technical challenges to reducing subsonic transport · pdf file ·...

1 1 Subsonic Fixed Wing Project Fundamental Aeronautics Program

Technical Challenges to Reducing Subsonic Transport Weight

AIAA Aerospace Sciences Meeting January 9-12, 2012

Karen Taminger

Technical Lead - Lightweight Airframe & Propulsion Systems (LAPS) Subsonic Fixed Wing Project

[email protected] 757-864-3131

mailto:[email protected]


TC6 - Revolutionary tools and methods enabling practical design, analysis, optimization, & validation of technology solutions for vehicle system energy efficiency & environmental compatibility

TC4 - Reduce harmful emissions attributable to aircraft energy consumption

TC5 - Reduce perceived community noise attributable to aircraft with minimal impact on weight and performance

TC1 - Reduce aircraft drag with minimal impact on weight (aerodynamic efficiency)

TC2 - Reduce aircraft operating empty weight with minimal impact on drag (structural efficiency)

TC3 - Reduce thrust-specific energy consumption while minimizing cross-disciplinary impacts (propulsion efficiency)

SFW Strategic Thrusts & Technical Challenges

Reduce TSEC

Reduce OWE

Reduce Drag

Reduce Noise Reduce

Emissions

Economically Viable

Revolutionary Tools and Methods

Maintain Safety

Enable Advanced Operations

Energy Efficiency Thrust (with emphasis on N+3) Develop economically practical approaches to improve aircraft efficiency

Environmental Compatibility Thrust (with emphasis on N+3) Develop economically practical approaches to minimize environmental impact

Cross-Cutting Challenge (pervasive across generations)

Energy & Environment

TSEC

Clean

Weight

Drag

Noise

Tools


NASA Subsonic Transport System Level Metrics …. technology for dramatically improving noise, emissions, & performance

FAA/CLEEN NASA/ERA NASA SFW


Weight Weight

Weight

N+3 Subsystem Concepts Goal-Driven Advanced Concepts 1. Tailored Fuselage

2. High AR Elastic Wing

3. Quiet, Simplified High-Lift

4. High Efficiency Small Gas Generator

5. Hybrid Electric Propulsion

6. Propulsion Airframe Integration

Near Term/Cross-cutting

7. Alternative Fuels

8. Tool Box (MDAO, Systems Modeling, Physics-Based)

SFW N+3 Opportunities from Goal-Driven Advanced Concepts broadly applicable . . . .

Tools


Efficiency Challenge: Reduce Weight

What are we trying to do? • Reduce aircraft operating empty weight without negatively impacting drag, noise Why? • Reduction in structural weight directly contributes to a reduction in fuel burn How is it done today, and what are the limits of current practice? • Replacement of conventional materials with lower density materials fails to take

full advantage of weight reduction potential What is new in our approach? • Integrated structural, aeroelastic and control designs with new, high-

performance materials to improve structural efficiency What are the payoffs if successful? • Projected 20-25% reduction in operating empty weight • Designs also reduce drag and noise to improve other performance metrics


Structural Weight Sensitivity

• B 777 “like” aircraft – Mission

• Payload: 300 pax • Range: 7500 nm • Cruise Mach: .85

– Active Constraints • Takeoff field length • 2nd segment climb gradient • Fuel volume

• Observations

– Diminishing returns for structural impact (other sensitivities become higher) – Growth Factor is a measure of technology need and vehicle sensitivity

Computed by Mark Guynn and Mark Moore, SACD, NASA LaRC, Aug. 2010


wing, 23%

empennage, 4%

fuselage, 20%

landing gear, 8%

engine+nacelle, 18%

furnishings, 11%

Misc*., 15%

Historical Airframe Component Weights

Aircraft Included: 737-200 MD-80 727-100 757-200 A-300 DC-10-30 747-100

*Misc. includes equipment such as avionics, APUs, hydraulic/electrical/ pneumatic systems, anti-icing, etc.


wing, 23%

empennage, 4%

fuselage, 20% landing gear, 8%

engine+nacelle, 18%

furnishings, 11%

Misc*., 15%

Historical Airframe Component Weights

Aircraft Included: 737-200 MD-80 727-100 757-200 A-300 DC-10-30 747-100

*Misc. includes equipment such as avionics, APUs, hydraulic/electrical/ pneumatic systems, anti-icing, etc.


Tailored Fuselage Focus: Develop lightweight fuselage structures and related materials/processing techniques for tailoring fuselage structures

Goal: Reduce weight of fuselage structure by 25%

Approach: •Fuselages vary considerably amongst N+3 vehicle concepts (hybrid wing-body, distributed/embedded propulsion systems, double-bubble configuration, truss-braced wing)

•Challenges in supporting complex loading because complexity in various configurations is different

•Develop generic tools to design and analyze tailored structures and fabrication methods to enable these designs

• Tailored Load Path Structures – Curvilinear metallic stiffeners – Tow-steered carbon fibers

• Designer Materials – Composite protective skins – Carbon nanotube hybrid composites – Functionally graded metallics


Composite Structural Design and Analysis Tool Development

• Fiber winding and automatic tape placement are industry standards

• Fiber tow steering places individual fiber tows, enabling tighter radii curves and control of fiber distribution

• Fiber tow steering equipment exists, but design and analysis tools to effectively tailor localized laminate properties are lacking

• Develop analysis and design tools to optimize structures through tailored placement of fibers within composite

• Fibers from axial along keel and crown to 45° along sides for shear; steer fibers around cutouts for continuity

Fiber tow placement plan within a single ply (cylinder split along keel for purposes of image); validate through test of cylinders 28” dia. x 40”


Composite Protective Skin

• Smoothing, Thermal, Absorbing, Reflective, Conductive, Cosmetic (STAR – C2 )

• Composite primary structure with external protective skin

• Multifunctional skin provides protection external to primary structure:

– Cosmetic finish – Acoustic treatment – Thermal insulation – Lightning strike protection – Smoothness to facilitate laminar flow – Impact detection/indication – Ice protection – Easily produced and repaired

• Weight reduced by driving towards lighter gage primary structure and combining other functions in multifunctional skin

Energy Absorbing Foam

(Impact, Sound, Thermal, etc.)

Frame

Stringer

Skin

Conductive skin

(Lightning, EMI, Paint,

Smoothness for laminar flow)

Schematic of STAR-C2 concept (under development on Cessna NRA contract)


Metallic Fuselage Design and Fabrication

Design optimization tools developed at VA Tech through NRA contract

• Engineered materials coupled with tailored structural design enable reduced weight and improved performance

• Multi-objective optimization: ̶ Structural load path ̶ Acoustic transmission ̶ Durability and damage tolerance ̶ Minimum weight ̶ Materials functionally graded to satisfy

local design constraints

• Additive manufacturing using new alloys enables unitized structure with functionally graded, curved stiffeners

• Weight reduction by combined tailoring structural design and designer materials

High toughness alloy at stiffener base for damage tolerance, transitioning to metal matrix composite for increased stiffness and acoustic damping


High Aspect Ratio Elastic Wing Focus: Develop aeroelastically tailored wing structural designs with distributed controls to reduce weight and drag on high aspect ratio wings

Goal: Reduce weight of wing system by 25% while enabling reduced drag configurations

Approach: •Laminar flow drives to higher aspect ratio, lower sweep wings as seen in most N+3 vehicle concepts •Reductions in structural weight and thinner airfoils will result in more flexible wings, so aeroelasticity must be considered early in structural design •Develop generic tools to design and analyze high aspect ratio wings with integrated control surfaces

• Tailored Load Path Structures – Passive aeroelastic tailored structural design

• Designer Materials – Variable stiffness nanocomposite skins

• Active Structural Control – Aeroservoelastic design – Control law architecture – Distributed controls and control surface design


High Aspect Ratio Elastic Wing


Propulsion Airframe Integration

Focus: Develop lightweight composite fan blades with integrated shape memory alloys for blade shape change to reduce noise at take-off and landing and improve engine efficiency (reduced specific energy consumption)

Goal: Reduce weight of propulsor fan elements by 15% while enabling efficiency improvements

Approach: •Lightweight, high temperature solutions (such as low density superalloys and ceramic matrix composites) contribute to weight reduction in propulsion systems but are being worked elsewhere because primary focus is related to other technical areas in the project •Focus of weight reduction is composite development for propulsor fans, also applicable to lightweight fan cases

• Adaptive Fan Blades – Polymer composite with integrated shape memory alloys

• Lightweight Fan Blades – Tailored nanocomposite – Aeroelastic tailoring of thin blades – Impact dynamics for bird strike


Adaptive Fan Blades

• Mission-adapted propulsor fan blades for high lift, low noise performance during take-off and landing transition to fuel-efficient shape in cruise

• Shape memory alloys integrated to enable blade twist or camber change

• Polymer matrix development for compatibility with shape memory alloys enabling flexure and rigidity

• Integration and analysis of blade dynamics during shape transitions

• Computationally-designed shape memory alloy synthesis, process and integrated design

Shape change in fan blades through integration of shape memory alloy ribbons in composite


Lightweight Fan Blades

• Thin, hollow composite blade development for reduced weight

• Aeroelastic tailoring required to locally stiffen lightweight blades to avoid flutter

• Elimination of metallic leading edges, replaced by functionally graded nanocomposite to toughen blades to survive wear and bird strike impact

• Material developed also applicable to lightweight fan cases for blade-out containment and adaptive fan blade designs

Composite fan blade design showing regions of functional gradients to improve toughness

Nanofillers improve composite toughness


Tools Focus: Develop fundamental, high-fidelity tools and methods specifically for aeroelastic tailoring, structures, materials, and controls geared towards enabling design and analysis of lightweight, multifunctional structures

Goal: Enable reduction in OWE through improved analysis and understanding of uncertainties

Approach: •Tools supporting specific areas of work are being developed as part of the N+3 Subsystem concepts already described •General tools for broader applications are also being worked:

– Aeroelastic Probabilistic Tools: Analysis of experimental and analytical uncertainties in aeroelastic prediction and testing will improve aeroelastic prediction tools and understanding of the errors in current methods

– Uncertainty Analysis of Composite Structural Design Allowables: Design allowables based on calibrated analysis and “rare event" simulation enable more efficient designs with improved confidence at lower cost

– Testing Methodology for Lightweight, Flexible Structures : develop new structural testing methods for ground and flight research as wing structures become lighter weight, they will become more flexible and conventional testing techniques may not be capable of evaluating performance


Multidisciplinary Approach to Weight Reduction

• To effectively reduce subsonic transport weight, a multidisciplinary approach is required to balance trade-offs between weight and performance

• Improvements in structural efficiency must also consider the unintended consequences: increased elastic response, impact on noise and drag, etc.

• This effort targets a 25% reduction in fuselage weight, 25% reduction in wing system weight, and 15% reduction in propulsor fan weight

• Focus is to develop design and analysis tools, materials and fabrication processes that can be demonstrated for specific configurations but broadly applicable to other configurations

• Building block approach will result in empirical, computational, and physical tools to reduce weight for N+3 subsonic transport aircraft

technical challenges to reducing subsonic transport · pdf file ·...

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