S-55 general technical description

The S-55 is a conventional helicopter using a main and anti-torque rotor, a design developped successfully from 1939 by Igor I. Sikorsky.

The fuselage is a semi-monocoque structure consisting on two main sections.

The front section incorporates the cabin, the engine, the transmission an the main rotor, while the rear section comprises the tail boom, the tail rotor and the stabilizers.

On some versions, to minimize the danger of a tail boom strike, the tail boom is angled down by 3 degrees. At customer’s request this modification was possible using a special retro-fit kit.

The forward section can readily be removed in case of necessity such for example for air transportability. The S-55 could be easily transported inside the popular Fairchild C-82 cargo aircraft.

The fuselage is a semi-monocoque structure consisting principally of alluminium and magnesium outer skin.

The main rotor, the main transmission, the tail rotor tramission and the controls are easily accessible. To inspect the main rotor on both sides of the pilot’s cabin there is a small folding platform.

The main rotor pylon consists of steel tubes from the cabin roof to the top of the main gear box. This structure thus becomes a self-contained unit, consisting of the rotor head, the main transmission with its own oil system and accessories, and the complete hydraulic servo control system.

The two-man cockpit is placed above and slightly forward of the passenger/cargo cabin with two seats placed on either side of the drive shaft. The cockpit may be entered from the outside the pilot’s window, adjacent to the large cabin door, thereby providing excellent visibility for rescue operations.

The cockpit is also accessible from the passenger’s cabin, but the passage is a bit narrow and uncomfortable. That is why usually the pilot enters from the outside using some handles and footrests. If the rotor is turning, the pilot must pay attention.

Visual in generally good on all directions. On some versions the front windshield is divided in two or four portions.

The instrument panel is located directly in front of the pilot and provides for both normal and night flying with red lighting. Easy access to the rear instrument panel is provided by removing the top fairing. Special attention has been given to the instrument grouping in accordance with numerous pilot’s requests.

The fully articulated main rotor is similar to that proved on the S-51, even if it is simpler. It has three interchangeable all-metal rotor blades. All blades are individually interchangeable and any three, including spare blades, make a flyable set, a novelty at that time. Not to be forgotten that the main rotor blades are manually foldable for easy storage.

The tail rotor assembly is similar to that which has been CAA approved for the S-51, with a two all-metal interchangeable blades see-saw arrangement.

The tail rotor is protected from ground strikes by a skid plate.

The flight controls are full dual with the pilot on the starboard side, thus permitting ready use of the left hand for radio and other controls without removing the right from the cyclic stick. The hydraulic servo control system operates on both the cyclic and the collective pitch control.

The rudder pedals are adjustable fore and aft and have individual toe brakes.

A stabilizer made of two small fins forming an inverted V is provided at the aft of tail cone to maintain optimum trim for all flight conditions and increase aircraft stability.

The helicopter has a 200 amp generator driven from an accessory drive pad on the main gear box and thus operates whenever the main rotor is turning. The 24V battery is located under the radio compartment, behind the cargo/passengers cabin.