Helicopter Simulation Validation Using Flight Data PDF Download

A method for developing and performing a rotorcraft flight simulation in the airwake behind a bluff body is investigated and compared to flight test data. This method is broadly composed of two parts: an atmospheric boundary layer computational simulation that is unsteady and time-accurate, and a UH-60 flight dynamics program that can be coupled with an airwake developed from the atmospheric boundary layer simulation. The airwake simulations are performed using the open source CFD software OpenFOAM with a solver package originally developed by the National Renewable Energy Laboratory. The flight dynamics program is an implementation of the GENHEL model known as PSUHeloSim. The computational fluid dynamics airwake solution is developed to recreate the airwake present for the validation case flight tests that were used to collect the flight test data. The validation case flight test data was collected from a variety of station-keeping tasks performed in the wake of a hangar on land. For the current investigation, two kinds of flight simulations were performed: piloted simulations in a flight simulator facility and flight simulations performed using a pilot model. Comparisons between flight test data and simulated flight data were made based on power spectral density analyses of both pilot control activity and aircraft motion. Comparisons of pilot control stick activity reveal that pilots in the simulated flight tests used higher control activity energy than the flight test validation case pilots. An analysis of the vehicle angular rates yielded similar results, with the overall trends of power versus frequency being similar but a significantly higher power being seen for the piloted flight simulations. Limited data did show sizeable differences in pilot control activity for the same simulated flight task flown by different pilots in the flight simulation facility. Pilot variability, combined with other obfuscating effects such as inherently higher pilot control energy in a simulated environment than in physical rotorcraft, make an exact reproduction of the validation case flight test data infeasible for this investigation. That being said, a number of unknowns and methodological improvements were identified and discussed. The pilot model was not used to compare simulated flights to validation case flights, but was useful for analyzing sensitivity of flight simulations to positioning error within a simulated airwake as well as for comparing flight simulations in different airwakes to each other without the variability associated with human pilots. It was found that flight simulations in airwakes generated with an atmospheric boundary layer flow required higher pilot control activity than flight simulations in airwakes generated by a simple uniform inflow.