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At least 19 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

Coaxial Ceramic Direct Ink Writing on Heterogenous and Rough Surfaces: Investigation of Core–Shell Interactions

In this work, coaxial conductor–ceramic direct ink writing enables the printing of sensitive or encapsulated materials onto heterogeneous and rough substrates. While encasing the core fluid within a stiff ceramic shell, continuity may be maintained, even while printing onto conventionally challenging substrates. Here, we report the development of a coaxial ceramic direct ink writing suite and explore coflow interrelationships based on microfluidic principles. A coaxial nozzle is designed to facilitate the coextrusion of an alumina shell, whereas indium–tin-oxide inks constitute the core. In this manner, a core–shell ceramic element may be printed onto rough substrates for future high-temperature applications. Colloidal inks are engineered to provide the required rheological and sintering performance. Moreover, flow simulations in conjunction with microfluidic coflow principles are used to explore the coaxial printing processing space, thus controlling the core–shell architectures. Physical modeling is further used to analyze core deformations and eccentricity. As a result, simulations are validated experimentally, and the analyses are used to deposit coaxial ceramic features onto heterogeneous, high-temperature ceramic substrates.

20 FOSSIL-FUELED POWER PLANTS↗
NASA NTRS1986

Influence of large-scale motion on turbulent transport for confined coaxial jets. Volume 2: Navier-Stokes calculations of swirling and nonswirling confined coaxial jets

The existence of large scale coherent structures in turbulent shear flows has been well documented. Discrepancies between experimental and computational data suggest a necessity to understand the roles they play in mass and momentum transport. Using conditional sampling and averaging on coincident two-component velocity and concentration velocity experimental data for swirling and nonswirling coaxial jets, triggers for identifying the structures were examined. Concentration fluctuation was found to be an adequate trigger or indicator for the concentration-velocity data, but no suitable detector was located for the two-component velocity data. The large scale structures are found in the region where the largest discrepancies exist between model and experiment. The traditional gradient transport model does not fit in this region as a result of these structures. The large scale motion was found to be responsible for a large percentage of the axial mass transport. The large scale structures were found to convect downstream at approximately the mean velocity of the overall flow in the axial direction. The radial mean velocity of the structures was found to be substantially greater than that of the overall flow.

Weinberg, B. C.↗
NASA NTRS2016

Computational Study of Flow Interactions in Coaxial Rotors

Although the first idea of coaxial rotors appeared more than 150 years ago, most helicopters have used single main-rotor/tail-rotor combination. Since reactive moments of coaxial rotors are canceled by contra-rotation, no tail rotor is required to counter the torque generated by the main rotor. Unlike the single main rotor design that distributes power to both main and tail rotors, all of the power for coaxial rotors is used for vertical thrust. Thus, no power is wasted for anti-torque or directional control. The saved power helps coaxial rotors reach a higher hover ceiling than single rotor helicopters. Another advantage of coaxial rotors is that the overall rotor diameter can be reduced for a given vehicle gross weight because each rotor provides a maximum contribution to vertical thrust to overcome vehicle weight. However, increased mechanical complexity of the hub has been one of the challenges for manufacturing coaxial rotorcraft. Only the Kamov Design Bureau of Russia had been notably successful in production of coaxial helicopters until Sikorsky built X2, an experimental compound helicopter. Recent developments in unmanned aircraft systems and high-speed rotorcraft have renewed interest in the coaxial configuration. Multi-rotors are frequently used for small electric unmanned rotorcraft partly due to mechanical simplicity. The use of multiple motors provides redundancy as well as cost-efficiency. The multi-rotor concept has rarely been used until recently because of its inherent stability and control problems. However, advances in inexpensive electronic flight control systems have opened the floodgates for small drones using multirotors. Coaxial rotors have started to appear in some multi-rotor configurations. Small coaxial rotors have often been designed using a hundred year old approach that is "sketch, build, fly, and iterate." In that approach, there is no systematic way to explore trade-offs or determine logical next steps. It is neither possible to account for multiple real-world constraints up front in design nor possible to know what performance is possible with a given design. Since unmanned vehicles are sized and optimized for the particular mission, a modern low-fidelity conceptual design and sizing tool that has been used for the design of large helicopters can be used for design of small coaxial rotorcraft. However, unlike most helicopters with single main rotor, the interactions between the upper and lower rotors emerge as an important factor to consider in design because an increase in performance of a multi-rotor system is not proportional to the number of rotors. Interference losses and differences in thrusts between the upper and lower rotors were investigated by theoretical methods as well as a computational fluid dynamics (CFD) method using the Reynolds-Averaged Navier-Stokes (RANS) equations. In this work, hybrid turbulence models are used to investigate the physics of interactions between coaxial rotors and a fuselage that are not well understood. Present study covers not only small-scale drones but also large-scale coaxial rotors for heavy-lifting missions. Considering the recently proposed FAA drone rules that require the flight only in visual line-of-sight, a large multirotor might be used as an airborne carrier for launch and recovery of unmanned aircraft systems with a human operator onboard. For applications to civil operations, their aerodynamic performance and noise levels need to be assessed. Noise is one of the largest limiting factors to rotorcraft operations in urban area. Since the high-frequency noise of multi-rotors may increase the annoyance, noise may turn out to be a key issue that must be addressed for market acceptability. One of the objectives of the present work is to study the effects of inter-rotor spacing and collectives on the performance, efficiency, and acoustics of coaxial rotor systems.

Study↗
NASA NTRS2008

Coaxial Electric Heaters

Coaxial electric heaters have been conceived for use in highly sensitive instruments in which there are requirements for compact heaters but stray magnetic fields associated with heater electric currents would adversely affect operation. Such instruments include atomic clocks and magnetometers that utilize heated atomic-sample cells, wherein stray magnetic fields at picotesla levels could introduce systematic errors into instrument readings. A coaxial electric heater is essentially an axisymmetric coaxial cable, the outer conductor of which is deliberately made highly electrically resistive so that it can serve as a heating element. As in the cases of other axisymmetric coaxial cables, the equal magnitude electric currents flowing in opposite directions along the inner and outer conductors give rise to zero net magnetic field outside the outer conductor. Hence, a coaxial electric heater can be placed near an atomic-sample cell or other sensitive device. A coaxial electric heater can be fabricated from an insulated copper wire, the copper core of which serves as the inner conductor. For example, in one approach, the insulated wire is dipped in a colloidal graphite emulsion, then the emulsion-coated wire is dried to form a thin, uniform, highly electrically resistive film that serves as the outer conductor. Then the film is coated with a protective layer of high-temperature epoxy except at the end to be electrically connected to the power supply. Next, the insulation is stripped from the wire at that end. Finally, electrical leads from the heater power supply are attached to the exposed portions of the wire and the resistive film. The resistance of the graphite film can be tailored via its thickness. Alternatively, the film can be made from an electrically conductive paint, other than a colloidal graphite emulsion, chosen to impart the desired resistance. Yet another alternative is to tailor the resistance of a graphite film by exploiting the fact that its resistance can be changed permanently within about 10 percent by heating it to a temperature above 300 C. A coaxial heater, with electrical leads attached, that has been bent into an almost full circle for edge heating of a circular window is shown. (In the specific application, there is a requirement for a heated cell window, through which an optical beam enters the cell.)

Strekalov, Dmitry↗
NASA NTRS2016

A Study of Coaxial Rotor Performance and Flow Field Characteristics

As a precursor to studying the acoustics of a coaxial rotor system, the aerodynamics and flow field of a coaxial rotor were simulated to better understand the interaction between the two rotors. RotUNS, an unsteady Navier-Stokes solver that uses a simplified blade aerodynamics model, was used to predict coaxial rotor performance in hover and forward flight. RotUNS steady hover calculations showed improved performance compared to blade element momentum theory. Prior to examining the complex 3D flow field of a coaxial rotor in detail, two airfoils traveling in opposite directions with a vertical separation distance equivalent to the separation between the upper and lower rotor of the coaxial system were simulated. The pressure field generated by the two airfoils aided our interpretation of the more complex coaxial rotor system flow field. The pressure fields above, between, and below the coaxial rotor system were then examined for different azimuth positions of the upper and lower rotor blades.

Barbely, Natasha L.↗
DOE OSTI2021

RG217 V2-V2 Coaxial Cable Acceptance Test

The ECSE Solid State Pulsed Power unit is a high current, high power solid-state pulse modulator. The RG217 V2-V2 Coaxial Cable Assembly is the interface cable between the Solid State Pulser and the load. This document covers the testing procedure for the RG217 V2-V2 Coaxial Cable Assembly. This assembly is comprised of RG217 Coaxial Cable with a LRU Connector on either end. This test procedure verifies the cable is undamaged and assembled correctly, the correct cable connectors are installed properly onto the cable, and that the entire assembly meets conductivity and holdoff voltage requirements. This procedure will verify that the RG217 Coaxial Cable Assembly meets all assembly and functional requirements. In particular, this procedure verifies the Cable Shield and Center Conductor meet conductivity requirements by testing their resistances. Additionally, this procedure ensures the RG217 Coaxial Cable Assembly meets holdoff voltage requirements by applying high voltage and verifying the RG217 Coaxial Cable Assembly does not experience any breakdowns or arcing.

42 ENGINEERING↗
DOE OSTI2024

Test and Validate Distributed Coaxial Cable Sensors for in situ Condition Monitoring of Coal-Fired Boiler Tubes

This project aims to test, validate, and advance the technology readiness level (from TRL5 to TRL7) of a novel low-cost distributed stainless-steel/ceramic coaxial cable sensing (SSC-CCS) technology for in situ monitoring of the boiler tube temperature in existing coal-fired power plants. The novel SSC-CCS sensing technology and associated condition-based monitoring (CBM) software to be demonstrated in this project will lead to an improved understanding of the boiler tube failure mechanisms and a prognostic system to improve the overall performance, reliability, and flexibility of the nation’s coal-fired power plant fleet. A boiler tube monitoring system with distributed coaxial cable temperature sensors and a sensor acquisition system was constructed. The high-temperature coaxial cable sensor with a length of 1.3m was made by using a quartz tube (1mm inner diameter (ID) and 6mm outer diameter (OD)) to concentrically separate a 304 stainless-steel (SS) rod (1mm OD) and SS tube (7.94mm OD and 6.16mm ID). The sensor acquisition system includes a vector network analyzer (VNA), a radio frequency (RF) power amplifier, multiple switches and a USB hub. The distributed stainless-steel quartz coaxial cable sensor (SSQ-CCS) had a linear response to temperature with a resolution uncertainty of σ = 0.77℃. To withstand the harsh conditions of 3,300 steam pressures and 800℃ high temperatures, the sensor was shielded by a protective tube made of the same material as the boiler tube. The protection tube had an OD of 1.5 inches and a thickness of 0.25 inches. In the laboratory tests, the sensor showed good sensitivity and fast response. The drift was bounded between +0.33% and -0.67% during a test at 600℃ for 350 hours, indicating good stability of the sensor. A field test was conducted where four sensors were welded on four superheat tubes (SH-Ts) at a coal-fired power station over 400 days. Conventional thermocouples were welded to the superheater tubes alongside the coaxial cable sensors for the purpose of comparison. Two sensors were capable of distributed sensing, with three multiplexed sensing sections. The other two sensors were single section. During the 400-day test period, the power plant experienced startups and shutdowns. At the steady state operations, the temperature of the boiler tube is about 600℃ (1112°F). The sensors recorded the entire coal-firing processes (start-up, steady state, and shut-down) and the glitch event. A GSM modem and a Watchdog were added to the system to ensure reliable data recording. The GSM modem sent daily messages to plant managers and Clemson team to inform the status of the sensor system. If the system was not normally working, the Watchdog would reboot the system automatically. The new coaxial cable based distributed sensing technology has been proven to be successful in both laboratory and field tests. A comprehensive four-stage multi-physics computational framework has been developed to assist the design, optimization, installation, and operation of SSQ-CCS. With the consideration of various operation conditions, we predict the distributions of flue gas temperatures within coal-fired boilers, the temperature correlation between the boiler tube and SSQ-CCS, and the safety of SSQ-CCS. A conditional-based monitoring system is implemented as well. The computational framework developed in this work can guide the future operation of coal-fired plants and other power plants for the safety prediction of boiler operations.

01 COAL, LIGNITE, AND PEAT↗
NASA NTRS1994

The Aeroacoustics of Supersonic Coaxial Jets

Instability waves have been established as the dominant source of mixing noise radiating into the downstream arc of a supersonic jet when the waves have phase velocities that are supersonic relative to ambient conditions. Recent theories for supersonic jet noise have used the concepts of growing and decaying linear instability waves for predicting radiated noise. This analysis is extended to the prediction of noise radiation from supersonic coaxial jets. Since the analysis requires a known mean flow and the coaxial jet mean flow is not described easily in terms of analytic functions, a numerical prediction is made for its development. The Reynolds averaged, compressible, boundary layer equations are solved using a mixing length turbulence model. Empirical correlations are developed for the effects of velocity and temperature ratios and Mach number. Both normal and inverted velocity profile coaxial jets are considered. Comparisons with measurements for both single and coaxial jets show good agreement. The results from mean flow and stability calculations are used to predict the noise radiation from coaxial jets with different operating conditions. Comparisons are made between different coaxial jets and a single equivalent jet with the same total thrust, mass flow, and exit area. Results indicate that normal velocity profile jets can have noise reductions compared to the single equivalent jet. No noise reductions are found for inverted velocity profile jets operated at the minimum noise condition compared to the single equivalent jet. However, it is inferred that changes in area ratio may provide noise reduction benefits for inverted velocity profile jets.

Dahl, Milo D.↗
NASA NTRS2006

Local Heat Flux Measurements with Single Element Coaxial Injectors

To support the mission for the NASA Vision for Space Exploration, the NASA Marshall Space Flight Center conducted a program in 2005 to improve the capability to predict local thermal compatibility and heat transfer in liquid propellant rocket engine combustion devices. The ultimate objective was to predict and hence reduce the local peak heat flux due to injector design, resulting in a significant improvement in overall engine reliability and durability. Such analyses are applicable to combustion devices in booster, upper stage, and in-space engines, as well as for small thrusters with few elements in the injector. In this program, single element and three-element injectors were hot-fire tested with liquid oxygen and ambient temperature gaseous hydrogen propellants at The Pennsylvania State University Cryogenic Combustor Laboratory from May to August 2005. Local heat fluxes were measured in a 1-inch internal diameter heat sink combustion chamber using Medtherm coaxial thermocouples and Gardon heat flux gauges. Injectors were tested with shear coaxial and swirl coaxial elements, including recessed, flush and scarfed oxidizer post configurations, and concentric and non-concentric fuel annuli. This paper includes general descriptions of the experimental hardware, instrumentation, and results of the hot-fire testing for three of the single element injectors - recessed-post shear coaxial with concentric fuel, flush-post swirl coaxial with concentric fuel, and scarfed-post swirl coaxial with concentric fuel. Detailed geometry and test results will be published elsewhere to provide well-defined data sets for injector development and model validatation.

Jones, Gregg↗
NASA NTRS2013

Swirl Coaxial Injector Testing with LOX/RP-J

Testing was conducted at NASA fs Marshall Space Flight Center (MSFC) in the fall of 2012 to evaluate the operation and performance of liquid oxygen (LOX) and kerosene (RP ]1) in an existing swirl coaxial injector. While selected Russian engines use variations of swirl coaxial injectors, component level performance data has not been readily available, and all previously documented component testing at MSFC with LOX/RP ]1 had been performed using a variety of impinging injector designs. Impinging injectors have been adequate for specific LOX/RP ]1 engine applications, yet swirl coaxial injectors offer easier fabrication efforts, providing cost and schedule savings for hardware development. Swirl coaxial elements also offer more flexibility for design changes. Furthermore, testing with LOX and liquid methane propellants at MSFC showed that a swirl coaxial injector offered improved performance compared to an impinging injector. So, technical interest was generated to see if similar performance gains could be achieved with LOX/RP ]1 using a swirl coaxial injector. Results would allow such injectors to be considered for future engine concepts that require LOX/RP ]1 propellants. Existing injector and chamber hardware was used in the test assemblies. The injector had been tested in previous programs at MSFC using LOX/methane and LOX/hydrogen propellants. Minor modifications were made to the injector to accommodate the required LOX/RP ]1 flows. Mainstage tests were performed over a range of chamber pressures and mixture ratios. Additional testing included detonated gbombs h for stability data. Test results suggested characteristic velocity, C*, efficiencies for the injector were 95 ]97%. The injector also appeared dynamically stable with quick recovery from the pressure perturbations generated in the bomb tests.

Greene, Sandra Elam↗
NASA NTRS1993

CFD simulation of coaxial injectors

The development of improved performance models for the Space Shuttle Main Engine (SSME) is an important, ongoing program at NASA MSFC. These models allow prediction of overall system performance, as well as analysis of run-time anomalies which might adversely affect engine performance or safety. Due to the complexity of the flow fields associated with the SSME, NASA has increasingly turned to Computational Fluid Dynamics (CFD) techniques as modeling tools. An important component of the SSME system is the fuel preburner, which consists of a cylindrical chamber with a plate containing 264 coaxial injector elements at one end. A fuel rich mixture of gaseous hydrogen and liquid oxygen is injected and combusted in the chamber. This process preheats the hydrogen fuel before it enters the main combustion chamber, powers the hydrogen turbo-pump, and provides a heat dump for nozzle cooling. Issues of interest include the temperature and pressure fields at the turbine inlet and the thermal compatibility between the preburner chamber and injector plate. Performance anomalies can occur due to incomplete combustion, blocked injector ports, etc. The performance model should include the capability to simulate the effects of these anomalies. The current approach to the numerical simulation of the SSME fuel preburner flow field is to use a global model based on the MSFC sponsored FNDS code. This code does not have the capabilities of modeling several aspects of the problem such as detailed modeling of the coaxial injectors. Therefore, an effort has been initiated to develop a detailed simulation of the preburner coaxial injectors and provide gas phase boundary conditions just downstream of the injector face as input to the FDNS code. This simulation should include three-dimensional geometric effects such as proximity of injectors to baffles and chamber walls and interaction between injectors. This report describes an investigation into the numerical simulation of GH2/LOX coaxial injectors. The following sections will discuss the physical aspects of injectors, the CFD code employed, and preliminary results of a simulation of a single coaxial injector for which experimental data is available. It is hoped that this work will lay the foundation for the development of a unique and useful tool to support the SSME program.

Landrum, D. Brian↗
NASA NTRS1997

A Survey of Theoretical and Experimental Coaxial Rotor Aerodynamic Research

The recent appearance of the Kamov Ka-50 helicopter and the application of coaxial rotors to unmanned aerial vehicles have renewed international interest in the coaxial rotor configuration. This report addresses the aerodynamic issues peculiar to coaxial rotors by surveying American, Russian, Japanese, British, and German research. (Herein, 'coaxial rotors' refers to helicopter, not propeller, rotors. The intermeshing rotor system was not investigated.) Issues addressed are separation distance, load sharing between rotors, wake structure, solidity effects, swirl recovery, and the effects of having no tail rotor. A general summary of the coaxial rotor configuration explores the configuration's advantages and applications.

Coleman, Colin P.↗
NASA NTRS2011

Coaxial Cables for Martian Extreme Temperature Environments

Work was conducted to validate the use of the rover external flexible coaxial cabling for space under the extreme environments to be encountered during the Mars Science Laboratory (MSL) mission. The antennas must survive all ground operations plus the nominal 670-Martian-day mission that includes summer and winter seasons of the Mars environment. Successful development of processes established coaxial cable hardware fatigue limits, which were well beyond the expected in-flight exposures. In keeping with traditional qualification philosophy, this was accomplished by subjecting flight-representative coaxial cables to temperature cycling of the same depth as expected in-flight, but for three times the expected number of in-flight thermal cycles. Insertion loss and return loss tests were performed on the coaxial cables during the thermal chamber breaks. A vector network analyzer was calibrated and operated over the operational frequency range 7.145 to 8.450 GHz. Even though some of the exposed cables function only at UHF frequencies (approximately 400 MHz), the testing was more sensitive, and extending the test range down to 400 MHz would have cost frequency resolution. The Gore flexible coaxial cables, which were the subject of these tests, proved to be robust and displayed no sign of degradation due to the 3X exposure to the punishing Mars surface operations cycles.

Ramesham, Rajeshuni↗
NASA NTRS1976

Gas Filled Coaxial Accelerator with Compression Coil

A self-energized plasma compressor which compresses plasma discharged from a coaxial plasma generator. The device includes a helical shaped coil which is coaxially aligned with the center axis of the coaxial plasma generator. The plasma generator creates a current through the helical coil which, in turn, generates a time varying magnetic field that generates a force which acts radially upon the plasma. A seal is carried on the end of the coaxial plasma generator for containing gas therein. As the plasma is accelerated out the outer end of the generator, it forces the gas outwardly also compressing such. Beads are carried adjacent the small end of the helical shaped coil for being accelerated to hypervelocities by the plasma and gas. As a result of utilizing gas in the coaxial plasma generator, such minimizes ablation of the beads as well as accelerates such to higher velocities.

Espy, Patrick N.↗
DOE OSTI2026

A novel approach to RF power coupling in Radio-Frequency Quadrupole (RFQ) structures: built-in coaxial double-loop coupling port

Efficient and reliable RF power couplers in accelerating cavities require precise impedance matching and mechanical stability to ensure optimal beam energy transfer. In radio-frequency quadrupole (RFQ) accelerators, power is commonly delivered using waveguide iris or coaxial loop couplers. Iris couplers can handle high RF power but lack tunability, while coaxial loop couplers offer tuning flexibility but are limited in power handling and thermal performance. We propose a new RFQ power coupling concept utilizing a single input coaxial center-fed double-loop antenna built into a vane in an RFQ structure . The design integrates back-to-back loops into the RFQ vanes, fed by a TEM coaxial transmission line with standard 50-Ω characteristic impedance. The configuration can allow straightforward and easy ceramic window replacement without retuning, and coupling strength is adjusted with protruding tuning rods. Numerical simulations, performed with both a simplified RFQ model and the Spallation Neutron Source RFQ, demonstrate improved RF performance and reduced dipole mode excitation. The results establish the coaxial double-loop coupler as a practical alternative for high-power RFQ coupling applications.

Lee, Sung-Woo [ORNL] (ORCID:000000030915835X)↗
DOE OSTI2021

Scaling of oxygen-methane reacting coaxial jets using x-ray fluorescence to measure mixture fraction

Stoichiometric mixing length L s of reacting coaxial jet flames is a critical scaling parameter for liquid rocket engine combustors. Previous studies have shown that L s for shear coaxial flames can be scaled like their non-reacting counterparts using a non-dimensional momentum flux ratio J. In addition, stoichiometric mixing lengths of reacting and nonreacting coaxial jets collapse upon a single line by altering J using an effective outer flow gas density. This effective density is calculated from a modified version of the equivalence principle, originally developed by Tacina and Dahm [1, 2] and accounts for the effects of heat release on mixing. However, previous studies also required a second nonphysical scaling constant S c for the reacting jets, which is not predicted by the equivalence principle [3]. It was originally hypothesized that S c is attributed to the limitation of hydroxyl (OH) planar laser-induced fluorescence, which only infers L s . Direct quantitative measurement of conserved scalar fields using conventional optical diagnostics is difficult due to the lack of a tracer that easily fluoresces, survives high temperature oxygen flames, and is not dominated by quenching effects. To measure a conserved scalar field, this work implements x-ray fluorescence of Kr and Ar tracers to obtain quantitative mixture fraction fields. From these mixture fraction fields, stoichiometric mixing lengths for two CH 4 /O 2 flames are calculated and scaled against nonreacting coaxial mixing lengths using the equivalence principle. By directly measuring the stoichiometric mixing length, it is established that the additional constant is a byproduct of the OH measurement technique and the equivalence principle fully captures the scaling. Finally, comparison with high-fidelity simulation of the flame further supports this conclusion. In addition to further strengthening this scaling method, this work represents the first use of x-ray fluorescence to make quantitative conserved scalar measurements in turbulent flames.

33 ADVANCED PROPULSION SYSTEMS↗
NASA NTRS2017

Computations of Torque-Balanced Coaxial Rotor Flows

Interactional aerodynamics has been studied for counter-rotating coaxial rotors in hover. The effects of torque balancing on the performance of coaxial-rotor systems have been investigated. The three-dimensional unsteady Navier-Stokes equations are solved on overset grids using high-order accurate schemes, dual-time stepping, and a hybrid turbulence model. Computational results for an experimental model are compared to available data. The results for a coaxial quadcopter vehicle with and without torque balancing are discussed. Understanding interactions in coaxial-rotor flows would help improve the design of next-generation autonomous drones.

Torque↗
NASA NTRSDate not supplied

Designing A Coaxial Quadrotor for Urban Air Mobility

The NASA Revolutionary Vertical Lift Technology Project has created several Urban Air Mobility reference design vehicles to aid the burgeoning UAM industry. With over 700 conceptual designs already proposed, much interest has been generated across many unique configurations to bring vertical flight to the masses. The quadrotor configuration is one of the NASA reference vehicles, and does have some conceptual designs proposed in the industry. This study looks at the conceptual design of a coaxial quadrotor vehicle as an extension of the NASA RVLT quadrotor concept vehicle. The coaxial quadrotor has a similar layout to the quadrotor, but with a coaxial rotor at each of the four corners of the vehicle. Trade studies carried out using the NASA Design and Analysis of Rotorcraft (NDARC) tool analyzed the vehicle sizing, design gross weight, and performance for four design variants. The variants all use the baseline coaxial quadrotor layout, but analyze the effects of two major design choices: 1) variable pitch vs variable speed rotor control, and 2) motor to rotor power transmission via a gearbox vs direct-drive. The results indicate one design variant may have more benefits on some of the design objectives while another configuration may better satisfy the others.

UAM↗