If the CG cannot be positioned within the CG envelope in ForeFlight, consider these common issues:
1. Incorrect CG Envelope Definitions
If the CG envelope appears slanted or the CG is not within the envelope, verify that the values entered that define the CG envelope are Arms rather than Divided Moments. Some Pilot Operating Handbooks (POH) display CG envelopes using Moments divided by 100 or 1000. This presentation can make them appear similar to Arm values.
An example of divided moment values being used to define the CG envelope instead of arms.
NOTE: Values shown as "in-lb" are Moment values. Values stated as "in" are Arm values.
Solution:
Multiply the displayed Moment by the divisor (e.g., 1000 if Moments are divided by 1000).
Divide the resulting value by the corresponding weight to calculate the Arm.
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- Formula: Arm = (Moment × Divisor) / Weight
- Example: If the displayed Moment is 23.5 and divided by 1000 at a weight of 1650 lbs, the equation is as follows:
Arm = (23.5 × 1000) / 1650
Arm = 23,500 / 1650
Arm = 14.24
2. Empty Weight Data Problem
If the CG envelope appears narrow or shifted, the issue may stem from incorrect Empty Weight data entered in the aircraft profile.
An example of a divided moment value being used instead of an arm.
Solution: Review and verify that the empty weight and Arm (not a Moment value) are entered correctly based on the aircraft's weight and balance documentation. If a Moment value needs to be converted to an Arm, see the equation in the section above.
3. Fuel Moment Table Problem
If using a Variable Fuel Station (Fuel Moment Table), enter the values in Moments rather than as Arms. Verify that the fuel moment table units are correct (in-lb). If the Moment is divided by an amount (Moment/100), multiply the Moment by the divisor before entering it into the ForeFlight Fuel Moment Table.
Example of correctly entered Moment values in the Fuel Moment Table.
For more details about setting up a weight and balance profile, see the Weight & Balance in ForeFlight Mobile guide (also available within ForeFlight Mobile under Documents > ForeFlight.)
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