Tag Archives: Franklin Engine Company 6V6-245-B16F

12 February 1947

Sikorsky S-52 NC92823, serial number 52001. (Vertical Flight Society)

12 February 1947: The Sikorsky Model S-52, NC92823, made its first flight.

The S-52 was an completely new design helicopter based on the company’s experience with the earlier R-4 and R-5/S-51 models. It was a two-place light helicopter of  monocoque construction, using primarily aluminum and magnesium.

This was the first Sikorsky helicopter to use an offset flapping hinge in the main rotor, which greatly increased the helicopter’s maneuverability. This feature has been incorporated in every Sikorsky helicopter from that time on.

The three-bladed fully-articulated articulated main and two-bladed tail rotor were also of all metal construction. The main rotor had a diameter of 33 feet (10.058 meters) and rotated counter-clockwise as seen from above. (The advancing blade is on the right side of the helicopter.) The blades were construced of aextruded aluminum spar with a sheet duralumin skin riveted and glued. The blades used the NACA 0012 airfoil, a symmetrical profile which was common in early helicopters. The blades had  -6° twist.

The semi-rigid tail rotor was mounted on the left side of the tail boom in a pusher configuration. It had a diameter of 6 feet, 4 inches (1.930 meters) and rotated counter clockwise, as seen from the helicopter’s left. (The advancing blade is at the top of the tail rotor arc.)

The prototype was powered by an air-cooled, normally-aspirated, 333.991-cubic-inch-displacement (5.473 liter) Franklin Engine Company 6V4-165-B32F vertically-opposed 6-cylinder overhead valve engine, rated at 165 horsepower at 2,800 r.p.m. The S-52-1 that followed was equipped with a 425.29-cubic-inch-displacement (6.97 liter) Franklin 6V6-245-B16F (O-425-1). This engine was rated at 245 horsepower at 3,275 r.p.m.

The helicopter’s Civil Aeronautics Administration type certificate was approved 25 February 1948.

The prototype Sikorsky S-52 on public display at Radio City Music Hall. (Sikorsky Historical Archives)

© 2021, Bryan R.. Swopes