Hi Guys,

Im struggling with a question from exercise 4.4 on page 82 of the PERF book -

1. Find the distance, time and fuel required for a cruise climb in an Echo from sea-level to 10,000ft on an ISA day, if take off is at 2500KG.

*** my method was 15-2*10= -5 entered the chart at -5, up to 10,000 and extracted an answer very close to the answer in the book, i feel like im missing something.

I know to use the cruise climb chart on page 15 of the extract and how to use the chart if PRESSURE HEIGHT is given (or even to calculate to density height if needed)... but how do i extract pressure height out of the question with the information provided?...

i think ive cooked my brain on Perf.

Thank you in advance, Dan.

how do i extract pressure height out of the question with the information provided?...

Clue - Find the distance, time and fuel required for a cruise climb in an Echo from sea-level to 10,000ft on an ISA day, if take off is at 2500KG.

The highlighted bit says that the atmosphere, today, is exactly as defined by the ISA model. Therefore, your QNH is standard, all the lapse rates are as the model and what the altimeter reads is pressure height, ie there is no need for any conversion calculations to determined Hp.

Hi John,

Thank you for your reply. So my method was correct?. I extracted an answer slightly different from what was in the book... not by much ... 21ish nautical miles and fuel, time seemed to close to tell... Bobs answer was 19.5NM... i tried to redo the lines to match his answer but couldnt get within that margin..

Apologies if you are saying my answer isnt correct... this is my third read through of the text book, i think i might need to step away for a few days so i can think clearly again.

Cheers, Dan.

Dan,

I don't have a copy of Bob's book so I don't know just what it might say.

The only concern I might have with your first post is that it is more traditional to take weather conditions part way through a climb or descent, This is done to reflect the non-linear nature of the typical variation with height.

That your answer is a longer distance might tend to suggest that Bob's technique might not take the final climb to height level for the ambient conditions input ? Perhaps you might have a re read of his technique discussions ?

Hi John,

I think i understand now, thank you.

PERF is my last exam, and i have to say this one seems to be the most complicated in extracting the needed information as there is always a lot of different factors to consider. I will definitely be happy when this one is over!.

Appreciate your help.

Cheers, dan.

This chart is the cruise-climb chart for the CASA exam aeroplane Echo. It allows you to extract the distance, time and fuel to climb to a given height in no wind (see attachment).

If the conditions are equal to ISA, it means that the pressure height and density height are the same. You dont need to know the temperature. Just run up the ISA line to the height in question. That is where ISA temperature occurs at each pressure height (density height).

Cheers Bob, that makes perfect sense.

The answer i extracted still remains the same, Im guessing it must be due to poor line drawing skills.

(up to the 10,000ft mark on the ISA line and across and down).

Cheers,

Dan.

With the graphic, I can run a calculation. Reading via a drawing package (which allows for very accurate plotting), the answer looks to be 20.6nm for the distance.

The weight lines have a slope which makes for little variation in the distance read. Something doesn't quite gel if the nominated answer is 19.5nm. Will need Bob's input for that to be resolved.

Plot follows. I am presuming that 2500kg is the middle line - rather difficult to read the numeral with the scale line overlying.

Hi John,

I agree, my answer is the same as yours. Bob is it possible to get the answer updated. The question is on page 80 of the PERF book.
I have attached screenshots for reference.

Appreciate your help with this one as always!.

Cheers Dan.

Dan, John

I agree with both of you and have amended the answer to reflect that

Cheers
Stuart