IOTL, George Cayley figured out how to make an airplane...
No he didn't. He built gliders, beautiful manned gliders which allowed him to be the first to identify several basic aerodynamic concepts, but he was far from making an "airplane".
... (he even did a few glider experiments) ...
And that's one of the reasons he was rather far from making an airplane; he did far too few glider experiments.
... but was unable to invent powered flight because he couldn't get the internal combustion engine to work.
No. Cayley lacked three things:
- A sufficiently light and robust airframe
- A sufficiently light and powerful engine
- An understanding that powered flight is dynamic and requires constant control inputs from the pilot.
Cayley is prevented from achieving the first; the airframe, by the materials technology and construction techniques of his day. While Cayley actually invented "tension-spoke" wheels, the materials and techniques available to him meant he could not produce an airframe which would be light enough to fly while also being robust enough to carry an engine and withstand the stresses produced in flight.
Cayley is prevented from achieving the second; the engine, by the materials technology of the day. Dippy gunpowder fueled IC engines aside, metallurgy in 1825 was not up to the task of building a powerful engine that was also "light". Seventy five years later and decades after IC engines had entered general use, the Wrights were still rebuilding the IC engines available to them in order to increase those engines' horsepower to weight ratio.
Cayley is prevented from achieving the last; understanding the dynamic nature of flight, by his own lack of experimentation. As well as corresponding with flight researchers worldwide, the Wrights personally experimented with and flew gliders for years before attempting powered flight and their true breakthrough, the idea of dynamic control, was a result of all those years of painstaking experimentation. While they did allow him to identify several basic aerodynamic concepts, Cayley's handful of glider flights - none of which he actually piloted - simply weren't enough to give him the same insight the Wrights gained.
I cannot stress more strongly the importance of dynamic or three-axis control for powered flight. It was the Wright's
true invention. Everyone else attempting to achieve powered flight, and there were thousands of them in the decades prior to 1903, had access to pretty much the same airframe and engine technology that the Wrights did. What made the Wrights was their insights into three-axis control and that put them years ahead of their competitors.
For example, while Santos-Dumont, another extremely important aviation pioneer, was loudly acclaimed in France for a single flight of a few hundred meters for less than 30 seconds in late 1906, the Wrights had already flown
40 kilometers for nearly
40 minutes in
1905.
It was the Wright's insight into three-axis control which gave them such a lead, a lead so great that when the Wrights finally flew in public in Europe in 1908 the nascent aviation community quickly tossed aside their own designs and adopted variations of the Wrights'.
So, Cayley sadly has three strikes against him, one conceptual and two technological. In order for him to overcome the first, Cayley is going to have to fly many more gliders much more often and either pilot them himself or use pilots who aren't children or farm hands. In order for him to overcome the last two, you'll need to advance technological progress so that Cayley has available to him what was available to the Wrights. That will require PODs which will change the 1825 of your time line all out of recognition and that makes your suggestions a non-starter.
Sorry.
Gasoline will be used earlier.