Chp. 10 Weight and Balance

Arm

horizontal distance from reference datum line to the CG

Basic empty weight

standard of empty weight plus the weight of the optional special equipment that has been installed (the w in ARROW). Some will include the oil.

Datum

vertical line selected by manufacturer where all moment arms and cg is measured 

Licensed empty weight

airframe, engine, unusable fuel, undrainable oil, plus standard and optional equipment

Moment

the weight multiplied by the arm. Expressed in pounds per inches.

Total moment is the total weight multiplied by the distance between the datum and CG.

Payload aka useful load

occupants, cargo, and baggage weight

How much does gasoline weight?

6 pounds per gallon

How much does fuel weight per gallon?

6lbs

MAC means

mean aerodynamic chord - Average distance of leading edge to the trialing edge of wing. Calculated for CG

GAMA means

General aviation management association

Multi-engine weight must be checked every _____

36 months

Effects of forward CG

• Elevator becomes less efficient. 

• Need longer runway to take-off 

• Higher stall speeds

Negative and positive arms exist:

• + if measured after datum 

• - if measured before datum 

• Positive times negative equals negative and is subtracted from total moments

water weighs

8lbs/gallon

oil weighs

7.5lbs/gallon

CG range

distance between forward and aft(back) cg

Maximum ramp weight

greater than the take-off weight, the weight taxied

Moment index

a moment divided to simplify weight

Standard weight

all weight which cannot be moved

Which items are included in the empty weight of an aircraft?

unusable fuel and undrainable oil

Useful load includes:

Passengers, bags, fuel,

Delta in aviation means

is a triangle showing the change of values

floor load limit

maximum weight floor can sustain per square foot

Fuel load

only usable fuel, not fuel to fill the lines or those that get trapped in the tubes

maximum zero fuel weight

maximum weight excluding of usable fuel

Once you have calculated your total moments. With this information you can find the center of gravity by

total moments/ total weight = CG

How to calculate moment change

weight shifted/ total weight = Delta CG/distance weight shifted

formula

moment ontop weight / arm

moment is

what currently is happening to the aircraft when manuvering with weight. It should be within CG limits