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FS9 PMDG 737-800 takeoff performance


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24 replies to this topic

#1 mserin

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Posted 11 October 2010 - 12:43 AM

I have been flying PMDG 737-800 in my FS9 for a while.I believe that PMDG has done a great job. I have a problem with the takeoff performance. As I have read from the real 737-800 CFM56-7B26 manual and have used TOPCAT takeoff performance calculation tool I should be able to takeoff from LTBA Istanbul airport runway 06(runway length:2300 m.elevation:93ft. ) with no winds, QNH 1013 and 15 degree celcius temperature with maximum 75.000 kg of gross weight. Air conditioning is on and anti ice is off. THe optimum flap setting should be 5 degree flap and trim setting (actually sepends on the CG) is about 6.0. N1 is 98.1 %. Rotation speed is 151 kt. But in the the simulation even when I make the air condition and engine bleed of the takeoff is most often at the very end of the runway when there's only about 50 metres of pavement is left which is neither acceptable or can be considered safe. I live in Istanbul and I see lots of 737-800' which are I believe at least 70.000 kg ( because I know that some of them have destinations at least 2000 nm away) can takeoff on a standart day at the middle of the runway 06 only after about 1200 metre takeoff roll they reach rotation speed.

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#2 mserin

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Posted 11 October 2010 - 08:26 AM

I have been flying PMDG 737-800 in my FS9 for a while.I believe that PMDG has done a great job. I have a problem with the takeoff performance. I have read from the real 737-800 CFM56-7B26 operations manual and have used TOPCAT takeoff performance calculation tool to check my takeoff performance. I should be able to takeoff from LTBA Istanbul airport runway 06(runway length:2300 m.elevation:93ft. ) with no winds, QNH 1013 and 15 degree celcius temperature with maximum 75.000 kg of gross weight. Air conditioning is on and anti ice is off. The optimum flap setting should be 5 degree flap and trim setting (actually depends on the CG) is about 6.0. N1 is 98.1 %. Rotation speed is 151 kt. But in the the simulation even when I make the air condition and engine bleed off the takeoff is most often at the very end of the runway when there's only about 50 meters of pavement is left which is neither acceptable or can be considered safe. I live in Istanbul and I see lots of 737-800s which are I believe at least 70.000 kg ( because I know that some of them have destinations at least 2000 nm away) can takeoff on a standart day at the middle of the runway 06. Only after about 1200 meters takeoff roll they can reach rotation speed.

#3 downscc

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Posted 11 October 2010 - 10:42 AM

Double post? Full names in this forum please.Verify you have proper trim for takeoff, she behaves more like a bus than a plane if that is set too much nose down.

#4 mserin

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Posted 11 October 2010 - 01:24 PM

I am sorry for the double post . I am new in this forum I did it by mistake. I am calculating the trim setting with the help of the TOPCAT software. I think it's the most accurate and realistic way to calculate trim. But still the acceleration of the aircraft is too slow.

#5 Jack_C

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Posted 11 October 2010 - 10:33 PM

That sounds like a condition that requires a full rated thrust with flaps 25Jack C

#6 DHG750R

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Posted 11 October 2010 - 11:22 PM

I have been flying PMDG 737-800 in my FS9 for a while.I believe that PMDG has done a great job. I have a problem with the takeoff performance. As I have read from the real 737-800 CFM56-7B26 manual and have used TOPCAT takeoff performance calculation tool I should be able to takeoff from LTBA Istanbul airport runway 06(runway length:2300 m.elevation:93ft. ) with no winds, QNH 1013 and 15 degree celcius temperature with maximum 75.000 kg of gross weight. Air conditioning is on and anti ice is off. THe optimum flap setting should be 5 degree flap and trim setting (actually sepends on the CG) is about 6.0. N1 is 98.1 %. Rotation speed is 151 kt. But in the the simulation even when I make the air condition and engine bleed of the takeoff is most often at the very end of the runway when there's only about 50 metres of pavement is left which is neither acceptable or can be considered safe. I live in Istanbul and I see lots of 737-800' which are I believe at least 70.000 kg ( because I know that some of them have destinations at least 2000 nm away) can takeoff on a standart day at the middle of the runway 06 only after about 1200 metre takeoff roll they reach rotation speed.

I attempted a performace calculation using the condiations you specified.+_15c / calm wind / QNH1013 / EAI off / A/C on / runway 06Performace limt 166117lb / 75,350kgActual takeoff weight 165345lb / 75tonsThe margin is 551feet

TAKE-OFF LTBA/IST RWY 06 TORA 7546FT N301TZ BOEING 737-800 CFM56-7B26ATATURK TEMP +15C ALT 29.92 WIND 000/00 (00KT HW)------------------ CONDITIONS ------------------- ** FLAPS 5 ** TO ** DRY ** ** AIR COND ON ** ANTI ICE OFF ** ASSUMED TAKE-OFF WEIGHT 165345 LB ------------------ FULL THRUST -------------------//+15C 166117 OBS© 151 151 155 551FT 98.1%***************************************************DO NOT EXCEED MAX STRUCT TAKE-OFF WGHT OF 173000 LB***************************************************

This calulation is for same conditions, except for *A/C off*Notice the stop margin is higher (610ft) with more power being used

TAKE-OFF LTBA/IST RWY 06 TORA 7546FT N301TZ BOEING 737-800 CFM56-7B26ATATURK TEMP +15C ALT 29.92 WIND 000/00 (00KT HW)------------------ CONDITIONS ------------------- ** FLAPS 5 ** TO ** DRY ** ** AIR COND OFF ** ANTI ICE OFF ** ASSUMED TAKE-OFF WEIGHT 165345 LB ------------------ FULL THRUST ------------------- +15C 167550 OBS© 151 151 155 610FT 98.9%---------------- REDUCED THRUST -----------------//+30C 166482 FIELD 151 151 155 289FT 96.4% +31C NOT AUTH +32C NOT AUTH***************************************************DO NOT EXCEED MAX STRUCT TAKE-OFF WGHT OF 173000 LB***************************************************

ThanksDarrell Gordon

#7 mserin

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Posted 12 October 2010 - 09:44 AM

Thanks for the calculations. This is exactly my point. I should be able to takeoff with 75 tons gross weight safely. But in the simulation I can leave the ground at the very end of the runway. I don't believe that in real world this would be considered safe. In case of rejected takeoff just before V1 it wouldn't be possible to stop safely before the end of runway.

#8 Jack_C

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Posted 12 October 2010 - 10:40 AM

that depends on what your V1 speed is.Jack C

#9 ronzie

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Posted 12 October 2010 - 12:30 PM

Looking at the current chart it looks like for 5/23 the intersections are at 2/3 of the runway length just over 1700 metars, plenty for a 738. I've done this fully loaded on a standard day at KMDW with about 5300 foot roll availability. On a hot day they reduce weight slightly (in the real world). Other weight restrictions are due to runway surface conditions.Many airline policies dictate using full runway length including starting the roll in the displaced threshold area (not overrun) for takeoff of jetliners to provide maximum abort distance. Apparently they do not practice this there.

#10 ronmarks

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Posted 14 October 2010 - 03:46 AM

I agree with the OP's unstated point - that the 737 NG physics might be off a tad. I think so. My impression is that the pmdg 737s ( and original MS 737) are a bit sluggish on the TO roll. After rotation, it seems about right.There is a very large increase in drag upon rotation. With low flap setting, the wheel and aero drag prior to rotation will only be in the high 100's or low 1000's lbf , but will increase more than 10,000 lbf with rotation. So the TO roll net thrust to accelerate the aircraft is only a little less than the engine thrust. It should not be too hard to do an estimate of the effective TO roll thrust, just time the TO roll from brake release to V1 and see what you get... f = ma and all that.

#11 mserin

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Posted 15 October 2010 - 02:03 AM

I have been thinking of a way to check whether the TO roll thrust is realistic in 737 PMDG or not. I believe that I come up with a solution at last. Every 2 engine jet aircraft must be able safely climb out ( at least to 2000 ft so you can go back to the airport and land) in the event of an 1 engine failure at V1 with the maximum gross weight. So I tried this in 737-800 PMDG. You can also try it yourself. At V1 shutdown one of the engines and try to climb to a safe altitude. I was not able to climb :( At maximum gross weight plane can not climb out safely in the event of an engine failure at V1!! . I believe this should prove that the takeoff thrust in the simulation lower than it should be.

#12 downscc

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Posted 15 October 2010 - 10:38 AM

Try a little more nose-up trim? Calibrate your controller? She certainly will get in the air unless there is a problem, not sure that the simulation exactly replicates real performance since this is a very old (written for fs2002 and updated for fs2004) but the basic stuff like you are trying to accomplish are within the simulator's ability.

#13 ronzie

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Posted 15 October 2010 - 02:11 PM

Refresh my memory;Does the MCP N1 button or TOGA button give maximum thrust beyond the limitation set in the FMC?Also, as I recall isn't it v2 that is the SE safe climb speed, not V1, the take-off abort speed?

#14 Mats_J

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Posted 15 October 2010 - 09:44 PM

Ron,

Does the MCP N1 button or TOGA button give maximum thrust beyond the limitation set in the FMC?

As far as I recall one push on the TO/GA button gave you MCP thrust while two gave you max thrust. But then again that could be for a GA event now when I think about it. I certainly need to be recertified on the NG.

Also, as I recall isn't it v2 that is the SE safe climb speed, not V1, the take-off abort speed?

Correct as far as I recall:

V2, the Take Off Safety Speed, is the lowest speed at which the aircraft complies with the handling criteria associated with climb after take off, following the failure of an engine.V2 is also defined as the target speed to be attained at the screen height with one engine inoperative and is maintained to the point where acceleration to Flap Retraction Speed is initiated.

Merdan,

Thanks for the calculations. This is exactly my point. I should be able to takeoff with 75 tons gross weight safely. But in the simulation I can leave the ground at the very end of the runway. I don't believe that in real world this would be considered safe. In case of rejected takeoff just before V1 it wouldn't be possible to stop safely before the end of runway.

Reading this thread I do remember having problems with high take-off speeds (or low acceleration if you like) with the -800. I can't for the life of me remember what I did to correct the issue. What I do remember is that there was something that made this happen on occasion.Not much help I know but anyways...Cheers,

#15 ronmarks

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Posted 15 October 2010 - 11:21 PM

I have been thinking of a way to check whether the TO roll thrust is realistic in 737 PMDG or not. I believe that I come up with a solution at last. Every 2 engine jet aircraft must be able safely climb out ( at least to 2000 ft so you can go back to the airport and land) in the event of an 1 engine failure at V1 with the maximum gross weight. So I tried this in 737-800 PMDG. You can also try it yourself. At V1 shutdown one of the engines and try to climb to a safe altitude. I was not able to climb http://forum.avsim.net/public/style_emot... At maximum gross weight plane can not climb out safely in the event of an engine failure at V1!! . I believe this should prove that the takeoff thrust in the simulation lower than it should be.

This issue was challenging, so I followed my advice from my previous post and did a bunch of max GW take-off rolls and eng-off rollouts with the PMDG 737-800 sim. I did most of the runs at 1/2 speed to make the timing more accurate. and used the stopwatch function of the panel clock(upper left) for timing the acceleration and decelerations. This is what I got:The average TO roll drag is about 10,800 lbf. This seems to be excessive, but this is what the tests produced. The drag at 150 kt just prior to rotation was 13,000 lbf.The average net thrust during the TO roll was 33,000 lbf total (both engines)Adding the drag and net thrust gave 43,800 lbf total, or about 21,900 for each engine. This is a significant thrust deficit.So, Dr Serin's suspicions are confirmed. The PMDG 737-800 badly needs new engines and some air in the tires. :Worried:I also confirmed that, single engine at gross, the -800 is impossibly marginal. It will only maintain any climb at all if the speed is above V2, so yanking it off earlier will only get you to the first obstruction or an "urban renewal" crash landing.

#16 sssspecialista

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Posted 16 October 2010 - 04:35 AM

Hi thereI made some test of take off with derated take off with a real 738 pilot, and the conclusion was that PMDG 737 is a little bit underpowered.

#17 mserin

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Posted 17 October 2010 - 04:46 AM

Thank you very much Ron Marks. I am very impressed with your calculations.

#18 mserin

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Posted 17 October 2010 - 06:11 AM

I did a calculation depending on Ron Marks calculation that the thrust is actually 21.900 lbs per engine in PMDG 737-800. It seems that the thrust in reality should be 26.000 lbs per engine. 26.000/21.900 is 1.18. So the thrust should be 1.18 times more than it is now. So in the aircraft.cfg file I replaced the following number with this number:[jet_engine]thrust_scalar=1.0 ( I deleted this number and replaced it with 1.18)With this number replaced I think that the takeoff performance becomes more realistic. But this time I realised that the climb and cruise performance becomes unrealisticly higher than it should be :(

#19 Jack_C

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Posted 17 October 2010 - 01:42 PM

I did a calculation depending on Ron Marks calculation that the thrust is actually 21.900 lbs per engine in PMDG 737-800. It seems that the thrust in reality should be 26.000 lbs per engine. 26.000/21.900 is 1.18. So the thrust should be 1.18 times more than it is now. So in the aircraft.cfg file I replaced the following number with this number:[jet_engine]thrust_scalar=1.0 ( I deleted this number and replaced it with 1.18)With this number replaced I think that the takeoff performance becomes more realistic. But this time I realised that the climb and cruise performance becomes unrealisticly higher than it should be http://forum.avsim.net/public/style_emot...

Hey Merdan. Just out of curiosity what were your climb and cruise performance stats that you thought were unrealistic. Can I get the numbers?Jack C

#20 mserin

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Posted 17 October 2010 - 04:34 PM

I have a pilot friend who works for an airline. He is flying 737-400 and 737-800 aircraft. I was able to get a QRH(quick reference handbook) for 737-800 for CFM56-7b26 engine from him.In the "long range cruise section control" section for 75.000 kg gross weight at 31.000 ft the N1 setting should be 87.4 at 0.778 mach and the fuel flow for each engine should be 1414 kg. If you leave the thrust scalar at 1.0 you can get this values with PMDG 737-800. But if you change the thrust scalar to 1.18 than the N1 value becomes something like 79 for the same condition.Also for the climb stage the QRH manual states that around 20.000 ft. with 70.000 kg of gross weight with maximum climb thrust set the vertical speed should be around 2100 ft./per minute for 0.76/280 climb on a standart day. If you leave the thrust scalar at 1.0 you can get this value approximately. But if you change the thrust scalar to 1.18 for the same conditions the vertical speed becomes something like 3000 ft/per minute.

#21 eparot

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Posted 17 October 2010 - 05:07 PM

As far as I could read in the aircraft.cfg of the 737-800 PMDG the static thrust is 24.200 lbs and not 21.900 lbs, so the ratio should be 1.087 instead of 1.20 (not 1.18). This value of 24.200 is corresponding to CFM56-7B24/3 that is the lowest version for the -800/-900.The CFM56-7B26/3 (26.300 lbs) is also available for the -700/-800/-900/BBJ. There's also the CFM56-7B27/3 (27.300 lbs) highest version available for the -700/-800-900/BBJ-BBJ2 and AEW&C.Most airlines that use the -800 with highest seats capacity don't choose the -7B24/3 that is a little bit underpowered. Most of the time, their choice goes to the -7B26/3. 2 x 2.100 lbs of thrust can make a huge difference during take off roll at MTOW.In the aircraft.cfg of the -800 and -900, on the same line as static_thrust=24200.0 there's also : // Adjusted to 26300.000 by EECDoes anybody know what's the exact meaning of this remark ? Regards,Emmanuel

#22 eparot

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Posted 17 October 2010 - 05:50 PM

Another interesting thread about takeoff roll with the 737 PMDG : http://forums1.avsim...700#entry723963And take a look here (.pdf 20 MB), chapter 3. Aircraft Performance (p. 182 to 209) you'll find all you want to know about takeoff roll under different conditions with all -800 engine variants. You also have the flaps setting needed that's very important too...regards,Emmanuel

#23 Spin737

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Posted 18 October 2010 - 03:10 AM

In the aircraft.cfg of the -800 and -900, on the same line as static_thrust=24200.0 there's also : // Adjusted to 26300.000 by EECDoes anybody know what's the exact meaning of this remark ? Regards,Emmanuel

Well, EEC can stand for Electronic Engine Control, if that's any help. I don't know why a 24k engine would be bumped to 26k by EEC, so I'm not sure that really helps.

#24 eparot

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Posted 18 October 2010 - 04:00 PM

Well, EEC can stand for Electronic Engine Control, if that's any help. I don't know why a 24k engine would be bumped to 26k by EEC, so I'm not sure that really helps.

Well, it could be. In fact, at high altitude all CFM56-7B engine variants have the same thrust. May be this adjustment could help to have a higher static thrust at low altitude.Emmanuel

#25 blueskyhq

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Posted 28 October 2010 - 03:57 AM

Hi everyonehere's how I fixed this performance problem. It's realy just cheating but I couldn't get of the runway at FADN. In the aircraft config file there are 2 things I changed.1. Thrust scalar is set to 1.0. I increased this to about 1.7 which gave me enough thrust to bring the performance about equal to the default 737-400.2. I also increased the parasite drag because I just couldn't bleed the speed fast enough to get it under 250 KIAS below 10000ft. It actually picked up speed even though I was decendng at only 1500 ft/min This also improved the landing performance after throttles are cut at about 30ft above the runway. Before I used to float in the air forever as the speed just wouldn't drop.Maybe this is cheating, but now at least I enjoy the aircraft.





   
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