PhD, Associate Professor A.I. Popova¹
G.Yu. Prokopenko¹
Postgraduate student E.D. Klimov^1
1Tchaikovsky State Institute of Physical Culture, Tchaikovsky

Keywords: ski jumping, flight phase, air flow, wind tunnel, flight simulator.

Background. Simulation practices and equipment are increasingly used by the modern ski jumping training systems for technical progress facilitation purposes like in many other sport disciplines. Focuses, intensities and technicalities of the trainer system assisted exercises will be prudently managed to facilitate individual ski jumping progresses. Thus, the main emphasis on short trampolines is generally made on the acceleration and take-off stance and skills, whilst on long trampolines the trainings give a special priority to the flight phase techniques. Individual progresses in the flight control skills and the progress facilitating training tools have always been ranked among the top priorities by the ski jumping researchers.

Objective of the study was to provide theoretical grounds for a wind tunnel trainer systems for modern ski jumping sport to effectively improve the flight control skills.

Methods and structure of the study. One of our key research methods was the analysis of the relevant theoretical and practical literature; with the theoretical analysis taking into account the designs of modern trampolines for ski jumping competitions and our practical ski jumping elite coaching experiences.

Results and discussion. It should be emphasized that the existing flight control skills mastering toolkit has certain limitations as the relevant flight modeling exercises give little means for the athlete to “feel the air” and effectively control it – as is the case in a real ski jumping sequence. Only highly experienced ski jumping elite is able to safely ride on the air flow keeping the right body angle and helping by the footwork and ski control skills – although even the top masters are not always stable and successful in their long jumps. When the athletes make a transition to a higher and longer trampoline, they are known to face multiple problems both in the technical and psychological aspects due to the radical changes in the flight controls and airflow speed, density and profile/ variability. Modern ski jumping training systems need to be effectively customized to not only the jump phase structure but also the new outfits and trampoline profiles, and this is the reason why different technical accessories and training simulators are increasingly used in the sport – with the wind tunnels apparently gaining a special popularity in the ski jumping elite training models [1, 2, 5, 6].

Such tunnels are generally designed to generate a stable air flow by air fans within some limited space – mostly an oval/ round tunnel. The more blades the air fan has, the more stable is the air flow – that is a key condition for the wind tunnel trainer system quality. The wind tunnel trainers may be horizontal or vertical; although the horizontal 3-4m diameter tunnels with the wind speeds of 95-120 km/h (26-30 m/s) are deemed to most closely mimic the real ski jumping flights and, therefore, dominate in the wind tunnel trainer system designs. Fully equipped athletes are suspended in the tunnel and air flow is controlled so that to simulate the real trampoline-specific flight conditions [2]. It should be emphasized, however, that the flight conditions simulated by the wind tunnel air flows often differ from the real ones: see Figures 1-2.

Thus, as was found by a few studies, in a real trampoline jump the skier flies along the landing surface keeping the air flow to horizon angle at about 36°, with the flow attack angle being varied in the flight phase. Moreover, the take-off angle may vary from 8° to 11.5° depending on the trampoline length and profile: e.g. on the K-90m and K-120 trampolines the take-offs were tested to vary from 8° to 6°, with the airflow attack angles in the flight phase varying from 25° to 36° [3, 4].

Figure 1. Airflow attack angle in the horizontal wind tunnel trainer

Figure 2. Natural airflow in a trampoline ski jump

As demonstrated by Figure 3, in a real jump the elite ski jumper’s skies and body are kept virtually horizontal to maintain the optimal aerodynamic flight control stance; whilst in the wind tunnel trainer system the body position is different versus the horizon (see Figure 1); and this is the reason why the wind tunnel training practices are rather limited in many real flight simulation aspects.

Figure 3. Airflow attack angles tested at К-90 and К-120 trampolines during the 2002 Olympic Games in Salt Lake City (Schmölzer & Müller, 2004)

Note that the airflow to horizon angles on the take-offs on the long trampolines make up 10-11.5° to further grow to 36-38° in the flight up to the landing point. Ideally, the wind tunnel ski jumping training systems shall vary the air flow angles and speeds to closely mimic the real flight and help the athletes better feel the natural airflow to train the body control aerodynamics. Practical solutions to simulate the real airflows as close as possible may differ: they may use special flow deflection blades inside the tunnel or tilt the tunnel to the air flow, or use a varied-angle modular platform, etc. Despite some practical complications, such solutions appear quite feasible as demonstrated by the world-only Indoor Wingsuit wind tunnel trainer system with the airflow angle of 35°- that was commissioned in 2017 in Stockholm for training parachutists in special glider outfits.

Presently every popular parachuting sport training system uses wind tunnel trainer systems, with more than 20 wind tunnels having been put into operation in Russia for the last decade only. Thus in 2018 six indoor wind tunnel systems were commissioned in Saint Petersburg, Miass, Tyumen and Orenburg cities. The growing popularity of the wind tunnel applications for flight trainings cannot but involves the modern ski jumping sport. As soon as such systems are introduced in the ski jumping elite trainings, they will undoubtedly give a new impetus for the training process. The controlled-air-flow wind tunnel trainer systems will effectively help train the air flow control skills for long trampoline jumps. One of the vertical wind tunnel systems, for example, was customized for the ski jumping trainings: see Figure 4.

Figure 4. Vertical wind tunnel trainer system for ski jumpers

This flight simulator (Figure 4) system is versatile enough for application by athletes of various skill levels. The real flight modeling by this simulator system is secured by variations in the air flow direction and speed but also by the virtual reality glasses. The air flow is so synchronized with the glass images that the athlete perfectly feels the air and fast masters the jumping skills, with special benefits for the mental conditioning in the stressful transition to a longer trampoline. This flight simulator system may be customized to model the trampoline-specific air flows to effectively facilitate the individual mental adaptation for the new jumping environment. The system helps advance the movement coordination skills in the simulated conditions fairly close to reality; and may be customized to train some critical elements including the flight-point-specific muscular controls, footwork, takeoff and flow control in the climb, descend and landing phases, with a special focus on the flow disturbance/ gusts control actions.

Conclusion. New customizable wind tunnel trainer systems are of great promise for the modern ski jumping training methods. The ski jumping community shall take special efforts to design and use modern aerodynamic simulator systems with versatile air flow control (direction and speed variation) units to mimic as close as possible the trampoline-specific ski jumping air flows and facilitate progress in the ski jumping skills.

References

1. Brady H. Digital Experiences. Go for Gold: Olympic Aerodynamics [Electronic resource]. Available at: https://airandspace.si.edu/stories/editorial/go-gold-olympic-aerodynamics (date of access: 23.02.2018).
2. Chowdhurya H., Alama F., Mainwaringb D. Aerodynamic study of ski jumping suits. 5th Asia-Pacific Congress on Sports Technology (APCST) [Electronic resource]. Available at: https://core.ac.uk/download/pdf/81220142.pdf (date of access:  16.05.2011).
3. Md Abdullah Al Harun Khan Chowdhury. Aerodynamics of Sports Fabrics and Garments. A thesis submitted in fulfilment of the requirement for the degree of Doctor of Philosophy. School of Aerospace, Mechanical and Manufacturing Engineering. RMIT University, Melbourne, Australia, March, 2012.  195 p.
4. Schmölzer B., Müller W. Individual flight styles in ski jumping: results obtained during Olympic Games competitions. Journal of biomechanics.  2004. no.38. ppp. 1055-1065.
5. Virmavirta M., Kivekдs J., Komi P. Ski Jumping Takeoff in a Wind Tunnel With Skis. Journal of Applied Biomechanics.  2011. no. 27. pp. 375-379.
6. Yamamoto K., Tsubokura M., Baleriola S., Onishi K. Effect of postural change on the aerodynamic characteristics during takeoff in ski jumping.  34th International Conference on Biomechanics in Sport. Tsukuba, Japan 18-22 July 2016 [Electronic resource]. Available at: http://lasbim.taiiku.tsukuba.ac.jp/isbs2016-program/papers/o1603276_effect of postural change on the aerodynamic characteristics during takeoff in ski jumping.pdf (date of access:  04.08.2019).

Corresponding author: ski@chifk.ru

Abstract

Objective of the study was to provide theoretical grounds for a wind tunnel trainer systems for modern ski jumping sport to effectively improve the flight control skills.

Methods and structure of the study. One of our key research methods was the analysis of the relevant theoretical and practical literature; with the theoretical analysis taking into account the designs of modern trampolines for ski jumping competitions and our practical ski jumping elite coaching experiences.

Results and conclusions. Modern ski jumping training systems need to be effectively customized to not only the jump phase structure but also the new outfits and trampoline profiles, and this is the reason why different technical accessories and training simulators are increasingly used in the sport – with the wind tunnels apparently gaining a special popularity in the ski jumping elite training models.

The growing popularity of the wind tunnel applications for flight trainings cannot but involves the modern ski jumping sport. As soon as such systems are introduced in the ski jumping elite trainings, they will undoubtedly give a new impetus for the training process. The controlled-air-flow wind tunnel trainer systems will effectively help train the air flow control skills for long trampoline jumps.

New customizable wind tunnel trainer systems are of great promise for the modern ski jumping training methods. The ski jumping community shall take special efforts to design and use modern aerodynamic simulator systems with versatile air flow control (direction and speed variation) units to mimic as close as possible the trampoline-specific ski jumping air flows and facilitate progress in the ski jumping skills.