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Data pertaining to nonmotion factors affecting ride quality of transport aircraft were obtained as part of NASA in-house and sponsored research studies carried out onboard commuter-airline and research aircraft. From these data, quantitative effects on passenger discomfort of seat width, seat legroom, change in cabin pressure, and cabin noise are presented. Visual cue effects are also discussed.
The University of Virginia ride-quality research program is reviewed. Data from two flight programs, involving seven types of aircraft, are considered in detail. An apparatus for measuring physical variations in the flight environment and recording the subjective reactions of test subjects is described. Models are presented for predicting the comfort response of test subjects from the physical data, and predicting the overall comfort reaction of test subjects from their moment by moment responses. The correspondence of mean passenger comfort judgments and test subject response is shown. Finally, the models of comfort response based on data from the 5-point and 7-point comfort scales are shown to correspond.
The evolution of the standard, which is aimed at promoting research and production of more data, and providing some design guidance, is outlined and its contents summarized. Some of the assumptions and information on which it is based are analyzed. Its application to vehicle ride quality is considered in the context of the safety, efficiency and comfort of crew and passengers. The importance of establishing the precise criteria against which vibration limits are required is underlined, particularly the difficulties of first defining comfort and then postulating appropriate levels. Some current and future work related to improving the standard is outlined and additional suggestions offered.
The RQ trends which large flexible aircraft exhibit under various parameterizations of control laws and handling qualities are discussed. A summary of the assumptions and solution technique, a control law parameterization review, a discussion of ride sensitivity to handling qualities, and the RQ effects generated by implementing relaxed static stability configurations are included.
The relative merits of various category scales for the prediction of human discomfort response to vibration and the mathematical relationships that allow for transformations of subjective data from one scale to another scale were determined. A total of 16 category scales were studied and these represented various parametric combinations of polarity, scale type, and number of scalar points. Sixteen subject groups were used and each subject group evaluated its comfort/discomfort to vertical sinusoidal vibration using one of the rating scales. The passenger ride quality apparatus which can expose six subjects simultaneously to predetermined vibrations was utilized. The vibration stimuli were composed of repeats of selected sinusoidal frequencies applied at each of nine peak floor acceleration levels. A higher degree of reliability and discriminability was generally obtained from unipolar continuous type scales containing either seven or nine scalar points as opposed to the other scales investigated.
A new and easily used method of aircraft ride quality analysis is developed, and its use is illustrated by a numerical example using DC-8 airplane equations of motion. The method readily allows any type of stability augmentation system to be included for good handling qualities. A particularly powerful method of specifying and achieving all roots of a desired closed-loop characteristic equation by use of full state variable feedback is described and applied to the DC-8 example.
Scaling techniques appropriate for the measurement of ride quality subjective responses are evaluated. The major focal points of interest are summarized in succeeding paragraphs as follow: (1) scope of scaling, (2) goal of scaling, (3) category scales; including polarity, scalar points, and whether the scale is discrete or continuous in nature, (4) need and use of adjectives and/or adverbs, (5) role and use of magnitude estimation, (6) multiple response measures; and (7) related topics.
The state-of-the-art in ride quality control techniques for all the primary modes of transportation and the needs for the future are summarized.
The paper describes a comprehensive ride quality model that accounts for the effects of multifrequency and multitaxis vibration inputs as well as the interactive effects of noise and vibration upon passenger discomfort. The model is based on extensive experimental studies involving a realistic multi-degree-of-freedom laboratory simulator, and data relating to human discomfort response to vertical, lateral, and roll vibrations are presented. Results of studies involving vibration stimuli are expressed by sets of equal discomfort curves for each of three axes of vibration. A set of noise-vibration curves are obtained by an additive procedure, shown to be valid in the range under consideration, which combines the discomfort components due to noise and vibration. Other results from the study of human response to combined noise and vibration stimuli are reported.
The ride quality experienced by passengers is a function of airframe rigid-body, elastic dynamic responses, autopilot, and stability augmentation system control inputs. A frequency response method has been developed to select sinusoidal elevator input time histories yielding vertical load factor distributions, within a given limit, as a function of fuselage station. The numerical technique is illustrated by applying two-degree-of-freedom short-period and first symmetric mode equations of motion to a B-1 aircraft at Mach 0.85 during sea level flight conditions.
Quantitative relationships are presented which can be used to account for passenger ride quality in transport aircraft. These relations can be used to predict passenger comfort and satisfaction under a variety of flight conditions. Several applications are detailed, including evaluation of use of spoilers to attenuate trailing vortices, identifying key elements in a complex maneuver which leads to discomfort, determining noise/motion tradeoffs, evaluating changes in wing loading, and others. Variables included in the models presented are motion, noise, temperature, pressure, and seating.
A laboratory investigation was directed at the development of criteria for the prediction of ride quality in a noise-vibration environment. The stimuli for the study consisted of octave bands of noise centered at 500 and 2000 Hz and vertical floor vibrations composed of either 5 Hz sinusoidal vibrations, or random vibrations centered at 5 Hz and with a 5 Hz bandwidth. Results indicated that the total subjective discomfort response could be divided into two subjective components. One component consisted of subjective discomfort to vibration and was found to be a linear function of vibration acceleration level. The other component consisted of discomfort due to noise which varied logarithmically with noise level (power relationship). A model of subjective discomfort that accounted for the interdependence of noise and vibration was developed. The model was then used to develop a set of criteria (constant discomfort) curves that illustrate the basic design tradeoffs available between noise and vibration.
A ride quality meter is disclosed that automatically transforms vibration and noise measurements into a single number index of passenger discomfort. The noise measurements are converted into a noise discomfort value. The vibrations are converted into single axis discomfort values which are then converted into a combined axis discomfort value. The combined axis discomfort value is corrected for time duration and then summed with the noise discomfort value to obtain a total discomfort value.
A brief analytic exposition is presented to illustrate a central principle in flexible mode control, some of the pertinent pilot centered requirements are listed and discussed. The desired features of the control methodology are exposed and the methodology to be used is selected. The example Boeing supplied characteristics are discussed and approximated with a reduced order model and a simplified treatment of unsteady aerodynamics. The closed loop flight control system design follows, along with first level assessments of resulting handling and ride quality characteristics. Some of these do not meet the postulated requirements and remain problems to be solved possibly by further analysis or future simulation.
Commuter aircraft with low wing loading that operate at low altitudes are particularly susceptible to unwanted accelerations caused by atmospheric gusts. This paper describes the design and analysis of a longitudinal digital Ride Quality Augmentation System (RQAS). The RQAS designs were conducted for a Cessna 402B aircraft using the flaps and the elevator as the control surfaces. The designs are generated using linear quadratic Gaussian theory and analyzed in both the time and frequency domains. Nominal designs are presented at five flight conditions that cover a total mission. Trade-off studies are conducted to investigate the effect of sample time, computational delay time, servo bandwidth and control power.
A linear model of the Cessna 402B was used to determine if the control power available to a Ride Quality Augmentation System was adequate to trim an engine-out. Two simulations were completed: one using a steady state model, and the other using a state matrix model. The amount of rudder available was not sufficient in all cases to completely trim the airplane, but it was enough to give the pilot valuable reaction time. The system would be an added measure of safety for only a relatively small amount of development.
The continued investigation of the design of Ride Quality Augmentation Systems (RQAS) for commuter aircraft is described. The purpose of these RQAS is the reduction of the vertical and lateral acceleration response of the aircraft due to atmospheric turbulence by the application of active control. The current investigations include the refinement of the sample data feedback control laws based on the control-rate-weighting and output-weighting optimal control design techniqes. These control designs were evaluated using aircraft time simulations driven by Dryden spectra turbulence. Fixed gain controllers were tested throughout the aircrft operating envelope. The preliminary design of the hardware modifications necessary to implement and test the RQAS on a commuter aircraft is included. These include a separate surface elevator and the flap modifications to provide both direct lift and roll control. A preliminary failure mode investigation was made for the proposed configuration. The results indicate that vertical acceleration reductions of 45% and lateral reductions of more than 50% are possible. A fixed gain controller appears to be feasible with only minor response degradation.
Means were developed to measure the effect of vibration on human beings in a tank vehicle so as to determine the limits to which they might be taken in terms of operating effectiveness and also in terms of well being. Improved hardware for making these measurements, a method for relating tank hull input forces to ride quality, and installation and calibration of instrumentation to measure the hull forces are discussed.