Think about this: to concentrate the oxygen in the surrounding atmosphere, it takes energy. Lots of it, and that is even on the ground, where there is much more oxygen available. If you're going to put an oxygen concentrator in an airplane, you'd better have one large alternator or several very large batteries, even when the plane is flying at low altitude.
Since the number of oxygen molecules are far fewer at the altitudes where you require oxygen, the concentrator has to work that much harder. If the power goes out, you're out of luck, aren't you? To be safe, you'll need to descend immediately. Out West, that may not be a good alternative. Considering cost, weight, complexity, the amount of horsepower needed to generate the electricity, I wouldn't even consider it. There Ain't No Such Thing As A Free Lunch. TANSTAAFL - courtesy Robert A Heinlein. Even if the generator is free, the cost of your time will be substantial. Do you want to spend your time experimenting (along with an oxymeter to make sure you're getting what you need), or flying? The OXYFLY unit that is designed for high altitudes takes 15 amps at 28 volts. That's 420 watts. Probably, that's overkill, and you might be able to adapt a smaller, ground-based one, but even if you find one that's suitable that takes half the power for just you, that's still 210 watts (15 amps at 14 volts) draw on your system. Dan Branstrom