The economic impact of drag in general aviation

General aviation aircraft fuel consumption and operating costs are closely linked to drag reduction methods. Improvements in airplane drag are envisioned for new models; their effects will be in the 5 to 10% range. Major improvements in fuel consumption over existing turbofan airplanes will be the combined results of improved aerodynamics plus additional effects from advanced turbofan engine designs

The Bar-Halo Interaction - II. Secular evolution and the religion of N-body simulations

This paper explores resonance-driven secular evolution between a bar and dark-matter halo using N-body simulations. We make direct comparisons to our analytic theory (Weinberg & Katz 2005) to demonstrate the great difficulty that an N-body simulation has representing these dynamics for realistic astronomical interactions. In a dark-matter halo, the bar's angular momentum is coupled to the central density cusp (if present) by the Inner Lindblad Resonance. Owing to this angular momentum transfer and self-consistent re-equilibration, strong realistic bars WILL modify the cusp profile, lowering the central densities within about 30% of the bar radius in a few bar orbits. Past results to the contrary (Sellwood 2006, McMillan & Dehnen 2005) may be the result of weak bars or numerical artifacts. The magnitude depends on many factors and we illustrate the sensitivity of the response to the dark-matter profile, the bar shape and mass, and the galaxy's evolutionary history. For example, if the bar length is comparable to the size of a central dark-matter core, the bar may exchange angular momentum without changing its pattern speed significantly. We emphasise that this apparently simple example of secular evolution is remarkably subtle in detail and conclude that an N-body exploration of any astronomical scenario requires a deep investigation into the underlying dynamical mechanisms for that particular problem to set the necessary requirements for the simulation parameters and method (e.g. particle number and Poisson solver). Simply put, N-body simulations do not divinely reveal truth and hence their results are not infallible. They are unlikely to provide useful insight on their own, particularly for the study of even more complex secular processes such as the production of pseudo-bulges and disk heating.Comment: 23 pages, 18 figures, submitted to Monthly Notices. For paper with figures at full resolution: http://www.astro.umass.edu/~weinberg/weinberg_katz_2.ps.g

The United Kingdom Ministry of Defence – the Case for Followership as a key Element of Leadership Development

Published in Strategic Management Quarterly (2015) Vol 3 Issue 4Using the Kelley (1992) Followership Style instrument this study explores the role and perceptions of Followership within the UK Ministry of Defence. In particular, within the Armed Services and the Civil Service it was apparent from the literature that only the RAF formally recognised the role of Followership within their Leadership staff development programmes, hence the research aimed to see whether this was reflected in self-perceptions of Followership Style and the extent to which it is applied within the organisation. The analysis concluded that the analysed sample (298 responses) produced an atypical profile compared to other studies that have used the instrument. The RAF showed statistically significant higher scores than the other Armed Services or the Civil Servants and scores increased with Rank/Grade. The analysis also highlighted that the individuals seemed not to be recognised as good Followers by their leaders, they appeared not to recognise their reports as good Followers and in all cases the organisation seemed not to recognise their value. These aspects provide scope for further research to better understand the organisational culture, processes and practices that appear to act as a barrier to the extraction of the benefits of having good Followers even in an area where Star Followers dominate

Overview of external Nacelle drag and interference drag

A historical view of multi-jet engine installations is given that emphasizes integration of the powerplant and the airframe in aircraft design for improved reduction in external nacelle drag and interference drag characteristics

On the origin of cold dark matter halo density profiles

N-body simulations predict that CDM halo-assembly occurs in two phases: 1) a fast accretion phase with a rapidly deepening potential well; and 2) a slow accretion phase characterised by a gentle addition of mass to the outer halo with little change in the inner potential well. We demonstrate, using one-dimensional simulations, that this two-phase accretion leads to CDM halos of the NFW form and provides physical insight into the properties of the mass accretion history that influence the final profile. Assuming that the velocities of CDM particles are effectively isotropised by fluctuations in the gravitational potential during the fast accretion phase, we show that gravitational collapse in this phase leads to an inner profile rho(r) ~ r^{-1}. Slow accretion onto an established potential well leads to an outer profile with rho(r) ~ r^{-3}. The concentration of a halo is determined by the fraction of mass that is accreted during the fast accretion phase. Using an ensemble of realistic mass accretion histories, we show that the model predictions of the dependence of halo concentration on halo formation time, and hence the dependence of halo concentration on halo mass, and the distribution of halo concentrations all match those found in cosmological N-body simulations. Using a simple analytic model that captures much of the important physics we show that the inner r^{-1} profile of CDM halos is a natural result of hierarchical mass assembly with a initial phase of rapid accretion.Comment: Accepted for publication in MNRAS, references added, 11 pages, 8 figure

Spin-axis attitude estimation and magnetometer bias determination for the AMPTE mission

Algorithms were developed for magnetometer biases and spin axis attitude calculation. Numerical examples of the performance of the algorithm are given