And that's why I'm hanging in here, to make it interesting. PMDG isn't going to change it, nor am I.

 

 

This isn't too deep. This is a good discussion.

 

My NGX will remain untouched, as it does what it should; provide me with technical entertainment. I enjoy technical entertainment. My wife refers to my sim as "technical pornography", because I enjoy it too much (not porn, the sim...). :p0503:

 

If you guys will notice, I said several posts ago that there isn't enough computational power to accurately generate this effect in our PC's. I've got a +5GHz Core i7 with 16Gb of fast memory running dual GPU's and I would have to have this rig just run the engines and that's all it could run and even then it wouldn't be correct because there's just too many holes in the data required for accuracy.

 

But I do like talking about something I know about; thrust you can trust!

 

Kev

You could easily simulate these engine dynamics on a PC. I've run them on my old laptop. You just need the model data from Boeing to do it, and even PMDG don't get that.

 

Real time simulation models of engines are not done as a stage by stage analog of the real thing, which would indeed be a real time processing nightmare.

 

You could possibly get closer to real dynamics using the FSX engine model by adding a detailed FADEC simulation to the control input.

You could easily simulate these engine dynamics on a PC. I've run them on my old laptop. You just need the model data from Boeing to do it, and even PMDG don't get that.

 

Real time simulation models of engines are not done as a stage by stage analog of the real thing, which would indeed be a real time processing nightmare.

 

You could possibly get closer to real dynamics using the FSX engine model by adding a detailed FADEC simulation to the control input.

All you need to do is to work from the engine limitations schedule in the flight manuel or maintenance manuel,

All you need to do is to work from the engine limitations schedule in the flight manuel or maintenance manuel,

I guess you are referring to the additional FADEC simulation I talked about.  Yes, that would be a good start, but the limits don't tell you anything about the control loops used to apply them so it would be very much trial and error.

 

Parameter limits and performance tables don't tell you much about how engine parameters relate to each other so aren't much use in designing a better dynamic engine model than FSX provides.  The need for an independent N1 dynamic model makes me wonder whether the FSX turboprop engine model might possibly be more suitable as the basis for a medium to high bypass ratio turbofan.

Just a few general points regarding the CFM56-7 family. I fly the PMDG NGX most of the time and am employed as an aircraft mechanic with run/taxi certification on most variants of the 737. I also regularly jumpseat on 737 flights.On every takeoff I've seen, the crews employ a staggered throttle lever movement while advancing them up to takeoff power (by staggered, I don't mean a throttle mismatch). This is also the procedure mechanics use when doing ground runs. Throttle levers are brought up relatively quickly to a certain point usually around 45% N1, and then advanced more gradually from there. There are various reasons for this but one primary one is to allow the variable and transient bleed valves to attain their desired settings prior to full throttle advancements. These valves will unload or load the compressor especially during initial engine acceleration. Although the FADEC can control fuel delivery to an incredibly precise value based on factors too many to list, it still employs an array of actuators,bleed valves, etc , all mechanically moving components that require time to move and provide feedback to the engine control system. There is indeed an initial surge in acceleration but I suspect it has more to do with throttle inputs and the previously stated factors, Regards

I guess you are referring to the additional FADEC simulation I talked about.  Yes, that would be a good start, but the limits don't tell you anything about the control loops used to apply them so it would be very much trial and error.

 

Parameter limits and performance tables don't tell you much about how engine parameters relate to each other so aren't much use in designing a better dynamic engine model than FSX provides.  The need for an independent N1 dynamic model makes me wonder whether the FSX turboprop engine model might possibly be more suitable as the basis for a medium to high bypass ratio turbofan.

Fully agree.  The performance manual isn't going to fill the data holes, and performance/fuel and EPR scheduling is going to constantly change in the FADEC simulation as a result of ambient conditions among other things to be accurate.

 

We could probably do it, but is it worth the time and effort?

Fully agree.  The performance manual isn't going to fill the data holes, and performance/fuel and EPR scheduling is going to constantly change in the FADEC simulation as a result of ambient conditions among other things to be accurate.

 

We could probably do it, but is it worth the time and effort?

 

As previously stated by other..  "probably not worth the time and effort to need a change",  and I don't think anyone is actually expecting PMDG  to change anything  either.

 

However, it is a "Technically Interesting" thing to discuss in an "Aviation Forum", and I find it amazing that so many people are contributing from real world experiences.

 

Apart from a few "negative" posts, from those who seem to thing they can dictate what other choose to discuss,  this is probably one of the most enjoyable and informative post to follow.

As previously stated by other..  "probably not worth the time and effort to need a change",  and I don't think anyone is actually expecting PMDG  to change anything  either.

 

However, it is a "Technically Interesting" thing to discuss in an "Aviation Forum", and I find it amazing that so many people are contributing from real world experiences.

 

Apart from a few "negative" posts, from those who seem to thing they can dictate what other choose to discuss,  this is probably one of the most enjoyable and informative post to follow.

Actually, I disagree with "probably not worth the time and effort to change it". Taking things into fine detail is what PMDG strives for, right? PMDG takes detail to a much higher level than this, this is still nothing compared to what kind of details they model. They've said themselves that the big majority of details would go unnoticed by most of us. So if it's not worth modelling this, then what's even the point of modelling all those other details? And the the issue I described here, is not something that would go unnoticed by me. In fact, bothers me, because my engines take so much longer to stabilize than in the real world. That takes a little bit away from my immersion of realism. I wouldn't even necessarily need that overshoot. All I want is more responsive and quicker stabilizing engines, with average spool-up rate remaining as it is. This would be the icing on the cake for me.

 

We have so far not gotten any response from PMDG either. There are two possible reasons for that. One, they realised we are right and they cannot come up with evidence we are not. Or two, they are looking into this and re-evaluating their options to model this.

Actually, I disagree with "probably not worth the time and effort to change it". Taking things into fine detail is what PMDG strives for, right? PMDG takes detail to a much higher level than this, this is still nothing compared to what kind of details they model.  --------   etc etc etc

 

And you have every right to disagree  ...   but the reality is that PMDG probably higher propriety things to deal with, at the moment, than spending what may a considerable amount of extra development time, in reducing a spool up settling time by a couple of seconds, and to do it CORRECTLY, (not just FUDGE the Gauge)

 

If PMDG was to announce, that they were delaying the release of the 777, because Arjen had persuaded  them it was more important to correct a minor issue in the 737, I think you would get lynched !!

 

I do not think, by now, anyone is saying  that what you have proposed in incorrect,  but at this late stage in the release of the 737,  it does not seem to be that critical, and is only causes an issue during one small part of a flight.

 

Also, that fact that nobody from PMDG has come back to you and said anything, is probably good sign  .. at least they have not said they are NOT going to look into it.

 

A case of "No news is good news" 

We have so far not gotten any response from PMDG either. There are two possible reasons for that. One, they realised we are right and they cannot come up with evidence we are not. Or two, they are looking into this and re-evaluating their options to model this.

 

Arjen, they may be watching this thread, but I don't think it will motivate them to say anything.  Perhaps you'll see the change in a future update.  I don't think that they loiter here waiting to prove us wrong nor to endorse our comments.  We'll see...

 

Meanwhile, there is an attachment here for those of you who want to know more about the technical side of the CFM56 and it's control of airflow, RPM, etc.  It will help to explain what I was talking about earlier and will illustrate concepts for better understanding.  A quick look at pg 26 will be helpful to see core airflow/VSV scheduling and relationship to N₁/N₂.

 

Best,

 

Kev

Kattz, on 22 Aug 2013 - 6:39 PM, said:

Arjen, they may be watching this thread, but I don't think it will motivate them to say anything. Perhaps you'll see the change in a future update. I don't think that they loiter here waiting to prove us wrong nor to endorse our comments. We'll see...

 

Meanwhile, there is an attachment here for those of you who want to know more about the technical side of the CFM56 and it's control of airflow, RPM, etc. It will help to explain what I was talking about earlier and will illustrate concepts for better understanding. A quick look at pg 26 will be helpful to see core airflow/VSV scheduling and relationship to N₁/N₂.

 

Best,

 

Kev

Thanks for your service. I was in the Cold War at Nellis where we played war every month. You were in the real deal. I was looking at the PDF. It is pretty amazing. I have been a mechanic of some sort or another for most of my life. I was flipping through those pages and thinking about the engines in the ME-262 or even a Pulse Jet and that was just 60 years ago. Where will we be 60 years from now?????

 

Thanks,

Ron

Probably using an even more efficient version of something like this.  The warp drive is still a ways off...

 

I spent about a year at Nellis - 4450th Test Group, F-16XL. 

 

Cheers,

 

Kev

Today I decided to compare the engine spool-up of the real 777 vs the PMDG 777.

For now I only focussed on engine spool-up time.

For the real-world I used multiple videos and measured it with a stopwatch app. Of course I only measured the 777's featuring GE engines. On average the spool-up from Idle to 55% N1 took 5-6 seconds.

Compared it to the beta video here by Kyle (skip to 25:50)

http://www.youtube.com/watch?v=6h_IAoL6Pik

13 seconds.  :bad: 

Not trying to be a rant to PMDG, but an engine spool-up that's twice as slow as in the real world is going to be a gamebreaker for me.


 

 

Here's a Level D Sim of the 777. It does seem quite fast to get from Idle to 55%, and even faster to TO

I noticed what appeared to the slow spool up in Kyle's vid too.... but without being able to see Kyle's hardware throttle controller and how he spooled it up, I didn't reach any conclusions.  He certainly knows how to operate the plane well so I am assuming he wasn't slowly pushing the throttle at an unrealistically slow rate. :smile:

 

I also agree with the original reports raised here about the NGX's spool up.

 

However, I must admit it is one of the little gripes that I had mentally put into a cupboard called "it's a FSX limitation", whether that is the case or not, I've no idea.

 

Good discussion though and whether PMDG decide to look at this for V2 or not, it's still constitutes some great user input and group discussin.

 

Those who say "you're going too deep" etc must be happy to sit back and "take what they're given" in life; and never try to push to improve things.....

Just for an interest I've checked the same thing on the Ramzesses B777 for X-Plane 10. The spool-up from idle to 55% N1 takes about 7 seconds...