Opportunities & Trends for Progress in Aircraft Performance Sina Golshany
Preface - Priorities • Since the late 1990s, fuel cost constitutes the largest fraction of the operating cost of a commercial airplane. • In a long-term time-average sense, fuel cost has been rising steadily since the 1960s. This trend continues, with local anomalies. • Fully digital systems, more electric systems, and improvements in engine reliability have led to lower maintenance cost, therefore: Making fuel-burn reduction the primary emphasis in
commercial aircraft design now, and into the future.
Preface - Opportunities Breguet Range Equation:
Ri→ f
Vtrue L Wi = ⋅ ln TSFC D Wi − W f
Propulsive Efficiency, 1:1 Aerodynamic Efficiency, 1:1 corresponding to Range, corresponding to Range, given a specific fuel load given a specific fuel load
Weight Efficiency, less than 1:1 corresponding to Range, given a specific fuel load
Preface - Opportunities • As the top priority remains to reduce fuel burn, commercial airplanes have progressed to accommodate this in the past 40 years. • The most significant changes have occurred in areas that directly effect the Breguet’s range equation (as a surrogate for fuel burn) in the following order: 1- Improving the installed engine fuel efficiency (designing the airplane around the best engine available, or enabling better engines to be installed) 2- Increasing the lift-to-drag ratio, particularly at high-speed cruise 3- Reducing the empty weight of the airplane, mostly via improvements in materials
• Drawing on public domain material, this presentation explores 11 opportunities and trends that might be useful to a designer
Opportunity 1 – The high-speed fan • Fan propulsive efficiency is the most significant contributor to the overall fuel efficiency of a high BPR propulsion unit. 1.0 0.6
0.8
t/c = 6.0 % 2.0 %
FAN EFFICIENCY
0.9 0.8 t/c = 13.5 % 5 %
0.7
1.0 1.1
0.6
1.3 Mtip= 1.4
0.5 0.4
0
0.2
0.4
0.6
0.7
0.8
MACH NUMBER
1.0
1.2
Opportunity 2 – Turbine Inlet Temperature • Higher T4 temperatures are achievable in a simple cycle, but the PSFC improvements can be relatively small, especially considering the difficulties 0.8
PSFC LBM SHP - HR
Turbine Inlet Temperature [ ⁰F]
0.7
1700
1900
2100
2300
2500
4
0.6 6 0.5
8 10 12 14 16 20 18 Core pressure ratio
0.4 0.3
50
100
150
SHP SPECIFIC POWER LBM/SEC
200
250
Opportunity 2 – Turbine Inlet Temperature • For a ~ 50 % increase in T4, PSFC improves by 12 % • For a ~ 50 % increase in T4, Spec. Power increases by 84 % 0.8
PSFC LBM SHP - HR
0.7
1700
Turbine Inlet Temperature [ ⁰F] ~ 50 % 1900 2100 2300 2500
4
0.6
Core pressure ratio 6
0.5
8
~ 12 % 0.4
20
~ 84 % 0.3
50
100
150
SHP SPECIFIC POWER LBM/SEC
200
10 12 14 16 18
250
Opportunity 3 – Regenerative Cycles • Reheat, Recuperation, Intercooling, or wave-rotor equipped cycles can drastically improve fuel efficiency – note that pressure ratio relation is reversed. 0.8
PSFC LBM SHP - HR
0.7
20 1700
0.6
Turbine Inlet Temperature [ ⁰F] ~ 50 %
18 16
0.5
14 12 4 -6 108
0.4 0.3
1900
50
100
2100 2300 2500
150
SHP SPECIFIC POWER LBM/SEC
200
250
Opportunity 3 – Regenerative Cycles • Reheat, Recuperation, Intercooling, or wave-rotor equipped cycles can drastically improve fuel efficiency – note that pressure ratio relation is reversed. PSFC LBM SHP - HR
0.75 Basic Cycle
0.50
~ 25 % With Regeneration
0.25 0 100
Basic Cycle
% FUEL FLOW
50
0
With Regeneration
0
20
40
60
% Power
80
100
Opportunity 4 – Engine/Airplane Matching • Better design coordination will allow engine & airframes to be designed to compliment each other – Example
40,000
30,000 POWER PLANT CRUISE EFFICIENCY
ALTITUDE [FEET]
η = 0.25 0.24 0.23 0.22 0.21
20,000
Power Plant Overall Efficiency: 10,000
ηα
TSFC θ 0
0.2
0.4
0.6
0.8
1.0
MACH NUMBER
1.2
1.4
Opportunity 4 – Engine/Airplane Matching • Better design coordination will allow engine & airframes to be designed to compliment each other – Example Max Power = Required Power
40,000
MAX Thrust = Drag
30,000
POWER PLANT CRUISE EFFICIENCY
ALTITUDE [FEET]
η = 0.25 0.24 0.23 0.22 0.21
20,000
10,000
0
0.2
0.4
0.6
0.8
1.0
MACH NUMBER
1.2
1.4
Opportunity 4 – Engine/Airplane Matching • Better design coordination will allow engine & airframes to be designed to compliment each other – Example
40,000
30,000 POWER PLANT CRUISE EFFICIENCY
ALTITUDE [FEET]
η = 0.25 0.24 0.23 0.22 0.21
20,000 L = 12 D 14 16 18
10,000
0
0.2
0.4
0.6
0.8
1.0
MACH NUMBER
1.2
1.4
Opportunity 4 – Engine/Airplane Matching • Better design coordination will allow engine & airframes to be designed to compliment each other – Example
40,000 INCREASED L/D
30,000 POWER PLANT CRUISE EFFICIENCY
ALTITUDE [FEET]
η = 0.25 0.24 0.23 0.22 0.21
20,000 L = 12 D 14 16 18
INCREASED η
10,000
0
0.2
0.4
0.6
0.8
1.0
MACH NUMBER
1.2
1.4
Opportunity 4 – Engine/Airplane Matching • Better design coordination will allow engine & airframes to be designed to compliment each other – Example • 2 opportunities emerge:
• Better Engine Design • Alternative Cruise Mach numbers
40,000 INCREASED L/D
30,000 POWER PLANT CRUISE EFFICIENCY
ALTITUDE [FEET]
η = 0.25 0.24 0.23 0.22 0.21
20,000 L = 12 D 14 16 18
INCREASED η
10,000
0
0.2
0.4
0.6
0.8
1.0
MACH NUMBER
1.2
1.4
Opportunity 5 – Aircraft Development Costs • There is a serious need for reducing the cost of design & production of airplanes. MILLIONS OF DOLLARS
60 50 40 30 20 WW-2
End of Cold War
Korea
10 0 1920
Vietnam
30
40
50
60
70
80
90
2000
2010
2020
Opportunity 5 – Aircraft Development Costs • Although airplanes have become more complex, our capacity for efficient handling of complex data has increased much faster 2.50E+09
50 40
2.00E+09
30
1.50E+09
20
1.00E+09 WW-2
End of Cold War
Korea
5.00E+08
10 0 1920
CPU TRANSISTOR COUNTS
MILLIONS OF DOLLARS
60
Vietnam
1930
1940
1950
1960
1970
1980
1990
2000
2010
2020
Opportunity 6 – Natural Laminar Flow (NLF) • There is a valid case for use of NLF to reduce airplane drag • Developing better methods for transition prediction will be important SKIN FRICTION COEFFICIENT Cf =
τ0 q
10-2
10-3
Transition Band
10-4
10-5 103
105 U δ REYNOLDS #, Rδ = ν0 104
106
Opportunity 7 – NLF Wing Planforms • To make NLF practical, LE sweep instabilities (cross-wash induced) have to be minimized % MAC LAMINAR FLOW
60
AR= 15 AR= 14 AR= 13 AR= 12
50 40
AR= 11 AR= 10 AR= 9
30 20 10 0
0
5
10
15
20
QUARTER CHORD WING SWEEP [DEG]
25
Opportunity 7 – NLF Wing Planforms • To make NLF practical, LE sweep instabilities (cross-wash induced) have to be minimized % MAC LAMINAR FLOW
60
AR= 15 AR= 14 AR= 13 AR= 12
50 40
AR= 11 AR= 10 AR= 9
30 20 10 0
Reduced Sweep 0
5
10
15
20
QUARTER CHORD WING SWEEP [DEG]
25
Opportunity 7 – NLF Wing Planforms • To make NLF practical, LE sweep instabilities (cross-wash induced) have to be minimized AR= 15 AR= 14 AR= 13 AR= 12
50 40 30 20 10 0
AR= 11 AR= 10 AR= 9
INCREASED NLF
% MAC LAMINAR FLOW
60
0
Reduced Sweep 5
10
15
20
QUARTER CHORD WING SWEEP [DEG]
25
Opportunity 7 – NLF Wing Planforms • This presents interesting tradeoffs with wing aspect ratio, and most importantly, cruise Mach number MID CRUISE L/D @ OPTIMUM MACH #
25.5
AR= 15 AR= 14 AR= 13 AR= 12
25.0 24.5
AR= 11 AR= 10 AR= 9
24.0 23.5 23.0 22.5 22.0 21.5
-8
-3
+2 +7 +12 QUARTER CHORD WING SWEEP [DEG]
+17
+20
Opportunity 7 – NLF Wing Planforms • This presents interesting tradeoffs between wing aspect ratio, and most importantly, cruise Mach number MID CRUISE L/D @ OPTIMUM MACH #
25.5
AR= 15 AR= 14 AR= 13 AR= 12
25.0 24.5
AR= 11 AR= 10 AR= 9
24.0 23.5 23.0 22.5 22.0 21.5
Increased Sweep -8
-3
+2 +7 +12 QUARTER CHORD WING SWEEP [DEG]
+17
+20
Opportunity 7 – NLF Wing Planforms • This presents interesting tradeoffs between wing aspect ratio, and most importantly, cruise Mach number MID CRUISE L/D @ OPTIMUM MACH #
25.5
AR= 15 AR= 14 AR= 13 AR= 12
25.0 24.5
Increased AR
24.0
AR= 11 AR= 10 AR= 9
23.5 23.0 22.5 22.0 21.5
Increased Sweep -8
-3
+2 +7 +12 QUARTER CHORD WING SWEEP [DEG]
+17
+20
Opportunity 7 – NLF Wing Planforms • This presents interesting tradeoffs between wing aspect ratio, and most importantly, cruise Mach number MID CRUISE L/D @ OPTIMUM MACH #
25.5
AR= 15 AR= 14 AR= 13 AR= 12
Diminishing return on AR (weight)
25.0 24.5
Increased AR
24.0
AR= 11 AR= 10 AR= 9
23.5 23.0 22.5 22.0 21.5
Increased Sweep -8
-3
+2 +7 +12 QUARTER CHORD WING SWEEP [DEG]
+17
+20
Opportunity 8 – Aerodynamics of Close-Coupled Large Rotors
• A better understanding of the aerodynamics of close coupled large rotors will have large practical benefits for airplane efficiency • Pusher & Puller Installations need to be explored further CL
TC ’’
CL’’’
α -(CT+CD) αR
Opportunity 8 – Aerodynamics of Close-Coupled Large Rotor Installations 1.5
20 1.0 15
CL’’’(WING)
Net CL 10
0.5 TC ’’ 0 0.5 0.9
0 0
10
20
30
αR ≈ SIN-1[(1-TC ’’)0.5 SIN(α)]
40
5
50
-15
-10 -5 -(CT+CD)
0
Opportunity 9 – Leading Edge Active Flow Control • Large increases in CLmax can be achieved by temporarily energizing the flow near the leading edge, to delay leading edge separation
3.5 3.0
2.5
CL
2.0 1.5 1.0
No Flaps
0.5 0
4
8
12
α [DEG]
16
18
Opportunity 9 – Leading Edge Active Flow Control • Large increases in CLmax can be achieved by temporarily energizing the flow near the leading edge, to delay leading edge separation
3.5 3.0
2.5
CL
2.0 1.5
Flaps Deployed
1.0
No Flaps
0.5 0
4
8
12
α [DEG]
16
18
Opportunity 9 – Leading Edge Active Flow Control • Large increases in CLmax can be achieved by temporarily energizing the flow near the leading edge, to delay leading edge separation
3.5 3.0
2.5
CL
LE Active Flow Control Increased Flow Rate
2.0 1.5 1.0
No Flaps
0.5 0
4
8
12
α [DEG]
16
18
Opportunity 9 – Leading Edge Active Flow Control • Large increases in CLmax can be achieved by temporarily energizing the flow near the leading edge, to delay leading edge separation • The main consequence is reducing the required wing area, if sized by approach speed
3.5 3.0
~ 40 % increase in CLmax
2.5
CL
LE Active Flow Control Increased Flow Rate
2.0 1.5 1.0
No Flaps
0.5 0
4
8
12
α [DEG]
16
18
Opportunity 10 – Lower Sweep Wings • The high sweep of current wing planforms is primarily a function of the relatively high cruise speed and the airfoil technology implemented 1.5
1.0
∆P q
M=1.0
0.5 0
-0.5
M=0.6 -1.0
Opportunity 10 – Lower Sweep Wings • For a given airfoil technology, the effects of sweep on critical Mach number are well understood LEADING EDGE SWEEP [deg]
100 80 0.5 0.6 0.7 0.8 0.9 1.0 Mach Number Normal to Leading Edge (effective)
60 40 20 0
0
1.0
2.0
MACH NUMBER
3.0
Opportunity 10 – Lower Sweep Wings • For low-speed flight, a lower sweep wing can have significant reduction in wing area for the same approach weight 4.0
C L MAX
CLmax |Λ 0 = 1.0
3.5
CLmax |Λ 0 = 2.0
3.0
CLmax |Λ 0 = 4.0
CLmax |Λ 0 = 3.0
2.5 2.0 1.5 1.0 0.5 0
0
10 20 30 40 50 60 70
WING SWEEPBACK AT QUARTER CHORD [deg]
Opportunity 10 – Lower Sweep Wings • For low-speed flight, a lower sweep wing can have significant reduction in wing area for the same approach weight 4.0 A 25⁰ increase in wing sweep, causes a 20 % reduction in CLmax This corresponds to ~ 20% increase in required wing area for the same approach speed.
C L MAX
CLmax |Λ=0 = 1.0
3.5
CLmax |Λ=0 = 2.0
3.0
CLmax |Λ=0 = 4.0
CLmax |Λ=0 = 3.0
2.5 2.0 1.5 1.0 0.5 0
0
10 20 30 40 50 60 70
WING SWEEPBACK AT QUARTER CHORD [deg]
Opportunity 11 - Augmented High-Lift Systems • There is a significant opportunity for augmented high-lift systems, to reduce the required wing area for STOL airplanes of all sizes UNDISTURBED FLOW
TURBULENT WAKE FLAP JET
Opportunity 11 - Augmented High-Lift Systems
Capable of 2D buffet free CLmax of ~ 6.5
Opportunity 11 - Augmented High-Lift Systems UNDISTURBED FLOW
NO TURBULENT WAKE NO FLAP WAKE EXTENSION
40⁰ FLAP DEFLECTION
PROPELLER DISK
Capable of 2D buffet free CLmax of ~ 6.5
Opportunity 11 - Augmented High-Lift Systems • It is possible to optimally deflect thrust, to reduce the wing area required for a given approach speed & weight. 1.0
0.5
1.9
1.5
0.5
1.0
1.0
0.8
1.5 CL =1.9 AR
( WT ) 0.6 0.4 0.2
Optimum Jet Deflection No Jet Deflection
0
0
0.2
0.4
0.6
Low Speed Metric
0.8
1 CL AR
1.0
1.2
1.4
Opportunity 11 - Augmented High-Lift Systems • For Example 1.0
0.5
0.8
CL =1.9 AR
( WT ) 0.6
1.9
1.5
0.5
1.0
1.0 1.5
~ 30% Reduction
0.4 0.2
Optimum Jet Deflection No Jet Deflection
0
0
0.2
0.4
0.6
Low Speed Metric
0.8
1 CL AR
1.0
1.2
1.4
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