Bigfoot 10.4--where's the beef?

HMS Beagle wrote:

3 tons wrote:


The formula I provided here is the verbatim method the Army uses, and is what the USAF teaches where the (static) COG must be calculated for each single item positioned (or stationed per fuselage reference datum line) on the aircraft’s cargo floor.

3 tons

To calculate the CG you must pick a reference, but any reference will do as well as another. The answer (if done correctly) will be the same. Whether the moments are calculated about the front edge, the box bumpers, the rear bumper, or any place in between.

Yep, any point of reference will do. So why not pick the center-of-gravity point? Say L is the distance from the front jack to the center-of-gravity. Since the distance between the jacks is 137" and we know the location of the center-of-gravity is between them, then we can say the distance from the center-of-gravity to the back jack is 137-L. At the center-of-gravity the moments (force multiplied by distance) created by the loads at each jack are equal and opposite. The weight (force) on the front jack is 2057 pounds and the distance is L so you have a moment of 2057L trying to spin the camper one way. The weight (force) on the back jack is 1617 pounds and the distance is 137-L so you have a moment of 1617(137-L) trying to spin the camper the other way. Setting these moments equal to each other you have:

2057L = 1617(137-L)

Solving for L you get 60.3" so the center of gravity is 60.3" back from the front jack.

Statics is fun ... except when your professor gives you a test question he didn't set up right and you end up with a rope in compression :B