Negative or positive values, though, are important, because they refer to an arm that is forward or aft of the datum. Sometimes there are issues with decimal places, depending on how they word the sample problem, but it's usually easy enough to just look at the resulting number and deduce how many inches it really is. they are only considered individually, when you're trying to find the moment for a particular load. In other words, you should never be adding up arms. The number you get is the arm of the CG itself- its distance from the datum. Any calculator will speed that up, but it's still just grade-school arithmetic.Īnd as others have pointed out, all you need to do is add up all the moments (however you get them), add up all the weights, and divide the total moment by the total weight to find the CG. Weight times arm equals moment, that's all you need to know about that. Knowing this, it's really not a big deal to convert weight and arm to moment. "Moment" is the leverage exerted at the fulcrum by the weight of the load on that arm (expressed in foot-pounds). "Station" is pretty much the same as "arm" it can be expressed as the distance from the datum to the load, but it might be called "A", "B", etc on a diagram. "Arm" is the distance from the datum to the load. Remember: it is not the empty CG, although it's usually close to it. Why the datum is where it is doesn't really matter- just think of it as the point on which all these loads have to balance. "Datum" is just a reference point to take measurements from. The aircraft empty CG is not the fulcrum- it's just another load on an arm, exerting force at the datum. The datum is the pivot point, or fulcrum. It helps to visualize the loading problem as a seesaw, or any simple lever. General aviation covers a wide range of operations and aircraft, from powered parachutes and light-sport aircraft to turboprops and jets used for a. Click to expand.I know this may sound like I'm trying to complicate it when all you want is a simple understanding, but it may help you if you just remember the actual differences between all these terms. General Aviation Data Spreadsheet in MS Excel format (data updated on February 18, 2015) General aviation is the umbrella term for any operation that is not governed by Parts 121, 135, or 129.
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