by George S. Rossano
Air position with a straight rotation axis.
Angles as perceived by an observer are not what they appear.
This detail of the jump landing is taken from the last image at bottom right. It gives the appearance of a jump perilously close to being under-rotated.
The red line has been added perpendicular to the line of flight. A landing with the foot on the red line, or farther clockwise, would appear to meet the definition of under-rotated; i.e., perpendicular to the line of flight or past that, and thus missing one-quarter rotation or more.
Angles, however, are distorted by projection effects from the viewing angle of the observer. In reality, any foot position up to the short yellow line would be less than one-quarter rotation short of the line of flight for this jump.
Downgrade calls with the blade along the line of sight are unambiguous for all viewing angles, but under-rotation calls cannot be accurately made without taking into account the line of sight of the viewer.
Projection effects are worse the closer the viewer is to ice level and also depends on the orientation of the line of flight relative to the line of sight of the observer. Thus, the correction for projection effects is specific to the geometry of each jump and the location of the observer.
Current replay systems do not take into account projection effects when used to determine under-rotation calls in competition. An additional complication is that the viewing angle of the Technical panel in real-time is significantly different from the viewing angle of the replay camera.
(24 February 2020) The ISU is currently willing to give full credit to quad attempts no matter how little rotation they really have, as long as they give the illusion of a quad and are not under-rotated on the landing. So much so, you might come to think fully rotated quads just can't be done.
But that isn't the case.
We present here as an example, a quad Salchow executed by Yuzuru Hanyu in the Short Program of the 2019 Grand Prix Final that illustrates the geometry of a fully rotated quad. It doesn't get much better than this when it comes to complete rotations. This jump was 0.76 sec in the air, and ever so slightly under 3 3/4 rotations in the air. (1)
Fully rotated quads, where we define fully rotated to be near one-quarter rotation short of integer rotation, are not only achievable in theory, they are actually being executed by some of the best jumpers.
Due to the difficulty of a true quad compared to a triple, the high point values for quads in the Scale of Values compared to triples is warranted for jumps that are complete. Skaters who take shortcuts through pre-rotation, however, should not be rewarded with the same base points for doing a less difficult attempt, nonetheless called as a complete quad, that might only have 3 1/4 rotations in the air - though unfairly they currently are.
(1) Fully rotated Sachows do not have an integer number of rotations in the air. Due to the motion of throwing the free leg to the side across the skating leg during the takeoff, as the skater remains on a back inside edge, the jump takes off somewhat to the side instead of directly backwards. Fully rotated Salchows are near one-quarter rotation short of integer rotations, generally about one-eighth short each on the takeoff and landing, as was the case in this example.
(2) We define the air rotation efficiency to be the average rotation rate from takeoff to landing divided by the maximum rotation rate. Values of 0.8 to 0.9 are typical for skaters.
(3) If the skater were to refine the air position, a peak rotation rate of 6.5 rotations per second is within grasp. Food for thought: 6.5 rotations per second + 85% air rotation efficiency + 0.78 seconds air time + an acceptable one-quarter pre-rotation = quad Axel.
Text and all photos Copyright 2020 by George S. Rossano