Coaxial rotors

Abstract: The NASA Design and Analysis of Rotorcraft (NDARC) software is an aircraft system analysis tool that supports both conceptual design efforts and technology impact assessments. The principal tasks are to design (or size) a rotorcraft to meet specified requirements, including vertical takeoff and landing (VTOL) operation, and then analyze the performance of the aircraft for a set of conditions. For broad and lasting utility, it is important that the code have the capability to model general rotorcraft configurations, and estimate the performance and weights of advanced rotor concepts. The architecture of the NDARC code accommodates configuration flexibility, a hierarchy of models, and ultimately multidisciplinary design, analysis, and optimization. Initially the software is implemented with low-fidelity models, typically appropriate for the conceptual design environment. An NDARC job consists of one or more cases, each case optionally performing design and analysis tasks. The design task involves sizing the rotorcraft to satisfy specified design conditions and missions. The analysis tasks can include off-design mission performance calculation, flight performance calculation for point operating conditions, and generation of subsystem or component performance maps. For analysis tasks, the aircraft description can come from the sizing task, from a previous case or a previous NDARC job, or be independently generated (typically the description of an existing aircraft). The aircraft consists of a set of components, including fuselage, rotors, wings, tails, and propulsion. For each component, attributes such as performance, drag, and weight can be calculated; and the aircraft attributes are obtained from the sum of the component attributes. Description and analysis of conventional rotorcraft configurations is facilitated, while retaining the capability to model novel and advanced concepts. Specific rotorcraft configurations considered are single-main-rotor and tail-rotor helicopter, tandem helicopter, coaxial helicopter, and tiltrotor. The architecture of the code accommodates addition of new or higher-fidelity attribute models for a component, as well as addition of new components.

Abstract: An aerial vehicle adapted for vertical takeoff and landing using a set of wing mounted thrust producing elements and a set of tail mounted rotors for takeoff and landing. An aerial vehicle which is adapted to vertical takeoff with the rotors in a rotated, take-off attitude then transitions to a horizontal flight path, with the rotors rotated to a typical horizontal configuration. The aerial vehicle uses different configurations of its wing mounted rotors and propellers to reduce drag in all flight modes.

Abstract: Note presenting an investigation to determine the static-thrust performance of a coaxial helicopter rotor with blades tapered both in plan form and thickness ratio in the full-scale tunnel. Tests of the coaxial-rotor and single-rotor configurations were made for a range of blade-pitch setting and for a range of tip speed up to 500 feet per second. Results regarding the hovering performance, effect of variation in directional control, and variation of rotor figure of merit with ratio of thrust coefficient are provided.

Abstract: We describe a new configuration of fixed-pitch miniature robot rotorcraft that combines the energetic efficiency of a helicopter and the mechanical simplicity of a quadrotor. The large power required to hover is proportional to the inverse of the rotor radius; thus, for a given diameter footprint, a single large rotor will energetically outperform several smaller rotors within the same boundary. However, smaller rotors are able to respond more quickly than large rotors, which require complex actuation to provide control. Our “triangular quadrotor” configuration uses a single large rotor for lift and three small rotors for control, gaining the benefits of both. The small rotors are canted slightly to also provide the same service as a conventional helicopter's tail rotor. Momentum theory analysis shows that a triangular quadrotor may provide a 20% reduction in required hover power, compared with a quadrotor of the same mass and footprint. This is particularly valuable for flying robots working indoors where maximum rotor size is constrained. Using conventional quadrotor and a triangular quadrotors constructed to be a similar as possible, we demonstrate that the triangular quadrotor uses 15% less power, without optimization. A power efficiency budget is provided, and the influence of drive system efficiency is explored. We present a dynamic model and demonstrate experimentally that the aircraft can be stabilized in flight with simple PID control.