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.

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

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 :(

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 :(

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

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.

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

Another interesting thread about takeoff roll with the 737 PMDG : http://forums1.avsim.net/topic/109012-take-off-calculations-require-help/page__p__723963__hl__takeoff%20%20flaps%20%20737-700#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

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.

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

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.