Accuracy of Tilt Rotor Hover Performance Predictions

The accuracy of various methods used to predict tilt rotor hover performance was established by comparing predictions with large-scale experimental data. A wide range of analytical approaches were examined. Blade lift was predicted with a lifting line analysis, two lifting surface analyses, and by a finite-difference solution of the full potential equation. Blade profile drag was predicted with two different types of airfoil tables and an integral boundary layer analysis. The inflow at the rotor was predicted using momentum theory, two types of prescribed wakes, and two free wake analyses. All of the analyses were accurate at moderate thrust coefficients. The accuracy of the analyses at high thrust coefficients was dependent upon their treatment of high sectional angles of attack on the inboard sections of the rotor blade. The analyses which allowed sectional lift coefficients on the inboard stations of the blade to exceed the maximum observed in two-dimensional wind tunnel tests provided better accuracy at high thrust coefficients than those which limited lift to the maximum two-dimensional value. These results provide tilt rotor aircraft designers guidance on which analytical approaches provide the best results, and the level of accuracy which can be expected from the best analyses

Reduction of tilt rotor download using circulation control

The effect of boundary layer control blowing on the download of a wing in the wake of a hovering rotor was measured in a small scale experiment. The objective was to evaluate the potential of boundary layer control blowing for reducing tilt rotor download. Variations were made in rotor thrust coefficient, blowing pressure ratio, and blowing slot height. The effect of these parameter variations on the wing download and wing surface pressures is presented. The boundary layer control blowing caused reductions in the wing download of 25 to 55 percent

Wing force and surface pressure data from a hover test of a 0.658-scale V-22 rotor and wing

A hover test of a 0.658-scale V-22 rotor and wing was conducted in the 40 x 80 foot wind tunnel at Ames Research Center. The principal objective of the test was to measure the surface pressures and total download on a large scale V-22 wing in hover. The test configuration consisted of a single rotor and semispan wing on independent balance systems. A large image plane was used to represent the aircraft plane of symmetry. Wing flap angles ranging from 45 to 90 degrees were examined. Data were acquired for both directions of the rotor rotation relative to the wing. Steady and unsteady wing surface pressures, total wing forces, and rotor performance data are presented for all of the configurations that were tested

Performance and loads data from a hover test of a 0.658-scale V-22 rotor and wing

A hover test of a 0.658-scale model of a V-22 rotor and wing was conducted at the Outdoor Aerodynamic Research Facility at Ames Research Center. The primary objectives of the test were to obtain accurate measurements of the hover performance of the rotor system, and to measure the aerodynamic interactions between the rotor and wing. Data were acquired for rotor tip Mach numbers ranging from 0.1 to 0.73. This report presents data on rotor performance, rotor-wake downwash velocities, rotor system loads, wing forces and moments, and wing surface pressures

Performance and loads data from a hover test of a full-scale advanced technology XV-15 rotor

A hover test of a full-scale, composite, advanced technology XV-15 rotor was conducted at the Outdoor Aerodynamic Research Facility at Ames Research Center. The primary objective of the test was to obtain accurate measurements of the hover performance of this rotor system. Data were acquired for rotor tip Mach numbers ranging from 0.35 to 0.73. The rotor was tested with several alternate blade root and blade-tip configurations. Data are presented on rotor performance, rotor-wake downwash velocities, and rotor system loads

High Fidelity Aerodynamic Force Estimation for Multirotor Crafts in Free Flight

Aerodynamic investigation of multirotor crafts under non-hover conditions plays a vital role in the development of efficient and stable systems. Non-hover conditions include any flight scenario where the craft is no longer subject to to an infinite, stationary and undisturbed fluid. Examples of non-hover conditions are forward-flight, axial descent, and flying under ground effects. This paper presents the experimental framework for estimating multirotor free-flight forces. The presented method does not require rigid mounting of the craft to a load cell. Instead, the forces on the craft are estimated using two complementary methods-- one based on rigid body dynamics obtained by motion capture measurements and the other inferred from rotor rotational speed measurements. By considering these two independent estimates, with the dynamically-derived forces serving as a continuous reference, we are able to evaluate relative rotor performance, even under conditions where net forces on the craft are fluctuating. In order to map rotor rotational rates to rotor forces, we developed a closed-form expression which incorporates Reynolds number and rotor-rotor interaction effects. Using our free-flight force estimation technique, we accurately estimated rotor performance during various vertical flight conditions (i.e. ascent, descent, and hover with and without ground effects) with a high degree of accuracy

High Fidelity Aerodynamic Force Estimation for Multirotor Crafts in Free Flight

Aerodynamic investigation of multirotor crafts under non-hover conditions plays a vital role in the development of efficient and stable systems. Non-hover conditions include any flight scenario where the craft is no longer subject to to an infinite, stationary and undisturbed fluid. Examples of non-hover conditions are forward-flight, axial descent, and flying under ground effects. This paper presents the experimental framework for estimating multirotor free-flight forces. The presented method does not require rigid mounting of the craft to a load cell. Instead, the forces on the craft are estimated using two complementary methods-- one based on rigid body dynamics obtained by motion capture measurements and the other inferred from rotor rotational speed measurements. By considering these two independent estimates, with the dynamically-derived forces serving as a continuous reference, we are able to evaluate relative rotor performance, even under conditions where net forces on the craft are fluctuating. In order to map rotor rotational rates to rotor forces, we developed a closed-form expression which incorporates Reynolds number and rotor-rotor interaction effects. Using our free-flight force estimation technique, we accurately estimated rotor performance during various vertical flight conditions (i.e. ascent, descent, and hover with and without ground effects) with a high degree of accuracy