Stating the obvious, this page badly needs to be fleshed out. For now, here are a few bare-bones facts.
Although the 1902 flyer was the first truly-effective heavier-than-air craft, it didn't have a propulsion system, and so counts only as a glider, not as an airplane. The problem for the Wrights in 1903 was to develop a powered machine.
They had to make one more breakthrough to be successful here: understand how propellers work. This was harder than it seems, as no one really understood that a propeller was nothing more than a wing that rotates on its axis, and lifts the plane forward. So, the Wrights turned to the ship-building literature and discovered that empirical principles were used, but there was no theory of propulsion. They then reasoned out the basic mental model of the propeller as a moveable wing. This allowed them to test propeller shapes in their wind tunnel, discovering an efficient shape. For their 1903 plane, they needed all the efficiency they could get.
To drive a propeller, you need a powerplant. The Wrights wanted a lightweight gasoline engine that would provide the necessary oomph. They tried to buy an engine, but no one was willing to build one to their specs. So, with the able assistance of Charles Taylor, they built their own. It was a state-of-the-art four-cylinder model. Taylor hand-tooled the crankshaft on the Wright shop lathe. Its power-to-weight ratio was better than anything around. Even still, in the words of Charles Taylor, "It weren't much of an engine." There was no carburator. The raw gas was just dumped into the cylinders. It was air-cooled, without even the benefit of fins. To control the engine speed, the spark could be advanced or retarded. It had the horsepower -- barely -- to drag the 1903 machine into the dense December ocean air. As the engine broke in the next year, it began to produce more horsepower, and better flights.
On another front, Orville and Wilbur Wright filed a patent application on March 23 of this year. The patent was awarded May 22, 1906.
Click on grid for 5" wide picture
THE ORIGINAL WRIGHT BROTHERS AEROPLANE
THE WORLD'S FIRST POWER-DRIVEN,
HEAVIER-THAN-AIR MACHINE IN WHICH MAN
MADE FREE, CONTROLLED, AND SUSTAINED FLIGHT
INVENTED AND BUILT BY WILBUR AND ORVILLE WRIGHT
FLOWN BY THEM AT KITTY HAWK, NORTH CAROLINA
DECEMBER 17, 1903
BY ORIGINAL SCIENTIFIC RESEARCH THE WRIGHT BROTHERS
DISCOVERED THE PRINCIPLES OF HUMAN FLIGHT
AS INVENTORS, BUILDERS, AND FLYERS THEY
FURTHER DEVELOPED THE AEROPLANE,
TAUGHT MAN TO FLY, AND OPENED
THE ERA OF AVIATION
Inscription on the 1903 flyer at the Smithsonian Institution