- Email: [email protected]
Inclined Wind Tunnel for the Study of Human and Large Animal Flight
WILDERNESS & ENVIRONMENTAL MEDICINE, ], ]]]–]]] (2016)
Letters to the Editor Inclined Wind Tunnel for the Study of Human and Large Animal Flight To the Editor: Wingsuit fatalities are increasing to epidemic levels. A major risk factor is flight path miscalculations.1 Future
areas of research should examine flying and training techniques, and it would be highly desirable if wingsuit flight training for both beginners and experts could be undertaken in a safe environment enabling detailed evaluations. A candidate technology for creating such an environment is the wind tunnel. The use of horizontal wind
Figure 1. Sustained human flight. On May 22, 2016, using a small wingsuit, one of the authors (70 kg, 1.79 m) was able to take off from the floor into sustained (40 s) flight in a large inclined wind tunnel having an airflow of 27 m/s directed obliquely upwards at an adjustable angle relative to the direction of gravitational acceleration.
2 tunnels to simulate flight of anchored wing profiles has played a central role in the development of aircraft. Another type of wind tunnel is the vertical, in which gas flows directly opposite to the direction of gravitational acceleration, creating a force equilibrium at which untethered objects float on the pillar of ascending air; among applications are rotameters2 and skydiving simulators.3 Neither horizontal nor vertical wind tunnels can accommodate actual flight. A third type of wind tunnel is the inclined tunnel, with airflows directed obliquely upward, allowing sustained gliding flight. Using small wind tunnels that are tiltable as a whole, the flight of small animals has been studied.4,5 Further biology research is frustrated by physical dimensions and achievable flows, but variable inclination wind tunnels of greater capacity are difficult to construct with existing technology, since weight and size of recirculating wind tunnel systems limit what is feasible to tilt in its entirety. Using existing technology, it is virtually impossible to design training facilities for wingsuit flight. We hypothesized that by attaching a “bending knee” segment, having an adjustable relative inclination to a fixed (horizontal/vertical) recirculating wind tunnel system, capacity limitations can be mitigated since the rest of the recirculating system may be designed for maximum performance, regardless of dimensions or weight. By “stretching or bending” the “knee” and, simultaneously, adjusting the gas flow, conditions enabling sustained gliding flight in a controlled environment at a great range of angles of attack and airspeeds would be achievable. We also hypothesized that a “bending knee” segment can be attached (retrofitted) to any of the many existing horizontal or vertical recirculating wind tunnel systems in use today, facilitating a fast and inexpensive implementation. To test these hypotheses, we retrofitted a large horizontal wind tunnel with a proof-of-concept, variable angle, inclined test section of a design based on available wingsuit aerodynamics literature.6 After trials in a specially designed safety system, on May 22, 2016, the principal author (70 kg, 1.79 m) was able to take off from the floor into sustained (40 s) wingsuit flight, demonstrating the basic functionality of the technology (Figure 1). We invite wingsuit pilots to consider its possible use in flight training but must emphasize that wingsuit flying in a wind tunnel never can foster the parachuting skills necessary for backcountry BASE jumping.
Letters to the Editor
Figure 2. Flying skills developments. During aerodynamic analysis of the proof-of-concept inclined wind tunnel system, the authors (who had never flown a wingsuit before the start of the project) have made a number of flights in it themselves, noting considerable developments in flying skills. On July 18, 2016, two of the authors were able to maintain sustained flight side by side in an airflow of 25 m/s, gently touching the walls of the tunnel with their hands at will, as well as shake hands, while flying.
Nevertheless, based on the considerable flying skills developments observed among ourselves during work with aerodynamic analysis of the proof-of-concept section (Figure 2), it is suggested that variable inclination wind tunnels may provide desirable conditions for comparably safe and efficient wingsuit flight training. It is quite possible that ambitious wingsuit flying indoors may lead to the development of yet-unknown, tunnelspecific flight techniques; the transferability of such skills, and their interaction with new suit designs, to outdoor wingsuit flying remains to be systematically investigated, including the classic question of landing a wingsuit without a parachute.1 Wearable gyroscopes may be of some benefit in such studies. The testing of new wingsuit designs under comparably safe and controlled conditions may enable manufacturers to improve both performance and safety of future glide ratio–enhancing garments. Human flight with—or, given higher airspeeds, without—wingsuits in a controlled environment may enable biomechanics studies, and it seems reasonable to assume that variable inclination wind tunnels of greater capacity may spur developments in animal flight research, such as the study of greater wingspans and airspeeds, flocking behavior, and aspects of flapping-wing flight. The possibility is also raised for developments in vehicle flight research, as well as training and research in sports having aerodynamics variables (eg, Nordic ski jumping).
Letters to the Editor
3
Anton Westman, MD, PhD The Motion Laboratory, Karolinska Institutet, Department of Neurobiology, Care Sciences and Society, Division of Physiotherapy, Stockholm, Sweden E-mail address: [email protected] Peter Georén, PhD Integrated Transport Research Lab, Royal Institute of Technology (KTH), and Inclined Labs, Stockholm, Sweden Johan Strömberg Inclined Labs, Stockholm, Sweden
References 1. Mei-Dan O, Monasterio E, Carmont M, Westman A. Fatalities in wingsuit BASE jumping. Wilderness Environ Med. 2013;24:321–327.
2. Foregger R. The rotameter and the waterwheel. Anaesthesist. 2001;50:701–708. 3. Metni N, Kitchen W, Mort K. Recirculating vertical wind tunnel skydiving simulator. US patent US 7156744 B2 2007. 4. Pennycuick C, Alerstam T, Hedenström A. A new lowturbulence wind tunnel for bird flight experiments at Lund University, Sweden. J Exp Biol. 1997;200:1441–1449. 5. Henningsson P, Spedding GR, Hedenström A. Vortex wake and flight kinematics of a swift in cruising flight in a wind tunnel. J Exp Biol. 2008;211(Pt 5):717–730. 6. Robson G, Andrea RD. Longitudinal stability analysis of a jet-powered wingsuit. Proceedings of the AIAA Guidance, Navigation, and Control Conference. August 2–5, 2010; Toronto, Ontario, Canada. American Institute of Aeronautics and Astronautics AIAA 2010-7512:1–9.
Letters to the Editor Inclined Wind Tunnel for the Study of Human and Large Animal Flight To the Editor: Wingsuit fatalities are increasing to epidemic levels. A major risk factor is flight path miscalculations.1 Future
areas of research should examine flying and training techniques, and it would be highly desirable if wingsuit flight training for both beginners and experts could be undertaken in a safe environment enabling detailed evaluations. A candidate technology for creating such an environment is the wind tunnel. The use of horizontal wind
Figure 1. Sustained human flight. On May 22, 2016, using a small wingsuit, one of the authors (70 kg, 1.79 m) was able to take off from the floor into sustained (40 s) flight in a large inclined wind tunnel having an airflow of 27 m/s directed obliquely upwards at an adjustable angle relative to the direction of gravitational acceleration.
2 tunnels to simulate flight of anchored wing profiles has played a central role in the development of aircraft. Another type of wind tunnel is the vertical, in which gas flows directly opposite to the direction of gravitational acceleration, creating a force equilibrium at which untethered objects float on the pillar of ascending air; among applications are rotameters2 and skydiving simulators.3 Neither horizontal nor vertical wind tunnels can accommodate actual flight. A third type of wind tunnel is the inclined tunnel, with airflows directed obliquely upward, allowing sustained gliding flight. Using small wind tunnels that are tiltable as a whole, the flight of small animals has been studied.4,5 Further biology research is frustrated by physical dimensions and achievable flows, but variable inclination wind tunnels of greater capacity are difficult to construct with existing technology, since weight and size of recirculating wind tunnel systems limit what is feasible to tilt in its entirety. Using existing technology, it is virtually impossible to design training facilities for wingsuit flight. We hypothesized that by attaching a “bending knee” segment, having an adjustable relative inclination to a fixed (horizontal/vertical) recirculating wind tunnel system, capacity limitations can be mitigated since the rest of the recirculating system may be designed for maximum performance, regardless of dimensions or weight. By “stretching or bending” the “knee” and, simultaneously, adjusting the gas flow, conditions enabling sustained gliding flight in a controlled environment at a great range of angles of attack and airspeeds would be achievable. We also hypothesized that a “bending knee” segment can be attached (retrofitted) to any of the many existing horizontal or vertical recirculating wind tunnel systems in use today, facilitating a fast and inexpensive implementation. To test these hypotheses, we retrofitted a large horizontal wind tunnel with a proof-of-concept, variable angle, inclined test section of a design based on available wingsuit aerodynamics literature.6 After trials in a specially designed safety system, on May 22, 2016, the principal author (70 kg, 1.79 m) was able to take off from the floor into sustained (40 s) wingsuit flight, demonstrating the basic functionality of the technology (Figure 1). We invite wingsuit pilots to consider its possible use in flight training but must emphasize that wingsuit flying in a wind tunnel never can foster the parachuting skills necessary for backcountry BASE jumping.
Letters to the Editor
Figure 2. Flying skills developments. During aerodynamic analysis of the proof-of-concept inclined wind tunnel system, the authors (who had never flown a wingsuit before the start of the project) have made a number of flights in it themselves, noting considerable developments in flying skills. On July 18, 2016, two of the authors were able to maintain sustained flight side by side in an airflow of 25 m/s, gently touching the walls of the tunnel with their hands at will, as well as shake hands, while flying.
Nevertheless, based on the considerable flying skills developments observed among ourselves during work with aerodynamic analysis of the proof-of-concept section (Figure 2), it is suggested that variable inclination wind tunnels may provide desirable conditions for comparably safe and efficient wingsuit flight training. It is quite possible that ambitious wingsuit flying indoors may lead to the development of yet-unknown, tunnelspecific flight techniques; the transferability of such skills, and their interaction with new suit designs, to outdoor wingsuit flying remains to be systematically investigated, including the classic question of landing a wingsuit without a parachute.1 Wearable gyroscopes may be of some benefit in such studies. The testing of new wingsuit designs under comparably safe and controlled conditions may enable manufacturers to improve both performance and safety of future glide ratio–enhancing garments. Human flight with—or, given higher airspeeds, without—wingsuits in a controlled environment may enable biomechanics studies, and it seems reasonable to assume that variable inclination wind tunnels of greater capacity may spur developments in animal flight research, such as the study of greater wingspans and airspeeds, flocking behavior, and aspects of flapping-wing flight. The possibility is also raised for developments in vehicle flight research, as well as training and research in sports having aerodynamics variables (eg, Nordic ski jumping).
Letters to the Editor
3
Anton Westman, MD, PhD The Motion Laboratory, Karolinska Institutet, Department of Neurobiology, Care Sciences and Society, Division of Physiotherapy, Stockholm, Sweden E-mail address: [email protected] Peter Georén, PhD Integrated Transport Research Lab, Royal Institute of Technology (KTH), and Inclined Labs, Stockholm, Sweden Johan Strömberg Inclined Labs, Stockholm, Sweden
References 1. Mei-Dan O, Monasterio E, Carmont M, Westman A. Fatalities in wingsuit BASE jumping. Wilderness Environ Med. 2013;24:321–327.
2. Foregger R. The rotameter and the waterwheel. Anaesthesist. 2001;50:701–708. 3. Metni N, Kitchen W, Mort K. Recirculating vertical wind tunnel skydiving simulator. US patent US 7156744 B2 2007. 4. Pennycuick C, Alerstam T, Hedenström A. A new lowturbulence wind tunnel for bird flight experiments at Lund University, Sweden. J Exp Biol. 1997;200:1441–1449. 5. Henningsson P, Spedding GR, Hedenström A. Vortex wake and flight kinematics of a swift in cruising flight in a wind tunnel. J Exp Biol. 2008;211(Pt 5):717–730. 6. Robson G, Andrea RD. Longitudinal stability analysis of a jet-powered wingsuit. Proceedings of the AIAA Guidance, Navigation, and Control Conference. August 2–5, 2010; Toronto, Ontario, Canada. American Institute of Aeronautics and Astronautics AIAA 2010-7512:1–9.