The United States Air Force's Landing Gear Systems Center of Excellence - A Unique Capability

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The United States Air Force’s
Landing Gear Systems Center of Excellence
- A Unique Capability -
-
J. Greer McClain
United States Air Force, Branch Chief, Landing Gear Systems Center of Excellence
Wright Patterson Air Force Base, Ohio 45433
Martin Vogel
United States Air Force, Operations Manager, Landing Gear Systems Center of Excellence
Wright Patterson Air Force Base, Ohio 45433
And
Dennis R. Pryor
Jacobs Technology, Inc, Operators of the US Air Force Landing Gear Systems Center of Excellence,
Wright Patterson Air Force Base, Ohio 45433
Hugo E. Heyns, III
Jacobs Technology, Inc, Operators of the US Air Force Landing Gear Systems Center of Excellence,
Wright Patterson Air Force Base, Ohio 45433
Abstract
Military and commercial airborne systems are carefully designed, developed, and manufactured to be safe,
reliable, and effectively meet the mission for which they are intended. Test and evaluation is one of the
fundamental components of the systems development process that assures the user that a system will do its
job right the first time and every time. The means and source of testing becomes a key consideration for
every aircraft system designer, developer, and user. Aircraft landing gear systems is one system where test
and evaluation is generally required, and must be done carefully and accurately. It is also a parasitic system,
in that adds weight and complexity without increasing the payload, which may result in more and less
attention than it deserves. If this system does not do its job properly and completely, however, aircraft
effectiveness may be limited to a single flight. For landing gear systems and components design, development
and test, the US Air Force’s Landing Gear Systems Center of Excellence (LGSCE) is a unique national
treasure. Within the walls of its historic building resides the world’s only capability to test all landing gear
systems and all their components, including the wheels, brakes, tires, struts, and actuators, both statically and
dynamically. The LGSCE, including its capable and qualified test engineering, instrumentation, and test
support, and the major test equipment resources, is independent and totally focused on providing test results
and information which is clear, accurate, complete, and unbiased by any consideration other than testing.
The LGSCE’s reports provide the recipient with the complete, accurate, and reliable information with which
to make reasoned and factually based design, configuration and performance decisions. This paper describes
the infrastructure contained within the US Air Force’s LGSCE and how its resources are being applied to
improving conceptual and developmental landing gear systems, sustaining and improving existing military
and commercial landing gear systems and component design, development, test, integration, and failure
investigation efforts.
U.S. Air Force T&E Days
13 - 15 February 2007, Destin, Florida AIAA 2007-1638
Copyright © 2007 by the American Institute of Aeronautics and Astronautics, Inc.
The U.S. Government has a royalty-free license to exercise all rights under the copyright claimed herein for Governmental purposes.
All other rights are reserved by the copyright owner.
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Table of Contents
I Introduction________________________________________________________________________________3
II Today’s Perspective ________________________________________________________________________3
III Anticipating Tomorrow_____________________________________________________________________4
IV LGSCE Infrastructure _______________________________________________________________________5
V Landing Gear Systems Infrastructure for Tomorrow _______________________________________________16
VI Conclusions and Summary __________________________________________________________________17
Table of Figures
Figure 1 - Landing Gear Test Facility at Wright Patterson Air Force Base, Ohio ___________________________5
Figure 2 - 84" Dynamometer and Specifications _____________________________________________________7
Figure 3 - 120" Dynamometer - South Carriage _____________________________________________________7
Figure 4 - 120" Dynamometer North Carriage ______________________________________________________8
Figure 5 - 120" Dynamometer Test Article Build-Up Area _____________________________________________8
Figure 6 - 168" Internal Drum Dynamometer _______________________________________________________9
Figure 7 – 168" Internal Drum Dynamometer - East Carriage__________________________________________9
Figure 8- 192" Dynamometer____________________________________________________________________9
Figure 9 - 192" Dynamometer - Upper Carriage____________________________________________________10
Figure 10 - 192" Dynamometer - South Carriage showing the many plates used to change flywheel inertia______10
Figure 11 - Drop Tower No 1___________________________________________________________________10
Figure 12 - Drop Tower No 2___________________________________________________________________11
Figure 13 – Drop Tower No. 3__________________________________________________________________11
Figure 14 - Drop Tower No. 4 __________________________________________________________________12
Figure 15 - Large Baldwin Compression/Tension Machine____________________________________________12
Figure 16 - Small Baldwin Compression and Tension Machine ________________________________________13
Figure 17 Tire Force Machine _________________________________________________________________13
Figure 18 - TFM Output: Shear Pressure _________________________________________________________13
Figure 19 - Fatigue Test Machine _______________________________________________________________14
Figure 20 - Burst Pit__________________________________________________________________________14
Figure 21 - Wheel Spin-Up Rig _________________________________________________________________15
Figure 22- Vibration Generation Machine_________________________________________________________15
Figure 23 - Vibration Generation Machine Performance _____________________________________________15
Equipment Specifications Tables
Table 1 - 84" Dynamometer Specifications _________________________________________________________7
Table 2 - 120" Dynamometer Specifications ________________________________________________________8
Table 3 - 168" Dynamometer Specifications ________________________________________________________9
Table 4 - 192" Dynamometer ___________________________________________________________________10
Table 5 - Drop Tower No 1 Specifications_________________________________________________________10
Table 6 - Drop Tower No. 2 Specifications ________________________________________________________11
Table 7 - Drop Tower No. 3 Specifications ________________________________________________________11
Table 8 - Drop Tower No. 4 Specifications ________________________________________________________12
Table 9 - Compression/Tension Machines' Specifications _____________________________________________13
Table 10 - Tire Force Machine__________________________________________________________________13
Table 11 – Spin-Up Rig Specifications____________________________________________________________15
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I Introduction
onsidering that most professionals in the aircraft acquisition, design, manufacture, and operations
communities feel that landing gear is, among other things, demonstrated technology, low tech, simple
mechanical design, and not a real design challenge to most capable engineers, one might wonder why so
much attention is afforded this system. This paper addresses this question, but to be successful, this paper must
also answer the following questions: What is an aircraft landing gear system (LGS)? What are commonly
considered the LGS’s component parts? Why is the LGS important? What are the LGS’s costs and benefits to the
aircraft’s mission? What are some the design challenges facing the LGS designer? Why do we have to test such a
low tech system? What is the best way to go about such testing? Once these fundamentals are in perspective and
the need to properly test the LGS and its components, the majority of this paper describes the testing infrastructure
provided by the United States Air Force’s Landing Gear Systems Center of Excellence (LGSCE) to meet this
challenge.
II Today’s Perspective
Landing gear systems for today’s military and commercial aircraft appear to be simple assemblies of various
also relatively simple components which, when properly assembled, provide an aircraft mobility allowing it to
taxi, turn, takeoff, and land. While somewhat simplistic, this is a pretty apt description of the purpose of a landing
gear system, but its simplicity is deceiving. When the veil of this over simplification is removed an objective
observer finds a reasonably complex system composed of apparently simple components which are very carefully
and precisely designed to meet the continuously competing demands facing all aircraft designers: cost, weight,
and performance. Landing gear also has another handicap: they are parasitic systems that add cost and weight,
reducing aircraft performance without increasing aircraft payload. Therefore, aircraft designers are constantly
trying to find ways to reduce the internal space, weight, and power budgeted to the landing gear system, driving
the system’s designers to increasingly creative responses that carefully meet each of the design constraints, with
limited margins. Landing gear, once properly designed and installed, provides the aircraft with the intended
mobility and a means to efficiently take off and land, absorbing the shocks from bumpy taxiways, runways, and
landings without having impact on aircraft structural integrity. The LGS is designed to reliably repeat the process
as many times as the remainder of the aircraft is able. Landing gear can, then, be considered a force multiplier.
A landing gear system designer’s primary task is to design the system to provide mobility and direction while
simultaneously absorbing the wide variety of anticipated shocks and loads, attenuating those loads and
transmitting only those that the aircraft structure can safely absorb without yielding. This design effort is
significantly constrained by the in-aircraft volume, configuration, and location (all of which is considered “turf”)
allocated to the landing gear system. While generally an iterative process, the parasitic nature of landing gear
becomes part of the decision process facing the aircraft system’s configuration control decision makers that decide
most of these “turf” questions. Ultimately, designing the capable landing gear systems to fit within the allocated
“turf” forces trade studies and sometimes delicate compromises which may have impact on long term reliability,
supportability, and operational capability, as well as constraining future operational mission expansion. Because
such technical compromises are a component part of all aircraft design, most systems and all those that are critical
to the aircraft’s mission success are tested to assure their proper operation. Thus, the reason landing gear systems
are tested is to assure that the compromises made during design were made properly and that the system will do its
job accurately, completely, safely, and reliably.
An aircraft’s landing gear system is composed of several individual components, including: struts, wheels,
brakes, tires, retract, extension, and steering actuators, and landing gear braking and steering control systems.
Many, if not all, of these components are unique and designed specifically for installation on a particular aircraft.
The aircraft system designer/integrator is responsible for development of the individual component specifications
and approval of selected supplier’s qualification testing to assure each deliverable is within specification
compliance. The designer/integrator is also responsible for system level testing to assure that the various
components, once assembled, will work together effectively and meet aircraft needs. Testing of landing gear and
its components is accomplished by a variety of different sources. Component testing is usually accomplished by
the component manufacturer using a test procedure that has been reviewed by the landing gear manufacturer, the
aircraft prime manufacturer, with some oversight provided by the ultimate aircraft user. Similarly, the landing
gear assembly, including the strut, wheel, brake, tire, and other components critical to system operation, is
subjected to full system testing, including drop testing to assure that the gear will operate properly under all
C
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possible loading conditions. There are also independent, third party testing agencies fully capable of completing
such testing without a manufacturer’s bias.
As part of today’s perspective it is also prudent to consider the aircraft design and development process,
particularly those actions being accomplished in isolation because of proprietary, competitive, or security
concerns. These actions often have impact on systems development. Landing gear design and development
challenges are significantly exacerbated when the aircraft concepts, early designs and even outer mold lines are
developed in isolation because of these external concerns. These early efforts often describe a conceptual
response to a customer’s requirements and may drive significant increases in aircraft weight, loads, and flotation
combined with reductions in available “turf,” as well as other environmental factors which potentially stretch the
structure and systems state of the art. While these efforts still only result in a “conceptual” product, many of these
early design decisions become the basis for the eventual aircraft’s design and cause those arriving later, such as
the landing gear design team, to justify “design changes” to the “concept” to accommodate the needs for an
effective system. Such “design changes” are not really changes to a fixed design; they must be justified as if they
were.
With the full recognition that design, development, test and evaluation, and fielding of new aircraft systems is
important, it is potentially more important that consideration be given to the long term sustainment of these same
aircraft and systems. Landing gear systems sustainment involves the test and evaluation of existing systems to
repeat field failures and develop solutions preventing their recurrence or resulting damage. This effort might
involve the research and development and the test and evaluation of new materials, component designs, or
processes improvements that are under consideration before making any final configuration decisions.
Sustainment test and evaluation efforts are similar to developmental efforts, except that the lab is testing existing
and possibly worn components to identify the unexpected failure modes and effects. When these failure modes
are repeated in a lab environment, they can be more closely studied for the means to resolve the issue. The
modification process might then include the investigation into some of the new and evolving designs, materials,
and processes for possible application to the existing aircraft fleets.
With landing gear systems design, development, test, integration and sustainment now brought into some
perspective, we’ll examine what the future landing gear systems designers will face. Then, the remainder of this
paper will focus on the US Air Force’s Landing Gear Systems Center of Excellence and the test infrastructure it
offers to the military and commercial aircraft development and sustainment communities, today and into the
future.
III Anticipating Tomorrow
While tomorrow will certainly bring aircraft design and development process improvements and material
advances, the future will also bring continuing demands for aircraft capable of accomplishing more with an
accompanying demand for aircraft systems improvements. While predictions of future customer demands are always
speculative, below is a short review of what can be anticipated with some reasonable confidence:
a New materials will be developed and applied to landing gear systems. These lighter, stronger, and
more easily produced materials will help reduce the system’s dedicated space and weight while still
meeting system design requirements.
b Shock and load attenuation demands will change landing gear requirements. The shock and load
attenuation demanded of the landing gear will likely increase proportional to the size of the aircraft as
aircraft trade studies compare structural weight, strength, and stiffness with mission requirements and
increased systems capabilities.
c Turf (space, weight, and power) allocated to landing gear systems will decrease. Landing gear will
remain a parasitic system, generally reducing aircraft mission range and payload. Therefore, space and
weight dedicated to landing gear will continue to be constrained, forcing this system’s designers to
seek ever more creative ways to reduce demands for them.
d Increased flotation demands will be imposed on military transports. The new landing gear designs will
allow these transports to traverse rough and much softer terrain to meet the new mission demands.
Increased flotation demands will dictate either more and lower pressure tires, tracked landing gear, or
some form of air cushion to effectively spread aircraft weight over the landing/taxiing, and parking
surface.
e Each of these advancements will similarly demand increased capability to verify and validate their
properties and effectiveness, thus, increasing test capability consistent with these growing demands.
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With the increasing acquisition and operations and maintenance cost associated with new aircraft, sustainment
will become increasingly more important, allowing existing aircraft to continue their service, sometimes well
beyond what had been their projected life. Tomorrow’s sustainment activities will focus on both test and
evaluation to identify and replicate a field failure and failure modes as well as research and development to
identify and evaluate technological solutions for the challenge presented. In many cases these efforts will
include the possibility of applying new materials, unique ways to resolve unanticipated loads and stresses, and
new designs to allow the existing configuration to improve performance or meet new requirements. Each of
these possibilities will then be fully tested, evaluated, and analyzed before it is finally installed on an aircraft for
further testing before modifying the fleet.
IV LGSCE Infrastructure
Because test and evaluation is such a significant component of many aircraft acquisition and sustainment
decisions, all facets of its accomplishment must be carefully planned, accomplished, relevant data recorded, and
reported. Within this rather broad scope, conducting landing gear systems and component test and evaluation is a
relatively specialized science. Landing gear system and component testing demand unique skills, methods,
procedures, and equipment to accomplish it accurately and completely. In addition, because landing gear system
components are diverse, with different customers, suppliers, and test requirements, most test and evaluation is
accomplished by the system or component manufacturer, in-house, with the T&E function focusing exclusively on
the component that organization also delivers. Test and evaluation, even under these circumstances, demands
absolute integrity: a sincere dedication to carefully and accurately conduct the various tests and measuring and
reporting all relevant parameters of the unit under test, without preconceived conclusions or biases of any kind.
Questions about the integrity of the tests performed under these circumstances have been and can be verified or
denied by an independent and unbiased source of testing such as the Landing Gear Systems Center of Excellence at
Wright Patterson Air Force Base, near Dayton, Ohio.
The following describes the Landing Gear Systems Center of Excellence infrastructure, supporting system and
component test and evaluation. It includes: the role of management and the overall approach to testing which
assures this independence; the people responsible for all facets of the activity; the facility and the equipment
operating within it; and the processes and procedures used to successfully complete the necessary testing. It is also
appropriate to provide a short history of the facility. This, then, becomes an outline for the remainder of this paper.
A. History
Since the United States military’s first aircraft purchase, system test and evaluation has played a significant role
in those systems being acquired for the war fighter’s use. In the late 1920s and early 1930s, the US Army Air
Service (USAF predecessor) established Wright Field and built Building No. 31 (see Figure 1). Eventually, this
building became home to the Landing Gear Test Facility (LGTF), at Wright Patterson Air Force Base, Ohio, as a
part of what evolved into the US Air Force Research
Laboratory. The Landing Gear Systems Center of
Excellence, as it is now known, remains housed in this
historic building located on what is now Area B of
Wright Patterson Air Force Base, near Dayton, Ohio.
The building was originally used for aircraft assembly
and later transitioned into aircraft and systems testing,
with wheels, brakes, tires, and struts coming thereafter.
The capability to test complete, full scale aircraft
landing gear systems and their various component parts
grew over the years as added, “world” unique
equipment was purchased and installed. With each
additional piece of equipment, another part of the
puzzle was completed. The facility can now perform
the full spectrum of test and evaluation efforts on the
vast majority of the landing gear systems for all aircraft
in the US military inventory and most of those in the commercial environment as well. This capability to
independently accomplish test and evaluation of landing gear systems and each of their components within a single
facility is unique in the world. With this capability, the US Air Force’s Landing Gear Systems Center of Excellence
Figure 1 - Landing Gear Test Facility at Wright
Patterson Air Force Base, Ohio
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provides a totally reliable source of independent, unbiased, accurate, and complete landing gear systems and
component test information with which a designer and developer can make informed, fact based decisions as to the
system’s and component’s capability to accomplish their individual and combined assigned tasks.
B Management and Leadership
The Landing Gear Systems Center of Excellence (LGSCE) is operated under US Air Force leadership and
supervision provided by a small cadre of US Air Force civilian personnel managing a contract with Jacobs
Technology, Inc, who provides the technical and administrative manpower to accomplish all landing gear systems
and component testing, as well as equipment maintenance and support. Within this context, the LGSCE provides the
United States Air Force warfighters, its international allies, and commercial entities with a full range of aircraft
landing gear development, test, and evaluation capability, assuring them that the landing gear designed, developed,
and manufactured actually meets the performance requirements imposed on the designer and manufacturer.
Ultimately, landing gear thus tested and evaluated will provide our nation’s warfighters and allies with weapons
systems having both safe and effective landing gear systems, fully suitable for their anticipated operational modes:
aircraft taxi, take-off, landing, braking, and other ground operations, for the system’s design life. As for the future,
the LGSCE’s vision is to become more than a building filled with test equipment for use by its experienced and
highly qualified operators - it must become a concept, continually adapting to the changing demands for independent
testing while maintaining its “World Class” performance. It must remain the place where a customer can come for a
full spectrum of complete, accurate, independent, and unbiased information on aircraft landing gear systems design,
materials development, technology, capabilities, and operations while retaining and improving the capability to fully
and completely test these same systems.
The Landing Gear Systems Center of Excellence continues to provide this high level of service to the various
departments of the United States Department of Defense, the nation’s allies, and to the long list of tire, wheel, brake,
and strut manufacturers who have already applied its services to their test needs.
C Technical Team
Aircraft systems testing infrastructure is more than simply test equipment, interface fixtures, and data recorders.
A solid testing infrastructure must also include consideration of the ability to fully utilize the capabilities represented
by this hardware. That means highly qualified personnel applying their extensive skills and capabilities toward
producing testing services and test reporting that is accurate, complete, and objective. These personnel must work
together - engineers, operators, and administrative personnel, to create this result. For the LGSCE, this cadre is a
combination of US Air Force personnel and their contracted support. The LGSCE is a United States Air Force
facility, with a small cadre of talented, knowledgeable US Air Force civilian engineering and management
personnel. These USAF civilians provide overall leadership, technical guidance, and management control over the
contracted engineering, operations, instrumentation, procurement, quality, administration, and maintenance efforts.
Jacobs Technology, Inc provides the engineering, operations, instrumentation, maintenance, administrative, and
operations management personnel to operate the facility. Many of these personnel have been employed
continuously in this facility for more than 25 years, applying their high level of landing gear systems expertise and
direct experience operating this facility. Because the major items of LGSCE test equipment are unique, these
engineers and technicians and their skills and knowledge are crucial to the efficient and effective use and operations
and to that of the LGSCE.
D Facility and Testing Equipment
A successful organization’s infrastructure is always a principal source of its strength. The LGSCE’s strength is
its unique combination of major testing equipment items and the personnel to operate each of them. The
knowledgeable, experienced personnel are described above. This part of the paper describes each item of the
LGSCE’s major equipment and how this combination makes it “world” unique.
The LGSCE does not have the only dynamometers in the world, but it does have unique testing capabilities,
including tire testing with 3-Axis force and moment measurement and a state of the art internal drum aircraft tire
tread wear dynamometer. It does not have the only drop towers in the world – but it does have four of them
allowing testing on landing gear systems with loads from less than 1000 up to 150,000 lbs. Its tension/compression
machine may not be either the only or even the largest, but with the capability to apply 3,000,000 lbs of compression
or 1,000,000 lbs of tension load, it is more than adequate for landing gear systems applications. The LGSCE is also
not the only source of laser based tire shearography, but it is the organization that NASA and its tire manufacturer
trust to inspect every tire that has or will ever fly on its Space Shuttle.
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The equipment listed below and the capability each brings to the LGSCE is the hardware infrastructure that
provides the foundation for this unique facility. This equipment is listed in groupings of similar equipment with the
equipment specifications and the varied uses of each item.
1. Dynamometers. Dynamometers provide a rolling surface with which to test, measure, and evaluate wheels,
brakes, and tires in a dynamic, laboratory controlled environment to determine their various component
characteristics and properties. The LGSCE has four operating dynamometers, each of which is focused on
test and evaluation of specific components.
(a) 84” Dynamometer. The 84” Dynamometer is the LGSCE’s smallest operational dynamometer and is
used primarily for straight roll brake, wheel, and tire testing with varying loads and inertia. It is
powered by a single 500 horsepower motor. There are two test carriages (North and South). Figure 2,
below shows a photo of the 84” Dynamometer, with the North carriage open and the unit’s operating
specifications.
The 84” Dynamometer is particularly well suited for and has been used for numerous long wheel roll
qualification testing as well as smaller aircraft braking systems testing, failure investigations, and
operations checks.
(b) 120” Dynamometer – The 120”
Dynamometer provides a
powerful and extremely flexible
platform for tire testing, allowing
the test engineer to dynamically
control flywheel speed as well as
the three degrees of freedom
(load, yaw, and camber) while
measuring their loads and
associated moments, all within the
South Carriage’s (See Figure 3)
computer controlled test profile
and data recording system.
Similarly, on the North Carriage,
load is computer controlled while
yaw and camber changes are
made manually either prior to or
during a pause in dynamic testing. Additionally, South Carriage testing is enhanced by automated test
article movement from the test position into and out of eight cooling stations and two environmentally
Table 1 - 84" Dynamometer
Specifications
Flywheel
Diameter: 84 in.
Width: 14-38 in.
Max Speed: 250 mph
Max Acceleration: 21 feet/sec²
Inertial Equivalent: 2,445–20,063lb
Max Kinetic Energy: 41,750,000 ft-lb
South Carriage
Max Load: 40,000 lbs
Max Torque: 375,000 in-lb
Max Tire Size: 64 in.
North Carriage
Max Load: 25,000 lbs
Max Torque: 72,000 in-lb
Max Tire Size: 48 in.
Figure 2 - 84" Dynamometer and Specifications
Figure 3 - 120" Dynamometer - South Carriage
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controlled test chambers. This unit also has a test article build-up area with overhead crane access to
the test article inspection station and then to the test, cooling and environmental stations.
The 120” Dynamometer is a real workhorse. The South Carriage’s cooling stations and environmental
chambers combined with its high speed operation and computer controlled, dynamically variable load,
camber and yaw is in nearly constant wheel and tire testing demand. .The North Carriage has similarly
computer controlled, variable loading with a manually variable camber and yaw and is used for general
tire and wheel testing as well as for nose landing gear shimmy investigations and solution verifications.
See Figures 4-6 for photos of each of these areas, and Table 2 for this unit’s test specifications.
(c) 168” Internal Drum Dynamometer (See Figures 6-7 and Table 2) – This dynamometer is primarily
used for tire tread wear testing and tire life cycle cost studies. Its unique configuration allows for a
more operationally representative tire footprint (patch) that doesn’t require a flywheel curvature based
tire air pressure correction, resulting in somewhat more realistic pressure distribution and traction
forces in the tire footprint. The configuration also allows for the installation of actual tire wear
surfaces, further enhancing its capability to simulate operational conditions. The dynamometer, with
East and West Carriages, is computer controlled and can apply dynamically controlled load, yaw, and
camber as well as controlled braking forces or controlled slip.
Figure 4 - 120" Dynamometer North Carriage
Figure 5 - 120" Dynamometer Test Article Build-Up Area
Flywheel Cooling/Inspection
Diameter: 120 in. Overhead Carrier System
Width: 24 in. Single Location Control
Max Speed: 350 mph 6 cooling stations
Max Acceleration: 24 feet/sec² 2 temperature controlled stations
Temperatures from -50° F to 375° F
South Carriage 2 Inflation/Inspection stations
Max Load: 150,000 lbs
Max Yaw: ±20 deg. Build-Up
Max Camber: ±20 deg. 2 Build-Up Stations
6 component force measurement 1 Bead Breaker Station
Dynamic control of Load, Side Mandrel Storage
Load, Yaw, and Camber
Data
North Carriage Integrated 12 - 16 bit Data
Max Load: 84,000 lbs Acquisition and processing
Max Yaw: ±15 deg.
Max Camber: ±15 deg.
Table 2 - 120" Dynamometer Specifications
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The 168” Dynamometer was specifically designed and developed to perform tire life cycle cost (LCC)
studies and LCC comparisons between competing tire manufacturers, allowing for more accurate,
value based procurement. The internal drum design also allows the installation of a wide variety of
runway surfaces for tire wear profile testing under actual runway conditions, such as US Navy carrier
deck “non skid” or US Air Force and commercial airport concrete surfaces.
Table 3 - 168" Dynamometer Specifications
(d) 192” Dynamometer
/Integrated Drop Tower
is used to accomplish
brake testing but has
been modified to allow
non-standard drop testing
onto the moving
flywheel surface, which
is directly beneath a
landing gear mounted in
the upper carriage (see
Figures 8, 9 and 10).
The 192” Dynamometer
Upper Carriage was
successfully used during a
recent acquisition program
to verify and validate the
dynamic shimmy stability
Figure 6 - 168" Internal Drum Dynamometer
Figure 7 – 168" Internal Drum Dynamometer - East
Carriage
Flywheel
Diameter: 168in.
Width: 30 in.
Max Speed: 350mph
Max Acceleration: 16 feet/sec²
East Carriage
Max Load: 50,000 lbs
Max Yaw: ±20deg.
±10deg.
West Carriage
Max Load: 150,000 lbs
Max Yaw: ±20deg.
Max Camber: ±10deg.
Machine Specifications
Both Carriages provide dynamic
control of Load, Yaw, and Camber
as well as 6 component force
measurement
Grit paper can be applied to the
Road wheel surface to simulate
runway surfaces
Figure 8- 192" Dynamometer
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of an installed nose landing gear before first flight.
2 Drop Towers. Drop towers provide the ability to simulate aircraft
landings in a laboratory environment, using variable sink rates,
masses, and wing lift, while accurately recording the loads
imposed on the landing gear as they would be transmitted to the
aircraft structure. Such tests demonstrate the full spectrum of
aircraft landing and mobility situations from normal to worst case
without endangering aircrew or aircraft.
(d) Drop Tower No. 1 – This is the smallest drop tower in the
LGSCE, and is intended to test landing gear for relatively
small aircraft while still providing the full range of test
measurements and reporting documentation (See Figure 11
and Table 5).
Table 5 - Drop Tower No 1 Specifications
Figure 9 - 192" Dynamometer - Upper Carriage
Flywheel
Diameter: 192 in.
Width: 17.5 – 79 in.
Max Speed: 200 mph
Max Acceleration: 2 fps²
Inertial Equivalent: 10,147 – 162,987 lb
Kinetic Energy: 205,000,000 ft-lb
South Carriage
Max Load: 301,500 lbs
Max Brake Torque: 5,800,000 in-lb
North Carriage
Max Load: 40,000 lbs
Max Brake Torque: 1,610,000 in-lb
Upper Carriage
Configurable for a variety of non-standard tests.
Table 4 - 192" Dynamometer
Specifications
Figure 10 - 192" Dynamometer - South Carriage showing the
many plates used to change flywheel inertia
Figure 11 - Drop Tower No 1
Specification Accessories
Load Range: 750 – 3,600 lb. One Load Platforms Available
Max Head Travel: 15 ft. * 8,000 lb max vertical
Width between Guides: 3 ft.* Up to 200 mph Pre-rotation
Platen Size: 33 x47 in. Up to 200 mph Pre-rotation
Wing Lift: 200-3,600 lb. Dynamic Load Simulator
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(e) Drop Tower No. 2 (see Figure 12 and Table 5), is somewhat
larger than No. 1, but still focused on smaller aircraft landing
gear systems
(f) Drop Tower No 3. - Drop Tower # 3 (See Figure
13 and Table 6) is considerably larger than the
first two and capable of testing landing gear struts
for much larger aircraft, including most military
fighter aircraft
Table 7 - Drop Tower No. 3 Specifications
Figure 12 - Drop Tower No 2
Specification
Load Range: 2,000 – 10,300 lb.
Max Head Travel: 20 ft.
Width between guides: 6 ft.
Platen Size: 63 x 65 in.
Wing Lift: 200-10,300 lb.
Accessories
Two Load Platforms Available
• XYZ Force Measurements
• 40,000 lb max vertical
Up to 200 mph Pre-rotation
Dynamic Load Simulator
Table 6 - Drop Tower No. 2
Specifications
Figure 13 – Drop Tower No. 3
Specifications
Load Range: 5,000 – 35,000 lb.
Max Head Travel: 25 ft.
Width between guides: 8 ft.
Platen Size: 84 x 72 in.
Wing Lift: 200-35,000 lb.
Accessories
Three Load Platforms Available
XYZ Force Measurements
200,000 lb max vertical
40,000 lb max vertical
8,000 lb max vertical
Up to 200 mph Pre-rotation
Dynamic Load Simulator
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(d) Drop Tower No. 4 – Drop Tower No 4 (See
Figure 14 and Table 7) is the facility’s
largest drop tower, able to support testing of
landing gear for all but the largest aircraft
landing gear in operation today.
Table 8 - Drop Tower No. 4 Specifications
3 Specialized Testing Equipment/Facility. In
addition to equipment specifically designed to
duplicate various aircraft operating modes in a
laboratory environment, there are equipment items
with which engineers and test technicians can
investigate the fundamental properties of aircraft
landing gear systems and components and their
response to specific stimulus.
(a) Baldwin Compression and Tension Machines.
The Baldwin Compression/Tension Machines
(see Figures 15 & 16 and Table 8) provide the
capability to calibrate landing gear strut test
article strain gages prior to drop testing. While
these units provide the application of significant
compression and tension loads, the addition of a
hydraulically operated platform to the large
Baldwin allows for very precise tire property
measurement, including tire stresses as the
platform under a test tire is moved while under
very significant test loading. The test tire can be
positioned such that platform movement can be at
any angle from fully longitudinal testing the
tire/wheel interface to 90º lateral to determine the
tire’s bead seat and sidewall roll over properties,
and any angle in between. Available laser profile
measurement to accurately measure the test tire’s
profile under this lateral movement adds to this
unit’s capability. Hardware is also available to
perform a wide variety of static load tests including load-deflection, tire-wheel slip, load vs. stroke
definition, cable bruising, and ultimate static wheel loading
Figure 14 - Drop Tower No. 4
Specification
Load Range: 35,000 – 150,000 lb.
Max Head Travel: 15 ft.
Width between guides: 10 ft.
Platen Size: 33 x 47 in.
Wing Lift: 200-150,000 lb.
Accessories
Two Load Platforms Available
XYZ Force Measurements
200,000 lb max vertical
40,000 lb max vertical
Up to 200 mph Pre-rotation
Dynamic Load Simulator
Figure 15 - Large Baldwin
Compression/Tension Machine
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The Baldwin Machines are used for a variety of tests and test preparation efforts; for instance, drop
test strut instrumentation (strain gages) are usually calibrated prior to actual testing using the strong,
accurate, and very controllable Baldwin compression.
(b) Tire Force Machine. The Tire Force Machine (See Figure 17 and
Table 9) measures tire properties under a wide variety of
dynamic and static conditions, fully describing the test article’s
mechanical tire properties. The instrumented load head and table
measure tire stresses induced as a measured load is applied to the
tire and the table moves longitudinally. The tire can also be
yawed or cambered prior to table movement. As the tire
completes at least one complete revolution, it rolls over a 39
sensor measurement plate mounted near the end of the table.
These sensors measure the x, y, and z traction forces on the
contact patch, data which can then be translated into a colored
stress representation of the tire footprint as shown in Figure 18.
Figure 16 - Small Baldwin
Compression and Tension
Machine
Large Baldwin
Max Compression: 3,000,000 lb.
Max Tension: 1,000,000 lb.
Max Stroke: 60 in
Max Height: 28 ft.
Max Width: 10 ft.
Platen Size: 60.5 x 96 in.
Small Baldwin
Max Compression: 200,000 lb.
Max Tension: 200,000 lb.
Max Stroke: 12 in.
Max Height: 6 ft.
Max Width: 2.5 ft.
Platen Size: 30 x 30 in.
Table 9 - Compression/Tension
Machines' Specifications
Specifications
Max Vertical Load: 75,000 lb.
Max Side Load: 30,000 lb.
Max Brake Torque: 240,000 in-lbs
Max Yaw: ±20deg.
Max Camber: ±10deg.
Max Tire Size: 56 in.
Width: 40 in.
Length: 20 ft.
Max Travel Speed 4 in/sec.
Capabilities
- 74 Sensors/Pressures Footprint/Traction/
Slip measurement attachment
Fixturing available for
• Rolling relaxation length
• Lateral Stiffness
• Torsional Stiffness
-Surface Material can be changed to meet
customer requirements
- 6 Component Force Measurements
- 16 bit Data Acquisition System
Table 10 - Tire Force Machine
Specifications
Figure 17 Tire Force Machine
Figure 18 - TFM Output: Shear Pressure
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(c) Fatigue Test Machine (See Figure 19). The
Fatigue Test Machine (FTM) provides the
capability to apply operational stresses to the
various landing gear systems and components,
allowing them to accumulate significant wear life
and exhibit normal fatigue and wear patterns well
before they would occur in normal field
operations. This test unit consists of a steel
superstructure on which the test article(s) and
electric and hydraulic loading equipment are
mounted and operated.
The FTM has been used to define landing gear
systems, bearings, and trunion fatigue
characteristics, among other such tests.
(d) Burst Pit - This safety enclosure (below grade) is used to determine the ultimate strength of a wheel or
tire. The test article is filled with water and pressure increased until tire or wheel failure. The pressure
at failure is recorded as is a video recording of the failure as it occurs.
The Burst Pit has been used to overpressure a
wide variety of tires to describe their failure
characteristics and help describe the impact
of such rapid events within a wheel well.
Figure 19 - Fatigue Test Machine
Figure 20 - Burst Pit
Specifications
 Size of the pit: 72” x 120” x 126”
 Water pressure limit: 5,000 psi
 Rate of Inflation: 10 psi/min average
Data Acquisition
 Sampling is done continuously to customer
specifications
 Video recordings of unit failure can be
accomplished if desired
Table 11
Specifications: Burst Pit
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4 Supporting Equipment. The testing equipment discussed above provides the means to accomplish the
necessary testing and data recording. The following equipment supports testing without actually being part
of the test, data collection, or data analysis process.
(a) Spin-Up Rig – This equipment is
used to drive the drop test article’s
wheel and tire up to landing speed
simulating landing wheel spin-up
and spring back when dropped
(See Figure 21 and Table 11)
(b) Load Simulation/Vibration Generator – This
equipment item, used in association with the
drop towers, is used to simulate the various
loads encountered by a landing gear in its
normal operation. Runway roughness profiles,
including bomb damage repair profiles, can be
programmed to test landing gear dynamic
response to surface roughness. This machine
can also be used to “shake test” various
aeronautical equipment, including large shock
loading conditions (See Figures 22 & 23).
Figure 21 - Wheel Spin-Up Rig
Specifications:
Motor: 30 Hp
Maximum Tire Pre-Rotation: 200 mph
Table 11 – Spin-Up Rig Specifications
Fi
g
ure 22- Vibration Generation Machine
Figure 23 - Vibration Generation Machine Performance
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E Test Processes and Procedures
The Landing Gear Systems Center of Excellence has been certified to International Standards Organization
specification 9001: 2000, and has continued that level for more than four years. The Center’s processes and
procedures are audited both by internal sources as well as a certified ISO standard auditor performing audits
semiannually. These audited processes and procedures provide a solid foundation to assure successful testing, and
consistently meeting or exceeding customer demands.
V Landing Gear Systems Infrastructure for Tomorrow
As landing gear technology, materials, and production processes evolve into improved landing gear with increased
capability to meet the challenges posed by the customer (for commercial aircraft) and the threat (for military
systems), the test and evaluation infrastructure must both retain its existing capability while evolving to assure that
the product of the designers and producers imagination actually complies with their intent and meets the then
established performance requirements and/or specifications. This is a dual track process: capability retention and
evolution, both of which will be addressed here.
A Retaining Existing Capability.
The LGSCE was developed in the 1930s and 40s, by the predecessor to the United States Air Force as they
recognized the need to define, develop, and establish an independent, organic landing gear systems test and
evaluation capability with which to both assure that developmental landing gear struts, wheels, brakes, tires, and
actuators met established performance requirements and that operating systems sustainment challenges could be
similarly evaluated and resolved. Continued equipment upgrades to meet changing test capability requirements
justify the retention of the LGSCE mission. Because the equipment selected and installed was both strong and
durable, the only thing that has changed is its age. Much of the LGSCE equipment is more than 40 years old, but
with the continued operating controls and data acquisition updates, it retains its significant value. As we move into
the future, this equipment should continue to age without any significant impact to its operating capability. This
does assume the existing corrective and preventative maintenance program continues, and that the enhanced
predictive maintenance program recently initiated is further developed. Efforts focused on identifying and applying
technology enhancements as they evolve to upgrade the existing equipment would continue to improve operating
efficiencies and limit existing operations and maintenance cost growth. These efforts might include:
1 Motor power increase. Several of the LGSCE’s dynamometers were designed and installed many years
ago. While many of these units are old, their motors are clearly industrial grade and have been well
maintained. In some cases, as the Center has evolved, several of these motors are too small to accomplish
some of the tasks being assigned to it. Where these motors are too small for some existing requirements,
they should be either supplemented with additional, similar motors in series, or completely replaced with
more powerful motors.
2 Digital Controls and Data Acquisition Systems. Most of the equipment controls and data acquisition
systems were designed and built with earlier technology and updated as the state of the art evolved. While
still functional, it is important that this evolutionary technology replacement process be continued to both
improve the accuracy and reliability of the resulting data as well as improving system reliability.
3 Conversion from pneumatic to hydraulic loading system on one major dynamometer. The 192”
dynamometer South Carriage has recently been converted from pneumatic loading power to hydraulic.
Consideration should be given to similarly converting the North Carriage as well, thereby providing the
same system performance and reliability improvements that will soon accrue to the South Carriage.
4 Automating equipment operations. The largest operations and maintenance costs associated with the
LGSCE is the manpower it takes to operate the Center’s equipment. The Center is studing a strategy to
increase equipment automation, ultimately allowing for unmanned testing operations, reducing equipment
operating costs, and allowing the existing personnel to expend their efforts where their touch is required.
B Increased Capability to Meet New Demands
As landing gear systems evolve through new materials, processes, and design paradigm changes, the LGSCE will
increase its capability to allow continued effective test and evaluation of these new landing gear while also
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providing the continuing capability to aid existing system sustainment, and more. This evolutionary process will
include a wide variety of equipment modifications and new equipment to meet the established and future customer’s
needs. Among the test and evaluation capabilities that will need to be considered include the following:
1 Combined tire/wheel technology that is beginning to appear. This developing and evolving technology will
demand new test techniques in combination with existing test and evaluation processes. It will also
demand development of a reasonable set of technical standards and design criteria with which to compare
actual test results.
2 Tracked wheel testing. As commercial and military aircraft customers demand increased flotation, or the
ability to operate from increasingly softer surfaces, designers will consider continued decreases in tire
pressure until wheels and tires are replaced by some form of tracked landing gear, spreading the aircraft
loads over a larger area. Test and evaluation of this new configuration will initially tax existing capabilities
until the full recognition of the impact that these new designs will have on the test and evaluation
community. New test processes, procedures, and equipment will be needed, with the actual configuration
yet to be defined.
3 Air cushion landing gear systems testing. The same increased flotation demands could also drive designers
further, to air cushion systems designs, further spreading aircraft loads across a broader area. Here, again,
existing test and evaluation capabilities are likely to be totally inadequate. Such air cushion technology
will demand a significant change in the existing test and evaluation paradigm.
4 Landing Gear Systems Integration. Historically, landing gear systems integration into the aircraft has been
the responsibility of the aircraft manufacturer with the customer maintaining an interested observer role.
As aircraft systems costs have escalated and systems complexity increased, the prime manufacturer has
sought ways to both reduce costs and decrease their responsibility for separable parts of the aircraft
development process. Aircraft manufacturers have responded by contracting with the landing gear
manufacturer to assume responsibility for meeting established interface controls from the aircraft structure
(the trunion mount) to the concrete, including wheels, brakes, tires, struts, and other systems interfaces,
including hydraulics, electrical, and flight control systems that are increasingly used to control the aircraft
braking. Component and subsystem supplier’s competitive and proprietary technologies have and will
continue to challenge the landing gear manufacturer’s efforts in this arena. The LGSCE is particularly well
suited to assume an increased role in this process because of its existing test and evaluation capability,
complete independence, and long history of capability and integrity. Responding to such a challenge is
primarily a demand for an extension of the specialized manpower existing within the LGSCE to include a
group dedicated to landing gear systems integration into the aircraft.
C Commitment and Funding
As the LGSCE continues evolving and progressing while consistently providing complete, accurate, independent,
and unbiased test and evaluation services to its military and commercial customers, it will need the continued, far
sighted attention to its future capability requirements in order to remain viable. It is vital that LGSCE, the Air Force
Material Command overseers, and its customer decision makers, all recognize the existing capabilities as they are
used and the need to support continued capability improvement and growth to address the needs of the future.
VI Conclusions and Summary
Landing gear systems are apparently simple; designs based on mature technology, manufactured using known
materials and processes, and assembled using some commercial off the shelf hardware. This appearance is
deceptive. The deception is the system’s complexity and precision that results from the significant constraints and
challenges imposed on the landing gear designer by the aircraft designer’s allocation of aircraft space, weight and
power. Because landing gear is a parasitic system, generating only negative impact on the mission and payload,
aircraft designers tend to de-prioritize its needs and relative value to the aircraft resulting in these more complex
designs, exotic materials, and limited growth potential. All this points to the need for a more robust landing gear test
and evaluation effort to assure that even after these aggressive design compromises, the system still meets its
required performance requirements. The US Air Force’s Landing Gear Systems Center of Excellence is DoD’s
single source for test and evaluation of all the various landing gear systems and components, including the strut,
wheels, brakes, tires, and actuators and their successful integration with the aircraft. The LGSCE equipment includes
dynamometers, drop test towers, a tire force machine, a fatigue test machine, significant compression and tension
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machines, as well as all the ancillary controls, data collection, recording, and analysis equipment, supporting
equipment, and the engineers and technicians to make it all work.
While test and evaluation is a critical component of the system design and development process, system
sustainment is similarly critical to the long term system viability. The LGSCE will continue to be an active
participant in systems sustainment by using its existing and future capabilities to repeat field failures in a laboratory
environment, thereby allowing engineers to evaluate the failure and identify and test modifications needed to
eliminate their source. In addition, the LGSCE’s wide variety of landing gear systems test and evaluation equipment
allows active participation in sustainment related research and development, identifying possible technological
solutions to the existing field failure modes. These fleet sustainment capabilities will continue to evolve in concert
with LGSCE equipment modifications and improvements.
LGSCE capability will continue to evolve as aircraft and systems evolve allowing it to addresses the new
materials, processes, and designs and the need to test and evaluate their ability to meet the performance capabilities
imposed upon them. In addition, the LGSCE is prepared to move into other areas where its independence, accuracy,
and complete test and evaluation capabilities can be best utilized. These areas include such diverse demands as
landing gear systems /aircraft systems integration supporting the aircraft and landing gear manufacturers as well as
the ultimate aircraft user. With the commitment of the US Air Force, and the LGSCE’s customers and supporting
activities, the LGSCE will celebrate another 75 years of active participation in the aircraft design, development, test,
evaluation, manufacture, and sustainment business. Ultimately, the LGSCE survives and thrives because it provides
the unique capabilities required to continue meeting the war fighter’s needs while also providing the integrity
needed to satisfy the demands of its commercial customers.
The United States Air Force Landing Gear Systems Center of Excellence has the existing capability to provide
complete, accurate, and independent test and evaluation efforts on all of a landing gear system’s components in one
place using the existing infrastructure and planned modifications, improvements, and anticipated capability
development. The US Air Force’s Landing Gear Systems Center of Excellence represents a unique capability in the
world and, as such, is indeed a national treasure
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