Table 1505 was intended to work as a corrected fuel flow parameter that would allow the modeling of variable fuel consumption based on mach (Ram drag varies by mach, reducing fuel efficiency.)

This is what a properly modeled table for an example turbofan would have looked like:

If you take the x value and multiply it by static thrust * (total pressure ratio / sqrt total temperature ratio) you get the correct fuel flow rate at any altitude, temperature, or mach. In the image, the x value shown is 0.3030. This engine produces 25000 pounds at that CN2-->CN1 RPM. So at static sea level

25000 * 0.3030 * (delta2/sqrt(theta2)) = 7,575 pounds/hr

At Mach 1 and 36,000 feet under ISA conditions, fuel flow would be calculated in a similar manner.

But since the table is also used to affect "Spool rate vs RPM", which should be it's official name, this is what the table should look like:

The distance between each line is the time the engine will take to reach the next CN2. Perfectly horizontal lines will never reach the next line, while vertical lines will reach the next CN2 instantly. To slow the spool rate down, simply add more time (x value) between two lines.

When adding/removing time, you need to maintain the interval between lines for any segments that are already correct.

The actual x values will depend on fuel_flow_gain setting in the aircraft.cfg file and table 1501 (be sure to set both). A setting of 1.0 is equal to x=2,048 per minute. Most engines, taking 30-50 seconds from start to full throttle, will use a top value between 1200-1700 * fuel_flow_gain.

I recommend starting from engine start RPM and editing CN2 lines (Y values) from least to greatest.

X= 0 should always be at Y = Highest fuel on RPM There should be no Y lines below fuel cut on.

This renders corrected fuel flow useless, but MSFS never used corrected fuel flow anyway.

I can't be sure, but I suspect the MSFS programmers tried to make it work but realized too late that the engine spooling was coded with the CFF. I would imagine it is easier to change fuel calculations to rely on thrust than to write a whole separate spool code. Or they realized it is completely useless if table 1506 does not work properly. No one will ever know, but in any case, the corrected fuel flow has no effect on actual fuel flow drained from tanks. It should, as MSFS is using corrected fan speeds and corrected thrust....correctly. No pun intended.

For reference, the table used above is:

x=0, y=23 CN2 (Lowest ignition CN2)

x=250, y=25 CN2

x=450, y=30 CN2

x=600, y=40 CN2

x=680, y=50 CN2

x=760, y=60 CN2 (you should be around idle RPM here)

x=830, y=70 CN2

x=890, y=80 CN2

x=990, y=100 CN2

x=1100, y=120 CN2

Remember Y = CN2 that will change at the rate of X slope. x=0 is engine light up. Also, I use "fuel_flow_gain=1.000" in my cfg files and table 1501 spool rate when setting up this example.

Edit: Keep in mind that 1505 controls CN2 while we typically are measuring our spool rate by watching CN1. You should watch CN2, because CN1 spool rate is affected mathematically by table 1502, CN1 vs. CN2. That can change things and cause confusion. If CN2 is correct, but CN1 is not, the problem is with table 1502, not 1505.

This is what a properly modeled table for an example turbofan would have looked like:

If you take the x value and multiply it by static thrust * (total pressure ratio / sqrt total temperature ratio) you get the correct fuel flow rate at any altitude, temperature, or mach. In the image, the x value shown is 0.3030. This engine produces 25000 pounds at that CN2-->CN1 RPM. So at static sea level

25000 * 0.3030 * (delta2/sqrt(theta2)) = 7,575 pounds/hr

At Mach 1 and 36,000 feet under ISA conditions, fuel flow would be calculated in a similar manner.

But since the table is also used to affect "Spool rate vs RPM", which should be it's official name, this is what the table should look like:

The distance between each line is the time the engine will take to reach the next CN2. Perfectly horizontal lines will never reach the next line, while vertical lines will reach the next CN2 instantly. To slow the spool rate down, simply add more time (x value) between two lines.

When adding/removing time, you need to maintain the interval between lines for any segments that are already correct.

The actual x values will depend on fuel_flow_gain setting in the aircraft.cfg file and table 1501 (be sure to set both). A setting of 1.0 is equal to x=2,048 per minute. Most engines, taking 30-50 seconds from start to full throttle, will use a top value between 1200-1700 * fuel_flow_gain.

I recommend starting from engine start RPM and editing CN2 lines (Y values) from least to greatest.

X= 0 should always be at Y = Highest fuel on RPM There should be no Y lines below fuel cut on.

This renders corrected fuel flow useless, but MSFS never used corrected fuel flow anyway.

I can't be sure, but I suspect the MSFS programmers tried to make it work but realized too late that the engine spooling was coded with the CFF. I would imagine it is easier to change fuel calculations to rely on thrust than to write a whole separate spool code. Or they realized it is completely useless if table 1506 does not work properly. No one will ever know, but in any case, the corrected fuel flow has no effect on actual fuel flow drained from tanks. It should, as MSFS is using corrected fan speeds and corrected thrust....correctly. No pun intended.

For reference, the table used above is:

x=0, y=23 CN2 (Lowest ignition CN2)

x=250, y=25 CN2

x=450, y=30 CN2

x=600, y=40 CN2

x=680, y=50 CN2

x=760, y=60 CN2 (you should be around idle RPM here)

x=830, y=70 CN2

x=890, y=80 CN2

x=990, y=100 CN2

x=1100, y=120 CN2

Remember Y = CN2 that will change at the rate of X slope. x=0 is engine light up. Also, I use "fuel_flow_gain=1.000" in my cfg files and table 1501 spool rate when setting up this example.

Edit: Keep in mind that 1505 controls CN2 while we typically are measuring our spool rate by watching CN1. You should watch CN2, because CN1 spool rate is affected mathematically by table 1502, CN1 vs. CN2. That can change things and cause confusion. If CN2 is correct, but CN1 is not, the problem is with table 1502, not 1505.

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