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Boeing Vertol CH-46 Sea Knight

United States (1964)

Detailing the development and operational history of the Boeing Vertol CH-46 Sea Knight Medium-Lift, Tandem Rotor Transport Helicopter.

 Entry last updated on 2/13/2018; Authored by Staff Writer; Content ©

  Boeing Vertol CH-46 Sea Knight  
Picture of Boeing Vertol CH-46 Sea Knight Medium-Lift, Tandem Rotor Transport Helicopter

The Boeing Vertol CH-46 Sea Knight is to the United States Marine Corps what the CH-47 Chinook is to the United States Army.

The Boeing Vertol CH-46 "Sea Knight" is similar in battlefield form and function to the more popular CH-47 "Chinook" tandem-rotor transport helicopters serving the American military. Both provide unobstructed access to the cargo hold by positioning engine components high above in their designs and both utilize the patented tandem three-blade main rotor arrangement that makes the Chinook family easy to identify. Despite these similarities, the Chinook is the dimensionally larger helicopter of the two and the primary workhorse for the United States Army whereas the Sea Knight serves the United States Marine Corps and, to a degree, the United States Navy.

The civilian market form of the CH-46 was the BV 107-II Vertol.

The CH-46 began life as the Vertol Model 107 in 1956 and intended to succeed the line of outgoing early-Cold-War-era haulers such as the tandem-rotor Piaseki H-21. The primary upgrade was in the CH-46's installation of turboshaft engines over that of earlier piston-driven engine types like those featured in the H-21. The promise of improved performance was enough to launch several programs to find more viable medium- and heavy-lift transports for United States military service.

As the V-107 prototype, the new helicopter went airborne for the first time on April 22nd, 1958. Testing continued into the early 1960s with waning interest had on the part of the United States Army - which had commissioned for ten YHC-1A evaluation models in their pre-production standard form in 1961. However, this commitment was later reduced to just three examples. All was not lost, however, for the United States Marine Corps service liked the potential of the new helicopter and adopted the Model 107M to form the basis for its CH-46 "Sea Knight" product.

Just a single Model 107 prototype served the CH-46 program. The Model 107-II was developed as a civilian market form and the Model 107M was the model set aside for the USMC based in the BV-107-II-2. Two were built in a transport guise for evaluations. The Army tested the YHC-1A and this later became the YCH-46C with three built. The USMC then took this mark as the HRB-1 prior to the 1962 designation reorganization to become the CH-46A.
Picture of the Boeing Vertol CH-46 Sea Knight Medium-Lift, Tandem Rotor Transport Helicopter
Picture of the Boeing Vertol CH-46 Sea Knight Medium-Lift, Tandem Rotor Transport Helicopter

The CH-46 fitted a pair o General Electric T58-GE-8 series turboshaft engines of 1,250 horsepower each and 160 of this mark were produced for the USMC (as well as a single static test article). The UH-46A were fourteen utility-minded types adopted by the USN but very similar to the USMC's CH-46A models. The HH-46A came online as fifty CH-46As converted to the Search and Rescue (SAR) role for the USN. The RH-46A was a planned form of the CH-46A intended as a minesweeper for the USN. The UH-46B was considered by the USAF but eventually passed on.

The YCH-46C (becoming the YHC-1A in 1962) was used by NASA in vertical autonomous landing trials for a time.

The CH-46D was another USMC model but this carried 2 x General Electric T58-GE-10 turboshaft engines of 1,400 horsepower each and 266 were built to the standard. Existing HH-46A models were upgraded to the HH-46D in small numbers for SAR duties. Additions included Doppler radar and an in-built hovering capability over water, The UH-46D was used by the USN in the at-sea replenishment role and ten were built up from the CH-46D stock.

The CH-46E numbered 275 untis built up from the A-, D- and F-models. These all included modernized avionics suites, improved transmission boxes and upgraded T58 General Electric turboshaft engines. The HH-46E were three SAR conversions for the USMC from the CH-46E stock. The VH-46F was formed from the CH-46F and used as a VIP support model.

CH-46X was a proposed, all-modern successor to the CH-46 line but not followed-up on.

Production of 524 total CH-46 helicopters was had from 1962 until 1971 with the USMC becoming the type's largest global operator. The aircraft was produced under the Vertol Aircraft Corporation and Boeing Vertol brand labels for its time. The United States Navy also began to rely on the type as did the United States State Department for a time. The USMC fielded the system during the latter half of the Vietnam War (1955-1975) where it was used in all manner of roles - general transport, assault support, Search and Rescue (SAR), MEDical EVACuation (MEDEVAC) and special operations support. The USN gave up use of the CH-46 in 2004 and the USMC followed until 2015.

Other operators went on to include the Canadian Army and Air Force who both operated the type as the CH-113 Voyageur and Labrador (respectively). Japan operated the type as the KV-107II through a series of variants and also took on license local production of the helicopter. The Japanese used the CH-46 across their air, army, marine and police services for a time. The Saudi Ministry of Interior and the Royal Thai Army both relied on the CH-46 (both being former operators).

Sweden purchased ten UH-46B in 1963 from the United States stock and designated them as Hkp 4A in service. This was further bolstered by another eight KV-107 helicopters built by Japan-based Kawasaki under license (becoming the Hkp 4B in Swedish service). The Swedes also made use of the Hkp 4C and Hkp 4D marks in service.

With its inherent power of two turboshaft engines driving wide-spanning main rotor blades (these effectively cancelling out torque and making for a more stable rotary-wing platform), the CH-46 carried a crew of three and held space for up to 25 troops or 15 medical litters and their accompanying staff. The Sea Knight, like its Chinook counterpart, could also be arranged to carry an external sling load under the fuselage as needed.

Though the United States Army elected to take on the dimensionally larger C-47 Chinook into service, the Marine Corps accepted their CH-46's in 1961 to replace their aging UH-34 helicopter series. By 1964, deliveries were in full swing. The USMC no longer relies on the CH-46 as a workhorse and the series in mainly in use with the US Department of State and several private civilian market companies.
Boeing Vertol CH-46E Sea Knight Specifications
National Flag Graphic
United States
Year: 1964
Status: Active, Limited Service
Type: Medium-Lift, Tandem Rotor Transport Helicopter
Manufacturer(s): Boeing Vertol - USA
Production: 524
Supported Mission Types
Ground Attack
Close-Air Support
Airborne Early Warning
Electronic Warfare
Aerial Tanker
Passenger Industry
VIP Travel
Business Travel
Special Forces
Crew: 3
Length: 44.82 ft (13.66 m)
Height: 16.70 ft (5.09 m)
Empty Weight: 11,585 lb (5,255 kg)
MTOW: 24,299 lb (11,022 kg)

Installed Power
2 x General Electric T58-GE-16 turboshaft engines developing 1,870 horsepower and driving tandem three-blade rotor systems.

Standard Day Performance
Maximum Speed: 166 mph (267 kph; 144 kts)
Maximum Range: 690 mi (1,110 km; 599 nm)
Service Ceiling: 9,498 ft (2,895 m; 1.80 mi)
Rate-of-Climb: 1,715 ft/min (523 m/min)


Operators List
Canada; Japan; Sweden; Saudi Arabia; Sweden; Thailand; United States

Series Model Variants
• Model 107 - Vertol Prototype Model; fitted with 2 x Lycoming T53 turboshaft engines.
• YCH-1A - US Army Prototype Evaluation Model designation of which three were produced.
• HRB-1 - Initial Production Designation for US Marine Corps, later redesignated to CH-46 after 1962.
• CH-46A - Initial Production Designation from HRB-1 after 1962; 107 produced for US Marine Corps usage; fitted with General Electric T58-GE-8 turboshaft engines.
• UH-46A - Similar to the CH-46A but for US Navy use; 14 such delivered.
• CH-46D - USMC model fitted with T-58-GE-10 powerplants.
• UH-46D - US Navy model similar to CH-46D USMC model.
• CH-46E - Upgraded CH-46D and CH-46F models; fitted with T58-GE-16 powerplants; improved crew survivability features.
• CH-46F - Improved avionics
• CH-113 "Labrador" - Canadian CH-46A search and rescue models.
• CH-113A "Voyageur" - Canadian CH-46A transport models.
• HKP-4 - Swedish variant fitted with Rolls-Royce powerplants.
• KV 107 - Japan license-produced Model 107 series of various role types.

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