New Equipment - New W&B

Jaybird180

Jaybird180

Final Approach
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Jaybird180
I have a question about W&B reports. When an aircraft gets a significant retrofit and the W&B is done, what figures change on the report that account for the shift in CoG?

For example an airplane with steam gauges gets new lightweight glass cockpit with black boxes in the rear of the airplane. The CoG has now shifted rearward. When I do W&B calculations pre-flight, how do I account for the shifted CoG of the 'new' empty aircraft?
 
Anytime something gets installed or deinstalled in the airplane you should get a new W&B sheet reflecting that change. Often the airplane isn't actually weighed, the changes are merely calculated. It's a good idea to get the airplane actually weighed every so often (maybe every 5 years) as they have a tendency to weigh more than the calculated W&B says they do.
 
Jaybird180 said:
... what figures change on the report that account for the shift in CoG?

... how do I account for the shifted CoG of the 'new' empty aircraft?
Click to expand...

Jaybird, the updated Weight & Balance worksheet will have both a new empty weight and a new moment arm for the empty airplane. The new empty weight accounts for the weights of items added &/or removed. The new moment arm accounts for the locations of items added &/or removed, and represents the new COG of the empty plane.
 
I get that there will be a new report. What I don't get is how I incorporate the new CoG into my calculations? The CoG of the empty airplane doesn't get used or does it change the shape of the rhombus on the chart?
 
Jaybird180 said:
I get that there will be a new report. What I don't get is how I incorporate the new CoG into my calculations? The CoG of the empty airplane doesn't get used or does it change the shape of the rhombus on the chart?
Click to expand...
Whatever the latest CG and weight is...MUST be used with the calculation.

How do you currently calculate weight and balance? (The method and details how you do it)
 
Jaybird180 said:
I get that there will be a new report. What I don't get is how I incorporate the new CoG into my calculations? The CoG of the empty airplane doesn't get used or does it change the shape of the rhombus on the chart?
Click to expand...

The empty moment goes into your calculation of the loaded Cg, right?

As you change the weight or location of things, the empty moment (weight * Cg distance) changes (it includes the new empty Cg).

When you use the new empty moment in your calculation, you end up with the loaded Cg in a different place than you would have before with the same cabin / fuel load. The forward / aft limits for the Cg (or limits of the moment as a function of weight) don't change.
 
Okay. I was having a short bus moment. Looking at a sample report cured it. I saw that Arm and Moment are columns alongside the Basic Empty weight.
 
jesse said:
Whatever the latest CG and weight is...MUST be used with the calculation.

How do you currently calculate weight and balance? (The method and details how you do it)
Click to expand...

You read my mind. I think there is a definition issue here. I think he is asking if the shape of the envelope on the graphic changes, and is missing that the initial point of the CG will be forever changed within that graph before the mission specific weights and moments are computed.
 
Jaybird180 said:
I get that there will be a new report. What I don't get is how I incorporate the new CoG into my calculations? The CoG of the empty airplane doesn't get used or does it change the shape of the rhombus on the chart?
Click to expand...

The size and shape of the acceptable envelope (what I believe you mean by the rhombus) does not change.

You use the moment arm (I.e., COG) of the empty plane as you normally do to calculate w&b. Specifically, you multiply the empty weight times the moment arm of the empty plane to calculate the moment of the empty plane. Add to that the moments for fuel (fuel weight times moment arm for the fuel tank), for the pilot (pilot weight times the moment arm for the pilot seat), etc. Add up all the weights to calculate the total weight. Then divide the sum of all the moments by the total weight, and the result is the COG for the full plane.

The total weight should not exceed the Max Gross weight. The COG for the full plane should be within allowable limits front to back. In other words, the values should fit into the "rhombus".
 
Jaybird180 said:
I get that there will be a new report. What I don't get is how I incorporate the new CoG into my calculations? The CoG of the empty airplane doesn't get used or does it change the shape of the rhombus on the chart?
Click to expand...

Same way you did it before:lol:
 
Jaybird180 said:
I get that there will be a new report. What I don't get is how I incorporate the new CoG into my calculations? The CoG of the empty airplane doesn't get used or does it change the shape of the rhombus on the chart?
Click to expand...
The cg and weight limits (the "rhombus") don't change -- that's part of the basic limitations of the aircraft design. What changes are the empty weight and empty cg you use as the starting point for your load computations, and those new empty figures will be on the new W&B.
 
If the limits (the shape of the envelope) change, that's a major modification and there's going to be real paperwork involved. Often as specified, minor changes are either marked as negligable or the weight and moment of the items removed are subtracted and the ones installed are added to the previous w&b paperwork. Depending on the aircraft there should also be a specific list of what the installed equipment is.

Oddly enough after 50 years of "computed" changes to my plane, I had the plane weighed when I put the big engine in it. It wasn't very far off at all. Probably less than the weight of the hydraulic fluid soaked into the carpet over the years.
 
The How to's are all here

http://rgl.faa.gov/Regulatory_and_Guidance_Library/rgAdvisoryCircular.nsf/list/AC%2043.13-1B/$FILE/CONTENTS.pdf
 
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