hein22 Posted June 13, 2020 Posted June 13, 2020 So the hornet loses almost everything if no generators are online, which gives me the idea that the whole MC, DDI, INS, GPS, etc. is using AC power. But that doesn't sound right since most complex electric systems with micro chips and computers need DC power. So I'm asking here about the real hornet, how does it provide that needed DC power to these systems if the generators are only providing AC power (obviously). If it came from the essential or 28vdc bus then the batteries should make those systems work, but it doesn't. So how did they do to overcome this? I can't solve this question with NATOPS, there is limited information about what the different buses are sending current to. Thanks. Stay safe
Rainmaker Posted June 13, 2020 Posted June 13, 2020 Transformer rectifiers are used to convert AC to DC. When it comes to emergencies, it’s about ‘essential systems’ and ability to keep the jet airworthy...not so much about things that it ‘could’ power. DC also draws a lot of amps...and aircraft wiring has it’s limitations.
hein22 Posted June 13, 2020 Author Posted June 13, 2020 Transformer rectifiers are used to convert AC to DC. When it comes to emergencies, it’s about ‘essential systems’ and ability to keep the jet airworthy...not so much about things that it ‘could’ power. DC also draws a lot of amps...and aircraft wiring has it’s limitations. Hi rain! Maybe I keep messing my posts up, I wasn't talking about that at all, sorry. My question was how does the system provide the needed DC power for the system that require DC (like MC, DDI, INS, GPS, etc) if the generators are only providing AC power. Remember that these systems cannot work with AC; And the DC buses that appear on NATOPS are all powered by battery and battery won't energize any of the systems I mentioned above. Did I make it more clear now? Stay safe
Rainmaker Posted June 13, 2020 Posted June 13, 2020 Hi rain! Maybe I keep messing my posts up, I wasn't talking about that at all, sorry. My question was how does the system provide the needed DC power for the system that require DC (like MC, DDI, INS, GPS, etc) if the generators are only providing AC power. Remember that these systems cannot work with AC; And the DC buses that appear on NATOPS are all powered by battery and battery won't energize any of the systems I mentioned above. Did I make it more clear now? Still not sure I get your question. Are you just asking how DC exists on the airplane during normal operation? If so, the answer is still by the generators. AC is converted to DC by transformer rectifiers. They feed your DC buses.
hein22 Posted June 13, 2020 Author Posted June 13, 2020 (edited) Still not sure I get your question. Are you just asking how DC exists on the airplane during normal operation? If so, the answer is still by the generators. AC is converted to DC by transformer rectifiers. They feed your DC buses. No, I know how electrical systems work on airplanes. You need to understand that some systems cannot work on AC, like MC, DDI, INS, GPS, etc. So the question is not how power is converted in life but how the hornet manages to have those systems working if the generators power, of course, the AC buses. The DC buses that appear on NATOPS are all powered by battery (when GENs are off) and battery won't energize any of the systems I mentioned above (in DCS at least). Edited June 13, 2020 by hein22 Stay safe
Rainmaker Posted June 13, 2020 Posted June 13, 2020 Yeah, I’m still not on the same page with yah yet. And out of curiosity, is there a statement that says that DC buses are only powered by the battery? That’s normally not the case from the aircraft that I know of. Battery would power DC buses, but usually only under emergency circumstances, and only those buses labeled emergency/essential. Everything else would be disabled and cut out of the loop to save on power draw against the battery.
hein22 Posted June 13, 2020 Author Posted June 13, 2020 Yeah, I’m still not on the same page with yah yet. And out of curiosity, is there a statement that says that DC buses are only powered by the battery? That’s normally not the case from the aircraft that I know of. Battery would power DC buses, but usually only under emergency circumstances, and only those buses labeled emergency/essential. Everything else would be disabled and cut out of the loop to save on power draw against the battery. That's the case! NATOPS shows the DC buses powered by the U battery. But your question made me look a bit deeper and it seems that there are two DC buses that the battery doesn't power, so there lays the answer I think. Thanks Rain. Stay safe
Rainmaker Posted June 13, 2020 Posted June 13, 2020 Yes. TR units are your normal DC power provider. If they go down, batt is going to take over...but it’s only going to give you minimal essential items. Those are usually going to be listed as ‘essential’ bus items. Your other 28 VDC buses are going dead in the water. For better or worse, they are the ones that the designers said you could live without if things got that bad for ya. Some of the stuff is going to require DC and AC, and if gens are dead...well, it isn’t going to work anyway. I don’t know if the F/A-18 has an inverter or not...so there could be some AC capability there...I just dunno the answer to that.
hein22 Posted June 13, 2020 Author Posted June 13, 2020 It doesn't have inverter. But yeah, the picture in NATOPS wasn't very clear IMO. Stay safe
Rainmaker Posted June 13, 2020 Posted June 13, 2020 It doesn't have inverter. But yeah, the picture in NATOPS wasn't very clear IMO. They never usually are, you’d have to get into the maintenance manuals to really get a clear picture of what powers what. I haven’t combed through the EPs of the F-18 manual, but ones like the F-15 manual for example will give you a go/no-go list there of what you can expect to be operative vs inoperative under certain operating conditions. That can be a bit more useful than looking at the bus diagrams which tend to be very generic and not provide a lot of info for those situations.
hein22 Posted June 13, 2020 Author Posted June 13, 2020 They never usually are, you’d have to get into the maintenance manuals to really get a clear picture of what powers what. I haven’t combed through the EPs of the F-18 manual, but ones like the F-15 manual for example will give you a go/no-go list there of what you can expect to be operative vs inoperative under certain operating conditions. That can be a bit more useful than looking at the bus diagrams which tend to be very generic and not provide a lot of info for those situations. Yes, NATOPS has that as well and if very useful. But this time I did want to get more in deph. Stay safe
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