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At least 955 records · Page 53

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NASA NTRS1990

An in-flight interaction of the X-29A canard and flight control system

Many of today's high performance airplanes use high gain, digital flight control systems. These sytems are liable to couple with the aircraft's structural dynamics and aerodynamics to cause an aeroservoelastic interaction. These interactions can be stable or unstable depending upon damping and phase relationships within the system. The details of an aeroservoelastic interaction experienced in flight by the X-29A forward-swept wing airplane. A 26.5-Hz canard pitch mode response was aliased by the digital sampling rate in the canard position feedback loop of the flight control system, resulting in a 13.5-Hz signal being commanded to the longitudinal control surfaces. The amplitude of this commanded signal increased as the wear of the canard seals increased, as the feedback path gains were increased, and as the canard aerodynamic loading decreased. The resultant control surface deflections were of sufficient amplitude to excite the structure. The flight data presented shows the effect of each component (structural dynamics, aerodynamics, and flight control system) for this aeroservoelastic interaction.

Kehoe, Michael W.↗

NASA NTRS1990

The use of an airborne lidar for mapping cirrus clouds in FIRE, phase 2

The Univ. of Washington (UW) and Georgia Tech have recently built a dual wavelength airborne lidar for operation on the UW's Convair C-131A research aircraft. This lidar was used in studying aerosols and clouds. These studies demonstrated the utility of airborne lidar in a variety of atmospheric research and prompt the suggestion that this facility be included in the next FIRE cirrus experiment. The vertically pointing airborne lidar would be used as a complement to ground based lidars. The airborne lidar would ensure extended coverage of IFO cases that develop upwind of the surface lidars or which miss the ground based lidars while still being the focus of satellite and aircraft in situ studies. The airborne lidar would help assure that cirrus clouds were simultaneously viewed by satellite, sampled by aircraft, and structurally characterized by lidar. System specifications are listed and a schematic is shown of the lidar system aboard the C-131A.

Radke, Lawrence F.↗

NASA NTRS1990

NASA programs in advanced sensors and measurement technology for aeronautical applications

NASA involvement in the development, implementation, and experimental use of advanced aeronautical sensors and measurement technologies is presently discussed within the framework of specific NASA research centers' activities. The technology thrusts are in the fields of high temperature strain gages and microphones, laser light-sheet flow visualization, LTA, LDV, and LDA, tunable laser-based aviation meteorology, and fiber-optic CARS measurements. IR thermography and close-range photogrammetry are undergoing substantial updating and application. It is expected that 'smart' sensors will be increasingly widely used, especially in conjunction with smart structures in aircraft and spacecraft.

Conway, Bruce A.↗

NASA NTRS1991

Maintaining the safety of an aging fleet of aircraft

The current status of the Douglas Aging Fleet is examined in light of increasing concern for the possibility of the onset of widespread cracking and recent industry activity to minimize the concern. A fleet monitoring program together with an augmented maintenance program is proposed as a possible means to reduce the concern. Six candidate options for maintenance program augmentation are examined which have been shown to be effective in detection of widespread fatigue damage. A brief example of how this system might be applied to the DC-9 Fleet is presented.

Aging Aircraft↗

NASA NTRS1991

Preliminary results on the fracture analysis of multi-site cracking of lap joints in aircraft skins

This paper presents results of a fracture mechanics analysis relevant to fatigue crack growth at rivets in lap joints of aircraft skins are presented. Multi-site damage (MSD) is receiving increased attention within the context of problems of aging aircraft. Fracture analyses previously carried out include small-scale modeling of rivet/skin interactions, larger-scale two-dimensional models of lap joints similar to that developed here, and full scale three-dimensional models of large portions of the aircraft fuselage. Fatigue testing efforts have included flat coupon specimens, two-dimensional lap joint tests, and full scale tests on specimens designed to closely duplicate aircraft sections. Most of this work is documented in the proceedings of previous symposia on the aging aircraft problem. The effect MSD has on the ability of skin stiffeners to arrest the growth of long skin cracks is a particularly important topic that remains to be addressed. One of the most striking features of MSD observed in joints of some test sections and in the joints of some of the older aircraft fuselages is the relative uniformity of the fatigue cracks from rivet to rivet along an extended row of rivets. This regularity suggests that nucleation of the cracks must not be overly difficult. Moreover, it indicates that there is some mechanism which keeps longer cracks from running away from shorter ones, or, equivalently, a mechanism for shorter cracks to catch-up with longer cracks. This basic mechanism has not been identified, and one of the objectives of the work is to see to what extent the mechanism is revealed by a fracture analysis of the MSD cracks. Another related aim is to present accurate stress intensity factor variations with crack length which can be used to estimate fatigue crack growth lifetimes once cracks have been initiated. Results are presented which illustrate the influence of load shedding from rivets with long cracks to neighboring rivets with shorter cracks. Results will also be included for the effect of residual stress due to the riveting process itself. All the results presented in this paper should be regarded as preliminary in the sense that further work by ourselves and others will be required to validate them and to establish their sensitivity to more embellished modelling assumptions.

Aging Aircraft↗

NASA NTRS1991

Status of the FAA flight loads monitoring program

In support of the Federal Aviation Administration Aging Aircraft Research Program, the Agency has established a Flight Loads Data Collection Program for Commercial Aircraft. The objectives of this Program are to: - Review existing data collected by other sources including but not limited to U.S., Foreign, Military, etc. - Collect current operational usage data from both large and small transport aircraft - Develop criteria for future generations of transports. This paper presents the status of the various programs which are completed, underway or planned. The FAA will be collecting, storing, and analyzing the data which characterize typical commercial transport operations. The airframe manufacturers will handle the task of calculating the loads and stresses.

Aging Aircraft↗

NASA NTRS1991

Federal Aviation Administration aging aircraft nondestructive inspection research plan

This paper highlights the accomplishments and plans of the Federal Aviation Administration (FAA) for the development of improved nondestructive evaluation (NDE) equipment, procedures, and training. The role of NDE in aircraft safety and the need for improvement are discussed. The FAA program participants, and coordination of activities within the program and with relevant organizations outside the program are also described.

Aging Aircraft↗

NASA NTRS1991

Inspection of aging aircraft: A manufacturer's perspective

Douglas, in conjunction with operators and regulators, has established interrelated programs to identify and address issues regarding inspection of aging aircraft. These inspection programs consist of the following: Supplemental Inspection Documents; Corrosion Prevention and Control Documents; Repair Assessment Documents; and Service Bulletin Compliance Documents. In addition, airframe manufacturers perform extended airframe fatigue tests to deal with potential problems before they can develop in the fleet. Lastly, nondestructive inspection (NDI) plays a role in all these programs through the detection of cracks, corrosion, and disbonds. However, improved and more cost effective NDI methods are needed. Some methods such as magneto-optic imaging, electronic shearography, Diffractor-Sight, and multi-parameter eddy current testing appear viable for near-term improvements in NDI of aging aircraft.

Aging Aircraft↗

NASA NTRS1991

Nondestructive inspection perspectives

This paper presents ideas for consideration by those concerned with commercial aircraft nondestructive inspection (NDI). The perspective is that of an individual with a background in military aircraft NDI, and important differences are indicated between the commercial NDI and military NDI activities. In particular, it is significantly more expensive to implement some new NDI technology, and therefore, in-depth cost-benifit studies for commercial users are recommended.

Aging Aircraft↗

NASA NTRS1991

Communication: An important element of maintenance and repair

People from the airlines, the FAA, and the manufacturers have worked together in an effort to improve the Service Difficulty Reporting system. Their work to date is summarized as follows. - Goals were generalized into three broad work statements; (a) design a worldwide reporting system to provide safety alerts to aircraft operators, manufacturers, repair facilities, and regulatory authorities. (b) design a companion system to provide worldwide reliability experience. (c) overhaul regulatory requirements to be consistent with (a) and (b) to provide information necessary and useful for public consumption.

Aging Aircraft↗

NASA NTRS1991

Using Intelligent Simulation to Enhance Human Performance in Aircraft Maintenance

Human factors research and development investigates the capabilities and limitations of the human within a system. Of the many variables affecting human performance in the aviation maintenance system, training is among the most important. The advent of advanced technology hardware and software has created intelligent training simulations. This paper describes one advanced technology training system under development for the Federal Aviation Administration.

Aging Aircraft↗

NASA NTRS1991

Revision of certification standards for aviation maintenance personnel

Part 65, Subparts D and E, of the Federal Aviation Regulations (FAR) identify the certification requirements for aviation mechanics and aviation repairmen. The training, experience, privileges, ratings, recordkeeping, and currency requirements for aviation maintenance personnel are also addressed by these parts of the FAR. The recent emergence of the aging fleet problem and the introduction of new technologies, aircraft, engines, and aeronautical products has caused certain portions of these rules to become obsolete. Further, international political arrangements, such as bilateral airworthiness and maintenance agreements, International Civil Aviation Organization (ICAO) standards, certain international agreements for maintenance personnel training, and mechanic certificate reciprocity, have all impacted on the current regulatory policy.

Aging Aircraft↗

NASA NTRS1991

The FAA aging airplane program plan for transport aircraft

The FAA Aging Airplane Program is focused on five program areas: maintenance, transport airplanes, commuter airplanes, airplane engines, and research. These programs are complementary and concurrent, and have been in effect since 1988. The programs address the aging airplane challenge through different methods, including policies, procedures, and hardware development. Each program is carefully monitored and its progress tracked to ensure that the needs of the FAA, the industry, and the flying public are being met.

Aging Aircraft↗

NASA NTRS1991

Transport Canada aging aircraft activities

A description is given of recent initiatives undertaken in Canada to address the problems of aging passenger airplanes. In addition to participation in and support of U.S. aging aircraft programs, independent activities were undertaken in such areas as regulatory control of nondestructive testing, aging fleet evaluations, and measures to address the airworthiness of aging Canadian-manufactured airplanes.

Civil aviation↗

NASA NTRS1991

Simplified computational methods for elastic and elastic-plastic fracture problems

This paper presents an overview of some of the recent (1984-1991) developments in computational/analytical methods in the mechanics of fracture: (i) analytical solutions for elliptical or circular cracks embedded in isotropic or transversely isotropic solids (the crack-plane being at an arbitrary angle to the axis of transverse isotropy), with crack-faces being subjected to arbitrary tractions; (ii) finite-element or boundary-element alternating methods for two- and three-dimensional crack problems; (iii) a "direct-stiffness" method for stiffened panels with flexible fasteners and with multiple cracks, using the alternating method; (iv) multiplesite-damage near a row of fastener holes; (v) analysis of cracks with bonded repair patches; (vi) methods for generation of weight-functions for 2- and 3-D crack problems, and (vii) domain-integral methods for elastic-plastic or inelastic crack mechanics.

Aging Aircraft↗

NASA NTRS1990

Statistically based material properties: A military handbook-17 perspective

This paper describes statistical procedures and their importance in obtaining composite material property values in designing structures for aircraft and military combat systems. The property value is such that the strength exceeds this value with a prescribed probability with 95% confidence in the assertion. The survival probabilities are the 99th percentile and 90th percentile for the A and B basis values respectively. The basis values for strain to failure measurements are defined in a similar manner. The B value is the primary concern of this paper.

Donald M. Neal↗

NASA NTRS1990

Proof test and fatigue crack growth modeling on 2024-T3 aluminum alloy

Pressure proof testing of aircraft fuselage structures has been suggested as a means of screening critical crack sizes and of extending their useful life. The objective of this paper is to study the proof-test concept and to model the crack-growth process on a ductile material. Simulated proof and operational fatigue life tests have been conducted on cracked panels made of 2024-T3 aluminum alloy sheet material. A fatigue crack-closure model was modified to simulate the proof test and operational fatigue cycling. Using crack-growth rate and resistance-curve data, the model was able to predict crack growth during and after the proof load. These tests and analyses indicate that the proof test increases fatigue life; but the beneficial life, after a 1.33 or 1.5 proof, was less than a few hundred cycles.

Newman, J. C., Jr.↗

NASA NTRS1992

Acoustic characteristics and dynamic structural loading of an ASTOVL aircraft in hover

Measurements of surface dynamic loading and freestream acoustics were made for an ASTOVL model in hover, to quantify the effects of elevated temperature on the acoustic field and surface loading. Data were acquired for a many combinations of operating parameters: model height above the ground plane, nozzle pressure ratio, and jet exit stagnation temperature. For many conditions, strong tones were observed, with amplitudes up to 150 dB. The frequencies of the strongest tones were well predicted by a model assuming feedback between the nozzle exit and the ground plane. The model also accounts for many of the variations in frequency observed with changes in model height, nozzle pressure ratio, and jet temperature. Broadband sound pressure levels up to 170 dB were also recorded. The maximum levels occurred at approximately 3 equivalent jet diameters above the ground plane. For the majority of the cases, the increase in noise due to temperature was less than expected based on free jet correlations.

Mitchell, L. K.↗