Propeller vs. Jet Engines

Confused about turboprop engine specs in MSFS? Learn about fixed vs. free turbines, critical altitude, and essential instruments to get your virtual turboprop flying right.

Hey there! So you're diving into the world of turboprops in Microsoft Flight Simulator, huh? It can seem a bit tricky at first, especially when you're setting up the Engine Specs and Panel. Let's break it down like we're just chatting over a cup of coffee. First off, the big question is whether your engine has a "free" or a "fixed" turbine. It sounds technical, but it's pretty straightforward: * Fixed Turbine: Think of it like this – the drive shaft is directly connected (through a reduction gear, of course) to the engine's turbine. Simple and direct. * Free Turbine: This one's a bit more complex. It actually has two turbines. The first one powers the compressor, and a second, independent turbine spins the drive shaft. It's like having a little helper engine just for the propeller. ### Which Turbine Type Should You Use? This often comes up when you're building a custom aircraft or trying to get a specific feel. If you're aiming for counter-rotating, constant-speed propellers, you'll want to go with a fixed turbine. Why? Because the constant-speed governor works best this way. If you try to use a free turbine with those, the propeller RPMs will bounce around all over the place, which isn't great for efficiency. ### Engine Specs Settings When you're setting up the engine specs, here are a few things to keep in mind: * Manually Regulated Engines: For these, just set the critical altitude to 0 ft. Easy peasy. * FADEC Equipped Aircraft: If your aircraft has a FADEC (that's the fully automated digital engine control), you'll need to find the specific critical altitude for that engine type. Getting this right is key for proper performance and control response. * Emergency Power: Many turboprops have an emergency power setting that gives you a nice boost. You can simulate this in the engine specs by setting a higher value for "max forward throttle." For instance, if an engine is rated at 1250 shp continuous and 1802 shp for emergency power, you'd set max forward throttle to about 1.44 (1802 / 1250). Heads up! If you use the autopilot's FLCH (flight level change) mode, it'll automatically go to 100% throttle. If you've set that 100% throttle to simulate emergency power, your autopilot might end up climbing at an unrealistic, super-high power setting. Just something to be aware of! ### Required Instruments What you need to monitor depends on your turbine type: For a "Fixed" Turbine: * Either engine RPM, N1, or propeller RPM (they're all linked, but propeller RPM is measured after the gearbox). * Either power or torque (power was more common on older types). * ITT (Inter Turbine Temperature). For a "Free" Turbine: * Either engine RPM or N1. * Either propeller RPM (Np) or N2 (N2 is usually for turbojets, but sometimes used here). * Either power or torque. * A separate gauge for propeller RPM. * ITT (Inter Turbine Temperature). Remember, each of these has a redline value. You'll need to keep an eye on all of them during flight to stay within limits. Just so we're all on the same page, here are some quick definitions: * TORQUE: How much twist is being sent to the propeller, usually in ft*lb(f) or a percentage. Too much can wreck your drivetrain. * ITT: Inter Turbine Temperature. It's measured inside the engine. Overheating can lead to turbine failure. * N1: The RPM of the compressor section. Sometimes shown as a percentage. * N2: The RPM of the power turbine section. Less common in turboprops, more in turbojets. Sometimes shown as a percentage. * RPM: The propeller's RPM. It'll be lower than N2 because of the reduction gearbox. ### Additional Instruments Most turboprop aircraft will also have these gauges: * Fuel flow indicator * Oil temperature gauge * Oil pressure gauge And if your engine uses a speed reduction gearbox, you might also see: * Transmission oil temperature. * Transmission oil pressure. That should give you a pretty good handle on setting up your turboprops. Happy flying!