EEC ALTN mode cannot redline?

[AzN1337c0d3r 3]

If you select EEC ALTN you can set a higher N1, about 2% more. I'm not sure what you expect to see, and how much relationship that bears to reality.

FCOMv2 says you can select up to N1 RPM limit (i.e. red-line) as all thrust protection limitations are lost, not some arbitrary 2% more.

[777simmer 117]

it seems you are not understanding what i believe to be wrong with the EEC alternate model.

The FCOMv2 says clearly that only N1 RPM protections remain in place after EEC alternate mode, you can thrust overboost as much as you want (because protections are lost), not some arbitrary FMC calculated 2% limit over 100% N1. You can't get anywhere close to the red line, which as yourself has previously stated in the other thread is the red line.

This "bug" in the limiting to the FMC value is exactly why Eng Limit Prot L/R warning isn't being triggered.

I do understand what you are saying.

If you are unwilling to accept a mere 2% overboost as an overboost then I can not help you any further. I call that denial, not a bug.

 

I mean what sort of overboost would make you happy then?

103%

104%

105%

106%

107%

108%?

109% = redline = engine limit/surge/stall checklist = pull back throttle

 

There just is not that much more you can get out of them engines past Amber Line.

Not without the risk of doing some major damage to them at N1 Redline.

Is that what you are looking for? You want to see if you can blow them appart?

Yeah maybe they did not simulate that part :-)

 

I looked into the 777 maintenance manual but found no helpfull further info.

You would need a GE manual which I dont have.

 

As far as I know you should never ever ever get close to Redline N1 even in alternate EEC mode. Unless that engine has a problem BEYOND the EEC being in alternate mode.

But like I said I have no data to prove me wrong or right. I dont know if it can do 103% or 105% or 107% with EEC off. And neither do you. So we can not say this is simulated correctly to the last bit or not.

[777simmer 117]

FCOMv2 says you can select up to N1 RPM limit (i.e. red-line) as all thrust protection limitations are lost, not some arbitrary 2% more.

I dont have the PMDG FCOM with me but I am pretty sure there is no difference between that and my personal FCOM. Which clearly states that N1 and N2 limit protection (redline) is available also in Alternate mode. That means that you can get passed the amber line and if there is some sort of an additional engine problem (governor for example) which would result in RPM increasing to redline then the EEC will prevent this by commanding reduced fuel flow. So no...you can not go up to N1 red line.

 

I hope you dont mind, but I have no further info on this subject.

Maybe a GE engineer can pickup from here ;-)

[AzN1337c0d3r 3]

I do understand what you are saying.

If you are unwilling to accept a mere 2% overboost as an overboost then I can not help you any further. I call that denial, not a bug.

 

I mean what sort of overboost would make you happy then?

103%

104%

105%

106%

107%

108%?

109% = redline = engine limit/surge/stall checklist = pull back throttle

 

There just is not that much more you can get out of them engines past Amber Line.

Not without the risk of doing some major damage to them at N1 Redline.

Is that what you are looking for? You want to see if you can blow them appart?

Yeah maybe they did not simulate that part :-)

 

I looked into the 777 maintenance manual but found no helpfull further info.

You would need a GE manual which I dont have.

 

As far as I know you should never ever ever get close to Redline N1 even in alternate EEC mode. Unless that engine has a problem BEYOND the EEC being in alternate mode.

But like I said I have no data to prove me wrong or right. I dont know if it can do 103% or 105% or 107% with EEC off. And neither do you. So we can not say this is simulated correctly to the last bit or not.

No you still do not understand. The FCOMv2 states there is no thrust overboost protection in EEC alternate mode. Not 2%N1 thrust overboost protection, there is NO protection. 102% N1 also doesn't mean 2% more thrust than 100%N1, it doesn't work like that.

 

The N1 RPM limit is 110.5%. As part of the certification process for the GE90-115B engine, they were ran for 60 hours at N1, N2, AND EGT redline while developing 127,900 lbf. I don't call that "not much more", that's 10% more thrust than rated (115,300).

 

Which will be certainly very helpful in a MTOW + engine out + unexpected windshear situation even if it means that the engines will need a check by maintenance afterwards.

 

[tcas_climb 45]

From the FCOM

 

 

 

Thrust protection is not provided in the alternate mode and maximum rated

thrust is reached at a thrust lever position less than full forward. As a result,

thrust overboost can occur at full forward thrust lever positions. The EICAS

caution message ENG LIMIT PROT (L, R) is displayed if the thrust lever position

commands an N1 greater than the maximum rated thrust (maximum N1). N1

and N2 red line protection is still available in the alternate control mode.

 

RED LINE protection is still available, but thrust overboost protection is not available in ALTN mode.

[AzN1337c0d3r 3]

I dont have the PMDG FCOM with me but I am pretty sure there is no difference between that and my personal FCOM. Which clearly states that N1 and N2 limit protection (redline) is available also in Alternate mode. That means that you can get passed the amber line and if there is some sort of an additional engine problem (governor for example) which would result in RPM increasing to redline then the EEC will prevent this by commanding reduced fuel flow. So no...you can not go up to N1 red line.

 

I hope you dont mind, but I have no further info on this subject.

Maybe a GE engineer can pickup from

Now you have added some hypothetical "governor". That's certainly not in the docs. I really doubt PMDG looked at a GE engine document and said "Hmm, we'll just introduce this hypothetical "governor" into our EEC code that the FCOM documents don't mention".

 

The FCOM also says that ENG LIMIT PROT message will show up if the thrust lever position commands an N1 greater than the maximum rated thrust. Why did PMDG even bother programming that message in if there's no way a sim user can trigger it (without mashing F4/slamming throttles).

 

It is far more likely this is a bug instead of your hypothetical governor and that the EEC simulation programmer didn't consider that thrust overboost protection needs to be turned off instead of following the FMC calculated values.

[777simmer 117]

From the FCOM

Thrust protection is not provided in the alternate mode and maximum rated

thrust is reached at a thrust lever position less than full forward. As a result,

thrust overboost can occur at full forward thrust lever positions. The EICAS

caution message ENG LIMIT PROT (L, R) is displayed if the thrust lever position

commands an N1 greater than the maximum rated thrust (maximum N1). N1

and N2 red line protection is still available in the alternate control mode.

RED LINE protection is still available, but thrust overboost protection is not available in ALTN mode.

I know, that is what I have been saying the whole time. He is just not getting that there is a difference between THRUST LIMIT PROTECTION (a protection against too much force) and N1 LIMIT protection (a protection against too high RPM).

I dont know how else to explain it too him :-(

[AzN1337c0d3r 3]

RED LINE protection is still available, but thrust overboost protection is not available in ALTN mode.

Whose point are you trying to make anyways?

 

My point is that it doesn't get anywhere close to redline, it's always 1-2% above amber line (and 8-9% below redline). Unless everyone else on this thread seems to get close to 110.5% N1.

[kevinh 409]

No you still do not understand. The FCOMv2 states there is no thrust overboost protection in EEC alternate mode. Not 2%N1 thrust overboost protection, there is NO protection. 102% N1 also doesn't mean 2% more thrust than 100%N1, it doesn't work like that.

 

The N1 RPM limit is 110.5%. As part of the certification process for the GE90-115B engine, they were ran for 60 hours at N1, N2, AND EGT redline while developing 127,900 lbf. I don't call that "not much more", that's 10% more thrust than rated (115,300).

 

Which will be certainly very helpful in a MTOW + engine out + unexpected windshear situation even if it means that the engines will need a check by maintenance afterwards.

I think it's you who don't understand. No protection does not mean that the scheduled N1 is not limited.  Full throttle could be scheduling 105% N1, or some other figure less than the red line. I don't know about the 777, but on the 747-400 (with FADEC engines) if you switch to ALTN mode and firewall the throttles the engines do not red line. They run at a higher N1, but not near the red limit.

 

Also did you not read my post earlier when I referred to what PMDG said about this.

I asked PMDG support about red exceedance indications on EICAS I got after takeoff once and they said the EEC limits were hardcoded in the sim so they can't be exceeded. However if you slam the throttle forward (or hold F4 down) you can see the commanded N1 go to maximum.

I read that as meaning the EEC is always limiting in their model, possibly because of FSX limitations. To be able to set 110.5% N1 with limits off, the throttle position for the EEC normal case would be somewhat reduced. It's all a compromise, you shoud not expect perfection everywhere.

[777simmer 117]

No you still do not understand. The FCOMv2 states there is no thrust overboost protection in EEC alternate mode. Not 2%N1 thrust overboost protection, there is NO protection. 102% N1 also doesn't mean 2% more thrust than 100%N1, it doesn't work like that.

.

Yes it does work like that. In Alternate mode EEC THRUST LIMIT protection is gone but you still have EEC N1 RPM limit protection!!!! Two different thing, that is what I have been trying to explain to you all the time.

 

Ok good N1 redline is 110.5%

Like I said I am looking at my own (my airlines) FCOM and we have the GE90-90B with max 109% N1.

[AzN1337c0d3r 3]

I think it's you who don't understand. No protection does not mean that the scheduled N1 is not limited. I don't know about the 777, but on the 747-400 (with FADEC engines) if you switch to ALTN mode and firewall the throttles the engines do not red line.  They run at a higher N1, but not near the red limit.

 

Also did you not read my post earlier when I referred to what PMDG said about this.

 

I read that as meaning the EEC is always limiting in their model, possibly because of FSX limitations.  To be able to set 110.5% N1 with limits off, the throttle position for the EEC normal case would be somewhat reduced. It's all a compromise, you shoud not expect perfection everywhere.

You do not state if is the PMDG 747 or the real 747. Also, you dont state what the atmospheric conditions are. It's possible that you are EGT or N2 limited in that scenario.

 

I read your PMDG post. EEC is hard-coded isn't actually saying anything. However, if you look at your VC model while you are throttle-slamming/F4 pushing, you can see that the throttles bounce back when you let go, so the sim is definitely capable of at least seeing 117% N1.

 

 

[kevinh 409]

This "bug" in the limiting to the FMC value is exactly why Eng Limit Prot L/R warning isn't being triggered.

The FMC never limits N1. It manages thrust ratings/limits that are used by the EEC. The EEC is what provides the actual limits. Whatever may be wrong with the FADEC, it's not to do with the FMC.

[AzN1337c0d3r 3]

Yes it does work like that. In Alternate mode EEC THRUST LIMIT protection is gone but you still have EEC N1 RPM limit protection!!!! Two different thing, that is what I have been trying to explain to you all the time.

 

Ok good N1 redline is 110.5%

Like I said I am looking at my own (my airlines) FCOM and we have the GE90-90B with max 109% N1.

We agree on all the points I have quoted. What I dont understand is why that some here think there is some magical protection before 110.5% N1 in EEC ALTN mode.

The FMC never limits N1. It manages thrust limits that are used by the EEC. The EEC is what provides the actual limits. Whatever may be wrong with the FADEC, it's not to do with the FMC.

If the thrust overboost protection code of the PMDG is set by the amber line, and the amber line is calculated by the FMC in EEC ALTN mode...

[777simmer 117]

Compare it to a car if you want.

(purely hypothetical I know cars dont have PS limit protection)

 

Take a car with max 150PS. More than 150PS does damage to the engine, the bearings or whatever.

That is where your Thrust Limit Protection comes in. It prevents you from producing more than 150PS even with the peddal floored.

That is what the EEC can only do in normal mode.

 

Then there is the RPM. The engine redlines for example at 8000RPM.

Beyond that you again do damage to the engine.

Not because of 150PS but purely centrifugal forces blowing the engine apart.

That is where N1 Redline protection comes in.

This EEC prtection works in normal as well as Alternate mode.

[kevinh 409]

You do not state if is the PMDG 747 or the real 747. Also, you dont state what the atmospheric conditions are. It's possible that you are EGT or N2 limited in that scenario.

 

I read your PMDG post. EEC is hard-coded isn't actually saying anything. However, if you look at your VC model while you are throttle-slamming/F4 pushing, you can see that the throttles bounce back when you let go, so the sim is definitely capable of at least seeing 117% N1.

 

 

It was on a 747 full flight simulator if you must know. CF6-80B5F engines. ISA standard conditions at sea level.  Not that that really makes any difference to the bigger picture.

 

I think the throttle movement you see in the VC is FSX fighting the way PMDG are limiting the engine.  PMDG are limiting N1 by applying a soft limit to the thrust lever position. But they haven't made a limit to the keyboard controls (as they didn't with thrust reverse in flight).  All the time you hold F4 the PMDG EEC model is bypassed.  Clearly the engine model can cause a red line situation, but there may be other reasons why PMDG are not letting it get there in EEC ALTN mode.  One of which may be that the real thing can't either.  As all you know is what the FCOM says in general you don't actually know either.