The Sikorsky S-59 was a groundbreaking experimental helicopter that played a pivotal role in ushering rotorcraft into the turbine age. Developed during the early 1950s by Sikorsky Aircraft, the S-59 demonstrated the enormous potential of gas turbine engines in helicopter operations. Although only a handful of aircraft were built, the S-59 established world records, influenced future military helicopter development, and proved that turbine-powered helicopters were the future of vertical flight.
Sikorsky S-59
The Origins of the Sikorsky S-59
In the years following World War II, helicopter manufacturers sought ways to improve aircraft performance, reliability, and payload capacity. Piston engines had powered most early helicopters, but engineers recognized that gas turbine technology offered significant advantages, including greater power-to-weight ratios and improved operational efficiency.
To explore these possibilities, Sikorsky modified its existing S-52 helicopter design and created the S-59. The project was conducted in partnership with the U.S. Army, which designated the aircraft as the XH-39. The objective was simple but ambitious: evaluate the practicality of turbine-powered helicopters and determine whether they could outperform conventional piston-engine rotorcraft.
Development of the Sikorsky S-59
The Sikorsky S-59 was extensively modified from the earlier S-52 platform. Engineers introduced several innovative features, including:
A Continental/Turbomeca Artouste II XT51-T-3 gas turbine engine
A fully articulated four-blade main rotor system
A three-blade tail rotor
Strengthened fuselage structure
Retractable landing gear
Modernized avionics and flight systems
The result was a lightweight, high-performance helicopter capable of achieving speeds and altitudes previously unattainable for rotorcraft of its era.
First Turbine-Powered Helicopter Milestone
One of the most significant achievements of the S-59 program was demonstrating the viability of turbine propulsion in helicopters.
The aircraft utilized a 400-horsepower Continental/Turbomeca Artouste II turbine engine that weighed substantially less than comparable piston engines while delivering impressive power output. This technology marked a major turning point in rotorcraft engineering and directly influenced future military and civilian helicopter designs.
The success of the S-59 helped convince military planners and manufacturers that turbine engines represented the future of helicopter propulsion.
World Record-Breaking Performance
The Sikorsky S-59 quickly earned international attention through a series of record-setting flights.
World Speed Record
On August 26, 1954, U.S. Army Warrant Officer Bill Wester flew the XH-39 variant of the S-59 to a world helicopter speed record of 156 mph (251 km/h) over a three-kilometer course. This achievement made the S-59 the fastest helicopter in the world at the time.
World Altitude Record
Only weeks later, on October 17, 1954, Wester established another world record by flying the S-59 to an altitude of 24,500 feet (7,474 meters). This accomplishment demonstrated the superior high-altitude performance made possible by turbine propulsion.
These records confirmed that turbine-powered helicopters could dramatically outperform many piston-powered competitors.
Technical Specifications of the Sikorsky S-59
General Characteristics
Manufacturer: Sikorsky Aircraft
Military Designation: XH-39
Type: Experimental turbine helicopter
Crew: 2
Passenger Capacity: 2 passengers
Dimensions
Main Rotor Diameter: 35 ft (10.67 m)
Overall Length: 41.8 ft (12.5 m)
Height: 9.6 ft (2.74 m)
Powerplant
Engine: Continental/Turbomeca Artouste II XT51-T-3
Power Output: 400 hp
Performance
Maximum Speed: 136 knots (251 km/h)
Range: 243 nautical miles (451 km)
Service Ceiling: 23,700 ft (7,223 m)
Rate of Climb: 2,000 ft/min (610 m/min)
These figures were remarkable for a helicopter operating during the mid-1950s.
Innovative Engineering Features
Beyond its turbine engine, the Sikorsky S-59 introduced several advanced concepts.
Quick Change Unit (QCU)
The helicopter featured a modular "Quick Change Unit" that combined the engine, gearbox, and rotor head into a single assembly. Maintenance crews could replace the entire unit in approximately two hours, significantly reducing downtime.
Fully Articulated Rotor System
The new four-blade rotor design improved flight stability, maneuverability, and aerodynamic efficiency. This rotor system became an important stepping stone toward more advanced rotorcraft technologies.
Retractable Landing Gear
Unlike many helicopters of its era, the S-59 incorporated retractable landing gear, reducing drag and contributing to its record-breaking speed performance.
Competition and the Rise of the Huey
Despite its impressive achievements, the Sikorsky S-59 did not enter large-scale production.
The U.S. Army evaluated the XH-39 alongside the competing Bell XH-40 helicopter. While the S-59 demonstrated excellent performance, the Army ultimately selected the Bell design, which evolved into the legendary Bell UH-1 Huey.
Although the S-59 lost the competition, it provided valuable data regarding turbine-powered helicopter operations that would benefit future military aviation programs.
Legacy of the Sikorsky S-59
The Sikorsky S-59's influence extends far beyond its limited production run.
Its achievements helped validate turbine technology as the standard power source for modern helicopters. Lessons learned from the S-59 contributed to the development of later Sikorsky helicopters, including military transport, rescue, and utility rotorcraft.
Many aviation historians regard the S-59 as one of the most important experimental helicopters of the 1950s because it bridged the gap between the piston-engine era and the turbine-powered future.
Surviving Aircraft
Today, surviving examples of the Sikorsky S-59 and XH-39 can be found in aviation museums, preserving the legacy of this pioneering aircraft.
One restored S-59 is housed at the New England Air Museum, while the record-setting XH-39 is preserved at the United States Army Aviation Museum. These aircraft continue to showcase an important chapter in helicopter history.
Conclusion
The Sikorsky S-59 was far more than an experimental helicopter—it was a technological breakthrough that transformed rotorcraft development. By proving the effectiveness of turbine propulsion, setting world speed and altitude records, and introducing innovative engineering concepts, the S-59 helped shape the future of helicopter aviation.
Although it never achieved production success, its contributions paved the way for generations of turbine-powered helicopters that continue to serve military, commercial, and humanitarian missions around the world. For aviation enthusiasts and aerospace historians, the Sikorsky S-59 remains a landmark achievement in the evolution of vertical flight.
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