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The ability to compute the weight and balance of a helicopter in flight under general conditions is an enabling technology for future condition based maintenance systems as well as advanced automatic flight control systems. This paper creates a real-time weight and balance estimation algorithm using an extended Kalman filter framework. To highlight estimation characteristics, the algorithm is exercised on the OH-6A helicopter in a variety of flight regimes. The algorithm is examined in hover and forward flight as well as situations where loads are dropped and picked up in flight. For sample scenarios considered, the algorithm quickly estimates station line and butt line mass center position (1 s) and more slowly converges on helicopter weight (10 s). To estimate the helicopter waterline, the algorithm requires modest flight maneuvering where a nonzero roll rate is present. The algorithm is also shown to be reasonably robust relative to sensor and model errors with increasing estimation error with increasing levels of model mismatch and sensor error. DOI: 10.2514/1.41018

Data from a recent experimental study aimed at investigating the allowable errors in vehicle models for use in rotorcraft flight simulators are employed in the exercise of a pilot/vehicle analysis tool. It is demonstrated that a simplified multiaxis pilot model emulating pursuit tracking behavior can provide estimates of tracking performance and handling qualities. In an approximate manner, this model can accommodate the quality of visual cues. The experimental study also produced a limited but useful database for assessing current open-loop frequency-domain envelopes for maximum unnoticeable added dynamics. This database is employed to develop a closed-loop pilot/vehicle procedure for assessing maximum unnoticeable added dynamics with an ultimate goal of assessing the effects of "higher order" vehicle dynamics on closed-loop pilot/vehicle control. The assessment of added dynamics is undertaken with a more detailed structural pilot model, emphasizing compensatory, as opposed to pursuit, tracking behavior. Index Terms--Aerospace simulation, helicopter control, human pilot modeling.

We present in this paper the modeling and flight-control-system design for the yaw channel of an unmanned-aerial-vehicle (UAV) helicopter using a newly developed composite nonlinear feedback (CNF)-control technique. The CNF-control method has been proven to be capable of yielding a fast transient response with no or very minimal overshoot in tracking a specific target. From the actual flight tests on our UAV helicopter, it has been found that the commonly used yaw dynamical model for the UAV helicopter proposed in the literature is very rough and inaccurate, which might cause the helicopter to shake severely in certain flight conditions. This motivates us to first obtain a more accurate model for the yaw channel of our UAV helicopter. The CNF-control method is then utilized to design an efficient control law, which gives excellent overall performance. In particular, our design has achieved a Level I performance according to the standards set for military rotorcraft. The results are verified through actual flight tests. Index Terms--Aircraft control, modeling, nonlinear control, unmanned-aerial-vehicle (UAV) helicopters.

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 A Self-surveying Camera Array (SSCA) is a vision-based local-area positioning system consisting of multiple ground-deployed cameras that are capable of self-surveying their extrinsic parameters while tracking and localizing a [...]

This paper presents recent work concerning a small tiltrotor aircraft with a reduced number of rotors. The design consists of two propellers which can tilt laterally and longitudinally. A model of the full birotor dynamics is provided, and a controller based on the backstepping procedure is synthesized for the purposes of stabilization and trajectory tracking. The proposed control strategy has been tested in simulation. Index Terms--Backstepping methodology, helicopter dynamics modeling, tiltrotor rotorcraft, trajectory tracking.

A set of experiments were conducted on the University of Toronto Institute for Aerospace Studies flight research simulator to determine the effects of translational and yaw motion on pilot performance, workload, fidelity, pilot compensation, and motion perception for three helicopter yaw control tasks. The three control tasks were a yaw capture, a disturbance rejection task, and a tracking task. The yaw capture experiment was a duplication of an experiment previously run at a different simulator facility. The results of the yaw capture task were in general agreement with the previous study with the exception that, in the current study, yaw motion had a larger impact on pilot performance than the previous study. The current study found that translational motion improves performance and increases fidelity for all three tasks. Yaw motion increased performance for the yaw capture and disturbance rejection tasks. Translational motion generally improved fidelity and was easier to detect than yaw motion for all three tasks. Finally, if translational motion was present, the addition of yaw motion usually provided little additional benefit to performance, workload, compensation, or fidelity for all three tasks. DOI: 10.2514/1.21900

Routine shipboard helicopter operation on many classes of ships requires that helicopters be maneuvered and traversed along the ship deck using installed helicopter securing and handling equipment. This paper describes the derivation, implementation, and validation of a four-degrees-of-freedom mathematical model for predicting and analyzing the behavior of shipboard aircraft under the influence of external aircraft handling forces. The resulting model is suitable both for engineering analysis and training applications. The helicopter model includes the coupled dynamics of the aircraft, landing gear, and optionally steerable or castorable auxiliary wheel assembly. Detailed tire modeling addresses the transient development and release of tire deflection and cornering forces related to yawed and unyawed relaxation lengths as well as direct application of forces by the handling system. Verification and both qualitative and full-scale experimental validation of the model, performed using a number of simple maneuvers to validate specific aspects of the simulation, are discussed. It is shown that the resulting HeliMan simulation captures the underlying dynamics of the shipboard helicopter maneuvering process. Full-scale validation data show that in many cases the simulation is able to reproduce closely the measured data. The effect of tire side loading on longitudinal rolling resistance has been identified as a shortcoming of existing rolling tire models and the most probable cause for differences that exist between simulated and measured results in some validation cases.

Abstract In this paper we propose a vision-based stabilization and output tracking control method for a model helicopter. A novel two-camera method is introduced for estimating the full six-degrees-of-freedom pose [...]

Abstract: In this paper, an adaptive impedance control algorithm is developed for the Smart Spring to suppress helicopter rotor vibration through individual blade control. The harmonic frequencies of the blade [...]

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 undergoes only small reductions. This counterintuitive observation is explained. The reduced downwash with auxiliary propulsion, or upwash with combined lift and propulsion, puts the rotor in a partial autorotation state, drastically reducing the induced drag, main rotor torque, and power. Auxiliary lift produces modest reductions in main rotor power, primarily because of a reduced profile drag associated with lower rotor loading. Because the rotor loading is lower with auxiliary lift than with auxiliary propulsion, but larger vibration reductions are produced with the latter, it can be deduced that vibration reductions are less a result of 'unloading' of the rotor per se and more because of overall changes in trim, especially the reduction in longitudinal cyclic pitch (seen with auxiliary propulsion).

A new study compares the handling characteristics of two visually coupled systems, one in a research helicopter and one in a simulator.

Low altitude flight is extremely demanding on the rotorcraft pilots. This fact has motivated the research in automating various components of low altitude rotorcraft flight operations. Concurrent with the development of guidance laws, efforts are underway to develop systems for locating the terrain and the obstacles using inputs from passive electro-optical sensors such as TV cameras and infrared imagers. A passive obstacle location algorithm that uses image sequences from cameras undergoing translational and rotational motion is developed. The algorithm is in a general form and can operate in multicamera imaging environments. Performance results using an image sequence from an airborne camera are given.