Structure Of The Human Powered Aircraft And The Industry - Literature review Example

? A Literature Review for the Structure of the Human Powered Aircraft and the Industry By Candi s FACULTY OF ENGINEERING, DEPARTMENT OFAERONAUTICAL ENGINEERING (This page intentionally left blank) Introduction Human beings have always had a fascination with flying, and this has served as an impetuous for design of all types of devices that will fulfil their dreams (Abzug, 2002, Pp. 1 – 10). However, human powered aircraft and gliders that depend on the power delivered to them as their pilot jumps off to try to take off and fly have very limited power available to them to sustain flight (Cruz, 1989, Pp. 1 – 5). Thus, a capacity for flying over the longest possible distance on limited power available from humans is a critical measure of performance for small human powered aircraft and jump type hang gliders, which must maintain a low weight while ensuring a degree of stability, safety, controllability and structural soundness. Because one of the largest weight components of an aircraft is its primary structure, the proper design of aircraft structure for human powered aircraft and hang gliders remains a challenge that decides about the success or failure of a design. The appropriate design flight conditions and the structural loads caused by a flight are variable and not immediately apparent, with flight regime and manoeuvring requirements placing additional demands on aircraft structures. Thus, for hundreds of years, if not thousands, the idea of man-powered flight has inspired many brave men to design strange contraptions with which to rival the birds (Grosser, 2004, Pp. xvii – xix). The International Worthing Birdman Competition is an annual event held in the picturesque Worthing Town, located on England’s South Coast that encourages creativity in design and innovation for human powered / glider type flying machines (Worthing Birdman, 2011,” Worthing International Birdman Festival”). Participants in the Worthing International Birdman Festival present working models of aircraft / gliders that will glide a horizontal distance of at least 100 m once their pilot jumps off in these from the Worthing Pier. The wingspan for aircraft participating in the Worthing International Birdman Festival must not exceed 9.14 m and the runway for take-off is limited to 4 m, with the pilot providing all the power when running and jumping from the Worthing Pier. Because of the limitations imposed on designs of aircraft that are eligible to participate in the Worthing International Birdman Festival, no single entry to date has succeeded in gliding over the required 100 m distance. This literature review presents an examination of designs for human powered aircraft and hang gliders that will most likely present a winning entry for the Worthing International Birdman Festival. An emphasis exists for deciding about the structure of the aircraft, and the literature review should appeal to all those with an interest in human powered aircraft and gliders. Because Para gliders are gliders with no rigid form and only a simple fabric wing, with a pilot attached to the wing with high-strength cords, these designs cannot meet the specifications mentioned for the Worthing International Birdman Festival (Demand Media, 2011, “What Are Three Different Glider Designs?”). The length of the high-strength cords in a Para glider design connected to the pilot will not permit pilots to travel far after a jump from the pier before they land in the sea. Thus, this literature review only considers hang gliders and other human powered type structures, excluding human powered helicopters (which do not have a wingspan) that are more likely to provide a pilot with the maximum height to travel before landing in the sea to present a win in the competition. It is important to note that human powered helicopters must lift the weight of the human and power engine as well as the weight of the entire aircraft structure to demand exceptionally large and lightweight rotary wings that present great complexities to render such designs ineligible for the Worthing International Birdman Festival (Silvester, 2008, Pp. 1 – 10). Literature Review According to Huang (2006, Pp. 2 – 4), a hang glider is a glider that is capable of being carried, foot launched and landed solely using the pilot's legs. Thus, a hang glider is the ideal type of aircraft design that will satisfy design requirements for the Worthing International Birdman Festival. Class 1 hang gliders have a relatively flexible structure that enables the pilot to shift weight to maintain control over the hang glider without resorting to any control surfaces. However, Class 2 hang gliders have control surfaces that assist with control of the hang gliders although control surfaces add to the drag on the hang glider to reduce the maximum possible length of flight from a jump. Thus, because control surfaces add to the drag on a hang glider to reduce the maximum length of a flight, it is only proper to discard any thought of using Class 2 type hang gliders as an entry for the Worthing International Birdman Festival. Most hang gliders are variants of the highly successful Rogallo wing, which has existed as a simple and inexpensive approach to recreational flying that has existed since the 1950s (Nankivell, 2007, Pp. 2 – 5). Figure 1: Components of a Typical Hang Glider, from (Dees, 2010, Pp. 4) According to Langford (1984, Pp. 32 – 58), it is possible to design human powered aircraft that use human energy to rotate propellers to fly an airplane the distance of 100 m to qualify for the Worthing International Birdman Festival. However, the required wingspan for a propeller driven human powered aircraft is likely to be longer than the 9.14 m permitted by rules for this competition and this means that a human powered propeller aircraft is not a serious option worthy of consideration. In addition, a propeller and the mechanical gear required to rotate this propeller in a human powered aircraft are likely to add weight to such an aircraft structure, and this will present a need for a larger wing area. Figure 2: Snowbird, a Typical Propeller Driven Human Powered Aircraft, from (Eco Friend, 2011, “10 Prototype Aircrafts Harnessing Human Power for a Zero-Emission Flight”) Many ingenious prototype aircraft harnessing human power for a zero emission flight already exist, but all of these aircraft have very large wingspans that violate the 9.14 m wingspan limit for the Worthing International Birdman Festival entries (Eco Friend, 2011, “10 Prototype Aircrafts Harnessing Human Power for a Zero-Emission Flight”) and (Roper, 2011, “Up to Date”). The complexity of a design involving a propeller human powered aircraft is also likely to present overkill for the Worthing International Birdman Festival. Nevertheless, it is worth noting that it is possible for high-class athletes to deliver a maximum of 2.5 KW of mechanical power for short bursts that will suffice to sustain flight for 100 m required under the rules of the Worthing International Birdman Festival (Jansen, 2011, Pp. 48 – 52). Larger wings present larger wing deflections and these wing deflections require complex structure support that is not sustainable for small aircraft of the type competing in the Worthing International Birdman Festival (Chong-Seok, 2006, Pp. 1 – 10). However, it is worth noting that aircraft designers have succeeded in building prototypes of aircraft expected to approach flight distances of 100 miles on human power, and the Raven is an example of such an aircraft (Gottschalk, 1995, Pp. 84 – 88). Figure 3: The “Da Vinci III”, a Human Powered Helicopter, from (Silvester, 2008, Pp. 18) According to Bruhn (1973, Chapter A 1), the design of aircraft structures is one of the most important design challenges that confronts aircraft designers because aircraft structures must be able to take the stresses imposed during flight without failure and cope with the loads imposed on aircraft during flight or when on ground. Component analysis for aircraft structure, including analysis for wing, fuselage, tail, etc. should maintain permitted levels of yield, fracture, fatigue, creep, buckling, thermal effects, etc. to ensure aircraft safety and integrity at all times. An aircraft structure should meet the required stiffness criteria for aircraft in practical use to present the right dynamic response, control system stability and vibrations that will maintain humans during flight. Mechanical, lift force and aerodynamic stresses as well as thermal stresses in an aircraft structure must remain within permissible levels at all times to ensure that the aircraft will survive a flight to remain useful. Thus, materials of construction for an aircraft structure are important because these materials should be able to cope with all imposed forces / stresses at all times, both during flight and at take-off or landing. This means that it makes sense to ensure that the structure and materials for aircraft design for the Worthing International Birdman Festival will be able to take all that is possible. Dees (2010, Pp. 1 – 12) presents a discussion about the design and performance of hang gliders, which are now the obvious choice for entry to the Worthing International Birdman Festival, in light of the previous discussion. A tail-less design is likely to serve best for aircraft design for the Worthing International Birdman Festival because the emphasis in this competition is to present a flight of 100 m and manoeuvrability of the aircraft is not a significant issue. Thus, because a tail is likely to add to the weight of the aircraft structure without presenting additional lift, it makes sense to design a structure that only retains wings under which a pilot is strapped, ready and capable of 100 m flight after the jump from the pier. According to Dees (2010, Pp. 4 – 8), flex-wing design hang gliders are inexpensive and easier to fly compared to rigid wing types, and this means that it makes sense to focus on a flex-wing design even though rigid-wing designs have achieved superior lift / drag ratios (Dees, 2010, Pp. 8 – 12). Nankivell (2007, Pp. 6 – 14) presents a discussion about the various types of hang glider designs used today. The delta wing, flexible wing, single surface gliders, double surface gliders and the rigid wing gliders all offer possibilities that are worth investigating for the Worthing International Birdman Festival. However, it makes sense to try to prefer designs with the highest possible glide ratios because success in the Worthing International Birdman Festival depends on flying 100 m after jumping from the Worthing pier, which is not very tall. Figure 4: A Modern Double Surface Hang Glider, from (Nankivell, 2007, Pp. 11) A wing, a frame, cables and items to hold these in place are essential structural elements for a hang glider. These structural elements should present the minimum possible weight while delivering a capacity for withstanding the stresses induced on members (Nankivell, 2007, Chapter 6). Although earlier hang gliders used balsa wood, the rigid structural elements are now made of aluminium or aluminium alloys of magnesium, zinc, and copper. However, those structural elements that must withstand the maximum possible stresses are made of stainless steel, which is an alloy of iron, a small amount of carbon, and 12-18% chromium. Composite materials are also used, but it is likely to be difficult for a team presenting an entry to the Worthing International Birdman Festival to work with structural elements made of composite materials. Thus, use of aluminium tubing is most likely, with connecting fittings made of stainless steel. Those with an interest in testing or simulating hang glider designs or structural elements of a hang glider may want to use Finite Element based software packages, including ABAQUS, CalculiX or similar (Simula, 2011, “Unified Finite Element Analysis”) and (IBIS, 2011, “Free Aircraft Design Software”). Although early hang gliders used canvas or cotton fabric treated with dope as the material for sail of a hang glider, nowadays polyester (polyethylene terephthalate, known by the trade name Dacron) is now widely used sail material (Nankivell, 2007, Chapter 6). Thus, it should be possible to buy rolls of polyester cloth, cut them to a pattern and then sew these using industrial sewing machines to deliver a sail for the hang glider. Depending on the solid aluminium structure that is decided and the stainless steel joints with cables or nylon ropes for connecting separate components, it should be possible to produce complex sail shapes as desired for a prototype for the Worthing International Birdman Festival competition. However, it makes sense to try to adhere to airworthiness requirements for hang gliders presented in The German Aviation Authorities (LBA) (2009, Pp. 2 – 7) or similar. Cui (2010, Pp. 24 – 46) and Dees (2010, Pp. 1 – 12) present a discussion about aspects of hang glider design that need considering when designing a prototype for the Worthing International Birdman Festival competition. However, comparisons of hang glider designs presented in Nankivell, 2007, Pp. 7 – 14) suggest that although a Delta wing design may work, this design suffers from a possibility of deflating that will result in very rapid descent with no lift. Thus, a double surface for wing approach with a flexible wing is likely to work better even if this means that the design of the wing will become slightly more complex. Double surface gliders present reduced drag, increased glide ratios and a reduced danger for presenting no lift because of the two pieces of sail material, one at the top of the wing shape and the other at the bottom. A delta wing shape with kingpost will be tolerable for the design, but a rigid wing approach is likely to become too complicated for any prototype design for the Worthing International Birdman Festival competition. It is important to consider practical designs available in the market to decide about what is best for a prototype for the Worthing International Birdman Festival competition. The Sensor 610 F5 made by Seedwings USA, the Target 21 made by Aeros Ukraine and the Avian JAVA made by Avian UK are similar to what is desirable for a prototype for the Worthing International Birdman Festival competition (Aeros, 2011, “New Target 21 Tandem”), (Seedwings, 2011, “Sensor 610 F5”) and (Avian, 2011, “Avian JAVA 140”). Figure 5: The Aeros New Target 21 Hang Glider, from (Aeros, 2011, “New Target 21 Tandem”) Figure 6: The Seedwings Sensor 610 F5 Hang Glider, from (Seedwings, 2011, “Sensor 610 F5”) Figure 7: The Avian JAVA 140 Hang Glider made by Avian UK, from (Avian, 2011, “Avian JAVA 140”) After an examination of the abovementioned glider designs, it is important to note that all three of these designs have a wingspan of around the 9.14 m limit for a Worthing International Birdman Festival entry and it should be able to reduce the length of the kingpost and harness for strapping a pilot on these designs. The Sensor 610 F5 138 has a wingspan of 10.1 m and the Aeros New Target 21 Tandem has a wingspan of 9.6 m, while the Avian JAVA 140 has a wingspan of 9.2 m (Aeros, 2011, “New Target 21 Tandem”), (Seedwings, 2011, “Sensor 610 F5”) and (Avian, 2011, “Avian JAVA 140”). Thus, it will be proper to suggest that a prototype for the Worthing International Birdman Festival competition should modify the design of an Avian JAVA 140 by reducing the wingspan to 9 m or slightly less, and reducing the depth of the harness for attaching the pilot to as much as possible. It should also be possible to reduce the length of the kingpost slightly while ensuring that the remaining kingpost is still capable of adequately supporting the wings. Cutting off about 5 cm for either side of the wing aluminium structure for the Avian JAVA 140 design and trimming the wings to suit while making reasonable reduction in lengths of pilot harness and kingpost will present a prototype that may perform best while meeting specifications. Such a prototype will present the best possible wings for a winning glide of 100 m after a jump from the pier. It is important to note that in the present day and age, hang gliders enjoy much popularity in Europe and other Western countries, and a great market exists for hang gliders around the world (Icon Group, 2008, Pp. 1 – 34). However, a commercial market for human powered propeller aircraft is non-existent because these aircraft are all experimental prototypes. Thus, well-designed gliders should sell well if they establish a reputation among gliding enthusiasts. Conclusion This literature review presented an examination of published literature for human powered aircraft and hang gliders with a view to trying to develop a design for the Worthing International Birdman Festival. After examining aspects of wing design, design of aircraft structure, materials for design and latest in hang glider designs, it is possible to conclude that a modified design based on the Avian JAVA 140 design will prove to be a winning prototype. It is necessary to reduce the wing length of an Avian JAVA 140 design on either by 5 cm, together with reducing the length of pilot harness and the kingpost while ensuring structural strength to present the best possible prototype. 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