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Why do some engines not reach max rpm shown on guages?


imacken
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Sorry about the basic question, but I was wondering, why do some modules engine RPM guages never go up to the max available?

This is most notable in the F-14, A-10C, Viggen, F-16 and Mirage AFAICS.

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Not sure why this was moved. I neither have a problem nor want to report a bug!

 

I’m simply curious why this is.

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Seems to be in the right forum area then:

 

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Seems to be in the right forum area then:

 

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No, it’s in the ‘Bugs and Problems’ area. Not right at all!

 

F-14 EIG are from different model - WIP.

F-15C goes 96% max as IRL.

 

Sorry, don’t understand what you mean.

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Sorry, don’t understand what you mean.

F-14 engine instruments are wrong at the moment.

F-15 can reach only 96% engine rpm and that is how it was in real life.

Clear now?

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F-14 engine instruments are wrong at the moment.

F-15 can reach only 96% engine rpm and that is how it was in real life.

Clear now?

 

Thanks. I wasn’t asking about the F-15.

The F-14 is maybe WIP, but the Viggen, A-10C and Mirage aren’t. Just seemed to me that there are a lot of modules exhibiting this and wondered if there is something weird about my controls.

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Just gave examples that I'm sure of although am quite sure other modules are realisticly simulated in this regard. You said that it was most notable with the modules you provided so the F-15 is another one to show some commonality.

There are better methods for testing the controls like the control setup menu and axis tune there or just hit RCtrl+Enter.


Edited by draconus

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Thanks. I wasn’t asking about the F-15.

The F-14 is maybe WIP, but the Viggen, A-10C and Mirage aren’t. Just seemed to me that there are a lot of modules exhibiting this and wondered if there is something weird about my controls.

 

100% is not always a value for MAX power mode. It can be less or more than 100%, depending on engine type, atmospheric conditions, engine control system logics, etc.

 

You can try, for example Su-27, and watch the n1/n2 max values at -20C and +30C, at the ground and at high M at 11 km.

The same is right for idle rpm as well.

 

These values, generally, are stated in manuals. Very often - as graphs.

 

THe same is for Ka-50 (depends on altitude and power limitations), MiG-29, A-10, L-39. A bit different , of course, depending on the engine.


Edited by Yo-Yo

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I'm pretty sure it's just an odd quirk of the designs. For example, the Harrier's maximum continous power setting is like 102% of something, which, logically... should be 100%. But it's not. That other aircraft are slightly under is not surprising to me.

 

As for why, you'd probably have to get into somevreally technical intensive info. Like, it's my understanding an engine, once mounted with intake and all that stuff, has its power output negatively affected compared to ''on a workbench'' specs.

 

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So, basically, like my car reaches max HP @6600rpm, but redline is 7500rpm?

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Thanks for all your input, guys. I get what you are all saying.

I've tried various modules at different altitudes, weather, etc. and I can't see any change in the percentage behaviour.

All seems kind of odd to me. For example, it would be understandable for the 'mounted' engine to show less than 100% compared to a 'workbench' test, but some modules show up to 110%.

I'm still a little confused. Maybe we just put it down to different planes have different ways of showing full power, etc. and not think any more about it!

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The aspect you have to consider is that Takeoff Rated Thrust (TRT, MAX power, whatever you want to call it) is defined by more factors than just RPM on one or more of the spools.

 

Using the A10 as an example, when you select MAX thrust, the aircraft is electrically regulating fuel flow to maintain ITT and compressor discharge pressure within limits. So just as YoYo eluded, your fan (n1) RPM at MAX power is going to vary with atmospheric conditions. Page A2-31 of your TO 1A-10A-1-1S-10 shows the chart for predicted takeoff fan speed (PTFS). In the case of the A10, it can range from 86.5 on a brutally cold day down to 77.5 on a extremely hot day.

 

As many have said, the A10 is be no means unique. A turbine engine will always have operating limitations that encompass more than just fan or turbine speed to establish max power, and max power really has no relationship at all to a 100% indication on a single gauge.

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I'm pretty sure it's just an odd quirk of the designs. For example, the Harrier's maximum continous power setting is like 102% of something, which, logically... should be 100%. But it's not. That other aircraft are slightly under is not surprising to me.

 

As for why, you'd probably have to get into somevreally technical intensive info. Like, it's my understanding an engine, once mounted with intake and all that stuff, has its power output negatively affected compared to ''on a workbench'' specs.

 

-ninja'd by Yoyo

 

So, basically, like my car reaches max HP @6600rpm, but redline is 7500rpm?

 

Can't say much about jet engines... but with cars it is because of this: They down tune engines once manufactured to meet CO2 emission standards and for engine longevity.

 

This is why there is often so much 'extra performance' to find when you install a performance chip in the engine, for example.

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