Weight and Balance

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Weight and Balance

• Dave Horne, CFI
• Shoreline Flying Club

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Objectives

• Understand the effects of weight on an airplane
• Be able to explain how balance affects stability
  and the center of gravity
• Understand the weight and balance terms
• Be able to conduct basic weight and balance
  calculations

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Associated Text

• PHAK
• Chapter 8
• POH
• Section 6

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Why is Weight an Balance Important?

• Wings can only produce so much lift if we are
  too heavy the airplane may not be able to fly
• Increases in weight adversely effect performance
• We must operate within a specified CG limit

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Heavy Airplane Characteristics

• Higher take off speed
• Longer take off run
• Reduced cruising speed
• Reduced maneuvering
• Higher stall speed
• Longer landing roll

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Weight Changes

• Aviation Fuel (100LL) weights 6lbs per gallon
• May reduce fuel load to bring an airplane within
  limits range will be affected with less fuel

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Balance

• Location of the CG
• Point where the airplane would balance if it were
  suspended at that point
• CG shifts around
• We must make sure that it is within allowable
  limits

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Forward CG

• More weight is acting towards the front of the
  airplane
• Control Pressures change
• Tail-Down force
• Increased Stall Speed
• Increase in take off and landing roll

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Aft CG

• Weight of the airplane is acting towards the tail
• Control Pressure
• Shorter t/o roll ? over-rotate
• Stall recovery may be hindered

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Danger Zone

• Operating out of the limits may make the airplane
  impossible to control

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Pre-Flight Actions

• Current WB
• WB for your flight
• Make the necessary changes to bring the airplane
  within CG limits

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Weight Terms

• Licensed Empty Weight is the empty weight of
  the aircraft that consists of the airframe,
  engine(s), unusable fuel, and un-drainable oil
  plus standard and optional equipment as specified
  in the equipment list.

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Weight Terms

• Standard Empty Weight consists of the airframe,
  engines, and all items of operating equipment
  that have fixed locations and are permanently
  installed in the aircraft including fixed
  ballast, hydraulic fluid, unusable fuel, and full
  engine oil.
• Basic Empty Weight includes the standard empty
  weight plus optional and special equipment that
  has been installed.

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Weight Terms

• Fuel
• Usable Fuel fuel which can be used for flight
  planning
• Unusable Fuel fuel which cannot be use in
  flight due to fuel tank design

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Weight Terms

• Miscellaneous Weights
• Useful Load total usable fuel, passengers, and
  cargo
• Maximum Ramp Weight Basic Empty Weight Useful
  Load
• Payload passengers and cargo

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Weight Terms

• Loaded Aircraft
• Maximum Ramp Weight maximum allowable mass for
  ground operations
• Maximum Takeoff Weight maximum allowable mass
  for initiation of takeoff roll
• Maximum Landing Weight maximum allowable mass
  at touchdown
• Gross Weight mass of fully loaded aircraft
• Zero fuel weight everything but fuel, used to
  calculate how fuel the aircraft can carry

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Standard Weights

• Gasoline 6 lbs. per gallon
• Oil 7.5 lbs. per gallon
• Water 8.35 lbs. per gallon

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Balance Terms

• Datum reference base for location of components
• Arm distance from the datum measured along the
  longitudinal axis
• Station position of a specific point in the
  fuselage
• Center of Gravity point of a mass through which
  gravity acts
• Moment tendency of a mass to cause a rotation
  about the Center of Gravity

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Basic WB Math

• Moment Weight X Arm
• Center of Gravity

Sum of All Moments
Gross Weight
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Practice

• Basic Empty weight of the airplane
• 1400 lbs
• Pilot
• 150 lbs
• Co-Pilot
• 185 lbs
• Backseat Passenger
• 120 lbs
• Baggage
• 50 lbs
• Fuel
• 38 gallon tanks useable

• Question
• How much fuel can we take and be within normal
  limits?

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Chart Method

• PA28R 201 Arrow

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Table Method

• Beechcraft B33 Debonair

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Summary

• Calculate your WB to ensure that your CG is
  within normal operating limits
• Extreme CGs both forward and aft will adversely
  affect your performance