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UH-1

The Bell UH-1 Iroquois is a military helicopter powered by a single, turboshaft engine, with a two-bladed main rotor and tail rotor. The helicopter was developed by Bell Helicopter to meet the United States Army's requirement for a medical evacuation and utility helicopter in 1952, and first flew on 20 October 1956. Ordered into production in March 1960, the UH-1 was the first turbine-powered helicopter to enter production for the United States military, and more than 16,000 have been produced worldwide.

The first combat operation of the UH-1 was in the service of the U.S. Army during the Vietnam War. The original designation of HU-1 led to the helicopter's nickname of Huey. In September 1962, the designation was changed to UH-1, but Huey remained in common use. Approximately 7,000 UH-1 aircraft saw service in Vietnam.

 

Development

In 1952, the Army identified a requirement for a new helicopter to serve as medical evacuation (MEDEVAC), instrument trainer and general utility aircraft. The Army determined that current helicopters were too large, underpowered, or were too complex to maintain easily. In November 1953, revised military requirements were submitted to the Department of the Army. Twenty companies submitted designs in their bid for the contract, including Bell Helicopter with the Model 204 and Kaman Aircraft with a turbine-powered version of the H-43. On 23 February 1955, the Army announced its decision, selecting Bell to build three copies of the Model 204 for evaluation, designated as the XH-40.

 

Design

The UH-1 has a metal fuselage of semi-monocoque construction with tubular landing skids and two rotor blades on the main rotor. Early UH-1 models featured a single Lycoming T53 turboshaft engine in versions with power ratings from 700 shp (522 kW) to 1,400 shp (1,040 kW). Later UH-1 and related models would feature twin engines and four-blade rotors.

All aircraft in the UH-1 family have similar construction. The UH-1H is the most-produced version, and is representative of all types. The main structure consists of two longitudinal main beams that run under the passenger cabin to the nose and back to the tail boom attachment point. The main beams are separated by transverse bulkheads and provide the supporting structure for the cabin, landing gear, under-floor fuel tanks, transmission, engine and tail boom. The main beams are joined at the lift beam, a short aluminum girder structure that is attached to the transmission via a lift link on the top and the cargo hook on the bottom and is located at the aircraft's centre of gravity. The lift beams were changed to steel later in the UH-1H's life, due to cracking on high-time airframes. The semi-monocoque tail boom attaches to the fuselage with four bolts.

The UH-1H's dynamic components include the engine, transmission, rotor mast, main rotor blades, tail rotor driveshaft, and the 42-degree and 90-degree gearboxes. The transmission is of a planetary type and reduces the engine's output to 324 rpm at the main rotor. The two-bladed, semi-rigid rotor design, with pre-coned and under-slung blades, is a development of early Bell model designs, such as the Bell 47 with which it shares common design features, including a dampened stabilizer bar. The two-bladed system reduces storage space required for the aircraft, but at a cost of higher vibration levels. The two-bladed design is also responsible for the characteristic 'Huey thump' when the aircraft is in flight, which is particularly evident during descent and in turning flight. The tail rotor is driven from the main transmission, via the two directional gearboxes which provide a tail rotor speed approximately six times that of the main rotor to increase tail rotor effectiveness.

The UH-1H also features a synchronized elevator on the tail boom, which is linked to the cyclic control and allows a wider center of gravity range. The standard fuel system consists of five interconnected fuel tanks, three of which are mounted behind the transmission and two of which are under the cabin floor. The landing gear consists of two arched cross tubes joining the skid tubes. The skids have replaceable sacrificial skid shoes to prevent wear of the skid tubes themselves. Skis and inflatable floats may be fitted.

Internal seating is made up of two pilot seats and additional seating for up to 13 passengers or crew in the cabin. The maximum seating arrangement consists of a four-man bench seat facing rearwards behind the pilot seats, facing a five-man bench seat in front of the transmission structure, with two, two-man bench seats facing outwards from the transmission structure on either side of the aircraft. All passenger seats are constructed of aluminium tube frames with canvas material seats, and are quickly removable and reconfigurable. The cabin may also be configured with up to six stretchers, an internal rescue hoist, auxiliary fuel tanks, spotlights, or many other mission kits. Access to the cabin is via two aft-sliding doors and two small, forward-hinged panels. The doors and hinged panels may be removed for flight or the doors may be pinned open. Pilot access is via individual hinged doors.

While the five main fuel tanks are self-sealing, the UH-1H was not equipped with factory armour, although armoured pilot seats were available.

The UH-1H's dual controls are conventional for a helicopter and consist of a single hydraulic system boosting the cyclic stick, collective lever and anti-torque pedals. The collective levers have integral throttles, although these are not used to control rotor rpm, which is automatically governed, but are used for starting and shutting down the engine. The cyclic and collective control the main rotor pitch through torque tube linkages to the swash plate, while the anti-torque pedals change the pitch of the tail rotor via a tensioned cable arrangement. Some UH-1Hs have been modified to replace the tail rotor control cables with torque tubes similar to the UH-1N Twin Huey.

 

General characteristics

Crew: 1-4

Capacity: 3,880 lb including 14 troops, or 6 stretchers, or equivalent cargo

Length: 57 ft 1 in (17.40 m) with rotors

Width: 8 ft 7 in (2.62 m) (Fuselage)

Height: 14 ft 5 in (4.39 m)

Empty weight: 5,215 lb (2,365 kg)

Gross weight: 9,040 lb (4,100 kg)

Max takeoff weight: 9,500 lb (4,309 kg)

Powerplant: 1 × Lycoming T53-L-11 turboshaft, 1,100 shp (820 kW)

Main rotor diameter: 48 ft 0 in (14.63 m)

 

Performance

Maximum speed: 135 mph (217 km/h; 117 kn)

Cruise speed: 125 mph (109 kn; 201 km/h)

Range: 315 mi (274 nmi; 507 km)

Service ceiling: 19,390 ft (5,910 m) (Dependent on environmental factors such as weight, outside temp., etc)

Rate of climb: 1,755 ft/min (8.92 m/s)

Power/mass: 0.15 hp/lb (0.25 kW/kg)

 

Armament

Variable, but may include a combination of:

2× 7.62 mm M60 machine gun, or 2x 7.62 mm GAU-17/A machine gun

2× 7-round or 19-round 2.75 in (70 mm) rocket pods

2× 7.62 mm Rheinmetall MG3 (German Army and German Luftwaffe)

2× .303 Browning Mk II (Rhodesian, twin machine guns mounted on port side)