Bestandskraft Posted February 27, 2016 Posted February 27, 2016 Note: A link to the .pdf version of the "MiG-21 Pilot's Operating Instructions" referenced in this thread can be found at http://forums.eagle.ru/showthread.php?t=138880. Page numbers referring to that manual refer to the hardcopy page number, not the .pdf page number. This question might only be interesting or answerable for those with in-depth knowledge of the real aircraft's fuel system, but bear with me if you will: 1) Page 76 of the manual states that when performing a lamps test with ground power connected and the Battery as well as the AC GEN ~ GND PWR switches ON, the No. 1/3 TK GP empty (1/3 ГР. ВАКОВ) lights illuminate only with the No. 1/3 TK GP Pump circuit breakers turned on. For me, this implies that neither the DC generator nor the Inverter PO-750A No. 1 exclusively power the mentioned lights; it is probable that they are powered by the battery. 2) Page 94 of the manual states that when flying with partially filled fuel tanks, one should check the amount of fuel contained in the tanks on the ground, before starting the engine, by turning on the No. 1 TK GP Pump circuit breaker for 2 - 3 minutes and making sure that the No. 1 TK GP empty caption does not illuminate. For me, this implies once again that the DC generator, which is not functional without a running engine, does not power the No. 1 TK GP empty light. 3) Page 195 of the manual states that No. 1 TK GP Pump is powered by the DC generator. It does not directly state, however, that the No. 1 TK GP empty light is also powered by that generator. 4) Bullet point 6, column 3 on page 4 of a German MiG-21U manual (http://www.mig-21-online.de/Vorschriften/Anlassen_66.pdf) states that when switching on the No. 3 TK GP Pump prior to starting the engine, with the battery on and external power connected, the No. 3 TK GP empty light will illuminate for a short time, then extinguish. From points 1) and 4) combined I deduce that contrary to the current in-game implementation, when doing a cold start and with the battery on, but with the No. 3 TK GP Pump circuit breaker turned off, the No. 3 TK GP empty light should not be illuminated, even when performing a lights test. From points 1), 2) and 3) combined one COULD deduce that doing the check as per page 94 of the manual, one is not in fact checking the functioning of the No. 1 TK GP Pump, but only of the No. 1 TK GP empty light, which would illuminate if there was insufficient fuel in the tanks. Therefore, when doing a cold start, the engine and/or the DC generator switched off, but the No. 1 TK GP Pump switched on, only the No. 1 TK GP empty light is actually capable of working, but not the No. 1 TK GP Pump itself. In this case and contrary to the current in-game implementation, when starting with fully filled tanks, the No. 1 TK GP empty light should not be illuminated unless doing a lights test as per 1). HOWEVER, what I find strange is that as per 2), one is supposed to switch on the No. 1 TK GP Pump circuit breaker for 2 – 3 minutes. If it was just about checking the light, this would surely not be necessary. Also, if the No. 3 TK GP empty light illuminates for a short time when switching the No. 3 TK GP Pump circuit breaker to on, I fail to see why the same should not be true for the No. 1 TK GP empty light and the No. 1 TK GP Pump circuit breaker. In this case, the check as per 2) would not make any sense, as the light would always come on, at least for a short time. Maybe, however, the No. 1 TK GP Pump can also be driven by DC external power, which would enable the pilot to perform the low fuel check without the DC generator operating. In this case, the fact that external DC power needs to be connected to perform the test is not mentioned on page 94. In conclusion, here is what I think should happen during a cold start: When the battery and DC ground power are switched on, both the No. 1 and No. 3 TK GP empty lights should not be illuminated. When the respective circuit breakers are switched on, the lights illuminate for a short time, then go out (except if there is insufficient fuel in the tanks, in which case the No. 1 TK GP empty light remains on; assuming the tanks are even less full, the 450 liters remaining and No. 3 TK GP empty light would probably also come/remain on). The No. 3 TK GP Pump is normally driven by the battery bus, thus it can also be driven by DC external power or the DC generator if those are available, while the No. 1 TK GP Pump can only be driven by the DC generator or DC external power, but not the battery alone. While doing a lights test, both lights come on, provided the circuit breakers are on. The only problem with this hypothesis is that it does not handle the fact that the No. 1 TK GP empty light would still illuminate for a short time in all cases when switching on the circuit breaker, which it is not supposed to do according to page 94 if enough fuel has been filled in the tank. Maybe the No. 1 pump is built differently from the No. 3 pump and the short illumination of the light does not occur, or page 94 implies that only a prolonged or constant illumination of the No. 1 TK GP empty light is a problem. It is worth nothing that according to the real-world English manual, the No. 3 pump is switched on after engine start and not prior, as stated in the German manual. If both the No. 1 and No. 3 TK GP Pump circuit breakers remain off, the green lights will remain off for the entire duration of the flight. The fact that both fuel pumps also remain off will probably lead to a flameout even prior to fuel depletion. If both the No. 1 and No. 3 TK GP Pump circuit breakers are switched on after starting the engine, as per the real manual, the green lights, other than quickly illuminating at the moment of fuel pump switch-on, will remain dark from the time of entering the cockpit until the fuel level drops to the respective values, in which case the lights illuminate. Could anyone who was able to follow my train of thought please check it for any logical flaws or incorrect assumptions regarding the real MiG-21Bis' fuel system and/or "fill in the blanks"? If my reasoning is correct, I plan to submit this as a bug report. Otherwise there are just too many unknowns to determine how the system really works, even though it is clear from the real-world manual that some aspects of the current in-game implementation are most probably unrealistic.
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