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NASA NTRS1976

B-52 control configured vehicles: Flight test results

Recently completed B-52 Control Configured Vehicles (CCV) flight testing is summarized, and results are compared to analytical predictions. Results are presented for five CCV system concepts: ride control, maneuver load control, flutter mode control, augmented stability, and fatigue reduction. Test results confirm analytical predictions and show that CCV system concepts achieve performance goals when operated individually or collectively.

Arnold, J. I.↗

NASA NTRS1976

Design of active controls for the NASA F-8 digital fly-by-wire airplane

The design of a set of control laws for the NASA F-8 digital fly by wire research airplane is described. These control laws implement several active controls functions: maneuver load control, ride smoothing and departure boundary limiting. The criteria and methods which were used in the design of the control laws are also included. Results of linear analyses and nonlinear simulation are summarized.

Gera, J.↗

NASA NTRS1978

The Total In-Flight Simulator (TIFS) aerodynamics and systems: Description and analysis

The aerodynamics, control system, instrumentation complement and recording system of the USAF Total In/Flight Simulator (TIFS) airplane are described. A control system that would allow the ailerons to be operated collectively, as well as, differentially to entrance the ability of the vehicle to perform the dual function of maneuver load control and gust alleviation is emphasized. Mathematical prediction of the rigid body and the flexible equations of longitudinal motion using the level 2.01 FLEXSTAB program are included along with a definition of the vehicle geometry, the mass and stiffness distribution, the calculated mode frequencies and mode shapes, and the resulting aerodynamic equations of motion of the flexible vehicle. A complete description of the control and instrumentation system of the aircraft is presented, including analysis, ground test and flight data comparisons of the performance and bandwidth of the aerodynamic surface servos. Proposed modification for improved performance of the servos are also presented.

Andrisani, D., II↗

NASA NTRS1979

Systems implications of active controls

Control configured vehicle design and system considerations are outlined and representative applications of active control for fighter and transport aircraft are summarized. Specific examples include relaxed static stability and angle of attack limiting on the F-16, envelope limiting and ride smoothing on the F-8, maneuver load and control and relaxed static stability on the L-1011, load alleviation for the C-5, and B-1 ride control. Principal features, problem areas, and mechanization trends for these and projected future active control applications are outlined.

Kurzhals, P. R.↗

NASA NTRS1980

Thermostructural analyses of structural concepts for hypersonic cruise vehicles

A matrix of structural concepts suitable for Mach 5 hydrogen-fueled hypersonic vehicles are defined, and a thermostructural analysis of each is presented. The thermal environment encountered in this flight regime mandates hot structures of superalloy materials or insulated structures using more conventional materials such as titanium, aluminum, and composites. This paper compares the thermostructural performance of several concepts. The various structures are initially sized to carry a 2.5 g subsonic maneuver load. The structural weights are determined, and these components are then evaluated in a transient heating program along with various thermal protection systems to determine the minimum weight combination. The temperature profiles generated for these minimum weight solutions are used as input to a structural analysis along with a model of the appropriate structural concept to calculate thermal stresses. Generally, hot structure concepts have higher thermal stresses. In most cases, the thermal stresses are below the yield strength of the material. It is shown that integral tanks have weights similar to nonintegral tank concepts for the same level of technology. Moreover, an insulated tubular aluminum-composite structure with nonintegral tanks appear attractive for near-term vehicles.

Taylor, A. H.↗

NASA NTRS1982

Nonlinear analysis of rotor-bearing systems using component mode synthesis

The method of component mode synthesis is developed to determine the forced response of nonlinear, multishaft, rotor-bearing systems. The formulation allows for simulation of system response due to blade loss, distributed unbalance, base shock, maneuver loads, and specified fixed frame forces. The motion of each rotating component of the system is described by superposing constraint modes associated with boundary coordinates and constrained precessional modes associated with internal coordinates. The precessional modes are truncated for each component and the reduced component equations are assembled with the nonlinear supports and interconnections to form a set of nonlinear system equations of reduced order. These equations are then numerically integrated to obtain the system response. A computer program, which is presently restricted to single shaft systems, has been written and results are presented for transient system response associated with blade loss dynamics with squeeze film dampers, and with interference rubs.

Nelson, H. D.↗

NASA NTRS1981

Space Operations Center, shuttle interaction study, volume 1

The feasibility of the shuttle remote manipulator system (SRMS)-aided space operations center (SOC)/orbiter berthing was evaluated to determine: (1) whether the initial rates between the SOC and the orbiter can be removed by the arm; (2) what is the best strategy to be used; (3) whether the post-capture and maneuvering loads are within the capability of the SRMS; (4) can the SOC berthing port be brought in the immediate proximity of the orbiter berthing port; and (5) what is the best way to remove the residual relative motions. Various notational conventions are established and various important locations on the orbiter and SOC structures are defined. Reference frames are defined together with the mass properties of both the SOC and the orbiter.

Source record↗

NASA NTRS1991

Model order reduction applied to a hot-bench simulation of an aeroelastic wind-tunnel model

Simulations of an aeroelastically scaled wind-tunnel model were developed for hot-bench testing of a digital controller. The digital controller provided active flutter-suppression, rolling-maneuver-load alleviation, and plant estimation. To achieve an acceptable time scale for the hot-bench application, the mathematical model of the wind-tunnel model was reduced from 220 states to approximately 130 states while assuring that the required accuracy was preserved for all combinations of 10 inputs and 56 outputs. The reduction was achieved by focussing on a linear, aeroelastic submodel of the full mathematical model and by applying a method based on the internally balanced realization of a dynamic system. The error-bound properties of the internally balanced realization significantly contribute to its utility in the model reduction process. The reduction method and the results achieved are described.

Buttrill, Carey S.↗

NASA NTRS1991

Technology needs for high speed rotorcraft (3)

The spectrum of vertical takeoff and landing (VTOL) type aircraft is examined to determine which aircraft are most likely to achieve high subsonic cruise speeds and have hover qualities similar to a helicopter. Two civil mission profiles are considered: a 600-n.mi. mission for a 15- and a 30-passenger payload. Applying current technology, only the 15- and 30-passenger tiltfold aircraft are capable of attaining the 450-knot design goal. The two tiltfold aircraft at 450 knots and a 30-passenger tiltrotor at 375 knots were further developed for the Task II technology analysis. A program called High-Speed Total Envelope Proprotor (HI-STEP) is recommended to meet several of these issues based on the tiltrotor concept. A program called Tiltfold System (TFS) is recommended based on the tiltrotor concept. A task is identified to resolve the best design speed from productivity and demand considerations based on the technology that emerges from the recommended programs. HI-STEP's goals are to investigate propulsive efficiency, maneuver loads, and aeroelastic stability. Programs currently in progress that may meet the other technology needs include the Integrated High Performance Turbine Engine Technology (IHPTET) (NASA Lewis) and the Advanced Structural Concepts Program funded through NASA Langley.

Detore, Jack↗

NASA NTRS1992

Multifunction tests of a frequency domain based flutter suppression system

The process is described of analysis, design, digital implementation, and subsonic testing of an active control flutter suppression system for a full span, free-to-roll wind tunnel model of an advanced fighter concept. The design technique uses a frequency domain representation of the plant and used optimization techniques to generate a robust multi input/multi output controller. During testing in a fixed-in-roll configuration, simultaneous suppression of both symmetric and antisymmetric flutter was successfully shown. For a free-to-roll configuration, symmetric flutter was suppressed to the limit of the tunnel test envelope. During aggressive rolling maneuvers above the open-loop flutter boundary, simultaneous flutter suppression and maneuver load control were demonstrated. Finally, the flutter damping controller was reoptimized overnight during the test using combined experimental and analytical frequency domain data, resulting in improved stability robustness.

Christhilf, David M.↗

NASA NTRS1992

Multifunction tests of a frequency domain based flutter suppression system

This paper describes the process of analysis, design, digital implementation and subsonic testing of an active controls flutter suppression system for a full span, free-to-roll wind-tunnel model of an advanced fighter concept. The design technique employed a frequency domain representation of the plant and used optimization techniques to generate a robust multi-input/multi-output controller. During testing in a fixed-in-roll configuration, simultaneous suppression of both symmetric and antisymmetric flutter was successfully demonstrated. For a free-to-roll configuration, symmetric flutter was suppressed to the limit of the tunnel test envelope. During aggressive rolling maneuvers above the open-loop flutter boundary, simultaneous flutter suppression and maneuver load control were demonstrated. Finally, the flutter suppression controller was reoptimized overnight during the test using combined experimental and analytical frequency domain data, resulting in improved stability robustness.

Christhilf, David M.↗

NASA NTRS1992

Acoustic flight test experience with the XV-15 Tiltrotor aircraft with the Advanced Technology Blade (ATB)

An acoustic model that predicts the discrete frequency noise characteristics of helicopter rotors has been utilized in an analysis to help identify source characteristics. This technique incorporated a NASA Langley developed acoustic prediction technique, and a simplified flow field model to account for rotor wake reingestion in hover. The vehicle rotor system was modified to include the ATBs that were designed to provide for higher operating weights and improved maneuver load factor in helicopter and transition modes of operation.

Hoad, Danny R.↗

NASA NTRS1991

Cooperative implementation of a high temperature acoustic sensor

The current status and results of a cooperative program aimed at the implementation of a high-temperature acoustic/strain sensor onto metallic structures are reported. The sensor systems that are to be implemented under this program will measure thermal expansion, maneuver loads, aircraft buffet, sonic fatigue, and acoustic emissions in environments that approach 1800 F. The discussion covers fiber development, fabrication of an extrinsic Fabry-Perot interferometer acoustic sensor, sensor mounting/integration, and results of an evaluation of the sensor capabilities.

Baldini, S. E.↗

NASA NTRS1955

A Study of Normal Accelerations and Operating Conditions Experienced by Helicopters in Commercial and Military Operations

An analysis is presented of the normal accelerations and operating conditions encountered by two different airmail helicopters and a military pilot-training helicopter. The results, based on 4,325 flights (618 hours of flying time), indicate that maneuvers are usually responsible for the relatively large accelerations encountered, whereas gusts contribute primarily to the large number of smaller accelerations and the corresponding increase in the amount of time spent in the accelerated state. The largest maneuver loads recorded to date are increments (measured from the 1 g normal-flight condition) of 1.40g and -1.25g, whereas the largest gust-acceleration increment was 0.90g. The percentages of total flight time spent in the various flight conditions and speed ranges, as well as the acceleration time histories, are very similar for the two airmail helicopters and appear to follow a definite pattern as contrasted to the varied operating conditions of the military pilot-training helicopter.

Marlin E Hazen↗

NASA NTRS1992

Dumbo heavy lifter aircraft

The world is rapidly changing from one with two military superpowers, with which most countries were aligned, to one with many smaller military powers. In this environment, the United States cannot depend on the availability of operating bases from which to respond to crises requiring military intervention. Several studies (e.g. the SAB Global Reach, Global Power Study) have indicated an increased need to be able to rapidly transport large numbers of troops and equipment from the continental United States to potential trouble spots throughout the world. To this end, a request for proposals (RFP) for the concept design of a large aircraft capable of 'projecting' a significant military force without reliance on surface transportation was developed. These design requirements are: minimum payload of 400,000 pounds at 2.5 g maneuver load factor; minimum unfueled range of 6,000 nautical miles; and aircraft must operate from existing domestic air bases and use existing airbases or sites of opportunity at the destination.

Riester, Peter↗

NASA NTRS2004

New Tool Released for Engine-Airframe Blade-Out Structural Simulations

Researchers at the NASA Glenn Research Center have enhanced a general-purpose finite element code, NASTRAN, for engine-airframe structural simulations during steady-state and transient operating conditions. For steady-state simulations, the code can predict critical operating speeds, natural modes of vibration, and forced response (e.g., cabin noise and component fatigue). The code can be used to perform static analysis to predict engine-airframe response and component stresses due to maneuver loads. For transient response, the simulation code can be used to predict response due to bladeoff events and subsequent engine shutdown and windmilling conditions. In addition, the code can be used as a pretest analysis tool to predict the results of the bladeout test required for FAA certification of new and derivative aircraft engines. Before the present analysis code was developed, all the major aircraft engine and airframe manufacturers in the United States and overseas were performing similar types of analyses to ensure the structural integrity of engine-airframe systems. Although there were many similarities among the analysis procedures, each manufacturer was developing and maintaining its own structural analysis capabilities independently. This situation led to high software development and maintenance costs, complications with manufacturers exchanging models and results, and limitations in predicting the structural response to the desired degree of accuracy. An industry-NASA team was formed to overcome these problems by developing a common analysis tool that would satisfy all the structural analysis needs of the industry and that would be available and supported by a commercial software vendor so that the team members would be relieved of maintenance and development responsibilities. Input from all the team members was used to ensure that everyone's requirements were satisfied and that the best technology was incorporated into the code. Furthermore, because the code would be distributed by a commercial software vendor, it would be more readily available to engine and airframe manufacturers, as well as to nonaircraft companies that did not previously have access to this capability.

Lawrence, Charles↗

NASA NTRS2016

Static and Dynamic Aeroelastic Tailoring With Variable Camber Control

This paper examines the use of a Variable Camber Continuous Trailing Edge Flap (VCCTEF) system for aeroservoelastic optimization of a transport wingbox. The quasisteady and unsteady motions of the flap system are utilized as design variables, along with patch-level structural variables, towards minimizing wingbox weight via maneuver load alleviation and active flutter suppression. The resulting system is, in general, very successful at removing structural weight in a feasible manner. Limitations to this success are imposed by including load cases where the VCCTEF system is not active (open-loop) in the optimization process, and also by including actuator operating cost constraints.

Stanford, Bret K.↗

NASA NTRS2017

Optimal Control Surface Layout for an Aeroservoelastic Wingbox

This paper demonstrates a technique for locating the optimal control surface layout of an aeroservoelastic Common Research Model wingbox, in the context of maneuver load alleviation and active utter suppression. The combinatorial actuator layout design is solved using ideas borrowed from topology optimization, where the effectiveness of a given control surface is tied to a layout design variable, which varies from zero (the actuator is removed) to one (the actuator is retained). These layout design variables are optimized concurrently with a large number of structural wingbox sizing variables and control surface actuation variables, in order to minimize the sum of structural weight and actuator weight. Results are presented that demonstrate interdependencies between structural sizing patterns and optimal control surface layouts, for both static and dynamic aeroelastic physics.

Stanford, Bret K.↗