Sikorsky R-4 end of the boom near the tail rotor while others had it positioned at the midpoint of the boom. Additionally, some had short "stub" exhaust pipes from the engine while others had a much longer one which extended vertically and then aft above the main landing gear struts. Sikorsky R-4 The Sikorsky R-4 is a two-seat helicopter designed by Igor Sikorsky with a single, three-bladed main rotor and powered by a radial engine. The R-4 was the world's first large-scale mass-produced helicopter and the first helicopter used by the United States Army Air Forces, the United States Navy, the United
Sikorsky S-10 Sikorsky S-10 The Sikorsky S-10 was a Russian Empiren military twin-float seaplane that served with the Baltic Fleet from the summer of 1913 to 1915. After Igor Sikorsky built the successful Sikorsky S-6 for the Russian military, he tried to build another successful aircraft for them. The S-10 was a modified S-6B built by the Russo-Baltic Carriage Factory. Approximately sixteen production versions of the S-10 were built. It had a less powerful engine and generally weaker structure than the S-6. They had either an 80 HP Gnome Monosoupape or a 100 HP Argus Motoren engine. Some were deployed on the