Phase II Final Report - NASA's Institute for Advanced Concepts

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Planetary Exploration Using Biomimetics An Entomopter for Flight on Mars 84], Entomopter wings (unlike those of the Hawk Moth) should be able to generate positive lift not only the downbeat but the upbeat as well. These wind tunnel tests have shown that coefficients of lift exceeding the theoretical maximum by 500% for the given wing shape can be achieved without the complexity of active angle-ofattack modulating mechanisms. A chemically fueled reciprocating chemical muscle has been designed and is in its fourth generation of development at the time of this writing. This actuator system has demonstrated 70 Hz reciprocation rates with throws and evolved power levels necessary to support flight, crawling, or swimming of a self-contained fully autonomous Entomopter system [187]. The reciprocating chemical muscle uses the energy locked in various chemical fuels to produce reciprocating motion for propulsion as well as waste gas products for the operation of gas bearings, an ultrasonic obstacle avoidance ranging system, and full flight control of the vehicle. 1.2.1 Why Flapping Wing Flight? Rotary wing vehicles have been proposed as a method for achieving slow controlled flight in the Mars atmosphere while allowing takeoff and landing. Unfortunately, the rarefied atmosphere brings with it a lower speed of sound. Rotor tips rapidly exceed the speed of sound at rotational speeds that are insufficient to lift the vehicle. This has forced those considering such an approach to use multiple smaller diameter articulated rotors or variable speed propellers. The redundancy of transmissions, motor casings, control mechanisms, and the structure to support the multiple rotor system are at the expense of performance (added weight). In addition, those techniques that rely on pitch changes in the rotor or the vehicle’s fixed propeller’s angle of attack, result in unwanted blade stall conditions due to the sensitivity of the low Reynolds number flow over these critical airfoils. This makes horizontal translation of the vehicle difficult. Tests of a small unarticulated propeller in JPL’s Mars atmosphere simulation chamber produced lift, but performance was disappointing compared to that which was originally predicted.[146] Another way to move air over a wing without fuselage translation is to move the wing relative to the fuselage and the surrounding air in a flapping motion rather than a rotary one. It could be argued that a flapping wing implementation is an inherently lower bandwidth system than one using a helicopter rotor or fixed pitch fans. Both systems require cyclic (once-per-flap or onceper-revolution) control inputs to maintain vertical lift and stability, but the frequencies at which these inputs must be generated can be much lower for comparably sized flapping implementations. Because of the lower flapping frequencies required of a lower aspect ratio wider chord wing as opposed to a narrow high aspect ratio rotor, the tips do not approach supersonic speeds. The lift of a flapping wing can be superior to that of a fixed or rotary wing, however it is still not optimal based on any conventional wing shape when operating in the atmosphere of Mars. Techniques such as active flow control of blown wing surfaces offer the potential to create significant added lift, thereby making a blown flapping wing plausible as a method for achieving relatively slow controlled flight in the lower Mars atmosphere. This can be done by “blowing” the surfaces of the wing to keep flow attached and to increase lift in an intelligent manner by using an internally-generated pressure source. This has been demonstrated in manned aircraft and certain 10 Phase II Final Report
Chapter 1.0 Introduction 1.2 Origins of the Entomopter Concept experimental unmanned vehicles, but is typically inefficient unless there is a source of gas pressure already available (such as bleed air from a gas turbine engine). Flapping wings are more survivable and robust in the presence of foreign object damage (FOD) and grazing impacts than rotary wings. The flapping wing operates over a range of energies from zero at the top and bottom of the stroke, to maximum at mid-flap. Rotors and propellers on the other hand, concentrate all of their energy at their rotational frequency and tend to explode when coming in contact with objects. It is a well documented fact that birds and insects are able to sustain collisions with walls (or one another) without major damage when they become trapped indoors. Further, the reciprocating nature of flapping wings lends itself to resonant operation with its accompanying energy efficiencies. Rotors can not be resonant in rotation and rotary wing designs tend to avoid resonance rather than capitalizing upon it. It should be noted that all insects store energy in a substance called “resilin” to recapture flapping energy in a resonant fashion. [188] There is another reason to consider flapping wing flight, and that is due to the leading edge vortex phenomenon. Recently, flow visualization studies on the Hawk Moth Manduca sexta and a 10x scale mechanical model have identified dynamic stall as the high-lift mechanism used by most insects [281]. During the downstroke, air swirls around the leading edge of the airfoil and rolls up into an intense leading-edge vortex (LEV). The direction of circulation in the LEV augments the bound vortex and hence the lift. LEV grows until it becomes unstable at a distance of three to four chord lengths at which time it breaks away from the wing causing deep stall. Ellington and associates have shown that a strong axial (spanwise) flow in the LEV, when coupled with the swirling motion of the vortex, results in a spiral LEV with a pitch angle of 46 degrees across the surface of the flapping wing [78, 265, 266, 281]. The axial flow convects vorticity out toward the wing tip, where it joins with the tip vortex and prevents the LEV from growing so large that it breaks away. Thus stabilized, the LEV prolongs the benefits of dynamic stall for the entire downstroke. Helicopter rotors also experience spanwise pressure gradients, but these beneficial large-scale axial flows have not been observed [53], leading one to surmise that resonant flapping wing solutions in the rarefied Mars atmosphere will be more successful in producing required lift than nonresonant rotary wing attempts. During the mid 1990s the Defense Advanced Research Projects Agency began considering the feasibility and uses for tiny terrestrial flying vehicles on the scale of small birds and insects. In response to this interest, the notion of the 'Entomopter' (entomo as in entomology + pteron meaning wing, or a “winged insect machine”) was borne as an internal research and development (IRAD) program within the Georgia Tech Research Institute (GTRI). Nothing in creation exhibits fixed wing flight behavior or propeller-driven thrust. Everything that maintains sustained flight, uses flapping wings. Even though there has been considerable analysis in the literature of mechanisms for bird flight [73] and insect flight [13, 29], and ornithopter-based (bird flight) machines have been demonstrated, the unsteady aerodynamics of blown flapping wings is an absolutely new area of research and the work performed to date by GTRI's terrestrial Entomopter design team has been pioneering (Figure 1-9) 11
Page 1 and 2: Planetary Exploration Using Biomime
Page 3 and 4: Table of Contents Table of Contents
Page 5 and 6: List of Tables List of Tables Table
Page 7 and 8: List of Figures List of Figures Fig
Page 9 and 10: List of Figures Figure 3-54: Pressu
Page 11 and 12: List of Figures Figure 3-138: Stere
Page 13 and 14: List of Figures Figure 4-24: Averag
Page 15 and 16: List of Contributors List of Contri
Page 17 and 18: Executive Summary Executive Summary
Page 19 and 20: Chapter 1.0 Introduction Chapter 1.
Page 21 and 22: Chapter 1.0 Introduction Figure 1-2
Page 23 and 24: Chapter 1.0 Introduction 1.1 Histor
Page 25 and 26: Chapter 1.0 Introduction 1.2 Origin
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Page 35 and 36: 1.3.3.1 Surface Imaging The Entomop
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Chapter 3.0 Vehicle Design 3.2 Wing
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3. Density: 1.40E-2 kg/m 3 4. Press
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Chapter 3.0 Vehicle Design 3.4 Reci
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Chapter 3.0 Vehicle Design 3.5 Fuel
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Chapter 3.0 Vehicle Design 3.6 Powe
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Chapter 4.0 Entomopter Flight Opera
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Chapter 5.0 Potential Payload Funct
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Chapter 6.0 Media Exposure 6.1 Intr
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Chapter 6.0 Media Exposure 6.3 Onli
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Chapter 6.0 Media Exposure 6.6 Spec
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Chapter 7.0 Conclusion Chapter 7.0
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Appendix A: Mars Atmosphere Data JP
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Appendix A: Mars Atmosphere Data Ge
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Appendix A: Mars Atmosphere Data Ma
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Appendix B: Sizing Results Appendix
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Appendix B: Sizing Results 30 Wing
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Appendix B: Sizing Results 16 Wing
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Appendix B: Sizing Results Length 0
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Appendix B: Sizing Results Lenght 0
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Appendix C: List of References Appe
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Appendix C: List of References 41.
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Phase II Final Report - NASA's Institute for Advanced Concepts

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