Opportunistic soaring by birds suggests new opportunities for atmospheric energy harvesting by flying robots

The use of flying robots (drones) is increasing rapidly, but their utility is limited by high power demand, low specific energy storage and poor gust tolerance. By contrast, birds demonstrate long endurance, harvesting atmospheric energy in environments ranging from cluttered cityscapes to open landscapes, coasts and oceans. Here, we identify new opportunities for flying robots, drawing upon the soaring flight of birds. We evaluate mechanical energy transfer in soaring from first principles and review soaring strategies encompassing the use of updrafts (thermal or orographic) and wind gradients (spatial or temporal). We examine the extent to which state-of-the-art flying robots currently use each strategy and identify several untapped opportunities including slope soaring over built environments, thermal soaring over oceans and opportunistic gust soaring. In principle, the energetic benefits of soaring are accessible to flying robots of all kinds, given atmospherically aware sensor systems, guidance strategies and gust tolerance. Hence, while there is clear scope for specialist robots that soar like albatrosses, or which use persistent thermals like vultures, the greatest untapped potential may lie in non-specialist vehicles that make flexible use of atmospheric energy through path planning and flight control, as demonstrated by generalist flyers such as gulls, kites and crows.

The role of the Clinical Governance Adviser in supporting quality improvement in general dental practice: the Glasgow Quality Practice Initiative

AIM

The purpose of this paper is to share information derived from the Glasgow Quality Practice Initiative with general dental practice teams, Dental Practice Advisers and others involved in quality improvement.

METHOD

A sample of 16 general dental practices was selected from volunteers to receive assistance in working towards a Quality Practice Award. Two Clinical Governance Advisers were appointed to provide this support.

DATA COLLECTED

Quantitative, qualitative and observational data were collected, and comparisons made between practices that had and had not received support.

RESULTS

Selected results are presented demonstrating both the baseline position and comparisons of the 'Intervention' and 'Non-Intervention' groups.

CONCLUSIONS

and recommendations Baseline levels of quality assurance were generally poor. It is asserted that the practices receiving Clinical Governance Adviser support benefited from the experience and made meaningful improvements. This has implications for the development of national policy in Scotland.

An investigation into the use of bitewing radiography in children in Greater Glasgow

AIM

In recent years there have been a number of reviews and guidelines published with respect to the diagnosis and management of caries in children. Bitewing radiography remains the recommended method of choice for caries diagnosis in most circumstances. The aims of the study were to investigate the usage of bitewing radiography by general dental practitioners (GDPs) in Greater Glasgow, for the diagnosis of caries in children and to assess the usefulness of the technique as perceived by these dental practitioners.

DESIGN

A questionnaire for self completion was sent to all GDPs with an NHS list number in the Greater Glasgow area.

RESULTS

An 80% response rate was obtained with 303 GDPs responding. Less than half the dentists (44%) indicated that they always carried out caries risk assessments for all children, but 71% reported doing this for 6 and 7-year-old children. Approximately 60% of dentists stated they had read the recent radiation and caries management guidelines. Only 72% stated that they used radiography as a caries diagnostic tool in children, with 12 GDPs (4%) indicating they would never consider using bitewing radiography in children. Only 17% would consider taking bitewing radiographs in children under 6 years, and the majority of dentists (61%) reported that they would first consider taking radiographs in the 6-11-year-old age group. However, only a low proportion of children in this age band had dental x-rays taken. Bitewing radiography was considered to be more important for 12-year-olds than for 6-year-olds. Recommended methods for decreasing radiation exposure such as rectangular collimation and film holders were not being used universally, with 41% and 58% respectively using these devices.

CONCLUSIONS

A significant proportion of dentists in Greater Glasgow are not complying with recent guidelines and recommendations and it would appear that the value of bitewing radiography as a diagnostic tool in children is not being fully exploited.

Animal flight dynamics II. Longitudinal stability in flapping flight

Stability is essential to flying and is usually assumed to be especially problematic in flapping flight. If so, problems of stability may have presented a particular hurdle to the evolution of flapping flight. In spite of this, the stability of flapping flight has never been properly analysed. Here we use quasi-static and blade element approaches to analyse the stability provided by a flapping wing. By using reduced order approximations to the natural modes of motion, we show that wing beat frequencies are generally high enough compared to the natural frequencies of motion for a quasi-static approach to be valid as a first approximation. Contrary to expectations, we find that there is noting inherently destabilizing about flapping: beating the wings faster simply amplifies any existing stability or instability, and flapping can even enhance stability compared to gliding at the same air speed. This suggests that aerodynamic stability may not have been a particular hurdle in the evolution of flapping flight. Hovering animals, like hovering helicopters, are predicted to possess neutral static stability. Flapping animals, like fixed wing aircraft, are predicted to be stable in forward flight if the mean flight force acts above and/or behind the centre of gravity. In this case, the downstroke will always be stabilizing. The stabilizing contribution may be diminished by an active upstroke with a low advance ratio and more horizontal stroke plane; other forms of the upstroke may make a small positive contribution to stability. An active upstroke could, therefore, be used to lower stability and enhance manoeuvrability. Translatory mechanisms of unsteady lift production are predicted to amplify the stability predicted by a quasi-static analysis. Non-translatory mechanisms will make little or no contribution to stability. This may be one reason why flies, and other animals which rely upon non-translatory aerodynamic mechanisms, often appear inherently unstable.

Mechanics and aerodynamics of insect flight control

Insects have evolved sophisticated fight control mechanisms permitting a remarkable range of manoeuvres. Here, I present a qualitative analysis of insect flight control from the perspective of flight mechanics, drawing upon both the neurophysiology and biomechanics literatures. The current literature does not permit a formal, quantitative analysis of flight control, because the aerodynamic force systems that biologists have measured have rarely been complete and the position of the centre of gravity has only been recorded in a few studies. Treating the two best-known insect orders (Diptera and Orthoptera) separately from other insects, I discuss the control mechanisms of different insects in detail. Recent experimental studies suggest that the helicopter model of flight control proposed for Drosophila spp. may be better thought of as a facultative strategy for flight control, rather than the fixed (albeit selected) constraint that it is usually interpreted to be. On the other hand, the so-called 'constant-lift reaction' of locusts appears not to be a reflex for maintaining constant lift at varying angles of attack, as is usually assumed, but rather a mechanism to restore the insect to pitch equilibrium following a disturbance. Differences in the kinematic control mechanisms used by the various insect orders are related to differences in the arrangement of the wings, the construction of the flight motor and the unsteady mechanisms of lift production that are used. Since the evolution of insect flight control is likely to have paralleled the evolutionary refinement of these unsteady aerodynamic mechanisms, taxonomic differences in the kinematics of control could provide an assay of the relative importance of different unsteady mechanisms. Although the control kinematics vary widely between orders, the number of degrees of freedom that different insects can control will always be limited by the number of independent control inputs that they use. Control of the moments about all three axes (as used by most conventional aircraft) has only been proven for larger flies and dragonflies, but is likely to be widespread in insects given the number of independent control inputs available to them. Unlike in conventional aircraft, however, insects' control inputs are likely to be highly non-orthogonal, and this will tend to complicate the neural processing required to separate the various motions.

Animal flight dynamics I. Stability in gliding flight

Stability is as essential to flying as lift itself, but previous discussions of how flying animals maintain stability have been limited in both number and scope. By developing the pitching moment equations for gliding animals and by discussing potential sources of roll and yaw stability, we consider the various sources of static stability used by gliding animals. We find that gliding animals differ markedly from aircraft in how they maintain stability. In particular, the pendulum stability provided when the centre of gravity lies below the wings is a much more important source of stability in flying animals than in most conventional aircraft. Drag-based stability also appears to be important for many gliding animals, whereas in aircraft, drag is usually kept to a minimum. One unexpected consequence of these differences is that the golden measure of static pitching stability in aircraft--the static margin--can only strictly be applied to flying animals if the equilibrium angle of attack is specified. We also derive several rules of thumb by which stable fliers can be identified. Stable fliers are expected to exhibit one or more of the following features: (1) Wings that are swept forward in slow flight. (2) Wings that are twisted down at the tips when swept back (wash-out) and twisted up at the tips when swept forwards (wash-in). (3) Additional lifting surfaces (canard, hindwings or a tail) inclined nose-up to the main wing if they lie forward of it, and nose-down if they lie behind it (longitudinal dihedral). Each of these predictions is directional--the opposite is expected to apply in unstable animals. In addition, animals with reduced stability are expected to display direct flight patterns in turbulent conditions, in contrast to the erratic flight patterns predicted for stable animals, in which large restoring forces are generated. Using these predictions, we find that flying animals possess a far higher degree of inherent stability than has generally been recognized. This conclusion is reinforced by measurements of the relative positions of the centres of gravity and lift in birds, which suggest that the wings alone may be sufficient to provide longitudinal static stability. Birds may therefore resemble tailless aircraft more closely than conventional aircraft with a tailplane.

Evaluation of row spacing and population density effects on grain sorghum over a range of northern Australian environments

Fifteen experiments were conducted between 1976 and 1978 to determine the response of grain sorghum to row spacing and population density over a range of soil types, planting dates and seasonal conditions. One experiment was at Kununurra, Western Australia, and the rest were in southern and central Queensland. The trials virtually covered the full range of growing conditions likely to be experienced in the sorghum growing area. Narrow and standard single rows (0.33 m to 1.07 m spacings) yielded as well as or better than more widely spaced (1.50 to 4.27 m) single or twin rows (0.33 or 0.36 m apart) at equivalent population densities over a wide range of yield levels. Only at yield levels below 900 kg ha-l was there a trend for 2.00 or 2.13 m twin rows to outyield the 0.33 or 0.36 m single row spacing. Significant yield reductions resulted in a number of trials, at yield levels above 1600 kg ha-l, from the use of wide row spacings. Where there was severe water stress, grain yields were also reduced by high population densities (>150,000 plants ha-l), particularly at the 0.33 or 0.36 m row spacing. There was no evidence that response to row spacing differed between cultivars. In the one experiment where it was studied, root pruning had no effect on grain yield under conditions of ample moisture supply, but yield was reduced by root pruning of wide row sorghum (1.8 m spacing) under conditions of moisture stress.