The Zero Lift Axis (ZLA) - page 2

In judging - when should we use CGT and when should we use ZLA?

• When the aircraft is flying horizontal lines or curving, rotating or rolling manoeuvres you should judge the aircraft on CENTRE OF GRAVITY TRACK (CGT).
• When we are judging vertical or 45° lines up or down you should use the aircraft ZERO LIFT AXIS (ZLA)
• Note: CGT is therefore used during the course of any rolls placed on vertical or 45° lines.
• For rolls placed on a curve, the curved flight path must continue accurately during the roll.

Tail piece

Be aware that aircraft types whose Zero Lift Axis does not pass centrally through the tail will appear to spiral during a perfect roll - even though the ZLA is bang-on target. The Pitts above shows what to expect.