737NGX engine options

[Michael_LOWW 0]

hey all!

 

are there different engine options for the PMDG 737NGX (as for the ifly 737)?

 

best regards,

 

michael

[NGXfanatic 85]

Unfortunately, the answer is no. I'm surprised it's not offered, as PMDG went to great lengths to offer the user so many options on just about every facet of this addon.

But there is a workaround. The -800 has 26k rated engines. To give your NGX 24k thrust rating, you can select TO1 to derate to that rating. And use TO2 to get 22k engines.

[rsvit 16]

It's too expensive to buy performance data for all engine types from Boeing.

 

But there is a workaround. The -800 has 26k rated engines. To give your NGX 24k thrust rating, you can select TO1 to derate to that rating. And use TO2 to get 22k engines.

 

Works just from pressing TOGA to thrust reduction altitude.

[NGXfanatic 85]

I see, but can you then select clb1 or clb2 to correspond with the derated takeoff "cheat"?

I ran into this question in my mind when I was simulating Southwest Airlines ops. As you may know, they use 22k engines, so I made it a policy to always use TO1 to fool the NGX into thinking it was a 22k (instead of 24k) rated engine. But when I chose CLB1, I noticed a surge in the engine tone/thrust when it should have been reduced at accel height, unless I mistakenly used CLB by mistake. It was a while ago, but I do wonder if perhaps we would have been better served by having an option to have the different thrust ratings modeled like the iFLY product.

[G-CIVA 62]

I see, but can you then select clb1 or clb2 to correspond with the derated takeoff "cheat"?

 

That's not really how it works I am afraid. As you know two fixed climb thrust derates can be selected on the N1 LIMIT page:

 

CLB–1 provides a climb limit reduced by 3% N1 (approximately 10% thrust).

 

CLB–2 provides a climb limit reduced by 6% N1 (approximately 20% thrust).

 

The reduced climb setting gradually increases to full rated climb thrust by 15,000 feet.

 

But when I chose CLB1, I noticed a surge in the engine tone/thrust when it should have been reduced at accel height, unless I mistakenly used CLB by mistake.

 

That's also not strictly true - if you have entered an Assumed Temperature with TO–1 the N1 may actually be LESS than the CLB–1 N1...so you may indeed have experienced an increase in N1 as CLB–1 was automatically set.

 

The same can also be said for full TO N1 (in the case of a large assumed temperature)...however...if a reduced thrust takeoff has been specified, then either CLB–1 or CLB–2 may be automatically specified by the FMS to avoid a climb N1 value greater than the specified reduced thrust takeoff N1. In other words if you override the FMS automatic selections of either CLB–1 or CLB–2 you may get an increase in thrust at the THR Reduction ALT, if you opt to accept what the FMS automatically selects you should see a reduction in thrust at the THR Reduction ALT.

 

But if your N1 Limit selections have worked successfully for you then who can criticise? <_<

 

To have modelled more than one type of engine may have delayed the release date of the NGX - it would have involved a large amount of number crunching, PMDG may not have had access to the data at that time either.

 

All is not lost...we are promised a much awaited patch to the NGX once the initial release of the T7 has been rolled out.

 

As RR has already stated - some of the innovation included into the T7 (& future products beyond) will be 'rolled back' into the NGX.

[NGXfanatic 85]

Thanks for your detailed explanation Steve. Upon review of what you have said, (I had to read over it a few times, LOL) I now understand why the fixed derate "workaround" is not a perfect solution. My takeaway from this, is that from the moment climb thrust is selected to interception of the cruise altitude, the engines cannot truly perform as if they are 22k or 20k simply because of the fact that the climb derate is constantly changing up to a specified height, 15000ft, and then reverts to it's full 26k thrust rating at that altitude until flight completion. So basically, the NGX only "thinks" its 24k or 22k during the takeoff phase, and from climb thrust onwards, its back to the full 26k rating, at least from 15000ft and above.

 

That's also not strictly true - if you have entered an Assumed Temperature with TO–1 the N1 may actually be LESS than the CLB–1 N1...so you may indeed have experienced an increase in N1 as CLB–1 was automatically set.

That sounds like what I may have experienced. I am pretty sure I did select CLB-1 to match the derated TO-1 setting, and it must have been my selection of an assumed temp, as I do know that while Southwest doesn't use fixed derates, they are allowed to use assumed temps. Good catch!!!!!!

 

As I have said, its not a perfect solution, but it is one I feel we may have to live with. But at least I learned something about the fundamentals of how the NGX climb thrust model works.

[Fabo 213]

The question lies, how do the engines in real planes work like. The best thing we could do is to find someone who flies in an airline with two different rated engines on a same variant and see how they perform.... Now I used to know of such airline, but it has been bust long before NGX came out...