The Effect of Rotor Cruise Tip Speed, Engine Technology and Engine/Drive System RPM on the NASA Large Civil Tiltrotor (LCTR2) Size and Performance

A multi-year study was conducted under NASA NNA06BC41C Task Order 10 and NASA NNA09DA56C task orders 2, 4, and 5 to identify the most promising propulsion system concepts that enable rotor cruise tip speeds down to 54% of the hover tip speed for a civil tiltrotor aircraft. Combinations of engine RPM reduction and 2-speed drive systems were evaluated. Three levels of engine and the drive system advanced technology were assessed; 2015, 2025 and 2035. Propulsion and drive system configurations that resulted in minimum vehicle gross weight were identified. Design variables included engine speed reduction, drive system speed reduction, technology, and rotor cruise propulsion efficiency. The NASA Large Civil Tiltrotor, LCTR, aircraft served as the base vehicle concept for this study and was resized for over thirty combinations of operating cruise RPM and technology level, quantifying LCTR2 Gross Weight, size, and mission fuel. Additional studies show design sensitivity to other mission ranges and design airspeeds, with corresponding relative estimated operational cost. The lightest vehicle gross weight solution consistently came from rotor cruise tip speeds between 422 fps and 500 fps. Nearly equivalent results were achieved with operating at reduced engine RPM with a single-speed drive system or with a two-speed drive system and 100% engine RPM. Projected performance for a 2025 engine technology provided improved fuel flow over a wide range of operating speeds relative to the 2015 technology, but increased engine weight nullified the improved fuel flow resulting in increased aircraft gross weights. The 2035 engine technology provided further fuel flow reduction and 25% lower engine weight, and the 2035 drive system technology provided a 12% reduction in drive system weight. In combination, the 2035 technologies reduced aircraft takeoff gross weight by 14% relative to the 2015 technologies

Reflections on the one-minute paper

This paper captures the perceptions of both a new academic and his students on the use of the one-minute paper (OMP). Much of the originality of this paper derives from the multi-layered qualitative approach which provides a deeper insight into the direct and indirect mechanism through which the OMP is perceived to work. This paper argues, more than the prevailing literature suggests, that in order to increase the benefits of using the OMP then considerable investment in time is required. The findings show that the academic’s cost in terms of time is greatest when asking ‘lecturer effectiveness’ type questions, but the benefits derived are potentially longer term than standard ‘lecture content’ based question. Students value the use of the OMP, principally because it demonstrates respect for them; this helps to create an atmosphere of trust which can encourage engagement and an active approach to student learning. The research informs a discussion on how practical implementation techniques can be used to maximise the benefits and limit the costs

The role of academic motivation in Computer-Supported Collaborative Learning

In recent years, increasing attention has been devoted to virtual learning. In the last decade, a large number of studies in Computer-Supported Collaborative Learning (CSCL) have assessed how social interaction, learning processes and outcomes in virtual settings are intertwined. Although recent research findings indicate that learners differ with respect to the amount and type of discourse contributed in virtual settings, little is known about the causes of these differences. The research presented here looks into the effects of motivation of learners on their contribution to discourse using the Deci and Ryan framework of (intrinsic/extrinsic) motivation. This study of 100 participants who were randomly distributed in six groups of 14 members collaborated in a virtual setting to remediate deficiencies in economics indicates that individuals differed with respect to the amount of discourse activity. Furthermore, an integrated multi-method approach (Content Analysis, Social Network Analysis and Academic Motivation Scale) was used in order to examine the impact of academic motivation on the type of discourse activity contributed and on the position of the learner in the social network. The results indicate that highly intrinsically motivated learners become central and prominent contributors to cognitive discourse. In contrast, extrinsically motivated learners contribute on average and are positioned throughout the social network. The research results reveal that differences in academic motivation influences the type of contributions to discourse as well as the position a learner takes within the social network

The role of scaffolding and motivation in CSCL

Recent findings from research into Computer-Supported Collaborative Learning (CSCL) have indicated that not all learners are able to successfully learn in online collaborative settings. Given that most online settings are characterised by minimal guidance, which require learners to be more autonomous and self-directed, CSCL may provide conditions more conducive to learners comfortable with greater autonomy. Using quasi-experimental research, this paper examines the impact of a redesign of an authentic CSCL environment, based upon principles of Problem-Based Learning, which aimed to provide a more explicit scaffolding of the learning phases for students. It was hypothesised that learners in a redesigned ‘Optima’ environment would reach higher levels of knowledge construction due to clearer scaffolding. Furthermore, it was expected that the redesign would produce a more equal spread in contributions to discourse for learners with different motivational profiles. In a quasi-experimental setting, 143 participants collaborated in an online setting aimed at enhancing their understanding of economics. Using a multi-method approach (Content Analysis, Social Network Analysis, measurement of Academic Motivation), the research results reveal the redesign triggered more equal levels of activity of autonomous and control-oriented learners, but also a decrease in input from the autonomous learners. The main conclusion from this study is that getting the balance between guidance and support right to facilitate both autonomous and control-oriented learners is a delicate complex issue

Wave interactions in three-dimensional boundary layers

The roles of weakly nonlinear triad interactions and the self-interaction of primary instabilities in the transition-to-turbulence process in three-dimensional boundary layers are investigated. Resonant triad interactions are studied in the boundary layer on the leading edge of a swept wing under typical commercial jet cruise conditions. Both compressible and incompressible models are developed using the method of multiple scales and a spectral collocation numerical method. Detuning parameters for the wavenumbers and frequencies and the effects of the growth of the boundary layer are included in the modeling. The spatial and temporal growth of numerous triads consisting of different combinations of crossflow (CF) and Tollmein-Schlichting (TS) modes are studied for a specific laminar flow control wing.Calculations using the model indicate that the spatial evolution of the triad amplitudes is strongly dependent upon the initial spectrum of amplitudes and phases. Specific predictions are impossible without this information, but general conclusions regarding interaction strength are possible. Calculations indicate that triads consisting of three crossflow modes are abundant, but the interaction between the modes is relatively weak. Triads with two TS modes and one CF mode are also numerous and the interaction may strongly affect the CF mode.Comparison of results from the compressible and incompressible theories show significant differences in some cases. Compressibility is stabilizing to individual modes and usually weakens the interactions among them as well. Nonparallel effects are usually destabilizing according to both models and may significantly affect the evolution of the triad amplitudes.The self-interaction of disturbances is investigated in the three-dimensional boundary layer over a rotating disk. The method of multiple scales is used to model the weakly nonlinear growth of the critical stationary crossflow mode. The Landau constant is evaluated using a spectral collocation numerical method. Results indicate that nonlinearity is destabilizing, so subcritical instability and super-exponential growth is possible.U of I OnlyETDs are only available to UIUC Users without author permissio