Roy Holmes
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Strange, but the full variable is A:TURB ENG JET THRUST:x,pounds, where x is the index for the specific engine. That is the only reason I can think of
Roy
Roy
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Jet Engine Performance
- Thread starter mgh
- Start date
And you were playing with the fuel flow from simconnect?
Roy Holmes
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jx_
Yes, it is thrust over pressure ratio.
Did you get my IM yet?
Roy
Yes, it is thrust over pressure ratio.
Did you get my IM yet?
Roy
Roy Holmes
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I'm not sure what you mean by "debug" in this instance. I use a pop-up flight test gauge in real time in the sim and the thrust etc is always displayed.
Roy
Roy
JB3DG
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Guess i should install AFSD then....I use Visual Studio VC++ Express. I use the debugger in it to output the values of all variables used in the gauge. RPM and all the rest work fine....only the engine thrust obstinately remains at 0. Even tried feeding it to a text display on my gauge and got 0.
JB3DG
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Just a question though, where can i get hold of the air pressure and air temperature ratios you said are used in the calculation of corrected fuel flow? So far i think setting the corrected fuel flow affects the actual fuel flow....the reason i need to know is some of my projects require controlling the actual fuel flow instead of the corrected fuel flow and the only way I can get that right is to know the air pressure and temp ratios so i can fit them in to the calculation to get the actual fuel flow that i want.
Ambient Pressure variable / Sea Level Pressure variable
same with temp
Ambient / SL
If you put those in a gauge the sim will calculate them live.
Guys,
I've got some old papers of my turbine works, so I spent some time recently doing test on 1505 table and the complete startup process.
I still need to find conclusive results , but so far I've found that:
(Turbine Engine Analysis only)
1) ThrustSpecificFuelConsumption variable is excluyent in fuel flow calcs; if it is not present, it defaults to 0.5, and if it 0, standard FF (not the corrected) is 0 at any sim situation, so the aircraft won't drain its fuel tanks ever.
2) CN1, which comes from 1502 table, is excluyent in Thrust Factor calcs; if it is 0 Gross Thrust (Net Thrust + Ram Drag) will be always 0 at any sim situation, which is pretty logical.
3) The startup process, from starter crank to combustion, is hard wired in the sim and uses no one of the tables we've been talking about except CN1/CN2 relationship in table 1502
4) When combustion starts, and up to CN2 corresponding to 0 throttle position in tables 1503/1504, Fuel Flow is a constant value and equals
Static_thrust * 0.065 * ThrustSpecificFuelConsumption * (CN1 <> 0)
I'm now trying to figure out whether 0.065 is a true constant or maybe a "hidden" (to me
) value from any table.
5) As a product of these conclusions, Fuel Flow in PPH is an erratic variable, because:
-From Starter crank to Combustion, even with all fuel valves off, shows Net Thrust * TSFC, which is obviously wrong -in real, Fuel cut = No Fuel Flow-
-From Combustion to 0 Throttle position 1502 table reference, it shows a fixed value that is extracted in a different way than the previous; in real this value also varies while the engine spools up to idle.
-From 0 Throttle Position and on (idle to max) it uses Net Thrust * TSFC, the same as in the first part of the cycle.
6) Table 1505 is looked up from combustion to max power. I am still working on it, but it seems to only affect the spool up process, there is a PID algorithm used for the calcs, being Fuel Flow Gain variable the GAIN factor. I steel need to figure out if CFF or the factor itself are used on the calculations.
7) Using Simconnect, you can reproduce the exact fuel flow equation of a real aircraft at any time, and put that in the gauges to display proper fuel values at any sim situation, and all of this independant of thrust. As jx_ stated many times -and he was correct in this case
- SFC is the key. I know you all know Fuel Flow is a read only variable, BUT, how about-Fuel Tank quantity ??
Tom
I've got some old papers of my turbine works, so I spent some time recently doing test on 1505 table and the complete startup process.
I still need to find conclusive results , but so far I've found that:
(Turbine Engine Analysis only)
1) ThrustSpecificFuelConsumption variable is excluyent in fuel flow calcs; if it is not present, it defaults to 0.5, and if it 0, standard FF (not the corrected) is 0 at any sim situation, so the aircraft won't drain its fuel tanks ever.
2) CN1, which comes from 1502 table, is excluyent in Thrust Factor calcs; if it is 0 Gross Thrust (Net Thrust + Ram Drag) will be always 0 at any sim situation, which is pretty logical.
3) The startup process, from starter crank to combustion, is hard wired in the sim and uses no one of the tables we've been talking about except CN1/CN2 relationship in table 1502
4) When combustion starts, and up to CN2 corresponding to 0 throttle position in tables 1503/1504, Fuel Flow is a constant value and equals
Static_thrust * 0.065 * ThrustSpecificFuelConsumption * (CN1 <> 0)
I'm now trying to figure out whether 0.065 is a true constant or maybe a "hidden" (to me
) value from any table.5) As a product of these conclusions, Fuel Flow in PPH is an erratic variable, because:
-From Starter crank to Combustion, even with all fuel valves off, shows Net Thrust * TSFC, which is obviously wrong -in real, Fuel cut = No Fuel Flow-
-From Combustion to 0 Throttle position 1502 table reference, it shows a fixed value that is extracted in a different way than the previous; in real this value also varies while the engine spools up to idle.
-From 0 Throttle Position and on (idle to max) it uses Net Thrust * TSFC, the same as in the first part of the cycle.
6) Table 1505 is looked up from combustion to max power. I am still working on it, but it seems to only affect the spool up process, there is a PID algorithm used for the calcs, being Fuel Flow Gain variable the GAIN factor. I steel need to figure out if CFF or the factor itself are used on the calculations.
7) Using Simconnect, you can reproduce the exact fuel flow equation of a real aircraft at any time, and put that in the gauges to display proper fuel values at any sim situation, and all of this independant of thrust. As jx_ stated many times -and he was correct in this case
- SFC is the key. I know you all know Fuel Flow is a read only variable, BUT, how about-Fuel Tank quantity ??Tom
Last edited:
Roy Holmes
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Jx_
I think it went as an email
Naruta
You can calculate air temp ratio by
theta = (288.15-1.98*altitude/1000)/288.15, obviously uses degrees kelvin. 288.15 Kelvin is 15°C, standard sea level temp
From there you can get the air pressure ratio, delta
delta = theta^5.256
Ram air pressure, delta2 is
delta2 = delta*(1+(M^2)/5)^3.5
Total air temperature, theta2 is
theta2 = theta*(1+(M^2)/5)
These equations apply up to 36089 feet altitude, above that the air temperature is constant to around 65000 ft and different equations apply to air pressure ratio.
Roy
I think it went as an email
Naruta
You can calculate air temp ratio by
theta = (288.15-1.98*altitude/1000)/288.15, obviously uses degrees kelvin. 288.15 Kelvin is 15°C, standard sea level temp
From there you can get the air pressure ratio, delta
delta = theta^5.256
Ram air pressure, delta2 is
delta2 = delta*(1+(M^2)/5)^3.5
Total air temperature, theta2 is
theta2 = theta*(1+(M^2)/5)
These equations apply up to 36089 feet altitude, above that the air temperature is constant to around 65000 ft and different equations apply to air pressure ratio.
Roy
Last edited:
Roy Holmes
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Tom,
I'm asking this because I do not understand much about simconnect.
You can obviously calculate fuel rate from fuel taken from the tanks over time, but what drives that fuel rate, the one inherent in FSX because of the TSFC/thrust relationship or the calculated fuel flow rate from simconnect?
Roy
I'm asking this because I do not understand much about simconnect.
You can obviously calculate fuel rate from fuel taken from the tanks over time, but what drives that fuel rate, the one inherent in FSX because of the TSFC/thrust relationship or the calculated fuel flow rate from simconnect?
Roy
Roy,
FSX drains the tanks using TSFC/thrust relationship, which you can't manipulate unless you varies Thrust. But if you know a proper TSFC curve, you can play with the fuel remaining in the tanks to simulate Fuel Flow in PPH acording to that curve, instead of using the static value from default FF calcs.
Tom
Roy Holmes
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Tom,
Very clever method. In a way it is like a fuel control system that bleeds excessive HP fuel flow back to the LP portion of the system. I like it, just got to get to grips with C++ and simconnect.
Thanks
Roy
Very clever method. In a way it is like a fuel control system that bleeds excessive HP fuel flow back to the LP portion of the system. I like it, just got to get to grips with C++ and simconnect.
Thanks
Roy
Roy,
The reason I asked about Fn delta, if you think of Fn Delta as what static sea level thrust would be at any altitude you can think of CN1 as what N1 would be at any pressure by isolating the temperature (and thus pressure altitude). This is probably a bad way to explain it, but basically, it gives you a flat line at all temps up to the limit, as opposed the upside down V where N1 increases with temp increase up to the temp limit. This is all for a given power setting in thrust of course.
So once you have the flat line, all you need is the ambient temperature and pressure to figure out the altitude and you can extrapolate the N1 vs thrust.
Also, the CN1 flat line runs parallel (in theory) to EPR and thrust pounds... so...
By using thrust delta and CN1 formula you get table 1506 entries.
FN Delta difference * sea level reference = what your table 1506 entry should be that would render accurate results.
So if the real airplane outputs
At mach 0.5 at 25,000 feet:
N1 75.2% --> Corrected to 25,000 feet = 75.2 / ( square root of 0.8281 which is temp ratio at 25,000 ) = 75.2 / 0.91 = CN1 82.63%
So at 25,000 feet... the sim will look up CN1 82.63% on table 1506 by mach 0.5, then output (your factor value here). The question now becomes does your value match the real aircraft? Altitude is already accounted for because of the temp ratio linkage to altitude.
Let's look at a real world example...
Real aircraft:
Thrust actual: 12,199, delta: 32,873
delta thrust / actual thrust = 32,873 / 12,199 = 2.694 Fn difference
Now M0.50 @ Sea level:
N1 75.2 --> Corrected to Sea level = CN1 75.2%
Thrust actual: 16920, delta: 16920
delta / actual = 1.00 Fn difference
so you see at Mach 0.5 you could do every altitude (which would have a different CN1) and never have same mach at different altitudes become an issue. At the same mach, CN1 will ALWAYS be different for different altitudes. Now, that brings in the question, what if the temperature changes from ISA?
Because of the reduction in thrust with higher temps and vice versa, you still get the appropriate thrust output.
Lastly, I stated:
FN Delta difference * sea level reference = what your table 1506 entry should be that would render accurate results.
What this means is the 2.694 in the 25,000 foot example is the Fn delta difference and we have to multiply that by the seal level thrust reference.
If the example engine is a 10,000 pound engine, at SSL takeoff thrust.
then the sea level 16,920 at 75.2% CN1 is entered into 1506 as
(16920 / number of engines) / SSL thrust rating (whatever is in cfg file!!!! Very important to use the cfg reference number!)
16920 / 2 engines = 8460lbs per engine / SSL rating of 10,000 per engine = 0.8460 entered into 75.2% CN1 at mach 0.5
then our 82.63% CN1 would be Sea Level 1506 entry * Fn delta difference at 82.63% CN1 = 1506 entry
Sea level 1506 reference for 75% N1 is 0.8460 * 2.694 Fn difference at 25,000 = 2.279 to enter into 1506 at 82.63% CN1 by mach 0.50
And there you have it. At sea level 75% gage N1 will produce 16,920 lbs thrust (0.846) while 75% gage N1 at 25,000 will produce 12,199 (2.279) just like the real plane.
The Mach 0.50 entry of 1506 at 75% would be 0.864, while the 82.63 entry would be 2.279.
*It should be noted all calculations should be done in static or at one airspeed! If you don't have static info, pick the airspeed that the airplane can fly at it's highest altitude and sea level in a clean configuration.
The reason this is important is you will have to go back after to make 1507 tweaks, to get the thrust lbs exact at all airspeeds, and your fuel flow will be screwed due to SFC changes in the real engine. Ignore fuel flow until you are nearing the end. Don't panic when your thrust is off either, double check that the math is right and if it is TRUST IT! Then go tweak 1507 to get the output changes at all airspeeds.
The reason I asked about Fn delta, if you think of Fn Delta as what static sea level thrust would be at any altitude you can think of CN1 as what N1 would be at any pressure by isolating the temperature (and thus pressure altitude). This is probably a bad way to explain it, but basically, it gives you a flat line at all temps up to the limit, as opposed the upside down V where N1 increases with temp increase up to the temp limit. This is all for a given power setting in thrust of course.
So once you have the flat line, all you need is the ambient temperature and pressure to figure out the altitude and you can extrapolate the N1 vs thrust.
Also, the CN1 flat line runs parallel (in theory) to EPR and thrust pounds... so...
By using thrust delta and CN1 formula you get table 1506 entries.
FN Delta difference * sea level reference = what your table 1506 entry should be that would render accurate results.
So if the real airplane outputs
At mach 0.5 at 25,000 feet:
N1 75.2% --> Corrected to 25,000 feet = 75.2 / ( square root of 0.8281 which is temp ratio at 25,000 ) = 75.2 / 0.91 = CN1 82.63%
So at 25,000 feet... the sim will look up CN1 82.63% on table 1506 by mach 0.5, then output (your factor value here). The question now becomes does your value match the real aircraft? Altitude is already accounted for because of the temp ratio linkage to altitude.
Let's look at a real world example...
Real aircraft:
Thrust actual: 12,199, delta: 32,873
delta thrust / actual thrust = 32,873 / 12,199 = 2.694 Fn difference
Now M0.50 @ Sea level:
N1 75.2 --> Corrected to Sea level = CN1 75.2%
Thrust actual: 16920, delta: 16920
delta / actual = 1.00 Fn difference
so you see at Mach 0.5 you could do every altitude (which would have a different CN1) and never have same mach at different altitudes become an issue. At the same mach, CN1 will ALWAYS be different for different altitudes. Now, that brings in the question, what if the temperature changes from ISA?
Because of the reduction in thrust with higher temps and vice versa, you still get the appropriate thrust output.
Lastly, I stated:
FN Delta difference * sea level reference = what your table 1506 entry should be that would render accurate results.
What this means is the 2.694 in the 25,000 foot example is the Fn delta difference and we have to multiply that by the seal level thrust reference.
If the example engine is a 10,000 pound engine, at SSL takeoff thrust.
then the sea level 16,920 at 75.2% CN1 is entered into 1506 as
(16920 / number of engines) / SSL thrust rating (whatever is in cfg file!!!! Very important to use the cfg reference number!)
16920 / 2 engines = 8460lbs per engine / SSL rating of 10,000 per engine = 0.8460 entered into 75.2% CN1 at mach 0.5
then our 82.63% CN1 would be Sea Level 1506 entry * Fn delta difference at 82.63% CN1 = 1506 entry
Sea level 1506 reference for 75% N1 is 0.8460 * 2.694 Fn difference at 25,000 = 2.279 to enter into 1506 at 82.63% CN1 by mach 0.50
And there you have it. At sea level 75% gage N1 will produce 16,920 lbs thrust (0.846) while 75% gage N1 at 25,000 will produce 12,199 (2.279) just like the real plane.
The Mach 0.50 entry of 1506 at 75% would be 0.864, while the 82.63 entry would be 2.279.
*It should be noted all calculations should be done in static or at one airspeed! If you don't have static info, pick the airspeed that the airplane can fly at it's highest altitude and sea level in a clean configuration.
The reason this is important is you will have to go back after to make 1507 tweaks, to get the thrust lbs exact at all airspeeds, and your fuel flow will be screwed due to SFC changes in the real engine. Ignore fuel flow until you are nearing the end. Don't panic when your thrust is off either, double check that the math is right and if it is TRUST IT! Then go tweak 1507 to get the output changes at all airspeeds.
Roy Holmes
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JX_
I need some to digest this, have read about it before. Would help if you could send me what I asked for in my email
Thanks
Roy
I need some to digest this, have read about it before. Would help if you could send me what I asked for in my email
Thanks
Roy
Tom,
Just FYI about your comment with the numbered sections. Table 1505 is mislabeled. Ignore the title. It is simply "Time to N2"
However, the 0.065 comment is accurate. But, that number varies, and the hard coded statement (not affected by tables) is incorrect.
The starter has varied for me from 16%-23% and fuel flow during start is only tied to the single engine TSFC * SSL thrust * 0.065-0.072. This is the min flow threshold I spoke of before.
I suspect, although I can not reliably reproduce, the starter is looking at CN1 and 1505 (which looks at CN2 at x=0) to determine a start point.
I also suspect it is the point where these two inquiries are true:
CN2 greater than 16%
CN1 greater than 3%
and whether the engine will actually start depends on:
1505 x = 0 CN2 is greater than starter point
I have not tested these thoroughly.
All that aside, if you guys figure out how to manipulate your fuel burn or thrust with simconnect you'll be good to go. Too bad I prefer FS9
Just FYI about your comment with the numbered sections. Table 1505 is mislabeled. Ignore the title. It is simply "Time to N2"
However, the 0.065 comment is accurate. But, that number varies, and the hard coded statement (not affected by tables) is incorrect.
The starter has varied for me from 16%-23% and fuel flow during start is only tied to the single engine TSFC * SSL thrust * 0.065-0.072. This is the min flow threshold I spoke of before.
I suspect, although I can not reliably reproduce, the starter is looking at CN1 and 1505 (which looks at CN2 at x=0) to determine a start point.
I also suspect it is the point where these two inquiries are true:
CN2 greater than 16%
CN1 greater than 3%
and whether the engine will actually start depends on:
1505 x = 0 CN2 is greater than starter point
I have not tested these thoroughly.
All that aside, if you guys figure out how to manipulate your fuel burn or thrust with simconnect you'll be good to go. Too bad I prefer FS9
Okay I will go look for the email. I don't see it yet.