour). Its service ceiling was 19,200 feet (5,852 meters).

In 1955, Piasecki became Vertol and eventually Boeing Vertol. The company would continue to produce tandem rotor helicopters such as the H-46 Sea Knight and the CH-47 Chinook, which is still in production.

Piasecki CH-21B Workhorse, 51-15857, at the National Museum of the United States Air Force. (U.S. Air Force)
Piasecki CH-21B Workhorse, 51-15857, at the National Museum of the United States Air Force. (U.S. Air Force)

© 2019, Bryan R. Swopes

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