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The S-4 (aka. YH-24 or “Skyhawk”) was a light helicopter built by the Seibel Helicopter company. It first took flight in January of 1949. The S-4 is a more advanced continuation of the experimental S-3, which only existed to prove the feasibility of some of Charles Seibel’s designs. The US military were in contact with Seibel, providing feedback on the S-4, which has potential as a light military aircraft. The Air Force too was interested and it was the US armed forces that dubbed the S-4 the Skyhawk. Just as with the S-3, the S-4 made use of only a single engine and a very simplified two-bladed rotor. The transmission too was relatively simple compared to other contemporary designs.The anti-torque system also featured a two-bladed design mounted on the tail boom. The frame of the S-4 was a welded box frame made from steel tubing. It had two decks. The lower deck had the control panel, pilot's seat, wheeled trike landing gear and a relatively small passenger or cargo area. While the Army and Air Force showed interested and evaluated the two prototypes that were built, ultimately the S-4 did not have enough load capacity or power for their needs and it was passed on. The Cessna CH-1 Skyhook would however be borne from the S-4B’s design and is the only helicopter ever to be made by Cessna.
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