Here's something that's been bothering me for a while... The unreasonable effectiveness of aircraft at holding altitude. You set your power, you trim, then after a moment or two to settle an aircraft will hold +- a few hundred feet with no further intervention.
It just doesn't seem feasible to me that you can trim an aircraft to fly so precisely level that it flies for 50 nm and only gains 200 feet. My theory is that it's partly to due with power loss at altitude - if you gain altitude because of a slight mis-trimming, then the engine produces less power; conversely if you lose altitude then the engine will produce slightly more power, and you'll regain it.
I'd be interested to hear whether this mechanism is at least partly responsible for aircraft being so good at holding altitude, but also wondered whether it has repercussions when it comes to electric aircraft, where power output is linked much less strongly to altitude. Will this make them difficult to fly accurately... Will people need to build an altimeter into the control circuitry?