Message from CS:
As everyone has his own opinion on how the 737 supposed to feel like in the FSX, you are welcome to share and discuss the flight dynamics tweaks in this thread. There is the user's [flight_tuning] section in the aircraft.cfg you can play with. Basically all you need is a Notepad and some imagination
Make sure to back up the original aircraft.cfg BEFORE it's broken. The original values are all =1.0.
Here we go:

Hello.. In aircraft.cfg for the -200 and -200 adv, drop the induced and parasitic drag scalars between .40-.50 .. I'm still workin on it, but now it doesn't slow in the descent and lands way more realistic and you have more realistic N1 settings.. Drop the thrust to about 17000 as well for starters because that wasn't the real issue.. Cheers..

Are you talking about the Static thrust??

These are the settings I used following fontaine32's advice:

• [flight_tuning]
  cruise_lift_scalar   = 1.0
  parasite_drag_scalar   = 0.5 /1.0
  induced_drag_scalar    = 0.5 /1.0
  elevator_effectiveness = 1.0
  aileron_effectiveness  = 1.0
  rudder_effectiveness   = 1.0
  pitch_stability        = 1.0
  roll_stability         = 1.0
  yaw_stability          = 1.0
  elevator_trim_effectiveness = 1.0
  aileron_trim_effectiveness  = 1.0
  rudder_trim_effectiveness   = 1.0

• [TurbineEngineData]
  fuel_flow_gain = 0.002                          //Gain on fuel flow
  inlet_area = 19.6                               //Square Feet, engine nacelle inlet area
  rated_N2_rpm = 29920                            //RPM, second stage compressor rated value
  static_thrust = 17000 /23000
  afterburner_available = 0                       //Afterburner available?
  reverser_available = 1                          //Thrust reverser available?
  ThrustSpecificFuelConsumption = 0.385             //Thrust specific fuel consumption (Jets)
  AfterBurnThrustSpecificFuelConsumption = 0      //TSFC with afterburn/reheat engaged[/list
  
  And it performs very well using those settings. It climbs relatively fast (but not superfast) and "it doesn't slow in the descent and lands way more realistic and you have more realistic N1 settings".
  
  Mark

The original 737-200 had a 14,500–17,400 lbf (64–77 kN) thrust rating, you can try within those parameters i guess 

Eeerrrrr.... so how come CS got this so wrong?

Ok try this. Found this link in my Office while catching up on my log book. http://www.boeing.com/commercial/startup/pdf/historical/737-200_perf.pdf

Mark,

   If we want to approach the reality we have to take into consideration gross weight, EPR (let´s forget all the rest for a while) and different flight levels for cruising purposes. It´s impossible to consider everything is FS so we have to find an acceptable average. Let´s fix 46.000 kgs as gross weight reference (737-200 maximum landing weigh is about 48.500 kgs). Using a VARIG performance data table and testing in FL´s 100, 150, 200, 250 and 290, the nearest numbers I managed to find, according to the table, were accomplished with:

static_thrust = 17000
parasite_drag_scalar   = -0.02
induced_drag_scalar    = -0.02

I think is impossible to do much better with only these 3 parameters. I didn´t check the descent speed issue with these new parameters.



Markoz wrote on Apr 23^rd, 2012 at 6:25am:

Actually i thought that Capt. Billy Bob - is a real pilot of 737, and CAF440Sq - real pilot for sure!

P.S. In my country we fixing a lot with hammer. Dirceu, arent we from same country?

Sometimes older aircrafts needs em.

Please correct to:
static_thrust = 17000
parasite_drag_scalar   = 0.68
induced_drag_scalar    = 0.68


dirceu wrote on Apr 23^rd, 2012 at 4:09pm:

Currently riding the values from Mark and, without having seen anything before 1.0, this is way better for me. She still climbs good, but I don't blow my flaps or the gear out right after takeoff. But, true, she needs quite some thrust to start taxi.

Ok, when looking at the PDCS, it says some EPR 2.18 and a speed of 261 kts for an ECON climb. I still overshoot the speed by a large margin, when I set that EPR while already climbing with 4000+ ft/min. So I guess some higher drag may be advised. That's at some 49t GW in the -200.

I will try Dirceu's values later.

CoolP wrote on Apr 24^th, 2012 at 11:18am:


Induced drag probably should not be reduced as much as parasite drag in this case.

Parasite drag is generally caused by the aircraft surface moving through the air. It could be reduced to achieve proper idle-power descent.

This lower parasite drag will naturally also reduce the amount of thrust needed for accurate cruise EPR sttings, therefore a lower static_thrust value is needed too.

IF these two modified values give us the desired descent configuration (idle thrust @ -2700 fpm) and normal cruise EPR,
but not enough power for proper climb EPR, then we reduce induced drag.

Induced drag is caused by increased angle of attack. If this value is reduced then the 737 should climb with less effort, and by default the CS732 has no shortage of climbing power. So we don't want to begin our tweaking with significantly reduced induced drag.

And lastly, approach speed/pitch attitude will also need to remain realistic. So there will need to be slight compromise in all areas for a well rounded FDE. I think keeping within .05 EPR in all phases of flight is acceptable and achievable.

So, to summerize:

Reduce parasite drag for proper descent rate with idle thrust (rate varies with altitude of course).
Reduce static thrust to compensate for the reduced parasite drag.
Reduce induced drag only as necessary to compensate for the reduced static_thrust, for accurate EPR settings whenever there's a nose-up pitch (climb, approach, etc)

Process illustrated here:
http://www.youtube.com/watch?v=3EdeuVL-nv8

Looks good. I still struggle a bit with the video link as my balloon always blew up.  More seriously, the tested values of yours look very promising. Keep up the good work.

I'm still wondering if this has something to do with the weight.. I've said it a few times, any 737 needs to just get rolling then you taxi at idle thrust.. I think the drag tweaks that I recommended are just band aid fixes for an inaccurate model.. Just throwing that out there.

I wouldn't focus on the rather high 'start taxi' values. FSX models too much friction there (e.g. helping a lot on breaking) and the only way to circumvent this one would be an engine model outside of FSX' scope, to allow a higher thrust while the gauges read close to no increase. Sort of cheating the pilot due to that too high friction level.

Since the 737 is bound to the default FSX engine model, you can't really establish that one. So we may look at it as a tradeoff of some kind. You folks are right to focus on the regimes the plane mostly operates in, that's everything on the flying.

So if Bud's values give us some nice numbers on the climb, cruise (most important) and descent, that's a big win.

sab39v, are you using realistic thrust settings / EPR to climb with only static_thrust = 15500 ?
I don't think I can hold 2000 fpm at 2.13 EPR with that static_thrust value unless I reduce drag some more. I'll try it and see.

bud7h7 wrote on May 13^th, 2012 at 6:12am:


Hi bud7h7,

no I'm not that deep into ciphering things . I do wanna use the correct thrust, because at the beginning it felt like this small 737 was powered with 2 CFM56-7B of the NG series 

That EPR stuff is something I should look into. But first I'm trying to finish up my paints. One of them being a real "pita".

As this seems to be the only fd tweak thread,

try this:

[TurbineEngineData]
fuel_flow_gain = 0.002                          //Gain on fuel flow
inlet_area = 9.6                               //Square Feet, engine nacelle inlet area
rated_N2_rpm = 29920                            //RPM, second stage compressor rated value
static_thrust = 15500
afterburner_available = 0                       //Afterburner available?
reverser_available = 1                          //Thrust reverser available?
ThrustSpecificFuelConsumption = 0.385             //Thrust specific fuel consumption (Jets)
AfterBurnThrustSpecificFuelConsumption = 0      //TSFC with afterburn/reheat engaged

An inlet area of 19.6 sq. ft.  is too much for a 737-200, 9.something seems to work much better.

Markoz wrote on May 17^th, 2012 at 3:09am:


I kept the drag as it was. By reducing the inlet area you also reduce drag.

pbrwr wrote on May 17^th, 2012 at 7:34am:

OK. I did a test with the parasite_drag_scalar=1 and induced_drag_scalar=1 (only because you had not answered at the time) and I I like it. It isn't like a rocket ship with those setting. Still powerful enough, but not too powerful. Thanks.

I like those values a lot. But they still leave us unable to descend at about 280kts/2500 fpm/ idle thrust. Without going into the air file, the only .cfg value that I've seen affect that area is parasite drag. Since the effects of parasite drag and ram drag (inlet_area) both begin at higher airspeed, it's difficult to reduce the inlet area that much and still be able to reduce parasite drag enough to descend properly.

I'm very close now using .6 parasite drag, .8 induced_drag, 15.5 inlet_area, and 15500 static_thrust.

With some minor tweaking to the air file I'm getting closer to achieving acceptable idle descent rates (260 KIAS/ 2800 fpm) as well as taxi thrust (about 40% n1 to break loose, then nearly idle to taxi).

Here's where I'm at now:

[flight_tuning]
parasite_drag_scalar   = 0.6
induced_drag_scalar    = 0.72

[TurbineEngineData]
inlet_area = 16.3
static_thrust = 15000

For testing, I used EPRs averaged between econ and full, but leaning more toward full, also watching for realistic n1:

takeoff: 2.12 EPR (flaps 5)
elevation 800 , temp 22c

climb: 2.12 EPR (280 IAS / m 0.7)
** from 10,000 to about FL250 she holds 2800 to 3000 v/s

cruise: 1.69 - 1.72 EPR (m 0.73 @ FL300)

With additional minor air file edits, idle descent is about 255 IAS @ -2800 v/s , and thrust needed to start taxi is now only 39% n1 (103.0k lbs gross weight). More to come on that.

Dietmar, I use the freeware app "aircraft airfile manager". I have not uploaded yet because I'm still working on the idle thrust descent rate. My goal is at least 270 KIAS at -2800 v/s, without affecting other areas of flight.

Has anyone tried to play with the autopilot settings so far?

My concern was the max bank angle it allowed (and used) on the larger scale turns. It was set to 30 degrees which not only gave the altitude hold feature a hard time (altitude loss and/or large hectic movements), but may also exceed what's nice for the passengers.

So reducing it to more suitable 25 degrees seems to help and does not cause much trouble for the actual turn rates needed for procedures. Always watch your speeds though, catching the ILS at 250kts will never really work with the old ship. A standard rate of turn (3°/s) will be achieved at 180kts with that 25 degree bank angle. Good speed for a 737. 

You can still manually command higher bank angles of course, it's just that the AP stops at 25°. keeping the altitude more stable and reducing the workload for himself. Passenger drinks may also like it, well, just keep it coordinated of course, which is easier at lower angles as the yaw damper works slowly.

Look for the line
[autopilot]
max_bank=30,25,20,15,10
in the aircraft.cfg.

Take away the '30' and receive
max_bank=25,20,15,10

Done.  If she's flying backwards now or always turns to the moon, you've mixed something up. Then use your backup! 

PS. The 727 and 707 also feature a 25° maximum right out of the box.

toelg wrote on May 23^rd, 2012 at 9:30am:


Best I could get was about 240 kts at a rate of 2800. BUT, after CS releases the next 1.x update I will probably rework the FDE (if needed) and this time I'll finish editing the descent speed before working out the level flight and climb drag/thrust. I made the mistake of trying to get that all done at the same time and it's impossible to edit the descent rate without messing up cruise/climb etc.