The Boeing Vertol CH-46 Sea Knight is a medium-lift tandem rotor transport helicopter. It is used by the United States Marine Corps (USMC) to provide all-weather, day-or-night assault transport of combat troops, supplies and equipment. Additional tasks include combat support, search and rescue (SAR), support for forward refueling and rearming points, CASEVAC and Tactical Recovery of Aircraft and Personnel (TRAP). The Sea Knight was also the U.S. Navy's standard medium-lift utility helicopter until it was phased out in favor of the MH-60S Knighthawk in the early 2000s.

Canada also operated the Sea Knight, designated as CH-113, and operated them in the SAR role until 2004. Other export customers include Japan, Sweden, and Saudi Arabia. The commercial version is the BV 107-II, commonly referred to simply as the "Vertol".

Development

Origins

Piasecki Helicopter was a pioneering developer of tandem-rotor helicopters, with the most famous previous helicopter being the H-21 "Flying Banana". Piasecki Helicopter became Vertol in 1955 and work began on a new tandem rotor helicopter designated the Vertol Model 107 or V-107 in 1956. The V-107 prototype had two Lycoming T53 turboshaft engines, producing 877 shp (640 kW) each.  The first flight of the V-107 took place on 22 April 1958. The V-107 was then put through a flight demonstration tour in the United States and overseas. In June 1958, the U.S. Army awarded a contract to Vertol for ten production aircraft designated "YHC-1A".

The order was later decreased to three, so the U.S. Army could divert funds to the V-114, also a turbine powered tandem, but larger than the V-107.  The Army's three YHC-1As were powered by GE-T-58 engines. The YHC-1As first flew in August 1959, and were followed by an improved commercial/export model, the 107-II.  During 1960, the U.S. Marine Corps evolved a requirement for a twin-turbine troop/cargo assault helicopter to replace the piston engine types then in use. Following a design competition, Boeing Vertol was selected to build its model 107M as the HRB-1, early in 1961.  Boeing had acquired Vertol in 1960 and renamed the group Boeing Vertol.  In 1962 the U.S. Air Force ordered 12 XCH-46B Sea Knights with the XH-49A designation. but later cancelled the order due to a delay in the delivery schedule. They opted for the Sikorsky S-61R instead.

The Sea Knight was first procured in 1961 by the U.S. Marine Corps to meet their medium-lift requirements.^[7] Its first flight in August 1962 was followed by a change in designation to CH-46A. Fleet introduction of CH-46As with the Marines and the Navy's UH-46As was in November 1964. The UH-46A variant was modified for use in the vertical replenishment role.  The CH-46A was equipped with a pair of T58-GE8-8B turboshaft engines rated at 1,250 shp (930 kW) each and could carry 17 passengers or 4,000 pounds (1,815 kg) of cargo.

Further developments

Production of the improved CH-46D followed with deliveries beginning in 1966. Its improvements included modified rotor blades and more powerful T58-GE-10 turboshaft engines rated at 1,400 shp (1,040 kW) each. The increased power allowed the D-model to carry 25 troop or 7,000 pounds (3,180 kg) of cargo. The CH-46D was introduced to the Vietnam theater in late 1967, supplementing the U.S. Marine Corps' existing unreliable and problematic CH-46A fleet.  Along with the USMC's CH-46Ds, the U.S. Navy received a small number of UH-46Ds for ship resupply.  Also, approximately 33 CH-46As were upgraded to CH-46Ds.

The Marines also received CH-46Fs from 1968 to 1971. The F-model retained the D-model's T58-GE-10 engines but revised the avionics and included other modifications. The CH-46F was the final production model.  The Sea Knight has undergone upgrades and modifications. Most of the U.S. Marine Corps' Sea Knights were upgraded to CH-46E standard. The CH-46E features fiberglass rotor blades, airframe reinforcement, and further uprated T58-GE-16 engines producing 1,870 shp (1,390 kW) each. Some CH-46Es have been given doubled fuel capacity.  The Dynamic Component Upgrade (DCU) incorporated starting in the mid-1990s provides for increased capabilities through strengthened drive systems and rotor controls.

The commercial variant, the BV 107-II, was first ordered by New York Airways in 1960. They took delivery of their first three aircraft, configured for 25 passengers, in July 1962.  In 1965, Boeing Vertol sold the manufacturing rights of the 107 to Kawasaki Heavy Industries. Under this arrangement, all Model 107 civilian and military aircraft built in Japan are known as KV 107.  On 15 December 2006, Columbia Helicopters, Inc acquired the type certificate for the Boeing Vertol 107-II, and is in the process of acquiring a Production Certificate from the FAA. Plans for actual production of the aircraft have not been announced.

Design

The CH-46 has tandem contrarotating rotors powered by two GE T58 turboshaft engines. The engines are mounted on each side of the rear rotor pedestal with a driveshaft to the forward rotor. The engines are coupled so either could power both rotors in an emergency. The rotors feature three blades and can be folded for on-ship operations.  The CH-46 has fixed tricycle landing gear, with twin wheels on all three units. The gear configuration causes a nose-up stance to facilitate cargo loading and unloading. The main gear are fitted in rear sponsons that also contain fuel tanks with a total capacity of 350 US gallons (1,438 L).

The CH-46 has a cargo bay with a rear loading ramp that could be removed or left open in flight for extended cargo or for parachute drops. An internal winch is mounted in the forward cabin and can be used to pull external cargo on pallets into the aircraft via the ramp and rollers. A belly sling hook (cargo hook) which is usually rated at 10,000 lb (4,500 kg). could be attached for carrying external cargo. Although the hook is rated at 10,000 lb (4,500 kg)., the limited power produced by the engines preclude the lifting of such weight. It usually has a crew of three, but can accommodate a larger crew depending on mission specifics. For example, a Search and Rescue variant will usually carry a crew of five (Pilot, Co-Pilot, Crew Chief, Swimmer, and Medic) to facilitate all aspects of such a mission. A pintle-mounted 0.50 in (12.7 mm) Browning machine gun is mounted on each side of the helicopter for self-defense.  Service in southeast Asia resulted in the addition of armor with the guns.

Operational history

United States

Known colloquially as the "Phrog", the Sea Knight has been used in all U.S. Marine combat and peacetime environments since its introduction.  As of 2011, it is still regularly flown by the U.S. Marine Corps, its longevity as a reliable airframe has led to such mantras as "phrogs phorever" and "never trust a helicopter under 30".

CH-46E Sea Knights were used by the U.S. Marine Corps during the 2003 invasion of Iraq. CH-46Es transported personnel, brought supplies to forward arming and refueling points (FARP), carried ammunition and various tasks. Marine CH-46Es and CH-53Es carried U.S. Army Rangers and Special Operations troops in a mission to extract captured Army Private Jessica Lynch from an Iraqi hospital on 1 April 2003.

While the United States Navy retired the airframe on 24 September 2004, replacing it with the MH-60S Knighthawk,  the Marine Corps plans to maintain its fleet until the MV-22 is fully fielded.  In March 2006 Marine Medium Helicopter Squadron 263 (HMM-263) was deactivated and redesignated VMM-263 to serve as the first MV-22 squadron. The replacement process is expected to continue through the other medium helicopter squadrons into 2014.

Canada

The Royal Canadian Air Force procured six CH-113 Labrador helicopters for the SAR role and the Canadian Army acquired 12 of the similar CH-113A Voyageur for the medium-lift transport role. The RCAF Labradors were delivered first with the first one entering service on 11 October 1963.  When the larger CH-147 Chinook was procured by the Canadian Forces in the mid-1970s, the Voyageur fleet was converted to Labrador specifications to undertake SAR missions. The refurbished Voyageurs were re-designated as CH-113A Labradors, thus a total of 15 Labradors were ultimately in service.

The Labrador was fitted with a watertight hull for marine landings, a 5,000 kilogram cargo hook and an external rescue hoist mounted over the right front door. It featured an 1,110 kilometer flying range, emergency medical equipment and an 18 person passenger capacity. By the 1990s, heavy use and hostile weather conditions had taken their toll on the Labrador fleet, resulting in increasing maintenance costs and the need for prompt replacement.  In 1981, a mid-life upgrade of the fleet was carried out by Boeing Canada in Arnprior, Ontario. Known as the SAR-CUP (Search and Rescue Capability Upgrade Program), the refit scheme included new instrumentation, a nose-mounted weather radar, tail-mounted auxiliary power unit, a new high-speed rescue hoist mounted over the side door and front-mounted searchlights. A total of six CH-113s and five CH-113As were upgraded with the last delivered in 1984.

In 1992 it was announced that the Labradors were to be replaced by 15 new helicopters, a variant of the AgustaWestland EH101, designated CH-149 Chimo. The order was subsequently cancelled by the Jean Chrétien Liberal government in 1993, resulting in cancellation penalties, as well as extending the service life of the Labrador fleet. However, in 1998, a CH-113 from CFB Greenwood crashed on Quebec's Gaspé Peninsula while returning from a SAR mission, resulting in the deaths of all crewmembers on board. The crash placed pressure upon the government to procure a replacement, thus an order was placed with the manufacturers of the EH101 for 15 aircraft to perform the search-and-rescue mission, designated CH-149 Cormorant. CH-149 deliveries began in 2003, allowing the last CH-113 to be retired in 2004.  In October 2005 Columbia Helicopters of Portland, Oregon purchased eight of the retired CH-113 Labradors to add to their fleet of 15 Vertol 107-II helicopters.

Civilian

The Civilian version, the BV 107-II Vertol was developed prior to the military CH-46, and was operated commercially by New York Airways, Pan American World Airways and currently solely by Columbia Helicopters.  As of 15 December 2006 Columbia Helicopters has purchased the Type certificate of the Model 107 from Boeing. Currently the company is seeking FAA issuance of a Production Certificate to produce parts with eventual issuance of a PC to produce aircraft

Specifications (CH-46E)

General characteristics

• Crew: 5: 2 pilots, 1 crew chief, 1 aerial gunner/observer, 1 tail gunner
• Capacity:
  
  • 24 troops or
  • 15 stretchers and two attendants or
  • 2270 kg (5,000 lb)
• Length: 44 ft 10 in fuselage (13.66 m
• Fuselage width: 7 ft 3 in (2.2 m)
• Rotor diameter: 50 ft (15.24 m)
• Height: 16 ft 9 in (5.09 m)
• Disc area: 3,927 ft² (364.8 m²)
• Empty weight: 11,585 lb (5,255 kg)
• Loaded weight: 17,396 lb (7,891 kg)
• Max. takeoff weight: 24,300 lb (11,000 kg)
• Powerplant: 2 × General Electric T58-GE-16 turboshafts, 1,870 shp (1,400 kW) each

Performance

• Maximum speed: 166 mph (144 knots, 267 km/h)
• Range: 633 mi (550 nmi, 1,020 km)
• Ferry range: 690 mi (600 nmi, 1,110 km)
• Service ceiling: 17,000 ft (5,180 m)
• Rate of climb: 1,715 ft/min (8.71 m/s)
• Disc loading: 4.43 lb/ft² (21.6 kg/m²)
• Power/mass: 0.215 hp/lb (354 W/kg)

Armament

• Guns: 2× Door mounted GAU-15/A .50 BMG (12.7 x 99 mm) machine guns (optional), 1 Ramp mounted M240D 7.62 x 51 mm machine gun (optional)

Source: Wikipedia