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AeroVelo initiated the Atlas Human-Powered Helicopter Project in August 2011 to win the American Helicopter Society Sikorsky Prize, which despite prior attempts had remained unclaimed for over 30 years. The Sikorsky Prize required a human-powered helicopter to sustain flight for 60 s, momentarily reach a height of 3 m, and maintain position within a 10-by-10-m area. A configuration study was undertaken using low-fidelity aerodynamic analysis and estimated mass figures. An aerostructural optimization framework was developed for rotor design, including a novel vortex-ring aerodynamic model with included ground effect prediction, finite element analysis including integrated composite failure analysis, and a detailed weight estimation scheme. The airframe comprised a wire-braced truss structure, and innovative designs were developed for many of the aircraft's lightweight-focused subsystems. After initial flight testing in August 2012, experimental optimization and performance improvement led to a second testing program beginning in January 2013. Testing in 2013 led to a reduction in required power, and improved understanding of the structural dynamics and control strategy. The project culminated with the successful American Helicopter Society Sikorsky Prize flight on 13 June 2013. [ABSTRACT FROM AUTHOR]

This paper presents a new active in-flight rotorblade tracking control system for helicopters equipped with trailingedge flap actuators on the rotor blades. The objective of the in-flight rotorblade tracking controller is to minimize vibrations in the helicopter cabin and vibratory loads at the rotor hub induced by static blade dissimilarities. The control design is based on a steady-state transfer matrix from flap inputs to vibration outputs, which is first identified experimentally and then symmetrized. For this design model, an analytically derived Moore-Penrose pseudoinverse, which plays a key role in overcoming restrictions of existing approaches, such as the dependency on full-rank transfer matrices, is used. The system is verified through flight tests carried out with a full-scale experimental helicopter. The results demonstrate that the presented in-flight tracking system effectively minimizes the tracking error induced vibrations. [ABSTRACT FROM AUTHOR]

The purpose of this paper is to optimize helicopter flight trajectories to reduce ground noise in the landing approach using an optimization technique and to conduct flight experiments to confirm the effectiveness of the optimal solutions. The Japan Aerospace Exploration Agency has thus far measured helicopter noise under various flight conditions. This study builds a noise model of the helicopter in which the level of noise generated from a point noise source is a function of the flight path angle and bank angle. Then, we define optimal control problems that minimize the noise levels measured at points on the ground surface using equations of motion of 3 degrees of freedom for three-dimensional flight, and obtain the optimal controls for some flight constraints and wind conditions. The obtained optimal flights avoid the flight path angle that generates a great deal of noise and skirt the measurement points; these optimal flights are different from the conventional flight. Finally, this study verifies the validity of the optimal flight patterns by means of flight experiments with an experimental Japan Aerospace Exploration Agency helicopter. The actual flights following the optimal flights result in noise reduction and prove the effectiveness of the optimization. [ABSTRACT FROM AUTHOR]

This paper examines the vibration reductions caused by the introduction of auxiliary lift and propulsion, individually, as well as in combination, on a light [5800-lb (2640 kg)] helicopter with a four-bladed hingeless rotor, at flight speeds close to the maximum cruise velocity of the baseline helicopter. The changes in trim (vehicle orientations and control settings) because of auxiliary lift and propulsion are also examined in detail, and the fundamental mechanisms that produce the changes in trim and associated vibration reductions are identified. Based on results using a comprehensive aeroelastic analysis, it was concluded that auxiliary lift, alone, produces relatively small reductions in vibration. On the other hand, significant vibration reductions were obtained through auxiliary propulsion alone. A combination of lift and propulsion was most effective and reduced the vibration index by over 90%. It was also observed that auxiliary lift significantly reduces the main rotor thrust but increases the nose-down pitch attitude and tip-path-plane forward tilt to provide the required propulsive force. This increases the downwash through the rotor disk and requires a larger rotor longitudinal cyclic pitch input. In contrast, auxiliary propulsion that minimizes vibration produces little reduction in main rotor thrust, but results in a slightly nose-up pitch attitude (the auxiliary propulsion exceeds vehicle drag) along with a backward tilt of the tip-path plane. This decreases the downwash through the rotor disk and requires a smaller rotor longitudinal cyclic pitch input. A combination of auxiliary lift and propulsion minimizes vibration results in an even larger backward tilt of the tip-path plane and a net upwash through the rotor disk. The rotor collective pitch undergoes little change as a result of auxiliary lift, even though the main rotor thrust is decreased. In contrast, for auxiliary propulsion it decreases significantly even though the rotor thrust... [ABSTRACT FROM AUTHOR]

Presents an analysis of flight test data from an OH-6A helicopter using Lissajous figures. Identification of commensurateness and the relative phase between measured quantities; Applications to higher harmonic control flight test data; Right pilot seat vertical acceleration; Rotor mast lateral bending.

The article presents information on the ground dynamics model validation through the use of landing flight test. The model performance was able to meet the tolerances set by the U.S. Federal Aviation Administration for one-engine inopertive and autorotation landings. According to the article, the mathematical model improved understanding of the behavior of the helicopter during touch down. It adds that the theory and priniciples developed in the model can be used for the validation of other helicopter landings.

In 1982, flight tests were conducted on a modified OH-6A helicopter that incorporated an active higher harmonic control system to reduce vibratory loads on the rotor system. While reducing vibrations up to 90%, open-loop higher harmonic control data showed significant reductions in the main rotor shaft torque and engine power indicating that higher harmonic control may be also providing performance improvements. In this study, unsteady, rotary-wing, potential flow theory for a thin, oscillating airfoil is used to explain the mechanism behind the performance improvements seen on the OH-6A. Equations for the 2-D, unsteady, rotary-wing aerodynamic forces and moments with a finite number of wakes, or shed layers of vorticity, beneath the rotor are developed and applied specifically to the pitch and flap oscillations seen in the hover flight-test data. A modified finite-wake lift deficiency function is developed for this finite-wake theory that is analogous to the classical Theodorsen and Loewy lift deficiency functions, and is used in used to calculate the horizontal time-averaged propulsive force (negative drag) derived by Garrick to show that unsteady aerodynamics can provide the order of magnitude effects necessary to quantify the performance improvements seen on the OH-6A. [ABSTRACT FROM AUTHOR]