Aerospace Careers: Controls and Dynamics Engineers
Engineers in the Controls and Dynamics Branch at NASA's Dryden Flight
Research Center are concerned with the integrated operations of aerospace
vehicles. They design, develop, integrate and test flight control systems
for piloted, remotely piloted and autonomously operated research and experimental
aircraft and space vehicles.
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| NASA Dryden controls and dynamics engineers
were integral to the development of the X-29.
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Flight control systems on many modern aircraft are computerized units
that have replaced mechanical linkage - bell cranks, push rods and wire
cables - between the cockpit and flight control surfaces such as ailerons
on the wings, and rudder and elevator on the tail surfaces. The control
system provides the basic stabilization in all three axes - pitch, yaw,
and roll, and provides the actuator commands for aircraft maneuvering.
Modern flight controls systems increasingly incorporate additional processing
capabilities to perform navigation, guidance, fault identification and
control system reconfiguration. Piloted or remotely piloted vehicles can
use these capabilities and the controls engineers are required to understand
the issues and implications of their use.
The branch is also involved in the development and validation of new
methodologies for controlling aircraft; testing and evaluating flying
and handling qualities and vehicle stability in a wide range of flight
conditions; developing new test and evaluation techniques; and developing
and validating simulation models. When designing or modifying aircraft
control systems, the controls engineer can also be responsible for identifying
required sensor characteristics, processing requirements, and developing
actuator specifications. Due to the Controls and Dynamics Branch involvement
in the flight testing and flight research of experimental vehicles, flight
safety is one of the overall concerns during any activity.
What are Flight Controls?
A modern flight control system incorporates the three disciplines of
guidance, navigation and control with the vehicle systems and subsystems
to meet the design requirements effectively. The flight controls engineer
must understand interaction between sensors, control laws and actuators.
The development of simulation models for these systems is often required.
The engineers develop the ability to write specifications for hardware
to meet overall control and guidance algorithms.
Development and flight test of control systems for modern research vehicles
require a sound understanding of classical and modern control methodologies
and the ability to apply them prudently. Understanding of linear, nonlinear,
and hardware-in-the-loop simulations is required. The flight control engineer
has the ability to understand bare airframe dynamics and designs the inner
loop stabilization. This includes both stability and robustness analyses
through classical stability margins or a variety of more modern methods.
Guidance and navigation have been increasingly integrated with the electronic
flight control system. For piloted vehicles, this has usually been done
through autopilot modes to reduce pilot workload or to enhance a vehicle's
capabilities. This has become more important in remotely piloted vehicles
and is essential for autonomous aircraft. These autonomous vehicles must
be programmed to operate in the absence of human intervention with the
guidance and control system responsible for all operations from taxi through
takeoff and flight.
Flight control engineers can be required to support research vehicle
development from inception to the final flight. These duties include simulation
development, software specification, hardware specification, flight test
development, ground testing and flight test support. These are opportunities
to develop new control concepts for unique vehicles, and to develop new
analysis and validation methods.
What is Flight Dynamics?
The discipline of flight dynamics tends to deal with the behavior of
flight systems - how they perform, how they can be modeled, and how they
can be improved to enhance an aircraft's handling and flying qualities.
One of the duties required for this aspect of engineering is to develop
simulation requirements, models and databases. When the simulation is
developed, flight studies are conducted to validate and improve the fidelity.
Simulations are then used to conduct flying qualities, ride qualities,
and handling qualities studies. These are used as the basis to develop
flight test requirements to conduct a subset of these studies. Flight
data are used in conjunction with pilot comments and ratings, when available,
to assess the flying qualities and flight characteristics. The combined
data are used to compare new aerospace vehicles with existing criteria
and to develop new criteria. Many of the flight regimes currently being
explored, such as high angle of attack or the hypersonic flight regime,
do not have validated criteria.
The Work of Control and Dynamics Engineers
Developing and evaluating a flight control system begins when a Controls
and Dynamics Branch customer defines a requirement for a system. The customer
can represent an aerospace project at Dryden, another NASA center, or
a commercial contractor developing a vehicle.
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| NASA Dryden controls and dynamics engineers were
integral to the development of the X-29. |
Flight control system design and development work are tailored to the
specific vehicle requirements. The performance required has to be traded
against the schedule and funding available to develop the overall system
that best meets the customer requirements.
Each project is unique in its requirements and passes through multiple
phases before flight testing is finally complete. Initial design phase
begins with an assessment of the requirements for a specific vehicle.
System specifications begin to be developed along with linear and nonlinear
simulation development. As the mature and more complete data are incorporated,
such as from wind tunnel tests, the fidelity and confidence in the simulations
improve. These simulations will be used throughout the life of the project
and will be continuously improved.
As the designs mature, the simulation testing and analysis become more
complex and thorough. The engineers begin developing the test plans and
hardware specifications that are required for systems integration, verification
and validation testing. Even at this early stage of the project, hazard
analysis and system safety are critical issues to be addressed. Flight
controls engineers work closely with other discipline engineers and pilots
to ensure that design requirements are met in an appropriate manner.
Simulation development and complexity continue to grow as flight hardware
is integrated into the system. Ultimately this activity will be transferred
to the actual flight vehicle. Throughout this process, the branch engineers
are actively involved, understanding and assessing control system operation
in real-world environments.
At Dryden, this activity culminates in the actual flight testing. Branch
engineers continue to be actively involved, supporting the flight readiness
review process and preparing for the flight testing that will ultimately
validate the control system design. Control engineers are involved in
all aspects of the flight: designing maneuvers or techniques to assess
performance, monitoring the flight from the control rooms, and conducting
post-flight data analysis. As required, this whole process repeats as
flight data indicate the need for redesign and testing of the system.
The People and the Projects
Engineers working on flight control systems and in the field of flight
dynamics have been associated with nearly every aeronautical research
project flown at Dryden in the past half century.
Flight control and dynamics engineers played a big role in NASA's rocket-powered
X-15 research aircraft project. Flown from 1959 to 1968, the X-15 is considered
among the most productive and successful of all NASA research aircraft.
It extended piloted aircraft research to a speed of 4,520 mph and it reached
an altitude of over 354,000 feet - records still standing for a winged
aircraft. Flying at these speeds and altitudes required an extremely precise
and dependable flight control system. One of the X-15's important contributions
to the space program was information gained from the use of rocket-thrusters
(reaction controls) for attitude control while on the fringes of space.
The reaction control system thrusters were located in the nose and on
the wings for pitch, yaw and roll control and were a part of the aircraft's
central flight control system.
Rugged and dependable flight control systems were also critical to the
success of Dryden's lifting body program, flown between 1966 and 1975.
The five wingless vehicle designs obtained information about controllable
atmospheric reentry. Program results solidified the concept of the space
shuttles gliding back into the atmosphere from space and landing, without
engines, at a predesignated airfield. The lifting body fleet began with
the unpowered plywood M2-F1, followed by the five rocket-powered designs:
the M2-F2, M2-F3, HL-10, X-24A and the X-24B.
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| As the designs mature, the simulation testing
and analysis become more complex and thorough. This is a photo
of the X-31 flight simulator.
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One far-reaching project at Dryden was the F-8 Digital Fly-By-Wire aircraft.
It pioneered the concept of the electronic flight control system now used
on the majority of military and commercial aircraft. The testbed was a
former United States Navy F-8 Crusader, which used a surplus Apollo spacecraft
flight control computer. The project, which demonstrated the feasibility
of digital-fly-by-wire control systems, is considered one of the most
significant research projects carried out at Dryden.
Several more recent projects have also led to improved performance and
maneuverability. These include the X-29, the F-18 High Alpha Research
Vehicle (HARV), and the X-31 Enhanced Fighter Maneuverability (EFM) aircraft.
The X-29 demonstrated that forward-swept wings, coupled with moveable
canards, reduced drag by up to 20 percent at transonic speeds. The statically
unstable aircraft required an active control system to maintain control
and demonstrated better-than-expected maneuverability at angles of attack
of up to 45 degrees.
NASA's participation in the X-31 program helped show the value of thrust
vectoring for close-in air combat maneuvering at angles of attack up to
70 degrees. The digital flight control system was also used to drive the
rudder in a manner to simulate a tailless aircraft with the thrust vectoring
paddles providing the stabilization and yaw control for maneuvering. The
five-year program, which ended in July 1995, logged 559 research missions,
the most flights ever for an "X" series experimental aircraft.
NASA's High Angle-of-Attack Research Vehicle (HARV), a modified F/A-18,
also used thrust-vectoring paddles. This program included research in
computational fluid dynamics, in-flight flow visualization, modern control
methodologies, evaluation of high angle of attack handling qualities criteria,
and advanced control effectors such as active forebody strakes.
The F-15 Advanced Control Technology for Integrated Vehicles (ACTIVE),
using axisymmetric thrust vectoring nozzles, has continued the evaluations
of modern control methodologies. In the Intelligent Flight Control System
(IFCS) project, a neural net used to identify the aerodynamic coefficients
was an integral part of the flight control system.
Controls and dynamics engineers have also participated in the Propulsion
Controlled Aircraft (PCA) experiments, where modulation of engine thrust
on multi-engine aircraft has been used to provide control forces in moments
in place of aerodynamic surfaces. This has been successfully demonstrated
on F-15 and MD-11 aircraft and could be used as an emergency control system
in the event of hydraulic system failure.
Controls and dynamics engineers are involved in projects covering the
spectrum of atmospheric flight, from the subsonic regime of current commercial
transport, to the supersonic and hypersonic flight regimes of the high
performance and Access to Space programs. While maintaining an emphasis
on flight safety, the Controls and Dynamics Branch is expanding its expertise
in flight control system design, analysis, development and test.
Education and Experience
Flight control and dynamics engineers at Dryden have a bachelor of science
degree in physics, aeronautical, mechanical or electrical engineering.
Individuals interested in working in this NASA career field should have
a broad working knowledge of aircraft dynamics, stability and controls.
Control and dynamics engineers must also have the ability to communicate
skillfully. Oral and written communications are essential for fulfilling
NASA's mission to disseminate information. Branch engineers are expected
to have the ability to communicate with other discipline engineers and
all levels of management, not only at the Dryden but also at other NASA
centers, government agencies and commercial firms.
Document Number: IS-2000-10-010-DFRC
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