Turbine engines are all normally aspirated. They lose power as they climb. The way around this is to flat rate the engine. For example, say the turboprop engine at sea level can thermodynamically make 1000 hp but is flat rated to 700 hp. The pilot advances the throttle at sea level to get 700hp and stops. The engine could produce more in theory but is limited by the gearbox, prop, airframe etc.

As the plane climbs the engine loses power. To get back that power the pilot advances the throttle. Just like a normally aspirated piston engine.

A turbocharged piston engine uses the turbocharger to compress the air to make the engine "think" it is at sea level even though it may not be.

All engines have compressors.

On a NA piston engine, it is the piston by itself. Higher compression ratio is higher power capability. IO-520 is 8.5 to 1, typically.

On a turbocharged piston engine, the turbo does a little bit of the compression first, then the piston does the rest. TSIO-520 is 7.5 to 1 compression ratio, less than an IO-520, since some of the compression was done by the turbo.

On a turbine engine, the compression is all done by the compressor section, no piston. On my TPE331, the compression ratio is 10:1.

You could, for example, put an IO-520 in a Cessna 150, flat rate it to 100 HP, and then the Cessna 150 would be able to make "sea level power" to, say, about 22,000 ft. This is exactly analogous to flat rating in a turbine which is nothing more than putting in a bigger engine and artificially limiting the power.

You can do the same thing for a turbocharged piston engine. Close the wastegate at sea level and make as much MP as you can. Only problem is that the engine will blow up, it can't handle all that extra power. Some highly boosted engines (think Reno racers) do basically that with complex systems to control detonation (which don't always work, alas).

For turbines, the weight of the engine doesn't scale with power that much so you don't gain much weight if you put in a 1200 HP engine versus a 600 HP engine. Then you can have "600 HP" all the way to 18,000 ft. This is basically what the TBM is, an engine twice the power it really needs so at altitude it scoots along.

The downside of a highly derated turbine engine is that at low altitude, you have a turbine engine at partial power and the fuel specifics get terrible. Having a 1200 HP compressor operating in thick air when you only need 600 HP is a lot of power that isn't going into propulsion. You can really see this at idle, the turbine engine is sucking fuel like crazy and making no power at all! Thus, turbine flyers go high as fast as they can to lower fuel burn.

Mike C.