Transcript Lecture 1 Introduction and Course Overview

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
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3
Concept
Source: Don Galbraith, 1979
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High Lift Technology Turbine Technology
C.P. (Case) van Dam
Department of Mechanical and Aeronautical
Engineering
UC Davis
Wind
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
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Fuel Share of Direct Operating Cost
Schrauf (2006)
Trip length = 6000nm,
Fuel: $0.60/US gallon Fuel: $1.80/US gallon
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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
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Potential Reduction in Fuel Consumption
Szodruch&Hilbig (1998)
20
0
8%
L/D
SFC
Structures,
materials,
systemd
40
23 %
Engine
technology
60
Aerodynamics
Trip Fuel/Distance ~
W/(L/D)SFC/M∞
36 %
80
Current technology status
Time frame ~ 20 years
Trip Fuel per unit Distance
100
W
Conclusion: > 50% reduction in fuel consumption is feasible
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Potential Improvement in Aerodynamic
Efficiency
Schrauf (2006)
Drag
Decomposition
Technologies
Drag Reduction
Potential
Shock control
Novel configurations
-3%
Shape optimization
Adaptive wing devices
Wingtip devices
Load control
-7%
Laminar flow technology
Turbulence control
Flow separation control
Conclusion: Total improvement of 25% in L/D is feasible
-15%
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Breguet Range Equation for Transport Jets
Range performance of a transport jet at constant lift
coefficient and speed (cruise-climb cruise) is governed by:
a
L W0
R
M ln
T SFC
D W1
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
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
Performance Characteristics of Transport
Jets in Cruise
T  D  C D 1 pM2 S
2
W  L  C L 1 pM2 S
2
Simple parabolic drag polar:
Minimum required thrust
condition:

 T 
1
  
W min (L /D) max
CD  CD0  C2L /(  AR  e)
CL (C Dmin )  CD 0    AR  e
CD min  2C D 0
L 
1   AR  e
  
D max 2
CD0
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
 AR for given cruise condition and wing
of laminar flow and high
loading
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Aerodynamic Efficiency Evolution of
Long-Range CTOL Airplanes
Airplane range > 4,500 n.mi., Callaghan & Liebeck (1990)
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Design Space for Long-Haul CTOL Transports
Initial cruise conditions: M∞ = 0.80 at h = 30,000 ft (SA)
100
20
80
Conventional
CDo = 0.0145
AR = 7.5
e = 0.80
(L/D)max = 18.0
CDo = 0.0025
W/S = 147 lb/f t2
15
60
0.0050
(L/D)max
10
0.0100
AR.e = 5
40
0.0150
0.0200
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Re duce d zerolift drag
Incre as ed effective
as pe ct ratio
0
0
50
100
150
200
250
300
350
2
Wing Loading W/S, lb/ft
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Design Space for Personal Air Vehicles
Initial cruise conditions: h = 8,000 ft at 200 KTAS (SA)
100
25
CDo = 0.0025
20
80
15
0.0050
60
(L/D)max
10
0.0100
Reduce d ze rolift drag
AR.e = 5
40
0.0200
0.0300
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Current
technology
W/S and
(L/D)max
Increas e d e ffe ctive
as pe ct ratio
0
0
20
40
60
80
100
Wing Loading W/S, lb/ft2
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Stall Speed and Maximum Lift for GA Aircraft
Holmes (1982)
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Modern PAV Design
Lancair 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
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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.
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Evolutionary Versus Revolutionary
Progress
• Technical progress for a
product tends to occur
along an S-curve
Value
• 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
Time
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Circulation Control Wing (CCW) Concept
Linton (1994)
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Circulation Control Airfoils and Wings
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Effect of Circulation Control on Lift
t/c = 0.17 supercritical airfoil, Englar et al (1993)
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Modifications to A-6/CCW Airplane
Nichols (1979)
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Trimmed Lift Curves of A-6/CCW Airplane
Nichols (1979)
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Flight Test Results of A-6/CCW Airplane
Nichols (1979)
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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, directlift 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
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Wind Turbine Technology
•
•
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•
•
•
•
•
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)
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QuickTime™ and a
Motion JPEG OpenDML decompressor
are needed to see this picture.
Trend in
Turbine Size and
Power Output
S. Johnson
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Innovations in Utility Scale Wind Turbines
Advanced Tower Designs
Advanced Drive Trains
Advanced Blades
Jack-up concept
Telescoping concept
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Design Advancement Opportunities
Source: Ashwill, SNL
– 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
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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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