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 10 High Pressure Start (Read 11364 times)
CoolP
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Re: High Pressure Start
Reply #15 - Oct 27th, 2010 at 1:34am
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Well, in my theory, the 4 after 3 makes sense. If 3 is running, the ways to supply 4 are short. Shorter than going for the 2.
"Inboards first" means "initially first" then.

I can't say anything about the C130, I don't own it.
But, as said, some aircraft require a certain sequence because of the equipment attached to certain engines only. I don't know about the C130 but there are other birds around that need their utility hydraulics stuff or brake circuits to be powered first, so the external crew can disconnect and the plane gets self-sustaining.

All APU driven ones are self-sustaining of course (if they use their APU), birds like this 707 or a Concorde are not and you don't want to have them on the ramp with all engines running for various reasons.
So you usually target for the self-sustaining aspect first and then push the thing off the ramp without the need to counteract the idle thrust of too much engines and without a too big danger for people and vehicles close to turning blades.

I could think of a Prop like the C130 being less "stable pressure" depended than the 707 and therefor the placement of the actual external air connector might no be as important as on the 707.
  
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LOU
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Re: High Pressure Start
Reply #16 - Oct 27th, 2010 at 2:19am
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Hi Mark,

I believe that the bottle (containing high pressure air) is used to start the #3 engine when a ground power/air cart was not available or not working. Then, once #3 was running, you would use the blead air from #3 to start the remaining engines. The light would come on and remain on because you discharged the bottle and ground crew would have to recharge or replace the bottle again.
Normally, you would use low pressure (ground cart) to start #3. The bottle would not come into play then.

Maybe Lou are some one else can correct me if I"m wrong, as I'm not a real pilot.

Rick


Rick is correct. The high pressure bottle was used only as a last resort at some out station where start carts were not available. With the high pressure start you could start on only the battery for ignition. In all the years I flew the 707, the only time we used the bottle was in the simulator. If anything went wrong with the start ( hot, hung, no ignition etc.) you had no way to clear the engine. With the start cart air available, you could motor the engine to clear out the hot gases or raw fuel.

Now for the start sequence. Engine start was sometimes controlled by Jetway placement, bag loading, etc. If the front (L1) door was still opened we would not start 1 or 2 because of the noise. It did not matter which engine you start first, however only engine 1,2 & 3 had turbo compressors so you would rarely start 4 first in case the cart would die. Some (very few) 707 had 4 turbo compressors. Also, you would delay start on an engine that did not have a working generator for the same reason - in case the ground power would quit - which they did often.
  

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CoolP
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Re: High Pressure Start
Reply #17 - Oct 27th, 2010 at 2:23am
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Thanks for your answer, Lou. Always interesting readings.
  
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Markoz
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Re: High Pressure Start
Reply #18 - Oct 27th, 2010 at 2:53am
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Hi Lou.

Thank you. You have cleared that up for me. A Low Pressure engine start is normal.

Mark
  

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Re: High Pressure Start
Reply #19 - Oct 27th, 2010 at 3:08pm
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Thanks for the clearup Lou Smiley
  

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