Re: Static from Cross-feed

Date:         13 Jan 97 18:35:32 
From: (Gary Moffitt)
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> When a plane is at a gate, I assume those yellow/orange flexible pipes
> are the ones used to supply air to the plane. But I would also assume
> that electrical power is also supplied from the ground so that the
> aircraft need not rely on its APU. Is this a correct assumption ?

Both assumptions are correct.

> So, if the airport does not supply forced air, wouldn't the aircraft at
> least use ground electrical power to run its fans and airconditioners ?

Fans, of course, run off of electicity, but the air conditioning is run
off of hot pressurized bleed air from either the apu or engines.

> Furthermore, I am somewhat puzzled at the though that the air
> conditioners under the fuel tanks would have caused the tanks to heat up
> so much.
> Where/how do air conditioning units on an aircraft dump their excess
> heat ?
> (at ground and during flight). Do they just dump in in the cargo hold ?

As mentioned previously hot bleed air runs the airconditioning. This hot
bleed air is changed to cool conditioned air through aircycle machines and
heat exchangers. The exhaust from the heat exchangers is dumped overboard
on the ground and in the air. So, no, it does not dump into the cargo
holds. The outlets for these heat exchanges are in different places on
different aircraft. On a DC-9 they are on the upper aft fuselage, on an
F-100 they are on the nose, on most other airliners they are on the belly.
On all aircraft it can be said that they are close to wherever that
particular airplains air conditioning packs are located since the heat
exchangers and their outlets are part of the airco packs. In my experiance
working on airliners, I have never heard it said that the hot air blown
out of any airconditioning system heat exchanger has ever caused a fuel
tank to heat up. Even on those aircraft where the airco packs are located
in a compartment directly under and adjacent to a fuel tank I have never
read a caution or warning about pack operation causing heating of the
fuel. So, I too, would be skeptical if someone told me pack operation
causesd significant warming of a fuel in a tank.

Gary S. Moffitt