PSU Zephyrus
Transcription
PSU Zephyrus
PSU Zephyrus: Design Of A Human-Powered Aircraft For Sport Alan R. Campbell,∗ Andrew J. Weinert,† Jason C. Slaby,∗ Kirk P. Miles,∗ Nathan T. Depenbusch,∗ and Kevin T. Show∗ The Pennsylvania State University, University Park, PA, 16802, U.S.A. Following the announcement of a new Kremer Prize by the Royal Aeronautical Society, the Flight Vehicle Design and Fabrication class at Penn State University has been working on the design and construction of the PSU Zephyrus, a human-powered aircraft (HPA), for the Sport Challenge. The design phase is currently nearing completion, testing of some construction methods is ongoing, and full-scale construction is beginning. The Sporting Kremer Prize mission requires the aircraft to traverse an equilateral triangle with 500meter length sides once in each direction. A total flight time of seven minutes or less is required. The major factor in this competition is a wind requirement; during the entire flight the wind must maintain an average speed of 5 m/s, and must not drop below that limit for more than 20 consecutive seconds. The design process began with a survey of previous HPAs and iterated toward the present configuration. For the “nearly frozen” design, the pilot will be seated, reclined, in a pod hanging from the main boom and will power a tractor propeller with a diameter of 3.0 m. The empty weight of the aircraft will be approximately 25 kg and will require about 285 W output by the pilot. The wing will consist of a straight center section (7.0 m) and outboard tapered sections (5.25 m) each. The root chord will be 0.75 meters with a tip chord of 0.5 meters. The wing shall be supported by a carbon fiber tube spar made up of two ±45◦ heat-shrunk sleeves and 14 plies of uni-directional carbon at the root. The empennage will be of a conventional configuration with an all-flying horizontal tail for pitch control. The rudder will provide yaw control, as well as some roll due yaw, which will also be supported with ailerons, powered by local servos, on the outboard sections of the wing. Nomenclature C L R Re S T V b e g n x α γ General force coefficient Lift force, N Turning radius, m Reynolds number Reference area, m2 Tail volume coefficient Velocity, m/s Wingspan, m Span efficiency Gravitational acceleration, m/s2 Load factor Reference length, m Angle of attack, degrees Climb angle, degrees ∗ Undergraduate Student, Department of Aerospace Engineering, 229 Hammond Building, University Park, PA 16802, Student Member, AIAA. † Undergraduate Student, College of Information Sciences and Technology, 332 IST Building, University Park, PA 16802, Student Member, AIAA. 1 of 11 American Institute of Aeronautics and Astronautics ν ρ ϕ ω Kinematic viscosity, m2 /s Density, kg/m3 Bank angle, degrees Rotational velocity, rad/s Subscript D Total drag H Horizontal tail L Total lift V Vertical Tail W Wing d Two-dimensional drag i, vor Vortex-induced l Two-dimensional lift max Maximum I. A. Background and Motivation AERSP 204/404H As a project-based learning experience, AERSP 204/404H (Sailplane) offers an opportunity for students to work on real-world design issues under the shelter of a scholastic setting. One of the current projects is the design and construction of a Human-Powered Aircraft (HPA) to compete for the Sporting Kremer Prize offered by the Royal Aeronautical Society (RAS). The HPA team is part of a Penn State course, AERSP 204/404H, Flight Vehicle Design and Fabrication, affectionately known as Sailplane. Sailplane is an upper-level engineering and capstone design course taught by Dr. Mark Maughmer. The course is partially funded as a member of the Space Grant Colleges and Pennsylvania Space Grant Consortium and holds the following course objectives: • Complete the preliminary design for an aircraft such that it satisfies assigned specifications • Design a system, component, or process that meets given requirements in aircraft systems • Identify, formulate, and solve engineering problems • Function on multi-disciplinary teams • Communicate and present effectively the results and consequences of their technical efforts • Determine what the ethical responsibilities are to themselves, to employers, and to society This course is unqiue because it of its strong “hands-on” component and that the curriculum is based on the German Akafliegs. Starting in 1989, the curriculum has been broken into three components: lecture, design, and fabrication; with projects typically spanning multiple semsters. The main purpose of the lecture component is to provide the students with the theoretical background required for their design and fabrication activities, the lecture topics are specifically requested by the team to address current design or construction problems. The second component is concerned with design groups of four to six students, in which the students design and analyze sailplanes, such as their performance, structure, stability and control, etc. The third component is the fabrication of parts that have been designed and analyzed theoretically, with an engineering lab assigned to the course for this purpose. Overall, the course gives students the experience of a cooperative, multi-disciplinary team environment that is essential for solving problems related to the design of an aerospace vehicle.1 In recent years the traditional class focus on sailplanes has shifted; with current projects including the annual AIAA Design, Build, Fly competition and wing loading experiments, in addition to the Zephyrus. The goal of all projects in the Sailplane class is to give the students a practical knowledge of the aerospace engineering process, particularly focusing on aeronautics. The HPA was begun with this in mind as well. It didn’t take long, however, for the traditional mindset of “let’s get this to fly” to be taken over by “let’s get this to win.” It is a result of the added competitive drive and motivation from the Kremer Prize that has pushed this design to its current state. 2 of 11 American Institute of Aeronautics and Astronautics B. Kremer Prize The Kremer Prize was initially funded by Henry Kremer, via the RAS, in 1959 for progress toward the goal of human-powered flight. Two Kremer Prizes are currently available: a Sporting prize worth £ 100,000 and a Marathon prize worth £ 50,000. Past Kremer Prizes have been awarded for completion of various tasks in human-powered flight. Prior winners include Paul MacCready’s Gossamer aircraft, MIT’s Monarch B, and the German-based Musculair aircraft. The Gossamer Condor won the initial Kremer Prize for its milelong oval flight in 1977. The next prize was won by the Gossamer Albatross in 1979 for flying the Engligh Channel. Following the Gossamer’s victories, numerous smaller prizes have been awarded for improving human-powered aircraft speed records. The current prizes were established in 2007.2 This particular mission provides several interesting design problems that must be resolved. To start, the basic mission goal is to traverse an equilateral triangle with sides of 500 meters once in each direction in seven minutes (see Fig. 1 for course details). A particular area of interest, as noted on the course diagram, is the wind and its direction. The competition specifies a minimum average wind speed of 5.0 m/s during the flight. In addition, for a flight to be considered official, the wind cannot drop below 5.0 m/s for a period of more than 20 seconds. The course shall be aligned with the prevailing wind direction as shown.3 Figure 1. Course Setup for Sporting Kremer Prize II. A. Design Fuselage Sizing the fuselage began by essentially measuring out a dimension range for the pilot, putting these dimensions in the correct orientation, and drawing a fuselage around it. Dimensions were based on a 5’10” (1.78 m) pilot, with the assumption that someone of the necessary power to weight ratio to fly the aircraft will be no more than this height. Once the internal characteristics of the fuselage were completed, the external shape was considered. To do this, a minimum volume “bubble” was drawn around the internal structure. The aerodynamic performance of this shape was then considered. Constraints considered in this process include minimum widths for pilot comfort and desired center of gravity of the aircraft. The shape of the pod was designed to be a low-drag 3 of 11 American Institute of Aeronautics and Astronautics body that will not generate lift regardless of angle of attack. In addition, the length of the shape was reduced to allow for aircraft maneuverability in crosswind. The internal structural members are designed to firmly hold the seat configuration in place, yet still provide a maximum field of vision for the pilot. Structural members attach to the main boom at a hardpoint located behind the trailing edge of the wing. The chain will rise vertically from the gear to the drive shaft to provide torque to the propeller. B. Propeller To successfully complete the sport challenge, it was determined that the propeller would need to produce 27.5 N of thrust when cruising at 12.5 m/s and spinning at 135 rpm (as opposed to the 150 rpm by the Musculair 2). To meet these requirements, the propeller design underwent many alterations during the design process. Gottingen 796 (inboard) and 795 (outboard) were initally chosen, however the final design employs a series of Eppler propeller airfoils: Eppler 858 at the hub to Eppler 850 at the propeller tip. Additonally during the design process, the blade length was increased from 1.34 meters (based on Musculair 2) to 1.5 meters which will yield an increase in efficiency. The propeller is theoretically more than 80 % efficient in the speed range 10-16 m/s, which is advantageous given the chance of gusts during flight.4 Also, the propeller should be capable of creating more than 20 N of thrust when the aircraft is still, enough to get the plane moving. The blade is designed in two components: a structural shell of blasa wood, unidirectional carbon and kevlar for the shear web and a kevlar fabric D-tube to take the torsional load. C. Wing Starting from a parent aircraft approach, primarily using the Musculair 1 and 2, but also including the Monarch B, Daedalus, and Velair models, a first iteration choice for an airfoil was made. A modified version of the FX-76MP, as used for the Musculair 2 was chosen. Taking characteristics from this airfoil, using an initial weight buildup, the wing planform size was determined. Then, assuming a take-off weight of 81 kg (27 kg empty weight), sea-level air density, and using a CL at cruise of 0.8 obtained from the Musculair reports on our chosen airfoil, a range of velocity values were obtained through the lift equation (see Eq. 1) to examine the correlation between wing area and possible cruise velocity.5 1 2 ρV SW CL (1) 2 From this, a range of span and chord lengths were determined for varying velocities. Considering the time and distance requirements as stated in the competition rules, a cruise speed of 12.2 m/s was chosen. This cruise speed necessitates a wing area of 10.90 m2 . A span of 17.5 meters was chosen based on parent aircraft sizes and differences in mission requirements. This resulted in a mean chord of 0.62 meters. Following a more accurate structural design and weight build-up, further iteration of the planform was performed. Beginning with a range of airspeeds, roughly 6.7 m/s to 13.4 m/s (15 to 30 mph), and standard sea-level density and viscosity, the lift equation was again used iteratively to size the wing. This process resulted in a span of 17.5 m and a mean chord length of 0.625 m, giving a wing area of 10.93 m2 , a stall speed of 9.8 m/s (22 mph), and Figure 2. Profile, induced, and total wing drags for the a cruise speed of 12.5 m/s (28 mph). The opera- PSU Zephyrus tional CL ’s range from a CLmax of 1.3 to a CL of 0.7 at 13.4 m/s, with a cruise CL of 0.8. The calculated Reynolds number (Eq. 2) range at the mean chord, over this velocity range, is from 440,000 at stall to 600,000 with cruise at 560,000. L= Re = Vx ν 4 of 11 American Institute of Aeronautics and Astronautics (2) Following this step, an initial leading edge taper was introduced from a root chord of 0.75 m to a tip chord of 0.5 m resulting in a taper ratio of 0.667. This taper results in an increased Re at the root of 530,000 at stall to 724,000 at maximum speed, with a cruise Re of 675,000. In addition, the airfoil selection was changed to the Eppler 395 human-powered aircraft airfoil. Further planform iterations were performed via a panel method drag build-up code written in MATLAB. For this part of the process, the code was isolated for wing drag calculations. In addition, construction ease and dynamic performance was taken into consideration. The current planform consists of a 7.0 meter rectangular center section with a chord of 0.75 meters and two outboard sections each 5.25 meters in length. The outboard sections are straight-tapered from 0.75 m to 0.50 meters at the tip. In addition, the trailing edge is now the tapered side to allow for straight spar connections. The wing area is 11.81 m2 . Drag calculations were performed for a set number of wing panels. The mean chord of each panel was used to determine a panel Reynolds number. XFOIL results for varied Re were interpolated for the twodimensional lift and drag coefficients (Cl and Cd ) for each panel.6 These were then integrated over the spanned to determine the wing lift and drag coefficients (CL and CD ). Induced drag was calculated via Eq. 3. See Fig. 2 for the calculated drag of the wing design. CDi,vor = D. CL2 2 πe bS (3) Spar Two spar structure options were considered, an Ibeam and D-tube construction as well as a tube spar with additional caps for bending. To decide between the two, rough weight calculations were preformed. For the tube spar calculations, the structure was broken into two parts: a tube to take torsion loads and caps to take bending loads. For the I-beam and D-tube method it was assumed that the I-beam took all the bending and the D-tube took all the torsion. Scaling the E395 airfoil to the wing platform and using the maximum thickness point as the location of the spar, the size of the structure in both methods was calculated. Applying a linear lift distribution the weights of the structures required were compared and it was found that the tube spar structure was lighter than the equivalent I-beam. The tube spar renders the D-tube as a primarily aerodynamic feature, taking neither bending nor torisonal loads. The D-tube would then only be a layer of finished glass or sheets of foam 3-5 mm thick, similar to past HPAs. Using this assumption, 10 mm was subtracted from the thickest point of the airfoil to allow for the D-tube. This new outer dimension became the furthest distance from the two caps on Figure 3. Cross-section of the wing spar at the root. the spar. The width of the spar caps was determined based on the size of the workable area, considering that wider caps bending around the tube would be less effective. For a first iteration, the caps were set as geometric rectangles and a linear lift distribution was assumed. Basic beam bending calculations were completed to set the initial cap thickness. After it was seen that the thickness seemed reasonable and fit inside the allowable distance, a second round of calculations were preformed using an elliptical load distribution. The number of cap plies was determined by tabulating the calculated thickness and dividing it by the thickness of unidirectional carbon. Since composites are subject to large stress concentrations at the edges of layers, great care was taken to reduce the number of drop-offs of plies along the spar caps. The thickness of the top and bottom caps was then accounted for in the outer diameter of the torsion tube (see Fig. 3 for dimensions). 5 of 11 American Institute of Aeronautics and Astronautics This new outer dimension underwent basic beam torsion and aerodynamic loading calculations to determine the wall thickness of the tube along the span. The wall thickness was subtracted from outer dimension to determine the minimum diameter of the carbon tube. It was determined that two full carbon sleeves would be required for the tube. E. Control Surfaces The control system was one of the hardest aircraft components to design because of the lack of data available and the mission specific design of the aircraft. It has been noted that on previous Kremer Prize winning flights, the pilot is constantly actively attempting to control the aircraft. For example, Bryan Allen in the Gossamer Albatross could not even look at his watch during the 2 hour and 49 minute flight due to constant adjustment of the controls.2 The necessary pilot input resulted in a design approach where multiple calculations of the same parameter with different variable values was used. This results in a lack of constant variables. Each calculation, however, had a key variable identified. Also, a majority of the control parameters were calculated at the cruise velocity of 12.5 m/s. Since each of the control surfaces effects all of the others, one had to be chosen as the starting point. The ailerons were chosen since more prototyping had been conducted on the wing, along with the aileron sizing being necessary to determine D-tube specifications and rib spacing. First, the flight mechanic parameters of turning radius (Eq. 4), load factor (Eq. 5), centripetal acceleration and force, and angular velocity were calculated for a range of bank angles from 10◦ to 45◦ at 5◦ increments. These parameters were calculated using a student generated Java GUI, increasing time efficiency. All parameters determined at a bank angle of 30◦ were confirmed through hand calculations to ensure accuracy (see Eq. 6). Based on the course layout and structural strength of the aircraft, 30◦ was targeted as the ideal bank angle. The aircraft also must be capable of operating at other bank angles because the desired bank angle will most likely not be achieved every turn. The load factor produced by a 30◦ turn was determined to be 1.155, however, an averaged value, from other bank angles, of 1.162 was used. The averaged load factors have only a percent difference of 0.63% from the the desired load factor, this is within the 1% tolerance specified by literature.7 Basic roll oscillations were also calculated to measure the damping forces along the wing during a turn, as a result of the bank angle. V2 g × tan(ϕ) (4) cos(γ) p 2 2 ω V + g2 g (5) R= n= 1 ϕ = arccos( ) (6) n The hinge moment was calculated next using the same methodology to be 0.88 N-m with a moment of inertia of 2.22 N around the spanwise axis. The hinge moment was set at 1.06 N-m instead due to the servo control design; many servos are rated for 150 oz-inches, which is 1.06 N-m.8 Multiple tail hinge moments were calculated based on velocity and angle of attack. Due to the control design, the hinges take majority of the load, and therefore, analysis of this structure becomes a priority. It was important to note the difference in the moment at different speeds because the lack of a constant power output. Using XFoil and an MS Excel spreadsheet, the hinge moments were calculated and the max and min was identified for each velocity. The tail control elements were then based off these max and mins.8 See Fig: 4 for hinge moment as a function of α. The aileron geometry was then sized, dependent upon two factors: percent chord length and percent span length. Additionally density (ρ), velocity, and climb angle (γ) were constrained to be constants at 1.28 kg/m2 , 12.5 m/s, 0.0553◦ respectively. The calculated aileron weight was minimized and the force on the surface along the control span was maximized in the calculated range. Using the values from the flight mechanics process and comparing them to the calculated force on the main surface along the control span values, a range based upon percent span length was identified. Based upon aileron weight and force on the main surface along the control span, along with the overall geometry of the outboard wing sections, ailerons spanning 5 meters on each outboard section were chosen with a chord of 0.1425 meters. These ailerons will cover an area of 0.428 m2 and were estimated to weigh 592 grams. 6 of 11 American Institute of Aeronautics and Astronautics Moment (Nm) With the size calculated, three aileron designs were considered: Kevlar strip, submerged, and piAngle of Attack vs Tail Hinge Moment 20.000 ano hinge, all of which could be controlled via servo motors. The 15.000 PSU DBF teams utilize the Kevlar strip method, which consists of con10.000 structing the wing and cutting the wing at the hinge point into two 5.000 sections, which would be then reconnected with a spanwise Kevlar 0.000 -15 -10 -5 0 5 10 15 20 25 strip. Although this is a low weight -5.000 design, it is too weak for a full scale aircraft and does not provide -10.000 enough structure. The submerged method is utilized in professional -15.000 Angle of Attack, alpha (degrees) sailplanes; the front of the aileron 14.75 m/s 12.5 m/s 10 m/s is rounded off and mounted to the airfoil via socket and control arm. This method provides the greatest structural support but exceeds weight requirements, along with be- Figure 4. Aileron hinge moment as a function of angle of attack for 10, 12.5, and 14.75 m/s ing the most complex considered design. The current design incorporates a piano hinge attached near the upper surface, so the upper surface incorporates the leading edge radius, so that the upper surface maintains smooth flow. The bottom surface can be covered with Kevlar or a tape which moves easily when the aileron deflects downward. Two equal spaced rods are mounted on the drag spar, and a single rod is placed on the aileron. The rods are then aligned and strung together using piano wires that are run through the larger mounted rods. This design was selected based on its weight efficiency and ease of construction. Furthermore this design has the simplest attachment of the control rods and servos. Initial tail sizing was performed using a parent aircraft approach, primarily focusing on the Musculair. Since the Zephyrus has a similar mission to that of the Musculair 2, it was deemed acceptable to estimate chord and span dimensions for the horizontal and vertical tails. The horizontal planform is rectangular while the vertical planform features swept-back rectangular sections above and below the boom. The horizontal distance of the elevator from the wing was calculated using a chord of 0.6 meters and a span of 2.0 meters and a tail volume coefficient range of 0.5 ≤ TH ≤ 0.65. For the vertical tail the volume coefficient range is 0.02 ≤ TV ≤ 0.05. The chord and span are 0.75 meters and 1.75 meters respectively. Until the sweep angle is determined, a rectangular platform for the vertical tail is estimated.5 III. A. Construction and Testing Wing Wing construction was divided into three major sections: spar, ribs, and D-tube. Spar construction was the most challenging, with various construction methods being considered. Three particular methods included winding carbon rovings to form the tube, constructing a half-mold to make a permanent inner tube of fiberglass around which the carbon would be wrapped, or constructing a removable foam core. The foam core method was chosen because winding the carbon rovings is not feasible for the scale of the spar and there is difficulty in joining the two half-molds. The core was constructed out of large cell polystyrene foam which is dissolved by acetone. Then, it was wrapped in painter’s plastic and sealed with tape and Super 77 spray adhesive to prevent the acetone from affecting the carbon tube. After the carbon and epoxy was set, the tube was wrapped in shrink tube or tape (depending on the construction step) and applied heat via a heat gun to expel excess epoxy. Rib construction consisted of cutting out the rib shape (E395 airfoil) out of large cell polystyrene foam. To allow for the aerodynamic D-tube a notch the thickness of the D-tube foam was cut into the rib shape 7 of 11 American Institute of Aeronautics and Astronautics around the front half of the lower airfoil and around the top surface as far back as the estimated transition point. Unidirectional carbon was laid onto the foam covering the entire outer surface to add structural stiffness. After the carbon cured, 5 mm wide ribs were cut out from the airfoil shaped foam using a band saw. No lightening holes were included in the design, because tests indicated there would be an additional cost of adding structural support causing an increase of weight. The D-tube was constructed from small cell Foamular 250. A CNC hot-wire machine was used to cut out one meter wide and 0.61 meters long sections of Foamular at 0.0036 meters thick. The Foamular strips were trimmed to 0.46 meters long for use on the top surface and 0.30 meters long for use on the bottom surface Figure 5. Wing rib cross-section (see Fig. 5 for rib crosssection). B. Fuselage and Main Boom The structure for the fuselage and main boom will be constructed in a similar method as the wing spar. The main difference is that the fuselage and boom must be designed for point loads rather than the distributed lifting load on the wing. For the main boom the structure is divided into two parts: the front, from the propeller to the rear connection of the fuselage, and rearward from the fuselage to the connections with the stabilizers. The front section is practically identical to the root section of the wing spar with carbon sleeves making a tube for torsional loads and unidirectional carbon strips for the bending. The aft section is more complex because it is a long tapering tube subject to point loads at the end. This leads to a greater threat of buckling. There are two general ways to solve the buckling problem. The first is to add more structure, in the form of carbon, to make the ultimate buckling load greater than what will be seen in flight. The problem with this method is that a great deal of weight is added. The second option, which has been used by previous HPAs, is to make the walls of the tube a sandwich beam. This is the option that will be tested with a removable foam core to lay-up around, similar to the spar. Then a layed-up carbon sleeve on the inside is followed by a thin layer of foam and finished with cloth and unidirectional caps. The advantage to this is method is that it reduces weight while increasing the wall thickness, further avoiding buckling. The fuselage structure to hold the pilot is also made out of carbon tubes constructed with the same removable foam core method. The fuselage structure will see a direct air stream, unlike the spar; therefore, it will not be a round tube. Most will be oval in shape to reduce their drag and to fit into a thin glass fairing for aerodynamics. The connection points will use foam inserts for gussets and strips of carbon for bindind. For the adjustable pedals, a thin aluminum tube will be bonded inside the lower fuselage tube during its construction. This will allow bolts to be drilled through to hold the sprocket and pedals. C. Control Surfaces Aileron construction follows the full scale rib construction. Ribs are first marked according to whether they support an aileron. Then, the marked ribs will be cut into two, based upon the aileron chord of 0.1425 meters. The aileron ribs will then be attached to a support structure of 2 ounce, fiberglass, sandwich panel. In addition, another sandwich panel will be constructed to act as the drag spar. The drag spar will be attached to the ribs on the wing with an epoxy-cotton flocks thick mix. Carbon tubing will be fashioned to the drag spar and aileron support spar to act as the hinge. There will be two hinges on the drag spar to each on the aileron. Each aileron will have three pairs of hinges placed 1.66 meters apart. Piano wire will be run through each hinge pair to join. Local 1.0 N servos will manipulate a control arm for each hinge pair. 8 of 11 American Institute of Aeronautics and Astronautics Each servo will be placed on the trailing edge of the wing supported by a double rib junction. The aileron will have a balsa wood trailing edge and will be covered with Mylar. The empennage construction method will model that of the wing. An all-flying horizontal tail is utilized for ease of construction, reduced weight, and increased performance. The elevator will be mounted at its quarter-chord so that excess weight is not added for structure. A standard configuration vertical tail will also be used. The vertical stabilizer will be mounted offset from the boom’s centerline and the rudder attached via carbon tube hinge. Both the elevator and rudder will be controlled mechanically using a pull-pull system of braided Kevlar control rods and nylon pulleys. D. Weight Estimate The weight of the HPA is very important due to the limited power available. Weight placement is also a delicate balance; if focus is entirely on weight, it will not be strong or rigid enough structurally. Therefore, the weight and structure were the object of a careful trade study to balance necessary power and the strength to handle flight loads. At each stage of the design and construction process, a weight buildup for the aircraft was performed. Since the wing has been most extensively designed and tested, it has the most detailed weight breakdown. The amount of epoxy used in the composite lay-ups was a major concern; the optimal ratio is dependent on the material but generally is 30-40 % epoxy by weight and never more than 50 %. Professional lay-ups utilize pre-preg carbon and high pressure autoclaves to produce a finished lay-up with 33-35 % epoxy by weight. “Homebuilder” lay-ups utilize a wet lay-up and shrink tape or vacuum bagging resulting in a ratio of about 50 % epoxy by weight. Through prototyping, it has been demonstrated that for relatively large lay-ups, 45 % epoxy by weight can be achieved. This was then set as the goal ratio. The base weight was calculated as the total weight of the carbon used in construction. This was calculated using density of the carbon and multiplying by the epoxy ratio; this estimate for the wing is 9.5 kg. The total rib weight was then calculated by measuring test ribs and calculating the required number of ribs based on a spacing of 0.33 meters. This estimate was calculated to be 1.28 kg, increasing the wing weight estimate to 10.78 kg. The aerodynamic D-tube of Foamular 250 was calculated next using test cuts leading to weight per unit area calculations. XFOIL was used to find the transition point on the airfoil to determine the area of the airfoil to be covered. This was used to calculate a D-tube weight estimate of 1.3 kg, which increased the wing weight estimate to 12.08 kg. The Mylar covering and structural hard points along with the drag spar and servos were the last components to add to the estimate, increasing the total weight to 14.1 kg. This estimate was used to scale the other aircraft components based on the assumption that the vertical and horizontal stabilizers have similar construction methods and structures to the outboard wing sections. The weight estimate of the empennage was based on the outboard sections scaled to the size of the each stabilizer, which results in a weight of approximately 1 kg each. The main boom and fuselage weight estimates were scaled based on the main spar. This was done assuming that a majority of the forces on the spar are a result of the pilot’s weight in the fuselage. Adding the fuselage, propeller, control stick, and the drive-train weight estimates to the wing and stabilizer weight results in a total weight of approximately 25.7 kg. Comparing our results with previous HPAs, our estimate appears reasonable. The Velair 89 and the Musculair 2 had empty weights of 30.67 kg and 25.0 kg respectively. Also, each had slightly larger wingspans than the Zephyrus but were not designed to fly in adverse wind conditions requiring higher wing loading. The PSU Zephyrus wing weight estimate is also comparable with the Velair 89’s wing weight of 15.96 kg. IV. Progress and Future Work The team is currently finalizing the testing phase and has begun full-scale construction of major components. The wing spar, ribs, propeller and fuselage are under construction. A working propeller-powered tricycle has been built and is undergoing thorough testing of propeller thrust and drive-train components. Further dynamic stability calculations are being performed to ensure appropriate control surface sizing, and detailed fuselage and empennage drag components are being implemented into the drag build-up. The next step is to continue construction of Zephyrus to the point of completion. Then, intensive flight testing will be performed to confirm the aircraft’s ability to perform as expected. If necessary, additional design iterations will be constructed to improve performance. Eventually, transportation must be obtained to an undetermined location in the United Kingdom to, hopefully, claim the Sporting Kremer Prize for PSU. 9 of 11 American Institute of Aeronautics and Astronautics Appendix Figure 6. PSU Zephyrus Three-View (1:20 scale) 10 of 11 American Institute of Aeronautics and Astronautics Penn State Zephyrus Theory Propulsion Flight Geometry Parent Aircraft Wing Airfoil Propeller Airfoil Propeller RPM Propeller Thrust (N) Cruise Velocity (m/s) Stall Reynolds number Cruise Reynolds number Minimum Reynolds number Root cord (m) Mean Cord (m) Tip Cord (m) Wingspan (m) Half-span (m) Trailing Edge Length (m) Tapered Section Area (m2) 2 Weight Musculair 2 E395 E858 / E850 135 27.5 12.5 600,000 560,000 440,000 0.750 0.6096 0.500 17.5 8.75 5.274 2.40 Total Wing Area (m ) 11.8 Total Aileron Area (m2) Aileron Deflection (degrees) Epoxy by weight ratio (%) Wing weight estimate (kg) Total weight estimate (kg) 0.428 20° 45 14.1 25.7 Figure 7. PSU Zephyrus Summary Table Acknowledgments First and foremost, the authors would like to pay homage to Harry Kremer and the RAS, the late Paul MacCready and his Gossamer team, Dr. Mark Drela and the MIT Daedelus team, and Prof Günther Rochelt and his Musculair group for laying the foundations in human-powered flight. Without their contributions, the field of human-powered flight would truly still be struggling to get off the ground. The authors would also like to collectively thank Dr. Mark Maughmer, Professor of Aerospace Engineering, Pennsylvania State University for inspiration and theoretical support in our attempt at the prize. In addition, we would like to thank Dave Benson and DuPont for their generous support of the project. Last but not least, we could not be where we are and cannot get to where we want to go without the help of the rest of the AERSP 204/404H class. References 1 Bramesfeld, G. and M. Maughmer, “The Penn State Sailplane Project - The First Decade”, Pennsylvania State Univeristy, 20th AIAA Applied Aerodynamics Conference, St. Louis, Missouri, June 24-26, 2002. 2 Grosser, M., The Gossamer Odyssey, Zenith Press, St. Paul, MN, 2004. 3 Royal Aeronautical Society, Human Powered Flight Group Website, http://www.raes.org.uk/cmspage.asp? cmsitemid=SG Hum Pow Home. [cited 15 November 2007]. 4 Schenk, H., Propeller Calculator, http://www.drivecalc.de/PropCalc/index.html, [cited 20 January 2008]. 5 Thomas, F., Fundamentals of Sailplane Design, College Park Press, 1999. 6 McCormick, Barnes W., Aerodynamics, Aeronautics, and Flight Mechanics, John Wiley and Sons Inc. 1995. 7 Pajno V., Sailplane Design, Salvo D’Acquisto, 2006. 8 Morelli, P., Static Stability and Control of Sailplanes, Levrotto and Bella, Torino, Italy, 1976. 11 of 11 American Institute of Aeronautics and Astronautics