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How not to kill your engine


MBot
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With the hard speed limits removed since the last patch, could we collect some guidelines on operational limits to prevent engine damage? So far I feel a bit lost on what to look for.

 

The manual states that RPM1 must never exceed 103.5% (the redline on the instrument), but I have never observed a higher RPM despite having several engine failures in testing low level high speed runs. Perhaps I just missed the very moment the RPM got above the limit.

 

Also g-load seems to have an effect aswell. In two instances I was in stabilized level flight in afterburner stage 1 for several minutes and got an engine failure as soon as I pulled into a turn.

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So you would think that the engine is somehow limited by air pressure at the intake alone, without actually overreving in the process?

 

Maybe also over temperature. I haven't taken a look at the EGT in those conditions, but it might be worth taking a look.

 

I am also not sure if it is just too little airflow causing a surge. At least the engine dosen't take permanent damage at low altitude, at it just can be restarted.

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I just ran some tests and yeah about 1300km/h IAS or Mach 2.1 seem to be the limits.

I tried running the burner at 700c at about 15km alt and I still reached 2.1 M and the engine shut down. So it is not overheating.

 

Below 5km alt with the 2nd burner activated the RPM goes out of the yellow range into the red but the engine doesn't shut down so it seems to be normal to redline it with 2nd burner active.

 

I was expecting to over rev the engine but as you guys have suggested maybe it is the supersonic intake air that causes a compressor stall? I restarted the engine many times so it doesn't appear to break it but it may be causing acumulative wear. I did eventually find myself unable to restart but I am not sure about the limitations on restarts. Maybe there are other factors?

 

Also the airframe over speed limits have been removed but I have been unable to get above about 1400km/h IAS and have not seen any damage to the airframe.

 

PS I think there may be a time limit on AB as well now. I think I may have had a couple of shut downs from running it too long.


Edited by Dirty Rotten Flieger
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Speed limitation is not caused by engine, that is why I do not understand why the engine shuts down at continous high speed (happened to me). The compressor is always fed with subsonic airflow no matter how fast any plane flies (exept for scramjet engine) and the outgoing gases are hipersonic always (that is why they are so noisy). The overspeed is an airframe issue.

The engines are allowed to run at reheat for any time given that the speed is more than 1000kph and fuel is 800l or more. There might be problems with initiating reheat at speed 500kph or less.

Furthermore reaching an operational limit does not mean that the plane will stall, fall apart or blow up. It just says that the "normal" or "safe" operation is not guaranteed by the developers for that regime. I think the flight model is way too strict in that manner.

 

Update: I flew some sorties again, an average of three stops per mission and I am not duing anything different than usual. I dont feel that this frequent change in flight code is a ucky choice, we are used to something go according to something has been writen and someone changes things which completelly messes up...


Edited by sissypilot
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