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Modified Concorde.air and Fuelburn.ini-files for more accurate Fuel Flow (v1.23) [UPDATE 27-04-2017]
Konstantin Didushok posted a topic in Concorde-XHello, As some of you know, I have been working on improving the accuracy of subsonic fuel consumption in Concorde-X. Having done some measurements, I have noticed that while the supersonic fuel consumption is very accurate, the subsonic fuel consumption at M0.95 deviates by more than 1000 kg/hr/e from the real-world counterpart at most altitudes, which is quite a lot. I have therefore taken some time to address this issue by modifying the Concorde.air-file and the very important fuelburn.ini-file. Here is an overview of the changes and improvements made to the files (you can download them below): Concorde.air: - The wave drag at M0.95 has been slightly reduced to achieve a (needed) lower fuel consumption at that mach number at all altitudes. No changes have been made whatsoever to the supersonic drag (and all other mach numbers). - The thrust gain from afterburners should be around 20% at lower speeds and progressively decreasing at higher altitudes and mach numbers. In the original air-file, the thrust gain from afterburners jumps up to 40% between Mach 0.0 to Mach 0.2, and then back to less than 10% at Mach 0.32. This has led to excessive afterburner fuel consumption during takeoff acceleration (reaching peak values of over 27000 kg/hr/e, as you can see in Ramon Cutanda's tutorial videos). Having watched a few takeoff videos made in the real-world Concorde cockpit, I have always seen the fuel flow needle rather stable at 22000-23000 kg/hr/e during the takeoff run. So I unless I'm missing something, I can't imagine that the pattern was realistic. I have equalized the thrust gain from afterburners to 20% during takeoff, so now the afterburner fuel flow during takeoff no longer reaches excessive values Fuelburn.ini: - The most important part of the modification of the fuelburn.ini-file is to match the subsonic fuel consumption better with real-world values. The real-world values can be extracted from this chart that seems to have been officially used by Air France. My goal is obviously to get the figures in Concorde-X as close as possible to the values in the chart. (Note: the table with the measured values that was listed previously is no longer valid, since the fuelburn.ini-file has been updated. Check the updated information below). - I have smoothed out some jumps of the fuel flow coefficient at low speeds and altitudes, preventing an excessive fuel consumption during approaches (many times, I had over 8000 kg/hr/e during final approach, while in Concorde videos from the cockpit (including the ones with Captain David Rowland in the well-known and comprehensive ITVV DVD), I have rarely seen the needle exceeding 5000 kg/hr/e). - [UPDATE 15-04-2017]: According to the French chart that lists the specific distance for different weights and altitudes at subsonic speeds, the specific distance should increase by 0.02 NM/1000 kg for each degree Celsius ambient temperature below ISA, and decrease by 0.02 NM/1000 for each degree Celsius above ISA. This was very poorly (if at all) reflected by the original AND my previously modified fuelburn.ini-file. (I only tested the fuel flow under ISA 0, assuming that the figures for ISA+XX and ISA-XX would be fine. I was wrong!) I have spent a good chunk of time adjusting the fuel flow for different temperatures, and I think that the results are quite good considering the limitations of the table structure. An updated table with the measured fuel flows and real-world target fuel flows for different altitudes, weights and temperatures can be found below. This table can help you see the improvements over the original fuelburn.ini-file, and you can find out what figures to expect on your flight. - [UPDATE 15-04-2017]: There is a problem with the supersonic fuel consumption under some circumstances. Since the release of v1.3, Concorde-X reads the fuel flow at altitudes above FL430 (where Concorde flies supersonically) no longer from the fuel flow coefficients as with subsonic speeds, but from direct fuel flow values for given altitudes, temperatures and weights that correspond to the real-world figures (if you open the fuelburn.ini-file and scroll down, you can see those values). While this is a good idea and sounds like it provides the best possible accuracy, there are unintended consequences in some situations. For example, unlike with simple fuel flow coefficients that can be altered for 30% N1, 50% N1 and 100% N1, there is no smooth and proportionate interaction between the listed fuel flow figures and the thrust lever setting (or the N1 number): The values in the table actually take effect at a thrust setting of 100%. I have seen quite often that decreasing thrust leads to an increase (!) in fuel flow at some altitudes and weights (e.g. FL540 and 120T), because when the throttle setting is reduced, the airplane apparently starts to use the simple coefficients instead of the directly listed figures to calculate the FF, and it seems like there is a mismatch between the two. I have modified the simple coefficients for high altitudes and mach numbers in a way that avoids an increase if fuel flow when you pull back on the throttle lever under the above described circumstances. - [UPDATE 15-04-2017]: Another problem with the direct values is that the weight directly affects the fuel flow, while it should only be affected indirectly. What I mean is that, for example, if your weight is 160 T and you have your throttle all the way forward climbing through FL450 using Max Climb mode, the fuel flow will be 6412 kg/h/e (assuming ISA 0). However, if you change the weight to 120 T (e.g. by jettisoning fuel), your fuel flow at the same altitude will change directly to 5648 kg/h/e, although you have not changed the throttle setting. In the real-world, the rate of fuel burned by the engines should not directly depend on aircraft weight (the engines don't care how heavy the airplane is, their fuel thirst primarily hinges on the thrust setting, pressure altitude, ambient temperature and velocity). The established fuel flow at Mach 2 and constant altitude for each weight should be taken care of by aerodynamics (lighter weight -> lower thrust setting -> lower fuel flow, and vice versa). The direct values entered in the table seem to refer to the cruise fuel flow (where the rate of climb is very low), and they don't allow you to achieve the correct climb fuel flow at full throttle that is obviously higher than the constant-altitude cruise fuel flow (due to the issue described in the point above). In the original state, you can achieve perfectly correct amounts of fuel consumed ONLY if you take off at near MTOW and transition to the supersonic regime quickly. However, if you take off with lower weights, your total fuel consumed will be too low because of the described problem. (To avoid the problems listed in this point and the point above, I would actually suggest to the developers of Concorde-X to remove the direct FF values in the lower part of the fuelburn.ini-file and resort back to the simple FF coefficients in the future, but have the values adjusted correctly and tested - I would be willing to do that). What I did in the update is to achieve the correct, identical fuel flow figures during supersonic climb at full throttle irrespective of the aircraft weight (except when the ambient temperature is unusually cold, and the airplane climbs faster than expected). The only disadvantage of this undertaking is that you won't get most accurate fuel flows if you intend to fly M2.00 at lower altitudes than the airplane is capable of (i.e. not having the throttle levers at max.). However, if you use "MAX CLIMB" and/or "MAX CRUISE" mode in combination with full throttle, the autopilot will let Concorde climb continuously, and for this purpose, the adjustment is perfectly suitable. - [UPDATE 15-04-2017]: On many of my previous flights, I ran into instances where during the deceleration from a supersonic flight at the deceleration point, the fuel flow at a throttle setting of TLA 18° (and then >18°) was hardly lower than during M2.00 cruise (for example, coming from a fuel flow of just 4500 kg/h/e at FL580, I had 4000 kg/h/e after I pulled back the throttle lever to slow down, but the descent rate was -4000 ft/min). With the update, I have reduced the fuel flow coefficients for low N1 values, which gives you lower idle fuel consumption during deceleration from supersonic flights. - [UPDATE 15-04-2017]: I made some additional small adjustments to have more consistent fuel flows at lower altitudes over a wide range of speeds. - [SECOND UPDATE 15-04-2017]: Established file version for better reference, added file version number in the fuelburn.ini-file, corrected one little inconsistency for FL370 between ISA+30 and ISA-30. - [UPDATE 18-04-2017]: Corrected the erroneous ground idle fuel flow error from the previous modifications (was 1400 kg/h/e, now is 1100 kg/h/e, as it should be). - [UPDATE 27-04-2017]: Tightened the deviations between the Concorde-X subsonic fuel burn figures and the real numbers at FL350 for all weights. Updated the Excel-table reflecting the new figures, and the table also indicates the deviations in absolute values and percentage changes. - [UPDATE 27-04-2017]: Reduced the fuel flow at high KIAS (350+ kts) between FL100 and FL200. (It was too high in the previous state, e.g. if you flew 395 KIAS at FL200 at light weight, you consumed almost twice as much as if you flew 395 KIAS at FL250. Now you consume a little less than that). [Update 2017-04-13: Important Information for FSX SP2 users] If you use FSX SP2, you will NOT be able to take full advantage of the improved fuel flow figures during subsonic flights! The reason is that FSX Acceleration introduced table 154a in the .air-file of supersonic airplanes, which allows adjustments of the wave drag vs. Mach number at variable Mach intervals, while the old table 430 only allows to do so at fixed Mach intervals of M0.2. FSX SP2 and previous releases/simulators (including FS2004, FS2002 and FS2000) are totally unfamiliar with the new table and only rely on the old one. Because the main part of my modification of the Concorde.air-file was done on table 154a, you will not reap full benefit if you DON'T use Concorde-X with either of the following simulators: FSX Acceleration FSX Gold Edition (which is basically FSX + FSX Acceleration) FSX Steam Edition Prepar3D (any version) It is not possible to have table 430 modified in a way that reflects the improvements by table 154a due to the less precise nature of table 430. The consequence is that when you use a simulator not listed above, the wave drag at M0.95 is still too high (and with it the fuel flow), while the sound barrier at M1.00 is too weak (meaning that you break too quick through it). You can check the following source for more information: http://www.fsdeveloper.com/forum/threads/fsx-acceleration-air-file.10602/ In this regard, if you use FSX SP2, I highly recommend upgrading your simulator to one of the above versions. [General information]: Note that if you downloaded the fuelburn.ini-file before the updated information on 27-04-2017, please redownload that file. Note that no changes were made to the Concorde.air-file with the update. I hope you will like these files and be able to achieve a more accurate fuel consumption during subsonic- and supersonic flights. I may update the files in future if needed - I will certainly notify you about it. Have fun flying! (Oh, and don't forget to make a backup of the original files!). If you wonder where to copy the files, here are the directions: Concorde.air: [FSX or P3D root folder]\SimObjects\Airplanes\FSLabs_BAe-Concorde FuelBurn.ini: [FSX or P3D root folder]\FSLabs\Concorde\Fuel Here are the files (latest version of the fuelburn.ini-file is v1.23): Concorde.air FuelBurn.ini