Takeoff weight option?

  • The beta 737 FMC seems to suggest a (landing optimised) take off weight of 43,600 kg.

    It is really light for a take off, using the 737 Technical Site's data for an undefined 737 I got a V1 of about 120 knots and a V2 of about 131 knots with a take off distance of somewhere about 3,700 feet for sea level at 15 degrees C and with a 10 knot headwind using the 737 site's comprehensive Takeoff Field Limit Graph.

    Petaluma in California's Runway 29 has a handy 3.600 feet runway and the light 737 sailed off early on full thrust, even on this exceptionally short runway.

    Would it be possible to offer a much heavier option for simulating take offs?

  • On my PC and old Aerofly 1 (F18), I used to go into the data file and mod the inertias (I think there were 2 or 3 to change from memory) to increase the aircraft weight. The AOA would sometimes get a bit messed up but it worked. It was never perfect but I have been modding aircraft weights for about 20 years on every sim I have. On aerofly 1 the files were able to be modified. Not sure about now?

    You might want to try that out. Just a thought.

    Another option is to mod the maximum thrust (lower it). But with aerofly I moded inertias directly. By doing a de-rated takeoff you can simulate a heavier weight as well (as a rough approximation).

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    Edited once, last by HKATER (May 7, 2023 at 1:16 AM).

  • Thanks HKATER, I’d been trying a suck it and see reduced thrust for a while, it is hard to know what Aerofly -500 features are effective and which are a still welcome, visual changes of state only. Adjusting the sim performance files might leave the big picture out of balance, the FMC data would or might also need modification.

    From other sims I’d guess that a -500 N1 of about 84% or less might correspond to a -2 26K to 22K reduced thrust state on a full function FMC as we can hopefully expect in the coming Aerofly NG 737-800. I tried this with about 93-94% for coolish full thrust takeoff. Some data from a digital -500 or even a -600 sim would help. I have old PMDG fs2004 disks which might be useful.

    The Takeoff Field Length Limit graph seems to work reasonably well with the Aerofly -500 and this presumed weight at full thrust. I’ll try it with perhaps -5% and -10% takeoff distances for fine tuning and see how it goes. I use Oakland 27/28 Left for a 6,200 ft runway for reduced thrust, 27/28 Right is a bit shorter at 5,500 ft.

    I like using a chosen length runway to get the visual feedback. Perhaps a V1 abort without going off the end will work too?

    I fiddled PC AF1 files to get the JustFlight Beech Duchess ‘seat height’ right.

    • Official Post

    You can backup the original b737.tmd file and then modify the text file and increase the mass of the rigidbodies. That increases the mass and inertia and the takeoff distances automatically get longer.

    I recommend not using 100% throttle input because you then produce more than the rated thrust on that engine. Move the throttle levers up to about 95% or so to set a takeoff EPR value of 1.5 (yellow bug). Then the engine produces the correct rated takeoff thrust. This way the N1 is also not in the yellow or red line area. If you arm the auto throttle, set on the FDs for takeoff and then push the TOGA buttons it will automatically set this thrust for you.

    Once we implement load and fuel masses you can obviously play around with this much easier and set a more realistic fully loaded mass for takeoff.

    Regards,

    Jan

  • You can backup the original b737.tmd file and then modify the text file and increase the mass of the rigidbodies. That increases the mass and inertia and the takeoff distances automatically get longer.

    I recommend not using 100% throttle input because you then produce more than the rated thrust on that engine. Move the throttle levers up to about 95% or so to set a takeoff EPR value of 1.5 (yellow bug). Then the engine produces the correct rated takeoff thrust. This way the N1 is also not in the yellow or red line area. If you arm the auto throttle, set on the FDs for takeoff and then push the TOGA buttons it will automatically set this thrust for you.

    Once we implement load and fuel masses you can obviously play around with this much easier and set a more realistic fully loaded mass for takeoff.

    Will we be seeing fuel any time within the next 8-9 months or in the far future?