Mike Busutil Posted October 13, 2015 Posted October 13, 2015 The supplied MiG-21 documentation has the start-up procedure beginning on page 76 (table 7.2) It states to turn ON the APU prior to engine start but does not state to turn OFF the APU anywhere in the checklist after engine start. Is it normal for the MiG-21 to continue flight operations with the APU on? Or is this an oversight in the checklist and should be turned off after the engine start procedure? If the APU is in fact supposed to be turned off after the engine start procedure then it should also be required to be turned ON for the in flight engine restart procedure. Correct? Thank you for any info. :book: [sIGPIC][/sIGPIC] Checkout my user files here: https://www.digitalcombatsimulator.com/en/files/filter/user-is-Mike Busutil/apply/
Tarres Posted October 13, 2015 Posted October 13, 2015 It's a bad traslation. It's a generator not an APU. Regards.
Mike Busutil Posted October 13, 2015 Author Posted October 13, 2015 So this is a different generator than the AC/DC generators? Looking closer to the checklist it states on page 78 in the engine start notes. "When the process is over, the APU switches OFF"... [sIGPIC][/sIGPIC] Checkout my user files here: https://www.digitalcombatsimulator.com/en/files/filter/user-is-Mike Busutil/apply/
Sokol1_br Posted October 14, 2015 Posted October 14, 2015 (edited) In English version of Mig-21 BIS manual (original) PDF linked there the switch is labeled "ENGINE STARTING UNIT". No reference to turn the switch OFF unless in emergency during engine starter. In game - QM with air starter - this switch is ON, if i turn then OFF and induce a engine stop (with suddenly nose down) the "Engine Emergency Air Start" will work only after the "APU" switch is turned ON. What indicates that is good measure leave the "APU" (or "ESU") switch always ON. :) Edited October 14, 2015 by Sokol1_br
OverStratos Posted October 14, 2015 Posted October 14, 2015 You don´t need to turn it off because the "APU" is not it. It the DC generator that doubles as engine starter. Once the engine is running, it automatically switch to generating DC.
1.JaVA_Platypus Posted October 14, 2015 Posted October 14, 2015 I thought modern jet engines are started pneumatically, not with electricity. It makes sense because some other systems are also pneumatically powered. Happy Flying! :pilotfly:
clanitho Posted October 14, 2015 Posted October 14, 2015 In English version of Mig-21 BIS manual (original) PDF linked there the switch is labeled "ENGINE STARTING UNIT". Hi, is it possible to have link to download original manual ? MSI Z97 Gaming 5 - Intel I7 4790K - Artic cooling freezer 7 pro rev 2 - GSKILL 32 Go - SSD Crucial M5 120 go - SSD Crucial 2To - HDD western digital caviar blue 1 TO - Gigabyte GTX 1070 Gaming G1 - Windows 10 home 64 bits
Sokol1_br Posted October 14, 2015 Posted October 14, 2015 http://www.avialogs.com/en/aircraft/ussr/mikoyangurevitch/mig-21/mig-21bis-pilot-s-flight-operating-instructions.html
clanitho Posted October 14, 2015 Posted October 14, 2015 http://www.avialogs.com/en/aircraft/ussr/mikoyangurevitch/mig-21/mig-21bis-pilot-s-flight-operating-instructions.html Many thank's MSI Z97 Gaming 5 - Intel I7 4790K - Artic cooling freezer 7 pro rev 2 - GSKILL 32 Go - SSD Crucial M5 120 go - SSD Crucial 2To - HDD western digital caviar blue 1 TO - Gigabyte GTX 1070 Gaming G1 - Windows 10 home 64 bits
OverStratos Posted October 15, 2015 Posted October 15, 2015 I thought modern jet engines are started pneumatically, not with electricity. It makes sense because some other systems are also pneumatically powered. It depend for ac to ac. Some are started by air pressure like the Saphir starter in the L-39 and others use a direct clutch like mechanism.
Lascaille Posted October 15, 2015 Posted October 15, 2015 A combined starter & backup-generator (which this unit is) is not uncommon for smaller engines which can be started electrically without needing a huge starter and battery. A similar starter/generator is in the huey, there is a switch on the top panel to change the function of the device from starter to standby generator.
Badger1-1 Posted October 15, 2015 Posted October 15, 2015 In many Airplanes, most of them with less then ~50 Pax the APU is NOT a Turbine, but the Battery itself. I is desgined to be able to give the Airplane its Power for a long enough time to start everything up.( for example Dash 8 ) I can imagine the Russians did the same with the Mig21. Source: My ATPL Airframes and System teacher :D
1.JaVA_Platypus Posted October 15, 2015 Posted October 15, 2015 I know that the T-33 uses ground power of 400Amps. That is a rather much. And the T-33 engine is smaller and far less advanced then the MiG-21's. The Turboprops on a DASH-8 are also very small compared to the Tumansky engine of the MiG-21. And I don't think there are huge batteries installed in the MiG and you don't need groundpower for it as well. But maybe the battery drives a pneumatic compressor? Happy Flying! :pilotfly:
Sokol1_br Posted October 15, 2015 Posted October 15, 2015 The starter is like in car engines. :) http://www.nva-forum.de/nva-board/uploads/post-22-1075369003.jpg GT~"As a permanent power source of the aircraft engine is equipped with alternator-starter GSR-ST-12000VT. The generator is used when the engine is started when the electric engine promotion. The aircraft provides a stand-alone engine start from onboard batteries." http://www.airwar.ru/enc/fighter/mig21pf.html "Properly, the GSR-ST-12000WT serves on the MiG-21 to start. On the ground he refers normally its tension from the outside (occasion cars), but it can also means the two onboard batteries perform his work. Then he becomes a DC voltage generator Air also serves the generator with battery power for starting." http://www.flugzeugforum.de/threads/23431-Frage-zu-Turbinen-Restart-im-Flug/page5
Lascaille Posted October 16, 2015 Posted October 16, 2015 I know that the T-33 uses ground power of 400Amps. That is a rather much. And the T-33 engine is smaller and far less advanced then the MiG-21's. The Turboprops on a DASH-8 are also very small compared to the Tumansky engine of the MiG-21. And I don't think there are huge batteries installed in the MiG and you don't need groundpower for it as well. But maybe the battery drives a pneumatic compressor? From a quick look the MiG-21 has 2x 15-SCS-45 batteries, each of 24v and 45Ah. If we assume the GSR-ST-12000WT starter is 12KW then at 24V you would draw 428A from the battery. Based on what you said about the T-33 needing 400A and also operating at 24V that seems reasonable. With the batteries being 45Ah each you could in theory run the starter for 12 minutes straight completely flattening the batteries in the process. If you were to try this I think either the starter, batteries or wiring would catch fire.
Art-J Posted October 16, 2015 Posted October 16, 2015 On a sidenote, the batteries on the MiG were of silver-zinc type, a bit uncommon today. They offer superior capacity-to-weight ratio and a hefty charge for startup compared to other types. On the other hand though, they get drained very quickly and don't really like low temps. i7 9700K @ stock speed, single GTX1070, 32 gigs of RAM, TH Warthog, MFG Crosswind, Win10.
1.JaVA_Platypus Posted October 16, 2015 Posted October 16, 2015 they get drained very quickly and don't really like low temps. That's why we got a battery heater on the MiG-21. ALtough, I think that one is also powered by the batteries themselves. :thumbup: Happy Flying! :pilotfly:
Cool-Hand Posted October 17, 2015 Posted October 17, 2015 (edited) In many Airplanes, most of them with less then ~50 Pax the APU is NOT a Turbine, but the Battery itself. I is desgined to be able to give the Airplane its Power for a long enough time to start everything up.( for example Dash 8 ) I can imagine the Russians did the same with the Mig21. Source: My ATPL Airframes and System teacher :D He might wanna check his sources because all the dashes Ive operated that have APUs installed ARE turbine engines to help with engine starting and electrical power\environmental while you are chilling and loading and unloading pax. You can get one engine cranked on the battery in a dash but it sure doesn't like it and get ready for some 800c+ ITT temps. ;) Edited October 17, 2015 by Cool-Hand reading comprehension, question was answered on first page lol [sIGPIC][/sIGPIC]
TheSnark Posted October 17, 2015 Posted October 17, 2015 (edited) That's why we got a battery heater on the MiG-21. ALtough, I think that one is also powered by the batteries themselves. :thumbup: I would hazard to guess that the heaters draw a relatively small current that doesn't inflict much of a penalty on the batteries. Very interesting thread so far, been learning a lot about the 21' systems. Coolhand, it seems that some of the Dash-8 series have a APU installed and it's an optional package. Some airliners actually removed them(I take it for reduced maintenance ops). Edited October 17, 2015 by TheSnark
Badger1-1 Posted October 17, 2015 Posted October 17, 2015 Yes the Dashes have an extra apu, but as you said, you CAN do it by the BAT ;) Try this in any Boeing and you lose :D
xxJohnxx Posted October 17, 2015 Posted October 17, 2015 That's why we got a battery heater on the MiG-21. ALtough, I think that one is also powered by the batteries themselves. :thumbup: Quit similar to some electric cars, where heated batteries are used. They have a high capacity, but require some of the stored engery just to keep warm. Check out my YouTube: xxJohnxx Intel i7 6800k watercooled | ASUS Rampage V Edition 10 | 32 GB RAM | Asus GTX1080 watercooled
Sokol1_br Posted October 17, 2015 Posted October 17, 2015 It's a bad traslation. It's a generator not an APU. ;) image upload with preview
Dirty Rotten Flieger Posted October 28, 2015 Posted October 28, 2015 This is interesting, now that you mention it I never even thought about why we leave the "APU" on. I wonder if the engine having 2 compressor stages makes it easier to start with less power? Maybe the starter spins up only one of the stages? I'm guessing the low pressure stage, which then spins up the high pressure. Maybe it is the other way around. Anyone know what the advantage of two stage compressor over one stage is?
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