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froggy

Rolls Royce EPR readout question

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This is just a question that come to my mind after trawling the Airbus X Extended forums.

 

A thread was posted regarding a possible separate IAE engine display (as the VC currently defaults to the a321 CFM for all models)

 

One of the Devs replied with this:

 

I am still collecting data on IAE engines before making a decision on whether to add in or not. I have looked at other competing products available and I know they dont simulate EPR properly.

 

In FSX, there is no EPR output, its totally bogus. If EPR were to be done, I will want to do it as best as I can, not fake and inaccurate values and that means I would have to spoof every single parameter of the EPR. The amount of work needed for this is massive and hence the decision whether it will be done will be based on the info I have on this.

 

PS: Please dont start telling me how important this is etc etc. The main factor to me is the value of the feature vs time taken needed to do it.

 

 

I get the impression that one of those 'Other' products may be the PMDG 744 RR, as well as the BBS 'bus

 

So, what actually goes into accurately simulating the EPR display?


Jarrad Symes

Perph, Western Australia

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Considering the PMDG 747 is quite an old bird now, I am sure the original coders would agree, some things may not be spot on with the knowledge and experience gained with the MD11, 737NG and the 777. Apparently the 747v1 is very close though. If, the comments are referring to the PMDG 747v1, it is a tad unfair to compare a new kid on the block to to one of very advancing years.

 

PMDG always seem to get their systems, operations, performance and handling as close to RW as possible as programming skills develop and detailed information is released to them by manufacturers. I am sure their 747v2 will be a magnificent piece of machinery that will become a yardstick for others to follow.

 

Jarrod, as for your question about simulating EPR displays, some one like Ryan(TABS) may find the time to respond, though, please Ryan if you read this, keep working on the 777...every thing else can wait.

Regards


Geoff Bryce

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The 747-400F expansion added EPR a long time ago, prior to that the data was based on N1. From what I remember it was The lead dev from FSlabs that created the original mathematical model when he used to work with them. Pretty sure that is correct, however my memory is a little hazy.

 

Anyway they seemed to have nailed the issue, the MD11 also models EPR


Rob Prest

 

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Check out the Coolsky DC9. They have an EPR that works properly. If you don't monitor the EPR as you climb, it will cook the engines.


Branton Turner

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I highly doubt that. It's a fun jet to fly, but the mechanics of things behind the scenes isn't the best. Then again, I could be wrong. They could've modeled EPR right and a whole bunch of other stuff casually (note, I didn't say wrong - I'm just implying it wasn't done to the highest standards).


Kyle Rodgers

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This is coming from the same developers who did a poor job of beta testing (I bought the plane when it came out and it was barely usable due to a few very major navigational bugs) but this has only made me appreciate PMDG's thoroughness a lot more. Yes they fixed the bug 3 days later or so but the plane itself could have been released a few days later to incorporate the fix.


Alex Jevdic KORD/KHOT/KPWK

A<380 love at first flight

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Check out the Coolsky DC9. They have an EPR that works properly. If you don't monitor the EPR as you climb, it will cook the engines.

That isn't how the JT8D fuel control unit is designed. You don't have to monitor EPR in the climb that closely. In the real aircraft you can set climb power after takeoff and not have to adjust the throttles much if at all as you climb. I have that on the very good authority of a Lufthansa 727 F/E. I agree the Coolsky EPR model is good, but it lags rather too much. It makes power setting for takeoff much more difficult than it should be.

 

I highly doubt that. It's a fun jet to fly, but the mechanics of things behind the scenes isn't the best. Then again, I could be wrong. They could've modeled EPR right and a whole bunch of other stuff casually (note, I didn't say wrong - I'm just implying it wasn't done to the highest standards).

The Coolsky DC-9 is very close to the real thing for an FSX addon. I can't imagine what you think hasn't been done to the highest standards in simulation terms. Visually the McPhatt VC isn't perfect but it's much improved since the last SP.

 

===========================================================

 

To return to the OP's question, EPR in the native FSX jet engine model is very approximate, you can't set power with it. Developers that add their own parameter modelling, like PMDG and Coolsky, can overcome this.

 

I was tempted by Airbus-X until I read about the lack of IAE engine modelling. So I'll be waiting for the FSL Airbus, however long that takes. Let's face it, even Wilco managed to make EPR work well on their Airbus.


ki9cAAb.jpg

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So I'll be waiting for the FSL Airbus, however long that takes

Agree. Three a/c I am waiting for right now; 777,747v2 and A320 from Fslabs. Have looked at the other "similar" a/c, but eye candy etc, does not make up for weakness in their systems. This can be by choice, eg, a light version to cater for sim flyers of the generic a/c in FSX.

Regards


Geoff Bryce

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I am a 747-400 NUT! Having said that, I have watched just about every video I can find about take offs etc in 744's from just about every operator I could find. What I can say about the PMDG 744's EPR ratings are that they are pretty much spot on!

 

When the aircraft was released, it only featured the GE engine's performance model, and therefore N1 was used as the primary indicator. When 1.20 was released for FS9, it added the P&W and RR engine variants to. That was when the other performance tables were added for those two engine variants.

 

Still love the old 744 - still my absolute most favourite long range bird! Cannot wait for the v2.0 and -8i/F!

 

Kind regards


 1hxz6d.png

Werner Gillespie CYB2400
Proud member of Cyber Air Virtual Airlines
AVSIM Staff Member

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The Coolsky DC-9 is very close to the real thing for an FSX addon. I can't imagine what you think hasn't been done to the highest standards in simulation terms. Visually the McPhatt VC isn't perfect but it's much improved since the last SP.

 

Not being able to fire up my sim rig (I managed to kill it - glad I insured it), I can't give answers in specifics, but I recall most of them were minor, nitpicky things (not a surprise with me, I'd imagine).

 

As I'm a visual person, what's sticking out to me is the overhead and pedestal, and I'm not simply talking about the visuals. At least one system on the overhead, and some system on the pedestal seemed off to me. I know that's not helpful, but I haven't flown the thing since October. For some reason, the pushback sticks out as the part of the checklist that it existed, so perhaps around the engine start process...


Kyle Rodgers

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I was tempted by Airbus-X until I read about the lack of IAE engine modelling. So I'll be waiting for the FSL Airbus, however long that takes. Let's face it, even Wilco managed to make EPR work well on their Airbus.

 

I have both current 'buses - AXE and the BBS version

 

AXE features the better graphics, but defaults to the cfm for sounds, vc, etc, whereas BBS has individual sounds, Gauges, and better (IMO) systems so far

 

I also find that their forums to be very hostile to requests, and/or constructive comments.......

 

To put it bluntly, BBS version (currently at 0.61) has had a good amount of flight time, whereas the AXE barely leaves the hangar. Unlike the competing 777 developer, BBS's beta system seems to be working too


Jarrad Symes

Perph, Western Australia

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Not being able to fire up my sim rig (I managed to kill it - glad I insured it), I can't give answers in specifics, but I recall most of them were minor, nitpicky things (not a surprise with me, I'd imagine).

 

As I'm a visual person, what's sticking out to me is the overhead and pedestal, and I'm not simply talking about the visuals. At least one system on the overhead, and some system on the pedestal seemed off to me. I know that's not helpful, but I haven't flown the thing since October. For some reason, the pushback sticks out as the part of the checklist that it existed, so perhaps around the engine start process...

The systems seem very authentic to me, but they are unusual. It is a DC-9 after all. B) They even modelled manual pressurisation.

 

Sorry to hear about your rig. Hope you're back up and flying soon.

 

I have both current 'buses - AXE and the BBS version

 

AXE features the better graphics, but defaults to the cfm for sounds, vc, etc, whereas BBS has individual sounds, Gauges, and better (IMO) systems so far

 

I also find that their forums to be very hostile to requests, and/or constructive comments.......

 

To put it bluntly, BBS version (currently at 0.61) has had a good amount of flight time, whereas the AXE barely leaves the hangar. Unlike the competing 777 developer, BBS's beta system seems to be working too

I nearly opted for the BBS 'bus, looks promising, but then remembered I'm still fairly happy with the feelthere 'bus, so I'm keeping my plastic in my pocket for the time being. Encouraging to hear their public beta is a good experience though.


ki9cAAb.jpg

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The systems seem very authentic to me, but they are unusual. It is a DC-9 after all. They even modelled manual pressurisation.

 

Sorry to hear about your rig. Hope you're back up and flying soon.

 

Eh...it sucks, but I'm glad the insurance paid off for once. Luckily it wasn't a complete failure (the NIC is dead, certain calls to memory are failing, among a few other things), so I was able to dump all of my data on the internal backup drive onto my externals one last time.

 

Once I'm back up and running, I'll at least PM you with my 'discreps'. That way you can tell me if I'm being an idiot, or if the claim is legit.


Kyle Rodgers

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That isn't how the JT8D fuel control unit is designed. You don't have to monitor EPR in the climb that closely. In the real aircraft you can set climb power after takeoff and not have to adjust the throttles much if at all as you climb. I have that on the very good authority of a Lufthansa 727 F/E. I agree the Coolsky EPR model is good, but it lags rather too much. It makes power setting for takeoff much more difficult than it should be.

 

 

It really seems strange that you would be able to leave the throttles at what constitutes climb thrust all the way up. I would be curious to pick your friends brain on that one as it doesn't seem to make sense to me. But maybe my understanding of EPR is worng. My assumptions have always been that EPR has nothing to do with the throttle position and everything to do with differential pressure between inlet and outlet. Sure adding fuel through the throttle will cause the engine to turn faster which generates a a greater differential pressure.

 

So.....here is the question for someone much smater than I am. As you go up, inlet pressure decreases. If the engine speed remains constant, then the ratio should stay the same. However, as you increase altitude, though the ratio would stay the same, the thrust would decrease. This is based on my understanding of Boyles law which summed up in this situation basically boils down to volume in = volume out. Now as the engines reach lower ambient temps, they are able to run a higher EPR and thus compensate for the loss of thrust that would exist if a constant EPR was kept. So whithout outside influence of throttle increase how is this possible? Does the 727 have better fuel control requiring less manual inputs?


Branton Turner

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