[INVESTIGATING]Big difference in windmilling RPM depending on shutdown method

[bbrz]

E.g. level flight 450kias, 1000ft.

 

Shut down the engine by moving the throttle to off: Engine spools down to ~18% within 30sec.

 

Shut down the engine by pushing the engine fire switch: Engine spools down to ~49% within 10sec.

[WindyTX]

Maybe the hydraulic pump is disabled on the fire button shutdown so you get a higher RPM but that's just a wag.

 

Sent from my GM1915 using Tapatalk

[bbrz]

In this case I'd assume that the windmilling rpm would be different at all speeds, but at e.g. 250kias it's 16% in both cases.

 

The -1 only mentions that the fuel is being shut off when pushing the eng fire switch.

 

If this behavior is indeed correct this would be another very impressive detail in the F/A-18 simulation.

[Pâte]

Thanks for the report bbrz :)

 

Maybe the hydraulic pump is disabled on the fire button shutdown so you get a higher RPM but that's just a wag.

 

Sent from my GM1915 using Tapatalk

 

The gydraulic pump isn't disable, all the systems linked to the AMAD still running in both case to retains vital systems. The only difference that i can spot from the NATO manual is that with the THROTTLE on IDLE the ignition is running non stop. But without fuel it shouldn't cause any RPM increase isnt ?

 

HERE A TRACK :

https://forums.eagle.ru/showpost.php?p=4019946&postcount=9t

(the forum didn't let me reupload the track so i'm giving the link of the original post)

 

- Solo flight

- Caucasus

 

Flight test :

- FIRE light L/R .... PRESS

- L throttle .............. OFF

- R throttle ............. IDLE

- Nose down, reach 350kt

- L eng 17rpm | R eng 46 rpm

- (ps gain was on oride to retract flap and gain speed more easly, tested with and without just to double check that it wasn't triggering the bug)

 

I did more test not on this track, if the sjpeed drop to 0 IAS, both eng drop to 0 RPM, but asap you gain speed again, OFF eng will gain RPM much slower than the IDLE one.

 

 

Here some picture of the difference

Edited August 28, 2019 by Pâte

[Pâte]

No REPORT ?

Edited August 28, 2019 by Pâte

[mvsgas]

I do not have the F/A-18 module and my only experience with the F404 was in the F-117. I do not know if this is intended behavior or accurate. I am just curious about the modeling withing DCS.

 

I wonder if the differences is with throttle off, your telling the engine computer to shut down the engine ( fuel off, ignition, etc) So the engine computer will do what is suppose to turn the engine off. Meanwhile, when using the fire light, you are just starving the engine out of fuel, so the engine computer is actively attempting to relight the engine, the guide vanes will be position for best air flow, ignition should fire up and other thing the computer will be doing to restart the engine, just it can't restart since there is not fuel. I am sure it can be very simple in the game to simulate this behavior ( if it is intended or accurate) by simple showing different RPM.

 

I know the F404 versions in the F-117 was super reliable. On one occasion, I pilot landed without defects, when we did the daily engine down load, we found it had 17 stalls, the pilot claim he did not even notice. So that version of the engine where very robust.

Edited August 28, 2019 by mvsgas
spelling

[Pâte]

I do not have the F/A-18 module and my only experience with the F404 was in the F-117. I do not know if this is intended behavior or accurate. I am just curious about the modeling withing DCS.

 

I wonder if the differences is with throttle off, your telling the engine computer to shut down the engine ( fuel off, ignition, etc) So the engine computer will do what is suppose to turn the engine off. Meanwhile, when using the fire light, you are just starving the engine out of fuel, so the engine computer is actively attempting to relight the engine, the guide vanes will be position for best air flow, ignition should fire up and other thing the computer will be doing to restart the engine, just it can't restart since there is not fuel. I am sure it can be very simple in the game to simulate this behavior ( if it is intended or accurate) by simple showing different RPM.

 

I know the F404 versions in the F-117 was super reliable. On one occasion, I pilot landed without defects, when we did the daily engine down load, we found it had 17 stalls, the pilot claim he did not even notice. So that version of the engine where very robust.

 

Very interesting :) . I'll try to find what the manual is saying about crossbleed & ducts. Thanks :thumbup:

Edited August 28, 2019 by Pâte

[mvsgas]

Very interesting :) . I'll try to find what the manual is saying about crossbleed & ducts. Thanks :thumbup:

 

Crossbleed and ducts? Not sure if I understand the correlational.

[bbrz]

I wonder if the differences is with throttle off, your telling the engine computer to shut down the engine ( fuel off, ignition, etc) So the engine computer will do what is suppose to turn the engine off. Meanwhile, when using the fire light, you are just starving the engine out of fuel, so the engine computer is actively attempting to relight the engine, the guide vanes will be position for best air flow, ignition should fire up and other thing the computer will be doing to restart the engine, just it can't restart since there is not fuel.

Very interesting info. Never thought about this posibility. This does sound very plausible and would also explain why the rpm difference vanishes at low IAS.

 

In almost every airplane you shut down the engine the 'normal' way in case of fire, failure or severe damage by moving the throttle to idle and thereafter immediately cutting off the fuel flow either with the throttle, fuel control switch, engine master switch etc.

 

Just tested and if you shut down the engine the 'opposite' way, engine fire switch first and after reaching windmilling rpm, throttle to off, the rpm decreases to the usual ~15%.

Edited August 28, 2019 by bbrz

[Pâte]

Crossbleed and ducts? Not sure if I understand the correlational.

 

Ho i may have missunderstood it, will double check. But i think i saw in the manual that the Hornet has some inlet duct doors avoiding low speed air entering toward the inlet. I was wondering maybe in the throttle OFF position, they close letting slow air into the engine giving less RPM during the windmill ?

 

Same with the bleedair/ATS duct valve, if closing or opening it automatically when throttle go OFF, if it can affect their airflow of the windmill

Edited August 28, 2019 by Pâte

[Pâte]

Still no report no investigation nothing ? Shall we consider that this is a ' CORRECT AS IS ' ?

Edited September 11, 2019 by Pâte

[BIGNEWY]

Marked as investigating, but I do not have an answer for you. We will enquire.

[Pâte]

Thanks for the title update:thumbup: