| Seibel YH-24 | |
|---|---|
| |
| YH-24 in flight | |
| Role | light helicopter |
| Manufacturer | Seibel Helicopter |
| Designer | Charles Seibel |
| First flight | January 1949 |
| Status | disassembled |
| Primary user | United States Army |
| Number built | 2 |
The Seibel S-4 was a two-bladed, single-engine helicopter built by Seibel Helicopter. Designed by Charles Seibel, the S-4 was evaluated by the United States Army under the designation YH-24 Sky Hawk, but would be rejected for service. The S-4B would serve as the basis for the design of the Cessna CH-1 Skyhoook, the only helicopter Cessna ever produced.
Development
editCharles Seibel began development on the S-4 after forming the Seibel Helicopter Company with funding from local Kansas oil investors. The S-4 was a continuation of his work on his previous design, the Seibel S-3, which he flew as a demonstrator for his design concepts; primarily a new design for a two-bladed rotor system and a simplified transmission. These features would also be incorporated into the S-4 design.
In January 1949, the S-4 lifted off the ground for the first time, piloted by Johnny Gibbs. In March 1950, certification tests where completed and on 23 April 1950, the S-4 received civil certification by the CAA. A larger engine, the Lycoming O-290B with 125 hp, would be installed in the aircraft, making it the S-4A.
Design
edit
The S-4 frame was a welded steel-tube box frame, with two decks. A lower deck supported the control panel, pilot's seat, wheeled, tricyle landing gear, and a small passenger/cargo area accessible from the rear, and an upper deck carried the engine, the fuel and oil tanks, and supported the transmission and rotor assembly. A tapered, monocoque, alloy tail boom with a two-bladed antitorque tail rotor was attached at the rear of the upper deck.
Operational history
editBoth the United States Army and the United States Air Force showed interest in the S-4. In 1951, the Army, ordered two helicopters for evaluation as a possible replacement for the OH-13 in the observation, utility, and aeromedical evacuation roles. The Army designated the S-4 as the YH-24 Sky Hawk. The first Sky Hawk, serial number 51-5112, was delivered to Fort Bragg, North Carolina in April 1951; the second YH-24, serial number 51-5113, was delivered to Wright Field. Based on feedback from the Army during the evaluation, Seibel, shortened the fuselage of the second YH-24 (51-5113) and widened the cockpit for a co-pilot's seat next to the pilots seat. Seibel also replaced that aircraft's original wheeled, tricyle undercarriage with landing skids. This aircraft would become the S-4B. Despite the simplicity of the S-4, the Army determined that it did not provide a sufficient payload capability and the aircraft were dropped from the inventory and returned back to Seibel in 1952.
In 1952, Seibel Helicopter was acquired through a stock transfer by Cessna Aircraft. The S-4B was used to familiarize Cessna engineers with helicopter design and to train test pilots, and then both S-4 helicopters were dismantled.
Variants
edit- S-4
- Original design, certified by the CAA in 1950.
- S-4A
- featured an upgraded, 125 hp Lycoming O-290B engine.
- S-4B
- Modified airframe based on Army recommendations during YH-24 evaluation. Two-seat cockpit and skid landing gear.
Specifications (S4-A / YH-24)
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Data from Jane's All the World's Aircraft 1953-54[1]
General characteristics
- Crew: 1
- Capacity: 1 / 583 lb (264 kg) payload
- Length: 27 ft 10 in (8.48 m) fuselage only
- 35 ft 1 in (10.7 m) including rotors
- Width: 7 ft 11 in (2.41 m) rotor fore-aft
- Height: 10 ft 1 in (3.07 m)
- Empty weight: 946 lb (429 kg) [citation needed]
- Gross weight: 1,529 lb (694 kg) [citation needed]
- Fuel capacity: 19 US gal (16 imp gal; 72 L)
- Powerplant: 1 × Lycoming O-290-D 4-cylinder air-cooled horizontally-opposed piston engine, 125 hp (93 kW)
- Main rotor diameter: 29 ft 1.5 in (8.877 m)
- Main rotor area: 666.3 sq ft (61.90 m2)
Performance
- Maximum speed: 70 mph (110 km/h, 61 kn)
- Cruise speed: 58 mph (93 km/h, 50 kn) [citation needed]
- Service ceiling: 2,400 ft (730 m) hover ceiling
- Absolute ceiling: 6,400 ft (1,951 m)
- Rate of climb: 713 ft/min (3.62 m/s)
- Power/mass: 0.08 hp/lb (0.13 kW/kg)[citation needed]
References
editSee also
editRelated development
Aircraft of comparable role, configuration, and era
Related lists
- ^ Bridgman, Leonard, ed. (1953). Jane's All the World's Aircraft 1953-54. London: Sampson Low, Marston & Company, Ltd. pp. 273–274.