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FS2004 How to modify the fuel flow on idle ?

Messages
97
Country
italy
Hi Friends
i'm looking for a help about the follow problem. I own some aircrafts (for example the Feelthere Wilco A320) where the fuel flow at idle is extremely high compared to the official fuel burn data. The strange thing is that on all other flight phases (takeoff, climb, cruise, descent) the flow is near to the reality but, as saied, at idle (after the engine start and untill taxi) the fuel burn is too high.

Maybe some of you can tell me wich parameter in the aircraft.cfg (or somewhere else) control the fuel flow at idle ? Or how can i apply a work-around to resolve this problem ? Thank you in advance for your gentle coperation.

Alby
 
Messages
102
Haven't used fs9 in years but at least in FSX/P3D increasing idle thrust is a method to overcome the friction problem. Higher thrust means higher fuel flow and since you can't control thrust and fuel flow independently, I don't think that there's a solution.

Bernt
 

Roy Holmes

Resource contributor
Messages
1,717
Country
us-virginia
As Bernt said, fuel flow is tied to thrust in the definition of Thrust Specific Fuel Consumption TSFC which is pounds fuel burnt per pound of thrust. Typical values for a modern turbofan are in the 0.5 region. You can reduce idle thrust and that would reduce idle fuel consumption, but you would have to know whether the real aircraft taxies at idle throttle or requires some throttle to move on the ground. If it requires throttle to move, then you can set the idle RPM in air file record 1502. to give you reduced N1 RPM which is what governs thrust. However real engines have TSFC that varies with RPM but in the sim TSFC is a constant once set.
Roy
 
Messages
97
Country
italy
Hi Roy and Bernt,
thank you for your answers. I'm not very familiar with this type of editing, but i can try to modify the air file as Roy told me. Which editor must be use to modfiy the air file ? Maybe you know where i can find some utilities to do this operation ? Thank you again for your help.
 

Roy Holmes

Resource contributor
Messages
1,717
Country
us-virginia
I use Aircraft Airfile Manager V2.2 which is a free download and probably the best air file editor. There are umpteen different ways to go wrong and only one to go right when you start editing airfiles. Just be sure you have backups for anything you edit.
Roy
 
Messages
80
Country
france
In addition to Roy answer, know there is a minimum fuel consumption and very often you will get it at idle power.
Normally sim calculates fuel consumption (PPH) as TSFC*engine net thrust
However if PPH calculated this way is below a minimum value, this minimum value is always observed whatever the engine thrust is
This minimum value is
MinPPH=0.065*StaticThrust*TSFC (StaticThrust=static_thrust*thrust_scalar)
I'm afraid there nothing you can do to lower this value, except hacking the Sim1.dll or rewriting Sim memory with some available tools

Hervé
 
Messages
97
Country
italy
Thank you both for you help but i don't get any good result.
I have downloaded and installed the Aircraft Airfile Manager V2.2 as Roy told me but it crash every few clics and it's impossibile to editing something without chrashes or application errors. Thank you anyway for your help, i'll continue to load some more fuel for the idle times in my fuel calculations ;-)
Regards

Alby
 
Messages
102
That's very strange. I never had the AAM crash in all the years I'm using it. Isn't there any error message when it crashes?
 

Roy Holmes

Resource contributor
Messages
1,717
Country
us-virginia
Are you editing the air file of an airplane that is running in the sim?
Roy
 
Messages
36
Country
unitedkingdom
as stated- You will never be able to set the correct FF for idle thrust and get accurate N1 breakaway settings because of the ridiculous legacy values for rolling friction coefficients in sim1.dll. You have to set a high FN value at mach 0 for the low idle to overcome the friction, this results in a high FB. If you then try and scale this using TSFC, it will screw up your cruise burn.

I make my own sim1.dll and AI player.DLL for personal use to get around these legacy problems, this with a custom airfile for my 777 sim, sadly nobody has listened to this issue until now with FS2020. So roll on FS2020 and the SDK!
 
Messages
26
Country
belgium
Hi,

but it crash every few clics and it's impossibile to editing something without chrashes or application errors

I've had this too, got the error as in the thread below. Even though AAMv2 claims to work with FS2004, it seems it doesn't...
So I use AAMv1 or AirEd.

Regards,
DDP.
 
Messages
97
Country
italy
Thak you Dirk for your good tip !
I've downloaded AirEd and it open the air file without crashes. When i have some free time in the next days i try to play with the record 1502 as Roy told me, but is just to try something because i'm a little scared to edit such a complicated and important file. Anyway many thanks to all for your cooperation.
 
Messages
23
Country
unitedkingdom
as stated- You will never be able to set the correct FF for idle thrust and get accurate N1 breakaway settings because of the ridiculous legacy values for rolling friction coefficients in sim1.dll. You have to set a high FN value at mach 0 for the low idle to overcome the friction, this results in a high FB. If you then try and scale this using TSFC, it will screw up your cruise burn.

I make my own sim1.dll and AI player.DLL for personal use to get around these legacy problems, this with a custom airfile for my 777 sim, sadly nobody has listened to this issue until now with FS2020. So roll on FS2020 and the SDK!
What is the sim1.dll address for the TSFC hack?
 
Messages
36
Country
unitedkingdom
Sim1.dll does not contain any TSFC values to my knowledge.

What I am describing is that because the sim physics for ground friction have been screwed for years, this in turn screws your fuel burn because it's linked to thrust. TSFC scales your thrust but because of the friction issue your static thrust values have to be set high to overcome the stupid ground friction.

You can now use simconnect to fix these environmental issues, but I have always modified sim1 to suit my real world thrust values.
 
Messages
23
Country
unitedkingdom
Sim1.dll does not contain any TSFC values to my knowledge.

What I am describing is that because the sim physics for ground friction have been screwed for years, this in turn screws your fuel burn because it's linked to thrust. TSFC scales your thrust but because of the friction issue your static thrust values have to be set high to overcome the stupid ground friction.

You can now use simconnect to fix these environmental issues, but I have always modified sim1 to suit my real world thrust values.
Thanks for the reply.
 
Messages
26
Country
belgium
Hi,
I've been using parts of Pedro Oliveira's A320 FDE with the Wilco A320, which seems to get the fuel burn close enough to real values.
Just replacing the aircraft.cfg and the .air file will screw up the engine displays on the Wilco panel.

p320v12.zip

It's still high on Static/SL, but better than the Wilco FDE (see the included .pdf). I don't recall everything I changed exactly, but it seems to work OK.
IIRC playing around with the inlet_area value of the [TurbineEngineData] section helps make the numbers work...

Regards,
DDP.
 
Last edited:

jx_

Messages
555
Country
unitedstates
just a thought, you can overcome this problem with a fuel dump module such as Doug Dawson's fuel dump script. You can have it burn the correct fuel flow per gross thrust at sea level and it's set for all altitudes.

then set Thrust in FS to whatever you need to get the correct taxi and idle descent performance
 
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