Just look at that plane! Elevator, rudder, ailerons. But the engine is really interesting, he built a very light weight four cylinder four stroke engine with only two pistons which were arranged in the style of a double acting steam engine. That is, his pistons had combustion spaces above and below. He built the engine himself and small parts of it survive.
His propeller could have been better and although the monument shows two blades there is some evidence he made a four blade propeller as we