Power required analysis is an important element of aircraft performance. The primary method for measuring this parameter is the classic PIW-VIW (power and velocity independent of weight) method which was developed in the first half of the 20th century. This method was originally developed for use with manned aircraft and therefore has some shortcomings when applied to unmanned aircraft, specifically those that are remotely piloted. The proposed method estimates the lift and drag models using the maximum likelihood technique which was applied to data acquired through acceleration and deceleration runs under the assumption that the pitch rate and lateral dynamics are negligible. The acceleration runs were performed by applying full throttle while the aircraft was flying just above the stall velocity and allowing it to naturally accelerate to maximum level flight velocity. The deceleration runs were performed in the opposite manner where the throttle was set to zero while the aircraft was ying at maximum velocity and allowed to naturally slow down until stall was reached. The collected data is reduced using the PIW-VIW technique whereby a single power curve is generated that is independent of aircraft weight and air density. Simulations indicate that deviations from the designed maneuvers, such as altitude changes and low pitch rates, are acceptable and do not change the resulting power curves. A hard limit on what constitutes low pitch rate was difficult to establish as system noise played a large role in determining the signal-to-noise ratio limit on the pitch rate. However, based on a model analysis it was concluded that the pitch rate could be safely ignored without consequences to the results. A low cost Raspberry Pi data collection system was designed for use on two test aircraft, the commercially available Nexstar and a reconfigurable research aircraft called Astraeus. Data points using the classic PIW-VIW method were collected during the flight test program for comparison against the dynamic method. The results show good agreement between the deceleration runs and the PIW-VIW method for both aircraft. The acceleration runs generally had a poorer overall fit and a larger spread. This is due to excessive sensor noise caused by vibrations from the propulsion system. The acceleration runs were also more difficult to perform as the pilot was not always able to keep the thrust-induced pitching effects low during throttle up. A throttle ramp up was performed in an attempt to mitigate this effect and improve data quality; however, the analysis revealed no difference in the resulting power curves. Overall the dynamic power analysis was found to be a valid analysis tool for power required, especially when the deceleration run was used. Besides the decreased noise over the acceleration run, the deceleration run offers the advantage of neglecting the thrust model, especially when using aircraft with electric propulsion systems since they can be turned off in flight resulting in zero residual thrust. This improves the accuracy of the resulting power required curves as well as saving time and effort since wind tunnel testing for propeller model generation can be avoided.
|School:||North Carolina State University|
|School Location:||United States -- North Carolina|
|Source:||DAI-B 78/08(E), Dissertation Abstracts International|
|Keywords:||Flight testing, Power required analysis, Unmanned aerial vehicles|
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