>>1168305There are 3 stages of development for any technology, airplanes are no exception.
The first is early proof of concept work: simple, clumsy implementations that are developed just to show that the inventor of the tech is not insane and it is possible, followed by some improvements and other test implementations that may or may not work. Many different and slightly crazy designs are tried during this period, although the total amount of money available for these experiments is not very high yet. This was achieved by the Wright brothers in the early 20th century, and followed by the early experimental aircraft during the start of the 1910s.
The second is major rapid innovation: having seen that the basic concept is feasible, and seeking potential commercial and military applications of the technology, investors start funding massive research into the tech, and as new discoveries are made the technology improves rapidly. Now that major corporations are involved, fewer crazy experiments are tried, but those experiments which are attempted are done with huge amounts of funding and can achieve breakthrough results. For airplanes, this period consisted of the first military use of airplanes during WW1, the rapid spread of air mail and shipping during the interwar period, and the rapid development of technologies such as turbine and rocket propulsion during WWII.
Once an efficient and capable design is settled on during the second phase, the third phase begins: refinement. Major research into experimental developments slows down, and most research is focused on making marginal improvements to a design which has already been proven. This is the are where the most money is made. Airplanes have mostly been in this stage since WWII, at least for commercial purposes. The military still funds some experimental aircraft, but with commercial planes in a stage where they work reliably and make money, there's no reason to expect major change anytime soon
