The Boeing CH-46 Sea Knight is a medium-lift tandem rotor transport helicopter, used by the United States Marine Corps (USMC) to provide all-weather, day-or-night assault transport of combat troops, supplies and equipment. Assault Support is its primary function, and the movement of supplies and equipment is secondary. Additional tasks include combat support, search and rescue, support for forward refueling and rearming points, CASEVAC and Tactical Recovery of Aircraft and Personnel (TRAP). The commercial version is the BV 107-II, commonly referred to as simply the "Vertol".
Piasecki was a pioneering developer of tandem-rotor helicopters, with the most famous previous helicopter being the H-21 "Flying Banana". Piasecki's former company Vertol began work on a new tandem rotor helicopter designated the Vertol Model 107 or V-107 in 1957. The V-107 had two Lycoming T53 turboshaft engines, producing 860 shp (640 kW) each. The first flight of the V-107 took place on April 22, 1958. The V-107 was then put through a flight demonstration tour in the US and overseas. In June 1958, the US Army awarded a contract to Vertol for ten production aircraft designated "YHC-1A".
The order was later decreased to three, so the 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 (USMC) 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.
The helicopter was first procured in 1961 to meet the medium-lift requirements of the Marine Corps. 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 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. The USMC received 160 CH-46As and the US Navy acquired 14 UH-46As.
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. A total of 265 CH-46Ds were produced. The Navy received 10 UH-46Ds for ship resupply. Also, approximately 12 CH-46As were upgraded to CH-46Ds.
The Marines also received 174 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 with the last helicopter being the 524th H-46 produced. The Sea Knight has undergone upgrades and modifications. Most USMC 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.
On December 15, 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.
The CH-46 has tandem contrarotating rotors that were 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 could be folded for on-ship operations.
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. A belly sling hook could be attached for carrying external cargo. It has a crew of three. A pintle-mounted 0.50 in (12.7 mm) Browning machine gun was mounted on each side of the helicopter for self-defense. Service in southeast Asia resulted in the addition of armor with the guns.
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 contained fuel tanks with a total capacity of 350 US gallons (1,438 L).
Known colloquially as the "Phrog", and used in all Marine combat and peacetime environments since its introduction. Still regularly flown by the 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 USMC during its 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 US 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 September 24, 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.
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 December 15, 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.
Total U.S. H-46 production amounted to 525, ending in 1971.
Published in July 2009.
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