Engine behavior at Mach 1.22 and greater

[Arink429]

Hi.

 

Not sure if there is a bug or it is normal, but flying at supersonic speeds, the engines do not respond for idle command at Mach 1.22 and greater. Over that speed and selecting idle, it seems to be stucked at 99% N2, and I have to wait for spool-down until passsing M1.22 decelerating for take control over the engines in full range again. Tested in all maps.

 

Thanks.

 

Antonio.

[Jak525]

This might be a bug but I think this may be due to the fact the aircraft is going so fast, the engine simply windmills to that speed regardless of power setting.

[Rainmaker]

Can’t attest to the accuracy, but this is normal for fighter engines to maintain higher thrust setting at high airspeeds. I’m not really smart on the subject, but from what I understand, it has to do with preventing compressor stalls/stags.

[Vitormouraa]

Not a bug. This is called RPM Lockup. This is done in order to avoid an inlet unstart. It's very similar to a compressor stall, in fact, they are both called/known as an aerodynamic disturbance. This happens when you vary the mass flow too much in the engine compared to the inlet, so most engines with EECs keep the engine at MIL or above to avoid this aerodynamic disturbance, some other engines used to open the nozzles, even more, reducing the thrust. So in order to slow down, you need to increase drag until you go past the speed at which computers think it's fine to reduce N2.

 

In other planes like the F-14A, MiG-19 even (IIRC), throttling down at supersonic speeds is prohibited. Although it has what's known as Mach lever to protect the engine from these aerodynamic disturbances.

[Andrei]

In other planes like the F-14A, MiG-19 even (IIRC), throttling down at supersonic speeds is prohibited. Although it has what's known as Mach lever to protect the engine from these aerodynamic disturbances.

 

Very much so, same applies for MiG-25 as well. They would usually not allow you to go much below full MIL power until you slow down.