Weight and balance

Arm, moment, the CG envelope, and shifting weight -- worked with real PHAK numbers from start to finish.

17 min read · The airplane: engine and systems

After this lesson you can

  • Compute the moment of a loaded item and the center of gravity of a fully loaded airplane from a weight-and-arm table.
  • Explain why being under maximum gross weight says nothing about whether the airplane is within its CG limits.
  • Compare the effects of a forward CG and an aft CG on stability, stall speed, and control feel.
  • Use the weight-shift proportion to determine how much weight must move, or how far, to bring a loaded airplane back within limits.

An overloaded or badly balanced airplane will often still fly. That is exactly what makes the problem dangerous: nothing warns a pilot during taxi or the first part of the takeoff roll, and the degradation shows up precisely when there is the least margin to deal with it -- late in the takeoff roll, or in the flare.

Two separate quantities are at stake. Total weight governs takeoff distance, climb performance, and stall speed. How that weight is distributed governs stability and how much elevator authority remains. An airplane can be safely under its maximum weight and still be outside its CG envelope, or the reverse.

14 CFR 23.23 requires the manufacturer to establish the weight and CG ranges within which the airplane can be operated safely, and 14 CFR 91.9 requires the pilot in command to comply with the limitations in the approved flight manual. Part 91 does not require a written calculation before every single flight -- it requires the result: a legally loaded airplane, however that confidence is reached.

The rest of this lesson

  1. 1.What an overweight or out-of-balance condition costs
  2. 2.The standardized vocabulary
  3. 3.Arm, moment, and the balance point
  4. 4.Standard weights for fuel and oil
  5. 5.A complete worked example: the computational method
  6. 6.The graph and table methods
  7. 7.Forward CG versus aft CG
  8. 8.Shifting, adding, and removing weight
  9. 9.Multiple weight limits, and how CG moves during a flight

These 9 sections, their figures, the checks along the way and the end-of-lesson quiz come with the PPL track. Paid once, yours for good.

See what the PPL track costsEvery module 1 is free to read, no account, no card.

Key terms

Try to recall each definition before turning the card.