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fass9
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what is hung start at afterburning engine

Wed May 09, 2018 6:35 am

1. hung start at afterburning engine is rpm is no increase to idle, EGT does not rise to the limit..
but according to my research, EGT increases slowly in hung start.. (with rpm hangs at sub-idle..)
I wonder why the afterburning engine does not increase to limit..
 
BravoOne
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Re: what is hung start at afterburning engine

Wed May 09, 2018 10:07 am

Where did you find this information as there is no significant difference between starts on AB engines and non AB engines? Specifically what make and model engine are you referencing?
 
mmo
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Re: what is hung start at afterburning engine

Wed May 09, 2018 12:19 pm

Have not quite figured out what you are asking. The engine will be running for it to go into A/B. There are times when the A/B will fail to light off or you get a "hard light" where there is a build up of fuel which caused a hard light as it lights up the excess fuel all at once.

If the nozzles are malfunctioning, that would cause a A/B fault as the engine is protecting itself against an over-pressure in the tailpipe.

Perhaps you could clarify what you mean?
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GalaxyFlyer
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Re: what is hung start at afterburning engine

Wed May 09, 2018 1:29 pm

AB fault in old J57s was noted by flames coming out both ends of the plane. The -21 burner on the Hun with the fancy overlapping petals on the nozzle was famous for AB lights causing compressor stalls. The T’birds had their petals washed and checked for each show and it was wonderful seeing 4 coming in and out of burner on over the top maneuvers.

GF
 
7673mech
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Re: what is hung start at afterburning engine

Wed May 09, 2018 5:49 pm

Pretty sure it's a translation problem.
A hung start in a jet engine typically will occur if there is a disruption to bleed air turning the starter. The EGT will rise slowly because at or around 24 percent fuel has been introduced but some how the engine is not getting enough air to start
 
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fr8mech
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Re: what is hung start at afterburning engine

Wed May 09, 2018 7:27 pm

[threeid][/threeid]
7673mech wrote:
Pretty sure it's a translation problem.
A hung start in a jet engine typically will occur if there is a disruption to bleed air turning the starter. The EGT will rise slowly because at or around 24 percent fuel has been introduced but some how the engine is not getting enough air to start


That is only one cause of a hung start. Others can include, but not limited to, bad fuel scheduling, bad bleed scheduling, and internal damage. We even had a pair of engines on a PW2037 equipped B757 hang because the IDG’s were incorrectly serviced. Resulted in a dual IDG change, with one shaft sheared. The oil in the other one came out purple. That also resulted in all sorts of training: videos, memos, OJT, etc.

A hung start is simply an engine that fails to accelerate to idle within the prescribed time limit.

The OP indicates that on an AB equipped engine, the EGT will stagnate along with N2. This tends not to be the case with large turbo-fans. EGT will continue to rise, though much slower than normal. A hung start can result in a hot start if allowed to continue. I’ve no idea how an AB equipped engine acts during a hung start, but I can’t imagine it’s that much different.
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fass9
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Re: what is hung start at afterburning engine

Thu May 10, 2018 2:51 am

fr8mech wrote:
[threeid][/threeid]
7673mech wrote:
Pretty sure it's a translation problem.
A hung start in a jet engine typically will occur if there is a disruption to bleed air turning the starter. The EGT will rise slowly because at or around 24 percent fuel has been introduced but some how the engine is not getting enough air to start


That is only one cause of a hung start. Others can include, but not limited to, bad fuel scheduling, bad bleed scheduling, and internal damage. We even had a pair of engines on a PW2037 equipped B757 hang because the IDG’s were incorrectly serviced. Resulted in a dual IDG change, with one shaft sheared. The oil in the other one came out purple. That also resulted in all sorts of training: videos, memos, OJT, etc.

A hung start is simply an engine that fails to accelerate to idle within the prescribed time limit.

The OP indicates that on an AB equipped engine, the EGT will stagnate along with N2. This tends not to be the case with large turbo-fans. EGT will continue to rise, though much slower than normal. A hung start can result in a hot start if allowed to continue. I’ve no idea how an AB equipped engine acts during a hung start, but I can’t imagine it’s that much different.





oh.. my question was not clear.. afterburnig engine is low bypass turbofan engine.. or J85 series..
They are used in military aircraft.. In the manual I read, it says that the egt will stabilize within the limit if a hung start occurs.
When hung start occurs, I think the reason why the exhaust gas temperature rises is because of the weak cooling air from the fan rotor. that is right??
 
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fass9
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Re: what is hung start at afterburning engine

Thu May 10, 2018 2:55 am

BravoOne wrote:
Where did you find this information as there is no significant difference between starts on AB engines and non AB engines? Specifically what make and model engine are you referencing?



that model are J85 series & F404, F110, F100 series..
 
GalaxyFlyer
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Re: what is hung start at afterburning engine

Thu May 10, 2018 3:19 am

The FADEC is probably tipping fuel to get TIT within limits. Hung starts are not specific to reheated engines, all jet engines can have starts hang. They engine just isn’t accelerating to idle, the AB has nothing to do with it. FADECs have protected the engine from overtemping

GF
 
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fass9
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Re: what is hung start at afterburning engine

Thu May 10, 2018 4:40 am

GalaxyFlyer wrote:
The FADEC is probably tipping fuel to get TIT within limits. Hung starts are not specific to reheated engines, all jet engines can have starts hang. They engine just isn’t accelerating to idle, the AB has nothing to do with it. FADECs have protected the engine from overtemping

GF



Yes.. I agree with your opinion, “hung Starts are not specific to reheated engines~”
But several manuals I read show that the EGT is stable within limits.
Did they give me inaccurate information because they were old?
In fact, the manuals were designed when their engines were designed.
I don’t know.. It’s too complicated to me..
I just wanted to think it only applies to civilian aircraft engines.
But there must be a reason why they said so..
it's hard to figure out.
Were they just lazy?
My lack of knowledge makes me sad.
 
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fass9
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Re: what is hung start at afterburning engine

Thu May 10, 2018 5:11 am

mmo wrote:
Have not quite figured out what you are asking. The engine will be running for it to go into A/B. There are times when the A/B will fail to light off or you get a "hard light" where there is a build up of fuel which caused a hard light as it lights up the excess fuel all at once.

If the nozzles are malfunctioning, that would cause a A/B fault as the engine is protecting itself against an over-pressure in the tailpipe.

Perhaps you could clarify what you mean?



I read some manuals, they were all engines with a afterburner.
It's actually a military aircraft engine.
Some of them are turbojet engines (J85’s) and turbofan engines.
Turbofan engines, of course, are low-bypass engines.
I should have written it more accurately, but it was my fault.
 
mmo
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Re: what is hung start at afterburning engine

Thu May 10, 2018 5:14 am

You are confusing a couple of things. A hung start on a A/B vs. Non A/B engine are the same. What happens, for a variety of causes, is the engine never or slowly accelerates to idle speed. In my experience, hung starts are more common on non-FADEC aircraft as the FADEC aircraft does a pretty good job of regulating fuel flow.
Hung starts are typically where the engine is slow to accelerate towards idle and what happens is the engine just hangs at a low N1/N2 and the EGT doesn't really get that high. Although over time, if you left it, the engine would overtemp. There is a time limit of 2 minutes where the engine has to get to IDLE rpm. If it doesn't you need to shut it down and investigate the problem. The hung starts I have experienced, out foo the sim, were typical "textbook" examples. Low Fuel flow on start, slow acceleration and the start seemed to stagnate at a low rpm with low FF.
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strfyr51
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Re: what is hung start at afterburning engine

Fri May 11, 2018 8:08 am

fass9 wrote:
1. hung start at afterburning engine is rpm is no increase to idle, EGT does not rise to the limit..
but according to my research, EGT increases slowly in hung start.. (with rpm hangs at sub-idle..)
I wonder why the afterburning engine does not increase to limit..

you don't start using he Afterburners. the engine is started in the non afterburner mode as a regular start it's not moved to AB until takeoff power is aplied Because a separate system supplies fuel to the afterburner.

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