B744 : engine simulation : one or three ?

[Headley 26]

Hi all,On the IVAO-forums there is a topic going on about the simulation of different engine models. Some people state that only the external models and sound is simulated.I have always believed that there was more simulated.Check here : http://gb.forum.ivao.aero/index.php/topic,104006.0.htmlHere is the text from this topic : >I and my friend from Brazil we discover : PMDG have only 1 engine model !>Only The "GE" .>The model PW and RR they only simulates the external model and the sound!>>Look !>>Quote>[TurbineEngineData]>//>// Model : CF6-80C2B1F ~58K>//>fuel_flow_gain = 0.0036 //Gain on fuel flow>inlet_area = 61.283 //Square Feet, engine nacelle inlet area [d=106 in]>rated_N2_rpm = 13635.0 //max RPM HPC>static_thrust = 58000.0 //Lbs, nominal SLS adjusted thru EEC>afterburner_available = 0 //Afterburner available?>reverser_available = 1 //Thrust reverser available?>>what you think on of this?>We have 3 models , but only 1 model is "True" !!!!>>the MD-11 and Level-d also only simulates 1 engine!>>Wilco and PSS simulates all engines !!Can someone clarify this ?

[craig_read 43]

I am sure that the different engines have different characteristics along with different sounds. If you look at the upper and lower EICAS display you'll also notice that there are even differences in the displays for the PW, GE engines compared with the RR engines. So I the statement "it's just the sound" is wrong.CheersCraig

[Guest pkav]

Hi everybody,I was just about to start a new topic about this concerning the MD11.But first of all I would like to reply to headly and craig_read: I do not yet have the PMDG 747 myself, but I just downloaded the documentation on the PMDG website and I found this on page 279 of the 747 Operations Manual:"The PMDG 747 engine mathematical performance model is based upon the GE CF6-80C2BF1F engine model at 58,000 lbs of thrust....It is important to understand that while we have included visual models of each engine type, we have only designed a single mathematical model for engine performance. This mathematical model is based upon the GE CF6 engine......"(some more sentences following, but these ar the essential ones)So you have the engine gauges of the RR and PW variants of course in the cockpit and on the outside model, but as stated in the AOM, they are all based on the GE engines.That is what was leading me to my question concerning the MD11. On the PMDG webpage it says, that both PW and GE engine indications featured, but nothing about both engines beeing mathematically modeled.In my aicraft.cfg I find the following differences:1. title=PMDG MD-11 GE CF6-80C2D1F Engines so the GE engine variant2. title=PMDG MD-11 PW4460 Engines so the PW engine variantso far so good, but further down in the [TurbineEngineData] section :Models : CF6-80C2D1F ~61.5K or PW4462 ~62Kthe fact I do not understand is , why are the PW4462 mentioned here and not the PW4460 as under 2. above?? I know the MD11 had two PW engine variants to choose from, but which type of engine is modelled here, and the more interesting question:Is there any difference between the GE and the PW engines? Or is it simply the same as with the 747, but concerning that, i did not find anything in the MD11 manual. And I am also not able to get the answer from the following strings of the [TurbineEngineData] section, because there I do not find any further seperated entries for the GE and the PW.But one thing is strange about that anyway, because with the PW engines I was able to enter a max. flex temp. of 50C into the fmc, any increase in temp from this value will not decrease takeoff EPR.And with the GE engines I was able to get the temp up to 70C where no further thrust reduction was achieved, so somehow there must be any difference in moddeling, but what is this difference? Because just looking at he total thrust numbers of 61.5K or 62K there is not so much space between as you could say the one is like the more powerful one or things like that, would a difference in modelling would even be noticable?It would be great if someone could explain that and help!Thank you very muchPhilipp

[iainsmith 9]

Because just looking at he total thrust numbers of 61.5K or 62K there is not so much space between as you could say the one is like the more powerful one or things like that, would a difference in modelling would even be noticable?Philipp

There's probably not much difference between the real engines. All the engine manufacturers would have been working around the same performance requirements and were, therefore, likely to come up with similar figures.Iain SmithP.S. Perhaps someone could explain to me what difference this makes to our simming experience? :(

[Guest pkav]

I just checked the FMC of the PW engine variant and on the AC status page it says PW4462 engines, but what I also found out is that on the perf page, when you enter the thrust limits page, on the right you can choose between a 60K and 62K setting, the differnece is 0.03 EPR for max takeoff thrust.Is this where you can change which type 4462 or 4460 engine you use?? I was not able to check if you can switch it in flight n

[FLEX1978 373]

I just checked the FMC of the PW engine variant and on the AC status page it says PW4462 engines, but what I also found out is that on the perf page, when you enter the thrust limits page, on the right you can choose between a 60K and 62K setting, the differnece is 0.03 EPR for max takeoff thrust.Is this where you can change which type 4462 or 4460 engine you use?? I was not able to check if you can switch it in flight n

[emvaos 13]

You missed the meaning of this line.static_thrust = 58000.0 //Lbs, nominal SLS adjusted thru EECPeople commenting know what EEC is ? Or what the word nominal SLS thrust implies ?The 744 does indeed have 3 engines types with different thrust limits. This is handled internally by the math, adapted to and fooling FS. CHeck it yourself. Load a 744 at MTOW and try RR, GE and PW engines. Rates of climb are different (least powerful RR, most powerful PW). You need the latest versions ofcourse or the -F model.I suggest simmers spend more time enjoying (and learning about) a very carefully tuned aircraft model rather than trying to unravel mysteries which are not there. This is not your average mickey-mouse sim dont treat it like one.Vangelis

[Guest pkav]

Thanks Rob,for your fast reply I understand the 60K/62K thing now.Vangelis,I also understand what you wrote about the different engine types beeing modeled, but what about my quote from the 747 AOM in post nr.4 ? It clearly says that only the GE variant is beeing modeled(and there are no different take off charts for example for the different engines) so I do not really get what you mean and I at least do not know what that means for the MD11 an its two engine variants.Are they both modeled or not?And I do not think that anybody talked about mysteries, I think it is just interseting to get things sorted out, exactly because it is a very interesing topic and it is great when things like that are possible within a simulator like FS2004 or FSX.RegardsPhilippP.S. : As I am willing to learn you could probably explain what static_thrust = 58000.0 //Lbs, nominal SLS adjusted thru EEC means concerning the aicraft.cfg

[FLEX1978 373]

Just though I would point out that Vangelis mentions that the extra engine models are only available to Freighter customers (also gets ported to the pax model) Rob

[emvaos 13]

Thanks Rob,for your fast reply I understand the 60K/62K thing now.Vangelis,I also understand what you wrote about the different engine types beeing modeled, but what about my quote from the 747 AOM in post nr.4 ? It clearly says that only the GE variant is beeing modeled(and there are no different take off charts for example for the different engines) so I do not really get what you mean and I at least do not know what that means for the MD11 an its two engine variants.Are they both modeled or not?And I do not think that anybody talked about mysteries, I think it is just interseting to get things sorted out, exactly because it is a very interesing topic and it is great when things like that are possible within a simulator like FS2004 or FSX.RegardsPhilippP.S. : As I am willing to learn you could probably explain what static_thrust = 58000.0 //Lbs, nominal SLS adjusted thru EEC means concerning the aicraft.cfg

OK I'll bite :) static_thrust is just a mutliplier for the non-dimensional thrust engine curve(s) in the airfile for a specific set of TAT, mach, N1. Note that static_thrust does not imply MAX thrust. This depdends on the aforementioned engine curves. N1 in turn depends on ambient pressure (delta), throttle position, mach and TAT (as defined in other airfile tables). If [a] one knows how the FS engine (thrust) model works for each set of conditions the airfile is carefully tuned and [c] has a significant amount of data for engine indications per type (for sets of conditions) then one can both move the FS throttle to produce as much thrust as exactly required on one hand, while on the other producing custom engine data (outside FS) for the EICAS that correspond precisely to a specific engine type. In other words : a virtual engine in the panel with correct thrust from the FS intrenal model (necessary for modelling performance). Takes a bit of time but evidently do-able.Best,Vangelis PS. Manual not my thing !

[Tom Wright 438]

(least powerful RR, most powerful PW).

Interesting - I was always led to believe the Rollers were the most powerful and the Pratts the least? Or is that only for the 747-200s?I've noticed the differences are certainly modelled in this. For a start the RB211 is a three spool engine so has N1, N2 and N3 and also has an EPR measurement. The CF6 is only a two spool so only has N1 and N2 and no EPR measurement. This is definitely implemented perfectly in the simulation. Well, everything is implemented perfectly really - the PMDG 744 is the best addon aircraft i've ever used if i'm honest!! It blows everything else away!!Kind regards,Tom Wright

[FLEX1978 373]

Interesting - I was always led to believe the Rollers were the most powerful and the Pratts the least? Or is that only for the 747-200s?I've noticed the differences are certainly modelled in this. For a start the RB211 is a three spool engine so has N1, N2 and N3 and also has an EPR measurement. The CF6 is only a two spool so only has N1 and N2 and no EPR measurement. This is definitely implemented perfectly in the simulation. Well, everything is implemented perfectly really - the PMDG 744 is the best addon aircraft i've ever used if i'm honest!! It blows everything else away!!Kind regards,Tom Wright

My father is on the 744F with Singapore they use the PW4000 and as far as I'm aware they are the most powerful, however like you I used to think that it went RR, GE, Then PW Rob

[Tom Wright 438]

My father is on the 744F with Singapore they use the PW4000 and as far as I'm aware they are the most powerful, however like you I used to think that it went RR, GE, Then PW Rob

They could be. I was thinking of the JT9D but they were on the Classics not on the -400s!! Not too familiar with PW engines! More of a RR fan myself!

[Guest DC-8 Jet Trader]

You missed the meaning of this line.static_thrust = 58000.0 //Lbs, nominal SLS adjusted thru EECPeople commenting know what EEC is ? Or what the word nominal SLS thrust implies ?The 744 does indeed have 3 engines types with different thrust limits. This is handled internally by the math, adapted to and fooling FS. CHeck it yourself. Load a 744 at MTOW and try RR, GE and PW engines. Rates of climb are different (least powerful RR, most powerful PW). You need the latest versions ofcourse or the -F model.I suggest simmers spend more time enjoying (and learning about) a very carefully tuned aircraft model rather than trying to unravel mysteries which are not there. This is not your average mickey-mouse sim dont treat it like one.Vangelis

Mmmh, yeah okay. But each engine variant has it's own characteristics. take for example that they would do a B747-200. If you would be flying a model with the CF engines, you take the performance charts of the CF engine and set the correct EPR values. Now what if the model is based on those old JT engines, they definitely need more power to reach the "same performance" ... So this way one can not enjoy and learn about it as it should be ...I know what I'm talking about since I'm studying the aspects of the .CFG and AIR file for our DC-8 Project. We are going to get the engines correct according to it's tables so when can actually fly the tables of that engine variant instead of flying with one variant model and using tables for another engine because the it's modelled that way ...Just my 2 cents

[FLEX1978 373]

Mmmh, yeah okay. But each engine variant has it's own characteristics. take for example that they would do a B747-200. If you would be flying a model with the CF engines, you take the performance charts of the CF engine and set the correct EPR values. Now what if the model is based on those old JT engines, they definitely need more power to reach the "same performance" ... So this way one can not enjoy and learn about it as it should be ...I know what I'm talking about since I'm studying the aspects of the .CFG and AIR file for our DC-8 Project. We are going to get the engines correct according to it's tables so when can actually fly the tables of that engine variant instead of flying with one variant model and using tables for another engine because the it's modelled that way ...Just my 2 cents

I dont think anyone is claiming that 'All varients of each engine are modelled, With RR the RB211 on the 744 has loads of varients and options depending on if they have a trent core among many other things (useless to us simmers since the marginal increase/decrease in fuel econemy means nothing to us flying in our messed up atmospheric model) These are some of the varients just for RRRB211-524GRB211-524HRB211-524G/HTAs long as TOPCAT is using the same data as the chosen PMDG Engine varient for Derates/assumed temps I'm happy.Rob