Avionics on or off during engine start?

[Guest IguanaKing]

Just wanted to ask this question, since a friend of mine is a recent "VFR PPL". Just asking of all you sim and RL pilots alike, should avionics be on or off during engine start? My friend is not sure of the sequence. Can I get our members to help him?

[AJ.eightFive]

Avionics Master off. The transient voltages generated during the start-up can damage the sensitive electronics if left on.

[Corsair7662]

Technically on a real aircraft, no. In LOMAC, their always on because the battery never runs out. But yes the avionics should be off during the engines start, but you can pop them on once done or in process(60%) of spooling. The only thing that should be on during start-up is the battery and generators.

[Guest IguanaKing]

Technically on a real aircraft, no. In LOMAC, their always on because the battery never runs out. But yes the avionics should be off during the engines start, but you can pop them on once done or in process(60%) of spooling. The only thing that should be on during start-up is the battery and generators.

 

 

Yup...you're both correct. Granted, during engine start on a jet, generators should only be switched on-line after engine start. All three are seperate power busses BTW, with their own switches and circuit breakers. AJ, that's a great description of why...sometimes the transient voltage during engine start can exceed 70 volts if the voltage regulator suddenly decides to s**t the bed. That'll fry your radios if you have them turned on during engine start.

[Prophet_169th]

IBTL :)

 

And for the Su-25T, you have to turn the avionics on first, let the HSI align, and then start the engines. At least in LOMAC.

[Guest IguanaKing]

...and that'll fry your HSI, but thanks for playing. :D

[nscode]

in LO it only matters as far as gyro spinup goes...

 

IRL - don't think... use the checklist ;)

[Corsair7662]

...and that'll fry your HSI, but thanks for playing. :D

 

Thats Russian quality/technology for ya:megalol:

[Guest IguanaKing]

Actually, this situation is more-likely in an American bird. :smilewink:

[STRIKER]

Dont know about Russian jets but for American ones you can turn on your avionics if you have a power cart hooked up. It will carry the load during start and regulate voltage untill your gen's come online to take over. Without the power cart (external power as we say) I couldnt tell ya for jets but would assume that you would be careful doing so. On helo's (which I fly on) the APU will carry the load for everything the entire time regardless of engine start or not.

[Karagiozi]

I think Prophet_169th is not far from the truth :thumbup:

 

As far as the mig29 is concerned, the AC and DC generator are activated before engine start, a surge limiter is also activated.

The HSI is also aligned before the 1st engine is started.

 

You can begin taxy on only 1 engine and start the second one later. So it would be annoying to have everything switched off in the pit!

[Guest IguanaKing]

American aircraft have voltage regulators on their generators too, but if it runs away (which they can do sometimes), then your radios get smoked if their bus is active. Having the avionics on prior to engine start can be done a thousand times without incident...its just that one time your regulator runs away that smokes your radios, so its normal practice to start the engine(s), get the generator(s) on-line, then turn on your avionics. It'll be interesting to see how these new glass pits deal with it, since the PFD and MFD usually have their power converters on the main bus. These things fail regularly if you look at them wrong, so it'll be interesting to see how they handle a 70 volt transient.

[RvETito]

It depends on the particular aircraft. If the APU provides AC/DC power than you can turn everything on, if not than you have to wait untill your engine(s) as at idle power with CSD running at nominal RPM to siwtch the generators on. Generaly speaking the engine start up is demands huge energy be it from the APU or external source. But in all cases you need to monitor the engine's gauges(RPM, EGT, oil pressure) during start up. Most gauges work on 36V or 115V AC, if you don't have external sources or APU generated AC power the usual solution are AC/DC invertrers that transfer the batteries' or external 28V DC supply into the appropriate AC voltage.

For example in the Ka-50 the EGT works on 115V AC from either main or emergency bus, the oils pressure gauge needs 36V 3-phased power supply. That's why you need to turn on the inverters during start up, they will recieve power from the batteries, external power or the STG-3 DC generator of the APU. And then, you must increase rotors' RPM above 85% in order to turn on the AC generators, which are gearbox driven. In flight you must not allow rotor RPM bellow 85% because the generators will automaticaly switch off and the system will turn on the inverters automaticaly.

[Guest IguanaKing]

Is the lower AC voltage on Eastern aircraft really 36 volts...or did you mean 26 volts? ;) In Western aircraft, BTW, the inverters are necessary to anything that needs AC, the generators don't provide that.

[Vekkinho]

As far as the mig29 is concerned, the AC and DC generator are activated before engine start, a surge limiter is also activated.

The HSI is also aligned before the 1st engine is started.

 

You can begin taxy on only 1 engine and start the second one later. So it would be annoying to have everything switched off in the pit!

 

Warn: (0%)

 

Exactly,

Fulcrums are designed to operate from unprepared unpaved and damaged airstrips, and Mikoyan's main goal in designing this particular aircraft was it's instant readiness. This pretty much explains intake covers that prevent suction of foreign objects (dirt, field animals...) MiG-29 are often tasked as Frontline fighters (GAI,CAS) and taxiing is possible with only one engine running (the other one spools as pilot taxis out). But before pilot starts his engine(s) he must allign HSI. In order to do so he must have some power and since he's got no main generator running he'll use battery power. Battery has enough power to start fuel pumps (needed for engine start). There's Emergency Power Unit in there: That's backup for electric and Hydro systems in case something goes wrong while airborne.

 

Before pilots starts his engine(s) he'll start Jet Fuel Starter. That's much smaller jet engine that's started by Hydro pressure. JSF is used to start Main Engines.

 

So 'Power up the Systems' is a priority with MiG-29A (9-12). There's not much sensitive computerish devices (Thank God) in Fulcrum of this type so you don't have to worry on frying anyting when engines kick in.

 

In fact nothing vital is controled by computers with MiG-29!!!

[Brit_Radar_Dude]

American aircraft have voltage regulators on their generators too, but if it runs away

Had a regulator go t1ts up on me on my first ever car. Coming up to a road junction and everything just died, and a bunch of steam and smoke coming from under the hood. Popped open the hood and managed to disconnect the battery pretty quickly (lucky I had some tools with me).

The regulator was just a smear of smelly melted plastic on the bulkhead, the battery was amazingly OK after a recharge.....

[Guest IguanaKing]

I had the regulator circuit in my jeep run away just due to a loose ground. Thankfully, nothing was hurt, but my voltmeter sure did go ape-s**t before I rectified the problem.

 

Just so others here know...some aircraft have the card drive and gyro power for the HSI on the main bus, others put it on the avionics bus. Its not even a question of computer this or computer that...its just all up to the aircraft manufacturer. A smart aircraft buyer just puts his money on one that has its sensitive avionics on their own bus. As I said earlier, 99% of the time, your avionics will do just fine if powered up during engine start...its just that 1% anomaly that ends up costing you thousands of dollars and hundreds of man-hours. AHARS will happily align without engine power, BTW, but is that the usual method for aligning AHARS prior to flight? Nope. The engines are running and generators are on-line.

[RvETito]

Is the lower AC voltage on Eastern aircraft really 36 volts...or did you mean 26 volts? ;) In Western aircraft, BTW, the inverters are necessary to anything that needs AC, the generators don't provide that.

 

36V 400Hz AC voltage is the russian standart. In russian aircraft the generators are the main power source. They give 208/115V 400Hz AC. Few systems use the 208V, for example in the Ka-32 the high voltage is used only for the rotor blades' antiice system and the electrically driven pump of the auxiliary hydraulic system. The 115V 400Hz AC is the line voltage of a generator's phase which supplies the main 115V bus. The 3-phased 36V AC is given by lowering transformers and this is the 36V main bus. The 28V DC for the main bus is given by rectifiers. The batteries are supplying the DC emergency bus and the inverters for the 36V and 115V, which are supplying the crucial systems and instruments. That's why when both generators go off the entire load will be taken by the accumulators and they will discharge pretty soon and to avoid this you must turn off some power consuming intruments you don't really need.

 

Anyway, generaly speaking in russian aircraft you can turn on some of the navigation intruments before having generators online but it is pointless since this will be an extra charge for either the batteries or the GPU. Engine start up is and will always be a delicate procedure and despite modern electronic technologies it must be monitored. So during start up one should pay more attention to engine and transmission gauges.

[Corsair7662]

haha I was totally about to say that Cali, this topic is over, it was answered in a short 3 replys lol. Its like nerds of the million dollar aircrafts :P.

[Guest IguanaKing]

Nah, its just something some of us do for a living. ;) The Russian stuff in the local MiG's, Aero's, and Su's hasn't broken yet so I haven't had to know their AC standards yet. Its nice to have an idea of what I should be looking for if they ever do have a problem in those areas. Thank you, Tito sir! :D That was very informative.

[leafer]

What kind of pc is used to run whatever software that's on these military aircraft? And how is it able to handle the G?

[666th_birdy]

Dont know about Russian jets but for American ones you can turn on your avionics if you have a power cart hooked up. It will carry the load during start and regulate voltage untill your gen's come online to take over.

 

Thats only true if the Ground Power Unit has a seemless power-transfer option which is not always the case. A GPU is essentialy build to be able to test avionics without the use of the generator.

 

The GPU can't regulate the generators' power so if avionics are on and the generator goes bananas, the radio will still be fried.

[nscode]

What kind of pc is used to run whatever software that's on these military aircraft? And how is it able to handle the G?

 

Something based on something nice and reliable... like 8086 :) no need for icons ;)

[Groove]

I have a cockpit video of a Dutch F-16 which is doing the complete startup procedere including engine spooling up.

[Alfa]

You guys read into this stuff WAYYYYYY to much.

 

What IK said :)

 

Tito works on Ka-32 helicopters for a living, so he has to know that much about the stuff in order to do his job ;) .

 

Cheers,

- JJ.