Looking at the possibility that man can fly like a bird onfolding wings worn as a backpack.
D.Reid PO Box 143 Oneroa, Waiheke Island, AUCKLAND 1840, New Zealand Email: email@example.com, www.wearablewings.ning.com OVERVIEWIs it possible to fly like a bird, with wings that fold into a backpack? This paper looks at the possibility of creating personal wings with sufficient performance to soar in most daytime weather conditions and concludes that this goal is indeed possible. I describe the approach I have taken towards realising the dream of wearable folding wings for soaring flight. For good penetration into headwinds and to fly between thermals, a lift to drag ratio of at least 30:1 is desirable. The threshold sinking speed for unlimited soaring ability is about 0.3 m/s and at least 0.4 m/s is achievable with wearable folding wings. LIMITATIONS OF EXISTING DESIGNS Hang-gliders and parafoils are the closest examples to wearable wings. Hang-gliders tend to suffer from poor lift distribution and high profile drag due to exposed wires and struts. Parafoils have very high profile drag due to numerous suspension lines and exposed pilot position. Increasing the performance of gliders demands drag reduction. For a sailplane to climb it has to have a sinking speed less than the speed of rising air currents. To fly long distances it must fly fast with low sinking speed. Combining the two requirements requires reduction in both induced and profile drags. Induced drag can be reduced through optimum lift distribution and increased wing span. Artificial wing tip feathers can also substantially reduce induced drag. Profile drag can be reduced by improved streamlining and surface area reduction. EXPERIMENTS DEMONSTRATING POSSIBILITIES A project in New Zealand involving Waikato University, the Waikato Technical Institute and Auckland University demonstrated a wing that met the above performance requirements. This was a membrane wing of 15 metre span and an aspect ratio of 27 and was mounted on a framework attached to a bus. Load cells measured lift, drag and pitching moment. Test results showed a best L/D of 50 at 18 m/s which translates to a sinking speed of 0.3 m/s. The sail was seamless and the internal kaugis did not touch the membrane, resulting in a very fair aerofoil contour for minimum drag. . Testing a Dereidactyl Wingexperiments at Hamilton Airport sponsored by NZ TV
Can a Human Fly Like a Bird?
STABILITY Finding performance possibilities has little future unless the resulting wings are stable in flight. This topic has long interested the author who has been fascinated by tailless aircraft designs. These were always limited by the need transfer tailplane function to the wing with consequent loss of efficiency. Thus the benefits of a tailless configuration were lost by the requirements for a larger wing. On the way to New Zealand from Germany to design a new competition sailplane for the New Zealand Gliding Federation I was able to observe albatrosses soaring behind the ship. It was clear from their relaxed flight style that the birds were very stable in spite of their near tailless configuration. I was determined to unlock natures stability riddle. I felt there must be a spring element involved yet experiments showed that there must be another factor. Flight muscle elasticity spring is the spring and to be effective there had to be a feedback element which compared wing lift with muscle tension. The missing aspect was discovered by Dr. A.D. Sneyd of Waikato University whose mathematical analysis showed that the spring had to have a reverse gradient. Looking again at bird anatomy, nature had achieved this through the deltoid crest on the humerus. The simple geometry of the deltoid crest provided the key to achieving pitch stability on an efficient cambered wing. All birds, bats and pterosaurs exhibit this geometry. This enables a mechanical feedback system that maintains a state of unstable equilibrium. I presented this theory as The Principles of the Constant g Stability System at CEAS2007. WEARABLE FOLDING WINGS Combining all the successful elements makes wearable folding wings possible. Making membrane wings that fold is not so difficult. Creating folding wings that tension themselves via lift forces to achieve an efficient aerofoil shape is more of a challenge. Making them fold easily and compactly is difficult and allowing the flyer to extend and furl the wings at will is a further test of ingenuity. There is great potential to incorporate retractable artificial wing tip feathers. Once optimised, the maximum L/D could rise to 40 and minimum sink reduce to 0.35 m/s. Thanks to a donation of some carbon fibre windsurfer masts, the structural weight will be reduced to perhaps 10 kg, a low value for a complete aircraft high performance sailplane. CONCLUSIONS It is both possible and practical to design and build high performance wearable folding wings which enable a flyer to exploit microlift and thus enjoy extended soaring throughout the year. This will greatly increase the opportunities for enthusiasts to enjoy the sport of soaring at a much reduced coat with enhanced convenience.
This was a very simple wing with no control system. While sweep forward and a flexible structure gave it static stability, it did not have the dynamic stability from a reverse gradient balance spring. Dereidactyl Specifications wing span wing area aspect ratio weight gross weight 15 m 27 18 kg 80 kg 8.3 m2
Can a Human Fly Like a Bird?
INTRODUCTION TO PERFORMANCEIn considering the possibility of a human flying like a bird, it is useful to consider what sort of gliding ability is necessary for reliable soaring. Humans are not strong enough to sustain flight through physical effort hence the ability to extract energy from the atmosphere is needed. There is always some movement in the atmosphere. A glider gains energy from gravity, sliding down a glide-path. To avoid reaching the ground it must find air rising faster than its descent speed. Thus the lower the descent speed the greater the chance to stay aloft. Hang-gliders and parafoils can only fly in conditions of strong lift. The same applies to most soaring birds where the larger species can live only where these conditions prevail. Recently gliders have been designed to utilise weak lift and are called microlift gliders. On the chart below, a falcon, parafoil,
hang-glider, microlift glider, Dereidactyl wing, and Wearable Wing are compared. My Dereidactyl wing shows the best performance. This wing never reached a man carrying state yet its measured performance shows the potential for development. The design of wearable folding wings demanded a size that could be folded into a backpack. Thus the long, narrow Dereidactyl configuration could not be considered. Nature uses finger-like wing tip feathers to disperse wing tip vortices in three dimensions. Emulating these was aided by excellent research by the Swiss engineer, LaRoche and his WingGrid. It is not only performance that is important; pilot safety is vital. The most dangerous phase of flying is landing. For a pilot to land on his feet, his approach speed must be slow resulting in the danger of an abrupt wing tip stall and injury. The wing tip feathers greatly reduce this hazard.
The above graph compares sinking speeds of a peregrine falcon, paraglider, hang glider, Archaeopteryx glider and Wearable Wings. The calculated performance of wearable wings with tip feathers extended is almost identical to the Archaeopteryx. With tip feathers retracted, the weratble wings show much better penetration. MINIMUM PERFORMANCE REQUIREMENTS Gliders design to utilise microlift are able to soar in weak lift and so extend opportunities for reliable flight. Can a wearable wing glider be designed and built with this kind of performance? To further the wearable folding wing project I developed a spreadsheet to explore the range of possibilities. As described in my CEAS2007 paper, The Principles of the Constant g Stability System, the spreadsheet can receive a wide variety of inputs and calculate stability, stresses and performance. MICROLIFT SOARING ABILITY PREDICTED The calculations, using drag coefficients dereived from the Dereidactyl experments, demonstrate the potential to create folding wearable wings able to soar in microlift conditions. CROSS COUNTRY FLYING Flying accross country involves two basic elements. The first is circling in thermals to gain altitude. The second is straight line flying between thermals. During cIrcling flight, the wing operates at a high lift coefficient and at g > 1. A typical circling radius involver g ~ 1.2. During this phase the ideal wing will have high camber and no twist. The wing-tip feathers will be fully extended and fanned. For high speed inter-thermal flying, the wing-tip feathers will be retracted and membrane tensioned held as high as possible. Here, minimum profile drag and surface want to be at a minimum. A streamlined pilot enclosure is important for this high speed flight with minimum loss of altitude. Page 2
Can a Human Fly Like a Bird?
WING FOLDINGFolding wings are the norm in nature. Creating high performance soaring wings that fold into a backpack is a challenge not yet realised. In this section will look at attempts to create a practical configuration that is light, compact, workable and reliable.
The wing plan shown above is the configuration of 1 september 2009. Here the wing spars are made from windsurfer masts. The wing tip feathers are formed from polypropylene foam with bamboo shafts. The kaugis are foam with carbon fibre caps. The photos of the FOLDED WING folded wing are of an early version of the wing without feathered tips, Jan. 2009. The drawings show my latest ideas for kaugi positions. FOLDED SIZE How compact should the the folded wings be? I wanted wings that could be carried on a bus, worn as a backpack on a bicycle and easily permit walking through doorways. Limiting joi