Fuel Flow For Cls 747-200/300 Too Low?

[Speedbyrd 0]

The Commercial Level 747's seem very accurate (as much as you can expect in a flightsim) except for the fuel flow. According to my claculations, the aircraft could fly about 28 hours depending on conditions when it should only be good for about 15 hrs (6,600 nm). Has anyone made adjustment on their fuel flow and what figure are you suing?Thanks,

[Johan_Dees 84]

The Commercial Level 747's seem very accurate (as much as you can expect in a flightsim) except for the fuel flow. According to my claculations, the aircraft could fly about 28 hours depending on conditions when it should only be good for about 15 hrs (6,600 nm). Has anyone made adjustment on their fuel flow and what figure are you suing?Thanks,

You can change it yourself, just try it out.In the cfg change the fuel_flow_scalar= 0.9001 to a higher number, she will burn more. maybe 1.5~6 will do ?Try it out. Just let us know!.

[Speedbyrd 0]

You can change it yourself, just try it out.In the cfg change the fuel_flow_scalar= 0.9001 to a higher number, she will burn more. maybe 1.5~6 will do ?Try it out. Just let us know!.

I've started at 0.925 and will go from there. Based on the fuel load and range specs, she should burn about 23,000 lb per hr. As it is right now she's only burning about 13K with the scalar at 0.8676 which was the default mine came with.All the other scalars seem pretty good as far as thrust, etc. Don't see anything else that needs tweaking.

[Johan_Dees 84]

I've started at 0.925 and will go from there. Based on the fuel load and range specs, she should burn about 23,000 lb per hr. As it is right now she's only burning about 13K with the scalar at 0.8676 which was the default mine came with.All the other scalars seem pretty good as far as thrust, etc. Don't see anything else that needs tweaking.

yes the rest seem to be reasonably right..... Oh, just want to have to systems modeled like the RFP..

[JSACKS 0]

yes the rest seem to be reasonably right..... Oh, just want to have to systems modeled like the RFP..

Hi, Johan:Is the fuel scalar a linear factor in FS9? Just curious. I tweaked a lot of scalars years ago but frankly I've forgotten how a lot of them worked. Sadly, I hardly have time to even turn the sim on these days!Hope you doing well.Thanks and Cheers!JS

[n4gix 4,947]

Hi, Johan:Is the fuel scalar a linear factor in FS9? Just curious. I tweaked a lot of scalars years ago but frankly I've forgotten how a lot of them worked. Sadly, I hardly have time to even turn the sim on these days!

All scalars are linear, and a value of 1.0 represents 100% of the .air file's value.So, 1.25 = 125% of the value in the .air file...

[JSACKS 0]

All scalars are linear, and a value of 1.0 represents 100% of the .air file's value.So, 1.25 = 125% of the value in the .air file...

Righto and thanks. Off I go !JS

[mnmon 0]

Well, what the scalars actually do is provide a multiplicative factor to the air file tables/graphs. In the case of the fuel flow, the scalar is multiplying all the values contained within table 1505. That table/graph plots fuel flow vs N2 and is often shaped like an exponential function, i.e. low vaues for fuel flow for low N2, and then the fuel flow values increase rapidly with N2 increasing in a non-linear fashion. Each plane, however, has a different shaped curve. The scalar will just give a change in the fuel flow across all N2 values. IF you want to increase the fuelflow at cruise, but are happy with the taxi consumption, then the FFS won't really be the way to go. Mike

[WarpD 824]

The fuel_flow_scalar setting is how you would set what is called the "thrust specific fuel consumption" or TSFC. It specifies how much thrust is produced for every pound of fuel consumed. It's value is determined by the following formula: TSFC = fuel_flow_scalar/2.For a value of 0.9001 that would result in a TSFC of 0.45 and for a value of 0.8676 it would be a TSFC of 0.4338.It's important to point out... it is not, unlike other scalars... a linear value or percentage multiplier.

[JSACKS 0]

The fuel_flow_scalar setting is how you would set what is called the "thrust specific fuel consumption" or TSFC. It specifies how much thrust is produced for every pound of fuel consumed. It's value is determined by the following formula: TSFC = fuel_flow_scalar/2.For a value of 0.9001 that would result in a TSFC of 0.45 and for a value of 0.8676 it would be a TSFC of 0.4338.It's important to point out... it is not, unlike other scalars... a linear value or percentage multiplier.

_______________________________________________________________________________________________I posted this at CLS 747 forum yesterday evening:The CLS default fuel flow is relatively low in at least one of the 747-200s: in the case of the model I have tested, it is the 747-200 with PW engines rated at 54,750lb.st.t I have run tests in this aircraft with the following data and fuel flow results:Conditions: Standard Atmosphere; "Clear Weather" in FS9: no wind, no clouds, no moistureFlight Weight: Approx. 615,000 lbs (279 metric tonnes) - A VERY important variable that MUST be accurate for testing like this!Altitude: FL350 (typical cruise alt for this weight)Speed: Mach 0.85 (IAS 298) - Cruise range speed varies from .84 to .86 but .85 was very typical in this classic model so I went with that. Fuel flow can vary to a significant extent with certain flight models in FS if you change the mach speed by even a factor of 0.01.Groundspeed: 490 knotsN1: 94% (default CLS--seems like a representative rate)Outside Air Temp: -54CTotal Air Temp: -22C (perfect!)Pitch: 3 degrees nose upResultant Fuel flow: 18,000 to 18,400 lbs/hr.Default CLS fuel scalar in AIR file for this 747: 0.8418The objective is to raise the cruise flow flow to around 23,500 lbs/hr. which is much more realistic.However, the calculation to do this proved to be non-linear; I forgot, I guess, that fuel flow scalars are not in fact linear after all. I experimented with several alternate fuel flow scalars and found that the one that seems to be working closest to the objective fuel flow is 1.23. This means that if you edit you aircraft.cfg file and insert the number 1.23 in the fuel flow scalar field you will get a fuel flow of around 24,000 lbs/hr with the above flight conditions. At present I am getting almost exactly 24,000 lbs/hr at a weight of 612,000 lbs. The weight I use incidentally is based on the BOEING table in the CLS manual (page 21). "At present" means I have allowed the aircraft to stabilize for at least 5 minutes after loading or reloading a saved flight with these parameters. It takes some minutes for speed to settle down, for N1 to stabilize, and for fuel flow to stabilize accordingly.I shall keep tweaking further but in general if one is within the ball park under Standard Atmosphere conditions in the sim with an aircraft model like this, you can't hope to get absolutely precise fuel flow data even if you drive yourself totally nuts. It can be done but it can be hugely time consuming. Also, it may work textbook in cruise, but fuel flow may not necessarily be textbook (but might be close enough) for takeoff, climb, descent, and approach. Nonetheless, for trip planning purposes, the figure of 1.23 should serve very well for any kind of longer distance flights.Hope this helps.Please post questions, objections, arguments, etc. Always good to discuss this stuff on forums!Thanks for looking.Cheers,JS

[WarpD 824]

The problem is... fuel_flow_scalar only affects the value of TSFC.The rest of the formula is contained within the aircraft's .air file.Someone stated that REC 1505 set fuel flow, it actually controls engine spool up during start.REC 1506 is actually the key to ensuring an aircraft has the right fuel burn rate through all phases of flight.Every turbine engine has a TSFC number. If you know it... you set the fuel_flow_scalar appropriately. Then you adjust REC 1506 to set up the correct thrust levels and your fuel burn will be accurate.

[psolk 3,040]

The problem is... fuel_flow_scalar only affects the value of TSFC.The rest of the formula is contained within the aircraft's .air file.Someone stated that REC 1505 set fuel flow, it actually controls engine spool up during start.REC 1506 is actually the key to ensuring an aircraft has the right fuel burn rate through all phases of flight.Every turbine engine has a TSFC number. If you know it... you set the fuel_flow_scalar appropriately. Then you adjust REC 1506 to set up the correct thrust levels and your fuel burn will be accurate.

This is a fascinating thread because I am going through the same thing with the CS757. Only in addition to the fuel burn issue the CS 757 also burns from the wings first so when you increase the fuel flow you end up landing with empty wings and fuel in the center... Last night I did KEWR-EGCC on 18k lbs of fuel LOL... It should be 56k lbs! I bumped it from 0.4 to 1.4 but do not know what other adverse affects I am in for...Fascinating stuff,-Paul

[psolk 3,040]

This is a fascinating thread because I am going through the same thing with the CS757. Only in addition to the fuel burn issue the CS 757 also burns from the wings first so when you increase the fuel flow you end up landing with empty wings and fuel in the center... Last night I did KEWR-EGCC on 18k lbs of fuel LOL... It should be 56k lbs! I bumped it from 0.4 to 1.4 but do not know what other adverse affects I am in for...Fascinating stuff,-Paul

Hey guys, After reading this thread I actually found an .air file editor last night and was able to dump the entire CS757 .air file to a .txt file. I can see the appropriate tables and I can update them with the contents of the PSS .air file but is the fuel tank burn order in the .air file as well or is that in the .mdl? The reason I ask is accurately depicting fuel flow on the CS757 means you will have empty wing tanks on long hauls. I was trying to figure out how to change the center tank to burn first but can't see that anywhere in the .air file. Any help would be greatly appreciated,Thanks in advance,-Paul

[WarpD 824]

It's in the gauge code.

[psolk 3,040]

It's in the gauge code.

Thanks Ed,Time to give up ;)-Paul