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Question #4 Exercise 4.17
julza2425
Topic Author
julza2425 created the topic: Question #4 Exercise 4.17
Hi Guys,
Can you please give me a FULL working answer on #Q4 Exercise 4.17 ? I have no problem interpolating between Weights & Heights but this one has really got me mind boggled since its interpolating between both weight & height and power settings for the Echo !! I came up with an answer 2 Gallons different to the answer and i cant work out why ! Could you please supply me with a full explanation to the answer thats more detailed than the one in the CPL book ??
bobtait replied the topic: Question #4 Exercise 4.17
Hi Julian
Firstly let me assure you that this kind of question is way beyond anything the examiner will ask in the exam. The question requires that you decide what power setting to use to obtain best ground nautical miles per gallon. For the Echo, that will always be either 55% power or 45% power. The OAT at 17500ft is -10 and the ISA temperature at that pressure height is -20, so the temperature to use is ISA + 10. Therefore you need to find a TAS for 55% power half way between 10000ft and 20000ft, half way between 5000kg and 2000kg and half way between ISA and ISA +20. You need to use that TAS to find the best ground nautical miles per gallon at 55% power. Add all of those numbers up and divide by 8. That gives us a TAS of 182.25kt for 55% power.
Repeat the same procedure for 45% power and choose the best answer to calculate the minimum fuel possible.
Remember you certainly will not get such a question in the CASA exam. They will simply give you a TAS to use.
