The engines.cfg allows us to define N2 - N1 for turbines using the N2_to_N1_table, for various Mach values. I assume this is a set at sea level.
However, the engine I’m doing has N2-N1 ratios that differ with altitude.
At sea level and Mach 0.8, 100% N2 is 95.9% N1,
But at 50.000 ft and Mach 0.8, 100% N2 should be 107% N1.
As result, N1 and thrust falls short at altitude (or, vice-versa, is overpowered at sea level).
Is there a way to set or tweak this?
Thanks.
Hello ElectronVolt714,
The n2_to_n1_table defines how corrected N1 depends on corrected N2 and inlet Mach number. This table establishes a one-to-one relationship between N1 and N2 for each inlet Mach number and, unfortunately, cannot be further adjusted using additional parameters such as altitude, air pressure, air density, etc.
Another way to link corrected N1 and corrected N2 is to not use this table. However, in that case, corrected N1 and corrected N2 will still remain uniquely coupled through a cubic equation. A Mach correction may also be applied to corrected N1 in that case, but again only as a function of inlet Mach, and not of any other parameters.
In both cases, there is a SimVar TURB_ENG_N1_LOSS that can be used to reduce corrected N1 (via RPN code), but only within a 1% range. Therefore, it is unlikely to provide significant help in this situation.
Given all of the above, at this point I can only suggest a workaround: replacing the displayed N1 (or N2) indication on the RPN side depending on altitude (pressure, density, etc.), while internally they would still remain uniquely coupled in the simulation for each inlet Mach number.
At the same time, gross thrust can also be reduced on the RPN side using the SimVar TURB_ENG_THRUST_EFFICIENCY_LOSS, which can take values from 0 to 1 depending on the conditions you define. In that case, gross thrust will be multiplied by (1 − TURB_ENG_THRUST_EFFICIENCY_LOSS).
Going forward, we will take note of the request to allow adjustment of the N1–N2 relationship based on parameters other than inlet Mach number.
Best regards,
Andrey/Asobo
Thank you @An.Petrovich
Understood. Unfortunately, we have another use in mind for the TURB_ENG_THRUST_EFFICIENCY_LOSS SimVar.
Here’s another solution that seems to be working, but it’s labour-intensive.
Using the Commanded_Ne tables I create an artificially high N2, that produces an N1 from the N2_to_N1 table that is never reached at low altitude, and then I tweak the n1_and_mach_on_thrust_table and the corrected_n2_from_ff_table to accomodate these high values. It needs higher limits (High_n2 and high_n1) too. But it seems to work.
It would require modification of the N1 or N2 readings that will go to the engine instruments.
ElectronVolt714, I’m glad you found a workaround.
By the way, we’ve released a turbojet/turbofan engine tuning Tool that may be helpful for your work:
Happy to assist if needed,
Best regards,
Andrey/Asobo
that looks pretty good @An.Petrovich
now , if this can tie in with flight_model.cfg and give us a full picture excel based expected Performance based on both the engine.cfg and the flight_model.cfg that would be awesome.
so essentially combining MSFS Turbojet static performance tool with PlanePerformance.xlsx
Thank you, will have a look. I was not aware of that.
I’ve been using the renowned https://www.gasturb.com/, which is a very good professional tool. It does allow to start from real-world parameters such as bypass ratio, mass flow, Turbine Entry Temperature etc. Afterwards, it still needs conversion to MSFS. I built my own tooling for that.
Hello @MarwanGH7929,
Yes, that would indeed be great, but I’m afraid it’s not realistically feasible.
The flight model depends on hundreds of parameters in a highly complex and interconnected way. While it might have been possible to build such an Excel-based tool for the legacy FM (FSX), for the modern FM the complexity of such a file would be overwhelming.
Instead, we plan to continue improving in-game tools that rely on the same underlying code as the FM itself, so they can assist with tuning more reliably and consistently.
This is similar to what was done for exporting turbine engine performance to a file via “Debug / Aircraft / Debug Aircraft Flight Performance” Debug Window - it was based on the same code that simulates the engine.
Best regards,
Andrey/Asobo
Thank you very much for this link!
Very interesting tool, I will take a look for sure!
Best regards,
Andrey/Asobo