The Sikorsky S-18 was a Russian twin engine aircraft designed by Igor Sikorsky and built by the Russian Baltic Railroad Car Works aviation division at Petrograd during World War I.
Igor Ivanovich Sikorsky (Russian: И́горь Ива́нович Сико́рский ; ] , "Ígor' Ivánovič Sikórskij"; , "Ihor Ivanovych Sikorskyi"; May 25, 1889 – October 26, 1972), was a Russian-American aviation pioneer in both helicopters and fixed-wing aircraft.
 First success came with the S-2, the second aircraft of his design and construction.
 His fifth airplane, the S-5, won him national recognition as well as F.A.I. license Number 64.
 His S-6-A received the highest award at the 1912 Moscow Aviation Exhibition.
 and in the fall of that year the aircraft won for its young designer, builder and pilot first prize in the military competition at Petrograd.
The Sikorsky S-67 Blackhawk was a private-venture, prototype attack helicopter built in 1970 with Sikorsky Aircraft research and development (R&D) funds.
 A tandem, two-seat aircraft designed around the dynamic drive and rotor systems of the Sikorsky S-61, it was designed to serve as an attack helicopter or to transport up to eight troops into combat.
The Charles Taylor Master Mechanic Award is an honor presented by the United States Federal Aviation Administration in honor of Charles Taylor, the first aviation mechanic in powered flight.
 The award recognizes the lifetime accomplishments of senior aviation mechanics.
 Taylor served as the Wright brothers' mechanic and is credited with designing and building the engine for their first successful aircraft.
The Sikorsky S-28 was a proposed four engine biplane bomber aircraft designed by Igor Sikorsky to be built in France during World War I.
 Sikorsky moved to France in March 1918 and soon met with officers of the "Armée de l'Air" who asked him to design an aircraft capable of carrying a new 1,000 kg (2,200 lb) bomb.
 Although the aircraft was initially designed to be powered by two Liberty L-12 engines, the technical section of the "Armée de l'Air" suggested using four Hispano-Suiza 8 engines instead.
The Sikorsky S-6 was a Russian single engine experimental aircraft similar to the S-5, built in 1911 by Igor Sikorsky.
The Sikorsky S-2 was the second fixed wing aircraft designed by Igor Sikorsky using the main wing section from the S-1 and a 25 hp Anzani three-cylinder engine in a tractor configuration.
 During the first flight attempt on June 3, 1910 the biplane reached a height of two to four feet and traveled approximately 200 yards.
 After several successful flights the S-2 was completely destroyed on June 30 when Sikorsky inadvertently stalled the underpowered aircraft at an altitude of 70 feet.
The Sikorsky S-10 was a Russian 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 world's first operational seaplane carriers.
The Cody Michelin Cup Biplane was an experimental aircraft designed and built in Britain during 1910 by Samuel Franklin Cody, a prominent showman and aviation pioneer.
 Cody had worked with the British Army on experiments with man-lifting kites and in October 1908 had successfully built and flown the British Army Aeroplane No 1, making the first officially verified powered flight in the United Kingdom.
 Cody broke the existing endurance record twice in the aircraft, the second flight, made on 31 December 1910, winning him the Michelin Cup for the longest-lasting flight made over a closed circuit in the United Kingdom before the end of the year.
The Sikorsky S-29-A was an all-metal, twin-engine biplane airliner, first flown in 1924.
 It was the first aircraft that aviation pioneer Igor Sikorsky designed and built after coming to the United States, hence the special "-A" suffix signifying "America".
 The pilot and mechanic sat in an open cockpit between the upper wing and the tail, while up to 16 passengers were accommodated within the streamlined fuselage.

Question: What was the first successful aircraft designed by the aviation pioneer who built the Sikorsky S-6?
Answer: S-2