ENG start
I've no idea, but I hope to high hell that you're sitting on a sofa with a computer in front of you when you are doing this instead of in the cockpit of a passenger jet! 
SHJ
SHJ
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Have you come across Chris Brady's excellent site about the 737 yet? I think it's worth a click. If you follow 'aircraft systems' and 'power plant' you'll find a good description of how the engines on a 737 are started.
Your assumption pilots would raise the start levers to idle according to what's usual seems to indicate a slight misconception about how a jet engine is started in practice, and might be the reason you haven't received any helpful answers yet. Since flying is very much about following procedures and checklists, every aircraft has its own engine starting procedure. However, 'flipping them as soon as N2 gets to 20%' seems to be representative of many real aircraft.
I, for my part, am happy when you sit on the sofa with a computer in front of you. That's how I became interested in flying. Well done for posting your question in the right forum, by the way.
Your assumption pilots would raise the start levers to idle according to what's usual seems to indicate a slight misconception about how a jet engine is started in practice, and might be the reason you haven't received any helpful answers yet. Since flying is very much about following procedures and checklists, every aircraft has its own engine starting procedure. However, 'flipping them as soon as N2 gets to 20%' seems to be representative of many real aircraft.
I, for my part, am happy when you sit on the sofa with a computer in front of you. That's how I became interested in flying. Well done for posting your question in the right forum, by the way.
Per Ardua ad Astraeus
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I've been flipping them as soon as N2 gets to 20%.
Which type and engine are we talking about here?
Fokker 70/100 with RR Tay: as soon as N1 rotation is indicated (the starter spins the N2 shaft, but waiting until N1 shows both provides sufficient N2 and shows the N1 shaft free to move);
DH8D with PWC150: immediately when Nh rotation is shown;
DH8C with PW123: between 10% and 20% Nh if I remember correctly (it has been a while); at high OATs and a warm engine preferably closer to the upper limit to keep ITT down.
Fokker 70/100 with RR Tay: as soon as N1 rotation is indicated (the starter spins the N2 shaft, but waiting until N1 shows both provides sufficient N2 and shows the N1 shaft free to move);
DH8D with PWC150: immediately when Nh rotation is shown;
DH8C with PW123: between 10% and 20% Nh if I remember correctly (it has been a while); at high OATs and a warm engine preferably closer to the upper limit to keep ITT down.
Last edited by Tu.114; 8th Mar 2013 at 13:59.
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An engine will have a max motor speed of usually around 20% N2, and a minimum motor speed for start of about 15%, a sick apu and during hot/high altitude this becomes important. As a general rule of thumb for the best balance for the health of the motor and starter motor, throw in the fuel over minimum motor preferably @ max motor but best at the point you see the N2 acceleration power curve start to drop off significantly. An early start is hard on the motor a late one tears up the starter. It is irritating to watch a pilot hit max motor and let it spin an additional few minutes before throwing in the fuel because they are scared of a hot or hung start.
737 NG is the same as the classic, start lever to idle at 25% N2 or max motoring. Never saw the need for max motoring though, 25% worked nice. Was rewritten about 2 years ago, before it was always at max motoring which was usually around 30% N2.
Most newer jets have an autostart function.
Start switch on and fuel cutoff switch to idle straight away. The computers handle the rest, including a hot/hung start, fuel shutoff, motoring and a second start attempt.
Start switch on and fuel cutoff switch to idle straight away. The computers handle the rest, including a hot/hung start, fuel shutoff, motoring and a second start attempt.
Most newer jets have an autostart function.
Start switch on and fuel cutoff switch to idle straight away. The computers handle the rest, including a hot/hung start, fuel shutoff, motoring and a second start attempt.
Start switch on and fuel cutoff switch to idle straight away. The computers handle the rest, including a hot/hung start, fuel shutoff, motoring and a second start attempt.
Last edited by oceancrosser; 9th Mar 2013 at 21:37.
@Lord Spandex, did i say anything different? Of course it means that, however on the NG max motoring at an N2 lower than 25% is something that never happens in my experience on APU starts, it might happen on external air starts if the airsource is particularly weak.
And i'm afraid oceancrosser has it right, neither will an EICAS or a renovated overhead panel happen.
And i'm afraid oceancrosser has it right, neither will an EICAS or a renovated overhead panel happen.
Last edited by Denti; 10th Mar 2013 at 11:48.
