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NASA NTRS1984

Applications of numerical optimization methods to helicopter design problems - A survey

A survey of applications of mathematical programming methods is used to improve the design of helicopters and their components. Applications of multivariable search techniques in the finite dimensional space are considered. Five categories of helicopter design problems are considered: (1) conceptual and preliminary design, (2) rotor-system design, (3) airframe structures design, (4) control system design, and (5) flight trajectory planning. Key technical progress in numerical optimization methods relevant to rotorcraft applications are summarized.

Miura, H.↗

NASA NTRS2019

Composites for Advanced Drive Systems

With the desire for increased power/weight for advanced drive system configurations, the investigation of materials, like composites is being explored to determine the feasibility of integration into advanced drive systems. This area of research directly aligns with the vision of the NASA (National Aeronautics and Space Administration) Revolutionary Vertical Lift Technology (RVLT) Project, which is to enable a generation of vertical lift vehicles that can achieve aggressive goals in the areas of high speed, high efficiency, high performance, low noise, and low emissions.Composite materials are lightweight, especially when comparing to the metallic materials commonly utilized in rotorcraft drive systems. By integrating composite materials into the drive system, the potential for improvements to power/weight exists as well as other potential benefits such as reductions in vibration and/or noise. Each of these areas of potential benefit will largely influence the overall performance and reliability of future vertical lift vehicles. Prior NASA research has been performed that developed a prototype hybrid double helical bull gear which was successfully demonstrated (LaBerge, Kelsen E.; Handschuh, Robert F.; Roberts, Gary; Thorp, Scott;, 2016) and current NASA research is being performed to optimize the hybrid gear design.While the potential benefits of composite materials in vertical lift drive systems mentioned above are highly desirable, many challenges exist that need to be addressed. To address the benefits and challenges with the integration of composite materials in advanced vertical lift drive systems, the identification of advanced drive system configurations and technical challenges is required. For this project, Bell Helicopter Textron identified an advanced drive system configuration and provided conceptual designs for this advanced drive system configuration, identified technical challenges, and provided recommendations as to how those challenges can be overcome.

transmission↗

NASA NTRS2012

Conceptual Design of a 150-Passenger Civil Tiltrotor

The conceptual design of a short-haul civil tiltrotor aircraft is presented. The concept vehicle is designed for runway-independent operations to increase the capacity of the National Airspace System without the need for increased infrastructure. This necessitates a vehicle that is capable of integrating with conventional air traffic without interfering with established flightpaths. The NASA Design and Analysis of Rotorcraft software was used to size the concept vehicle based on the mission requirements of this market. The final configuration was selected based upon performance metrics such as acquisition and maintenance costs, fuel fraction, empty weight, and required engine power. The concept presented herein has a proposed initial operating capability date of 2035, and is intended to integrate with conventional air traffic as well as proposed future air transportation concepts.

150-Passenger↗

NASA NTRSDate not supplied

Feasibility Study of a Robotic Science Arm on Future Martian Rotorcraft

Science arms are indispensable tools for planetary exploration, allowing vehicles to interact with and manipulate their surroundings in a manner similar to a human field geologist. A majority of the rovers and landers sent to Mars, beginning with Viking I and II in 1976, have made extensive use of these articulated, arm-like devices that allow for sample collection, surface preparation, instrument positioning, and the deployment of ground-contact sensors. Although proven useful, traditional rovers and landers are limited by the rough and difficult terrain of Mars. However, given the successful demonstration of flight on Mars by the Ingenuity helicopter, efforts are underway to outfit larger rotorcraft with science payloads to allow them to explore Mars’ surface and lower atmosphere with significantly more efficiency than land vehicles. Such vehicles could also be designed to work in tandem with landers or rovers. The Mars Science Helicopter (MSH) is a conceptual hexacopter design that is currently under early development by both NASA Ames and JPL. Equipping a vehicle like MSH with a science arm has the potential to further expand its scientific capabilities. This paper approaches the mission and design requirements to equip a science arm on MSH while highlighting the unique technical challenges for robotic arm and science instrument capability. Current plans for MSH development do not include the addition of a robotic arm to the vehicle. However, it is anticipated that future variants of the MSH design might well incorporate such adaptable surface interactive capabilities.

Robotic Science Arm↗

NASA NTRS2001

Vertical Lift Planetary Aerial Vehicles: Three Planetary Bodies and Four Conceptual Design Cases

NASA Ames Research Center has been studying the feasibility of vertical lift aerial vehicles to support planetary science and exploration missions. Besides Earth, it appears that there are three planetary bodies within our solar system where vertical flight might not only be theoretically feasible, but would also have unique mission capabilities that no other platform (ground-based, aerial, or orbital) could provide. Several vertical lift vehicle configurations might be applicable for planetary science missions. This paper presents a few representative conceptual design cases and the design challenges inherent in their development. Finally, more detailed comments are directed to the issues inherent in developing a NASA Mars Scout mission employing the use of a Martian autonomous rotorcraft.

Young, Larry A.↗

NASA NTRS2017

Tiltrotor Conceptual Design

This year end progress report summarizes our engineering study of a large, VTOL civil transport that we began in August 2015. The task has been to follow up on work reported in Reference 1, which described a NASA, 2005 design study showing that a 120 passenger, tiltrotor aircraft capable of cruising at 350 knots at 30,000 feet was quite feasible. The objective of our task this year has been to investigate the feasibility of a 120 passenger, tiltrotor aircraft capable of cruising at 425 to 450 knots at altitude and having VSTOL capability at Denver (i.e., 5,000 feet) with an outside air temperature (OAT) of 95°F. A corollary to our work has been to examine the suitability of the engineering tools available to conduct the concept design study we have begun. We have relegated two key pieces of corollary work to an appendix and used the body of this report to transmit progress in our preliminary performance trend studies. By way of background, in January of 2016, Mr. Harris presented a paper titled The VSTOL Performance Gap at the AHS Technical Meeting on Aeromechanics Design for Vertical Lift. This presentation is included in this year end report as Appendix A. A key concluding chart in that presentation is repeated here as Fig. 1. The Rotorcraft Branch at NASA Ames was already studying a tiltrotor suited for the regional carrier routes, but no effort beyond the 2005 results reported in Ref. 1 was going on. Therefore, we took on the task of extending the 350 knot, 120 passenger tiltrotor studies up to speeds associated with major airline routes.

Conceptual Design↗

NASA NTRSDate not supplied

A Synthesis Plugin for Auralization of Rotor Self Noise

This paper describes the development and architecture of a software plugin for the NASA Auralization Framework that synthesizes rotor modulating broadband self noise. A conceptual overview of the synthesis process is reviewed. The architecture description includes use of the plugin within a broader framework to auralize rotorcraft flyovers. Use of the plugin is demonstrated for a six-passenger quadrotor urban air mobility reference vehicle design using collective-pitch control.

Self Noise↗

NASA NTRSDate not supplied

A Synthesis Plugin for Auralization of Rotor Self Noise

Auralization↗

NASA NTRS2023

Exploration of Design Drivers for the RVLT Lift+Cruise Reference Aircraft

A trade study was performed on an all-electric version of the Lift+Cruise urban air mobility reference aircraft developed under the Revolutionary Vertical Lift Technology Project. The trade study varied the input parameters of mission range, takeoff altitude, mission reserve time, cell specific energy, disk loading, and payload weight. A step-by-step incremental change in the input parameters was also examined. Analyses were performed using the NASA Design and Analysis of Rotorcraft tool and a Rapid Sizing Tool for electric vertical takeoff and landing aircraft. A comparison of the analysis results between the two tools shows good agreement in trends with differences in slope. Overall, the analysis shows that the Lift+Cruise configuration performs poorly on a NASA-defined, energy-dominated mission due to poor aerodynamic efficiency in forward flight. This poor cruise-flight efficiency results in a large energy requirement, which increases the required battery sizing and corresponding aircraft gross weight. As such, continued conceptual design and refinement of the Lift+Cruise reference aircraft by the RVLT Concepts Team will likely be limited.

UAM↗

NASA NTRS2021

PEM Fuel Cell MODEL for Conceptual Design of Hydrogen eVTOL Aircraft

A model and software for design and analysis of a Proton Exchange Membrane fuel cell (PEMFC) system are developed for hydrogen eVTOL aircraft. Examples are provided of stacks designed for 80 kWe and 500 kWe net electrical power. Examples are provided of eVTOL designed for 250 and 400 lb payload. The trade-offs included stack characteristics, hydrogen storage characteristics, and aircraft payload and range. The objectives were to identify the key technology drivers of a hydrogen rotorcraft, establish technology targets for a viable aircraft, and recommend research to address the fundamental pre-competitive barriers. The current U.S. infrastructure on hydrogen informed the targets and recommendations. The key conclusion is that the advances made in cell electrochemical power density over the last decade might allow a PEMFC system to meet, or even beat, piston engine powered light-utility rotorcraft. The development must focus on the key drivers of a hydrogen eVTOL. The drivers are ultra-light stack cooling and short-term hydrogen storage. A stack system of net electrical power 100−150 kWe with specific power 1.1 kWe/kg including air, cooling, and electrical subsystems, and a tank storage of 15% weight fraction hydrogen are the minimum targets to meet the performance of a modern piston-engine rotorcraft, with a range of 180 nautical miles, payload of 400 lb, and gross weight of about 1400 lb. This is defined as the objective aircraft. If only one target is met, an aircraft of half the range could be produced, with a 30% greater gross take-off weight. This is defined as an intermediate aircraft. Because definitive conclusions are premature without weights and loads data on a flight-worthy stack system, it is recommended that a fuel cell powered hydrogen eVTOL demonstrator be built and flown. The existing hydrogen infrastructure for cars provide ample opportunity to create a pilot program. About 12 metric tons of retail hydrogen are available for cars every day in California, which is less than 0.05% of the yearly hydrogen production in the U.S.. A hypothetical fleet of 100 aircraft, operating 3 flights a day, would increase the demand by 2.25 tons per day and require 140 MWh of renewable electricity for green hydrogen.

PEM↗

NASA NTRS2010

Integration of Rotor Aerodynamic Optimization with the Conceptual Design of a Large Civil Tiltrotor

Coupling of aeromechanics analysis with vehicle sizing is demonstrated with the CAMRAD II aeromechanics code and NDARC sizing code. The example is optimization of cruise tip speed with rotor/wing interference for the Large Civil Tiltrotor (LCTR2) concept design. Free-wake models were used for both rotors and the wing. This report is part of a NASA effort to develop an integrated analytical capability combining rotorcraft aeromechanics, structures, propulsion, mission analysis, and vehicle sizing. The present paper extends previous efforts by including rotor/wing interference explicitly in the rotor performance optimization and implicitly in the sizing.

Acree, C. W., Jr.↗

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↗

NASA NTRS2009

Compressor Study to Meet Large Civil Tilt Rotor Engine Requirements

A vehicle concept study has been made to meet the requirements of the Large Civil Tilt Rotorcraft vehicle mission. A vehicle concept was determined, and a notional turboshaft engine system study was conducted. The engine study defined requirements for the major engine components, including the compressor. The compressor design-point goal was to deliver a pressure ratio of 31:1 at an inlet weight flow of 28.4 lbm/sec. To perform a conceptual design of two potential compressor configurations to meet the design requirement, a mean-line compressor flow analysis and design code were used. The first configuration is an eight-stage axial compressor. Some challenges of the all-axial compressor are the small blade spans of the rear-block stages being 0.28 in., resulting in the last-stage blade tip clearance-to-span ratio of 2.4%. The second configuration is a seven-stage axial compressor, with a centrifugal stage having a 0.28-in. impeller-exit blade span. The compressors conceptual designs helped estimate the flow path dimensions, rotor leading and trailing edge blade angles, flow conditions, and velocity triangles for each stage.

Veres, Joseph P.↗

NASA NTRS2009

Compressor Study to Meet Large Civil Tilt Rotor Engine Requirements

A vehicle concept study has been made to meet the requirements of the Large Civil Tilt Rotorcraft vehicle mission. A vehicle concept was determined, and a notional turboshaft engine system study was conducted. The engine study defined requirements for the major engine components, including the compressor. The compressor design-point goal was to deliver a pressure ratio of 31:1 at an inlet weight flow of 28.4 lbm/sec. To perform a conceptual design of two potential compressor configurations to meet the design requirement, a mean-line compressor flow analysis and design code were used. The first configuration is an eight-stage axial compressor. Some challenges of the all-axial compressor are the small blade spans of the rear-block stages being 0.28 in., resulting in the last-stage blade tip clearance-to-span ratio of 2.4 percent. The second configuration is a seven-stage axial compressor, with a centrifugal stage having a 0.28-in. impeller-exit blade span. The compressors conceptual designs helped estimate the flow path dimensions, rotor leading and trailing edge blade angles, flow conditions, and velocity triangles for each stage.

Veres, Joseph P.↗

NASA NTRS2018

Two-Speed Rotorcraft Research Transmission Power-Loss Associated with the Lubrication and Hydraulic Rotating Feed-Through Design Feature

An investigation was completed into the power loss associated with a rotating feed-through (RFT) design feature used to transfer lubrication and a hydraulic control signal from the static reference frame to a rotating reference frame in the NASA GRC two-speed transmission tests conducted in the Variable-Speed Drive Test Rig. The RFT feature, not commercially available, was created specifically for this research project and is integral to all two-speed transmission configurations tested, as well as a variant concept design for a geared variable-speed transmission presented at AHS Forum 71 in 2015. The experimental set-up and results from measurements in the isolated rotating-feed-through (RFT) experiments are presented. Results were used in an overall power loss assessment for a scaled conceptual 1,000 horsepower inline concentric two-speed transmission to support a NASA Revolutionary Vertical Lift Technologies (RVLT) Technical Challenge, demonstrating 50% speed change with less than 2% power loss while maintaining current power-to-weight ratios.

Rotorcraft↗

NASA NTRS2018

Two-Speed Rotorcraft Research Transmission Power-Loss Associated with the Lubrication and Hydraulic Rotating Feed-Through Design Feature

Rotorcraft↗

NASA NTRS2018

Two-Speed Rotorcraft Research Transmission Power-Loss Associated with the Lubrication and Hydraulic Rotating Feed-Through Design Feature

Rotorcraft↗

NASA NTRSDate not supplied

Urban Aerial Mobility Networks using Amphibious Vertical Takeoff and Landing Vehicles

This study considers novel urban aerial mobility (UAM) networks that address some of the key operator and community acceptance challenges inherent in proposed UAM operations. This paper seeks to examine three possible approaches to improve operator and community acceptance – specifically targeting cost, safety, and noise. First, the conceptual design space will be examined for VTOL amphibious vehicle technologies, including the implications of onwater versus in-flight time/speed. Second, the implications of minimizing community overflights by flying over-water will be examined. Third, the implications of the partial use of onwater, or near-shore/littoral, vertiports on UAM network performance will be examined. This study considers an alternate design trade space for urban aerial mobility systems. A large number of cities in the United States are located near or surround large bodies of water. Many of these same cities are considered to be candidates for metropolitan aerial transportation systems so as to moderate the impact of urban ground-transportation congestion. This paper will expand discussion and study of notional amphibious VTOL vehicles. There is nothing particularly new with regards to helicopters with amphibious takeoff and landing capability. For example, light rotorcraft have been outfitted with pontoons since the 1950s. Larger utility helicopters – used for carrying offshore oil-rig crew – have been designed, with varying degrees of success, to emergency land in rough waters in case of onboard mechanical system failures. The unique difference for the proposed amphibious UAM vehicles, as compared to these earlier amphibious rotorcraft, is that water operation is the norm rather than the exception and that, further, the water-born operation (and design) of such vehicles can be optimized to yield significant economic and operational benefits over solely UAM land-based stations and operations. Various different amphibious UAM networks will be discussed. A first-order set of analyses – employing novel mission metrics – is presented in this paper that will examine the operational performance of these amphibious networks. In particular, amphibious operations might address critical safety and community acceptance issues. An examination of the aerodynamic and hydrodynamic characteristics of amphibious VTOL UAM vehicles will be presented in this paper. One possible conceptual design for an amphibious UAM vehicle is a hybrid synchropter/hydroplane vehicle. As interest in urban aerial mobility grows, it is worthwhile to consider whether or not amphibious vertical takeoff and landing vehicles can play an important role in providing such mobility.

Urban Aerial Mobility↗