Staff Writer (Updated: 6/15/2016):
The aircraft was conceived of as a four-engine, luxury commercial passenger transport featuring such revolutionary amenities as cabin windows, an in-flight berth complete with a washroom, a heated and lit passenger compartment separated from the crew cockpit and relatively comfortable passenger seating for up to 16 on wicker chairs. The cabin floor was also glazed over to allow for a unique passenger perspective of high-altitude flight. Doors on either side of the fuselage permitted mechanics to service and repair the engines in flight.
Though hardly a spacious aircraft by today's standards, the Ilya Mourometz (IM) was ahead of its time in many ways, much to the credit of Sikorsky's forward-thinking vision. Electricity for the cabin was provided for by a wind-powered generator while heating was accomplished through radiators. First flight of the Ilya Mourometz was achieved on December 13th, 1913 while the aircrafts first passenger flight occurred a short time later on February 25th, 1914. In this event, 16 passengers were carried over Moscow for five hours, hitting an altitude of just over 6,500 feet and reaching speeds over 60 miles per hour. Production was handled at the Russo-Baltic Carriage Factory (RBVZ) in Riga beginning in 1913.
Design of the IM was dominated by her large unequal-span biplane wings with vertical struts and heavy cabling. The wings fitted over and under the central fuselage nacelle which contained the glazed cockpit (appearing much like a glass box) and passenger compartment. The four engines were placed between the top and bottom wing spars and each featured two-blade propellers. The IM proved a large design to say the least, towering some two stories from the top wing to the bottom of the wheels when at rest. The fuselage was a conventional straight surfaced design while the empennage was distinctive in incorporating three vertical tail fins along with a traditional tailplane surface. The undercarriage was fixed and featured two main landing gears and a tail skid.
During development, the IM was test flown around the nearby areas of the Russian Imperial Capital to much fanfare. Distance flights were a common display of any new aircraft development in an effort to showcase capabilities and work out any design kinks. One such flight occurred from June 30th to July 12th, 1914 - a single-stop, 14.5-hour, round trip flight from St. Petersburg to Kiev. The arrival was noted for an engine fire that was put out in-flight while the return trip was without incident. Some unstable air forced the crew to fly above the clouds at times, this being accomplished without any sort of access to visible navigation markers on the ground.
It seemed as though Sikorky's vision of the IM as the world's first dedicated, four-engine passenger transport was all but fulfilled until the arrival of World War 1. Sikorsky worked with the Russian Ministry of War to adapt his new aircraft to become the world's first purpose-designed strategic bomber. Supply of the German Argus engine series was in doubt so the Russians were forced, in some cases, to use the less-capable French-made Salmson series. Ten such aircraft were ordered for military use followed by a further 80 as the war progressed. These converted bombers were now armed with a variety of defensive machine gun and cannon armament while the passenger compartment was revised to take on internal racks for bombs. Protection in the form of armor (as thick as 5mm) was allocated to the engines. The aircraft was accepted into Russian Air Force service in August of 1914 and was formed into the world's first dedicated bomber squadron, Eskadra Vozdushnykh Korablei ("Squadron of Flying Ships") in February of 1915. Deliveries of the first of 10 IM bombers began on December 10th, 1914.
Since the origins of Sikorky's aircraft lay in a commercial passenger venture, there were no military-trained personnel available to teach incoming IM recruits the subtleties of the large aircraft. As such, civilian pilots with IM flight experience were enlisted to do just that. Despite itself being a capable and sound airframe, these sort of events were beginning to build a very negative image for the IM. Its civilian-inspired origins, lack of trained combat crews and pilots coupled with the requests of a wartime government all worked in painting a dreary early picture of the Ilya Mourometz line. Combat experience, however, would prove the IM detractors wrong.
The IM quickly became the showcase of the Imperial Russia Air Force bombing offensive. The aircraft proved her worth, capable of delivering respectable bombloads with accuracy across distances against railroad targets and key transportation routes including bridges. The lethality of a single IM element was reportedly capable of rendering enemy positions destroyed for weeks. Imagine what an entire flight of IM systems could bring. The bombsight in these militarized IM's was of particular note at a time where a pilots vision and prowess were utilized moreso than reliance on any sort of bombing assistance devices. Accuracy and resulting successes improved the opinion of IM aircrews to the point that they would sometimes give up their defensive machine gun armament to take on a greater bombload instead.