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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.



   
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