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Loading System Bravo
Mario created the topic: Loading System Bravo
Hi Bob and team and all out there.
Can you please explain your answer to Question 5 in RPL Book Section 9 Loading System Bravo ?
In your answer to determine minimum weight of cargo removed to obtain safe centre of gravity, you do this by obtaining another point on the Load vs Moment index graph. You picked an arbitrary 100lbs to be removed and then obtained a moment index of 15.1, then plotted this point.
My question is how you obtained this moment index? If I plot 100 lbs weight on the loading graph for cargo I get a lower moment index of about 11. why did you use a moment arm of 151 inches?
To get the moment index for 100lbs in the cargo compartment you have two choices. You can use the conversion graph for weight to moment index. Enter at 100lbs and go across to the rear baggage reference line then go down to the moment scale. That's a moment index of just over 15.
Or you can go to the example for Bravo and obtain the arm of the baggage compartment - 151 inches.
If you multiply the weight by the arm and divide by 1000 you get the moment. 100 X 151 ÷ 1000 = 15.1 moment index.
Actually Mario, you have brought up a good point. I notice that if you check out the example, there is no mention of 'cargo' anywhere. There is also no mention of 'cargo' in the description of the aircraft - only 'baggage'. However on the weight to moment index graph, there are two lines, one for 'cargo' and one for 'baggage'. I have only just noticed that after all these years!! I don't know why the 'cargo' reference line is there. There is no extra compartment on the aircraft where you can put 'cargo'. That's a mystery to me.
I usually tell my classes not to use the weight to moment index graph anyway. It is much easier to simply multiply the weight in each location by the arm given in the example table. In any case, if a question asks for the MINIMUM weight that must be removed, you would have to use the baggage compartment because it is the most rearward compartment so any weight removed from there would have the greatest effect on the CofG movement.
John.Heddles replied the topic: Loading System Bravo
I would need to have a play with the loading information to form a definite view. However, a quick looksee at the moment line chart suggests to me that "cargo" applies for an aircraft where the rear seats are removed and all the floor area aft of the front seats is used for cargo .. the cargo arm would then be that floor area's fore and aft centroid for loading calculation purposes.
It may well be that, when whichever examiner in the past lifted the loading system details from whichever aircraft out there in the wild, the cargo line in the chart was not picked up .. so Bob, probably, is not alone in wondering why it is there ...
Engineering specialist in aircraft performance and weight control.