Seibel S-4

Infobox Aircraft
name=Seibel YH-24


caption=YH-24 in flight
type=Multipurpose observation helicopter
manufacturer=Seibel Helicopter Company
designer=
first flight=1951
status=
primary user=United States Army
produced=
number built=2
unit cost=

The Seibel S-4 was the second helicopter type designed and built by Seibel Helicopter Company's 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

Charles 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 were 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.

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 pilot's seat. Seibel also replaced that aircraft's original wheeled, tricyle undercarriage with landing skids. This aircraft would become the S-4B.

Operational history

Both the U.S. Army and U.S. Air Force showed interest in the S-4. In early 1951, the U.S. Army ordered two examples for operational and engineering evaluation 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.

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.

Design

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.

Variants

;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.

pecifications (YH-24)

aircraft specifications

plane or copter?=copter
jet or prop?=prop
crew=1-2
capacity= 583 lbs (265 kg)
length main= 27 ft 10 in
length alt= 8.48 m
span main=
span alt=
height main= 10 ft 1 in
height alt= 3.05 m
area main=
area alt=
empty weight main= 946 lb
empty weight alt= 430 kg
loaded weight main=
loaded weight alt=
max takeoff weight main= 1529 lb
max takeoff weight alt= 695 kg
engine (prop)=
type of prop=
number of props=1
power main=127 hp
power alt=95 kw
max speed main= 62 mph
max speed alt= 105 km/h
cruise speed main= 58 mph
cruise speed alt= 93 km/h
range main=
range alt=
ceiling main= 4298 ft
ceiling alt= 1310 m
climb rate main=
climb rate alt=
loading main=
loading alt=
power/mass main= 0.08 hp/lb
power/mass alt= 0.22 kW/kg
armament=

References

* [http://www.globalsecurity.org/military/systems/aircraft/h-24.htm Global Security]
* [http://www.commercemarketplace.com/home/CollectAir/cessna.html Collect Air]
* [http://avia.russian.ee/helicopters_eng/cessna.html All The Worlds Rotorcraft]