Flying machines, also known as aircraft, are a product of gnomish and dwarven ingenuity, mechanical marvels that serve alongside the famed Wildhammer Gryphon Riders of Aerie Peak to form the backbone of Alliance air power.
Types of flying machines
Two types of flying machines exist: the lighter-than-air type (airships, balloons, zeppelins, dirigibles, etc) and the heavier-than-air type (dwarven gyrocopters, gnomish biplanes, etc).
While flying machines predate the First War, the earliest observed usage of flying machines in battle came during the Second War. Gnomish inventors, present in many Alliance settlements, constructed these craft and put them into the field. Unarmed and basically unarmored, they acted as spotters and scouts. Their ability to spot orcish turtle submarines was invaluable to the Alliance fleets. Those skilled in flying them are called Aces.
The invention of the flying machines can be credited to the Gnomes. The first pilots of these craft were gnomes as well. Gnomes had built sky-engines and whirligigs as early as the before the First War. They were suitable for scouting. Some of these earliest known types were autogyros, a type of hybrid aircraft with a lift rotor and a pusher propeller. Originally they were all referred to as 'Flying Machines', although the subsequent invention of other flying machines has made this term ambiguous.
The most famous tiny gnomish flying machines were the gnomish copters. The gnomes themselves have recently come out with the gnomish biplane (apparently a new version of the single winged sky-engines seen during the first war), a small static wing flying machine armed with forward mounted machine guns. There are even fabulous flying machines like gnomish airships.
After the second war, the Dwarves designed their own type of flying machine, the Dwarven gyrocopter. Heavier then the original models, the dwarven version replaced the single pusher prop with two wing mounted impellers and mounted weaponry. Large enough to accommodate a dwarven pilot, they were still poorly armored.
During the Third War the dwarven design was revisited. This new model was dubbed the Dwarven flying machine. Eliminating the lift rotor altogether, the improved version depended on wing mounted engines for lift but offered a significant improvement in protection for the pilot. Equipped with bombs and guns, these craft were slow moving but quite powerful.
After the third war, the integration of gnomes into Ironforge provided the dwarves with additional technical assistance in developing their flying machine design. The latest model of dwarven flying machine is similar to the previous version, with dual props on a monowing design with attached water sponsons; however it appears to lack the tilted rotors of its predecessor. Smaller and presumably carrying lighter armament, these new versions operate from an automated launching/dispatch facility buried deep inside Ironforge's Military Ward.
Other Alliance Development
While the human nations have largely steered clear of flying machines (preferring to employ ships and gryphons for communication and travel), the Alliance has experimented with scout balloons, and during previous campaigns on Northrend, employed flying machines extensively under the auspices of Bomber Command.
While the Gnomes (and their Dwarven counterparts) have favored heavier then air designs, Goblins are known for their zeppelins, which were integral to the Horde's campaigns in the Second War. The subsequent end of their ad-hoc alliance with the Orcs freed the Goblins to sell their services in the Third War, and Goblin zeppelins were a common sight among Horde and Alliance armies. With the reconstruction of the Alliance fleet and the completion of the Deeprun Tram, Alliance use of zeppelins has declined. The Horde continues to employ them extensively.
A goblin flying machine may also exist as alluded in this quote, "Barkeep Hann still yearns for the days past spent racing around all of Azeroth in his tricked out goblin flying machine, accompanied by an over-sized furbolg friend."
More recently, goblins have turned their engineering prowess to defeating their gnomish and dwarven counterparts by outfitting their familiar and time-tested shredders with anti-air weaponry.
Engineer Flying Machine
In Patch 2.3, engineer-only Flying Machines were released. They come in both epic and non-epic versions. It has the tiltable wing turbine/propeller rotors of the Dwarven Flying Machine, and a retractable lift rotor for higher altitudes. In action, it looks like this.