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Contributions in Aerodynamics
The Langley Research Center
has been a world leader in aerodynamics technology
for over eight decades. Langley was among the first
organizations worldwide to employ wind tunnels
for research and development, develop and refine
analytical and computational methods, develop advanced
instrumentation systems and measurement techniques
to define the fundamental character and physical
flow properties associated with critical aerodynamic
phenomena, and evaluate and validate aerodynamic
theory with aircraft flight tests. Many of Langley’s
contributions to the U.S. industry and the state
of the art in aerodynamics are legendary, including
such concepts as advanced airfoils and the engine
cowl. The scope of this research has encompassed
all critical facets of aircraft design, including
flow physics, similitude and scaling, high-lift
systems, airfoils and wing design, cruise performance,
stability and control, propulsion integration,
computational design and analysis methods, and
the impact of environmental factors such as rain
and icing on aerodynamic behavior.
Langley’s relationship
with the U.S. aircraft industry in the field of
aerodynamics has been extremely close and productive.
Initially, the unique expertise and wind-tunnel
facilities of the NACA and the Langley Memorial
Aeronautical Laboratory represented the sole source
of information for national interests. A close
bond existed between working-level aerodynamicists;
frequent consultations and cooperative studies
between Langley and industry were commonplace.
Technology transfer requirements for effective
and timely dissemination of results to industry
were accomplished by frequent national aerodynamic
conferences and symposia, as well as briefings
conducted at industry and Langley sites.
With the growth of the U.S.
aviation industry, companies rapidly expanded their
aero-dynamics personnel and constructed their own
wind-tunnel facilities and laboratories for proprietary
requirements. Meanwhile, as a NASA Center, Langley
continued its liaison with industry, but pursued
leading-edge problems identified by the accelerated
advances in aeronautical sciences. For example,
advanced cryogenic wind tunnels, which provide
more accurate simulation of full-scale flight conditions,
were built and calibrated with recent aircraft
experiences to provide the U.S. industry with powerful
tools for future development programs.
In the 1990s the mission of
Langley’s wind tunnels in support of civil
aviation was to study fundamental aerodynamic flow
physics issues, calibration of new facilities with
flight data and design tools, and the development
of advanced testing techniques. These wind tunnels,
in conjunction with powerful computer-based prediction
and analysis methods and a world-class staff of
experts, ably support the civil industry’s
requirements for advanced aircraft. The examples
presented herein are limited to those that resulted
in civil industry applications for specific aircraft
that were operational in the 1990s.
Winglets
Developed by Langley in the
1970s, winglets provide enhanced performance for
civil aircraft, especially those constrained by
wingspan limitations. Winglets were implemented
worldwide for large commercial transports, business
jets, and small personal-owner aircraft of the
1990s.
Supercritical Airfoil
Langley researchers developed
the supercritical airfoil concept in the late 1960s
as a means of reducing cruise drag for advanced
commercial transports and business jets. The concept
provides for trade-offs between cruise speed and
cruise efficiency by permitting the use of thicker
airfoils for wings with increased aspect ratio.
The civil aircraft industry has modified and refined
the concept for specific applications.
Low- and Medium-Speed Airfoils
In the 1970s Langley conducted
extensive experimental and computational research
to develop advanced airfoils for propeller and
jet-powered general aviation aircraft. Applications
of this family of airfoils to aircraft of the 1990s
included natural laminar flow airfoils.
Area Rule
The development of the area
rule by Langley provided a breakthrough analysis
capability for understanding and solving critical
aerodynamic phenomena, such as engine-pylon-wing
interference effects for commercial transports
and business jets at high subsonic speeds.
Flow Control Concepts
Innovative flow control concepts,
such as microvortex generators, were conceived
and matured by Langley research to the point that
applications for enhanced cruise and low-speed
performance occurred within the business jets and
general aviation communities in the 1990s.
Computational Methods
World-class computational
methods developed and validated by Langley have
been widely distributed within the U.S. civil aircraft
industry, where they have been integrated into
proprietary computer codes and design methodology.
The contributions range from mathematical modeling
(gridding) of complex aircraft configurations to
the development of rapid flow solvers and visualization
techniques to enhance the interpretation of results
for a variety of applications.
Wind-Tunnel–Flight Correlation
With the high Reynolds number
capability provided by the National Transonic Facility
(NTF), Langley has provided the results of wind-tunnel
tests at flight Reynolds numbers to directly guide
industry assessments in wind-tunnel–flight
correlation studies and flight prediction methods.
Advanced Instrumentation
Langley contributions include
the development of advanced measurement and instrumentation
systems used by industry in the aerodynamic design
and analysis of civil aircraft of the 1990s. The
concepts developed include multiport, rapid-scanning
pressure systems, pressure-sensitive paints, laser-velocimeter
systems, and other critical systems that have been
matured and transferred to the aircraft industry
and commercial companies. The applications by industry
have included ground-based activities as well as
in-flight studies.
Contributions in Flight Dynamics
Langley conducts generic and
applied research on stability, control, and flying
qualities of civil aircraft. The investigations
have included scale-model wind-tunnel tests, wind-tunnel
tests of full-scale general aviation aircraft,
piloted simulator studies of the handling qualities
of aircraft for various environmental conditions,
and flight tests of subscale models and full-scale
research aircraft to assess flight characteristics.
Langley’s contributions to the U.S. civil
aircraft industry in flight dynamics have largely
focused on personal-owner general aviation aircraft.
Langley’s operation
of unique facilities, such as piloted simulators
and the Nation’s only operational vertical
spin tunnel, has been a key factor in the interactions
with the civil aviation community. The challenge
of ensuring satisfactory spin and spin recovery
characteristics for personal-owner general aviation
aircraft was a major thrust for research at Langley
in the 1970s and 1980s. Because of the complex
aerodynamic interactions and piloting procedures
involved in spin technology, the U.S. industry
conducted extensive cooperative studies with Langley
researchers and consulted with Langley personnel
on numerous occasions during the development of
specific small general aviation aircraft. The contributions
made by Langley regarding design guidelines for
the geometric layout of aircraft, the general approach
to be utilized in spin investigations, and the
implementation of emergency spin recovery devices
for flight tests greatly enhanced the safety and
success of several specific aircraft programs.
The following examples of
Langley’s flight dynamics contributions to
civil aircraft of the 1990s resulted in application
of the research results and concepts to specific
aircraft.
Deep-Stall Recovery
Following a fatal accident
of a British commercial transport prototype, Langley
provided an early identification of the physical
causes of potentially catastrophic unrecoverable
“deep-stall” characteristics for T-tail
aircraft. Followed by extensive wind-tunnel and
piloted simulator studies, Langley provided an
approach for the analysis and prevention of this
phenomenon that was routinely used by designers
of T-tail aircraft of the 1990s.
Spin Technology
The results of an extensive
research program by Langley during the late 1970s
and 1980s on the stall and spin characteristics
of light general aviation aircraft have been incorporated
in the design methodology and analysis techniques
used by many aircraft companies. The technology
contributed by the ground-based and research aircraft
spin studies included guidelines for the design
of tail surfaces for satisfactory spin recovery,
the use of radio-controlled models for prediction
of spin characteristics, and the design and implementation
of emergency spin recovery parachute systems. The
Langley 20-Foot Vertical Spin Tunnel has also provided
industry with contractual mechanisms to conduct
spin research on specific configurations.
Wing Modifications for Spin
Resistance
As part of its stall and spin
program for general aviation, Langley conceived
and demonstrated the effectiveness of a discontinuous
leading-edge-droop wing modification that significantly
enhances the inherent spin resistance for general
aviation aircraft. Wind-tunnel tests and flight
tests of research aircraft documented the effectiveness
of the concept. As a result of cooperative research
on this concept with NASA, the Federal Aviation
Administration (FAA) modified its existing certification
requirements to include provisions for spin resistant
aircraft. Advanced general aviation aircraft emerging
in the late 1990s have incorporated the concept.
Contributions in Structures
and Materials
Langley augments the technical
leadership and expertise in structures and materials
of its research staff with unique, specialized
facilities and laboratories designed for applications
to national challenges in structures and materials.
The scope of the Langley research program includes
the fundamental development and applications of
advanced materials and polymers, the development
and validation of computational methods and analysis,
technologies associated with aeroelasticity, landing
loads and landing gear technology, crashworthiness
and impact dynamics, aging aircraft technology,
and structural component failure analysis.
Langley’s research contributions to major
NASA civil aircraft programs, such as the Aircraft
Energy Efficiency (ACEE) Program, have resulted
in widespread applications of advanced structures
and materials concepts to the civil aircraft fleet
of the 1990s. In particular, the development of
composites for aircraft applications has been a
major product of Langley’s research. Advanced
aluminums and other metallic materials have been
conceived and matured as well as advanced manufacturing
techniques. Unique facilities, such as the Langley
Aircraft Landing Dynamics Facility, the Langley
Impact Dynamics Research Facility, and the Langley
16-ft Foot Transonic Dynamics Tunnel, have provided
data and test opportunities for the civil aircraft
industry.
Composites Technology
Langley’s aggressive
research efforts in composites have covered all
critical technical aspects and challenges required
for transfer of the technology to the civil aircraft
sector. For example, Langley’s pioneering
contributions to the development of high-performance
polymers and matrix composite materials resulted
in numerous licensing agreements with industry
and guidance for industrial applications of high-performance
polymers. Langley and industry activities in the
ACEE Program provided design, fabrication, and
full-scale aircraft flight test verification of
composite secondary structures for commercial transports.
The joint activities led to the introduction of
secondary composite structures and limited primary
structures on aircraft of the 1990s. Research at
Langley on structural design criteria for composites,
including damage tolerance, has been adopted as
industry standards for assessing composite structural
designs. Langley’s leadership in the design
and fabrication of advanced composite structures,
especially stitched composites, has rapidly accelerated
the introduction of revolutionary composite material
and economically feasible fabrication techniques
for civil aircraft. Langley’s leadership
and participation in the Advanced General Aviation
Technology Experiments (AGATE) Program has led
to a new, more economically feasible approach to
the certification procedure for composite general
aviation aircraft.
Fatigue and Fracture Mechanics
Extensive research by Langley
in the critical areas of structural fatigue and
fracture mechanics has been adopted by industry
and the Department of Defense (DOD) for engineering
standard practice and design handbooks.
Aging Aircraft Technology
Stimulated by the tragic in-flight
structural failure of the upper fuselage skin and
structure of an Aloha Airlines transport in Hawaii
in 1988 and a subsequent request from the FAA for
increased research in the area, Langley augmented
its efforts in research on the structural integrity
of aging aircraft. In a national cooperative program
with the DOD, industry, and the FAA, Langley has
contributed methodology and instrumentation that
has significantly enhanced the prediction, detection,
and repair of structural failures in aging aircraft
components. For example, Langley developed and
validated a new method—now used as an industry
standard—to predict crack growth from multirivet
sites. Langley also developed an analysis procedure
for complex fuselage structural components, that
was used by industry in the design of recent commercial
transports. Contributions also include a thermal-bond
inspection system for large airframe structures,
a self-nulling eddy current probe for detecting
structural corrosion, and an ultrasonic system
for detecting disbonds and corrosion. Concepts
developed in this area by Langley were rapidly
embraced by commercial vendors, and were applied
to aircraft beginning in the mid-1990s.
Advanced Metallic Materials
Langley’s contribution
to advanced metals include the development of aluminum
and titanium materials, as well as forming and
joining technologies for these materials. Contributions
include corrosion protection for titanium alloys,
development of standard test methods to determine
stress-corrosion cracking properties of advanced
metallic alloys, brazing methods and weld bonding
for joining of aluminum and titanium panels, and
the development of techniques for superplastic
forming of complex components. Light metallic alloy
fabrication technology developed by Langley was
used by commercial vendors for aluminum alloys
for major commercial transports of the 1990s.
Computational Methods
The development of computational
structural methods by Langley has led to numerous
codes that have been incorporated into industry’s
proprietary analysis methods. A particularly noteworthy
contribution was Langley’s management of
the NASA Structural Analysis (NASTRAN) Program,
which spawned an entire industry in the field of
structural analysis.
Aeroelasticity and Flutter
The combination of a unique
national facility and decades of research on aeroelastic
phenomenon and flutter have resulted in an internationally
recognized leadership position for Langley. Langley
has cooperatively conducted extensive flutter tests
of commercial and business jet aircraft since the
early 1960s in the Transonic Dynamics Tunnel. By
validating flutter prediction methodology, identifying
potentially catastrophic characteristics prior
to flight, and reducing risk and the extent of
flights required for flutter-free flight demonstrations,
Langley contributions have significantly enhanced
the safety and reduced the developmental costs
of civil aircraft.
Contributions in Flight Systems
Cooperative research programs
between Langley, industry, and the FAA in flight
systems have been directed at pilot, airplane,
and air transportation system interfaces since
the early 1970s. Research and development of innovative
concepts typically progressed through ground-based
analytical and piloted simulator studies; the development
and systems verification of advanced avionics,
sensors, and other flight systems; flight assessments
and development in Langley’s unique Boeing
737 research aircraft; and extensive demonstrations
to potential users of the technology. Applications
to aircraft of the 1990s have been extensive, including
virtually all classes of civil aviation.
Contributions to flight systems
by Langley have been particularly focused on safety
problems, including the detection and accommodation
of potentially deadly wind-shear conditions, wake-vortex
hazards, and the rapid assessment of the health
of aircraft systems.
Digital Flight Controls
Research at Langley in the
1950s with analog fly-by-wire control systems and
the use of advanced digital computers in the NASA
Apollo Program led to major Langley contributions
in digital fly-by-wire technology. Partnering with
the Dryden Flight Research Center, Langley conducted
development efforts that led to the first flight
demonstration of this technology on a modified
F-8 research aircraft. Used widely in U.S. military
aircraft since the 1980s, fly-by-wire controls
were first implemented in U.S. commercial transports
in the mid-1990s.
Glass Cockpit Technology
In the early 1970s, Langley
began studying the advantages of displaying flight
management information to flight crews by using
cathode-ray tube (CRT) systems in commercial transports.
Using the unique Boeing 737 Transport Systems Research
Vehicle (TSRV) and ground-based simulators, researchers
impressed industry and airline decision makers
with the potential benefits of the advanced systems,
which helped to promote the widespread applications
of glass cockpit technology in virtually all modern
commercial transports and business jets.
Flight Management Systems
Concepts developed by Langley
for improved flight management by pilots in the
complex air transportation system included the
first piloted simulations and flight tests of time-dependent
(four-dimensional) navigation methods, algorithms
for computing air-traffic constrained fuel-conservative
flight paths, and data-link communications with
Air Traffic Control. Langley also played a critical
role in the mid-1970s during the demonstration
and ultimate acceptance of the U.S. Microwave Landing
System by the international community. Much of
Langley’s technology in flight management
is used in current commercial transports.
Crew-Aiding Systems
Research conducted at Langley
led to civil applications of subsystem monitoring
concepts that assist flight crews and help prevent
accidents. Contributions include an engine monitoring
and control system, a fault monitoring and diagnosis
aid, and updates of electronic approach plates.
(An approach plate is a flight-planning document
for a specific airport that gives details such
as minimum heights, safe headings, and weather
minimums and includes a horizontal map and often
a vertical profile for the approach to each instrument
runway.) Langley also developed a precision landing-flare
control algorithm, and demonstrated the accuracy
and impact of this concept on runway occupancy
time. The algorithm was studied and modified by
industry for commercial transports in the 1990s.
Digital Data Bus
In the mid-1980s, Langley
teamed with Boeing to develop, flight test, and
demonstrate the practical use of an innovative
concept that used a global data bus as an interface
between electronic flight systems onboard transport
aircraft. As a result of flight demonstrations
using the Langley Boeing 737 TSRV aircraft, the
system was adopted as an industry standard for
transport aircraft.
Reliability Tools
Langley researchers developed
extremely effective reliability estimation methods
for advanced controls and aircraft systems. In
addition, fault-tolerant architecture for advanced
aircraft avionics systems was developed. Industry
also adopted results from pioneering Langley research
in the application of formal methods, which utilized
mathematical logic for the design verification
of advanced digital aircraft systems.
Demonstrations of GPS Accuracy
Highly successful demonstrations
of the accuracy of the Global Positioning System
(GPS) by Langley and industry flight demonstrations
with the Langley Boeing 737 research aircraft provided
significantly increased confidence in the potential
use of GPS for automatic landings and guidance
under adverse weather conditions. Flight testing
in a cooperative Langley-industry flight evaluation
of differential GPS (DGPS) in 1993 demonstrated
remarkable accuracy, and several automatic landings
were made. Data from these demonstrations stimulated
the avionics community during the late 1990s.
Contributions in Noise Reduction
In recognition of the impact
and challenge of existing and future environmental
noise regulations to the aviation industry, Langley
participated in the development of noise-reduction
technology research and development in close cooperation
with industry, airport and airline operators, and
the FAA beginning in the early 1960s. Initially,
Langley’s efforts were part of a national
Aircraft Noise Abatement Program, directed by the
Department of Transportation. However, Langley
and other NASA centers and their industry contractors
conducted other focused efforts, such as the NASA
Acoustically Treated Nacelle Program. Widely disseminated
results from Langley studies on noise reduction
since that time have included the identification
of noise-generation mechanisms, noise-absorption
concepts, the development of analytical tools for
noise predictions of propeller- and jet-powered
aircraft (also rotorcraft), community noise acceptance
levels, reduction of structurally borne interior
noise, impact of modifications of aircraft flight
path operational procedures, and measurement and
predictions of noise levels contributed by nonpropulsive
airframe components.
In addition to analytical
studies of complex noise generation and interaction
phenomena, Langley uses specialized ground-based
laboratories, powered model wind-tunnel tests,
measurements from aircraft flight tests, and other
acoustic measurement devices to mature and validate
noise reduction technology.
Engine Liner Technology
The advent of jet-powered
commercial transports resulted in intensified research
to reduce noise levels at airports and surrounding
communities. As part of extensive cooperative and
contractual studies with the Boeing Company and
McDonnell Douglas Corporation, Langley led the
development of acoustic duct liners for jet propulsion
systems that were adopted and implemented in the
civil transport fleet.
Noise Prediction Codes
Langley researchers developed
and validated a noise prediction code known as
the Aircraft Noise Prediction Program (ANOPP) that
is widely used by the aircraft and engine industries
to predict operational noise levels of aircraft
configurations and the impact of modifications
to operational procedures.
Community Noise Impact
With volunteer evaluation
subjects and laboratory equipment that simulates
the critical characteristics of aircraft noise-generation
mechanisms, Langley has provided industry and regulatory
agencies with fundamental data on acceptability
and annoyance levels for a variety of noise-generating
mechanisms, such as sonic booms. In addition, analytical
research on the impact of modifications to operational
procedures has been verified by flight test measurements.
Interior Noise
The transmission of noise
generated by external sources, such as jet engines
and propellers, into the cabin of civil aircraft
has been studied analytically and experimentally
by using actual aircraft structures and noise-canceling
technology. Results of the studies have been disseminated
to the civil industry and implemented on several
general aviation aircraft.
Contributions in Operating Problems
Many of Langley’s most
valuable contributions to civil aviation involve
the development and maturation of concepts to alleviate
or eliminate major operating problems for civil
aircraft. Most of the topics directly study the
safety of the aircrew and passengers, especially
during adverse weather conditions. Langley researchers
successfully met the difficult technical and hazard
challenges embodied by research in this area, with
the result that aircrews and the flying public
greatly benefited by their contributions.
Operational problems typically
involve full-scale aircraft and atmospheric conditions
that cannot be simulated easily in subscale or
analytical studies. Thus, research efforts in this
area involved aircraft flight testing with its
particular safety and operational constraints.
Experiments with Langley’s research aircraft,
including the Boeing 737 and F-106B, provided unprecedented
data to designers and operators of the U.S. civil
aircraft fleet in the 1990s. Working in close collaboration
with industry, the FAA, and the National Transportation
Safety Board (NTSB), Langley researchers also provided
contributions by participation in accident investigations
involving specific operational problems. In addition,
participation in standards-setting activities provided
additional contributions and influence by the Langley
staff.
The following contributions
toward the alleviation of operating problems for
aircraft of the 1990s are particularly significant.
Airborne Wind-Shear Detection
A Langley, FAA, and industry
team conceived, developed, and demonstrated airborne
wind-shear detection systems designed to provide
flight crews with sufficient warning and strategy
for the avoidance of deadly wind-shear accidents.
The scope of activity in this very significant
accomplishment included mathematical modeling of
atmospheric wind-shear phenomena; identification,
development, and evaluation of candidate airborne
detection systems; refinement of radar characteristics
for low-altitude operations in clutter; the development
and demonstration of a standard-setting hazard
criteria known as the F-Factor; and extensive demonstrations
and evaluations by industry, the FAA, and airline
flight crews. In addition, Langley staff participated
in standards-setting and other regulatory studies
in wind-shear technology. The highly successful
research of the 1990s by Langley in this area led
to the commercialization of airborne detection
systems and implementation in most of the civil
transport fleet.
Wake-Vortex Hazard
Langley researchers have contributed
extensive information, data, and potential operational
solutions to the hazardous conditions created by
the powerful trailing vortices of large commercial
transports during approach and landing. Beginning
in the early 1970s, ground-based and flight studies
on the physical characteristics of the trailing
vortex phenomenon, and the impact of aircraft modifications
on those characteristics, contributed to the fundamental
understanding and characterization of the wake-vortex
hazard. Efforts in the 1980s were directed at defining
and modeling vortex behavior in various atmospheric
conditions. In the 1990s, Langley researchers conducted
a focused program to define technology approaches
to an integrated system for avoidance of vortex
encounters by trailing aircraft. The avoidance
system was demonstrated to airport managers and
the FAA in the late 1990s.
Lightning Protection
Langley addressed the potential
threats posed by lightning to advanced digital
systems and composite aircraft with laboratory
simulations and flight studies of the Langley F-106B
research aircraft in the 1980s. During intentional
flights into severe storms and lightning-prone
atmospheric conditions, unprecedented data on the
occurrence of lightning strikes, the mechanisms
involved in such encounters, and the magnitude
and characteristics of currents induced in the
aircraft were obtained for analysis. Coupled with
theoretical analysis, the experimental data provided
the basis for modifications to aircraft design
standards for lightning protection. Studies of
the conductive properties of composite structures
and approaches to minimize lightning damage also
provided extremely valuable design information
for all segments of civil aviation.
Runway Friction
Langley research on aircraft
tire braking and traction characteristics during
adverse weather conditions provided tire manufacturers,
the aircraft industry, the FAA, and DOD with fundamental
information on tire hydroplaning and potential
solutions to the problem. Runway grooving concepts
were conceived and extensively evaluated for many
aircraft during adverse weather landings. The highly
successful results of the Langley program were
incorporated in most of the Nation’s airport
runways, as well as major highways. Langley’s
leadership and participation in international studies
on runway characteristics during adverse conditions
are internationally recognized for their valuable
contributions; and Langley researchers have participated
in numerous accident investigations and other international
advisory activities.
Crashworthiness
Since the early 1970s, Langley
has investigated making aircraft crashes more survivable.
The staffs of the Langley Impact Dynamics Research
Facility and supporting laboratories have conducted
extensive research on failure mechanisms and loads
generated in typical crashes of general aviation
and rotorcraft vehicles. Unprecedented experimental
data generated by crash tests of full size general
aviation and rotor aircraft have been augmented
by the development and validation of analytical
methods for the prediction of crash loads and the
effect of energy-absorbing concepts. Extensive
cooperative testing with industry and other government
agencies have led to new concepts, such as energy-absorbing
seats and regulatory standards within the industry.
Pioneering contributions on impact characteristics
of advanced composite materials, cabin floors,
and engine support components have been incorporated
in design technology across the industry.
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