Seibel S-4/YH-24 Sky Hawk
The Seibel S-4 was a two-person light helicopter developed by Charles M. Seibel. A former engineer at Bell who worked under helicopter pioneer Arthur M. Young, Seibel developed an experimental, 800-lb (363-kg) helicopter called the S-3 at his home in Wichita, Kansas. In 1948, Seibel formed the Seibel Helicopter Co. Inc. in Wichita and began work on the successor to the S-3, the S-4. The latter incorporated a 129-shp (94-kW) Lycoming Model O-290-D four-cylinder piston engine and featured a 1,500-lb (680-kg) gross wight. Hailed for its low cost, the S-4 exemplified Seibel’s goal of simplifying helicopter production and maintenance. The S-4 made its maiden flight in January 1949. John Gibbs piloted many of the early of the early tests of the aircraft.
In 1951, the US Army acquired two examples of the Seibel S-4s, which it subsequently redesignated as the YH-24 Sky Hawk. The Army sought to evaluate the S-4’s suitability for casualty evacuation missions, though it did not place additional orders for the aircraft. Following Cessna Aircraft Co.’s acquisition of Seibel in 1952, Charles Seibel became the chief engineer of the airplane manufacturer’s new helicopter division. The S-4B, a variant of the S-4 that featured side-by-side seating, served as the basis for the CH-1 Skyhook, which made its first hover flight in 1953. However, Cessna closed its helicopter division in 1962 and Charles Seibel returned to Bell, where he was instrumental in designing the AH-1 Cobra attack helicopter.
Resources:
- Seibel S4A (YH-24 Skyhawk), Vertipedia, Vertical Flight Society
- Seibel S-4 "Skyhawk" / YH-24 (1951), Aviastar
Photo via generalaviationnews.com (USAF/Clouser/Handy collections)
Description by Dan Gettinger
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