Joined: Jan 18, 2010 Posts: 41 Location: Duns, Berwickshire
Posted: Fri May 11, 2012 10:48 pm Post subject:
Is it another one of those DALR is actually 2.5 deg C things? (ref other posts on helitorque)
Personally I think the actual quantification of this seems to be largely ridiculous - I expect there are a few theories, 1 exam paper quotes from one, 1 from another etc, nothing ever being as simple as it seems.
Sea Level Temperature: 16°C
1,000 ft 13°C (DALR)
2,000 ft 10°C (DALR)
3,000 ft 7°C (DALR)
4,000 ft 4°C (DALR... now temperature is the same as dew point)
5,000 ft 2.2°C (SALR)
6,000 ft 0.4°C (SALR)
7,000 ft -1.4°C (SALR)
8,000 ft -3.2°C (SALR)
9,000 ft -5°C (SALR)
10,000 ft -6.8°C (SALR)
And now we go back down the otherside:
10,000 ft -6.8°C
9,000 ft -5°C (SALR)
8,000 ft -3.2°C (SALR... now at the cloud base given in the question)
7,000 ft -0.2°C (DALR)
6,000 ft 2.8°C (DALR)
5,000 ft 5.8°C (DALR)
4,000 ft 8.8°C (DALR)
3,000 ft 11.8°C (DALR)
2,000 ft 14.8°C (DALR)
1,000 ft 17.8°C (DALR)
Sea Level 20.8°C (DALR)
So the answer I get is 21°C
-- or --
2. Short hand
If you know the cloud base on either side, you can use the formula:
Temperature Rise = Cloud Base on the Lee Side (in '000s) - Cloud base on Windward (in '000s) * 1.2
(Side track: the 1.2 comes from DALR - SALR)
We have already calculated the cloud base on the windward side as 4,000ft.
The question gave the cloud base on the lee side as 8,000ft.
So, Temp Rise = (8-4) * 1.2 = 4.8°C
The original temperature was 16°C, so the answer = 16 + 4.8 = 20.8°C
Which is the same answer as above... but not apparently the "correct" answer.
So my next thought was they are using the old SALR of 1.5° / 1,000ft.
Using my formula above:
4 * 1.5 = 6°C
16 + 6 = 22°C
Again, not the "correct" answer.
But using Tom's 2.5 DALR (and 1.8 SALR):
4 * 0.7 = 2.8°C
16 + 2.8 = 18.8°C
That is getting close to the "correct" answer of 18.5°C.
Errors do happen in the database... is it possible that this is one of them?
Yes Flip, I think youre right..there does seem to be quite a few errors in the Bristol bank as well as hordes of fixed wing questions. I dont think they can bothered to separate the questions which may be relevant to us rotary students.
There is a market there for a descent set of heli questions to practice your knowledge on.
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