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## Determining the Correct Stabilizer Trim Setting 

It is important before takeoff to set the stabilizer trim for the existing CG location. There are two ways the stabilizer trim setting systems may be calibrated: in percent MAC and in units airplane nose up (ANU). 

If the stabilizer trim is calibrated in percent MAC, determine the CG location in percent MAC as has just been described, then set the stabilizer trim on the percentage figure thus determined. Some aircraft give the stabilizer trim setting in units of ANU that correspond with the location of the CG in percent MAC. When preparing for takeoff in an aircraft equipped with this system, first determine the CG in percent MAC in the way described above, then refer to the stabilizer trim setting chart on the takeoff performance page of pertinent AFM. Figure 9-9  is an excerpt from the AFM chart on the takeoff performance of a Boeing 737. 

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Consider an airplane with these specifications 

CG location................................................ station 635.7 

LEMAC ........................................................ station 625 

MAC .................................................................. 134.0 in 

1. Determine the distance from the CG to the LEMAC by using the formula in Figure 9-10 . 

2. Determine the location of the CG in percent MAC by using the formula found in Figure 9-11 . 

Refer to Figure 9-9  for all flap settings and a CG located at 8 percent MAC; the stabilizer setting is 7 3 ⁄4 units ANU. 

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## Determining CG Changes Caused by Modifying the Cargo 

Since large aircraft can carry substantial cargo, adding, subtracting, or moving any of the cargo from one hold to another can cause large shifts in the CG. 

## Effects of Loading or Offloading Cargo 

Both the weight and CG of an aircraft are changed when cargo is loaded or offloaded. In the following example, the new weight and CG are calculated after 2,500 pounds of cargo is offloaded from the forward cargo hold 

Aircraft specifications are 

Loaded weight ................................................. 90,000 lb 

Loaded CG........................................ 22.5 percent MAC 

Weight change ................................................... 2,500 lb 

Forward cargo hold centroid...................... station 352.1 

MAC .................................................................. 141.5 in 

LEMAC ................................................... station 549.13 

1. Determine the CG location in inches from the datum before the cargo is removed. Do this by first determining the distance of the CG aft of the LEMAC. [Figure 9-12] 

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