[color=blue] What I have found in if we use 2505 + 5 kg our CoG will become 2679mm. However when using the calculative method, I found that 2505+3= 2508KG, CoG will become 2681 mm which is 1mm off.[/color]
Actually, had you run the sums for 4 kg, you would have been just about spot on. Not really worth worrying about in the real world as the numbers you start with for the sums are nowhere near that accuracy. So, 3 or 5 kg is fine. The answer to select for the question has to be 5 kg as that's the mass of the ballast items you have available to you. I doubt that the examiner would be interested in splitting hairs to the nearer kilogram so all should be fine for the exam as well.
It is obvious that you have run the sums, either longhand or in a spreadsheet, so I am a little surprised that you didn't pick up on the 4 kg - not to worry - it's a trivial point.
So, well done. I might have given you the odd clue along the way but you have successfully run the analysis and arrived at the correct final solution by yourself. Do you think this sort of problem will give you any further problems ? I shouldn't think so.
Perhaps run a few more examples to reinforce the approach and you will have this sort of question well and truly sorted out.
Engineering specialist in aircraft performance and weight control.
Thanks a lot for your help and explanation. Much appreciated! Is there a possibility whereby the examiner gives us data that both TOW and ZFW fall withing the CoG range? If so would I pick the one with the worst case scenario, like a ZFW more aft then TOW but still in range?
[color=blue]Is there a possibility whereby the examiner gives us data that both TOW and ZFW fall withing the CoG range?[/color]
Absolutely the case.
Add, say, another 10 kg to the previous 5 kg ballast. This puts the CG values to around 2670.4 (ZFW) and 2630 (TOW).
Simple enough then to pose a problem like the following -
"The aircraft will be expected to perform optimally for fuel burn if the CG is as aft as can be arranged. What is the minimum weight you need to leave behind for your flight to achieve this if you don't relocate the passengers ?"
Engineering specialist in aircraft performance and weight control.
No worries will have a look at problems like those as well. Thank you for all your help! You're a life saver 🙂
Not at all. You did the work, not I.
Engineering specialist in aircraft performance and weight control.
