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Understanding Mass and Balance in Aviation

Dec 2, 2024

Mass and Balance in Aviation

Introduction

  • Lecturer: Grant
  • Class: Fourth in the Mass and Balance series
  • Topics: Cargo loading, calculating forces, moments, center of gravity (CG)

Cargo Loading Limitations

  1. Max Load:
    • Maximum weight/mass in cargo hold
  2. Max Linear Load:
    • Load along a unit length of cargo floor
    • Measured in kg/m or lbs/ft
  3. Max Area Load:
    • Load per unit area of floor
    • Measured in kg/m² or lbs/ft²

Example Calculation for Box Load

  • Box Dimensions: 1ft x 2ft x 3ft
  • Max load: 250kg, Box weight: 50kg (No max load issue)
  • Area Calculations:
    • Area 1: 0.215 m²
    • Area 2: 0.323 m²
    • Area 3: 0.645 m²
  • Load per Area:
    • Area 1: 232.56 kg/m² (Exceeds limit)
    • Area 2: 154.78 kg/m² (Exceeds limit)
    • Area 3: 77.52 kg/m² (Acceptable)

Importance of Cargo Placement

  • Centre of Gravity (CG):
    • Intersection of aircraft's rotation axes
    • Comparable to a seesaw (teeter-totter)
  • CG Movement:
    • Affects aircraft control
    • More load at front/back shifts CG respectively

Example of CG Issues

  • National Airlines 102:
    • Cargo shifted, moved CG aft, caused uncontrolled pitch moment

Understanding Moments

  • Moment:
    • Causes rotation, expressed as force x distance
    • Positive (clockwise), Negative (anti-clockwise)

Example Calculation

  1. Seesaw Balance:
    • Mike: 70kg, 2m from center
    • Jenny: 50kg, X meters from center
    • Equation: 70 x 2 = 50 x X => X = 2.8m

Aircraft Forces and Moments

  • Forces:
    • Thrust: Forward from engines
    • Weight: Down from CG
    • Lift: Through center of pressure
    • Drag: Through center of pressure

Balancing Moments

  • Example Aircraft Calculation:

    • Mass: 10,000 kg
    • Lift: 98,100 N
    • Thrust: 100,000 kN
    • Drag: 50,000 N

    Moment Balance:

    • Clockwise (Thrust): 100,000 N * 1m = 100,000 Nm
    • Anti-clockwise (Lift): 98,100 N * 2m = 196,200 Nm
    • Adjustment Needed: 96,200 Nm from tail, needing 13,742.86 N force

Tail's Role in Balance

  • Counter Moment:
    • Tail adjusts for balance
    • CG position affects tail effectiveness

Summary

  • Cargo Loading: Max load, linear load, and area load limitations
  • CG Range: Must be within fixed limits for stability
  • Moments: Balance moments to prevent unwanted rotation
  • Aircraft Dynamics: CG and center of pressure interaction affects flight stability

Full transcript