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Review Questions Set 2 - Q 11

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Airspeed created the topic: Review Questions Set 2 - Q 11

Answer to this says 170Kg of fuel can be added, but the attached form I did shows 160Kg. The graph used in the answer doesn't seems to match with the graph from the supplement.

Have I done this wrong? See attached.
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John.Heddles replied the topic: Review Questions Set 2 - Q 11

Very difficult to offer comment - I don't have the question to hand and your trimsheet is only part completed (which may well be tied up with the question detail).

Can I suggest that you post the question of concern along with the solution trimsheet and then we can offer comment to assist ?

Engineering specialist in aircraft performance and weight control.
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Airspeed replied the topic: Review Questions Set 2 - Q 11

Sorry for delayed reply. Attached is is the worked answer I got on the Alpha load sheet. The addition of 40Kg to the rear puts the forward C of G at the 1600Kg mark, so 1600 - 1440 gives and answer of 160KG, not the 170kg I see as the books answer.

I get the same answer if I use the CASA load sheet from their CPL workbook or the one from the Bob Tait Perf Supp.

Questions reads:
Question No 11
An aeroplane which uses an Alpha loading system is loaded at Zero Fuel Weight as follows.
Zero Fuel Weight 1400 kg
Zero Fuel Moment Index -200
Both the nose and rear compartments are empty. If 40 kg of cargo is yet to be loaded, into which compartment
should it be loaded to allow the maximum fuel to be carried?
The 40 kg should be loaded into the ____________ compartment.
The maximum fuel that could be loaded is _____________________ kg
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Bosi72 replied the topic: Review Questions Set 2 - Q 11

Airspeed wrote: Have I done this wrong? See attached.


Short answer, I don't know.

However I noticed a couple of minor mistakes which can lead to significant sum of errors.

In your first post in the attached worksheet, the line at the top next to moment index is closer to reference line (at X), compared to the same line at the bottom (at Y).



In your last post, the distance between left side of the box at X appears to be greater than distance at Y.



Note at the original diagram, the distance of 13 doesn't appear proportional to 20 unless the line width counts.



For these diagrams, I used 0.5mm mechanical pencil, two large triangles and make sure the lines are parallel to the reference lines.
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John.Heddles replied the topic: Review Questions Set 2 - Q 11

The graph used in the answer doesn't seems to match with the graph from the supplement.

I think I know what your problem is.

However, I need to see the answer document's graph. Can you post a scan of it, specifically, please ?

This sort of question is a bit silly as it goes somewhat beyond the drawing precision of the graph being used, ie it indicates that the originator of the question didn't really have a good understanding of what he/she was doing. In general, one really needs to keep the precision requirements of a question compatible with the design of the graph.

Engineering specialist in aircraft performance and weight control.
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Airspeed replied the topic: Review Questions Set 2 - Q 11

Here is a screen capture of the answer from the book. If use CASA's, or Bobs supplement load sheet for Alpha and plot the original -200IU/1400KG, then add the 40KG to the rear to get the new ZFW of 1440KG. The intersection point is exactly at 1600KG, which is 160KG from 1440KG, not 170KG that the answer gives.

I did it again and corrected the small mistakes mentioned by Bosi72, but came up with the same answer.

Cheers
Matthew
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Bosi72 replied the topic: Review Questions Set 2 - Q 11

As an IT professional you wouldn't believe how much trouble can a screen size cause, especially in this age where screens are produced in all sorts of shapes and sizes.. Even worse, when you're printing something on a US Letter instead of A4, then you choose "Fit to screen" option in advanced menu, funny things happen.

To cut the story short, nothing wrong with your calculation. The example in the book is moving 4 boxes to the right, the same way as you've done. In the book the line crosses somewhere more than 170, in your worksheet it is 160.

Regardless, the same principle applies. Be precise and you'll be fine on the exam.
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John.Heddles replied the topic: Review Questions Set 2 - Q 11

Thanks.

The problem is not yours - your answer is fine.

The problem is that you are looking at an older copy of the question which refers to an earlier version of the trimsheet ? I presume that Bob updated it when I highlighted this problem previously ? I'll flick Bob a note to check on this.

The history is that

(a) the original Alpha sheet was one of Norm Overmeyer's for a Turbo Lance. Norm, now long gone, was a civil engineer and NSW-based WCO. The then examiner, many years ago, lifted that sheet from whichever aircraft for exam use. Who knows, it may have been an aircraft which he flew on the weekends ?

(b) subsequently, he got Bruce Clissold, a mate of his, ex-DCA, and an another very experienced WCO, to tidy up a few things in the sheet which he didn't like. How do I know this ? Norm I knew well and his sheets are easily recognisable while Bruce related the detailed story to me a couple of years ago.

(c) so you had two similar, but different, versions of the same sheet without any revision details to highlight the changed status of the later sheet - that's an absolute naughty no-no and should not have got through the system checking but that's what happened.

Your discrepancy is a simple consequence of running the question on two, different sheets. It's not at all surprising that you get two different answers.

You might like to read the previous thread on the problem.
bobtait.com.au/forum/performance/5279-we...0-may-2015-book#8645

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bobtait replied the topic: Review Questions Set 2 - Q 11

OK guys. Here is the amended diagram for that question using the new Alpha centre of gravity chart. The Alpha chart was changed and I didn't realise that. Hope we're still friends!!
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Airspeed replied the topic: Review Questions Set 2 - Q 11

bobtait wrote: OK guys. Here is the amended diagram for that question using the new Alpha centre of gravity chart. The Alpha chart was changed and I didn't realise that. Hope we're still friends!!


Haha. Always friends. Thanks for the update.
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