A fun Humpday question!
Thread Starter
A fun Humpday question!
Hey guys, and gals!
I'm just now in the middle of studying for the good'ol ATPL systems (fun right?)
I have a question for anyone in the know. In regard to subsonic flow through a convergent duct velocity increases, pressure decreases, but density? AFT's notes which I'm studying from say that density is constant with subsonic flow. A friend is studying Secombe's notes, and he reckons density decreases along with pressure. So WTF?
I realise someone will probably say call'em and ask. However, i figure they will both probably say "my notes are right."
I WANT THE TRUTH!!!! (In my best Tom Cruise from A Few Good Men)
Cheers,
Greaser
I'm just now in the middle of studying for the good'ol ATPL systems (fun right?)
I have a question for anyone in the know. In regard to subsonic flow through a convergent duct velocity increases, pressure decreases, but density? AFT's notes which I'm studying from say that density is constant with subsonic flow. A friend is studying Secombe's notes, and he reckons density decreases along with pressure. So WTF?
I realise someone will probably say call'em and ask. However, i figure they will both probably say "my notes are right."
I WANT THE TRUTH!!!! (In my best Tom Cruise from A Few Good Men)
Cheers,
Greaser
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"You can't handle the truth!!" .... sorry couldn't resist.
Subsonic flow is incompressible so velocity increases, pressure decreases and density remains constant.... so your notes are right.
knox
Subsonic flow is incompressible so velocity increases, pressure decreases and density remains constant.... so your notes are right.
knox
Subsonic flow is, if I recall correctly, actually compressible in a very small degree, however for all intents and purposes (and for the purposes of this exam) subsonic flow is assumed to be incompressible i.e. no density changes.
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and with supersonic flow through a convergent duct everything is reversed. I've just recently done the AFT Aerody and Systems course at maroochy and passed the exam. If you have any questions PM me while i can still remember.
300
300
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the REAL question should be .... " WHO THE FU&K CARES?" or maybe more precisely..." WHAT THE F*CK, can we, as pilots, do about it?"
in either case, the answer is ZERO!!!!!
as a pilot, there is NOTHING that you can do about it. there is NOTHING that you can change about it, and there are ZERO indications to you about it! IF you think about it too long, you will disrupt your mandated crew rest, and hence be unfit for returning to duty, making yourself a liability in the cockpit, as opposed to an asset.
IF you try to pick the other pilots brain about this matter, you will annoy the F**K out of him, and will become a LIABILTY on the flight deck, as opposed to an asset.ie F$CKWIT!!!!!... and be up for the cost of 10 beers each.
I suggest that you learn the correct answer to this question without trying to understand it....pass the required exams.... get yourself an airline job... and forget that this stupid question ever existed to start with. You will NEVER EVER EVER be asked this question again except in an interview with some insecure airline nazi who thinks it is his job to exploit the fact that you have a life outside of aviation theory... which he obviously doesnt!!!!
in either case, the answer is ZERO!!!!!
as a pilot, there is NOTHING that you can do about it. there is NOTHING that you can change about it, and there are ZERO indications to you about it! IF you think about it too long, you will disrupt your mandated crew rest, and hence be unfit for returning to duty, making yourself a liability in the cockpit, as opposed to an asset.
IF you try to pick the other pilots brain about this matter, you will annoy the F**K out of him, and will become a LIABILTY on the flight deck, as opposed to an asset.ie F$CKWIT!!!!!... and be up for the cost of 10 beers each.
I suggest that you learn the correct answer to this question without trying to understand it....pass the required exams.... get yourself an airline job... and forget that this stupid question ever existed to start with. You will NEVER EVER EVER be asked this question again except in an interview with some insecure airline nazi who thinks it is his job to exploit the fact that you have a life outside of aviation theory... which he obviously doesnt!!!!
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the REAL question should be .... " WHO THE FU&K CARES?" or maybe more precisely..." WHAT THE F*CK, can we, as pilots, do about it?"
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" WHAT THE F*CK, can we, as pilots, do about it?"
To me, what you're saying is "I'm a pilot but I don't know or care much about fluid mechanics... or how any of my equipment works for that matter"...
Come on guys.
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quote "To me, what you're saying is "I'm a pilot but I don't know or care much about fluid mechanics... or how any of my equipment works for that matter"...
well i must admit i am a bit like that.
I know wings create lift, but what good is all the theory behind it while i am flying?
the formula's etc.
i just know that if i keep pulling that stick back the plane is going to stall.
I got a good basic understanding about it all but thats al i really care about.
cheers
well i must admit i am a bit like that.
I know wings create lift, but what good is all the theory behind it while i am flying?
the formula's etc.
i just know that if i keep pulling that stick back the plane is going to stall.
I got a good basic understanding about it all but thats al i really care about.
cheers
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Fair enough, but what I'm getting at is that it is important to have a good understanding of how things work... so that when things stop working, you might be able to come up with a possible solution to the problem... That's what makes a good pilot, right?
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Nick, i agree with you there.
what i meant is that i am not into the nitty gritty like some people can be.
I do think it is importand to know the systems in your plane. like electrics and fuel.
But i am just not a theory man.
still beyond me how on earth i passed all the subjects without paying bribe lol
what i meant is that i am not into the nitty gritty like some people can be.
I do think it is importand to know the systems in your plane. like electrics and fuel.
But i am just not a theory man.
still beyond me how on earth i passed all the subjects without paying bribe lol
Thread Starter
Guys, the reason for my original question was because i have the systems exam coming up (that's why i give a f*@k), and i wanted to sort out the apparent discrepancy between two of Australia's most well known ATPL theory providers.
Apache, thanks for your post mate, it brightened my otherwise study intensive (dull) day!
Cheers,
Greaser
Apache, thanks for your post mate, it brightened my otherwise study intensive (dull) day!
Cheers,
Greaser
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For the low subsonic region where M < 0.3 (less than say 200 KTAS in ISA) incompressible flow is a common assumption. (You can then use a simplified form of Bernoulli's equation to analyse the flow.)
Does the question provide any more detail on "how subsonic" the flow is?
Does the question provide any more detail on "how subsonic" the flow is?
Thread Starter
No it just said subsonic flow. My friends Secombe notes said that pressure, and density always act together, and opposite to velocity. I've since read that below Mach .3 flow is considered incompressible therefore density remains constant. So i guess i'll just go with stick with Nathan's notes and hope for the best.
Cheers,
Greaser
Cheers,
Greaser
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My notes say..subsonic flow is essentially incompressible, so the density is considered constant..
I spose thats like getting your missus a little bit pregnant
I spose thats like getting your missus a little bit pregnant
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AGK in general
I sat the course a few months back at UNSW at YSBK. Great course and am yet to sit this exam. A mate sat the course with me and passed the exam easily. He also obtained Higgins notes and said that 10 out of the 50 exam questions weren't touched upon in either course and he guessed the answers for these. He checked this after the exam too. Pretty scary. Anyone found this to be true for them? I've sat 6/7 exams but am very cautious about this one so I haven't sat it yet. I'll bite the bullet and sit it next week.