GE CF6's engine crank selection

[EGKK.]

With no bleed air supplied to the manifolds, with crank selected can someone explain what is controlled closed? (valves)

what affect, if any, does this have on the cooling of the avionics ventilation?

what i'm trying to work out is will selecting crank damage anything if selected for long periods of time with no bleed air supplied, will the ventilation (blowers/fans) continue to do their jobs ventilating the avionics.

thanks.

[ampclamp]

If you select "crank" (ground?) without bleed air you will likely put elec power to a solenoid in /at the starter however without bleed air pressure the start valve wont open.This is kind of generic but what is likely the case.

Depending on the aircraft, the pack valves may close or you may need to do this manually.

Instrument / avio cooling can be aided by conditioned air but blowers are usually the primary source of cooling.

So many variables it is hard to answer with certainty.

[muduckace]

I believe you are talking about the A300/310. Crank does indeed turn off the avionics blower motors. On a hot day you could fry some electronics after extended periods, I would not worry about anything up to about 10 minutes unless extremely hot.

I believe you have confused the crowd here with your question, "controlled closed" Probably refers to configuration for engine start.

[NSEU]

what affect, if any, does this have on the cooling of the avionics ventilation?

Some aircraft types have electrical loadshedding during start under certain conditions. E.g. the 767 loadsheds all galley and utility busses when starting the first engine on the ground (with the APU generator as a single power source). If certain equip cooling fans are powered by these busses, then you may temporarily lose this cooling during start.

Looking at wiring schematics, the 767 engine start loadshedding circuit involves start relays (K10250 or K10247) and auxilliary contacts on the APB (Aux/APU Power Breaker "C905"), the APU Bleed Air Supply Control Valve relay (K23) and the engine GCBs.

In your scenario, you say there is no bleed available. Is this because APU is not running? If this is the case, then there should be no loadshedding because the APB will be open (if we are talking about 767's). If the APU is running, but APU Bleed is selected OFF (K23 de-energised), then, again, there should be no loadshedding (NB: These circuits are fairly complicated, so it's my best guess ;) )


Regards
NSEU

[EGKK.]

I think muduckase has hit the nail on the head.

My question is specific to the A300-600.

So the blowers will close (stop operating) when i select crank. I did assume this based on the cockpit sound significantly reducing when crank is selected with no bleed air (ie no APU/external bleed).

So prolonged use of crank with no bleed air will damage the avionics due to lack of ventilation. Makes sense.

So can someone just confirm what closes and what open with crank selected with no bleed pressure?

I assume the starter motor will not arm due to it being mechanically activated by bleed pressure and not an electrical signal from the starter switch (it must have both the switch in the right position and bleed pressure going to the starter motor).