Alterations, Weight and Balance

[JonJay]

Alterations included removing AP servo's and a remote magnesyn. A total weight reduction of 17 lbs!
I know the arm of each of the individual components and there weight.
I can calculate the affect of the removed components on my cg relative to my standard configurations, however, I would like to recalculate my entire Weight and Balance.

The part I am stumbling with is how to calulcate the affective weight reduction on the mains and tailwheel weights, and then get the new empty weight cg.

I am sure it is simple math, but math is not my strong suit. I can always weigh the aircraft again, but I would think this can be calculated.

[caryr]

jon

I can do the math, but not sure I can explain it with a keyboard.

Shoot me the weights and stations and I'll give u new numbers.

[JonJay]

Originally Posted by caryr

jon

I can do the math, but not sure I can explain it with a keyboard.

Shoot me the weights and stations and I'll give u new numbers.

I really want to know the formulas so I can deal with any future modifications. The numbers are at home and I would be happy to send them to you. Appreciate the help, but if anyone out there knows the formulas, let me know please.

[Greg Arehart]

JonJay,

I can send you an excel spreadsheet that contains this information if you would like. PM me (but I'm out of town the next couple days so unlikely to answer immediately).

greg

[nomocom]

Originally Posted by JonJay

The part I am stumbling with is how to calulcate the affective weight reduction on the mains and tailwheel weights, and then get the new empty weight cg.

I am sure it is simple math, but math is not my strong suit. I can always weigh the aircraft again, but I would think this can be calculated.

Weight on the wheels? You don't really need it.* The weight and arm of the removed equipment is used to calculate the new numbers. Old weight minus removed equipment weight is you new weight. And then individually, -weight x arm = moment inches. Add up all the moment inches totals and that gets applied against the old moment inch total, keeping in mind that removing weight aft of the datum should generate a negative moment inch.

For example..
1020# original minus 20# removed equipment. New weight 1000#
and
-10# * 30 in = -300
and
-10# * 70 in = -700
for a total of -1000

This would have you add -1000 moment inches from the original moment inch total. Then your new cg is just moment inches divided by weight.

Example- old moment inches = 51,000 plus -1000 = 50,000 so

50,000 / 1000 equal 50 inches, the new CG.

*The reason we know the weight on the wheels is that is the data that supported the original calculations, though a builder in theory could weigh each part and calcuate W&B based on part weight and installed location. Not really very practical in the case of RV's, considering how easy it is to weigh the finished product, but what i'm getting at is the weight on the wheels doesn't matter for the purposes of calculations, especially once we've got a good baseline weight and cg.

Enjoy that new lighter airframe!

[WingsOnWheels]

Nothing complicated about the calculations. Just the old W X A = M. You know the current CG Arm and empty weight multiply to get totoal moment. You know the W and A of the removed components multiply to get the M or each (will be negative since W is negative). Add all moments and devide by new weight (be sure to reduce the empty wight to account for the removed bits). This will give you the new empty CG.

[WingsOnWheels]

Originally Posted by nomocom

Weight on the wheels?...

Oops, you beat me to it.

[JonJay]

Especially Greg for the spreadsheet.