[Paper Summary] Can Ski Jumping Be Changed by "Ankle Angle"? Latest Aerodynamic Research to Increase Flight Distance
The most important point in determining the flight distance of a ski jump is the "flight posture." In particular, the angle of the skis (how they are angled, spread, and tilted) significantly changes the airflow and affects flight distance, stability, and the force applied to the ankles.
The paper introduced here, "Performance and Biomechanics in the Flight Period of Ski Jumping (2022)," uses computational fluid dynamics (CFD) to reproduce the aerodynamic drag, lift, and rotational moments of 125 different ski postures.
"What kind of ski angle allows for the longest flight?"
"How does the ankle angle affect it?"
This is a valuable paper that scientifically clarifies these points. In this article, we will explain the content in an easy-to-understand manner for the general public.
Research Objectives
The objectives of this research are the following three:
To investigate how ski angles affect aerodynamic forces (lift and drag).
To understand from a biomechanical perspective what kind of moments the tilt of the skis (roll angle) creates on the ankles.
To create a database for finding the "optimal ski posture" that leads to the longest flight distance.
Research Methods
1) Using Computational Fluid Dynamics (CFD)
To reproduce "125 types of ski angles," which is difficult in actual wind tunnel experiments, CFD was used to calculate the airflow.
2) Three ski angles examined
Angle of attack (α): The vertical tilt of the skis
Yaw angle (β): The degree of the V-shape spread
Roll angle (γ): The lateral tilt (corresponding to ankle twisting)
3) Wind speed is 30 m/s (108 km/h)
Set to match the speed during an actual jump.
4) Verification of 125 ski posture patterns
α (angle of attack) 0–40°
β (opening) 0–40°
γ (tilt) 0–40°
Thorough analysis of these combinations.
5) Calculated items
Lift: Force pushing upward
Drag: Air resistance
Lift-to-drag ratio (L/D): Most important for flight distance
Pitch, roll, and yaw moments(also related to strain on the ankles)
Research Results
The 'optimal posture' that leads to the greatest flight distance has been clarified
The best performance was achieved at an angle of attack of 30° × opening of 20° × roll of 0°
At this point, lift is maximized and the lift-to-drag ratio (flight distance indicator) is also high.
Influence of angle of attack (α)
Increasing the angle of attack up to 30° increases lift
Exceeding 40° leads to a 'stall,' causing lift to drop sharply
→ 30° is the ideal limit line
Influence of yaw angle (β: V-shape opening)
Opening moderately generates 'vortices,'creating a strong 'low-pressure region (LPR)' on the upper surface of the skis= increased lift!
However... opening too wide (40° or more) has the opposite effect → vortices weaken, and lift drops (stall phenomenon)
Influence of roll angle (γ: left-right tilt)
Conclusion: The more you tilt, the worse it gets
Increased roll angle reduces lift
Lift-to-drag ratio (flight distance) also worsens
Twisting (moment) on the ankle also increases
→ Makes control difficult and puts strain on the body
In other words, the roll angle should be kept as close to 0° as possible
The Importance of the Ankle
In skiing, the ankle angle is strongly related to the 'roll angle.' Since increased roll leads to decreased lift and shorter flight distance, it is necessary to suppress roll through ankle 'inversion' (tilting inward) = Ankle control is essential for increasing flight distance
The research also recommends innovations such as 'attaching curved supports to ski bindings to correct the roll angle.'
Discussion
Why Yaw Angle Increases Lift
When skis are opened in a V-shape, a 'vortex' is generated on the upper surface, expanding the low-pressure area
= The upward suction force (lift) increases.
Why Roll Angle Worsens Performance
When roll increases...
Airflow shifts left and right, weakening the vortex
Low pressure on the upper surface decreases → Lift decreases
Air resistance actually increases
The Ankle Holds the Key to Lift
Adjusting the roll angle equals ankle twisting control. Since decisions during a jump are made in less than a second, daily ankle flexibility, strength, and sensory adjustment are directly linked to performance
Conclusion
To increase flight distance, the optimal ski posture is '30° angle of attack, 20° opening, 0° roll'
A moderate V-shape opening increases lift. However, opening too wide is not recommended
The lateral tilt of the skis (roll angle) reduces lift and worsens flight distance
For roll angle adjustment, ankle manipulation is extremely important
Managing ski angles in 3D significantly improves the quality of aerial posture
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