Competition Judging

Where do we judge?  (we mean, other than on cold, windy and frequently wet airfields.....!)

All aerobatic figures are judged in and relative to the aerobatic performance zone - we call it the "box". This is nominally a 1,000m cube of air (effectively less 'tall' for any class below unlimited....) with its lower face at 100m above the ground and defined by two land-based axes:

• The "A" or main box axis is aligned with the competition wind (flight along this axis will by definition therefore be either into wind or down wind).

• The "B" or cross box axis is aligned at 90° to the main / "A" axis.

• Ideally, box markers on the ground define the centre and edges of the box.

• The height above the ground of the minimum allowable flying altitude (the "bottom" or "base" of the box) varies depending on the class of competition being flown – highest for Beginners, lowest for Unlimited.

• Judges sit in line with the "B" axis, but set back about 150m from the nearest edge of the box. This gives them the best vantage point to judge the flights.

• The "competition wind" can be from the left or right (always on the main axis) and is declared by the Contest Director or Chief Judge before competition flights start.

• The orientation of the box and the wind direction is important – figures must be flown in the correct direction and on axis, so it is important that judges understand the location and orientation of the box.

If a figure is intended to be flown on the main axis (as indicated by the sequence diagram), any deviations from this orientation of more than 5 degrees are penalised by a downgrade of 1 point per 5 degrees of error seen. This applies both to the main "A" axis and the cross "B" box axis. A figure may start on the main axis and finish on the cross box axis or vice-versa – in each stage of the figure, the correct axis orientation must be maintained.

Figures that start on the main or "A" axis must be flown in the correct direction (into wind or down wind) otherwise the figure is zeroed. This absolute requirement does not apply to figures started on the "B" axis.
Figures that start on the "B" or cross box axis do not have to be flown in a particular direction – although the direction chosen must make sense compared to the sequence diagram.
If a sequence is interrupted (ie. a "break" is taken) before the start of a particular cross box figure then on restarting that figure must be flown in the direction established by the pilot before the break was taken.

Figures that are flown too high, outside the "box" or that start behind the judges are penalised either 'by the book' or under the direction of the Chief Judge. Excursions beyond the four vertical corners of the box are either noted by line judges (sitting on the ground 50m outside the four corners of the box) and penalised accordingly, or are reflected in the Framing mark awarded to a pilot by each judge.

To judge how well - or badly! - the competing aeroplane flies each aerobatic figure we use one or other of two equally important criteria:
a)	Centre of Gravity Track	(explained on this page)
b)	Zero Lift Axis	(explained on the next three pages)
Centre of Gravity Track (CGT)
The Centre of Gravity Track (refer to it as the CGT) is the imaginary line that the aircraft centre of gravity draws as it flies along. Note that the longitudinal neutral axis of the aircraft (i.e. the Zero Lift Axis) almost always points away from this track (in pitch and/or yaw) by an amount which depends on the control inputs of the pilot, the wind, and the speed of the aeroplane - usually with larger angles at slower flying speeds.
•	Imagine the aeroplane condensed into a dot, and watch the path that the dot takes through the sky.
•	This is the Flight Path, or Track of the aeroplanes' Centre of Gravity.
•	Judging the flight path involves comparing the observed CGT path against fixed references such as the horizon or the 'A' or 'B' axes of the box.

Example-1:
The aeroplane is required to transit from a vertical down-line to horizontal flight. Although the ZLA remains horizontal after the 90° corner has been completed, the CGT continues to descend below the required horizontal line.

Example-2:
Here the transit is from a vertical up-line to normal horizontal flight. The CGT must remain in a level horizontal line, whilst the aircraft speed will increase from very slow to normal / fast.

Tip - 'screw your eyes up' and just concentrate on the movement of the blurred dot in the sky without moving your head. You can hold a finger up to where the horizontal line started to give you a fixed reference point for the start of the line. A climbing or descending CGT is usually obvious!

CGT and Angle of Attack Judges must always look at the CGT and not be "fooled" by a high angle of attack at low speed – this can be particularly noticeable when the aeroplane is inverted, as the nose will look un-naturally high.