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Adaptive Hexapod Simulator Motion Based on Aircraft Stability
Get PDFThis paper determined the feasibility of an adaptive hexapod simulator motion algorithm based on aircraft roll stability. An experiment was conducted that used a transport aircraft model in the Vertical Motion Simulator at NASA Ames Research Center. Eighteen general aviation pilots flew a heading-capture task and a stall task consecutively under four motion configurations: baseline hexapod, adaptive hexapod, optimized hexapod, and full motion. The adaptive motion was more similar to the baseline hexapod motion in the heading-capture task when the aircraft was more stable, and more similar to the optimized hexapod motion in the stall task when the aircraft was more unstable. Pilot motion ratings and task performance in the heading-capture task under the adaptive hexapod motion were more similar to baseline hexapod motion compared to optimized hexapod motion. However, motion ratings and task performance in the stall task under the adaptive motion were not significantly more similar to the optimized hexapod motion compared to baseline hexapod motion. Motion ratings and overall task performance under optimized hexapod motion as opposed to baseline hexapod motion were always more similar to the full motion condition. This paper showed that adaptive motion based on aircraft stability is feasible and can be implemented in a straightforward way. More research is required to test the adaptive motion algorithm in different tasks
Construction of an Airborne Data Inventory for Improved Data Discoverability and Access
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Estimation of the Tropical Cyclone Diurnal Cycle Using Simulated Observations from the NASA TROPICS Earth Venture Mission
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Advanced Air Vehicles Program: Advancing Research in Hypersonic Flight
Get PDFPresentation on Advancing Research in Hypersonic Flight at "Emerging Hypersonics Market" Panel at Transportation Research Boar
Space Science and Technology Partnership Forum: Integration with Commercial In-Space Assembly Activities
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Electrical Cable Design for Urban Air Mobility Aircraft
Get PDFUrban Air Mobility (UAM) describes a new type of aviation focused on efficient flight within urban areas for moving people and goods. There are many different configurations of UAM vehicles, but they generally use an electric motor driving a propeller or ducted fan powered by batteries or a hybrid electric power generation system. Transmission cables are used to move energy from the storage or generation system to the electric motors. Though terrestrial power transmission cables are well established technology, aviation applications bring a whole host of new design challenges that are not typical considerations in terrestrial applications. Aircraft power transmission cable designs must compromise between resistance-per-length, weight-per-length, volume constraints, and other essential qualities. In this paper we use a multidisciplinary design optimization to explore the sensitivity of these qualities to a representative tiltwing turboelectric UAM aircraft concept. This is performed by coupling propulsion and thermal models for a given mission criteria. Results presented indicate that decreasing cable weight at the expense of increasing cable volume or cooling demand is effective at minimizing maximum takeoff weight (MTO). These findings indicate that subsystem designers should update their modeling approach in order to contribute to system-level optimality for highly-coupled novel aircraft.
Mobility (UAM) vehicles have the potential to change urban and intra-urban transport in
new and interesting ways. In a series of two papers Johnson et al.1 and Silva et al.2 presented four
reference vehicle configurations that could service different niches in the UAM aviation category. Of those,
this paper focuses on the Vertical Take-off and Landing (VTOL) tiltwing configuration shown in Figure 1.
This configuration uses a turboelectric power system, feeding power from a turbo-generator through a system
of transmission cables to four motors spinning large propellers on the wings. Previous work on electric cable subsystems leaves much yet to be explored, especially in the realm of
subsystem coupling. Several aircraft optimization studies1, 3, 4 only considered aircraft electrical cable weight
and ignored thermal effects. Electric and hybrid-electric aircraft studies by Mueller et al.5 and Hoelzen
et al.6 selected a cable material but did not investigate alternative materials. Advanced cable materials
have been examined by a number of authors: Alvarenga7 examined carbon nanotube (CNT) conductors for
low-power applications. De Groh8, 9 examined CNT conductors for motor winding applications. Behabtu
et al.,10 and Zhao et al.11 examined CNT conductors for a general applications. There were some studies
that examined the thermal effects of cables but they did not allow the cable material to change; El-Kady12
optimized ground-cable insulation and cooling subject constraints. Vratny13 selected cable material based
on vehicle power demand, and required resulting cable heat to be dissipated by the Thermal Management
System (TMS). None of these previous studies allowed for the selection of the cable material based on a
system level optimization goal. Instead, they focused on sub-system optimality such as minimum weight,
which comes at the expense of incurring additional costs for other subsystems. Dama14 selected overhead
transmission line materials using a weighting function and thermal constraints. However, that work was not
coupled with any aircraft subsystems like a TMS.
The traditional aircraft design approach, which relies on assembling groups of optimal subsystems, breaks
down when considering novel aircraft concepts like the tiltwing vehicle. In a large part, this is because novel
concepts have a much higher degree of interaction or coupling between subsystems. For example, when a
cable creates heat, this heat needs to be dissipated by the TMS, which needs power supplied by the turbine,
and delivering the power creates more heat. The cable, the TMS, and the turbine are all coupled. A change
to one subsystem will affect all the other subsystems, much to the consternation of subsystem design experts.
Multidisciplinary optimization is the design approach that can address these challenges. However, to fully
take advantage of this, we must change the way we think about subsystem design. Specifically, we must
move away from point design, and focus on creating solution spaces.
The work presented in this paper uses the multidisciplinary optimization approach with aircraft level
models to study the system-level sensitivity of cable traits: weight-per-length and resistance-per-length.
Additionally, we examined the effects of vehicle imposed volume constraints on these traits. This is useful
for three purposes: (1) to demonstrate a framework that can perform a coupled analysis between the aircraft
thermal and propulsion systems, (2) to provide a method by which future cable designs can be evaluated
against each other given a system-level design goal, (3) to provide insight into what cable properties may
be promising for future research. This last element is explored given the caveat that the models contained
in this analysis do not represent high-fidelity systems. Thus, while we can demonstrate coupling in between
systems, the exact system-level sensitivity to a given parameter may change if a subsystem model or the
assumptions governing that model change.
The organization of this paper is as follows, in Sec II we outline a method to combine the VTOL vehicle
design and cable information in order to produce cables sensitivity studies. Results analysis and discussion
are contained in Sec III. Conclusions are presented in Sec IV
Pterodactyl: Control Architectures Development for Integrated Control Design of a Mechanically Deployed Entry Vehicle
Get PDFThe need to return high mass payloads is driving the development of a new class of vehicles, Deployable Entry Vehicles (DEV) for which feasible and optimized control architectures have not been developed. The Pterodactyl project, seeks to advance the current state-of-the-art for entry vehicles by developing a design, test, and build capability for DEVs that can be applied to various entry vehicle configurations. This paper details the efforts on the NASA-funded Pterodactyl project to investigate multiple control techniques for the Lifting Nano-ADEPT (LNA) DEV. We design and implement multiple control architectures on the LNA and evaluate their performance in achieving varying guidance commands during entry.First we present an overview of DEVs and the Lifting Nano-ADEPT (LNA), along with the physical LNA configuration that influences the different control designs. Existing state-of-the-art for entry vehicle control is primarily propulsive as reaction control systems (RCS) are widely employed. In this work, we analyze the feasibility of using both propulsive control systems such as RCS to generate moments, and non-propulsive control systems such as aerodynamic control surfaces and internal moving mass actuations to shift the LNA center of gravity and generate moments. For these diverse control systems, we design different multi-input multi-output (MIMO) state-feedback integral controllers based on linear quadratic regulator (LQR) optimal control methods. The control variables calculated by the controllers vary, depending on the control system being utilized and the outputs to track for the controller are either the (i) bank angle or the (ii) angle of attack and sideslip angle as determined by the desired guidance trajectory. The LQR control design technique allows the relative allocation of the control variables through the choice of the weighting matrices in the cost index. Thus, it is easy to (i) specify which and how much of a control variable to use, and (ii) utilize one control design for different control architectures by simply modifying the choice of the weighting matrices.By providing a comparative analysis of multiple control systems, configurations, and performance, this paper and the Pterodactyl project as a whole will help entry vehicle system designers and control systems engineers determine suitable control architectures for integration with DEVs and other entry vehicle types
A Machine Learning Approach to Jet-Surface Interaction Noise Modeling
Get PDFThis paper investigates using machine learning to rapidly develop empirical models suitable for system-level aircraft noise studies. In particular, machine learning is used to train a neural network to predict the noise spectra produced by a round jet near a surface over a range of surface lengths, surface standoff distances, jet Mach numbers, and observer angles. These spectra include two sources, jet-mixing noise and jet-surface interaction (JSI) noise, with different scale factors as well as surface shielding and reflection effects to create a multi- dimensional problem. A second model is then trained using data from three rectangular nozzles to include nozzle aspect ratio in the spectral prediction. The training and validation data are from an extensive jet-surface interaction noise database acquired at the NASA Glenn Research Center's Aero-Acoustic Propulsion Laboratory. Although the number of training and validation points is small compared a typical machine learning application, the results of this investigation show that this approach is viable if the underlying data are well behaved
Pterodactyl: Development and Comparison of Control Architectures for a Mechanically Deployed Entry Vehicle
Get PDFThe Pterodactyl project, seeks to advance the current state-of-the-art for entry vehicles by developing novel guidance and control technologies for Deployable Entry Vehicles (DEVs) that can be applied to various entry vehicle configurations. This paper details the efforts on the NASA-funded Pterodactyl project to investigate and implement multiple control techniques for an asymmetric mechanical DEV. We design multiple control architectures for a Pterodactyl Baseline Vehicle (PBV) and evaluate their performance in achieving varying guidance commands during entry. The control architectures studied are (i) propulsive control systems such as reaction control systems and (ii) non-propulsive control systems such as aerodynamic control surfaces and internal moving masses. For each system, state-feedback integral controllers based on linear quadratic regulator (LQR) optimal control methods are designed to track guidance commands of either (i) bank angle or (ii) angle of attack and sideslip angle as determined by the desired guidance trajectory. All control systems are compared for a lunar return reference mission and by providing a comparative analysis of these systems, configurations, and performance, the efforts detailed in this paper and the Pterodactyl project as a whole will help entry vehicle system designers determine suitable control architectures for integration with DEVs and other entry vehicle types