Developed from the US Navy’s HRP-2 Rescuer, the Piasecki PD-22 tandem-rotor helicopter prototype (US Air Force designation XH-21) was first flown on 11 April 1952 with Len LaVassar and Marty Johnson at the controls.

Piasecki PD-22 / H-21 Shawnee Article

Winner of a USAF competition for an arctic transport helicopter, the new craft looked almost like the HRP-2, but weighed 6630kg fully loaded, more than twice the earlier machine. A 1425hp Wright R-1820 engine (derated in early models to 1150hp) and a 0.9m increase in rotor diameter to 13.4m gave it much better performance than the HRP-2. The H-21 used the single engine with tandem three-blade rotors. Structurally, it was a new aircraft. (TC 1H12, 1H16, H1AL, H3EA, H8WE, H9EA, HR35).

The Work Horse could carry fourteen fully equipped troops or an equivalent weight of cargo. Features included a rescue hoist and inflatable donut-shaped floats around its wheels for landings even on marshy tundra. Winterized to support Distant Early Warning (DEW) Line radar stations far to the north, extensive cold-weather testing was performed atop Mount Washington, the highest peak in New Hampshire’s White Mountains, as well as in the climate hangar at Eglin Air Force Base.

Eighteen Model PD-22 / YH-21 helicopters had been ordered in 1949 for USAF evaluation, these being followed by an initial production batch of 32 H-21A helicopters, named Workhorse in USAF service. For use by the Military Air Transport Service Air Rescue Service, the H-21As were each powered by a derated 932kW Wright R-1820-103 engine; the first flew in October 1953. Six more were built to USAF contract but supplied to Canada under the Military Assistance Program. Vertol produced in 1957 a small number of Vertol Model 42A, exclusively Canadian civil conversion of RCAF H-21B helicopters used to supply stations of the mid-Canada radar chain.

The second production variant was the H-21B, which used the full power of the 1063kW R-1820-103 to cover an increase in maximum take-off weight from 5216kg to 6804kg. The Air Force eventually purchased 163, mainly for Troop Carrier Command, and these had autopilots, could carry external auxiliary fuel tanks, and were provided with some protective armour. They could carry 20 troops in the assault role.

The Army became aware of the H-21’s potential as a medium utility helicopter soon after the type’s maiden flight, and in 1952 awarded Piasecki a contract for the production of the H-21C variant. This aircraft retained the H-21B’s extensive armor plating and ability to carry two external fuel tanks, but had such additional features as increased troop capacity and a 4000-pound capacity belly sling hook. The Army procured 334 H-21C Shawnees, with deliveries beginning in August 1954. In addition, the Army obtained at least sixteen H-21B aircraft from the USAF; the majority of these machines were ultimately brought up to H-21C standard, and all were known as Shawnees despite their origins as Work Horses. The B and C variants of the H-21 were used in Vietnam, equipped with 12.7 or 7.62mm light machine guns which were fired through the cabin doors.

While the Navy’s helicopters had a 600hp Pratt & Whitney R-1340 engine, those for the Army had a Wright R-1820. Thirty-three of the H-21A were assigned to SAR units in the Arctic and another five were sent to Canada. Foreign operators of the H-21 included the German Army (26), French Army (98), French Navy (10), Japanese armed forces (10) and Swedish Navy (11).

The US Army’s equivalent was the H-21C Shawnee, of which 334 were built. This total included 98 for the French army, 10 for the French navy and six for Canada; 32 Shawnees were supplied to West Germany, serving with the army’s Heeresfliegerbataillon 300. The first deliveries to the Army were in September 1954 with production continuing until March 1959. The H-21C, redesignated CH-21C in July 1962, had an underfuselage sling hook for loads of up to 1814kg. Production deliveries were made between September 1954 and March 1959, later helicopters acquiring the company designation Model 43 when the Piasecki Helicopter Corporation became the Vertol Aircraft Corporation in 1956. The H-21 A and H-21B retrospectively became the Model 42. In 1962 the H-21B and H-21C were redesignated as, respectively, the CH-21B and CH-21C.

Two turboshaft conversions of H-21C airframes were the Model 71 (H-21D), with two General Electric T58 engines first flown in September 1957, and the Model 105 which had two Avco Lycoming T53s in 1958. The variant was not adopted for production. From the latter was designed the Vertol 107 (Boeing Vertol H-46 series).

Most Shawnees were withdrawn from the active inventory by 1965.

It set a closed-course distance record of 1,199 miles in Aug 1957 with extra fuel tank. It was a Shawnee dubbed ‘Amblin’ Annie that made the first non-stop helicopter flight from one coast of the United States to the other, being refuelled in flight from a U-1A Otter in Aug 1957. More significantly, the H-21 was the first American military helicopter type to be deployed in appreciable numbers to South Vietnam: the first four Shawnee units arrived in that country between December 1961 and September 1962. The H-21 also gained the dubious distinction of being the aircraft in which America’s first Vietnam casualties were killed; four Army aviators died in July 1962 when their Shawnee was shot down near the Laotian-Vietnamese border.

“I was working as a helicopter mechanic with the U.S. Army Aviation Service Test Board in 1954 and 1955 and we received some of the first production H-21Cs for operational testing; I was assigned to serial number 51-15888, tail number 115888, the eighth built, and I recall us having 115881 also which I believe was the one we picked up at Edwards AFB in 1955. The Air Force did all engineering flight testing for the Army and when they completed tests on the H-21C version (in preparation for their USAF H-21B version ordered after the “C”), a small group of us from the Fort Rucker Test Board went to Edwards to take over the ship and perform some high altitude and desert tests before flying back to Rucker. Arriving at Edwards, complete with papers and “secret” clearances, we promptly discovered that the USAF’s Army H-21C was in terrible condition and unairworthy. Much to their dislike and consternation, we hung around the air base for several days while we performed an inspection and changed the Wright 1820 engine – the desert flying had eaten up the cylinders and bearings to the point that the 19-gallon oil tank wouldn’t sustain a single flight! Needless to say, there was some exciting experimental jet activity going on at Edwards at that time and we GIs were in no hurry to leave as we had a front line seat on the test ramp. We spent a few weeks at an Apple Valley dude ranch, parking the helicopter in the desert, and refueling at George AFB. Each day we flew several sorties into the White Bear region and did a few exciting running takeoffs at White Bear Lake. We made an uneventful (mostly), but rather warm and humid, flight back to Rucker, taking a pretty straight course from San Antonio across Texas, Louisiana, Mississippi and into Alabama. A late evening thunderstorm threw us off course during a night flight leg and we made an “off-airport” landing in a drenched high school football stadium in Mississippi (still lit up following a game); the locals fed us and I wound up spending the night RON in a friendly funeral parlor. One of the Board’s test H-21s made the first non-stop flight across the U.S. in August, 1956; it took 37 hours and refueling by a fixed wing”.

1955 commercial developments of the H-21 included models 42, 43, 44, 63, and 71.

Gallery

YH-21 / PD-22
Engine: 1150hp Wright R-1820-103
Rotors: 44’6″
Length: 86’4″
Max speed: 131 mph
Cruise: 110 mph
Ceiling: 15,000′
Capacity: 14 fully-equipped troops

H-21 Shawnee / CH-21/UH-21
Engine: Wright R-1820-103, 1425hp
Rotor diameter: 44’0″
Length: 52’7″
Useful load: 4500 lb
Max speed: 130 mph
Cruise speed: 98 mph
Range: 265-400 mi
Ceiling: 9,4500 ft
Passenger capacity: 20

H-21A
Engine: 1150hp Wright R-1820-103
Medevac capacity: 12 litter patients

H-21B Work Horse
1957
Engine: 1425hp Wright R-1820-107
Capacity: 20 troops or 12 litters

H-21C
1957
US Army version

H-21D
1957
Engines: 2 x GE T58 gas turbines
First flight: September 1957

Vertol 42A
1954
Length : 52.165 ft / 15.9 m
Height : 15.354 ft / 4.68 m
Rotor diameter : 44.029 ft / 13.42 m
Max. speed : 110 kt / 204 km/h
Service ceiling : 10335 ft / 3150 m

Piasecki set to work on a specification, issued by the US Navy Bureau of Aeronautics in 1945, for a shipboard helicopter to be used on aircraft carriers and larger vessels for SAR, liaison, replenishment and plane guard duties.

Designated PV-14 (XHJP-1 by the US Navy), two XHJP-1 prototypes (37976 and ’77) were completed for US navy evaluation and three pre-production aircraft, the HUP-1, were ordered in 1948. From 1950-52 a further twenty-two HUP-1 Retrievers (PV-18) were delivered to the U.S. Navy. They differed little from the original XHJP-1, the major apparent change being the addition of inward-sloping endplate fins to the horizontal stabilisers below the rear rotor head. Both sets of 3-blade rotors could be folded for shipboard stowage and the HUP-1, powered by a single 391kW / 525hp Continental R-975-34 piston engine, could accommodate 4-5 passengers or 3 casualty litters in addition to the 2-man crew. The power-plant was installed at the center of the fuselage, which had a steel tube framework with particularly strong, fixed tricycle landing gear. The fin of the HUP-1 was subsequently eliminated, as further improved versions were fitted with an autopilot. The US Navy versions had all-weather instrumentation and some were equipped with sonar for antisubmarine warfare.

The HUP-1 had a smaller, more compact fuselage than its predecessors. This enabled the helicopter to be stowed without having to fold back the rotor blades. Once acceptance trials were over, the US Navy ordered 32 aircraft including 124588/124594, 124915/124929, 126706/126715, followed by another 165 of the HUP-2, which was fitted with a more powerful engine. The first squadron, HU-2, took delivery of its initial aircraft in February 1951.

Successful tests with a Sperry autopilot in the XHJP-1 enabled the HUP-2, to be built without tail surfaces and the more powerful 410kW Continental R-975-46 was installed in this and all subsequent production models. Another feature of the Retriever was a large rectangular rescue hatch offset to starboard in the floor of the front fuselage, through which a winch inside the cabin could lift weights of up to 181kg / 400 lb at a time. The U.S. Navy machines included some completed as HUP-2S submarine-hunting aircraft with dunking sonar equipment. Another HUP-2 was given a sealed, watertight hull and outrigged twin floats for waterborne tests, presumably as part of the development programme for the Boeing-Vertol 107 / CH-46 helicopter.

The Marines also used 13 HUP-2, while the Army acquired 70, designated H-25A (serials 51-16572 to -16641) powered by the R-975-46A engine, 50 of which were later transferred to the Navy as HUP-3s, three serving with the Royal Canadian Navy’s Squadron VH-21. One H-25A went to the USN as the HUP-3 prototype; 51-16641=149088.

339 HUP-2 were built (128479/128600, 129418/129522, 129978/130085, 134434/134437), of which some with radar as HUP-2S for anti-sub warfare. Redesignated as UH-25B in 1962.

The first H-25A entering regular Army service in early 1953. Those Army Mules that remained in Army service were used mainly as training or medical evacuation aircraft, and the type was totally withdrawn from Army service by 1958.

The Army H-25 Mule was basically similar in general layout to the HUP-2, sharing that aircraft’s all-metal fuselage, fixed three-point landing gear, and 550hp Continental R-975-42 engine. The H-25A differed from the Navy variant primarily in having hydraulically-boosted controls, a strengthened floor with cargo tie-down fittings, and modified doors intended to ease the loading and unloading of stretchers.

In 1951 the U.S. Army ordered a version of the HUP-2 with a reinforced cabin floor and hydraulically boosted controls, for general support and evacuation work. Seventy of these were delivered as H-25A Army Mule from 1953, as were fifty similar Naval HUP-3’s (including three for the Royal Canadian Navy) for ambulance and light cargo duties. Production of the three hundred and thirty-ninth and last aircraft was completed in July 1954. Shortly after this a proposal was made to boost the speed, range and payload of all H-25/HUP aircraft still in service by refitting them with 700hp Wright R-1300-3 engines. However, this did not take place and by the time the new tri-service designation system was introduced in July 1962 only the HUP-2 and HUP-3 remained in service; these became the UH-25B and UH-25C respectively. Neither type is now in U.S. front-line service, and the French and Canadian HUP types were withdrawn from service in 1966.

The 50 HUP-3 built were 147582/147630 and 149088], redesignated as UH-25C in 1962. The last one was former Army H-25A 51-16641.

The HUP-4 has the 800-h:p. Wright R-1300-3 engine, and earlier versions could be modified to that standard.

An amphibious conversion of the HUP-2 was used for research by the Edo corporation in New York. It had a reinforced hull-type lower fuselage, all-metal outrigger floats and a new engine cooling system.

Gallery

H-25A Army Mule
Engine: 550 hp Continental R975-42
Rotor dia: 35 ft
Length: 56’11”
Weight: 5,750 lb
Max. Speed: over 103 mph
Range: 340 mi
Seats: 6

HUP-1
Engine: 525 h.p. Continental R-975-34
Rotor diameter: 35 ft.
Rotors: 2 x 3-blade main rotors in tandem
Fuselage length: 32 ft
Loaded weight: 5,750 lb
Max speed: Over 103 mph
Ceiling: Over 10,000 ft
Typical range: 395 miles at 80 mph
Seats: 6.

HUP-2
Engine: 550 h.p. Continental R-975-46
Rotor diameter: 35 ft.
Rotors: 2 x 3-blade main rotors in tandem
Fuselage length: 32 ft
Loaded weight: 5,750 lb
Max speed: Over 103 mph
Ceiling: Over 10,000 ft
Typical range: 395 miles at 80 mph
Seats: 6.

HUP-3
Engines: 1 x 550 hp Continental R-975-42, 410kW
Speed: Max: 170 km/h
Range: Max 550 km
Weight: Empty: 1780 kg
Max weight: 2770 kg
Rotor diameter: 10.67 m
Length rotors turning: 17.35 m
Height: 3.80 m
Disc Area: 179 sq.m
Service ceiling: 3050m
Height: 3.80 m
Disc Area: 179 sq.m
Service ceiling: 3050m

HUP-4
Engine: 800h.p.Wright R-1300-3
Rotor diameter: 35 ft.
Rotors: 2 x 3-blade main rotors in tandem
Fuselage length: 32 ft
Loaded weight: 5,750 lb
Max speed: Over 103 mph
Ceiling: Over 10,000 ft
Typical range: 395 miles at 80 mph
Seats: 6.