The Sikorsky S-97 Raider is a high-speed scout and attack compound helicopter based on the Advancing Blade Concept (ABC) with a coaxial rotor system. Sikorsky planned to offer it for the United States Army’s Armed Aerial Scout program, along with other possible uses.
First proposed in response to a Request for Information for the Armed Aerial Scout (AAS) program in March 2010, the S-97 was formally launched on 20 October 2010. It was intended as a contender for a United States Army’s requirement to replace the Bell OH-58D Kiowa Warrior. Other military roles are possible, the U.S. Special Operations Command having expressed interest in the S-97 as a replacement for the MH-6 Little Bird, and the possibility of adapting it for civilian applications also exists.
Sikorsky plans to build two prototypes of the S-97 as demonstrators. One prototype (P1) will be used for flight testing, while the second (P2) is planned for use as a demonstrator.
Sikorsky started construction of the two prototypes in October 2012. In September 2013, Sikorsky began final assembly of the first S-97 following delivery of the single-piece, all-composite fuselage by Aurora Flight Sciences. In February 2014, construction of the first S-97 prototype was one-quarter complete. Simulated bird strikes testing had been conducted on the fuselage at speeds of up to 235 kn (435 km/h; 270 mph), the S-97’s expected maximum flight speed. Drop tests were also performed to ensure the fuel tanks’ safety in the event of a crash.
Sikorsky targeted the S-97 for the AAS program, aiming for the helicopter to fly before the Army down-selected. Sikorsky invested $150 million and its 54 suppliers (who provide 90% of the parts) spent the remainder of a total of $200 million on two prototypes; production models aim to meet the program’s $15 million unit cost target. However, the Army ended the AAS program in late 2013. Budget projections for FY 2015 included retiring the U.S. Army’s OH-58 Kiowa fleet and transferring AH-64 Apache attack helicopters from U.S. Army Reserve and U.S. Army National Guard to the active Army to perform the aerial scout role. Sikorsky suggested the possibility of buying the S-97 to replace lost Apache for armed helicopter needs. Sikorsky proposes S-97 as FVL-CS1; the light scout helicopter.
The S-97 design includes variable speed rigid coaxial main rotors and a variable-pitch pusher propeller, making the S-97 a compound helicopter. Like the X2, it has fly-by-wire control and dynamic anti-vibration actuators to cancel out shaking. The main rotors have hingeless hubs and stiff blades, to improve low-speed handling and efficiency of hover. At high speeds, the close spacing of the hubs reduces drag. The stiff blades allow each rotor to have low lift on the retreating side of its rotor disk (reducing drag), whereas each rotor on a conventional coaxial rotor with “floppy” blades needs nearly equal lift distribution. The propeller relieves the rotor of propulsion, further reducing drag.
Maneuverability is improved compared with earlier helicopters because of the ability to tilt the coaxial rotors together or tilt each one differently, and because of the variable pitch propulsor and active elevons. At low speed the S-97 yaws by differential torque of the upper and lower rotor, at high speed it uses rudders.
The S-97 is capable of carrying up to six passengers, in addition to a flight crew of two in a side-by-side cockpit. However, the production S-97 is projected to be capable of flying with either one or two pilots, or autonomously. Space for a targeting sensor has been reserved, however not installed in the prototype aircraft.
Based on the technology from the Sikorsky X2 demonstrator, the prototype S-97s is powered by a General Electric YT706 turboshaft (the same engine used on the MH-60M Black Hawk). Compared to the OH-58D Kiowa, the S-97 has significantly increased performance goals, such as cruising speeds upwards of 200 knots while carrying weapons, turning at three times the force of gravity at 220kt, and a high hover efficiency (Figure of merit). Sikorsky also aims for an operating cost of $1,400 per flight hour.
Its avionics were powered on in June 2014, with rollout on 2 October 2014. The first flight of the S-97 occurred on 22 May 2015. It flew for 1 hour instead of the planned 30 minutes, completing three takeoffs and landings; forward, rearward and sideward. For this initial flight, the Raider was flown with its triplex fly-by-wire flight control system in backup degraded mode so as to focus on basic airworthiness in the low-speed regime. This begins a year-long flight test program of about 100 flight-hours to expand the flight envelope to meet Sikorsky’s key targets of 220-knot cruise speed carrying weapons, hover at 6,000 feet on a 95F day and 3g maneuverability at speed. Toward the end of Phase 1 testing, software will be upgraded to Block 2, bringing in the propulsor and articulating tail to increase speed and enable the full flight envelope. The second prototype (P2) was displayed to the public in October 2015. After two flight hours and a few months of testbench validation of the propulsion drivetrain, P1 is scheduled for higher speed some time in 2016.
On 3 August 2017, an S-97 prototype suffered what Sikorsky described as a hard landing at their flight test facility in West Palm Beach, Florida; both airline transport pilots received minor injuries. The NTSB factual report on the incident stated that the helicopter lifted into a low hover and immediately experienced excessive roll oscillations which lead to intermeshing of the counter-rotating coaxial rotor system, and a hard landing. Damage to the helicopter included collapsed landing gear, structural cabin damage, and dynamic component damage, including rotor blade tip separation of all rotor blades. Video of the accident sequence showed aircraft roll oscillations exceeding 60–degree angle of bank during the course of 5 seconds, during which the upper and lower rotors collided at the 1 o’clock position.
On 25 June 2019, the S-97 returned to flight testing and reached a speed of 190 knots.
Sikorsky and partner Boeing are to use the S-97’s technology and design process as a basis to develop the SB-1 Defiant, a high-speed rigid rotor co-axial rotorcraft, for the army’s Joint Multi-Role Technology Demonstrator (JMR TD) program.
Powerplant: 1 × General Electric YT706, 2,600 shp (1,900 kW) Main rotor diameter: 1 (2 coaxial) × 34 ft (10 m) Propeller: 1 x 6-bladed variable-pitch, clutchable pusher propeller (7 ft (2.1 m) diameter) Length: 35 ft (11 m) Gross weight: 8,945 lb (4,057 kg) Max takeoff weight: 11,000 lb (4,990 kg) Cruise speed: 250 mph (410 km/h, 220 kn) (with external weapons) Never exceed speed: 280 mph (440 km/h, 240 kn) Range: 350 mi (570 km, 310 nmi) Endurance: 2 h 40 min Service ceiling: 10,000 ft (3,000 m) at 95 °F (35 °C) Crew: 0–2 pilots Capacity: 6 troops Armament: .50 cal gun with 500 rounds
The 1927 two-place Sikorsky UN-4 (ATC 2-23) were modified Curtiss JN-4D fuselage with a Sikorsky-Gluhareff high-lift wing. A number were built, including C2044 and 5469.
Powered by a 90hp Curtiss OX-5 engine, the wing was adapted for other types, as well—Travel Air, Standard, etc.
The Sikorsky Helicopter No.2 of 1910 was also known as the S-2; an identification later designated. Powered by the same Anzani 3-cylinder of 25 hp as in the No.1. Developing lift force using contra-rotating three-bladed rotors, reportedly it could almost lift itself.
In late 1971 the Army Air Mobility Research and Development Laboratory awarded Sikorsky a contract for the development of a single-engine research helicopter prototype designed specifically to flight test the company’s Advancing Blade Concept (ABC) rotor system. This new system consisted of two rigid, contra-rotating rotors which made use of the aerodynamic lift of the advancing blades. The XH-59A’s ABC system consisted of two three-bladed, coaxial, contra-rotating rigid rotors, both of which were driven by the craft’s single 1825shp PT6T-3 Turbo Twin Pac engine. During high-speed flight only the advancing blades of each rotor generated lift; this off-loaded the retreating blades and thereby eliminated the aerodynamic restrictions caused by blade-stall and the high mach number effect of the advancing blade tip. This, in turn, produced greater stability and manoeuvrability while eliminating the need for either a supplementary lift-generating wing or an anti-torque tail rotor. The XH-59A’s streamlined fuselage more closely resembled that of a conventional airplane than a helicopter, having a cantilever tail unit with twin endplate rudders, side-by-side seating for the two crewmen, and fully retractable tricycle landing gear.
First using scale models for wind tunnel tests at the Ames NASA research center, and then the real aircraft, the resultant Model S-69, which was allotted the military designation XH-59A and the serial number 73-21942 (c/n 69-002), made its first flight on 26 July 1973. This was extensively flight tested as a pure helicopter and, with auxiliary propulsion, flown at speeds in excess of 480 km/h / 300 kt and altitudes of more than 25,000 ft. This prototype was lost in an accident a month after the first flight.
The first prototype was written off and the cockpit was used in the Paris air-show to demonstrate a sighting system for LHX.
Following an enquiry, design modifications were requested, plus improvements to the control system. Tests were resumed in July 1975 with the second prototype incorporating several significant control system modifications. This second machine (73-21941 c/n 69-001) flew for the first time in 1975, completing the pure helicopter portion of the program, and in 1977 was converted into a compound rotorcraft through the installation of two 1350kg J60-P-3A turbojet engines. The modified machine was jointly evaluated by the Army, Navy, and NASA at NASA’s Moffet Field, California beginning in 1978, and was later able to reach and maintain speeds in excess of 515kph in level flight.
In 1982 the plan was to develop this aircraft into a new XH-59B configuration with advanced rotors, new power plant, and a ducted pusher propeller at the tail. This approach was seen as a possible solution to the Army’s search for a new light attack helicopter (LHX), and further funding was recommended. The S-69/XH-59 program was abandoned, however to pursue the XH15.
The existing XH-59A aircraft was officially transferred to the Army museum at Fort Rucker Alabama following the 1981 end of joint Army/Navy participation in the tri-partite flight test program.
The forerunner of an entirely new generation of production models, the S-62 was the company’s first amphibious helicopter, with a boat hull and powered by a single General Electric T58 turbine.
S-62 prototype
The Sikorsky S-62 was the first turbine-powered helicopter to be granted a type approval certificate by the U.S. Federal Aviation Agency, and was also the first type to pass new regulations introduced by the FAA to govern the operation of commercial passenger-carrying helicopters.
The design, drawn up in 1957-58, was based on using identical main and tail rotors and transmission systems, and other dynamic and mechanical features, of the proven piston-engined S-55. The fuselage was entirely new, being designed for fully amphibious operation with a flying-boat hull and main undercarriage wheels semi-retractable within the two outrigged stabilising floats. Power was provided by a single General Electric shaft turbine engine, mounted centrally above the main cabin and accommodation provided for a 2-man flight crew and 10 airline passengers or 12 troops.
Two S-62 prototypes were completed, with 1050shp T58-GE-6 engines derated to 670shp. The maiden flight on 22 May 1958, and subsequent world-wide demonstration flights, were made by N880, while N972 carried out trials for the FAA type certificate which was awarded on 30 June 1960; and a few days later the first production machine, designated S-62A, was delivered to a commercial customer.
Later S-62A’s have CT58-100 or -110 engines of 1250 (derated to 730) shp. The S-62B is essentially similar to the A model, but employs the rotor system of the Sikorsky S-58 with the main blades shortened by 0.33m. In February 1962, after service trials with a modified S-62A, the U.S. Navy ordered four of these aircraft on 21 June 1962 as HU2S-1G’s (redesignated as HH52A’s on September 1962 before delivery) for the U.S. Coast Guard. Initial deliveries, under the designation HH-52A and named Seaguard, were made in January 1963. This version powered by a 932kW CT58-GE-8 engine was replaced by the HH-3 Pelican.
Sikorsky HH-52A
In all, ninety-nine were built; 1352 to 1379, 1382 to 1413, 1415 to 1429, 1439 to 1450, and 1455 to 1466.
The HH 52A can carry six litters and can hoist 600 pounds on a cable at¬tached to an electric winch with an explosive guillotine cutter. The engine is a GE turbine that generates 1,250 shaft horsepower, de¬-rated, on this Coast Guard version to only 830 shp by limiting the size of the fuel flow orifices.
HH-52s based at Houston, Texas, frequently practised recovery of the NASA Apollo astronauts. One US Coast Guard machine was used in the film Airport ’77.
Subsequent naval orders for the HH-52A had raised the total to eighty-four by mid-1968 and it has been in use since early 1963. The HH-52A has the T58-GE-8 engine, military version of the CT58-110, and automatic stabilisation equipment. Additional features for coastal search and rescue work include a fold-down rescue platform and boat-towing gear. A rescue hoist can be mounted above the starboard cabin door to lift a maximum load of 272kg, or the S-62A can lift a 1361kg slung load by means of an under-fuselage hook.
Originally designated S-62B, the 1958 S-63 was S-62 with S-58 rotor system,
The S-62C is the equivalent of the HH-52A for commercial and foreign military customers. Apart from the U.S. Coast Guard, which remains the largest user of the type, the biggest single operator of S-62’s is Petroleum Helicopters Inc, which has a fleet of six for work in support of offshore oil-drilling operations in the Gulf of Mexico. Of the forty-six S-62 type helicopters ordered, up to summer 1968, other than those of the USCG, nearly half were for customers in Japan, where Mitsubishi hold the licence. Nine examples were built under licence for service with Japanese Maritime Self- Defence Force (JMSDF).
By mid-1993, no military, and only a very small number of civilian, S-62s remain in use.
In late 1953 the Army awarded Sikorsky a contract for the experimental conversion of two existing H-18 helicopters from piston to turbine power. The two aircraft selected for conversion were 49-2890 and -2891, the third and fourth H-18s built, with the former to be used for flight testing and the latter for static engineering evaluation. Sikorsky allotted the two craft the company designation S-59, and began the conversion work in early 1954.
On Jul 24, 1953 the S-52T (YH-18B) turbine powered version of the S-52 was first flown. It used a French Turbomeca Artouste I engine. A developed version designated YH-18B and powered by a T51-T-3 (Artouste) turbine is now re-designated XH-39.
Sikorsky H-39 49-2890
The H-39 retained the H-18’s basic pod-and-boom layout, but differed from the earlier machine in several ways. The H-39 was powered by a single 400shp XT51-T-3 Artouste II turbine engine, which drove a new, fully-articulated, four-bladed main rotor. Other changes included a modified tail rotor, strengthening of the fuselage, incorporation of retractable wheeled landing gear, and the addition of updated electronics.
The Model XH-39 (S-59), using a 400shp Continental XT51 turbine, was rejected by the US Army, despite its speed and the advantage of retractable landing gear, as being old-fashioned in design and unsuitable for further development. Instead, the Army chose the Bell XH-40 with a Lycoming XT53 turbine.
The H-39 was the Army’s first turbine-powered helicopter, and was for a time the world’s fastest rotorcraft.
On 29 August 1954 Army Warrant Officer Billy Wester flew a world speed record of 156 m.p.h / 251km/h over 3km was set up by Sikorsky XH-39.
On 17 October 1954 Army Warrant Officer Billy Wester flew a world height record of 24,500 ft / 7474m was set up by Sikorsky XH-39.
Sikorsky S-59 Engine: 1 x Continental/Turbomeca Artouste XT51-T-3 turboshaft, 300kW / 400 hp Rotors: 4-blade main 3-blade tail Main rotor diameter: 10.0m / 35 ft Fuselage length: 11.95m / 30 ft 3 in Height: 2.99m Max take-off weight: 1226kg / 3,560 lb Empty weight: 749kg Max speed: 176km/h / 156 mph Ceiling: 24,500 ft Hovering ceiling, IGE: 2804m Service ceiling: 4724m Range: 670km Typical range: 253 miles at 138 mph Seats: Pilot and 3 passengers, 800 lb. cargo or 2 stretchers and attendant.
Designed to overcome the range and offensive payload deficiencies of the anti-submarine HO4S version of the S-55 / H-19, the Sikorsky S-58 was developed to a US Navy order for a prototype XHSS-1 placed on 30 June 1952. The nose engine position was retained for the 1525hp / 1137kW Wright R-1820 engine, but a completely new semi-monocoque fuselage, larger-diameter four-bladed main and four-bladed tail rotors, and transmission system were introduced, together with main rotor and rear fuselage folding to facilitate shipboard stowage. The tail rotor has servo control and both main and tail rotors have brakes. Fuel capacity is from 750 litres to 1,164 litres depending on model.
With a completely redesigned, downward-sloping tail section, the S-58 also differed from the S-55 in having a three-point, tail-wheel landing gear. Air-oil shock-absorber struts. Mainwheels have rotating struts to reduce drag and weight and toe-operated brakes. Tailwheel is fully castoring and self-centring, with an anti-swivelling lock. Mainwheel tyres 11.00 x 12. Tailwheel tyre 6.00 x 6. Toe-operated mainwheel brakes. Track 3.66m. Wheelbase 8.75m.
Pilot’s compartment above main cabin seats two side by side with dual controls. Cabin normally seats 12 passengers. Up to eight stretchers can be carried. Sliding windows of pilot’s compartment removable in an emergency. Cabin and cockpit air conditioned and soundproofed.
Designated XHSS-1, it flew for the first time on 8 March 1954.
Designated XHSS-1, it flew for the first time on 8 March 1954. Three were built, 134668 to 134670, later redesignated as YHSS-1. They were again redesignated, as YSH-34G, in 1962.
After evaluation of the XHSS-1 an initial ten were ordered. The first production HSS-1 flew on 20 September 1954, and the type became operational in August 1955. A total of 215 were built: 137849 to 137858, 138460 to 138493, 139017 to 139029, 140121 to 140139, 141571 to 141602, 143864 to 143960, and 145660 to 145669, of which six were transferred to the USAF and in turn to Brazil (60-5424 to 5429) and six to the USCG as HUS-1G (1332 to 1336, and 1343). All redesignated as SH-34G in 1962.
Now designated SH-34G, it has the name Seabat and carries either dunking sonar search equipment or weapons for attacking submarines.
The 1957 HSS-1F was HSS-1 converted with two General Electric YT58-GE engines. Girst flown on 30 January 1957 and redesignated as SH-34H in 1962.
Later Seabats includes the ‘winterised’ LH-34D (formerly HSS-1L). These models in U.S. Navy service were replacement by the SH-3 Sea King and many were converted to utility transports with UH prefixes. Subsequent production orders totalled 427 (53-4475 to 4554, 54-882 to 937, -2860 to 2914, -2995 to 3050, 55-5241 to 5261, 56-4284 to 4342, 57-1684 to 1770, and 58-1721) included 21 transfers from the USN. Redesignated as CH-34A in 1962. In addition to redesignated ships, 21 H-34As were rebuilt as CH-34C.
One JH-34A was built; 53-4475.
The HSS-1N (SH-34J) was developed for night operations, equipped with Doppler for navigation, automatic stabilisation and automatic hover coupler. A single prototype YHSS-1N 143957 was built, redesignated as YSH-34J in 1962.
Production HSS-1N possibly totalled 167 including 145670 to 145712, 147631/147635, 147984/148032, 148934/148963, 149082 to 149087, 149131 to 149133, 149840 to 149842, 150730 to 150732, 150808 to 150819, and 150821 to 150822, of which 11 were procured as SH-34J (150733 to 150807) might also have been built and the total may or may not include exports to Chile, Germany, Italy, and the Netherlands, as well as some transferred to USAF as HH-34J.
A single HSS-1F (SH-34H) flown on 30 January 1957, was powered by two General Electric T58 turboshafts. In 1960 five HSS-1Z (VH-34D) helicopters joined the Executive Flight Detachment for Presidential and VIP transport duties. Seabats stripped of ASW equipment for utility duties were designated UH-34G and UH-34J.
In 1959 a US Marine Corps HUS-1 served as a launching platform for the Martin Bullpup air-to-surface missile during a series of tactical assault trials at Chesapeake Bay.
The Bullpup was claimed to be the largest radio-controlled missile ever fired from a helicopter.
A troop transport variant was simultaneously acquired by the Marine Corps as the HUS Seahorse. One example of this type was loaned to the Army for service test and evaluation. The Army had placed preliminary orders for production H-34A troop transport variants of the Navy XHSS-1 in April 1953 and the performance of the borrowed Marine Seahorse, essentially identical to the H-34 version, confirmed the Army’s belief that the type would be a vast improvement over the H-19s then in service.
H-34B were 1960 H-34A conversion, redesignated as CH-34B in 1962.
The US Marine Corps ordered the HUS-1 Seahorse (UH-34D) version on 15 October 1954; able to carry 12 Marines or a 1350kg load, this variant entered service in February 1957. The Marines received 570 of the S-58 in the utility version (HUS-1 / UH-34D and -1A, 143961 to 143983, 144630 to 144654, 145713 to 145812, 147147 to 147201, 148053 to 148122, 148753 to 148822, 149318 to 149402, 150195 to 150264, 150552 to 150580, 150691, and 150717 to /150729) and have used the type since 1957 primarily for utility transport and for recovery duties connected with the U.S. satellite programme. The 12-passenger UH-34D and UH-34E (formerly HUS-1 and HUS-1A / UH-34E) are basically alike, the latter being an amphibious version (eight built, 144655 to 144662 and 32 converted from HUS-1) with pontoons for landing on water. Inflatable flotation gear identified the US Marines’ HUS-1A and the US Coast Guard’s HUS-1G (Redesignated as HH-34F in 1962). Four HUS-1L (LH-34D) helicopters were modified for operation in the Arctic. Production continued as redesignated UH-34D after 18 September 1962.
The six 1958 HUS-1G were converted HSS-1 for the USCG. The six, 1332 to 1336, and 1343, were redesignated as HH-34F in 1962.
Four HUS-1, including 144658, 145719, and 150220, were modified for Antarctic duty. They were redesignated as LH-34D in 1962.
Eight HUS-1, 147161, 147179, 147191, 147201, 148803, 148804, 148805 and 150691, were converted as HUS-1Z Presidential aircraft. They were redesignated as VH-34D in 1962.
A total of 603 S-58s were delivered to the US Marines.
The US Army ordered several hundred H-34A, H-34B and H-34C Choctaw helicopters powered by 1063kW R-1820-84 engines and each carrying 16 troops or eight stretchers in the medevac role.
The Army accepted the first of 437 new-construction H-34As in April 1955, the first unit being equipped in September 1955. An additional twenty-one HUS-1 aircraft transferred from the Marine Corps during Fiscal Year 1955 were also designated H-34A (though at least five further USMC Seahorses operated by the Army between 1955 and 1957 retained their original Navy Bureau numbers).
In 1956 an early production example flown by Army Captains Claude E. Hargett and Ellis Hill set new world helicopter speed records on courses of 100 km (141.9mph), 500 km (136mph) and 1000km (132.6mph).
The H-34A was also the first helicopter judged safe enough for routine use by the U.S. President, and in 1957 the Army organized an Executive Flight Detachment equipped with specially modified Choctaws. These aircraft were fitted with extensive soundproofing, plush VIP interiors, and upgraded communications equipment, and were designated VH-34A.
The US Army H-34A, H-34B and H-34C Choctaw helicopters were powered by 1063kW R-1820-84 engines and each carrying 16 troops or eight stretchers in the medevac role. US Army CH-34s maintained a constant patrol along the border of West Germany with Czechoslovakia and East Germany. Army S-58’s have the name Choctaw, the CH-34A and CH-34C differing only in the equipment carried.
The H-34C, with SAR modifications, included 56-4305, -4331, -4333, 57-1692, -1698, -1709, and others. They were redesignated as CH-34C in 1962 along with 21 rebuilt and re-serialed H-34As (63-13190 to 13210.
In 1960 Sikorsky began modifying Army H-34As (and Air Force H-34As and -Bs) to -C model standard through the addition of automatic flight stabilization systems and other detail changes including relocation of Battery, Invertors, and Aux Hyd Reservoir. By January 1962 the Army had 190 H-34Cs and 179 H-34As in its inventory; under the Tri-Service designation system introduced later that year the aircraft were redesignated as, respectively, CH-34C and CH-34B. Several -C model aircraft were subsequently modified to VH-34C standard for VIP transport duties. The VH-34D is a VIP transport.
In 1964 U.S. Marines flying the HUS-1 version of the S-58 saved 1,500 Vietnamese villagers from floodwaters. The aircraft also was used to recover the space capsule of Alan B. Shepard, Jr., America’s first astronaut in space.
HSS-1
Twenty-three UH-34D went to USAF for export to friendly nations (63-8248/8259, -13006/13014, and -13139/13140) and 44 to USN (152686, 153116/153133, 153556/153558, 153695/153704, 154045, 154889/154902, and 156592/156598), of which 10 went to USAFR as HH-34D with new s/ns (60-6913, -6923, 61-4488/4491, -4529, 63-7972/7974).
The CH-34 did not see extensive Army service in Vietnam. The Army’s 1962 decision to deploy the Vertol CH-21 Shawnee to Southeast Asia instead of the faster and more capable Choctaw was based on two considerations. First, in accordance with then-current Army doctrine regarding the area-standardization of aircraft types, the CH-21 was already widely deployed in the Pacific area and the continental United States, whereas all but about thirty of the Army’s CH-34s were based in western Europe. US Army CH-34s maintained a constant patrol along the border of West Germany with Czechoslovakia and East Germany. It was therefore logical and logistically preferable that the CH-21, which was considered acceptable if somewhat past its prime, should be chosen for deployment to Southeast Asia. The Army’s second reason for sending the Shawnee rather than the Choctaw was a somewhat negative opinion of the Choctaw’s combat survivability, a belief based on French experience in North Africa. French forces had used both the CH-21 and the CH-34 in Algeria, the former flown by the Army and Air Force and the latter by the Navy, and official evaluations had indicated that the Shawnee was more likely to survive multiple hits by ground fire than was the CH-34. The French belief that the location and ‘fragile’ construction of the Choctaw’s fuel tanks made the craft extremely vulnerable to ground fire seemed to validate the U.S. Army’s decision to deploy the Shawnee to Vietnam pending the introduction into widespread service of the UH-1 Iroquois. The approximately twenty Army H-34s that did eventually reach Vietnam proved no more vulnerable than any other aircraft in the theatre, however, and ably carried out missions ranging from combat assault to aeromedical evacuation and general cargo transport. Most of these twenty aircraft were turned over to the South Vietnamese during the course of the war, though a few were ultimately reclaimed by the Army prior to the final collapse of the Saigon Government.
One SH-34G was exported to Germany; 152188.
SH-34J production in 1962 was for the USN (151729 to 151731, 152380 to 152381, and 153617 to 153622) of which several transferred to the USAF as HH-34J.
The CH-34 Choctaw remained in frontline Army service well into the late 1960s, and was standard equipment in many Army Reserve and National Guard aviation units for considerably longer. The last Choctaw was not officially retired until the early 1970s, by which time the type’s duties had been divided between the UH-1H Iroquois and the CH-47 Chinook.
The commercial S-58B and S-58D are passenger/cargo transport helicopters comparable with their military counterparts. The 12-seat airline version, certificated by the FAA in August 1956, was built for Chicago Helicopter Airways (eight), New York Airways (three) and Sabena (eight). First commercial deliveries of S-58C were made in 1956-57.
Substantial numbers of military S-58 variants have been exported, and in mid-1967 were serving with the Federal German Army (one hundred and forty-four); the navies of Argentina (five), Brazil (five), France (twenty-six), Germany, Indonesia, Italy (eighteen), Japan (fourteen) and the Netherlands (twelve); and the air forces of Belgium (nine), Cambodia (three), Canada (four), France (one hundred and ten), Germany, Israel (twelve), Thailand (twenty) and South Vietnam (sixty). Those in French and Belgian service were manufactured in France by Sud-Aviation.
Up to 1970 2,261 total all S-58s were built and production of the S-58 ended in December 1965 after 1766 had been built by Sikorsky, but started again to fulfil additional U.S. orders and one from the Italian Navy for six SH-34J’s.
In January 1970, Sikorsky announced the design of kits for the conversion to turbine power by the installation of the Pratt & Whitney PT6 Twin-Pac. First flight of the S-58T took place 19 August 1970 and in April 1971 Sikorsky received FAA approval for the S-58T PT6A Twin Pac-powered turbine conversion for H-34 airframes. One hundred and forty-six conversions, or conversion kits, were produced until, in 1981, the rights were sold to California Helicopter International. Since then customers for the California Helicopter (Sikorsky) S-58T included New York Airways, the Indonesian and South Korean air forces (now retired) and the government and air force of Thailand. The S-58T is also in service in Argentina with the Presidential Aircraft Squadron. Small numbers were built of S-58B and S-58D civil passenger and cargo transport helicopters, a 12-seat airline version being operated by Chicago Helicopter Airways, New York Airways and SABENA.
When he checked in for a Sabena S-58 flight, Igor Sikorsky was asked if his name was spelt like the helicopter’s.
When production was terminated in January 1970, Sikorsky had manufactured a total 1,820 S-58s of all versions.
The S-58T is a turbine conversion of the normally piston engined military H 34, or civilian S¬58, with the Curtiss Wright R 1820 piston radial engine removed from the nose and replaced by a pair of turbines fastened to a common drive transmission as the PT6T Twin Pac.
The PT6T Twin Pac unit fitted to the S-58T is basically two PT6 turboshaft engines mounted side-by-side and driving into a combining gearbox. Of the total 1800 shp available, only 1505 shp can be absorbed by the transmission during take-off and for continuous operations this is limited to 1254 shp. Should one engine fail, sensors automatically increase the good engine’s output up to the maximum 900 shp. Fuel is carried in 12 under-floor cells.
The useful load rose about 200 pounds on the Standard S 58T, it actually went down by some 80 pounds on the Mark II version, which has airline seating and windows. This increased power from 1,525 hp to 1,875 shp. Since the basic rotor blade system has been retained, there would also seem to be a speed handicap there that no amount of extra power could overcome.
By 1975 more than a hundred S 58Ts had been delivered or are under contract, more than half of them in the form of retrofit kits.
S-58T
The S-58T was first flown on 26 August 1970 with P&WC PT6T-3 twinpack turboshaft engine. Kits were built by Sikorsky but 160 conversions were carried out by California Helicopter International.
S-58T
Offering a 5,000 pound sling load, the Sikorsky S 58T has a 110 knots normal cruise, a 10¬knot edge on both the 212 and the 205A. Furthermore, while all three aircraft can hoist a 5,000 pound sling load, the 58T can do it at higher altitudes. The S 58T manages a gross lift at 6,500 feet.
When properly equipped, it’s IFR for two. Outsized wheel hubcaps house automatically inflatable bubbles for inadvertent oceanic dunking. With an engine out, though, the aircraft can hold onto a service ceiling of 4,300 feet.
While it turns out that the 430 pound weight saving gained by substituting the twin turbines for the old recip engine was pretty well swallowed by updating modifications, there was no loss of range with the same 283 gallons of fuel. Though the new turbines consume an extra 22 gph in cruise, the higher 110 knot cruise (versus 85 knots for the pis¬ton model) yields almost exactly the same 243 nm range at sea level.
Furthermore, the hovering altitude in ground effect on a warm day (ISA + 20) went way up from 2,600 feet in the piston model to 7,700 feet in the S 58T.
Whereas the “old” rotor blade system the 58T is saddled with might have seemed a handicap, the engineers at Sikorsky finessed their way around that by smoothing out the vibration levels, and that, in turn, permitted the boost in cruise speed, rather than the addition of brute power.
Instead of adopting the “Nodamatic” vibration damping technique used by Bell, where the cabin is “suspended” at harmonic vibration points, Sikorsky used something called a Bifilar vibration absorber. This consists of weights fastened to the main rotor hub between the rotor blades more specifically, “pendular dynamic masses.” The 120 pound installation not only provides a five to one reduction in vibration levels, according to Sikorsky engineers, but it greatly reduces tail stresses, mechanical failures and overall maintenance.
In addition to the California Helicopters version, Orlando Helicopters also offers S-58 conversions. An S-58 Heli-Camper, similar in fit to the OHA-S-55 Heli-Camper is available, powered by a Wright Cyclone R-1820-84 engine. A further Orlando S-58T conversion is the Orlando Airliner, an 18-seat all-passenger version with nine additional tinted windows fitted on each side of the cabin. By 1997 nearly 30 conversions have been completed.
Total of 166 also produced under licence by Sud-Aviation in France. Sud-Aviation were completing two modified examples of the Sikorsky S-58, each of which was fitted with a 1900shp Turbomeca Bi-Bastan shaft turbine engine, and the first of these machines flew on 5 October 1962. The S-58 development was not pursued.
After acquiring a licence in 1956 to manufacture the Sikorsky S-58 helicopter, Westland imported one of these aircraft in HSS-1 configuration. Given the British serial number XL722, this aircraft was test-flown for a time with its original 1525hp Wright R-1820-84 engine before being modified to accept a 1100shp Napier Gazelle NGa.11 gas turbine.
Napier Gazelle powered Wessex first flight 17 May 1957 at Yeovil
In its new form it was flown for the first time on 17 May 1957, and was later joined by two pre-production Wessex HAS Mk.1’s for Naval trials; the first of these flew on 20 June 1958.
Wessex features – Main and tail rotor each have four blades. Blades attached to hub by taper bolts. Main rotor blades fold manually. Rotor brake fitted. Shaft drive to main rotor through double epicyclic gear. Shaft drive to tail rotor through intermediate and tail gearboxes. Tail end folds to port and forward for stowage. Tail rotor carried at tip of vertical stabilising fin. Small horizontal stabiliser inset in leading-edge of fin.
All blades of light-alloy extruded spar and light-alloy bonded trailing-edge structure. The fuselage is a light-alloy semi-monocoque structure, with steel tube support structure for main rotor gearbox.
Landing gear is a non-retractable tailwheel type. All three units fitted with Westland oleo-pneumatic shock-absorber. Dunlop wheels, tyres and hydraulic disc brakes. Tubeless treaded mainwheel tyres, size 6.00 x 11. Tailwheel tyre size 6.00 x 6.
Compressor bleed air for heating. Ambient air circulation by fan. High-pressure hydraulic system for powered flying controls and 272kg capacity hoist. 24V DC electrical system, with two 6kW generators.
The HAS Mk.1, powered by a Napier Gazelle of 1,450shp (1081kW), went into production in 1959 for the Royal Navy as a submarine search and strike helicopter equipped with dipping Asdic and provision for one or two homing torpedoes. Powered by a 1450shp Gazelle Mk.161 engine, it began service trials with No.700H Flight in April 1960 and has since been delivered to Nos. 706, 737, 771, 815, 819 and 848 Squadrons. The first of these to commission, in July 1961, was No.815; the Wessexes of No.848 Squadron were for commando assault duties aboard H.M.S. Albion, having the ASW gear removed to make room for 16 troops or 8 stretchers and a medical attendant in the main cabin. Alternatively, a slung load of 1814kg can be suspended from an under-fuselage hook.
The original version was the Wessex HAS.Mk1, powered by a Napier Gazelle of 1,450shp (1081kW). The HAS.1 was undergoing service trials with No.700H Sqn during 1960, during which it first landed on an aircraft carrier.
The HAS.1 was supplanted by the Wessex HAS.Mk3 version popularly called the Camel because of its humpbacked search radar above the rear fuselage.
The most extraordinary feature of the Wessex HAS.3 is the stack of avionics and anti-submarine gear that the Royal Navy has fitted it with; the latter consisting of radar and sonar equipment linked together by a small computer to give a “total picture”. All this is operated by a third crewman seated at the rear of the aircraft, in an area which looks like a second cockpit. The sophisticated radar is used for navigation as well as sub hunting.
In August 1964 it was announced that the Iraqi Air Force was acquiring 12 Wessex HC.2. The cost was to be $8m including spares. The Gahanaian air force ordered two Wessex Mk.53.
Much more important numerically is the Wessex HU.Mk 5 version, the Royal Marine Commando assault ver¬sion. These twin engine machines once numbered almost 100. The Navy’s HU Mk.5, for which two orders were placed, entered service in summer 1964 as a commando-carrier assault transport.
In the early 1960s the RAF required a powerful general-purpose helicopter capable of troop-carrying, air ambulance and ground attack roles.
Following the first flight of the true prototype (XR588, this being preceeded by one of the Royal Navy pre-production variants which was later partly converted to an HC.2 version) on 5 October 1962, seventy-one examples of the Wessex HC.2 variant were delivered to the RAF, which first entered RAF service with No.18 Squadron, based at RAF Odiham, Hampshire, in January 1964, replacing the Whirlwind and Belvedere types. The HC Mk.2 was built as a transport helicopter for up to 16 troops, with redesigned gearbox and strengthened airframe.
And doors on each side of flight deck and on starboard side of cabin. Two flexible fuel tanks under cabin floor, total capacity 1,409 litres. Provision for carrying two 500 litre auxiliary tanks in cabin for ferry purposes. Refuelling point in starboard side of fuselage. Oil capacity 9 litres per engine, 19 litres in main gearbox.
Towards the end of 1959 two Whirlwinds joined the Queen’s Flight, designated HCC Mk.8, they had Alvis Leonides Major engines and special interiors.
HCC Mk.8
Westland Wessex HC Mk.2
In 1968 Westland Helicopters received an order for two Wessex aircraft to equip The Queen’s Flight. These were designated HCC4. The aircraft were built to HC2 standard but with the main cabin having a VIP interior finish, furnishings and sound proofing plus an external folding step below the cabin door. Additional Decca navigation equipment was installed on the flight deck. The first flight took place on 17 March 1969. The first official flight was on 1 July 1969 in support of the Investiture of the Prince of Wales at Caernarfon Castle, Wales. The helicopters in their distinctive red/dark blue paint scheme operated for many years from RAF Benson. From 31 March 1995 they moved to RAF Northolt and became part of No.32 (The Royal) Squadron. The Wessex HCC4 was retired in 1998 and No.32 (The Royal) Squadron gave up the task of providing helicopters for the Royal Family.
A commercial version was known as the Srs.60.
The RAAF ordered 27 Westland Wessex Mk31B carrier-borne anti-submarine/search & rescue helicopter from Westland Aircraft Ltd in July 1961. The first was delivered on 1 Nov 1962 and the last on 4 Nov 1963. The HAS Mk.31’s are similar to the HAS Mk.1 apart from their 1540shp Gazelle Mk.162 engines. Australia’s navy anti-submarine duties started in August 1962.
Westland built 356 Wessex in all (including those for the civil market): the HAS Mk.1 version for the Royal Navy; the HC Mk.2 tactical transport version for the RAF; the HAS Mk.3 antisubmarine version with 1550shp Gazelle NGa.18 turbine; the HU. Mk.5 for various roles on the Navy’s commando carriers; the HAS Mk.31 for the Royal Australian Navy; the Wessex Mk.52 for the Iraqui Navy (12); the Wessex Mk.53 for Ghana (3); the Wessex Mk.54 for Borneo and the Wessex Mk.60 commercial version. Seven Wessex Mk.60’s have been built for Bristow Helicopters Ltd. These are 10-passenger commercial equivalents of the Mk.2 and operate in support of the oil and gas drilling rigs in the North Sea.
CH-34A/H-34A Choctaw: Transport and general purpose helicopter for US Army.
CH-34C (formerly H-34C) Choctaw: Similar to CH-34A, but with airborne search equipment.
LH-34D (HSS-1L): Winterised version of Navy Seabat.
SH-34G (HSS-1) Seabat: Anti-submarine version ordered by US Navy 30 June 1952; accepted for service in February 1954.
SH-34J (HSS-1N) Seabat: Improved version of SH-34G.
UH-34D (HUS-1) Seahorse: Utility version for Marines; ordered 15 October 1954 and accepted for service January 1957.
UH-34E (HUS-1A) Seahorse: Version with pontoons for emergency operation from water.
VH-34D (HUS-1Z): VIP transport version of Seahorse.
S-58B: Commercial passenger/freighter version.
S-58C: Commercial passenger-carrying version with two doors on starboard side of cabin.
S-58D: Commercial passenger/freighter version.
S-58T: Turbine conversion with Pratt & Whitney PT6 Twin-Pac, comprising two PT6 engines and combining gearbox; improved performance includes greater speed and lifting power, and better hot-and-high operation.
Westland Wessex HAS. Mk 1 Initial production version, developed for the Royal Navy, with one 1,450shp Napier Gazelle 161 turboshaft engine. Re-engined with a 1,100shp Gazelle NGa.11, flew for the first time 17 May 1957.
Westland Wessex HC. Mk 2 High-performance development of the Mk 1 with two coupled 1,350shp Bristol Siddeley Gnome Mk 110/111 turboshaft engines. Power limitation of 1,550shp at rotor head. Prototype converted from Wessex 1, flew for the first time 18 January 1962, and the first production model (XR588) 5 October 1962.
Westland Wessex Mk 3 Similar to Mk 1, but with 1,850shp Gazelle NGa.18 165 turboshaft engine.
Westland Wessex HCC. Mk 4 Queen’s Royal Flight helicopter.
Westland Wessex HC. Mk 5: SAR helicopter of the Royal Air Force based in Cyprus.
Westland Wessex HU. Mk 5 Similar to Mk 2, for Commando assault duties from carriers of the Royal Navy. Design work began in April 1962 and construction of the prototype was started in May 1962. In service with A&EE (1) and 84 Squadron Akrotiri Cyprus (5).
Westland Wessex HAS. Mk 31 Generally similar to Mk 1, but with a 1,540shp Gazelle Mk 162 engine. Ordered for the Royal Australian Navy for anti-submarine duties from HMAS Melbourne.
Westland Wessex Mk 52 Similar to Mk 2, for Iraqi Air Force.
Westland Wessex Mk 53 Similar to Mk 2, for Ghana Air Force.
Westland Wessex Mk 60 Civil version in service with Uruguayan Navy.
Specifications:
Sikorsky S-58 / H-34 Choctaw Engine: 1 x Wright R-1820, 1137kW / 1504 hp Main rotor diameter: 56 ft / 17.1m Length: 17.3m Height: 4.9m Max take-off weight: 6350kg Empty weight: 3754kg Max speed: 178 km/h / 150 kt Cruising speed: 158km/h Rate of climb: 5.6m/s Service ceiling: 2900m Range: 450km Crew: 2 Passengers: 12-18
CH-34A/H-34A Choctaw Transport and general purpose helicopter for US Army. Engine: 1,525 hp Wright R 1820 84B/D piston. Rotors: 4-blade main; 4-blade tail. Operating speed: 40 – 128 knots Mainwheel tyres 11.00 x 12 Tailwheel tyre 6.00 x 6 Wheel track 3.66m Wheelbase 8.75m Cabin length: 13 ft Seats: 20
CH-34C / H-34C Choctaw Similar to CH-34A Operating speed: 40 – 128 knots Mainwheel tyres 11.00 x 12 Tailwheel tyre 6.00 x 6 Wheel track 3.66m Wheelbase 8.75m Cabin length: 13 ft
LH-34D / HSS-1L Winterised version of Navy Seabat. Engine: 1,425 hp Wright R-1820 Mainwheel tyres 11.00 x 12 Tailwheel tyre 6.00 x 6 Wheel track 3.66m Wheelbase 8.75m Cabin length: 13 ft
SH-34G / HSS-1 Seabat Anti-submarine version ordered by US Navy 30 June 1952; accepted for service in February 1954. Engine: 1,425 hp Wright R-1820 Mainwheel tyres 11.00 x 12 Tailwheel tyre 6.00 x 6 Wheel track 3.66m Wheelbase 8.75m Cabin length: 13 ft
HSS-1F / SH-34H Engines: two General Electric YT58-GE Length: 47’3″
SH-34J / HSS-1N Seabat Improved version of SH-34G. Engine: 1,425 hp Wright R-1820 Mainwheel tyres 11.00 x 12 Tailwheel tyre 6.00 x 6 Wheel track 3.66m Wheelbase 8.75m Cabin length: 13 ft
UH-34D / HUS-1 Seahorse Utility version for Marines; ordered 15 October 1954 and accepted for service January 1957. Engine: Wright R-1820-84 Main rotor: 56’0″ Length: 46’8″ Max speed: 123 mph Mainwheel tyres 11.00 x 12 Tailwheel tyre 6.00 x 6 Wheel track 3.66m Wheelbase 8.75m Cabin length: 13 ft
UH-34E / HUS-1A Seahorse Version with pontoons for emergency operation from water. Cabin length: 13 ft
VH-34D / HUS-1Z VIP transport version of Seahorse. Mainwheel tyres 11.00 x 12 Tailwheel tyre 6.00 x 6 Wheel track 3.66m Wheelbase 8.75m Cabin length: 13 ft
S-58B Engine: 1525hp Wright R-1820-84 Useful load: 5150 lb Max speed: 130 mph Cruise: 101 mph Range: 247 mi Ceiling: 9,500 ft
S-58C Commercial passenger-carrying version with two doors on starboard side of cabin. Engine: 1 x Wright R-1820-84, 1137kW Main rotor diameter: 17.1m Length: 17.3m Height: 4.9m Max take-off weight: 6350kg Empty weight: 3754kg Max speed: 198km/h Cruising speed: 158km/h Rate of climb: 5.6m/s Service ceiling: 2900m Range: 450km Crew: 2 Passengers: 12-18
S-58D Commercial passenger/freighter version.
S-58T Turbine conversion with Pratt & Whitney PT6 Twin-Pac. Engine: P&W PT6T-3 coupled turboshaft, 1525 shp Length: 50 ft 11 in Width: 5 ft 8 in Height: 15 ft 11 in Rotor dia: 56 ft MTOW: 13,000 lb Useful load: 5600 lb Slung cap: 5000 lb Fuel cap (useable): 286 USG Endurance: 2 hr 40 min Max cruise: 110 kt Max speed: 124 kt Fuel consp (cruise): 106 USG/hr Range (cruise speed, 20 min res): 260 nm HIGE: 8950 ft SE ceiling; 2100 ft Crew: 2 Pax cap: 17
S 58T Mark II Engine: UACL PT6T-6, 1,875 shp Main rotor dia: 56 ft Length: 50 ft. 11 in Height: 15 ft. 11 in Disc loading: 5.28 lb/sq.ft Seats: 10 16 Empty weight: 8,354 lb Useful load: 4,446 lb Payload with full fuel: 1,924 lb MTOW: 13,000 lb Power loading: 8.54 lb/hp Fuel capacity (standard): 283 USG/1,910 lb Fuel capacity (optional): 433 USG/2,923 lb ROC: 1,275 fpm Service ceiling: 12,000 ft Single engine service ceiling: 4,200 ft Vne @ 2,000 ft: 124 kt Normal cruise @ 2,000 ft: 110 kt Range @ normal cruise (45 min res. std tanks): 200 nm Endurance @ max cruise (no res, std tanks): 2.6 hr Range max fuel/ cruise: 401 nm/ 3.2 hr Range max fuel / range: 346 nm/ 3.2 hr ROC: 1260 fpm Max sling load: 5000 lb Hovering ceiling in ground effect: 10,400 ft Hovering ceiling out of ground effect: 6,500 ft
Westland Wessex Licence-produced UK version.
Westland Wessex HAS.I Engine: 1 x Napier Gazelle Mk.161, 1450 shp Main rotor diameter: 56 ft Length: 49 ft 11 in Height: 15 ft 10 in Main rotor disc area: 2460 sq.ft Empty weight: 7600 lb MTOW: 12,600 lb Fuel capacity: 266 gal Aux fuel capacity: 200 gal Max speed: 132 mph at SL Cruise sped: 115 mph Sevice ceiling: 14,200 ft Max range w/aux fuel: 600 mi
Westland Wessex HC Mk.2 Engine: 2 x Bristol Siddeley Gnome Mk.110 or Mk.111 turboshaft, 1007kW / 1350 shp total Type 10 coupling gearbox Rotor head rating: 1,550shp Main rotor diameter: 17.07m Length rotors turning: 20.04m Height: 4.93m Max take-off weight: 6123kg Empty weight: 3767kg Max speed: 212km/h Range with max fuel: 769km Crew: 1 -3 Capacity: 16 seats
Westland Wessex HC Mk.5 Engines: One Bristol Siddeley Gnome Mk 112 and one Gnome Mk 113 Type 11 coupling gearbox Main rotor diameter: 17.07m Length rotors turning: 20.04m Height: 4.93m Crew: 1 -3 Capacity: 16 seats / 1814 kg
Westland Wessex HU.Mk 6 Engine: one Rolls Royce Coupled Gnome twin turboshaft with two pow¬er sections each rated at 1,350 shp (1007 kW), combined output limit 1,550 shp (1156 kW). Main rotor diameter 17.07 m (56 ft 0 in) Length overall 20.03 m (65 ft 9 in) Height 4.93 m (16 ft 2 in) Main rotor disc area 228.81 sq.m (2,463.0 sq ft). Empty weight 3927kg (8,6571b) Maximum take off weight 6120 kg (13,500 lb) Maximum speed 214km/h (133mph) Cruising speed 195 km/h (121 mph) Range 769 km (478 miles) Armament: role kit can include two 7.62 mm (0.3 in) GPMGs firing ahead, one or two 20 mm cannon, two or four AS. 11 wire guided missiles, or rocket pods.
Westland Wessex Mk.31B Engine: 1 x 1,575 shp Napier Gazelle 161 free turbine Rotor diameter: 56 ft Length 65 ft 10.5 in Folded length: 38 ft 6 in Height: 14 ft 10 in Empty weight: 8,000 lb Loaded weight: 13,500 Initial Rate of Climb: 1,540 ft/min Ceiling: 14,100 ft Speed: 108 knots Range: 262 nautical miles Bomb load: 2 x torpedoes (external) Crew: 4
On 1 May 1949, Sikorsky’s technical department was tasked to create a new helicopter in seven months, which would be capable of carrying ten passengers in addition to a crew of two.
The H-19 was of all-metal pod-and-boom construction, had quadricycle wheeled landing gear, and carried its single piston engine in its nose. The engine was linked to the gear drive of the three-bladed main rotor by a long extension shaft, and was easily accessible via two large clamshell doors. The arrangement of powerplant and drivetrain allowed the placement of a large and unobstructed box-like passenger/cargo cabin directly below the main rotor blades, thus ensuring that loads of varying sizes and composition would not adversely affect the craft’s centre of gravity. The H-19’s two-man cockpit was placed above and slightly forward of the passenger/cargo cabin, with the seats placed one either size of the drive shaft, and offered excellent visibility to the front and sides. The craft’s high-set tailboom carried a vertical tailplane and a two-bladed anti-torque rotor, and was faired into the rear of the fuselage by a triangular fin.
Special attention was paid to the maintenance. The main parts were easily dismantled in an average of 12-15 hours and were all designed for ease of access (the engine, for example, could be changed in two hours, even without special equipment, and daily inspections took a maximum of 15-20 minutes). The S-55 had a monocoque metal fuselage with aluminum and magnesium light alloy bulkheads and skin. Except for the chrome-molybdenum steel-tube rotor pylon, structure is of aluminium and magnesium semi-monocoque construction. The three-blade main rotor had long-life metal blades (they demonstrated a life of over 20000 hours in lab tests). The main rotors are nitrogen filled with a hub mounted integral meter. The fuel was contained in two crash resistant tanks situated beneath the cabin in the lower part of the fuselage and had a total capacity of 700 liters. Each leg of the quadricycle undercarriage had its own shock absorber for maximum stability during take-off and landing and manoeuvres on the ground. Wheel track 3.35m. Floats could also be fitted to the legs for emergency landings on water, or the undercarriage could be replaced by permanent metal amphibious landing gear or permanently inflated rubber bag flotation gear. For use with the normal wheels, ‘doughnut’ pontoons were available which are stowed deflated on each wheel axle and can be inflated in under 5 seconds, when needed for landing on water.
The pilot’s compartment above main cabin seats two side by side with dual controls. Cabin located below main lifting rotor may seat from 7 (commercial) to 10 (military) passengers, the 10 passengers being seated three against front and rear walls and two on each side, all facing inwards. Up to six stretchers may be carried, which can be loaded by optional hydraulic power-operated hoist while aircraft is hovering. Pilot’s compartment may be entered from the outside or from the cabin so that co-pilot may act as attendant.
Engines were one Pratt & Whitney R-1340 S3H2 Wasp radial air-cooled engine rated at 410kW at 1,525m and with 447kW available for take-off at 915m, or one Wright R-1300-3 radial air-cooled engine rated at 522kW at 2,222m and with 596kW available for take-off at 1,675m. Engine on angular mounting in nose of fuselage with sloping shaft drive to rotor gear box below head. With the R-1300 engine, a hydromechanical clutch with free wheel system is used in the drive to the main transmission, and the drive-shaft from the free wheel unit to the main transmission has flexible rubber couplings on each end. Large clamshell doors in nose of fuselage allow complete accessibility to engine from ground level. Internal fuel capacity 700 litres.
In 1948 Sikorsky received a contract for five Sikorsky S-55 utility helicopters for US Air Force evaluation under the designation YH-19 (49-2012 to 49-2016). The first of these flew on 10 November 1949 and was characterized by a blunt-ended fuselage, which lacked the broad, triangular fillet connecting the fuselage to the tail boom which distinguished all the later series aircraft. Another characteristic of the YH-19 was the horizontal stabilizer applied to the starboard side of the tail, which was replaced in the production aircraft by two anhedral tail surfaces. These was powered by a 550hp Wright R-1340-S1H2.
Sikorsky YH-19 49-2012
In 1951 the US Air Force purchased fifty-five H-19A production machines (51-3846/3895, -17662/17666), fitted with 447kW / 550hp Pratt & Whitney R-1340-57 engine as the prototypes. Some were converted to Air-Sea Rescue SH-19A and HH-19A after 1962.
Near the end of 1951 the Air Force accepted the first of an eventual 270 more powerful and slightly modified H-19B aircraft (51-3896/3968, 52-7479/7600, -10991/10994, 53-4404/4464, -4878/4885, 56-6673/6674), and at the same time loaned a single H-19A to the Army for operational evaluation in the utility transport and aeromedical evacuation roles.
Sikorsky H-19B 51-3961
The H-19B had a 522kW / 700hp Wright R-1340-3 engine and a larger diameter main rotor. The total included the SH-19B version for use as a transport aircraft. Many were converted to Air-Sea Rescue SH-19B and HH-19B with rescue hoists after 1962. Redesignated as UH-19B in 1962.
In the fall of 1951 the Army ordered the first batch of an eventual seventy-two H-19C aircraft (serials 51-14242 through -14313). The Army’s H-19C was essentially identical to the Air Force H-19A and, like that aircraft, was powered by a 600hp R-1340-57 engine and had two small fins fitted to the lower rear of the tailboom in an inverted ‘V’.
They were subsequently nicknamed “Chickasaw” and redesignated UH-19C in 1962. Both variants remained in Army service well into the mid-1960s.
In late 1952 orders were placed for the first of some 336 examples of the more capable H-19D variant (52-7601/7625, 54-1408/1437, 55-3176, -3183/3228, -4937/4944, -4462/4504, -5235/5240, 56-1519/1568, -4246/4283, 57-1616/1641, -2553/2558, -5926/5982), sixty-one of which were transferred to friendly nations under various military assistance programmes.
The H-19D was the Army’s version of the Air Force -B model and shared that aircraft’s more powerful 700hp engine, downward-sloping tailboom, repositioned horizontal tail fins, and smaller-diameter tail rotor. Redesignated UH-19D in 1962.
July 1952 saw the world’s first transatlantic helicopter crossing when two USAF H-19s traveled from the USA to Wiesbaden (Germany) with stops in Labrador, Greenland, Iceland, Scotland, and the Netherlands on their way. Total flight time was about 52 hours, but because of stops the trip took 21 days.
Versions of the S-55 were also acquired by the US Navy, which signed its first contract on 28 April 1950. Between August 1950 and January 1958, the US Navy received 119 helicopters, including ten HO4S-1 (125506 to 125515, equivalent to the H-19A) and 61 HO4S-2, redesignated as UH-19F in 1962 (based on the H-19B, 30 of these were built as HO4S-3G for the US Coast Guard (1252 to 1258, 1281, 1298 to 1310, and 1323 to 1331, redesignated as HH-19G in 1962).
Sikorsky HO4S-3G 1300
Seventy-nine HO4S-3 were built for the USN (133739 to 133753, 133777 to 133779, 138494 to 138529, and 138577 to 138601) and two US Army H-19B transfers (150193 to 150194).
The Marines troop and assault transport versions were designated HRS-1 and HRS-2 (99 built), similar to the HO4S-1, 151 of which were delivered from April 1952. Eighty-four HRS-3 helicopters with Wright R-1300-3 engines were also built.
The aircraft assigned to the SAR divisions of the MATS and US Army Aviation arrived in Korea in January 1953 with the 6th Transportation Company, whereas the Marines were able to test their HRS-1s for rapid assault operations which anticipated full-scale landing operations. MATS Air Rescue versions were designated SH-19B and became HH-19B.
Powered by a Pratt and Whitney engine of 600 h.p. or a Wright engine of 800 h.p., the H-19 has a “brochure” capacity of eight troops, six litters, or a maximum of 1,500 lb of cargo, which can be carried over a distance of some 100 miles at a conservative gross weight of 6,835 lb. The maximum useful load is 3,033 lb, which gives a range of 400 miles, or 1,000 miles with extra tankage. The normal cruising speed is 80 to 86 m.p.h., with a fuel consumption of 31 Imp. gal/hr.
In actual service, the H-19 could be relied upon to bring a mean of two tons into the front line for each hour that the aircraft was at work. Of the 20 aircraft assigned to a company, 12 (or 57 per cent) were normally available at any time.
During operational missions, the average daily flight time was four hours per aircraft, a quarter-hour more than in the service of New York Airways, who operated civil S-55s.
The employment of cargo helicopters in Korea was not, of course, limited to the U.S. Army; the Air Force and, in particular, the Marine Corps, have had such aircraft in that theatre for over two years. An especially notable operation was carried out by Army and Marine Corps’ helicopters flying side-by-side, in which over 6,000 neutral Indian troops were “trucked” from a carrier in Inchon harbour to the Parimunjoin area. The H-19s were limited to 1,000 lb per lift.
The helicopter requires approximately three hours of maintenance after one day’s work. Refuelling time is approximately five minutes.
The 1953 HRS was a USN transport helicopter version of the S-55. First production was sixty as HRS-1; 127783 to 127842. Minor equipment changes were in the HRS-2. 101 were built (129017 to 129049, and 130138 to 130205), of which several were converted to HRS-3 standards. They were redesignated as CH-19E in 1962.
The HRS-3 were powered by a Wright R-1300-2 engine. Twenty-seven were upgraded HRS-2, four were transferred from the USAF, and 103 production were built (130206 to 130264, 137836 to 137845, 140958 to 140961, 141029, 141230, 142430 to 142436, 144244 to 144258, 144268 to 144270, 144666 to 144668, 146298 to 146302, and 146439), of which sixteen went to Spain. They were redesignated as CH-19E in 1962.
The HRS-4 was a planned version for Wright R-1820 engines, none was built.
HRS-3
The 1,000th Sikorsky-built helicopter of the basic S-55 type was delivered to the US Marine Corps in mid-1956. The H-19 Chickasaw holds the distinction of being the Army’s first true transport helicopter and, as such, played an important role in the initial formulation of Army doctrine regarding air mobility and the battlefield employment of troop-carrying helicopters. The Chickasaw made its combat debut during the last stages of the Korean War, and went on to serve in Southeast Asia during the first years of the Vietnam War.
Various techniques and roles were first tested with the S-55 in Korea which were later to form the basis of new military doctrine, such as landing operations behind enemy lines, troop support, recovery of damaged vehicles and their capacity for counterattack and engagement. Another primary task of the helicopter was casualty evacuation or the rescuing of pilots who had come down behind the enemy lines. In the ambulance role, the S-55 could carry up to six stretchers, five of which could be hoisted on board using a mechanical winch fixed outside the cabin. The spacious cabin was designed to accommodate various seating arrangements or freight; it could take up to ten men or a load of approximately 1300kg.
Sikorsky S-55
The S-55 received American civil type approval on 25 March 1952 and the model with the Pratt & Whitney R-1340 engines became the S-55A, while the version with the Wright engine was designated S-55B.
On commercial versions with the R-1300 engine, the tailcone has been sloped down approximately 3.5 degrees to increase clearance of the main rotor in a rough landing.
The first S-55 in commercial use in the world went into service in British Columbia to build the Alcan project in Kitimat, where the building of power lines by helicopter was another first. In 1952, the helicopter became the first rotary wing craft to be used for commercial links in Europe; it was then flown by the Belgian airline Sabena between the chief towns in Belgium and Lille, Rotterdam, Bonn and Cologne, starting on 1 September.
Sabena S-55
For a time BEA ran regular services with two Sikorsky S-55 between London Airport at Hounslow, Middlesex, and Waterloo in the centre of the city.
BEA S-55
The Whirlwinds were equipped with exterior emergency floatation gear.
UH-19
The RCAF included six H-34 transports for service with No.108 Comunication flight in duties connected with construction of the Mid-Canada radar line on the 55th parallel.
RCAF No.108 Comunication flight H-34
Sikorsky manufactured a total of 1,281 S-55’s in ten years of continuous production commencing in 1949 and another 547 were built under license by Mitsubishi, Sud Aviation, and Westland. It was used by many military services including the RCAF (as the UH-19 and by the RCN (as the HO4S-3) on ‘plane guard’ duties with aircraft carriers.
Licence-production was undertaken by SNCA du Sud Est in France as the Sud-Est Elephant Joyeuse, in Japan by Mitsubishi, and by Westland in the UK, the latter developing versions with the Alvis Leonides Major piston engine and with the Bristol Siddeley Gnome turboshaft under the family name Whirlwind. 2.HIBM in Turkey assembled the H-19 Chickasaw under licence from Sikorsky during 1958.
When Westland began producing the S-55, it specified that the American engine would be used until a more suitable British powerplant was available. To meet this requirement, Alvis developed a double radial called the Leonides Major, which delivered 882hp derated to 750hp. The re-engined Whirlwind flew in 1955. It was followed in 1956 by the Mk.7 version intended to replace the old Fairey Gannet antisubmarine aircraft.
The Series 1 and 2, powered respectively by a Pratt & Whitney R-1340 or Wright R-1300 engine or the 755hp Alvis Leonides Major 755. Installation of Wright R-1300 engines produced the Whirlwind Mk 3 in 1953, followed by the Mk 4 with new P&W R-1340 engines for use in the tropics; then Alvis Leonides Major engine.
The RAF also ordered this helicopter for transport and rescue missions: the Whirlwind HAR Mk.2 (the same as the naval version except for some differences in equipment) joined the Transport and Coastal Command Units from 1955. With Wright R.1300 engines, the Whirlwind Mk.3 went into production for the Royal Navy in 1953 and operated for many years from both ship and shore bases. The subsequent RAF HAR Mk.4 version was modified for use in the tropics and fitted with a new variant of the Pratt & Whitney R-1340. It was used in Malaysia.
WS.55 Whirlwind HAR.3
The turbine-powered S-55 made its first flight as the Whirlwind Series 3 in February 1959, powered by a General Electric T58 and introduced a new nose profile which offered better visibility. At the end of the year a Series 3 flew with a 1050shp Bristol Siddeley Gnorne free-turbine – the licence-built version of the T58. The new turboshaft engine was lighter and more powerful than the piston engine it superseded and offered improved performance and reliability.
The Royal Navy ordered a substantial number for anti-submarine duties under the designation Westland Whirlwind HAS.7. Deliveries began in May 1957.
Westland HAS.7
A total of sixty-eight new air-sea rescue HAR10 and transport HC10s were manufactured by Westland and a number of Whirlwind HAR2 and HAR4 piston-engined helicopters were subsequently re-engined.
Like the S-55, the Series 3 has a single door on the left side. The pilot and co-pilot sit above and behind the engine which places their cabin directly under the centreline of the main rotor. The rotor is hydraulically operated for both cyclic and collective pitch controls. Forward vision for landing was not ideal in earlier versions of the Whirlwind since the engine housing was in the nose. The turbine version was better since, though the nose was longer, it was at a more raked angle. Unlike the US turbine-powered S-55, the Whirlwind Series 3 has its engine exhaust on the left side almost immediately above the forward wheel, which can make cargo loading slightly hazardous if the engine is running or the exhaust hot. The turbine engine can be retrofitted to Series 1 and 2 machines.
Whirlwing HR.5
The first RAF unit to employ the HAR10 was No.225 Squadron, Transport Command, which became operational with the aircraft on 4 November 1961.
Used by the RAF in Europe, the Mediterranean and the Far East, the last squadron to be equipped with the aircraft Cyprus based No.84 Squadron converted to the Westland Wessex in March 1982.
Westland built a total of 364 S-55s under licence between 1953 and 1966, including 68 WS-55 civil aircraft. Most turbine-powered WS-55 Series 3s were converted from piston-engined Series 1s and 2s.
In 1964 Orlando Helicopter Airways Inc, of Sanford, Florida, was founded by Fred P. Clark to support, and in some cases, re-start production of Sikorsky helicopters no longer built by the parent company. In addition to a huge spares resource, Orlando Helicopters now holds the FAA type certificates for all H-19 and S-55 models. Several versions of the S-55 have since been developed by the firm. These include the OHA-S-55 Hen-Camper, a fully fitted out VIP version seating four passengers. New equipment includes a shower, wash-basin and toilet, air conditioning, carpeting and sound-proofing. An optional hydraulic winch, cargo sling or exterior spot-light can also be fitted. The Heli-Camper is powered by an overhauled and reconditioned 596kW Wright-Cyclone R-1300-3D engine.
The OHA-S-55 Nite-Writer is an unprecedented aerial advertising helicopter fitted with a 12.2m x 2.4m array of computer-controlled lights which can display messages and graphics, visible over a distance of 3.2km. More in demand is the OHA-S-55 Bearcat, for which Orlando has developed a quick-change hopper and spray system for crop and fertiliser spraying or seed spreading. Certified in 1991, the Bearcat is powered by a Pratt & Whitney R-1340 engine, which can run on automotive fuel, is fitted with a ‘quiet’ exhaust, and sold for US$300,000.
In October 1985 the company signed an agreement with China’s Guangzhou Machinery Tool Company to licence-build OHA-S-55 Bearcats. Under a 20-year joint venture Guangzhou Orlando Helicopters would first assemble American-built parts before progressing to manufacturing entire units. For carrying heavy external loads, such as logging or construction work, Orlando has developed the OHA-S-55 Heavy Lift which can deal with underslung weights of up to 1361kg. The company has also moved into a unique military market through modifying its S-55s for the US Army Missile Command. As QS-55 Aggressors they have been extensively modified to resemble Mil Mi-24 ‘Hind-E’s as flying targets. The Aggressors can be flown by a pilot or as drones (with dummy pilots in their cockpits) and have a new five-bladed main rotor, extensively redesigned nose, stub wings, and chaff and flare dispensers. A second, more aggressive military version is the armed OHA-AT 55 Defender, design of which began in 1990. Re-engined with a Garrett TPE331-3 turboshaft or a Wright R-1330-3 radial, the Defender also features a stub wing with pylons capable of carrying up to 500kg of weapons, and a five-bladed rotor. Capable of carrying up to 10 fully-equipped troops, the Defender can also be fitted out to accommodate six stretchers and two attendants.
In January 1971 Aviation Specialties Inc received certification for a turbine-powered conversion of Sikorsky S-55 helicopter powered with 1 x 840 hp AirResearch TSE-331, designated S-55-T. Aviation Specialties became Helitec Corporation in 1976.
Whisper Jet Inc produced a modified version of the S-55. The S-55QT is powered by a 650 shp Garrett Air Research TSE331-1OUA-511SW and fitted with a 5 blade main rotor head. Flown by a single pilot, the S-55QT can carry 9 passengers.
S-55C Engine: Pratt & Whitney R-1340 S3H2 Wasp radial, 447kW / 550 hp
YH-19 Engine: Pratt & Whitney R-1340 S3H2 Wasp radial, 447kW / 550 hp
H-19A Engine: Pratt & Whitney R-1340 S3H2 Wasp radial, 447kW / 550 hp AUW 3,263kg Crew: 2 Payload: 10 troops or six stretchers Internal fuel capacity: 700 lt
H-19A Engine: Pratt & Whitney R-1340-57, 600 hp Rotors: 3-blade main; 2-blade tail Rotor diameter: 49 ft. Fuselage length: 41 ft 8.5 in Loaded weight: 6,835 lb Max speed: 105 mph Ceiling: 12,900 ft Typical range: 440 miles at 90 mph Seats: 2 crew+13-10 passengers
H-19A / SH-19A Engine: Pratt & Whitney R-1340-57, 600 hp Rotors: 3-blade main; 2-blade tail Rotor diameter: 53′ 3″ Fuselage length: 41 ft 8.5 in Loaded weight: 6,835 lb Max speed: 115 mph Cruise: 90 mph Ceiling: 12,900 ft Typical range: 440 miles at 90 mph Seats: 2 crew+13-10 passengersInternal fuel capacity: 700 lt
H-19B / SH-19B / UH-19B 1951 Engine: Wright R-1300-3 Cyclone radial, 596kW / 700 hp Rotor diameter 16.16m / 53’0″ Length: 12.88 m / 42’3″ Height: 4.06 m Disc Area: 204.95 sq.m Empty weight: 2381 kg MAUW: 3583 Useful load: 2650 lb Top Speed: 180 km/h / 112 mph Cruise Speed: 146 km/h / 91 mph Range: 579 km / 360 mi Crew: 2 Payload: 10 troops or six stretchers. Internal fuel capacity: 700 lt
H-19C / UH-19C Engine: Pratt & Whitney R-1340 S3H2 Wasp radial, 447kW / 550 hp Maximum speed: 112 mph (180 km/h) Empty weight: 5,250 lb (2381 kg) Maximum weight: 7,900 lb (3583 kg) Rotor diameter: 53 ft (16.2 m) Fuselage length: 42 ft 3 in (12.9 m) Overall height: 14 ft 8 in (4.5 m) Crew: 2 Payload: 10 troops or six stretchers Internal fuel capacity: 700 lt
H-19C / UH-19C 1952 Engine: 600hp R-1340-57 Useful load: 2705 lb Max speed: 101 mpg Cruise: 85 mph Range: 450 mi Ceiling: 10,500 ft
H-19D / UH-19D 1952 Engine: Wright R-1300-3 Cyclone radial, 596kW / 700 hp Rotor diameter: 53 ft (16.2 m) Fuselage length: 42 ft 3 in (12.9 m) Overall height: 14 ft 8 in (4.5 m) Empty weight: 5,250 lb (2381 kg) Maximum weight: 7,900 lb (3583 kg) Useful load: 2650 lb Maximum speed: 112 mph (180 km/h) Cruise: 91 mph Range: 385 mi Ceiling: 12,500′ Crew: 2 Payload: 10 troops or six stretchers Internal fuel capacity: 700 lt
HH 19 Chickasaw Engine: Wright R-1300-3 Cyclone radial, 596kW / 700 hp Length: 42.257 ft / 12.88 m Rotor diameter: 52.986 ft / 16.15 m Max take off weight: 7900.5 lb / 3583.0 kg Weight empty: 5261.1 lb / 2386.0 kg Max. speed: 97 kts / 180 km/h Cruising speed: 79 kts / 146 km/h Range: 313 nm / 580 km Crew: 2 Payload: 10 Pax
HO4-1 U.S. Navy anti-submarine Engine: Wright R-1820, 1,025 hp
HO4-2 U.S. Navy anti-submarine Engine: Wright R-1820, 1,025 hp
HO4S Engine: P&W R-1340-57 Main rotor: 53’3″ Length: 42’1″ Max speed: 115 mph
Westland WS-55 Whirlwind HAS.7 Engine: 1 x Alvis Leonides Major Mk.155, 750 hp Rotor diameter: 53 ft Main rotor disc area: 2206 sq.ft Main rotor: 3 blade Fuselage length: 41 ft 8.5 in Height: 13 ft 3 in Empty weight: 5580 lb MAUW: 7800 lb Fuel capacity: 170 gal Max speed: 109 mph at SL Cruise speed: 86 mph Service ceiling: 13,800 ft Range: 400 mi Tail rotor: 2 blade
Westland WS-55 Whirlwind HAR.9 Rotor diameter 58 ft Fuselage length 41 ft 8.5 in Mauw 7500 lb Cruise speed 90 mph
Westland Whirlwind H.A.R. Mk. 21
Westland Whirlwind H.A.S. Mk. 22 Engine: Wright R-1820, 1,025 hp
Orlando Helicopter Airways OHA-S-55 Heavy Lift Slung load: 1361kg
Orlando Helicopter Airways QS-55 Aggressors Flying target Main rotor: five-blade
Orlando Helicopter Airways OHA-AT 55 Defender Engine: Garrett TPE331-3 turboshaft or Wright R-1330-3 radial Main rotor: five-blade Warload: 500kg Passangers: 10 fully-equipped troops or six stretchers and two attendants.
Aviation Specialties S-55-T Engine: 1 x 840 hp AirResearch TSE-331
Helitec Corporation S-55-T 1971 Engine: 1 x 840 hp AirResearch TSE-331-3U-303
S-55-GW Engine: 700hp Wright R-1300
Whisper Jet Inc S-55QT Engine: 650 shp Garrett Air Research TSE331-1OUA-511SW Main rotor: 5 blade Gross wt: 7700 lb Service ceiling: 14,100ft Max range: 365 miles Max cruise: 98mph Capacity: 9 passenger
All Aero 