ATPL Question
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ATPL Question
Hi everyone,
I sat ATPL Performance and Loading yesterday and sadly 68% was the best I could do.
In my KDRs was one of those minor questions that could make or break you.
I can't seem to find the correct answer in my study material.
I went for ( B ) and got it wrong.
Question, Holding Altitude for lowest SFC
A) as low as possible
B) as high as possible
C) Lower rather than higher
D) Higher rather than lower
I sat ATPL Performance and Loading yesterday and sadly 68% was the best I could do.
In my KDRs was one of those minor questions that could make or break you.
I can't seem to find the correct answer in my study material.
I went for ( B ) and got it wrong.
Question, Holding Altitude for lowest SFC
A) as low as possible
B) as high as possible
C) Lower rather than higher
D) Higher rather than lower
Join Date: Aug 2009
Location: Melbourne
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Hi JB235,
What notes are you using for study?
Let's look at what effects SFC:
RPM:
SFC reduces in the design RPM for a specific engine, Higgins puts it in the 92-98% range. An aircraft at a higher altitude will be holding at an engine RPM closer to the design RPM therefore a better SFC.
Temperature:
Not much of a change for a similar TAS; however
Altitude:
You'll get a better SFC with altitude up to the tropopause where the SFC will begin to become less-favourable again. This is where I think you've got the question wrong.
I'd be inclined to choose D in this case.
What notes are you using for study?
Let's look at what effects SFC:
RPM:
SFC reduces in the design RPM for a specific engine, Higgins puts it in the 92-98% range. An aircraft at a higher altitude will be holding at an engine RPM closer to the design RPM therefore a better SFC.
Temperature:
Not much of a change for a similar TAS; however
Altitude:
You'll get a better SFC with altitude up to the tropopause where the SFC will begin to become less-favourable again. This is where I think you've got the question wrong.
I'd be inclined to choose D in this case.
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Gday ConfigFull,
I am using AFT notes.
Yep I think your right.It was one of those curly ones.
I mean who is going to be holding above the tropopause
Thats why I went for as high as possible
Cheers
I am using AFT notes.
Yep I think your right.It was one of those curly ones.
I mean who is going to be holding above the tropopause
Thats why I went for as high as possible
Cheers
I wouldn't have answered 'as high as possible'. That implies the aircraft's absolute ceiling is a possibility, which does not equate with the most efficient use of fuel. 'Higher rather than lower' however doesn't include a particular altitude that is inefficient, leaving the exact altitude open to suit the circumstances.
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Altitude:
You'll get a better SFC with altitude up to the tropopause where the SFC will begin to become less-favourable again. This is where I think you've got the question wrong.
You'll get a better SFC with altitude up to the tropopause where the SFC will begin to become less-favourable again. This is where I think you've got the question wrong.
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I would have thought that SFC was more applicable for the cruise rather than in a holding pattern. More thrust for less fuel flow per hour.
In a holding pattern your best altitude will depend on your aircraft weight as you will want to fly at min F/F.
B777-300ER:
340T - min F/F at 10 000FT
180T - min F/F at 30 000FT
Mind you it has been a few decades since I did ATPL performance and yet again I didn't RTFQ!
Oz
In a holding pattern your best altitude will depend on your aircraft weight as you will want to fly at min F/F.
B777-300ER:
340T - min F/F at 10 000FT
180T - min F/F at 30 000FT
Mind you it has been a few decades since I did ATPL performance and yet again I didn't RTFQ!
Oz
