Important-For those with Climb performance issues

[tnorton776 0]

PMDG, I noticed an inconsistency in the cfg file with the realworld 737-800-900 NGX engine rating from both boeing manuals and wiki. [TurbineEngineData]fuel_flow_gain=0.002inlet_area=22.619rated_N2_rpm=13200.000static_thrust=24200.000 // Thrust by EEC [26300 TO SLS here]afterburner_available=0reverser_available=1AfterBurnThrustSpecificFuelConsumption = 0 -Should read-[TurbineEngineData]fuel_flow_gain=0.002inlet_area=22.619rated_N2_rpm=13200.000static_thrust=27300.000 // Thrust by EEC [26300 TO SLS here]afterburner_available=0reverser_available=1AfterBurnThrustSpecificFuelConsumption = 0 Static thrust is set at 24200, but according to boeing and wiki, Maximum static thrust for the 737-800/900 is 27300. After the 3k rating adjustment the plane behaves far more realisticly now after FL300, and climbs out at much more realistic rates at Climb settings for a reduced thrust take off N1 90-96%. I noticed in the FMC that N1 performance adjustments allow for a 27k max thrust take off which is available, but if the .cfg file is wrong then the plane was only giving 24k, even with 27k selected. If anyone else is having these issues, I would suggest adjusting this value in the .cfg file under TurbineEngineData. I'm sure PMDG knows the proper values, but may have just typed it in as a 600-700 variant by mistake, which have less powerful version of the CFM engines.

[ZachLW 37]

Perhaps they did this for a reason? I don't know but it's just an idea.

[Chaos81 110]

After the 3k rating adjustment the plane behaves far more realisticly now after FL300, and climbs out at much more realistic rates at Climb settings for a reduced thrust take off N1 90-96%.

You're basing this on what exactly?

[tnorton776 0]

no, no reason. It was just a typo. There are thousands of lines of information that the PMDG dev crew has to work on to get this thing flying. I guarantee you that you me, them or anyone is going to input inproper data from time to time when working on so much data and information. They put the info correctly into the FMC and it reads - 27k max thrust take off. If 27k is selectable, then why would the engines only have 24k max? obviously there is a discrepancy.

[ZachLW 37]

no, no reason. It was just a typo. There are thousands of lines of information that the PMDG dev crew has to work on to get this thing flying. I guarantee you that you me, them or anyone is going to input inproper data from time to time when working on so much data and information. They put the info correctly into the FMC and it reads - 27k max thrust take off. If 27k is selectable, then why would the engines only have 24k max? obviously there is a discrepancy.

Perhaps a workaround to an unrealistic behavior due to FSX's obvious limitations was to leave the rating at that? I would start a support ticket and get an answer before telling folks on here to fiddle with the aircraft settings. Nice catch, btw.

[tnorton776 0]

You're basing this on what exactly?

Basing this on the fact that it took me nearly a half hour to climb 9000 feet from FL300 to FL390 with 30% fuel and 50% passenger load (extremely light plane) before the adjustment, and after the adjustment it only took about 5 minutes, which is far more realistic for that light of a load. Also basing this on the fact of this - http://www.boeing.co...pf_800tech.html That information is directly off of boeings website, and it reads 27300.

[MattNischan 3,778]

I can almost guarantee that number is correct in the cfg. PMDG is doing some clever behind the scenes trickery with the engine and aero modeling which quite often requires "wrong" numbers to be input into FS because the FS models themselves are wrong. I modeled a Gulfstream G550 engine in FS at one point and let me tell you with 100% certainty that there was no way to achieve real world engine profiles with just inputting the correct performance numbers into the cfg. There are a couple big excel spreadsheets out there that give you the true results of the FS numerical inputs, and modeling close to reality engine performance definitely requires some non-optimal looking numbers in the cfg. But, I assure you, this has been done by PMDG on purpose. -Matt Nischan

[tnorton776 0]

I can almost guarantee that number is correct in the cfg. PMDG is doing some clever behind the scenes trickery with the engine and aero modeling which quite often requires "wrong" numbers to be input into FS because the FS models themselves are wrong. I modeled a Gulfstream G550 engine in FS at one point and let me tell you with 100% certainty that there was no way to achieve real world engine profiles with just inputting the correct performance numbers into the cfg. There are a couple big excel spreadsheets out there that give you the true results of the FS numerical inputs, and modeling close to reality engine performance definitely requires some non-optimal looking numbers in the cfg. But, I assure you, this has been done by PMDG on purpose. -Matt Nischan

If that is the case, then why are hundreds of people, including myself, having climb performance issues? Why does the FMC have a selectable 27k take off rating? All my other planes are at their true and proper values and perform correctly. I dont get where you are saying FS numerical inputs are somehow way different than real engine performance numbers. I had this same issue with the Captain sim 727 which was set nearly 6k less per engine than their actual real world value, and when I adjusted the numbers to their proper value, it solved the problem 100%. before I adjusted, I barely could get off the runway with 100% load and a 11,000 feet runway. The 727 is designed specifically for short field take offs even at full load it only needs around 5000* feet. so you tell me. The thrust scalar is set to 1.0 for the NGX. perhaps you had issues with your gulf stream because you did not have your thrust scalar set correctly. Chaning its value will drastically affect the static thrust value. Whatever people, do whatever you want. This fixed the problem for me. It might for you to. whatever.

[ZachLW 37]

If that is the case, then why are hundreds of people, including myself, having climb performance issues? Why does the FMC have a selectable 27k take off rating? All my other planes are at their true and proper values and perform correctly. I dont get where you are saying FS numerical inputs are somehow way different than real engine performance numbers. I had this same issue with the Captain sim 727 which was set nearly 6k less per engine than their actual real world value, and when I adjusted the numbers to their proper value, it solved the problem 100%. before I adjusted, I barely could get off the runway with 100% load and a 11,000 feet runway. The 727 is designed specifically for short field take offs even at full load it only needs around 7000 feet. so you tell me. Whatever people, do whatever you want. This fixed the problem for me. It might for you to. whatever.

Okay. Whatever. Lol. I'll say again. Support ticket before telling everyone to go and change there aircraft files. I said it nicely before, but apparently this isn't a discussion anymore.

[MattNischan 3,778]

Why does the FMC have a selectable 27k take off rating? All my other planes are at their true and proper values and perform correctly. I dont get where you are saying FS numerical inputs are somehow way different than real engine performance numbers.

FS cfg numbers are not functionally identical to real engine performance numbers because the FS model is not functionally identical to a real engine. FS's engine modeling has a number of limitations and simplifications that make "plug and play" engine modeling impossible. All this means is that if you read the performance specs of an engine, put those directly into the cfg with a properly modeled aero setup, you will not get correct engine performance profiles out from FS (honestly, the performance of the engines will likely not even be close to real life, in my experience). The FMC is totally unconcerned with the aircraft cfg file, and the selectable 27k rating piggybacks on the correct modeling that PMDG has provided in their file. With the amount of work that goes into modeling an engine given FS's constraints, there is no way that this number is a typo. I cannot speak to the authenticity of the model of a whole, having never flown the real aircraft, but I can guarantee the number there is there on purpose. Do not change this value unless PMDG changes this value. -Matt Nischan

[tnorton776 0]

So you are all saying it should take 30 minutes to climb from FL300 to FL390, when in real life as a passenger we got to FL360 at full load flying from oakland to Chicago midway in about 30 minutes? I timed it, and the pilot came on after about 30 minutes from take off saying we have leveled off at FL360. hmmm lets do some math here. 0 - 36000 feet in 30ish minutes in real life at near full load.... and PMDG NGX 30,000 to 39,000 at 50% load in 30 minutes.... Something doesnt add up.

[hookandbook2 0]

If you are using a weather addon, such as ASE, the problem may be the Outside Air Temperature (OAT) ....I've seen many times the ASE renders incorrect values making it warmer way up high, which makes air less dense, and thus your climb performance suffers. And yes, you should open a support ticket to get confirmation. One should never assume. Just my two cents.

[ahsmatt7 1,199]

So you are all saying it should take 30 minutes to climb from FL300 to FL390, when in real life as a passenger we got to FL360 at full load flying from oakland to Chicago midway in about 30 minutes? I timed it, and the pilot came on after about 30 minutes from take off saying we have leveled off at FL360. hmmm lets do some math here. 0 - 36000 feet in 30ish minutes in real life at near full load.... and PMDG NGX 30,000 to 39,000 at 50% load in 30 minutes.... Something doesnt add up.

your observations seem plausible by all accounts. When you get bad climb performance, what is yout total air temperature. I know a couple of times where the temperaturetl that fsx injects is way too high and unrealistic for the higher fligjt levels. This will naturally degrade climb performance because the air density is way to low.

[kjjj11223344 48]

Would the default fs weather (with active online updates cause excessively high TAT)? I did a flight from MMUN to KMIA today and it took me about 25 minutes to reach cruise I want to know if this is normal or Iif I'm experiencing any climb issues since I am used to the default 737 which, unrealistically, climbs like a rocket.Edit: I had about 9500 pounds of fuel and 9/12 passengers in first class and 113/150 in economy.

[Chaos81 110]

Basing this on the fact that it took me nearly a half hour to climb 9000 feet from FL300 to FL390 with 30% fuel and 50% passenger load (extremely light plane) before the adjustment, and after the adjustment it only took about 5 minutes, which is far more realistic for that light of a load.

What was your weather, specifically the outside temp? Because that's the most likely problem in my book. I just did your example (30% fuel, 50% pax) and it took me 6.5 minutes to climb from FL300 to FL390. No adjustment needed.