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# Calculation of %CG MAC

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Here is my problem. I need to calculate %CG MAC based upon typical aicraft.cfg variables.Let's say we have following (that's b763er):(WEIGHT_AND_BALANCE)reference_datum_position=0.000000,0.000000,0.000000empty_weight=196000.000000empty_weight_CG_position=0.306000,0.000000,0.000000station_load.0=1848, 53.72, 0.0, 0.0, Zone Astation_load.1=8904, 29.58, 0.0, 0.0, Zone Bstation_load.2=9072, -7.19, 0.0, 0.0, Zone Cstation_load.3=10080,-36.81, 0.0, 0.0, Zone Dstation_load.4=3209,50.66, 0.0, 0.0, Hold 1station_load.5=2240,29.47, 0.0, 0.0, Hold 2station_load.6=2170,-20.63, 0.0, 0.0, Hold 3station_load.7=1685,-38.87, 0.0, 0.0, Hold 4station_load.8=787,-52.02, 0.0, 0.0, Hold 5and fuel section:(fuel)Center1=8.000000,0.000000,-4.000000,12000.000000,3.000000LeftMain=-3.4000000,-30.500000,0.000000,6070.000000,3.000000RightMain=-3.4000000,30.500000,0.000000,6070.000000,3.000000From what i know the formula specifically for 767 is:%CG MAC = (B.A.

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You already have the calculations... what's missing is a basic understanding of what the values in the aircraft.cfg actually represent.

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>You already have the calculations... what's missing is a>basic understanding of what the values in the aircraft.cfg>actually represent.Ok, i've read a couple of related topics, as far as i understand datum in fs aicrafts is generally regarded as 25%CG MAC. In the case of "station_load.6=2170,-20.63, 0.0, 0.0, Hold 3"how do i convert "-20.63" to the "normal" balance arm, from the datum of 92.5 inch infront of the aircraft?

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I'm not sure what related topics you've read, but was one of them the actual SDK documentation? Here's a pointer to the ESP SDK Docs definition of Datum Reference Point (gotta love having these availabe on-line now, much easier to point at :-> ):http://msdn.microsoft.com/en-us/library/cc...mreferencepointand here's a pointer to the "Weight and Balance" section docs:http://msdn.microsoft.com/en-us/library/cc...#mozTocId243173Sounds to me like the Datum Reference Point is at the center point for the model and positive values are foreward of that point, negative numbers are aft of that point.

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Simply calculate the difference between FS's default datum point and your documentation's datum point and adjust accordingly.Technically, the reference datum point is abitrary and can be absolutely anywhere. Despite how it's presented in the SDK. ;) The point discussed in the SDK is model center... but you can adjust your reference datum point as an offset to that position and then change the aircraft.cfg entries based on your reference datum point.

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beatle, thanx for the links!WarpD, i thought about calculating the difference, but for that i need detailed sketches of the aicraft, which i don't have. To set an offset for datum in aicraft.cfg i again need to know the difference... Rather, iam trying to find algorithm that is used by FS to calculate %CG from given data in aircraft.cfg...

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Well... dunno if anyone but ACES has that information.Even Level-D uses their own external application to calculate the value you're wanting to solve for.

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level-d actually calculates %cg incorrectly. Simply if you take trim chart, from FCOM, and calculate it manually, you'll get different results in level-d's manager. The same with de-rated thrust. Many things in level-d are not as perfect as they seem.

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>level-d actually calculates %cg incorrectly. Simply if you>take trim chart, from FCOM, and calculate it manually, you'll>get different results in level-d's manager. The same with>de-rated thrust. Many things in level-d are not as perfect as>they seem.I could care less... the POINT is that they had to do the calculations externally.

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