The basic principles of internal combustion engines haven't changed in 100 years. The basic principles of thermodynamic engines haven't changed in 250 years. However, anyone who thinks that modern internal combustion engines are much like those of 100 years ago in terms of their engineering finesse doesn't really know much about them. I read a couple of papers recently about capturing unused fluid-dynamics cycles to make exhaust systems more efficient. This is stuff Ford never knew. My expertise has been used on high-end automotive engines, plus I have hands-on experience with a 1917 Ford engine. Dismissing the former as nothing more that 100-year-old technology is pretty naive.

Just last night, I read an interesting article in Kitplanes magazine (the July 09 edition) on turbo-compound engines. While these may not be viable for use in cars due to the wide range of RPMs, they were some of the most efficient airplane piston engines made. However, the rise of turbine engines cut development of turbo-compound engines short. There were several turbo-compound engine projects starting in WWII but the most successful was the later model Wright R-3350 radial engines (up to 3500 HP out of 3350 cubic inches with very good cruise fuel consumption specs).

When people go to the National Air and Space Museum and look at the Flyer enshrined in glory, I tend to look up at the smallish glider hanging from the ceiling, where the real breakthrough occurred.

The Wrights figured out 3 axis control with their 1900 glider (more of a kite). After bad results with their 1901 glider based on Otto Lilienthal's airfoil data, they built their own wind tunnel and tested airfoil sections. They found that Lilienthal's data (considered the best in the world at the time) was wrong. The result was their very successful 1902 glider. The big breakthroughs with their 1903 Flyer was the propellor. When the Wright Experience tested an Wright propellor in a wind tunnel, it was found to be within 1-2% as efficient as modern props. Their first engine only produced about 12 HP. Without an efficient prop, the plane would've never left the ground. Like they did with the airfoil, the Wrights found that existing propellor design was insufficient so they invented their own. In the process, they probably invented aeronautical engineering. Pretty amazing for two young men from Ohio who never even graduated high school.