Index
From the above graph, it can be noted that the fuel density variation has a double effect on the fuel vector:
1.
A vertical distortion (weight distortion) increasing with the fuel quantity and affecting points defined in volume (2, 5 and 6)
2.
A horizontal distortion (index distortion) increasing with the tank H-arm compared to HRef and affecting point defined in weight (1, 3 and 4).
C. BALANCE CHART DESIGN
3. OPERATIONAL LIMITS DETERMINATION
3.1. Calculation principle
The determination of the aircraft CG position using a paper or computerised trim sheet is affected by inaccuracy on the influence of item loading on the final aircraft CG position. Furthermore the aircraft CG position changes during flight because of different items moving (landing gear,…)
Before flight the aircraft CG position must be checked against the three certified envelopes. Due to the CG position uncertainties some margins must be determined between the certified envelopes and the ones used on the trim sheet : the operational limits.
On the balance chart the 3 operational limits . Takeoff, Landing and In-flight . are not represented because even if the Takeoff CG position check against its corresponding limit can be done after a manual or computerized computation, the determination of the Landing CG and furthermore the In-flight CG positions on a paper document is much more difficult, it is impossible to check these CG positions against their corresponding CG limits. So on balance charts two operational limits are represented :
. Operational Takeoff limit
. Operational Zero Fuel limit The Zero Fuel limit is determined to ensure that during the whole flight and at landing the aircraft CG remains within the limits.
3.2. Margins determination method
3.2.1. Method
To determine the aircraft ZFW, TOW and CG position during flight one needs to know : . aircraft CG position and weight before loading any item . weight and position of each item loaded on the aircraft (cargo, pax, fuel, any
additional item)
. possible CG movements due to moving items during flight. An inaccuracy on the final CG value can be introduced because of a lack of precision either on item weight, or on its location and/or CG position. The total possible inaccuracy made on CG estimation will result of a combination of all the individual errors :
. due to initial conditions (aircraft DOW and DOCG)
. due to cargo loading
. due to passenger boarding
. due to fuel loading.
In addition to these inaccuracy sources, the method used to determine the aircraft CG may also add an inaccuracy source if it needs index rounding or index interpolation. 中国航空网 www.aero.cn 航空翻译 www.aviation.cn 本文链接地址：Getting to Grips with Aircraft Weight and Balance(60)
