Browse Topic: Exteriors
This study presents computational analyses of coaxial rotor hub flows and validation against experimental data obtained from the fifth Rotor Hub Flow Prediction Workshop. Experiments were conducted in a 12-inch diameter water tunnel at Pennsylvania State Applied Research Laboratory, employing tomographic particle-image velocimetry (Tomo-PIV) and precise hub drag measurements. Three CFD codes (UMD Mercury, CREATETM-AV Helios, and OVERFLOW) utilizing hybrid Reynolds-Averaged Navier-Stokes (RANS) / Large Eddy Simulation (LES) modeling based on Spalart–Allmaras turbulence model, were applied to replicate and analyze hub flows. Counter-rotating coaxial rotor hubs under free-air condition was simulated as the simplest case and the hub drags are compared between the three CFD codes. The full water tunnel configuration, consisting of two hubs, a fairing, and shafts, was also simulated and compared to experimental results, with a focus on hub drag, wake velocity fields, and turbulence quantities. Results demonstrated that the computational frameworks effectively captured key flow physics, although some discrepancies in drag harmonics, wake velocity and turbulence intensity magnitudes were observed. Additionally, the study highlighted the impact of rotor hub geometry and installation of sail-fairing on drag and wake structures. These findings contribute to improve computational predictions, essential for designing high-speed rotor hub configurations.
A computational study is conducted on a coaxial rotor hub and sail fairing configuration to analyze hub surface forces and the characteristics of its downstream wake. The flow conditions and grids are based on experimental tests performed at the Penn State Applied Research Lab (ARL) Water Tunnel at a baseline Reynolds number. Grid development for the rotor hubs and sail fairing is done using Pointwise v18.04R1 and Chimera Grid Tools (version 2.2). Simulations are performed using NASA's OVERFLOW2.4b Reynolds Averaged Navier-Stokes solver. The drag forces on the rotor hubs are computed and compared to standalone drag data to analyze the effects of interactional aerodynamics. Flow features, frequency content and Reynolds stresses of the wake are analyzed. Frequency content and Reynolds stresses show clear spatial bias. The anisotropy of the Reynolds stresses is computed and used to determine the character of the wake turbulence.
ABSTRACT
ABSTRACT
This SAE Recommended Practice applies to the abrasion resistance testing of decorative tapes, graphics, and pin striping. It may also have relevance to certain vehicle labels and plastic wood grain film. The resistance to abrasive damage is judged qualitatively by its effect on the legibility, pattern, and color of the graphic marking. This recommended practice is intended as a guide toward standard practice but may be subject to frequent change to keep pace with experience and technical advances. This should be kept in mind when considering the use of this recommended practice.
Harold F. Pitcairn, American aviation and Autogiro pioneer, died from a single gunshot wound to the head in the late evening hours of April 23, 1960 at the age of 62 after a gala evening at which he presided over a celebration attended by more than 450 guests for his brother's Raymond's 75th birthday. Initially labelled a suicide by the press, Pitcairn's widow Clara declared that "she never wanted to hear another word about the tragedy", while friends and friendly local authorities made the argument, duly reported by Frank Kingston Smith in Legacy of Wings, his devotional Pitcairn biography (subsidized by the Pitcairn family), that the death was accidental because "there was no note, no indication of depression or unhappiness" and "the police investigation disclosed that two shots had been fired; one had penetrated the ceiling directly over the desk in the first floor study, another had struck Pitcairn in the eye" and that "the next morning it was discovered the semi-automatic pistol was defective: when cocked, it had a supersensitive "hair trigger," and it had a faulty disconnector so that it would fire more than one shot at a time, a condition known as "doubling."" The Pitcairn families, prominent and powerful, prevailed upon the local authorities to declare the death accidental and Kingston Smith's 1981account became the de facto authoritative story of the death of Harold F. Pitcairn. With the perspective, however, of six decades, it appears far more likely that Pitcairn's death was a suicide for reasons that were not readily evident, minimized, unappreciated or deliberately ignored at the time to craft a result that met the needs of Clara Pitcairn and her surviving family. These included the fact that while the claim was made that Pitcairn was making his nightly rounds to check on the estate’s ground-level windows (and had been doing so since the Lindbergh kidnapping in 1932), he actually died at his desk; that those in the house only reported a single shot; the 1907 Savage pistol had no reputation for a hair-trigger, and had not evidenced such a flaw in almost three decades of Pitcairn's nightly ritual; that even though Pitcairn had been assured that his almost-decade-long lawsuit against the United States government for Patent infringement of his Autogiro patents was going well, he was concerned about the impact this lawsuit was having on his aged associates who had been called to give depositions and he had voiced the sentiment that "if he had known that he would have to sue the government, he would not have gone into the Autogiro business"; that the lawsuit, itself intended as a vindication of Pitcairn's contribution to aviation was dragging on and would reach its first legal conclusion in 1967, and not finally conclude upon appeal until 1977; and most importantly, those who deny suicide and point to Pitcairn’s state-of-mind, have failed to take into account when the death occurred or ready evidence of his 'state of mind' To fail to see the tragic end of Harold F. Pitcairn is to forget that 29 years and one day earlier, he had been recognized for "the greatest achievement in aeronautics or astronautics in America, with respect to improving the performance, efficiency, and safety of air or space vehicles, the value of which has been thoroughly demonstrated by actual use during the preceding year." The memory of that day on the White House back lawn with the President was the high point of his life even as Pitcairn prepared to celebrate his older brother's achievements. The evidence, when marshalled and documented, conclusively points to suicide - a death of an American aviation pioneer before his contributions were vindicated in the largest patent infringement judgement against the United States in history. To fail to see the tragic end of Harold F. Pitcairn is to forget that 29 years earlier, he had been recognized for "the greatest achievement in aeronautics or astronautics in America".
In the winter months of January-March 2019, two Bell 525 test aircraft completed cold weather testing at Yellowknife Canada, some 1900 nm from Bell’s Flight Research Center in Arlington, TX. Testing was aimed at demonstrating aircraft stability, performance, and flight characteristics at extreme temperatures as required by CFR Part 29. Since regulations only permit limited temperature extrapolation, the cold temperature tests must include the limit of forward speed in a dive (VNE), and assessments of performance, controllability, autorotation, and static stability. This paper describes some of the unique environmental conditions and factors that any rotorcraft development program could experience in cold weather testing. The paper also gives a technical description of the required testing, where arctic conditions reached as low as -40° F or C (the temperature scales are the same at this temperature). Testing exposed the aircraft to overnight cold-soaks that brought fluids, seals, windshields, electronics, and elastomeric bearings to their low temperature specification, all at the same time. For the 525, test results demonstrated that the aircraft was ready for start-up and operation in extreme cold. The criteria necessary for meeting certification requirements in cold weather were also demonstrated in the series of tests and showed that the rotor was free from any adverse effects due to aerodynamic compressibility, had low vibration, acceptable loads and was free from any instability, even at speeds greater than VNE.
This work examines the handling qualities (HQ) rating scale from a psychophysical perspective, characterizing workload as the response to a stimulus composed of input to the pilot and pilot outputs. Previous work by the author examining three different display tracking tasks indicated that pilot workload is effectively a logarithmic function of tracking error rate and control rate. This approach, called the Spare Capacity OPerations Estimator (SCOPE), is extended to flight and Handling Qualities data collected (109 runs) for the slalom Mission Task Element (MTE) using the U.S. Army’s JUH-60A RASCAL aircraft. Attitude and Rate Command response types as well as various forcefeel configurations were tested. Based on flight data observation a novel and intuitive action model is proposed for the slalom MTE whereby the pilot operates on the relative angle between the ground track and the upcoming cone’s location (effectively the cone’s location on the windscreen relative to the aircraft nose, assuming a no-wind environment). Proximity to an approaching cone determines which of two strategies is active: maintaining a constant relative angle or maintaining the relative angular rate constant. A method is proposed for mapping Handling Qualities (HQ) ratings to flight data performance and the workload estimate, offering the possibility for easing the requirement that a pilot trained in HQ evaluation fly test maneuvers. Applying this approach to the slalom maneuver produced good correlation between actual and estimated HQ ratings over the varying aircraft and inceptor feel system dynamics.
Items per page:
50
1 – 50 of 4444