I think you’re a little confused. Yes, you can fly IFR in class E airspace. The majority of piston airplanes flying IFR do so in class E (the portion below 18

I think you’re a little confused. Yes, you can fly IFR in class E airspace. The majority of piston airplanes flying IFR do so in class E (the portion below 18,000 ft). Class E is not uncontrolled. I’m not sure about what you mean with “who flies in class A airspace?” Most airlines and bizjets cruise in class A because their fuel burn is ridiculous at lower altitudes. The reason that class A becomes to class E above 60,000 ft is because hardly any planes can fly that high. This plane almost certainly won’t go that high, regardless of what the patent application says. Edit for clarity on why helix’s comment doesn’t make a ton of sense- airspaces go like this: FL600 (approx 60k ft) and up: Class E 18k ft to FL600: Class A, only IFR flight is allowed, no VFR (even if the weather is good). below 18k ft to 700 or 1,200 ft above ground: Class E, except around airports, where it can be Class B (big airport), Class C (medium airport), Class D (small airport with control tower), or still Class E (small airport without control tower). below 700 or 1,200 ft above the ground: Class G, except around airports. Class G is uncontrolled, but you still have to follow the law- no buzzing residential areas and such. You cannot file an IFR flight plan in Class G space, mainly because ATC can’t reliably see you and prevent collisions with other planes. Class E is controlled airspace but you can fly VFR without filling a flight plan; you are required to fly at altitudes that are xxx,500 ft so you don’t hit planes flying IFR at the xxx,000 altitudes. You would have to file an IFR flight plan to get to 65k ft because you would transit Class A airspace during your climb and descent.