My rebuttal to the developer feedback on MiG-29 Thrust.
Previously the developers have answered users who discussed the wrong charts, but the chart they use is incorrect as well. I will go over each of their responses and why they do not apply here.
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Firstly, the devs respond as such:
"After the MiG-29 was added to War Thunder, we received many questions, why the static thrust of the aircraft in the game is lower than that declared by the manufacturer. There are many reasons for this, let us list the main ones.
Static thrust in full afterburner mode and no afterburner max speed are 8,300 kgf and 5,040 kgf. This thrust is given by the manufacturer for conditions of 0 m and 0 km/h, without taking into account the loss of thrust in the air intake ducts, power supply of onboard equipment and other factors that rise when the engine is mounted in the aircraft."
This is true. The uninstalled thrust of the engine is approximately 8,300kgf wet and 5,040kgf dry as mentioned on page 8.
However, they declare:
"According to the main source about the aircraft (“Аэродинамика самолёта МиГ-29”) “, the static thrust of the installed engine in the full afterburner mode (see “ПОЛНЫЙ ФОРСАЖ”) is about 8,000 kgf, and in the maximum speed mode (see “МАКСИМАЛ”) about 4,900 kgf, which are 300 kgf and 100 kgf, respectively, lower than declared. The graphs below do not reflect the influence of the MiG-29 inlet devices, which are represented by the blow-in door of the critical section of the air intake duct at the inlet, as well as the upper air intakes. In the take-off mode, the blow-in doors completely block the axial inlet of the air intake to prevent solid objects from entering it and damaging the engine, and all air supply to the engine goes through small slots in the lower part of the door, as well as through the upper inlet. The engine in this mode operates with a lack of air and is not able to gain the thrust indicated in graphs 3.16 and 3.17.”
The issue is that 8,000kgf is simply referring to thrust adjusted using a conditionally accepted standard of 0.97 x bench thrust. The first stage compressor blades are not located directly behind the cutoff, but further back and so the given installed thrust is using the “rule of thumb” 0.97 multiplier for intake losses from the pressure drop.
Chart 3.4 gives us the correct calculated air resistance, and should be calculated with the 0.97 intake losses chart. If we take 8,300kg and multiply it by 0.97 we get 8,031kgf. We know this is true because the static thrust to weight shown in my report is 1.14 on pages 12 and 179.
They show that for 13,000kg weight it has an overall T/W of 1.14. If we use the 8,031kgf figure multiplied by the traction (intake losses) coefficient 0.92 (intakes fully open) we come up with 7,388.52kgf and multiplied by 2 and divided by 13,000kg we get a T/W of approximately 1.1366 … rounded up to 1.14. This has to be the correct thrust.
The developers go on;
“At lower speeds the listed performance can not be achieved either. Due to the uneven mixing of flows from the upper and axial inlets, the air flow at the air intake is unstable, which results in the engine not having sufficient air supply. This phenomenon is described in the same source.”
This may be true, but the phenomena seems to be shown already in the incorrectly configured chart 3.17. We can roughly estimate the proper thrust losses by adjusting based on the correct multiplier from chart 3.4 (0.92x). I will adjust this chart with a new red line seen here. Blue is in-game thrust and red is the corrected thrust.
Still, the thrust is significantly more than what is found in-game.
The devs go on further;
"Furthermore, the engine is controlled and adjusted by a number of automatic systems, which may also cut thrust and engine speed.
As a result, the listed factors reduce the available thrust, affecting it most at lower speeds. The graph of the available thrust displays the full afterburner and full speed modes. Since our flight model operates the available thrust, this static available thrust is presented in the engine performance in the game."
This is true, but should not apply in the vacuum. There are reasons for this, none of which should affect the normal static thrust values. The in-game thrust is incorrect.
“The estimated available thrust also coincides with the estimates indirectly calculated from the graphs of the available longitudinal acceleration Nx (Fig. 5.3, 5.4), which, in fact, display the aircraft’s thrust-to-weight ratio minus the required thrust. The amount of available thrust is also confirmed by the graphs of maximum speeds, graphs of rate of climb, graphs of turn rates, as well as the take-off rate from the moment the brakes are released and the available acceleration at the start (paragraph 8.3.2 of the source). At the moment, the aircraft in the game shows all these characteristics quite close to the declared ones or even slightly exceeds them.”
They claim the estimated available thrust coincides with the estimates indirectly calculated from graphs of available longitudinal acceleration Nx… These are the erroneous charts shown in my report.
Graphs of maximum speeds, climb rate, turn rates, and take-off distance are all attributable to incorrect drag values, losses of the intake during takeoff due to the closed intake doors, etc. Overall, the discrepancies in the manual indicate an error in the Zhukovsky curves hence my report.
@V_S_N @iso_gate