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Cooling the ATR Cabin

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Cooling the ATR Cabin

Old 12th Jun 2007, 15:49
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Cooling the ATR Cabin

Ok you ATR gurus out there......here is something I'm pondering:
On ATR 42 and ATR 72 air conditioning system, the primary function of packs is is to provide conditioned air(cool) to respective compartments and the primary function of recirculation fans is to recirculate the air already in the compartments.
Suppose the aircraft is not preconditioned and passengers are on board, doors closed, engines running and HIGH FLOW selected and temp selectors close to min.......would selecting recirculation fans OFF increase cooling of cabin since there would no longer be any recirculation of warm cabin air with cool conditioned air from packs (With recirculation fans off only Conditioned(cool) air would be directed into compartments )
Your inputs greatly sought!
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Old 12th Jun 2007, 18:52
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Don't fly the ATR but the problem seems to be the same as the Dash 8. I don't think it would work, in fact it might even make things worse by reducing the overall airflow. With the air con packs working, the cold air pumped into the cabin is mixed with the hot air already in the cabin (primarily thru the recirc fans acting as mixers) and gradually cools everything. With the recircs off, the mixing process is slowed and I suspect overall cooling rate would be reduced.
Remember that as the cold air is pumped into the compts, the recirc is also recirculating that cooled air.
Hope I said that right.
P.S. We have the same cabin temp problems here - short sectors, average 30C outside, few APUs and fewer ground air con carts. It's amazing the difference with the APUs on after landing and running throughout the turnaround.
One technique used for quick cooling - but the jury's still out- is to set the cabin altitude to 4 or 5000ft and let the cabin climb at about 600/700fpm. As soon as the cabin reaches the altitude, return to automatic operation. The theory is that with the cabin climbing quickly, more air (warm air) is vented and replaced by the cooled air. Some people swear by this.
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Old 12th Jun 2007, 19:40
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Never experienced "recirc fan off" by itself as a cooling method.
Sounds to make sense though, since instead of cooling the cabin with the mix of tepid air (from recirc source) and cool air (from packs), you confine the cooling process to the coldest source (pack).
As for knowing its real contribution compared to keeping OVBD valve open until 4/5000 ft, I think it's got to be tested.
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Old 14th Jun 2007, 10:22
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IMHO. On the ground, nothing to do,only a good low pressure ground connection to solve the problem.Like Gooneyone said, the things can be worst if you turn off the rec's reducing the overhall airflow.
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Old 15th Jun 2007, 13:17
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I've always found it interesting how on many aircraft it takes a few days in the sim to handle it in abnormal conditions, but ages of real experience to milk the best out of the aircon.
Now, casting my mind back a few years, I seem to recall the following regarding the ATR:
Don't have the temp selectors at minimum. They are effectively a cabin temperature demand selector, not a supplied air temperature demand selector. In theory at least. In practice if you set them close to minimum you do get colder air, but potentially not as much of it. Try tweaking the temp selector UPWARDS and watching the supplied air temperature (I forget what thats called on the ATR. is it 'Duct temp' ?) You should sense a substantially increased flow rate before there is any significant increase in the suply air temperature.
i.e. to push it to extremes, your options are a lot of cool air or a little bit of very cold air. The former is the best bet for overall cooling.
The other thing that can happen in the ATR is that ice can form in the duct and choke off the air flow. In this case,again selecting a higher temperature is the way forwards. The ice will melt and come flying out like a little snow storm (providing a cooling sprinkling of ice particle onto the lucky recipient!). Once the duct has been melted out, start nudging the slector down again.
In summary, somewhat counter intuitively, ATR high cabin temperatures can often be attacked by turning the temperature knobs UP.
(Caveat: Haven't flown one for 7 years or so. Intervening years effects of FTLs have addled my memory completely so it everything I've written above may in fact be complete cobblers.)
pb
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Old 16th Jun 2007, 10:32
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Capt Pit Bull,

Your memory does not quit on you. Absolutely right.
The cooling problem is worst on ATR 42-300 series while on the 72's and -500 series the packs work quite well. Still need an experienced hand on the temp selectors.

Keeping the recirc fans on actually takes the warm air from under the floor out and cools it to some extent. having them off just prolonges the time it takes to cool down.

Best option is to run it in "HOTEL MODE" that is the right engine running as an APU without the prop spinning in high flow and the doors closed for 10 to 15 minutes. Or even better board as quick as possible and go flying above FL 100 it is usually fine.

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Old 18th Jun 2007, 10:45
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Originally Posted by Capt Pit Bull
Try tweaking the temp selector UPWARDS and watching the supplied air temperature (I forget what thats called on the ATR. is it 'Duct temp' ?) You should sense a substantially increased flow rate before there is any significant increase in the suply air temperature.
i.e. to push it to extremes, your options are a lot of cool air or a little bit of very cold air. The former is the best bet for overall cooling.
Capt Pit Bull

How much upwards should I "tweak" the temp selector ?
I understand the effect of that is to trigger a "subtantially increased flow rate" of very cold air. Can that be actually observed on the "duct temp" indicator?

Logic would dictates then that you would have to reset the temp selector to the "cold" position once the required effect is obtained (ie a temp drop temporarily read on the "duct temp" indicator).

Then can this process be used repeatedly within a short period of time ?

Thanks
Bleeds
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Old 18th Jun 2007, 10:57
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(At least in the Dash-8) This is what some Bombardier pilots showed me that worked as transition pilots for my company is opening up manually the forward outflow valve (On your pressurization panel)
This closes the rear outflow valves and pulls the hot cabin air into the cockpit and so out of the airplane. Also this increases the flow into the cabin from the packs. (The best way for this method of course is with the cockpit door open and this might be a problem for some operators )
By the way do not shut down your recirc fans this will only reduce the airflow.
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Old 20th Jun 2007, 00:13
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D-OCHO, what sort of SATs do you have on the ground? We operate at +30C and higher, and the cockpit is referred to as either the sauna or the microwave - the last thing we want to do is draw more hot air in during the initial flight.
As I mentioned earlier, and maybe you could try it, prior to departure select a cabin altitude of 5000ft and a rate of climb of about 600/700fpm on the pressurisation controller. The theory behind this is that the Dash 8 pressurisation system works by increasing the cabin differential pressure to almost max before allowing the cabin to climb. As such the rear outflow valve is only slightly open, and not much of the hot air is vented.
With the cabin altitude set at 5000ft, the flow out from the cabin thru the rear outflow valves is increased - therefore, more of the hot air is vented and replaced by the conditioned air.
Nothing in the AFM prohibits this operation (it's almost a manual operation as per the AFM). The only caveat is don't forget to reset the cabin altitude controller back to destination elevation once the cabin reaches the 5000ft.
It's a pity Bombardier never thought of putting cockpit side windows that could open as per the HS 748 - that would make a significant difference.
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