Presentation: Aircraft Design with Active Load Alleviation and Natural Laminar Flow

8/13/2019 Presentation: Aircraft Design with Active Load Alleviation and Natural Laminar Flow

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8 th AIAA Multidisciplinary Design Optimization Specialist Conference

Jia Xu, Ilan KrooAircraft Design Group

Stanford University


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Boeing Sugar Volt (Bradley and Droney, 2011)


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Structural EnablersActive load alleviation

Strut-braced wings

Aerodynamic FeaturesVery high span

Natural laminar flow


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15-25% wing weight reductionfrom active load alleviation

Assumed transition Reynoldsnumber: 15-17 million


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Incorporate active load alleviation andnatural laminar flow into conceptual design


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Motivation

Use active control to increaseeffective structural efficiency

Invest structural savings to

enable natural laminar flow


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Design Studies

Conclusion

Active Load Alleviation

Design Optimization

Natural Laminar Flow


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NLF can produce 5-12% fuel burn savings(Joslin 1998, Green 2008, Allison 2010)Performance subject to multidisciplinary

tradeoffsWing sweep is a critical trade at transonic speed


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10/117 Adopted from Rajnarayan and Sturdza (2011)

0

5

10

15

20

25

3035

40

0 10 20 30 40

S w e e p (

D e g

)

Transition Reynolds Number (Million)

NLF Region

Active LFC


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0

5

10

15

20

25

3035

40

0 10 20 30 40

S w e e p (

D e g

)


NLF Region

Active LFC


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0

5

10

15

20

25

30

35

40

0 10 20 30 40

S w e e p (

D e g

)


NLF Region

Active LFC


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0

5

10

15

20

25

30

35

40

0 10 20 30 40

S w e e p (

D e g

)


NLF Region

Active LFC


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Slow downPotentially increased direct operating cost (DOC)Challenge for air traffic control (ATC)

Increase structural efficiencyStrut/truss braced wing (Gur et al., 2010) Active load alleviation


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Design Studies

Conclusion

Design Optimization




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Reduce wing stresses under limit conditionsManeuver Load Alleviation (MLA)

Respond to commanded pseudo-static maneuvers

Gust Load Alleviation (GLA)Respond to unanticipated atmospheric turbulencePerformance limited by sensor and actuatorbandwidths


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Maneuver lift


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Maneuver lift with MLA


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1-Cosine gust (FAR Part 25)

3 gust encounter flight conditions

8 gust gradient lengths from 35 to 600 ft

Simulations include both aircraft and wing structural dynamics


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GLA system use control surface deflections to reducedynamic stresses in gust encountersDynamic control problem


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Design Studies

Conclusion


Design Optimization



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Program for Aircraft Synthesis Studies (Kroo,1992)

Extended for aeroservoelastic design


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W i i l th d ith


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Inverse wing design module withboundary layer solver andtransition model

Linear hexagonal wing boxmodel for stress and load-bearing weight calculations

Aircraft dynamic simulation andFEM/modal solution of structuredynamic response

Weissinger panel method withcompressibility corrections tomodel loads and stabilityderivatives


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Inverse wing design with integralboundary layer and transition model

Linear hexagonal wing box forstress and load-bearing weightcalculations

Aircraft dynamic simulation andmodal solution of dynamic structuralresponse

Weissinger method withcompressibility corrections to modelloads


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30 aerodynamic controlpoints along the semi-spanStatic stress constraints:


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Lumped mass FEM withlinear modal decompositionDynamic stress constraints:


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MLA flap deflections arevariables:


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Proportional-derivative GLAcontrol law

Control gains are variables:

Deflection and rate bounds


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Method of critical sectionsMaximum lift constraints atcontrol point span stations:


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Thin, high span wing is proneto aileron reversal

Aileron effectiveness

constraint:

Strip method to integrateaileron-induced wing torsion


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Define C p distributions atexposed sectionsExposed root section is

forced to be turbulentUse sweep/taper theory torelate 2D to 3D pressureSimilar to Campbell (1990)

and Allison et al. (2010)


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Cdc correlated to peak Machnumber (Allison et al., 2010)

l f l f


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Solve airfoil geometry from C p distribution

Apply geometry constraints:

l b d l i h


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Integral boundary layer withcompressibility correctionsTransition location is posed

as a design variablePredict transition using HR-xcriteria (Wazzan, 1986)Cdp from the Squire-Young

equation (Smith, 1980)


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Gradient-based optimizationMotivated by the large number of design variables

Objective

Cost estimated using an extended ATA method(Thomas, 1966; Liebeck et al. 1995 )


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Aircraft and Mission ( 11 )Takeoff weight, engine thrust, tail areaInitial and final cruise altitudes

Takeoff and landing flapWing Geometry ( 33 )

Trapezoidal wing area, sweep, AR, taper and root positionTwist and wing box geometry at breakpoints

Wing Inverse Design ( 40 )Pressure distribution and x-transition at breakpoints

MLA (8)MLA control surface deflections

GLA ( 8)GLA control channel gains


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Aircraft and Mission ( 31 )RangeBalanced takeoff and landing field performance2nd segment climb gradientThrust margin for operational climbTrim, tail maximum lift

Stability at all flight conditionsWeight and load factor compatibilityLanding gear geometry and load compatibility

Aileron effectivenessWing fuel volume


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Stress and Maximum Lift ( ~50,000 )

Wing maximum lift for all flight conditionsWing stresses in cruise, maneuver and gust

Inverse Design ( 40 )Wing box geometry compatibilitySection C l compatibilityRecovery Mach number limitsTransition location compatibility


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Conclusion

Design Optimization


Design Studies


Boeing 737 type aircraft


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Boeing 737-type aircraft162 passengers (3-Class)Mach 0.78

2000-nm range Aluminum constructionCFM56-7B class turbofanField length (7800/5600 ft)


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T u r b u

l e n

t

L a m

i n a r

Wing sweep of up to 40 degreesForced transition at 5% chord

Wing sweep restricted to less than 10degreesFree transition on upper surfaceForced transition on lower surface at 5%chord

Top surface produce most of the viscous dragContaminants and slat gaps


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No Alleviation MLA+GLAMLA GLA

T u r b u

l e n

t

L a m

i n a r


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T u r b u

l e n

t

L a m

i n a r


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0.7 0.72 0.74 0.76 0.78 0.80.92

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0.96

0.98

1

1.02

1.04

Cruise Mach Number

R e l a

t i v e

C o s t

Turbulent


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0.7 0.72 0.74 0.76 0.78 0.80.92

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0.96

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1

1.02

1.04

Cruise Mach Number

R e l a

t i v e

C o s t

Turbulent

Reference design

at Mach 0.78


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0.7 0.72 0.74 0.76 0.78 0.80.92

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0.96

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1

1.02

1.04

Cruise Mach Number

R e l a

t i v e

C o s t

TurbulentTurbulent MLA


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0.7 0.72 0.74 0.76 0.78 0.80.92

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0.96

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1

1.02

1.04

Cruise Mach Number

R e l a

t i v e

C o s t

TurbulentTurbulent MLATurbulent GLA


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0.7 0.72 0.74 0.76 0.78 0.80.92

0.94

0.96

0.98

1

1.02

1.04

Cruise Mach Number

R e l a

t i v e

C o s t

TurbulentTurbulent MLATurbulent GLA

Turbulent MLA+GLA

t


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T u r b u

l e n

t

L a m

i n a r

t


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T u r b u

l e n

t

L a m

i n a r


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0.7 0.72 0.74 0.76 0.78 0.80.92

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0.96

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1

1.02

1.04

Cruise Mach Number

R e l a t i v e

C o s t

LaminarLaminar MLA


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0.7 0.72 0.74 0.76 0.78 0.80.92

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0.96

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1

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Cruise Mach Number

R e l a t i v e

C o s t

LaminarLaminar MLALaminar GLA


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0.7 0.72 0.74 0.76 0.78 0.80.92

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0.96

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1

1.02

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Cruise Mach Number

R e l a t i v e

C o s t

LaminarLaminar MLALaminar GLA

Laminar MLA+GLA

t


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T u r b u

l e n

t

L a m

i n a r

t


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T u r b u

l e n

t

L a m

i n a r


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Wing Weight Fuel Weight Sea Level Thrust L/ D Cost0.6

0.7

0.8

0.9

1

1.1

1.2

1.3

R e l a

t i v e

V a

l u e

TurbulentTurbulent MLA+GLALaminar MLA+GLA


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0.7

0.8

0.9

1

1.1

1.2

1.3

R e l a

t i v e

V a

l u e

TurbulentTurbulent MLA+GLALaminar MLA+GLA

-5%-15%


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0.7

0.8

0.9

1

1.1

1.2

1.3

R e l a

t i v e

V a

l u e

Turbulent

Turbulent MLA+GLALaminar MLA+GLA

Weight versus aerodynamics


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0.7 0.72 0.74 0.76 0.78 0.80.92

0.94

0.96

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1

1.02

1.04

Cruise Mach Number

R e l a

t i v e

C o s t

TurbulentTurbulent MLA+GLA


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0.7 0.72 0.74 0.76 0.78 0.80.92

0.94

0.96

0.98

1

1.02

1.04

Cruise Mach Number

R e l a

t i v e

C o s t

TurbulentTurbulent MLA+GLALaminar


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0.7 0.72 0.74 0.76 0.78 0.80.92

0.94

0.96

0.98

1

1.02

1.04

Cruise Mach Number

R e l a

t i v e

C o s t

TurbulentTurbulent MLA+GLALaminar

Laminar MLA+GLA


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Up to 25 degrees of wing


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sweep Assume that crossflow can be

stabilized with no adverseeffect on T-S stabilityOptimistic model for 3-D NLFwing


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0.7 0.72 0.74 0.76 0.78 0.80.92

0.94

0.96

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1

1.02

1.04

Cruise Mach Number

R e l a t i v

e C o s t

Laminar MLA+GLALaminar25 MLA+GLA


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Design Optimization



Conclusion

Design Studies


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MLA and GLA are complementaryTurbulent MLA+GLA achieves 10% fuel reduction

The combination enables low-sweep NLF wingsLaminar MLA+GLA achieves 15% fuel reduction

Low-sweep MLA+GLA designs can serve asalternatives to crossflow-dominated NLFdesigns


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AerodynamicsUnsteady aerodynamicsFlutter and its suppression

ControlSensorsControl power and control allocation


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Allison, Eric. Kroo , I., Aircraft Conceptual Design with LaminarFlow, 2010

Ning, S. and Kroo , I., Multidisciplinary Considerations in the Designof Wings and Wing Tip Devices, Journal of Aircraft, 2010

Rajnarayan, D. Sturdza, P., Extensible Rapid Transition Predictionfor Aircraft Conceptual Design. 29th AIAA Applied AerodynamicsConference, 2011

Wakayama, S. and Kroo , I., Subsonic Wing Planform Design UsingMultidisciplinary Optimization, Journal of Aircraft, 1995

Xu, J, Kroo. I., Aircraft Design with Maneuver and Gust Load Alleviation, 29th AIAA Applied Aerodynamics Conference, 2011


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Laminar MLA+GLA Laminar-25 MLA+GLA DeltaMTOW (lb) 150920 149140 -1.2%

SLS Thrust (lb) 18128 18050 -0.4%L/D 21 21 0.5%Fuel Burn (lb) 22169 21915 -1.1%DOC (c/pax/nm) 4.86 4.82 -0.8%


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Wing Weight Fuel Weight Sea Level Thrust L/ D Cost

0.6

0.7

0.8

0.9

1

1.1

1.2

1.3

R e l a t i v

e V a l u e

Laminar

Laminar25


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0.6

0.7

0.8

0.9

1

1.1

1.2

1.3

R e l a t i v

e V a l u e

Laminar

Laminar25


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Turbulent



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Reduced t/c due towing unsweep


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Inboard t/c constrained bycompressibility and NLF


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Aeroelastic constraintsincrease outboard t/c


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0 5 10 15

0.92

0.94

0.96

0.98

1

1.02

1.04

Allowable Load Control Deflection (Deg)

R e l a t i v e

C o s t



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0 10 20 30 40

0.92

0.94

0.96

0.98

1

1.02

1.04

Load Control Deflection Rate (Deg/ s)

R e l a t i v e

C o s t



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0.7 0.72 0.74 0.76 0.78 0.8

0.92

0.94

0.96

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1

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1.04

Cruise Mach Number

R e l a t i v e

C o s t

Turbulent MLA+GLALaminar MLA+GLALaminar Bottom Surface


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0.7 0.72 0.74 0.76 0.78 0.8

0.92

0.94

0.96

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1

1.02

1.04

Cruise Mach Number

R e l a t i v e

C o s t

Laminar MLA+GLAGLA with aileron


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0.6

0.7

0.8

0.9

1

1.1

1.2

1.3

R e l a t i v e

V a

l u e

Turbulent MLA+GLAGate constrained


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0.6

0.7

0.8

0.9

1

1.1

1.2

1.3

R e l a t i v e

V a

l u e

Laminar MLA+GLAGateconstrained


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0.6

0.7

0.8

0.9

1

1.1

1.2

1.3

R e l a t i v e

V a

l u e

TurbulentGate constrained


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Long wave gustsHigh amplitudes

Aircraft can rise with the gust

Short wave gusts

Low amplitudesMuch faster than typical wing natural frequencyCan rate-saturate control actuators

Presentation: Aircraft Design with Active Load Alleviation and Natural Laminar Flow

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