Energy-maneuverability diagrams are an important tool that operational pilots use to understand helicopter maneuver performance across a wide range of conditions, however these representations are based upon a number of assumptions that have not been rigorously investigated. The present work reports the results of an investigation into the theory and application of helicopter maneuverability through simulation and flight test. The computational portion of the work focused on a systematic investigation into some of the key simplifying assumptions that are commonly applied in the creation of energy-maneuverability representations. This investigation included aerodynamic simulations of steady maneuvers using a dynamic inflow model as well as a free vortex method. The flight test portion of the work provided important operational context for understanding the practical application of the simulation results. The study illustrated that the fundamental assumption employed in estimating maneuver power requirements for energy-maneuverability representations appears to be reasonable in conditions of the greatest practical relevance, however another key assumption that is invoked to convert excess power into climb performance would likely lead to overestimating the vehicle capability in important operational conditions. Additionally, the flight test data demonstrated that energy-maneuverability results for high angles of bank should be considered for trending information rather than for detailed climb performance values.
A methodology is presented for the selection of approach-to-landing maneuvers that may result in improved brownout characteristics. The methodology is based upon a brownout metric that assesses the relative brownout cloud volume densities in critical regions of the pilot's field of view. The metric becomes the objective function of a procedure in which a typical visual approach profile is parameterized and optimized to minimize brownout in a representative landing maneuver. The optimization is constrained to avoid maneuvers that would be conducive to the onset of vortex ring state or would result in flight within the "avoid" regions of a typical helicopter height-velocity diagram. The analysis uses a free-vortex wake model and simulates the dynamics of the dust particles immersed in the rotor downwash. The results show that the optimal approach trajectories affect the resulting flowfield, particularly the development of a ground vortex ahead of the rotor disk, which influences the rate of development, size, and volume density of the brownout cloud. The results are compared with prior experimental results, and potential operational interpretations of the outcomes are examined. Nomenclature A= rotor disk area, πR 2 , ft 2 BX = objective function, Eq. (12) bX; t = particle count in the "best" region of the pilot's field of view, Eq. (11) C T = rotor thrust coefficient, T∕ρAΩR 2 D = main rotor diameter, ft FX = additional design objective function gX = constraint equation, Eq.(2) H = Hessian matrix h = rotor hub height above ground, ft n ent = number of entrained particles n P = number of particles p app X = series of discrete points describing approach X p HV = series of discrete points describing the "avoid" region boundaries on a height-velocity diagram p VRS = series of discrete points describing flight regime boundaries where VRS may occur R = rotor radius, ft r = longitudinal range from landing point, ft r pd = longitudinal range from landing point at which the peak deceleration occurs, ft S = unit vector T = rotor thrust, lb V = forward velocity, ft∕s or kt V c = climb velocity, ft∕s v h = hover inflow velocity, ft∕s v 0 = initial (asymptotic) velocity, ft∕s or kt X = vector of design variables, γ v 0 r pd T X u = aircraft stability derivative, ∂X∕∂u γ = approach angle, deg ϵ = tolerance value for defining behavior constraints, Eqs. (15) and (16) θ = aircraft pitch angle, deg θ P , ϕ P , ρ P = particle location (azimuth, elevation, distance) in a spherical coordinate systemfluid density, slugs∕ft 3 χ = wake skew angle, deg Ω = rotational frequency, rad∕s Subscripts app = approximation max = maximum allowable value (upper bound) min = minimum allowable value (lower bound) Superscript = value for optimum configuration
The present work reports the results of a research investigation into the handling qualities of a helicopter conducting a ship approach and landing task. The investigation was performed via fixed-base, pilot-in-the-loop flight simulation and included six test pilots with extensive operational and test experience in the shipboard environment. Representative approach/landing tasks were flown with three different response types to a field landing zone and to multiple spots on an amphibious assault ship. The ship was stationary, and there was no simulated ship airwake, so the fundamental differences between the field and ship approaches were limited to visual cueing. Traditional subjective handling qualities ratings were supplemented with multiple other analysis techniques, including pilot eye-tracking analysis and pilot control activity analysis. The results show that there are fundamental differences in the pilot gaze patterns between field and ship approaches that are caused by the different cueing environments. Additionally, subjective assessments indicated that pilots preferred higher degrees of aircraft stabilization in the shipboard environment than in the field environment, though there were not significant differences between pilot control techniques in these environments for a given aircraft response type.
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