Browse Topic: Vehicle ride
Small, highly maneuverable Urban Air Mobility (UAM) air taxis might exhibit motions during hover and low-speed flight that are unfamiliar to many passengers, and for which there are no established guidelines to predict passenger comfort. Researchers performed a study in the Armstrong Virtual Reality Passenger Ride Quality Laboratory to identify relationships between sudden motion characteristics and UAM passenger comfort and acceptance. Twenty-three volunteer test subjects from the Armstrong workforce each completed a 15-minute experience as a passenger in a virtual air taxi simulation. Subjects evaluated a series of flight maneuvers with varying levels of sudden motion using a five-point rating scale and indicated which motion(s) they found uncomfortable. Researchers then administered a post-test questionnaire to relate the passengers’ ratings to their willingness to fly on a real air taxi with similar levels of motion. The study results relate peak heave acceleration and jerk to passenger acceptance.
A piloted simulation study in the Vertical Motion Simulator at NASA Ames Research Center will investigate the handling and ride qualities of eVTOL configurations (lift-plus-cruise and tiltwing) for both civilian and military applications. The flight dynamics models were developed in the FLIGHTLAB modeling and analysis software environment, while explicit model-following control laws and high-fidelity powertrain models were developed in Simulink. The Joint Input-Output method was used to generate frequency responses for linear model verification, as the control effectors are highly correlated for these types of vehicles. The linear models were verified for the frequency range of interest for handling qualities. Once verified and tested individually, the three parts (flight dynamics model, control laws, and powertrain) will be integrated into the Vertical Motion Simulator for piloted simulation evaluations.
Advanced Air Mobility (AAM) faces operational challenges because a significant portion of AAM flight operations are likely to occur within the atmospheric boundary layer (ABL). In particular, terminal flight paths within the ABL roughness sublayer will involve flying through building wakes that will likely result in a considerable increase in significant dynamic and vibratory loads on the vehicle, affecting flight safety and ride quality. A new representative environmental method (REM) has been developed that provides real-time estimates of the unsteady wind environments, including the roughness sublayer. The approach has numerous advantages over computational fluid dynamics solutions of any fidelity, as no meshing is required and it can easily be modified to evaluate the sensitivity of different environmental factors on operations or design. This approach is explained, verified, and validated using computational and experimental data.
Helicopter aircrew are exposed to high levels of whole-body vibration (WBV) in fight operations, which may degrade their ride comfort and performance in the short-term, and contribute to some health issues in the long-term. This paper presents the latest development and flight test demonstration results of an active seat mount system that is designed to reduce helicopter aircrew WBV levels through active cancellation of the N/rev vibration peaks related to the helicopter main rotor speed. A prototype airworthy hardware of the active seat mount system has been developed based on previous bench-top-test designs to meet airframe integrity requirements for installation and flight testing on the Bell-412 helicopter. Extensive experimental results on human occupants using a shaker table facility and flight demonstrations on the NRC Bell-412 helicopter in representative flight conditions are presented and discussed. The active seat mount system has achieved significant reduction to the occupant WBV levels at the bottom seat cushion interface per ISO2631/MIL-STD-1472G metrics, and also showed effective mitigation to the occupant head vibrations. These investigations demonstrate that the active seat mount technology is a feasible solution for helicopter aircrew WBV mitigation.
Flight mechanics modeling and real-time simulation of rotorcraft have many challenges including the aerodynamics and dynamics of the rotor system, rotor inflow, and wake-airframe interactions. Furthermore, interactional aerodynamic effects are difficult to characterize, in particular during early configuration down-selection. Rotorcraft configurations under consideration for advanced air mobility applications are trending toward designs with coaxial rotor systems and multiple distributed propellers / rotors in close-proximity with one another and the airframe. This proximity leads to strong coupling between the rotor inflow and lifting surfaces (e.g., tiltwing and lift+cruise urban air mobility concepts). This paper describes recent work toward the development of a general-purpose modeling framework for flight mechanics analysis and simulation of rotorcraft and aircraft configurations proposed for advanced air mobility applications. This modeling framework was developed for assessment of aircraft ride qualities during urban flight operations; however, the focus of this paper is on the modeling framework development and application. Model validation with experimental data is another focus, examining scaled model data and flight test results.
The paper presents a novel strategy for minimum energy consumption in automatic conversion control of tiltrotor eVTOL aircraft, exemplified by the Aston Martin Volante Vision model. We introduce a tilt schedule methodology that strategically balances conversion and reconversion performance with climb, descent, and cruise phases to minimize overall energy expenditure. Our approach accounts for critical factors such as blade loading, operation handling qualities, and passenger ride comfort within a predefined conversion corridor. The optimized trajectories approximate the minimum energy pathway, essential for operational efficiency in urban air mobility. Analytical results demonstrate that our proposed conversion and reconversion phase profiles significantly reduce energy consumption, contributing to the sustainability of tiltrotor flight operations. This research not only enhances understanding of tiltrotor dynamics but also serves as a pivotal step toward achieving globally optimized energy usage, marking a significant advancement in autonomous flight technology for advanced air mobility systems.
The serial introduction of passive and active anti-vibration means lead primarily to the reduction of the vibration levels at blade passage frequencies Nb/rev. Consequently, other- previously unnoticed- sources of vibration are perceived by rotorcraft occupants. Therefore, a comprehensive vibration assessment metric is required to characterize the impact of different vibration sources of helicopters regarding passenger comfort. Since the advance of industrial/military aerial transport machines, several vibration assessment metrics were developed such as the Intrusion Index (ADS-27A-SP), the overall ride value av (ISO2631-1) and the NASA DISC model. However, these metrics have deficiencies regarding the evaluation of complex rotorcraft vibrations, e.g. the Intrusion Index favors only the rotor harmonics in the vibration evaluation, the overall ride value av is based on uniaxial, sinusoidal oscillations at discrete frequencies and the NASA DISC model considers only vibration measurements on the floor and not on other vibration contact surfaces. Since the rotorcraft vibrations are characterized by the presence of triaxial, multiple vibration sources it is unclear whether one of these metrics is appropriate to assess the perceived discomfort. The work presented in this paper addresses this topic. The suitability of existing vibration evaluation metrics, especially av, regarding typical rotorcraft vibration patterns is investigated. For that purpose, a systematic whole-body vibration campaign was performed, in which human subjects were seated in a helicopter seat on a motion platform and exposed to helicopter specific vibration patterns of which specific frequencies were systematically attenuated or increased. Participants rated the perceived discomfort using magnitude estimation. The campaign reveals, that the overall ride value av is not well-suited to predict and to compare the discomfort of different vibration spectra. Especially in vertical direction, the application of av will significantly overestimate the discomfort. This implies that this metric is not appropriate for evaluation of helicopter specific vibrations and could be improved. The results in this paper are a first step in that direction but more comprehensive analyses of helicopter specific vibrations and their impact on passenger comfort are necessary.
ABSTRACT Higher Harmonic Control (HHC) is an approach for achieving reduced helicopter vibration by controlling the vibratory rotor airloads in such a way that the fuselage excitation is minimized. This paper is a historical look at how a program aimed at helicopter vibration reduction started as an outgrowth of fixed wing flutter suppression at NASA Langley Research Center, proved the HHC concept on aeroelastically scaled wind tunnel models, and went on to demonstrate viability in full scale flight testing on the OH-6A helicopter in 1982. Following the OH-6A flight tests the helicopter research community was stimulated to prove the effectiveness of HHC on different configurations through analysis, wind tunnel tests, and flight tests. All of these investigations have shown HHC to be effective in reducing vibration to levels not attainable with conventional vibration control methods and without any detrimental side effects. HHC development has progressed to the point that the technology is available for production application. The literature demonstrates that helicopter ride quality equivalent to that of fixed wing aircraft is available with application of HHC.
ABSTRACT The original 505 Jet Ranger X prototype used a simple hard-mounted focal pylon to attach the transmission to the airframe. In developmental flight tests, the design resulted in 2/rev vibration levels that exceeded program objectives for ride quality in high speed forward flight. To address the vibration levels, a LIVE pylon mount was designed over a 4-month period to serve as a drop-in replacement with minimal impact to existing systems. An overview of the rapid design process is presented with supporting analysis and test data that led to its incorporation on the aircraft. The LIVE pylon design cut the vertical 2/rev vibrations in half, without negatively impacting existing structures, drive systems, flight controls, or handling qualities. The LIVE pylon mount is part of the Bell 505 Type Design that was certified in December 2016.
ABSTRACT Helicopter tailboom vibrations are easily excited and decay slowly due to the tailboom's low inherent structural damping. The resulting vibration causes poor ride quality for passengers, fatigues structural elements, and increases maintenance requirements for the helicopter. Fluidic Flexible Matrix Composite (F²MC) tubes are an emerging technology which can provide lightweight, compact vibration control when attached to a vibrating structure and coupled with a fluidic circuit. This paper presents experimental results to validate a method for combining a finite element structural model of a laboratory-scale tailboom with a model of the F²MC tubes and fluidic circuit dynamics. Reductions of over 70% in both bending and torsional vibration are demonstrated in a coupled 26.7 Hz lateral bending/torsion tailboom mode, indicating that F²MC vibration control is viable at higher frequencies and for more complex vibration modes than previous research had explored. A second group of experiments is performed to demonstrate the effectiveness of a novel fluidic circuit configuration which targets two tailboom vibration modes, in contrast to the previous F²MC treatment which can target only one mode. On the lab-scale tailboom testbed, vibration reductions of over 60% are demonstrated in two modes simultaneously when targeting both a 12.2 Hz vertical mode and a 26.7 Hz lateral bending/torsion mode. The circuit designed to reduce vibrations in two modes has a nearly identical weight to a comparable single-mode treatment but is much more effective in reducing vibrations at the second mode.
ABSTRACT The typical vibration level of helicopters is considerably higher than the levels found on fixed wing aircraft. The main reason for this are periodic airloads on the main rotor leading to elevated cabin vibrations at distinct frequencies equal to multiples of the main rotor speed. Thus, the development of technologies for vibration reduction mostly focuses on solutions that counteract the vibrations at rotor blade passage frequencies. As the reduction of those vibrations is performed efficiently, the question whether non-rotor induced vibrations are relevant for helicopter ride quality arises. The work presented in this paper addresses this subject. Existing vibration evaluation methods are assessed with respect to the capability of including non-rotor vibration sources. These evaluation methods are used for an enhanced comfort evaluation by isolation of vibration signals related to relevant discomfort sources. This approach enables comfort optimization considering arbitrary vibration sources. The application of the presented comfort evaluation procedure to flight test data reveals that non-rotor induced vibrations contribute a relevant amount to the discomfort of occupants of helicopters. This is especially the case if the vehicle is equipped with modern anti-vibration systems. Furthermore, the importance of non-rotor vibration sources is greatly increased on flights in atmospheric turbulences. Hence, existing vibration evaluation methods and procedures have to be evaluated as to how they should be extended accordingly. The provided comfort evaluation method can be used for detailed comfort analysis and the results can serve as a basis for the definition of comfort improvement means.
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