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When doing weight and balance calculations on fixed wing aircraft is the transverse axis (wingtip to wingtip direction) used? Or is only longitudinal axis considered?

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    $\begingroup$ Depends on the aircraft, sometimes all three are used, sometimes only one. $\endgroup$ – Ron Beyer Feb 2 '17 at 1:29
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@Ron Beyer's comment is correct. Here's a little more information.

Generally speaking, in narrow-body aircraft, it's sufficient to calculate the CG only along the longitudinal axis. There may be limits along the lateral axis but which would only be exceeded with severely imbalanced wing fuel loads, and that is often handled by specifying a maximum fuel load imbalance.

Wide body aircraft typically require looking at the lateral CG as well as the longitudinal CG. However, the allowed lateral moment about the longitudinal axis may be high enough that the limitation comes into play only when carrying cargo. That's the case with 747-100/200/400 aircraft. As I remember, the max lateral imbalance for a 747-400 is 10,000,000 inch-lbs.

There are some fixed-wing aircraft that require looking at the vertical CG. The 767-300 does. I don't know about other 767 models. It's not an issue for 747s.

If you're interested in playing with CG movement on 747-400 and 767-300 aircraft, you can go to 747.terryliittschwager.com and look at worked examples or do your own.

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  • $\begingroup$ Do you know if vertical CG was considered for external cargo 747's, specifically the shuttle transport? $\endgroup$ – Ron Beyer Feb 5 '17 at 4:03
  • $\begingroup$ @RonBeyer No, I do not. My guess (and it's only that) is that they certainly would have considered the vertical CG in the design for the shuttle transport; it was after all a heavily modified 747. I've seen, but do not have, Boeing manuals that detailed the external carriage of a spare engine. As I remember, though, there was no mention of a vertical CG check. $\endgroup$ – Terry Feb 5 '17 at 7:50

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