A comparison of theory and flight test of the BO 105/BMR in hover and forward flight

Four cases were selected for comparison with theoretical predictions using stability data obtained during the flight test of the Bearingless Main Rotor (BMR) on a Messerschmidt-Boelkow-Blohm BO 105 helicopter. The four cases selected form the flight test included two ground resonance cases and two air resonance cases. The BMR used four modified BO 105 blades attached to a bearingless hub. The hub consisted of dual fiberglass C-channel beams attached to the hub center at 0.0238R and attached to the blade root at 0.25R with blade pitch control provided by a torque tube. Analyses from Bell Helicopter Textron, Boeing Vertol, and Sikorsky Aircraft were compared with the data and the correlation ranged from very poor-to-poor to poor-to-fair

A comparison of theory and experiment for coupled rotor body stability of a bearingless rotor model in hover and forward flight

Seven cases were selected for correlation from a 1/5.86 Froude-scale experiment that examined several rotor designs which were being considered for full-scale flight testing as part of the Bearingless Main Rotor (BMR) program. The model rotor hub used in these tests consisted of back-to-back C-beams as flexbeam elements with a torque tube for pitch control. The first four cases selected from the experiment were hover tests which examined the effects on rotor stability of variations in hub-to-flexbeam coning, hub-to-flexbeam pitch, flexbeam-to-blade coning, and flexbeam-to-blade pitch. The final three cases were selected from the forward flight tests of optimum rotor configuration as defined during the hover test. The selected cases examined the effects of variations in forward speed, rotor speed, and shaft angle. Analytical results from Bell Helicopter Textron, Boeing Vertol, Sikorsky Aircraft, and the U.S. Army Aeromechanics Laboratory were compared with the data and the correlations ranged from poor-to-fair to fair-to-good

Control load envelope shaping by live twist

Rotor control systems experience a rapid load growth resulting from retreating blade stall during flight conditions of high blade loading or airspeeds. An investigation was undertaken to determine the effect of changing blade torsional properties over the rotor flight envelope. The results of this study show that reducing the blade stiffness to introduce more blade live twist significantly reduces the large retreating blade control loads, while expanding the flight envelope and reducing retreating blade stall loads

Wind-Tunnel Survey of an Oscillating Flow Field for Application to Model Helicopter Rotor Testing

A survey was conducted of the flow field produced by the Airstream Oscillator System (AOS) in the Langley Transonic Dynamics Tunnel (TDT). The magnitude of a simulated gust field was measured at 15 locations in the plane of a typical model helicopter rotor when tested in the TDT using the Aeroelastic Rotor Experimental System (ARES) model. These measurements were made over a range of tunnel dynamic pressures typical of those used for an ARES test. The data indicate that the gust field produced by the AOS is non-uniform across the tunnel test section, but should be sufficient to excite a model rotor

Dynamic stall modeling and correlation with experimental data on airfoils and rotors

Two methods for modeling dynamic stall have been developed. The alpha, A, B method generates lift and pitching moments as functions of angle of attack and its first two time derivatives. The coefficients are derived from experimental data for oscillating airfoils. The Time Delay Method generates the coefficients from steady state airfoil characteristics and an associated time delay in stall beyond the steady state stall angle. Correlation with three types of test data shows that the alpha, A, B method is somewhat better for use in predicting helicopter rotor response in forward flight. Correlation with lift and moment hysteresis loops generated for oscillating airfoils was good for both models

Skype in Qualitative Interviews: Participant and Researcher Perspectives

As Internet usage has increased, web-based technologies such as Skype and Face Time have become more common alternatives for qualitative interviewing, especially for research participants who are geographically distant from the researchers. Challenges to the use of these tools have been identified, but as technology is currently changing at a rapid pace, more recent research is needed to provide up-to-date information on the feasibility of web and video conferencing technologies for qualitative interviewing. This paper reflects on the experience of using Skype for qualitative research interviews (n=14) in a study of pregnancy and parenting in doctoral programs, including feedback from research participants who chose to complete the qualitative interview via Skype instead of telephone or face-to-face interviews. Twelve participants who completed Skype interviews provided feedback on their experiences using Skype for qualitative interviews. Feedback from participants highlight an overall positive perception of Skype interviews due to the availability of visual cues from researchers and flexibility, but participants also shared challenges in terms of technology issues and participants’ lack of expertise with the technology. Recommendations include the use of videoconferencing and digital technologies as an additional or alternative interview tool for qualitative interviews, especially for participants who have logistical challenges meeting researchers face-to-face