Aerodynamics and Design for Ultra-Low Reynolds Number Flight

More documents

Recommendations

Info

Chapter 7 efficiency is devastating to the concept’s feasibility, but it also appears to suffer an additional 2% loss, most likely due to the addition of the four rotor-ducts without consideration being given to the rotor design. As was seen in Chapter 6, this amount of variation could also be attributable to geometric variations in the four epoxy SDM rotors. In both cases, the motors and controllers are representative of the state-of-the-art in small, high speed electric motors. For the 5mm Smoovy motors, a significant portion, perhaps as much as half, of the losses are due to the high speed switching controller required for brushless motors. It might be possible to improve the overall efficiency and achieve a significant mass reduction by developing a suitable brushed or coreless direct-current motor, but this is only speculative and beyond the focus of this work. It is clear that significant gains must be made in the supporting technologies of electronics, electric motors, and energy storage before even optimal aerodynamic design would permit success at the scale of the 15g prototype. Storage-based electric power has been the focus of this effort, but there are other approaches that have not been explored. The absence of concepts such as beamed energy, combustion, and other novel concepts is not meant to imply that they should be discounted; the current focus has been chosen because the existing technology was thought to be scalable without significant development effort. 7.5.3 Rotor Aerodynamic Efficiency Given the large non-aerodynamic handicaps placed on micro-rotorcraft, maximizing rotor performance should be considered an even more critical issue than in larger applications. Inefficiencies in the rotor design are effectively multiplied through the inefficiencies of the motors, controllers, and energy storage system. As an example, any increase in rotor power is seen by the batteries as doubled when passed through a 50% efficient system such as the 150g prototype. Unfortunately, rotors at small scales face a fundamental reduction in performance relative to their large scale brethren. 162
Chapter 7 Basic rotor theory has been applied to develop a better understanding of the performance costs associated with micro-rotors and key factors responsible for these penalties. From this effort, reasonable expectations on performance can be established. Rotor figure of merit (M) is a common criteria for the comparison of rotor designs and represents the hovering efficiency of a given rotor relative to an idealized reference value. Figure of merit is defined as: The ideal power is taken as the induced power required for hover from momentum theory, absent any viscous effects. The ideal power can then be expressed as: Assuming than an optimized design will have an induced power close to the minimum, the largest factor in the variation of P actual from P ideal is the profile power, P profile . This replaces Eqn.7.1 with the approximate form: This idealized form makes no attempt to account for hub effects on induced power. Under the limitations of a constant chord blade, small inflow angles, and the assumption that the section drag and lift coefficients remain essentially constant, the profile power may be approximated by: P ideal M = P ideal --------------- P actual = = Tu ideal P ideal M ≈ ------------------------------------- Pideal + Pprofile P profile T 3 --------- 2ρA ρσCd( ωR) 3 A ≈ --------------------------------- 8 (7.1) (7.2) (7.3) (7.4) 163
Page 1 and 2:
AERODYNAMICS AND DESIGN FOR ULTRA-L
Page 3:
I certify that I have read this dis
Page 7 and 8:
Abstract Growing interest in micro-
Page 9 and 10:
Nomenclature A Rotor disk area B Nu
Page 11 and 12:
τ Shear stress ω, Ω Rotor angul
Page 13 and 14:
Contents Acknowledgments...........
Page 15 and 16:
Chapter 5..........................
Page 17 and 18:
List of Tables 3.1 Effect of Airfoi
Page 19 and 20:
List of Figures 2.1 Comparison of I
Page 21 and 22:
5.6 Small test fixture in the large
Page 23 and 24:
6.38 Predicted spanwise thrust dist
Page 25 and 26:
Chapter 1 Introduction 1.1 Looking
Page 27 and 28:
Chapter 1 wind-tunnel facilities an
Page 29 and 30:
1.3 Summary of Contributions Chapte
Page 31 and 32:
Chapter 2 Two-Dimensional Computati
Page 33 and 34:
Chapter 2 The artificial compressib
Page 35 and 36:
Chapter 2 The control volume method
Page 37 and 38:
2.2.4 Comparison with Experiment Th
Page 39 and 40:
Chapter 2 to diverge if significant
Page 41 and 42:
2.4 Flow Field Assumptions The INS2
Page 43 and 44:
Chapter 2 The results of these time
Page 45 and 46:
Chapter 3 Analysis and Design of Ai
Page 47 and 48:
Chapter 3 adverse gradient in the p
Page 49 and 50:
The canonical pressure coefficient
Page 51 and 52:
Chapter 3 reaches α=5.0 and a lift
Page 53 and 54:
��
Page 55 and 56:
Cl 0.50 0.40 0.30 0.20 0.10 0.00 -0
Page 57 and 58:
Re=6000 result due to Reynolds numb
Page 59 and 60:
FIGURE 3.10 NACA 0002 and NACA 0008
Page 61 and 62:
C l C l 0.8 0.7 0.6 0.5 0.4 0.3 0.2
Page 63 and 64:
Chapter 3 The maximum L/D for all n
Page 65 and 66:
3.5 Effect of Leading Edge Shape an
Page 67 and 68:
C l 0.60 0.50 0.40 0.30 0.20 0.10 0
Page 69 and 70:
Chapter 3 prominent droop near the
Page 71 and 72:
Chapter 3 Small improvements in lif
Page 73 and 74:
Chapter 4 Hybrid Method for Rotor D
Page 75 and 76:
Q/r D L Chapter 4 FIGURE 4.1 Typica
Page 77 and 78:
4.2.3 Elimination of Trigonometric
Page 79 and 80:
Chapter 4 applications of interest
Page 81 and 82:
4.2.7 The Distinction Between the A
Page 83 and 84:
Chapter 4 Two input parameters dete
Page 85 and 86:
Chapter 4 simplification, particula
Page 87 and 88:
4.3.3 Conservation of Angular Momen
Page 89 and 90:
Chapter 4 moves downstream is less
Page 91 and 92:
Chapter 4 of the pitch angle at the
Page 93 and 94:
FIGURE 4.6 Converged wake streamlin
Page 95 and 96:
Chapter 4 idealized models. The met
Page 97 and 98:
��
Page 99 and 100:
Chapter 5 Overview of Experimental
Page 101 and 102:
1. Substrate Preparation 2. Polymer
Page 103 and 104:
Chapter 5 surface finish and aids i
Page 105 and 106:
FIGURE 5.5 Small test fixture in th
Page 107 and 108:
Chapter 5 The direct influence of t
Page 109 and 110:
FIGURE 5.9 Large test fixture in th
Page 111 and 112:
5.4.1 Motor Power Supply All tests
Page 113 and 114:
Chapter 5 or roughly (+/-) 25% of t
Page 115 and 116:
Chapter 5 newly forming blade tip v
Page 117 and 118:
FIGURE 5.14 Near-body grid geometry
Page 119 and 120:
Chapter 6 Design Examples and Compa
Page 121 and 122:
Chapter 6 capable of speeds up to 1
Page 123 and 124:
FIGURE 6.2 The Astro Flight Firefly
Page 125 and 126:
t/c 0.5 0.4 0.3 0.2 0.1 0.0 FIGURE
Page 127 and 128:
c/R 0.0 0.2 0.4 0.6 0.8 1.0 r/R Cha
Page 129 and 130:
FIGURE 6.10 Carbon-fiber two-blade
Page 131 and 132:
Power Req. (W) 3.5 3.0 2.5 2.0 1.5
Page 133 and 134:
Chapter 6 TABLE 6.1 Comparison of p
Page 135 and 136: Electro-mechanical Efficiency 0.20
Page 137 and 138: these variations and possible solut
Page 139 and 140: upper and lower surface corners of
Page 141 and 142: Chapter 6 The Sample-1 rotor exhibi
Page 143 and 144: The static deformations described i
Page 145 and 146: Q( r) This problem is solved as a l
Page 147 and 148: Structural Analyses Chapter 6 The m
Page 149 and 150: Aero-Structural Twist (deg.) 0.00 -
Page 151 and 152: Thrust (g) 5 4 3 2 1 0 10000 20000
Page 153 and 154: Thrust (g) 4.5 4.0 3.5 3.0 2.5 2.0
Page 155 and 156: Torque per unit span (g cm) 0.75 0.
Page 157 and 158: Thrust per unit span (g) 3.5 3.0 2.
Page 159 and 160: V total / ωr 1.0 0.9 0.8 Classical
Page 161 and 162: Torque per unit span (g cm) 0.75 0.
Page 163 and 164: Chapter 6 Recall that this rotor wa
Page 165 and 166: Incidence (deg.) 30 25 20 15 10 5 0
Page 167 and 168: Thrust (g) 9 8 7 6 5 4 3 2 38000 40
Page 169 and 170: x/R 0.4 0.2 0.0 -0.2 Chapter 6 FIGU
Page 171 and 172: Cl 0.64 0.62 0.60 0.58 0.0 0.2 0.4
Page 173 and 174: C f 0.125 0.100 0.075 0.050 0.025 0
Page 175 and 176: Chapter 7 Micro-Rotorcraft Prototyp
Page 177 and 178: This vehicle does not currently inc
Page 179 and 180: FIGURE 7.2 The 65g prototype electr
Page 181 and 182: 7.4 The 150g Prototype Chapter 7 Th
Page 183 and 184: At hover, with a mass of 153g, the
Page 185: Using the 150g prototype as an exam
Page 189 and 190: most of the blade. These values are
Page 191 and 192: Chapter 7 For large scale helicopte
Page 193 and 194: Chapter 8 Conclusions and Recommend
Page 195 and 196: the significant performance gains a
Page 197 and 198: Chapter 8 are also opportunities to
Page 199 and 200: Chapter 8 formation flight, and man
Page 201 and 202: References [1] Spedding, G.R., Liss
Page 203 and 204: [28] Lamb, Sir Horace, Hydrodynamic
show all

Aerodynamics and Design for Ultra-Low Reynolds Number Flight

You also want an ePaper? Increase the reach of your titles

Delete template?

Save as template?