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#4157008 - 08/13/15 11:23 AM Ramp Start APU Shut-Down Question  
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Davemetalhead Offline
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During a cold ramp start, when should the APU be shut down? In Chuck's superb guide he says to shut down after the engines are stabilized, but in other checklists I've seen/used, the APU is shut down much later, almost one of the last things done.

Is the APU used for anything other than engine start?


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#4157019 - 08/13/15 11:57 AM Re: Ramp Start APU Shut-Down Question [Re: Davemetalhead]  
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Once you have the main engines stabilized and the main generators running, you can turn off the APU. When spooling up your first engine, you should get a Master Caution/APU GEN annunciator light to remind you (though I prefer to start both engines before securing the APU Gen and APU).


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#4157021 - 08/13/15 12:07 PM Re: Ramp Start APU Shut-Down Question [Re: Davemetalhead]  
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Originally Posted By: Davemetalhead
During a cold ramp start, when should the APU be shut down? In Chuck's superb guide he says to shut down after the engines are stabilized, but in other checklists I've seen/used, the APU is shut down much later, almost one of the last things done.

Is the APU used for anything other than engine start?


The APU's only purpose is to help the main engines spool up to idle speed. So in theory once the engines are spooled up you don't need it anymore since the engines' power output can drive practically anything in the aircraft.

That being said, the reason why the APU is shut down later in other checklists is that it is a security measure that you have some backup power in case of a random engine malfunction during start-up checks, which in all honesty is quite unlikely in a study sim (unless the mission has random failures implemented). For the sake of simplicity, I took the liberty of putting this step in an order that is more "practical" for the user rather than play through the cockpit left and right.

#4157048 - 08/13/15 01:34 PM Re: Ramp Start APU Shut-Down Question [Re: Davemetalhead]  
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For DCS purposes as said above as soon as both engines are started you can turn it off.

Real world our pilots, during the summer especially, leave it running most of the time until just before they taxi to EOR or just before leaving EOR and back on almost as soon as they clear the active runway. This is because it puts out more bleed air than the engines at low RPMs so it keeps the AC cooler.


Last edited by Snoopy_476th; 08/13/15 01:35 PM.
#4157057 - 08/13/15 01:49 PM Re: Ramp Start APU Shut-Down Question [Re: Davemetalhead]  
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Unless the APU has a generator built into it, it's strictly providing bleed air for engine start and AC.

Some aircraft (like my KC-135) have a squat switch that once weight off wheels has occurred, the APU is automatically shut off if forgotten.

-Jeff

#4157063 - 08/13/15 01:56 PM Re: Ramp Start APU Shut-Down Question [Re: ST0RM]  
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Originally Posted By: ST0RM
Unless the APU has a generator built into it, it's strictly providing bleed air for engine start and AC.

Some aircraft (like my KC-135) have a squat switch that once weight off wheels has occurred, the APU is automatically shut off if forgotten.

-Jeff


Uhm, I'm guessing you have never flown the A-10 in DCS world because you would know it has a generator.

Actually the A-10's APU can even supply hydraulic power (only on the ground) for one system at a time. And the APU has auto shutdown features but nothing like you describe above for the 135, they're simply because something isn't operating correctly.

Last edited by Snoopy_476th; 08/13/15 01:57 PM.
#4157064 - 08/13/15 01:58 PM Re: Ramp Start APU Shut-Down Question [Re: Davemetalhead]  
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komemiute Offline
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A more modern fighter I can't name but I know well also just shuts it down automagically as soon as both engine are up and stable.

Last edited by komemiute; 08/13/15 01:58 PM.

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#4157068 - 08/13/15 02:02 PM Re: Ramp Start APU Shut-Down Question [Re: Davemetalhead]  
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The original question is strictly about the A-10's APU so I'm answering specifically about the A-10, not any other aircraft so they aren't confused.

#4157073 - 08/13/15 02:14 PM Re: Ramp Start APU Shut-Down Question [Re: Davemetalhead]  
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Uhm, I was speaking generally. No need to try and come off like a jerk. And no, I dont "fly" the A-10C.

I was simply trying to elaborate on the differences on several types of APU functions.

#4157077 - 08/13/15 02:18 PM Re: Ramp Start APU Shut-Down Question [Re: Davemetalhead]  
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komemiute Offline
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No sweat St0rm, Snoopy is cool. I guess he was actually addressing me. smile
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Last edited by komemiute; 08/13/15 02:23 PM.

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"Himmiherrgottksakramentzefixhallelujah!"
Para_Bellum

"It takes forever +/- 2 weeks for the A-10 to get anywhere significant..."
Ice

"Ha! If it gets him on the deck its a start!"
MigBuster

"What people like and what critics praise are rarely the same thing. 'Critic' is just another one of those unnecessary, overpaid, parasitic jobs that the human race has churned out so that clever slackers won't have to actually get a real job and possibly soil their hands."
Sauron
#4157091 - 08/13/15 03:00 PM Re: Ramp Start APU Shut-Down Question [Re: Davemetalhead]  
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Davemetalhead Offline
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Perfick - thanks folks.

I've pretty much got the start-up, taxi and take-off down pat, as well as shut-down. Currently practising navigation and landing - haven't even gotten around to trying any weapon usage yet. But I learn a little more every time I fly.


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#4157231 - 08/13/15 10:38 PM Re: Ramp Start APU Shut-Down Question [Re: komemiute]  
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HarryR Offline
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Originally Posted By: komemiute
A more modern fighter I can't name but I know well also just shuts it down automagically as soon as both engine are up and stable.


That is very true. Allegedly. wink


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