S-61 HSS-2,SH-3A/B/D/G/H, S-61L/N, CH/HH-3C/E/F
insert s-61-1
Four Stacked Aircraft – October, 1960
Background
The Sikorsky S-61 designation was assigned to the company's first twin engine helicopter that was designed from the ground up to take full advantage of emerging turbo-shaft engine technology. This new model marked the end of reciprocating engine installations at Sikorsky and ushered in the era of the lighter and more compact turbine engines. The S-61 served all branches of the US Military as well as commercial airline service. It began its long production career as a model specifically tailored to anti-submarine warfare for the US Navy bearing the designation HSS-2. The model history described below focuses on this most important version of the S-61 helicopter series.
The threat of Soviet nuclear-armed submarines arose soon after the first Russian nuclear detonation in 1947 which immediately elevated anti-submarine warfare (ASW) to a mission of immense national importance. In 1950, at the height of the Cold War, the CIA noted an unconfirmed report that the only atomic bomb the Soviets had produced would have to be delivered by submarine. In 1955 the new Chief of Naval Operations, Adm. Arleigh Burke, asked the Committee on Undersea Warfare of the National Academy of Sciences to conduct an Anti-Submarine Warfare ASW study. That study, Project Nobska, concluded that “Confronted with quiet submarines of long endurance, a sufficiently accurate means of navigation, and suitable weapons, defense against shore bombardment by submarines becomes a huge problem.”
World War II experience in the North Atlantic demonstrated the futility of engaging submarines with surface vessels. The population of Nazi U-Boats peaked at 240 in 1943. Against this force, 875 sonar-equipped escorts could not conclusively prevail. There was a need to combine the sonar’s detection, localization, and targeting, with the speed of an aircraft.
insert s-61-2
SH-3H of HS-8 dipping SONAR
One of the solutions was the ASW helicopter with active dipping sonar, a concept first demonstrated on a Sikorsky HOS (R-6) helicopter by the Naval Research Laboratory in 1946.
Starting in the early 1950’s, the U.S. Navy, Sikorsky and the Pacific Division of Bendix Aviation Corp. began developing the technology for helicopter ASW, combining the speed of an aircraft with underwater sonar previously based aboard ships. Using Sikorsky HSS-1 (H-34) helicopters, hunter-killer technology and tactics were developed and fielded. One helicopter carried a submersible sonar sensor and an airborne processor to detect, locate, and display the target; another helicopter carried a torpedo to address it. Space and payload limits prevented one helicopter from carrying both.
Simultaneously, the Navy recognized the need for improved helicopter engine technology and in 1953 awarded General Electric a $3M contract for the XT-58 “baby gas turbine.” The engine was to weigh 400 pounds and produce 800 HP, a two-to-one improvement over the legacy, reciprocating Wright R-1820 engine powering the HSS-1. The result exceeded expectations. The resulting engine weighed 324 pounds and generated more than 1,000 HP in a 10 cubic-foot package compared with the legacy piston engine of 62 cubic-feet.
The increase of almost four times the power/weight ratio in a compact 1/6th size permitted Sikorsky, for the first time, to truly tailor a helicopter to a mission, rather than tailor a mission to fit the payload and space remaining after the engine was installed.
In the mid 1950’s the U.S. Navy requested that Sikorsky modify an existing HSS-1N to accommodate two T58 engines in place of the R-1820. This was designated as the HSS-1F and showed the significant benefit of turbo-shaft engines over piston engines. The engines were not only lighter and smaller but provided 2,000 horsepower compared to the 1,525 available from the piston engine.
insert s-61-3
Showing the Large Piston Engine Installation in the Nose
insert s-61-4
HSS-1F Showing the Compact Installation of the T058 Engine
The benefits of the turbo-shaft were profound. The light weight and small size allowed the Sikorsky designers to place all of the mechanical components (engine, main gearbox, driveshaft, tail gearboxes, and tail rotor) on the top of the fuselage and freed the cockpit and cabin design to be tailored to the mission requirements. Heretofore, the major design problem had been the location of the heavy piston engine with the cockpit and cabin squeezed into the remaining space.
With this new engine, Sikorsky was able to offer the Navy, in place of the HSS-1F, the HSS-2, an all-new design beautifully tailored to the ASW mission. Sikorsky Engineering Report 61007 documenting the October 1957 HSS-2 Mockup Review reported:
“The success of the HSS-1 piston engine helicopter as an anti-submarine search and attack vehicle has prompted the Navy and Sikorsky Aircraft Division to enter into the next logical step, the development of a turbine powered modification of the HSS-1, which incorporates twin turbine engines, amphibious characteristics, all the technological and functional advantages gained through experience with the HSS-1, with capability of performing a combined Hunter-Killer ASW mission.
A new, low frequency, sonar (AQS-11) is being developed concurrently by the Pacific Division of Bendix Aviation Corp. as Contractor Furnished Equipment. This sonar together with the four (4) hour endurance HSS-2 constitute the major components of the first weapon system to meet Navy’s ASW requirements.
insert s-61-5
HSS-2 Mockup - October, 1957
insert s-61-6
SH-3A’s over the USS Kearsarge in the early 1960’s
The Bendix dipping sonar system consisted of a sonar reeling machine, a reel of 500 feet of sonar cable, the submersible sensor, sonar data processing and display equipment, and a sonar operator control console. The HSS-2 also featured navigation and mission avionics and sensors to provide automated approach to, and maintenance of, a hover stabilized above the submersed sensor and provisions for carrying and firing torpedoes. This powerful mission suite was enclosed in an airframe with hull and sponson flotation based on the iconic Sikorsky Pan American Clipper flying boats with which Pan American Airlines had pioneered international transoceanic air travel two decades earlier.
Configuration Features
The HSS-2 was primarily intended for the ASW mission, but Marine Assault and Army Transport missions were also considered. Sikorsky Engineering Report 61003, Engineering Basic Data Report Model HSS-2, HUS-2, H34B Helicopters, 2/26/57 states:
“General design objectives are:
- Design to accomplish given missions
- Minimum weight
- Component life and Reliability
- Minimum drag and cleanest external surface
- Ease of maintenance
- Manufacturing simplicity.”
The most distinctive feature of the Sikorsky S-61 series is the use of a boat hull with outboard floats (called sponsons). The hull design with a 12 degree deadrise angle was derived from Sikorsky's extensive experience in flying boat design. The outboard sponsons significantly increased the lateral stability in the water. The main landing gear retracted into the sponsons and water take-off and landings were performed with the gear retracted. To increase lateral stability and buoyancy, inflatable floats were added to the outsides of the sponsons.
The other significant configuration item was mounting of the engines and drivetrain above the cabin.This completely separated the cockpit and cabin from the machinery and reduced noise while increasing safetycompared to the prior piston engine designs. As noted earlier, this was due to the significant reduction in the size and volume of the turboshaft engines.
insert s-61-7
HSS-2 hovers over deck of USS Champlain March 1961
The S-61 (HSS-2) was Sikorsky’s first model to employ a main transmission capable of providing almost 100- to-1 reduction ratio needed for the turbo shaft engine’s high, 20,000 rpm, output speed. Prior MGBs had reduction ratios of only 10 or 12- to-one reflecting the much lower output speeds of piston engines. Higher engine output speed forced advancements in free wheel unit technology and high speed bearings.
The main rotor head featured technology previously proven on the S-58, such as basic rotor configuration and the NACA 0012 airfoil, but for the first time offered oil-lubricated rotor bearings, a departure from the previous grease lubrication scheme. Oil lubrication eliminated the need for periodic grease system maintenance. Another important feature of the HSS-2 was the fully automatic main rotor blade fold. Along with simple manual fold of the tail rotor pylon, this allowed for a convenient, compact placement aboard ship. The rapidity and reliability of the blade fold was important operationally and became more so when S-61s were operated from vessels smaller than the ASW carriers on which they were initially deployed.
Automatically stabilized flight and an automated approach to, and maintenance of, a stable hover had been developed in the previous S-58 and S-56 models. An Automatic Stabilization System, ASE, provided electronically stabilized flight.Acoupler provided the autopilot functions to automatically approach and maintain a hover fifty feet above the ocean surface, into the wind, stabilized relative to the sonar cable supporting the submerged sonar transducer. A radar altimeter provided altitude; a Doppler radar system provided airspeed data for stabilization and auto approach. Earlier ASE and Coupler systems had consisted of vacuum tube circuits. For the first time HSS-2 systems were fully transistorized solid state circuits.
The HSS-2 was fitted with a two-piece personnel door on the left side, just aft of the cockpit. It also had a large siding door on the right side in the aft cabin. This greatly aided in moving equipment in and out of the cabin.
General Arrangement Drawing
insert s-61-8
HSS-2 three view drawing
Mission Systems
The HSS-2 was equipped with a comprehensive suite of mission electronics that allowed it to track submarines in all weather, day and night. This equipment included:
AN/AQS-10 / Dipping sonarAN/ARC-39 / low frequency ADF
AN/ARA-25 / UHF ADF
AN/APN-130 / Doppler radar
AN/APN-117 / Radar Altimeter
AN/ARC-52 / UHF Radio
AN/ARN-21 / TACAN
AN/ASA-13 / Navigation Plotter
AN/AYK-2 / Navigation Computer
AN/APX-6 / IFF
In addition, torpedoes could be carried and launched, making the HSS-2 a submarine hunter/killer.
General Characteristics and Performance
DimensionsLength, rotors turning / 72' 7
Height, rotors turning / 16' 10
Width, over sponsons / 16' 0
Length, folded / 46' 6
Height, folded / 16' 10
Width, folded / 16' 0
Main Rotor
Diameter / 62' 0
Number Blades / 5
Chord / 18 ¼”
Solidity / 0.0738
Rotor Speed (100%) / 203 rpm
Tail Rotor
Diameter / 10' 4”
Number Blades / 5
Chord / 7 11/32”
Solidity / 0.1885
Tail Rotor Speed (100%) / 1,244 rpm
Horizontal Tail
Span / 6' 0
Area / 20.0 sq ft
Taper Ratio / 1.5:1
Aspect Ratio / 1.80
Landing Gear
Type / Retractable
Configuration / Tail Wheel
Tread / 13' 0
Wheelbase / 23' 4
Engines
Number / 2
Manufacturer / GE
Model / T58-GE-6
Normal Rated Power / 900 hp
Military Power / 1,050 hp
Weights
Design Gross Weight / 16,237 lb
Alternate Gross Weight / 19,000 lb
Limit Load Factor DGW / +2.5g/-0.5g
Limit Sink Speed / 8 fps
Performance
Vmax, SLS / 135 kt
Vcruise, SLS / 125 kt
Service Ceiling / 14,000 ft
Combat Endurance / 4 hrs
Production History
The Sikorsky model designation for the HSS-2(SH-3A) is the S-61. Since 1959, Sikorsky Aircraft has produced 794 aircraft based on the original S-61. At the end of twenty years production, Sikorsky produced the last S-61 in 1980. Sikorsky licensees in Great Britain, Japan, Canada, and Italy have produced an additional 679. It is estimated that up until2010 S-61s had flown more than 24 million hours in military service and civil use.
insert s-61-9
S-61 flight hours through 2010
Sikorsky Production by Type
Sikorsky No / Design / QuantityS-61 / XHSS-2 / 10
S-61 / HSS-2 (SH-3A) / 245
S-61B-1 / CHSS-2 (CH-124) / 41
S-61 / HSS-2Z (VH-3A) / 8
Sub-total / 304
S-61A / CH-3B / 3
S-61A / S-61A / 52
S-61D / YSH-3D / 4
S-61D / SH-3D / 96
S-61D / VH3D / 11
S-61D / S-61D / 15
Sub-total / 181
S-61R / CH-3C / 74
S-61R / CH-3E / 45
S-61R / HH-3E / 14
S-61R / HH-3F / 40
Sub-total / 173
S-61L / S-61L / 13
S-61N / S-61N / 123
Sub-total / 136
Total / 794
Production Quantities
insert s-61-10
S-61 Production by year
insert s-61-11
S-61 Licensed Production
Related Models
Sikorsky developed a series of derivatives based on the S-61 (HSS- 2.)These models are summarized below.
S-61 Commercial Models
S-61L
The S-61L was designed 1961 with a longer fuselage without sponsons for commercial passenger transport.It first flew on November 2, 1961, and was 4 ft 3 in (1.30 m) longer than the HSS-2 in order to carry a substantial payload of freight or passengers. Initial production S-61Ls were powered by two 1350shp (1005 kw) GE CT58-140 turboshafts, the civil version of the T58. The S-61L features a modified landing gear to reduce weight. The S-61L was configured to carry up to 30 passengers.
insert s-61-12
First S-61L delivered to Los Angeles Airways
S-61N
This was followed by the S-61N which made its first flight on August 7, 1962. Identical to the S-61L except for retaining the HSS-2 (SH-3) floats, this version was optimized for overwater operations, particularly oil rig support. Both the S-61L and S-61N were subsequently updated to Mk II standard with improvements including more powerful CT58-110 engines giving better hot and high performance, vibration damping and other detail refinements.
The first S-61N Serial No. 61143 was delivered to Mitsubishi Corporation on September 26, 1962. This helicopter was still in service serving the Irish Coast Guard under a contract with CHC in 2013. Although the last S-61N was delivered in May 1980, many S-61N helicopters are still in service in 2013. Many modifications have been made over the years including removing to front fuselage plug (the Shortsky) to save weight and increase external lift capability, removing the sponsons and replacing with S-61L style landing gear and many avionic upgrades as technology has progressed.
insert s-61-13
The first S-61N still in service in 2013 with the Irish Coast Guard
CH-3B
On the military side, the U.S. Air Forceordered 3 SH-3A helicopters with the all ASW equipment removed to provide logistics support for 2 offshore early warning radar stations (TexasTowers)located out in the Atlantic Ocean off of the New EnglandCoast. These helicopters were based at Otis AFB, Massachusetts and designated as the CH-3B.
Not long after acceptance by the Air Force CH-3B (62-12574), dubbed the “Otis Falcon“, flew from Otis AFB Massachusetts to ParisFrance. Total flight time was 35.5 hours and included stops in Labrador, Canada, Greenland, Iceland and Scotland before landing in Paris. The “Otis Falcon” upon completing its European visit was returned to the US via ship.
insert s-61-14
U.S. Air Force CH-3B “Otis Falcon”
S-61R Models
The S-61R was a company funded model developed as a derivative of the S-61/SH-3 Sea King model. It featured a substantially-revised fuselage with a rear loading ramp, a conventional though water-tight hull instead of the S-61's boat-hull, and retractable tricycle landing gear. The fuselage layout was similar tothe larger S-65(H-53)variants.
insert s-61-15
2012 photo of S-61R N664Y, the S-61R prototype, with sponsons removed
General Arrangement Drawing
insert s-61-16
CH/HH-3C/E/F 3 view drawing
The S-61R prototype made its first flight in 1963. During its development, the U.S, Air Force placed an order for the aircraft, which was designated the CH-3C. The Air Force used the CH-3C for utility missions. A rescue version, HH-3C with camouflage paintand rescue equipment added was equipped to recover downed pilots. The CH-3E variant with more powerful engines followed in 1965.
insert s-61-17
U.S. Air Force CH-3C lifts Army jeep with mounted 105mm howitzer 1964
insert s-61-18
HH-3C flying over Vietnam 1968
The HH-3E featured protective armor, self-sealing tanks, a retractable inflight refueling probe, jettisonable external tanks, a high-speed hoist, and other specialized equipment. It was the work horse rescue helicopter in Vietnam until the arrival of the HH-53B/C. The HH-3E known as the “Jolly Green Giant”, saw wide and excellent service in search and rescue missions. One HH-3E, Serial No. 67-14709, had a long and distinguished history. Assigned to the 37th Air Rescue and Recovery Squadron at Da Nang Air Base, South Vietnam, it flew with the call sign “Jolly Green 2”in the Vietnam War. During 32 months of service in Vietnam, the crewmen assigned to it received one Air Force Cross and fourteen Silver Stars for heroism. In addition, they were credited with the rescue of 27 American Airmen. This helicopter has been restored and is on display at The National Museum of the Air Force, Dayton, Ohio.
The HH-3E featured in-flight refueling equipment permitting the world’s first non-stop helicopter flight across the Atlantic Ocean, from New York to Paris, in 1967. Two U.S. Air Force Sikorsky HH-3E "Jolly Green Giant" search and rescue helicopters departed New York on May 31st on their way to a 30 hour 46 minute flight to Paris. Refueled nine times each by C-130 tanker planes at altitudes of between 1,000 and 9,000 feet and speeds of 125 mph, the helicopters landed at Le Bourget during the 27th Paris Air Show. The two helicopters took off at 1:05 in the morning, New York time, in order to arrive during the middle of "Helicopter Day" at 1:51 in the afternoon, Paris time. Air Combat magazine remembered this .historic event in its April 1992 edition. A link to this article is provided below.
insert s-61-19
Air Force HH-3E pilots, Major Herbert Zehnder (left) and Major Donald Maurras (right) are greeted by|
Igor Sikorsky at the 27thParis Air Show after a non-stop Atlantic crossing in 1967.
insert s-61-20
U.S. Air Force HH-3E “Jolly Green Giant”rescue helicopter.
HH-3F
In 1965, the U.S. Coast Guard ordered a S-61R version designated HH-3F “Pelican” for all-weather extended range search and rescue (SAR) missions over the open sea. The HH-3F had a range of 655 nautical miles. The first of 40 HH-3F helicopters was delivered in 1969. Deliveries continued for the next four years. In addition the Coast Guard obtained five U.S. Air Force HH-3E helicopters and converted them to the HH-3F configuration. The HH-3F was removed from service after 25 years in 1994.
The unique HH-3F Avionics suite included:
AN/APN·195 Radar
The AN/APN-195 radar set was a lightweight, weather radar system consisting of a receiver transmitter, synchronizer, control panel, indicator and antenna. The radome was mounted on the nose of the helicopter. The radar provided an accurate and continuous picture of weather conditions (weather map) in the general sky area ahead of the helicopter and was used for weather avoidance, a navigation and search aid to extend the vision of the pilot. The radar had 3 ranges: 10, 30, and 60 miles.