A floatplane has slender pontoons mounted under the fuselage. Two floats are common, but other configurations are possible. Only the "floats" of a floatplane normally come into contact with water. The fuselage remains above water. Some small land aircraft can be modified to become float planes and in general floatplanes are small aircraft. Floatplanes are limited by their ability to handle wave heights typically greater than 12 inches (0.31 m). These float pontoons add to the empty weight of the airplane, and to the drag coefficient, resulting in reduced payload capacity, slower rate-of-climb and slower cruise speed.
With the S-5, Igor Sikorsky's fortunes began to change. Completed in late April 1911, with a 50hp Argus water-cooled engine, it was tested in a series of 20 to 30-second straight-line flights over a period of three weeks before the young designer was able to make what he called his first real flight of four minutes, in a circuit of the field, on 17 May.
The S-5 was larger than its predecessors, with a wing span of 12m, length of nearly 8.50m and weight of 440kg. After outperforming Russian Army aircraft during manoeuvres watched by Czar Nicholas II, it earned Igor Sikorsky his first money with a series of exhibition flights during a country fair at Belaya Tzerkov, near Kiev. Between nine and ten flying hours were logged before the S-5 was lost through engine failure.
After the in-flight failure of Anzani engine (S-4 model) I.I.Sikorsky incorporated German built Argus engines, which was heavier but more reliable. Upper wing span was increased. second seat was added.
The S-5, first flown in April , was able for sustained flight up to an hour. Flying this plane I.I.Sikorsky obtained his pilots license and established four Russian records: Few flights with passenger were performed on June 14, 1911.
The seaplane version S-5A had more powerful Gnome-Rhone engine, it was fitted with a 60hp Gnome (Rhone) engine. It had very slim fuselage, but it was rugged enough due to plywood cover. First version had pair large ski-shaped float and small cylinder float under the tail. Test flights by G.V.Alekhnovich proved that aircraft is underpowered and it was not accepted by Sea Department. Used later as a trainer.
Second version of S-5A seaplane had single large float, two small support floats under the wings and tail cylinder. 80hp Gnome provided more power, and aircraft proved to have better performance than 'Curtiss' and Farman-XVI. It was in active reconnaissance service in Revel (now Tallin) since September 1914.
The Sikorsky S-10 was a Russian military twin-float seaplane built by the RBVZ 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 a 80 HP Gnome Monosoupape or a 100 HP Argus Motoren engine. Some were deployed on the world's first operational seaplane carriers.
Sikorsky built a special S-10 for the 1913 military aircraft competition. This particular S-10 had a 80 HP Gnome engine. The wing span was increased by 150 mm and were fitted with outer panels that could be folded for storage. The two seats were fitted side-by-side, and the yoke could be switched between the pilot and co-pilot during flight.
The aircraft also took the first prize in the competition although it lacked the speed and manoeuvrability of the S-6B. Its payload of 48% of the aircraft weight was exceptional. After its wingspan had been reduced by another 3050 mm and the Gnome engine was replaced by a stronger Monosoupape engine, the S-10 served as both a reconnaissance and trainer on floats with the Baltic Fleet.
Russian test pilot Gleb Alekhnovich set a Russian record by flying non-stop 500km in 4 hours 56 minutes and 12 seconds with the S-10.
The Grigorovich M-16 was a reconnaissance floatplane, and not a flying boat as some sources claim. It was used by both the Russian Empire and Estonia during World War 1. The Russian Navy use it for performing coastal observation patrols.