Default 737 aircraft.cfg

[tgon]

I've been trawling various forums for posts relating to a parameter in the FSX default B738 aircrafg.cfg.

 

Under [TurbineEngineData] there have been numerous posts assigning the following value (or variances):

ThrustSpecificFuelConsumption = 0.36

 

I just tried a flight with this and found it quite underwhelming in power and low fuel consumption. (The latter is great but not "real"!) Any ideas what this value should be?

 

By the way, [GeneralEngineData], fuel_flow_scalar = 0.7392197 is set.

[stinger2k2]

Hi,

 

If you haven't already, it may be better to ask in the Aircraft Design forum. You'll get more takers there.

 

Good luck

Stinger

 

Sent from my SM-G935F using Tapatalk

[mallcott]

The aircraft .cfg works in conjunction with the .air file to define flight and engine characteristics.

 

Playing with that setting on its own will make things worse, not better. Some fields in the .air file work, many dont. Some may work with the .cfg file as a modifier. Many don't.

 

Ask in the Aircraft Design forum

[PhantomTweak]

Nothing wrong with adding the TSFC line to the aircraft.cfg.

HOWEVER: once you do, you need to ensure the fuel flow GAIN, not scalar, is correct, the sea level max thrust is correct, the N2 RPM value is correct, and the inlet size is correct, and that they then all match up to the 1502-1508 table's data in the .air file. And THOSE are a whole nother can-o'-worms.

BTW: 2 notes, if I may. First, the fuel flow SCALAR is normally set to 1, and left alone in MSFS jets. The proper adjustment is to the fuel flow GAIN.

Second, setting the correct inlet area is a bit tricky. Bearing in mind these are turbofan engines, you don't want the area of the main, front, inlet of the whole engine attached to the plane, you want the inlet area to the actual jet portion of the engine. Turbofan engines essentially have a relatively small jet engine, driving the large ducted fan section. Once you get ALL the other parameters correct, including the 15XX air file tables, setting the inlet area requires a number of test flights. Set up a flight at cruise altitude, max power, 50% fuel, no passengers or cargo. Save it. If the fuel consumption is too high, INCREASE the inlet area, too low, decrease it. Fly for a specific length of time, 30 min, an hour, whatever, and check the fuel consumption. Make sure the plane has accelerated to max airspeed.

Adjust the inlet area, and reload the saved flight, test again, etc etc etc. There are also a number of add-on gauges that can give you a fuel flow reading right away, so you don't need to fly the plane for hours on end.

A note on re-running a saved flight: To ensure the plane's files are all read correctly when reloading a plane, you need to have ALL AI trafic off. No aircraft, of any sort, boats, cars, nothing. If there AI present, the aircraft in question's parameters may be read from memory instead of it's files. A quirk MSFS has.

 

The most important things, though, are setting up the .air file 15XX tables. Very complex. Look for the table numbers over on the FSDev forums. There are a ton of threads and information on what to set and how to set it for each table. After those are correct, the aircraft.cfg settings are pretty much fine tuning.

 

Good luck!

You'll need it :D

 

Pat☺

[tgon]

Wowser Pat! Thank you...I think [emoji39]

 

Interesting that you say the parameter has been added. I assume it doesn't exist in the boxed FSX or subsequent updates? [emoji848]

 

And thanks to others for responding - I'll monitor the design forum and see what I can pick up there.

[PhantomTweak]

I assume it doesn't exist in the boxed FSX or subsequent updates?

No, I didn't mean to give that impression. I just looked at my "virgin" install, that I keep for emergencies. The TSFC parameter is, indeed, included in the default 737-800. It was 0.6. I think that's a default, or example setting, out of the SDK. At least in SE, and I'm going to presume FSX Boxed as well.

 

What I was indicating was that if the TSFC parameter didn't exist, there was nothing wrong with adding it. Properly. :D

Nothing wrong with adding, or changing a parameter, so long as you do it correctly, is all. Just remember that, especially jet engines, in MSFS, the entries that control them are very complex, and vastly interdependent. Just changing one or two isn't the "thing" to do. It may seem to solve one problem, but it can change so many other parameters that great care must be taken to do things right, to achieve any degree of accuracy.

As I think you discovered. :)

Same for ANY aircraft parameter, really, although some to a lesser degree than others. Even changing the [flaps.X] parameters, like lift, for example, one small change to one signifigant flap parameter, the amount of lift they add to the plane when in their various settings, requires changing the parameter in the aircraft.cfg, AND several parameters in the .air file as well.

Once you learn the "right" things to change, and in the "right" order, you can make some very important changes to an airplane. Improving it's realism, the way it flies as opposed to the real aircraft, can be a very rewarding experience. Even one small alteration can make a big difference. But it can take a long time, especially doing the research on how-to, and performing experiments. AND some small details can trip you up. Like ensuring AI traffic is totally off before reloading a plane to test a change you've made.

 

Some developers take great pains to ensure their aircraft is as "realistic" as the sim permits, others, I hate to say, don't, taking a somewhat slap-dash approach. Maybe they have a fantastic paint ability, but the engines are pretty much "default" settings out of the SDK. Just as an example.

 

Sorry, I ramble. So you know, the FSDeveloper forum is a huge reservoir of information. Dig into it. You will be amazed at the raw data available, as well as the assistance the "natives" are willing to provide.

I wish you great good luck, if/when you embark on this path :)

Pat☺

[mallcott]

He is rambling.

 

But it's a rambling subject not for the faint of heart.

 

The .air file is a proprietary file, NOT owned by Microsoft. Between FS2004 and FSX they actually reduced the number of actual file entries in the air file that actually did anything, substituting entries in the aircraft .cfg. Unfortunately (or by design, depending on which side of the conspiracy theory you stand) taking back control of those few parameters left a lot more - still in the .air file - that are inter-dependent on the aircraft .cfg entries.

 

So we have the present position where an entry in the aircraft .cfg file, instead of being a straightforward and single-purpose amendment, actually opens a can of worms of counter-intuitive and non-contiguous alteration to the aircrafts characteristics.

 

Now you know why we ramble, and why you should NOT rely on mods in the aircraft .cfg file to have the desired result... although some do!

 

Confused much? That's why I gave up developing flight models after a mentor of mine, the late Ron Freimuth, passed. You're dealing as much with art, as science. And that's why there are only a handful of true FDE professionals on the Planet.

 

And they nearly all inhabit FSDevelopers forum.

[tgon]

Thank you again Pat. I did some SDK browsing and can appreciate the science of flight modelling dynamics. It's both intriguing and scary at the same time [emoji4] I'm a member on FS Developer and have been tempted so often...

 

Again, many thanks for your comprehensive reply (not rambling).

 

Best,

Phil

[PhantomTweak]

My pleasure, Phil.

I'll ramble on, if it can help, any time.

 

Good luck, and enjoyable flying to you!

Pat☺