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Weights & Balances

Weights & Balances. Moment:. www.GeoffHatcher.com. Moment:. Torque. Torque and moment are expressed in in-lbs or ft-lbs. The measure of the distribution of mass or force relative to a given axis. (datum plane). Force x leverage(moment arm) = torque. Weight x Moment Arm = Moment.

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Weights & Balances

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  1. Weights & Balances Moment: www.GeoffHatcher.com

  2. Moment: Torque Torque and moment are expressed in in-lbs or ft-lbs The measure of the distribution of mass or force relative to a given axis. (datum plane) Force x leverage(moment arm) = torque Weight x Moment Arm = Moment www.GeoffHatcher.com

  3. Moment:The measure of the distribution of mass relative to a datum line. Mass x arm= moment One pound placed I foot from the datum….. If it is moved a foot further from the datum line….. It’s moment would increase to 2 foot pounds (2 ft·lbs) has a moment of one foot pound (1 ft·lb ) www.GeoffHatcher.com

  4. Mass x arm = moment Left side 20 X -4 = -80 Right side 20 x 4 = 80 Balance Bar 10 X 0 = 0 Total 50 0 ÷ 50 =0 Total Moment ÷ Total weight = center of gravity We use the formula Mass x arm = moment Finding a 3000 pound aircrafts balance point requires mathmatics because you can’t very well pick it up and balance the thing on your fingers. www.GeoffHatcher.com

  5. Mass x arm = moment Left side 20 X -4 = -80 Right side 20 x 6 = 120 Balance Bar 10 X 0 = 0 Total 50 40 ÷ 50 = .8 Moment÷ weight= arm center www.GeoffHatcher.com

  6. It’s important to notice that the placement of the datum line can be anywhere you want as long it is consistent throughout the calculations. • The Datum line is never the actual C.G. because it is constantly shifting. Mass x arm = moment Left side 20 X 2 = 40 Right side 20 x 10 = 200 Balance Bar 10 X 6 = 60 Total 50 300 ÷ 50 = 6 Total Moment ÷ total weight = total moment arm Center of gravity www.GeoffHatcher.com

  7. The Datum on an Aircraft is usually placed at the fire wall, the nose, or the base of the nose cone to avoid the complex arithmetic associated with negative numbers. Each Area of the plane is assigned a “station” according to how many inches away it is from the datum Negative numbers can cause spatial disorientation, in many pilots. 2,179 lbs at 41” moment 89,609 in·lbs Stations Forward seats 42 Fuel Tanks 52 middle seats 76 rear seats 101 rear baggage 128 The aircraft is drained of fuel and oil and its empty weight and C.G is determined. www.GeoffHatcher.com

  8. Mass X arm = moment Aircraft 2,179 lbs X 41 = 89,609 Forward seats 400 lbs X 42 = 16,800 Middle seats 400 lbs X 76 = 30,400 Rear seats 200 lbs X 101 = 20,200 Baggage 100 lbs X 128 = 12,800 Center of gravity Fuel 516 lbs X 52 = 26,832 Total 3,795lbs 196,641 ÷ 3795 = 51.82” Total Moment ÷ total weight = total moment arm www.GeoffHatcher.com

  9. Weight shift Problem Mass X arm = moment Aircraft 2,179 lbs X 41 = 89,609 Forward seats 400 lbs X 42 = 16,800 Middle seats 400 lbs X 76 = 30,400 Rear seats 200 lbs X 101 = 20,200 Baggage 100 lbs X 128 = 12,800 Center of gravity Fuel 516 lbs X 52 = 26,832 Total 3,795lbs 196,641 ÷ 3795 = 51.82” Total Moment ÷ total weight = total moment arm www.GeoffHatcher.com

  10. Weight shift Problem Lets drop off one of the two middle passengers (200 lbs) and move a rear passenger (150 lbs) to the middle. Mass X arm = moment 3,795 lbs 196,641 -200 lbs X 75 = -15,000 Passenger gets out of middle -150 lbs X 101 = -15,150 Passenger gets out of back 150 lbs X 75 = 11,250 And moves to the middle ÷ 3595 = 49.4 Total weight 3595 lbs 177741 Total Moment ÷ total weight = total moment arm www.GeoffHatcher.com

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