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Results for “Lift-plus-cruise”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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12 records
All sourcesNASA NTRSDOE OSTI
NASA NTRSDate not supplied

Authoring, Analyzing, and Monitoring Requirements for a Lift-Plus-Cruise Aircraft

Requirements specification and analysis is widely applied to ensure the correctness of industrial systems in safety critical domains. Requirements are often initially written in natural language, which is highly ambiguous, and as a second step transformed into a language with rigorous semantics for formal analysis. [Question/problem] In this paper, we report on our experience in requirements creation and analysis, as well as run-time monitor generation using the Formal Requirement Elicitation Tool (FRET), on an industrial case study for a Lift-Plus-Cruise concept aircraft. [Principal ideas/results] We study the creation of requirements directly in the structured language of FRET without a prior definition of the same requirements in natural language. We focus on requirements describing state machines and discuss the challenges that we faced, in terms of creating requirements and generating monitors. We demonstrate how realizability, i.e., checking whether a requirements specification can be implemented, is crucial for understanding temporal interdependencies among requirements. [Contribution] Our study is the first complete attempt at using FRET to create industrial, realizable requirements and generate run-time monitors. Insight from lessons learned was materialized into new features in the FRET and JKind analysis frameworks.

Requirements engineering↗
NASA NTRSDate not supplied

Authoring, Analyzing, and Monitoring Requirements for a Lift-Plus-Cruise Aircraft

Requirements specification and analysis is widely applied to ensure the correctness of industrial systems in safety critical domains. Requirements are often initially written in natural language, which is highly ambiguous, and as a second step transformed into a language with rigorous semantics for formal analysis. In this paper, we report on our experience in requirements creation and analysis, as well as run-time monitor generation using the Formal Requirement Elicitation Tool (FRET), on an industrial case study for a Lift-Plus-Cruise concept aircraft. We study the creation of requirements directly in the structured language of FRET without a prior definition of the same requirements in natural language. We focus on requirements describing state machines and discuss the challenges that we faced, in terms of creating requirements and generating monitors. We demonstrate how realizability, i.e., checking whether a requirements specification can be implemented, is crucial for understanding temporal interdependencies among requirements. Our study is the first complete attempt at using FRET to create industrial, realizable requirements and generate run-time monitors. Insight from lessons learned was materialized into new features in the FRET and JKind analysis frameworks.

Requirements engineering↗
NASA NTRS2021

Design of a Tiltwing Concept Vehicle for Urban Air Mobility

NASA is establishing a fleet of conceptual air vehicle designs to support research and development for Urban Air Mobility (UAM). This fleet of vehicles will enable examination of the sensitivity of UAM vehicle designs to technology assumptions, identify key research and development needs for UAM aircraft, and provide the UAM community with reference vehicles that are publicly available and based upon known assumptions. To date, four six-passenger reference vehicles have been established: a quadrotor, a side-by-side, a lift-plus-cruise, and a quiet single main rotor helicopter; this paper adds a tiltwing vehicle to the fleet. This paper details the design process that was followed in order to establish the tiltwing vehicle in the fleet, including early conceptual design decisions, sizing and configuration trades, structural analyses, proprotor design and aeroacoustic predictions, and aerodynamic analyses. The resulting tiltwing vehicle uses a turboelectric propulsion system to power six proprotors positioned on a tilting main wing and two tilting proprotors positioned on the horizontal tail. This paper also compares the resulting tiltwing vehicle with the other six-passenger reference vehicles, including an updated lift-plus-cruise vehicle, and then proposes future studies. The fleet of UAM reference vehicles will continue to evolve; subsequent versions of the reference vehicles will be based upon the results of future trade studies and technology developments.

Urban Air Mobility↗
NASA NTRSDate not supplied

Developing Urban Air Mobility Vehicle Models to Support Air Traffic Management Concept Development

To support Urban Air Mobility (UAM) research efforts at NASA, the Airspace Target Generator (ATG) software used in the FutureFlight Central (FFC) air traffic control tower simulator is undergoing updates to support physics-based UAM vehicle models. A process was developed to integrate UAM vertical takeoff and landing (VTOL) aircraft into the fixed-wing ATG modeling environment without significant change to the underlying equations of motion and vehicle model database. The VTOL aircraft models were converted from a six degrees-of-freedom (6-DOF) representation into a four degrees-of-freedom (4-DOF) representation for integration within ATG. Three vehicle designs from the NASA Revolutionary Vertical-Lift Technologies (RVLT) project were selected: a lift-plus-cruise (LPC) aircraft model and quadrotor, electric-powered (QEP) 1-seater and 6-seater models. With the LPC model comprised of a nonlinear force and moment build-up, and the QEP models comprised of linearized stability derivatives, two separate processes were developed to convert the lift, drag, and propulsion characteristics of each model into the ATG model database. Key aircraft performance characteristics including climb, cruise, and descent performance were preserved during the conversion process. Because ATG simulates fixed-wing aircraft through ground taxi and takeoff to approach and landing, acceleration command algorithms were developed to model the vertical takeoff and vertical landing phase of UAM operations. A strategy was then developed to transition the aircraft model to- and from- the new control mode.

urban air mobility↗
NASA NTRSDate not supplied

Power Quality Analysis for a High Voltage Power System for Urban Air Mobility Application

Maturation of electric power technologies has opened the door for deployment of new types of aircraft within urban air mobility (UAM) markets. These new types of aircraft use non-conventional designs, which do not fall within existing regulatory requirements; this is especially true for the design and verification of the high voltage primary power systems which are being proposed for many of these aircraft. The purpose of this paper is to investigate and inform integration requirements, mainly related to power quality, based on a point design of a NASA Lift-plus-Cruise Vehicle Electrical Power System (EPS) and Utilization Equipment (UE). The results will be used to inform normal and abnormal operating performance of the EPS and UE for future standards in regards to Power Quality.

Nuha S Nawash↗
NASA NTRSDate not supplied

Conceptual Design of a Tiltduct Reference Vehicle for Urban Air Mobility

NASA is establishing a fleet of conceptual air vehicle designs to support research and development for Urban Air Mobility (UAM). This fleet of vehicles will enable examination of the sensitivity of UAM vehicle designs to technology assumptions, identify key research and development needs for UAM aircraft, and provide the UAM community with reference vehicles that are publicly available and based upon known assumptions. To date, five six-passenger reference vehicles have been published: a quadrotor, a side-by-side, a lift-plus-cruise, a single-main-rotor helicopter, and a tiltwing. To increase the breadth of vehicle technologies encapsulated in the fleet of NASA UAM reference vehicles, this paper establishes a tiltduct vehicle as an addition to the fleet. The fleet will continue to evolve as future analyses and trade studies are performed. The tiltduct reference vehicle has six tilting ducted proprotors. This paper describes the initial configuration downselection; discusses ducted proprotor design rules of thumb as they applied to the conceptual design of the reference vehicle; describes the vehicle sizing, trade studies, and tuning of models performed; and finally, compares the resulting tiltduct vehicle against the other six-passenger NASA UAM reference vehicles. The high-level analyses performed for this study did not indicate significant differences in performance between the tiltduct and tiltwing reference vehicles, and so vehicle performance alone may not be a key driver in the selection of a tiltduct vehicle over a tiltwing vehicle. However, if ducts are found to have significant acoustical benefits, then acoustical priorities may provide a compelling reason to incorporate ducted proprotors. One significant limitation of the design presented in this paper is that the ducted proprotor performance was tuned based upon performance characteristics observed during historical tests with disk loadings (defined as thrust divided by proprotor disk area) of 125-250 lb/ft^2. The tiltduct vehicle designed in this study has a disk loading of 30 lb/ft^2, to be more representative of UAM vehicles; further studies to understand performance of ducted proprotors at representative disk loadings are warranted.

Tiltduct↗
NASA NTRS2022

Conceptual Design of a Tiltduct Reference Vehicle for Urban Air Mobility

NASA is establishing a fleet of conceptual air vehicle designs to support research and development for Urban Air Mobility (UAM). This fleet of vehicles will enable examination of the sensitivity of UAM vehicle designs to technology assumptions, identify key research and development needs for UAM aircraft, and provide the UAM community with reference vehicles that are publicly available and based upon known assumptions. To date, five six-passenger UAM reference vehicles have been published: a single-main-rotor helicopter, a side-by-side helicopter, a quadrotor, a lift-plus-cruise, and a tiltwing. To increase the breadth of vehicle technologies encapsulated in the fleet of NASA UAM reference vehicles, this paper establishes a tiltduct vehicle as an addition to the fleet. The fleet will continue to evolve as future analyses and trade studies are performed. The tiltduct UAM reference vehicle has six tilting ducted proprotors. This paper describes the initial configuration downselection; discusses ducted proprotor design rules of thumb as they applied to the conceptual design of the reference vehicle; describes the vehicle sizing, trade studies, and tuning of models performed; and finally, compares the resulting tiltduct vehicle against the other six-passenger NASA UAM reference vehicles. The high-level analyses performed for this study did not indicate significant differences in performance between the tiltduct and tiltwing reference vehicles, and so vehicle performance alone may not be a key driver in the selection of a tiltduct vehicle over a tiltwing vehicle. However, if ducts are found to have significant acoustical benefits, then acoustical priorities may provide a compelling reason to incorporate ducted proprotors. One significant limitation of the design presented in this paper is that the ducted proprotor performance was tuned based upon performance characteristics observed during historical tests with disk loadings (defined as thrust divided by proprotor disk area) of 125-250 lb/ft$^2$. The tiltduct vehicle designed in this study has a disk loading of 30 lb/ft$^2$, to be more representative of UAM vehicles; further studies to understand performance of ducted proprotors at representative disk loadings are warranted.

Tiltduct↗
NASA NTRSDate not supplied

An L1 Adaptive Control Augmentation for a Lift Plus-Cruise Vehicle

This paper presents anL1adaptive control augmentation for a Lift-Plus-Cruise (L+C)vehicle. This class of vehicles operates in three flight modes with different dynamic behavior: vertical, transition, and forward flight. A robust uniform controller is used as a baseline to stabilize the system throughout these flight modes. The uniform controller is a linear control law designed around trim conditions of the aircraft and includes control allocation to achieve the desired forces and moments on the vehicle. TheL1control augmentation is designed for each of these trim conditions to compensate for the nonlinear time- and state-dependent uncertainties in the vehicle dynamics. The augmented control output is then added to the desired force and moment commands on the vehicle. Simulation results demonstrate the effectiveness of control augmentation for reducing the effects of unmodeled dynamics, reduced actuator effectiveness, and time-dependent disturbances. Effectiveness is demonstrated through tracking error metrics.

Andrew Patterson↗
NASA NTRSDate not supplied

Effects of Motion Fidelity on Pilot Performance Using Mixed-Reality Visuals

This paper investigates the effects of simulator motion fidelity on pilot performance using mixed-reality visuals. In NASA’s Vertical Motion Simulator, eleven pilots flew a lift-plus-cruise electric vertical takeoff and landing vehicle in a vertiport approach and landing task with four different motion conditions: no motion, small hexapod motion, large hexapod motion, and full motion. The simulator motion condition statistically significantly affected: 1) the severity of cybersickness, 2) motion ratings, 3) final approach and take-off boundary crossing groundspeed, 4) longitudinal touchdown point, and 5) battery time remaining after landing. The findings suggest that motion systems are essential in simulators with virtual- or mixed-reality visuals when it is required to have pilot flying performance similar to that in real flight.

mixed reality↗
NASA NTRSDate not supplied

Effects of Motion Fidelity on Pilot Performance Using Mixed-Reality Visuals

This paper investigates the effects of simulator motion fidelity on pilot performance using mixed-reality visuals. In NASA’s Vertical Motion Simulator, eleven pilots flew a lift-plus-cruise electric vertical takeoff and landing vehicle in a vertiport approach and landing task under four different motion conditions: no motion, small hexapod motion, large hexapod motion, and full motion. The simulator motion condition statistically significantly affected: 1) the severity of cybersickness, 2) motion ratings, 3) final approach and take-off boundary crossing groundspeeds, 4) longitudinal touchdown point, and 5) battery time remaining after landing. These results suggest that the use of motion systems in simulators with virtual- or mixed-reality visuals is warranted.

simulation↗
NASA NTRSDate not supplied

Trajectory Planning and Online Performance Model Estimation for Advanced Air Mobility

We propose a framework for adaptive guidance based on optimal control and estimation using closed-loop performance models. In the proposed approach, parameters of a reduced-order performance model are estimated in real time so that trajectories and guidance commands are replanned with more accurate knowledge of the system's response and performance capabilities. To apply this methodology to flight control systems, we introduce a simple yet expressive performance model modified from a reference linear design model. The proposed framework is applied to guidance of a simulated Advanced Air Mobility class concept aircraft experiencing control effector failures. We demonstrate that, by optimizing performance model parameters in real time, guidance commands can be intelligently adjusted to recover system stability and the performance of a full-order vehicle model, even in the event of effector failures. Furthermore, the reduced-order performance model requires a fraction of the computational cost of the full-order model, facilitating real-time use of adaptive, optimal guidance.

Differential dynamic programming↗
NASA NTRSDate not supplied

Trajectory Planning and Online Performance Model Estimation for Advanced Air Mobility

We propose a framework for adaptive guidance based on optimal control and estimation using closed-loop performance models. In the proposed approach, parameters of a reduced-order performance model are estimated in real time so that trajectories and guidance commands are replanned with more accurate knowledge of the system's response and performance capabilities. To apply this methodology to flight control systems, we introduce a simple yet expressive performance model modified from a reference linear design model. The proposed framework is applied to guidance of a simulated Advanced Air Mobility class concept aircraft experiencing control effector failures. We demonstrate that, by optimizing performance model parameters in real time, guidance commands can be intelligently adjusted to recover system stability and the performance of a full-order vehicle model, even in the event of effector failures. Furthermore, the reduced-order performance model requires a fraction of the computational cost of the full-order model, facilitating real-time use of adaptive, optimal guidance.

Differential dynamic programming↗