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Question about Ex 1.4 & 1.5
marty_87
Topic Author
marty_87 created the topic: Question about Ex 1.4 & 1.5
Hi,
Just 2 question about Q5 in Ex 1.4 and Q1 in Ex 1.5. (Page 2.10)
1.
Q5 the pressure height is -80. In the worked answers the -80 is rounded to ZERO so the ISA is 15-2xZERO=+15
Q1 the pressure height is -270. In the worked answers the -270 is rounded to 0.5 so the ISA is 15+2x0.5=+16
2.
In the ISA working why is
Q5 15 MINUS 2 x zero = +15
AND
Q1 15PLUS 2 x 0.5=+16
Am I missing something or is this an error on the book??
Cheers
PS - Hope you can understand what I'm getting at???
bobtait replied the topic: Question about Ex 1.4 & 1.5
The ISA temperature lapse rate is 2° per 1000 feet of height increase. That means it must be 1° per 500 feet of height increase. There is no point interpolating beyond half way, so we have rounded up or down to the nearest 500 feet. In the example in Exercise 1.4, the pressure height came to -80 feet. That is much closer to zero than it is to -500, so the ISA temperature is 15°.
In the example in Exercise 1.5 Question 1, the pressure height came to -270 feet so it should be rounded to -500 feet [the nearest 500 feet]. If the temperature drops by 1° per 500 feet of height increase, it is reasonable to assume that it will increase by 1° per 500 feet of height decrease. So at -500 feet the temperature would be 1° warmer than 15 = 16°C.
I must admit that it is getting a bit fastidious to carry on with this degree of accuracy, but it is a theory exam.
