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Electric Aircraft Symposium May 23, 2007

Electric Aircraft Symposium May 23, 2007. Benefits of Electric Propulsion. Public Policy: Diversion from use of gasoline Reduced noise (radiated) Enhanced safety and performance Reduced air pollution Further increase efficiency of energy use. Concept Source: Don Galbraith, 1979.

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Electric Aircraft Symposium May 23, 2007

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  1. Electric Aircraft SymposiumMay 23, 2007

  2. Benefits of Electric Propulsion • Public Policy: • Diversion from use of gasoline • Reduced noise (radiated) • Enhanced safety and performance • Reduced air pollution • Further increase efficiency of energy use

  3. ConceptSource: Don Galbraith, 1979

  4. High Lift Technology - Wind Turbine Technology C.P. (Case) van Dam Department of Mechanical and Aeronautical Engineering UC Davis

  5. Outline • Introduction • High-Lift Technology • Wind Turbine Technology • Concluding Remarks

  6. Historical Jet Fuel Prices • Price information as of 15 May 2007: • NY Harbor $2.0904 • US Gulf Coast $2.0479 • LA $2.1179 • Rotterdam $1.9919 • Singapore $1.9321

  7. Fuel Share of Direct Operating CostSchrauf (2006) Trip length = 6000nm, Fuel: $0.60/US gallon Fuel: $1.80/US gallon

  8. Impact of Fuel Efficiency • Impact of fuel on aircraft operating cost is significant and is main component of DOC for long missions at current fuel prices • Reduction of fuel usage also has beneficial on air pollution with X% reduction of fuel burn for a given mission resulting in X% reduction in emissions • European Aeronautics Vision 2020 includes: • 50% reduction in fuel consumption (i.e., 50% reduction in CO2) • 80% reduction in NOx • 50% reduction in perceived noise

  9. Potential Reduction in Fuel ConsumptionSzodruch&Hilbig (1998) Time frame ~ 20 years Trip Fuel/Distance ~ W/(L/D)SFC/M∞ Conclusion: > 50% reduction in fuel consumption is feasible

  10. Shock control Novel configurations Shape optimization Adaptive wing devices Wingtip devices Load control Laminar flow technology Turbulence control Flow separation control -3% -7% -15% Potential Improvement in Aerodynamic EfficiencySchrauf (2006) Drag Decomposition Technologies Drag Reduction Potential Conclusion: Total improvement of 25% in L/D is feasible

  11. Breguet Range Equation for Transport Jets Range performance of a transport jet at constant lift coefficient and speed (cruise-climb cruise) is governed by: where: a∞ = speed of sound TSFC = thrust specific fuel consumption M∞ = Mach number L/D = airplane lift-to-drag ratio W0 = initial weight W1 = final weight = W0 - fuel weight

  12. Performance Characteristics of Transport Jets in Cruise Note: • Application of laminar flow reduces CD0 and, hence, CL(CDmin) • Increase in aspect ratio, AR, or Oswald’s efficiency factor, e, increases CL(CDmin) • Combined effect necessary in order to maximize beneficial effects of laminar flow and high AR for given cruise condition and wing loading Simple parabolic drag polar: Minimum required thrust condition:

  13. Aerodynamic Efficiency Evolution of Long-Range CTOL AirplanesAirplane range > 4,500 n.mi., Callaghan & Liebeck (1990)

  14. Design Space for Long-Haul CTOL TransportsInitial cruise conditions: M∞ = 0.80 at h = 30,000 ft (SA)

  15. Design Space for Personal Air VehiclesInitial cruise conditions: h = 8,000 ft at 200 KTAS (SA)

  16. Stall Speed and Maximum Lift for GA AircraftHolmes (1982)

  17. Modern PAV DesignLancair Legacy, Source: http://www.cafefoundation.org/ (W/S)TO = 26.66 lb/ft2 MTOW = 2,200 lb S = 82.5 ft2 CLmax,clean = 1.51 CLmax,flaps = 2.35 Vs = 56.9 kts

  18. PAV Design Observations • To achieve higher performance plateaus, higher wing loadings are required. • To maintain acceptable stall speeds (61-knot rule), higher maximum lift coefficients are required. • Lower viscous drag (lower CDo) can significantly mitigate the negative impact of higher wing aspect ratio on wing loading.

  19. Evolutionary Versus Revolutionary Progress • Technical progress for a product tends to occur along an S-curve • The S-curve models the evolutionary changes in technology • Leaps in technology are modeled in the form of jumps between S-curves • These jumps model revolutionary changes in technology • Leaps in technology are needed to extend the capabilities of the product to a new level

  20. Circulation Control Wing (CCW) ConceptLinton (1994)

  21. Circulation Control Airfoils and Wings

  22. Effect of Circulation Control on Liftt/c = 0.17 supercritical airfoil, Englar et al (1993)

  23. Modifications to A-6/CCW AirplaneNichols (1979)

  24. Trimmed Lift Curves of A-6/CCW AirplaneNichols (1979)

  25. Flight Test Results of A-6/CCW AirplaneNichols (1979)

  26. CCW Concept Advantages and Disadvantages • Advantages • Higher maximum lift than obtainable with conventional multi-element mechanical high-lift systems resulting in: • Improved takeoff/landing performance • Higher design wing loadings and, hence, improved cruise performance • Reduced complexity of high-lift system • Reduced complexity of control system by combining high-lift, direct-lift control and roll control into single multipurpose pneumatic surfaces • Disadvantages • Reduced efficiency due to (bleed-)air requirements • Airplane trim requirements may significantly reduce attainable maximum lift coefficient

  27. Wind Turbine Technology • Wind-based electric energy has become cost effective • Cost effectiveness has spurred large companies (FPL, GE, Siemens, etc.) to enter the market • Push to drive cost of energy down has resulted in much larger wind turbines • Square-cube law (rotor power goes by diameter-squared, rotor mass goes by diameter-cubed) has resulted in significant lighter composite rotor structures • Modern rotors have efficiency of approx. 52% vs. theoretical maximum of 59.7% • Modern rotors use variable speed to maximize efficiency and variable pitch to control torque/power • Technology developments are focused on lighter structures for given energy capture or increased energy capture through longer blades for unchanged rotor mass • Technology is bifurcating: • Land-based utility-scale wind turbines (blade length ≤ 45 m, P ≤ 3 MW) • Off-shore wind turbines (P ≥ 5 MW) • Wind turbines for residences and small businesses (P = 0.5 - 50 kW)

  28. Trend inTurbine Size and Power Output S. Johnson

  29. Innovations in Utility Scale Wind Turbines Advanced Tower Designs Advanced Drive Trains Advanced Blades Jack-up concept Telescoping concept

  30. Load alleviation Passive - twist coupling Sweep twist Active devices - microtabs Performance enhancement & control devices Pitch – collective & individual Flaperons, ailerons Active devices Variable diameter rotor Efficient internal blade architecture Anti-buckling concepts Slender blades Integrated structural/aerodynamic design Thickened airfoils Safety factor shakeouts Design Advancement Opportunities Source: Ashwill, SNL

  31. Conclusions • It is timely to (re-)consider electric aircraft • In order for these vehicles to achieve acceptable flight performance, they must have high L/D, and capable of generating high lift coefficients • Circulation control wing concept is proven technology to provide high lift performance • As we move forward and reduce our oil dependency and emissions, wind power may be able to provide a large percentage (>20%?) of electric energy needs in USA • Wind turbine technology is rapidly becoming very sophisticated

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