General aviation is still running on pistons. Not because small jet engines can't be built, but because they don't get cheaper as they get smaller. 6-passenger bizjet sized engines seem to be the lower economic limit.
Williams tried and tried. They built good small jet engines, all the way down to jetpack size, but those never got cheap.[1] There are "very light jets", but the smallest in production, the Cirrus Vision Jet, is around US$2 million.
https://turb.aero/ (latest news is from March 2023, not sure the company is still afloat?)
https://www.turbotech-aero.com/
Interestingly, the turbotech engines at least are recuperated engines, which is kind of unusual. But they claim it's necessary to get decent efficiency of such a small engine.
Exactly. It's bad enough with conservatively engineered piston engines. Adding apex seals is gonna make it a whole lot worse.
* High RPMs are bad in a aero engine. There are very few (no?) propellers on GA airplanes which operate above 3k RPM, so you need a reduction gearbox. That cuts into your weight savings and also reduces reliability.
* Vibration isn’t a significant concern for GA airplanes.
* Throttle response is not a significant concern in GA-sized reciprocating engines.
* Poor efficiency is a major problem because 1 lb of extra fuel is 1 lb less payload. All airplanes are limited by takeoff weight. (The 3000 HP-class radials built by Wright and P&W at the end of WWII are some of the most efficient reciprocating engines ever built)
* Maintenance is a huge concern for GA owners because labor costs $200/hr. Airplanes with 1200 TBO engines sell for a noticeable discount to airplanes with 2000 TBO engines.