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alex98

FMC Cost Index vs Engine variant

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Hi Kyle or Ryan,

 

I noticed that the Cost Index gives different ECON speeds depending on engine variant.

PW CI90 equals GE/RR CI180, more or less.

I thought it was more an FMC variant problematic (if any) than an engine one... Curious about that.

 

By the way, I would guess giving the real world data you may find around that the correct data is the PW one.

 

Cheers,

 

Alex

 

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I can only suggest:

Maybe the PW has a lower cost per hour? If for example the MTBF is higher than GE and the initial cost and maintainance costs are lower than RR this would make sense. The RR's are the most expensive to buy I know. I do not know if the GE are cheaper than PW though. Also PW's are using EPR rather then N1 for calculations. Engine thrust differs and 2 GE's have the same thrust only after coming from control stand. With time they differ in thrust where EPR gives the real thrust. So I can imagine the PW are more within trim if that matters.

 

But this are only assumptions not based on real data :)

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When we advertised difference performance for different engine variants we were not lying!

As far as flight dynamics and FMC database goes these are three different aircraft.

 

The numbers you see are straight out of very very detailed manufacturer data and related mathematical functions and graphs.

 

All ECON speeds (including climb, cruise, LRC, driftdown/EO and descend) are the real ones. The same applies to v-speeds,  buffet speeds, OPT/MAX ALT (4/3/2 engines) etc etc. Only VREF and take off trim settings are common.

 

Enjoy!

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An interesting question, but unless you have data, you're not going to get far.

 

The best thing for you to do is do some analysis between pfpx accurate 747 profiles and the accuracy of the pmdg 747. That is, if you are not accepting of the accurate performance of the pmdg 747.

 

The airplane is the same but the engine thrust capabilities is slightly different, between pw and rr/ge. You would expect the pw to have to perform conservatively to be on par with the ge/rr. What is unclear to the mere mortals is, by how much?

 

Hopefully Phillipe see's this thread and gives a critical view.

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When we advertised difference performance for different engine variants we were not lying!

As far as flight dynamics and FMC database goes these are three different aircraft.

 

The numbers you see are straight out of very very detailed manufacturer data and related mathematical functions and graphs.

 

All ECON speeds (including climb, cruise, LRC, driftdown/EO and descend) are the real ones. The same applies to v-speeds,  buffet speeds, OPT/MAX ALT (4/3/2 engines) etc etc. Only VREF and take off trim settings are common.

 

Enjoy!

 

Thank you very much for your prompt answer and for the insight!

It is in fact very interesting! I would have thought CI was basically linked to the FMC and did not know that engine variants did play some part in the process.

It is also true that of the 3 recent Boeing PMDG products (NGX, 777, 747QOTS II) the 747 is the only one with different engine manufacturers...

 

All that brings more depth to the simulation.

 

Cheers,

Alex

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