Every once in a while a speed skydiving score will show a higher speed than the raw max speed. This post explains why that’s correct — even if it doesn’t look quite right.
Speed skydiving scoring method
Section 5.5 of the FAI ISC Speed Skydiving Competition Manual defines: The score for a Speed Skydiving jump is the average vertical speed in kilometres per hour, to the nearest hundredth of a km/h, of the fastest 3 seconds, which the competitor achieves within the performance window.
The SSScoring API, FlySightViewer, SkyDerby, and all other scoring software use the difference in elevation at the start and end of each 3-second window, then divide that by time, to determine the 3-second window score. None of the tools uses the SMD’s vertical velocity for speed skydiving scoring. Some of the implementers have disagreed over time, but in the end we abide by the ISC rules and feedback from the judges. Vertical velocity is only used to calculate the vertical speed accuracy according to ISC rules in m/s to determine if the score is accurate or a re-jump is required.
Maximum speed
The maximum speed reported is the maximum value recorded in the time series of data points from exit until the end of the skydive. There can be a discrepancy in the max speed because the speeder can cover a slightly longer linear distance during the highest scored 3-second window, a linear and idealized value. Assuming that the SMD has locks on enough satellites and that the speed accuracy calculation is below the threshold, this result is considered accurate. The max speed is evaluated separately from the scoring value in competition terms, and can be used to establish state, national, continental, or world free fall speed records — NOT speed skydiving records.
Analysis
The performance plot shows the speed score green cross a few dots and 4 km/h above the reported speed curve — because it reflects the scoring calculation result as described earlier. The red diamond shows the time when the maximum instant free fall speed was reached, along the speed line. The discrepancy is more obvious when using the SSScore zoom tool to view both values next to one another.
Conclusion
Analyzing and interpreting speed skydiving data takes practice and understanding of the different rules applied to a jump’s results. It’s not hard, but it requires exploring the data and understanding the rules. That’s also why SSScore features the detailed jump data and all the 3-second sliding windows.
Comparing both datasets shows that the maximum score was achieved at 20.6 seconds from exit, while maximum effective speed was reached at 23.4 seconds from exit, at the right edge of the last 3-second window (20.6 to 23.4; the window closes at 23.6).
Please let me know your questions and comments — until next time: blue skies, go fast, and safety third!