Transition Distance Notes

Transition Distance

Definition

  • Transition distance is the distance an aircraft travels from the point of touchdown (main wheels contacting the ground) to the point where full braking configuration is achieved (nose gear touching the ground).
  • Denoted as S_T.
  • Touchdown speed is typically around 1.15 times the stall speed, derived from flight tests.

Factors Affecting Transition Distance

  • Auto Speed Brake System:
    • If equipped, auto speed brakes extend automatically upon main gear touchdown.
    • Activation occurs rapidly (within a few tenths of a second).
  • Manual Brake Activation:
    • Manual brake operation by the pilot takes at least one second, often longer.
  • Speed Decay:
    • The rate of speed decay during the transition phase significantly impacts the distance.
    • Established through flight testing.

Calculation Method

  1. Initial Speed (Touchdown Speed):

    • Determined by flight test data.
    • Example: 126 knots.

  2. Speed Decay Factor:

    • Obtained from flight test data.
    • Example: 0.9813.

  3. Brakes-On Speed (Speed at End of Transition):

    • Calculated by multiplying the touchdown speed by the speed decay factor.
    • V{\text{brakes-on}} = V{\text{touchdown}} \times \text{Speed Decay Factor}
    • Example: 126 \text{ knots} \times 0.9813 = 123.6 \text{ knots}

  4. Average Transition Speed:

    • Calculated by averaging the touchdown speed and the brakes-on speed.
    • V{\text{avg}} = \frac{V{\text{touchdown}} + V_{\text{brakes-on}}}{2}
    • Example: V_{\text{avg}} = \frac{126 \text{ knots} + 123.6 \text{ knots}}{2} = 124.8 \text{ knots}

  5. Convert to Meters Per Second:

    • Convert the average speed to meters per second (m/s) for standard units.
    • Example: 124.8 \text{ knots} = 64.2 \text{ m/s}

  6. Transition Time:

    • Obtained from flight test data.
    • Example: 1.2 seconds.

  7. Transition Distance:

    • Calculated by multiplying the transition time by the average transition speed.
    • ST = \text{Transition Time} \times V{\text{avg}}
    • Example: S_T = 1.2 \text{ s} \times 64.2 \text{ m/s} = 77.04 \text{ m}