Delta Wing Aircraft Research Articles

FLOW PATTERN AROUND THE RIGID CEPHALIC SHIELD OF THE DEVONIAN AGNATHANERRIVASPIS WAYNENSIS(PTERASPIDIFORMES: HETEROSTRACI)

Abstract: Palaeozoic armoured agnathans (or ostracoderms) are characterised by having an external, bone shield enclosing the anterior part of their bodies, which demonstrate great diversity of both forms and sizes. The functional significance of these cephalic shields remains unclear (they may have been a functional analogue of the vertebral column, or merely afforded protection). Here we assess the importance of the cephalic shield in terms of locomotion. In order to do this, we have studied flow patterns of the Devonian heterostracanErrivaspis waynensis(White, 1935), using an anatomically correct model ofE.waynensispositioned at different pitching angles. The fluid flow was visualised in a wind tunnel, using planar light sheet techniques, adding vaporised propylene glycol to the fluid. The flow pattern over the cephalic shield ofErrivaspisis dominated by the formation of leading‐edge vortices (LEVs). When the model was positioned at angles of attack of ‐2 degrees or higher a pair of nearly symmetrical, counter‐rotating primary vortices were produced, which flowed downstream over the upper surface of the cephalic shield. At moderate angles of attack, LEVs remained attached to the dorsal surface, but, as the angle of attack increased above 7 degrees, vortices began to separate from the surface at posterior locations. At a high angles of attack (around 12 degrees or 13 degrees), vortex breakdown (or vortex burst) occured. The body‐induced vortical flow around the cephalic shield is very similar to the that described over delta wing aircraft. This strategy generates lift forces through vortex generation (vortex lift). Based on this analogue and knowing thatErrivaspislacked pectoral fins or any other obvious control surfaces, vortex lift forces added through this mechanism may have played a major role in the locomotion of these primitive fishes, not only to counteract the negative buoyancy of the fish, but also as a means of manoeuvring.

Dynamic gain-scheduled control of the ICE 101-TV

AbstractThis paper shows the theoretical development and application of dynamic gain scheduled control – a novel method for the control of nonlinear systems – to an aircraft model. The idea behind this method is to schedule the control law gains with a fast varying state variable rather than with a slow varying state or an input parameter. This is advantageous as it is then possible to schedule the gains with a state variable that is dominant in the mode that we are most interested in controlling. The use of this type of gain scheduling is shown to improve the transient response of the aircraft model when stepping between trim conditions and to overcome some of the problems associated with conventional gain scheduled controllers (such as control surface position limit saturation). ‘Hidden coupling terms’ that introduce unwanted dynamics when scheduling gains with a fast state (rather than the input design parameter) are eliminated directly by applying a transformation to the classical parameter-scheduled gain distributions which are calculated using eigenstructure assignment. A second order longitudinal model and a 5th order longitudinal/lateral model of the ICE 101-TV tailless delta-wing aircraft configuration are used to demonstrate the design process.

Body-induced vortical flows: a common mechanism for self-corrective trimming control in boxfishes

Boxfishes (Teleostei: Ostraciidae) are marine fishes having rigid carapaces that vary significantly among taxa in their shapes and structural ornamentation. We showed previously that the keels of the carapace of one species of tropical boxfish, the smooth trunkfish, produce leading edge vortices (LEVs) capable of generating self-correcting trimming forces during swimming. In this paper we show that other tropical boxfishes with different carapace shapes have similar capabilities. We conducted a quantitative study of flows around the carapaces of three morphologically distinct boxfishes (spotted boxfish, scrawled cowfish and buffalo trunkfish) using stereolithographic models and three separate but interrelated analytical approaches: digital particle image velocimetry (DPIV), pressure distribution measurements, and force balance measurements. The ventral keels of all three forms produced LEVs that grew in circulation along the bodies, resembling the LEVs produced around delta-winged aircraft. These spiral vortices formed above the keels and increased in circulation as pitch angle became more positive, and formed below the keels and increased in circulation as pitch angle became more negative. Vortices also formed along the eye ridges of all boxfishes. In the spotted boxfish, which is largely trapezoidal in cross section, consistent dorsal vortex growth posterior to the eye ridge was also present. When all three boxfishes were positioned at various yaw angles, regions of strongest concentrated vorticity formed in far-field locations of the carapace compared with near-field areas, and vortex circulation was greatest posterior to the center of mass. In general, regions of localized low pressure correlated well with regions of attached, concentrated vorticity, especially around the ventral keels. Although other features of the carapace also affect flow patterns and pressure distributions in different ways, the integrated effects of the flows were consistent for all forms: they produce trimming self-correcting forces, which we measured directly using the force balance. These data together with previous work on smooth trunkfish indicate that body-induced vortical flows are a common mechanism that is probably significant for trim control in all species of tropical boxfishes.

SMOOTH SWIMMERS

Boxfishes are not exactly the sleek streamlined shape most people would have in mind when designing a fish; their angular bodies appear to be in danger of rotating when buffeted by turbulent waters. But watch them darting around in their tropical-reef homes and you'll notice that boxfishes are remarkably fast and stable swimmers. To discover how these odd-shaped creatures manage to swim so smoothly, Ian Bartol and colleagues put several boxfish species through their paces(p. 327).The ungainly appearance of these peculiar fishes is largely due to the rigid bony carapaces that cover their bodies. Carapaces produce slightly different body shapes in different boxfish species. To find out whether differently-shaped boxfishes use the same self-correcting mechanisms for stability while swimming, the team compared water flow along the carapaces of three boxfish species - the spotted boxfish, scrawled cowfish and buffalo trunkfish - using digital particle image velocimetry, pressure distribution measurements and force balance measurements. They found that the differently-shaped bodies of these three species directed water flow in very similar ways. Bartol explains that the ventral keels of these fishes are vortex generators, `producing flows around their bodies similar to those around the leading edges of delta-winged aircraft like the space shuttle.' The carapace surface pressures resulting from these flows contribute to forces on the carapace that allow the fish to make self-correcting movements while swimming, enabling them to swim in straight lines. Boxfishes' awkwardly-shaped bodies may also steady the fish while they hunt for coral-dwelling prey in their turbulent reef habitats.

Numerical Analysis of Asymmetric Vortex Breakdown in a Cylindrical Container Flow with a Rotating Disk

Numerical analysis has been performed for three-dimensional and time-depending vortex breakdown in an open and confined cylindrical container flow generated by a rotating disk. Vortex breakdown in swirling flows has been the sudject of much attention since it was first recognized in the tip of delta winged aircraft. Under certain conditions vortex flows undergo sudden structural changes near their rotation axis, called vortex breakdown, which are characterized by the existence of free stagnation point upstream of a region with reversed axial flow. Recently, experimental results suggest that the asymmetry of the vortex breakdown is found to be related to the existence of asymmetric flow separation on the container wall. Adding to this, it is important to reproduce such asymmetry vortex breakdown by numerical method because there is no report to predict an asymmetric vortex breakdown numerically. In the numerical calculation, boundary fitted coordinate system has been used for this flow in order to make the cause of asymmetry vortex clear. Calculated results of angular moment and flow vectors in circular cross section are compared with the experimental data in order to examine the validity of the presented numerical method. As a result of this analysis, it has been found out that the present method can reproduce vortex breakdown reasonably for an open and confined cylindrical container. Although the present method could not predict the separated flow near the wall which has been reported experimentally as the cause of asymmetry vortex generation, we have showed numerically that asymmetry vortex is also able to be produced by shifting rotating axis from center within the gap between rotating disk and cylindrical wall of experimental apparatus.

Comparison of Predicted and Measured Formation Flight Interference Effects

Results from a wind-tunnel test of two delta-wing aircraft in close proximity are presented and compared with predictions from a vortex lattice method. Large changes in lift, pitching moment, and rolling moment are found on the trail aircraft as it moves laterally relative to the lead aircraft. The magnitude of these changes is reduced as the trail aircraft moves vertically with respect to the lead aircraft. Lift-to-drag ratio of the trail aircraft is increased when the wing tips are slightly overlapped. Wake-induced lift is overpredicted slightly when the aircraft overlap in the spanwise direction. Wake-induced pitching and rolling moments are well predicted. A maximum induced drag reduction of 25% is measured on the trail aircraft, compared with a 40% predicted reduction. Three positional stability derivatives, change in lift and pitching moment with vertical position and change in rolling moment with lateral position, are studied. Predicted boundaries between stable and unstable regions were generally in good agreement with experimentally derived boundaries.

Conceptual Design Optimization of Fighter Trainer Aircraft with Double-delta Wing Configuration

Compared with a delta wing aircraft, the double-delta wing configuration has better aerodynamic performance at high angles of attack. An operational analysis was introduced as a method for evaluating training effectiveness of trainer aircraft. Approaches to the engineering estimation of aerodynamic characteristics for aircraft with a double-delta wing configuration were studied, and the procedures for determining aircraft performance indices formulated. Taking training effectiveness as the objective function and geometric parameters of the wing platform as design variables, through a numerical multivariate optimization arithmetic, the conceptual design optimization for a certain fighter trainer aircraft with double-delta wing configuration was carried out under the constraints of tactical and technical requirements and interrelated geometry. Agreement of a calculation example with engineering practice indicates that the optimal design has higher training effectiveness than the baseline design, and in addition, improves the structural force-bearing conditions.

Surface Pressure Estimates for Pitching Aircraft Model at High Angles-of-attack (Short Communication)

The surface pressure on a pitching delta wing aircraft is estimated from the normal force and the pitching moment characteristics. The pressure model is based on parametrising the surface pressure distribution on a simple delta wing. This model is useful as a first approximation of the load distribution on the aircraft wing. Leeward surface pressure distributions computed by this method are presented.

Development of an ROV operated both as towed and self-propulsive vehicle

A remote-operated vehicle (ROV) developed for investigations of the sea bottom over a wide area can be operated as both a towed and a self-propulsive vehicle. Called DELTA, the shape is similar to that of a delta-wing aircraft. The vehicle has two propellers and weight shift apparatus as actuators. The paper describes the design of the control system for the vehicle. Non-linear motion equations of the towing cable and DELTA are discussed, followed by a description of the LQI control system and robust control based on H ∞ control. Depth control performance was improved by the robust controller. Some successful experimental results are shown.

Generation of Comprehensive Longitudinal Aerodynamic Data Using Dynamic Wind-Tunnel Simulation

A novel method of generating comprehensive longitudinal aerodynamic data of aircraft using dynamic wind-tunnel simulation is presented. The method utilizes the motion and force responses of an aircraft model to control surface inputs to determine trim lift characteristics, longitudinal stability derivatives, and neutral point. In addition, large-amplitude lift and pitching moment responses characterizing the unsteady aerodynamic behavior are also generated using the same experimental setup. The new test method is demonstrated using a generic delta wing aircraft model with one degree of freedom in pitch. The model pitch attitude and lift force responses to elevon dynamic inputs are measured and used to deduce longitudinal aerodynamic data. Comparison of these results with static test data and Datcom estimates shows good agreement. Nomenclature CL = lift coefe cient, L/qS CLa = lift curve slope, rad 21

Use of neural networks in control of high-alpha maneuvers

A method is presented by which an appropriately constructed artificial neural network can be to predict the force and moment coefficients of a 70-deg sweep delta wing during a high-angle-of-attack excursion. The angle-of-attack time history is a sinusoidal motion from 0 to 90 deg and returning to 0 deg. Experimental data are used to train the network, and it is demonstrated that the network has indeed learned to model the behavior of the delta wing over a range of frequencies of this type of angle-of-atta ck time history. The longitudinal equations of motion for a delta wing aircraft are integrated for three sinusoidal angle-of-attack time histories using the predicted network aerodynamic data. This integration generates the longitudinal control deflection time histories required to produce these maneuvers. An exploration is then made as to whether a second artificial neural network can be trained as a neural stick gearing for such maneuvers. This is investigated by attempting to train a network to associate each required control deflection time history with a specified stick position schedule.

30th Lanchester Memorial Lecture - The wave drag of delta wings at supersonic speeds: a recent study

I felt indeed very honoured when I was invited to deliver the 30th Lanchester Memorial Lecture. I immediately started reading Frederick W. Lanchester's famous and impressive work ‘Aerodynamics’ published in 1907. It was very interesting to read but of course there was nothing to be found about delta wings at supersonic speeds, which I had offered to talk about, partly because I had studied this for the last 5–10 years and partly because Sweden had been developing delta winged military aircraft since 1948 or so. I also know of course that Great Britain had made impressive progress at the same time particularly Dietrich Küchemann and the group around him. I could therefore expect and fear to have a competent and critical audience to face.

A NEW SPECIMEN OF THE MOUNT DOOLING IRON METEORITE FROM MOUNT MANNING, WESTERN AUSTRALIA

A 701 kg iron meteorite has recently been discovered near the Mount Manning Range in Western Australia. The meteorite has a fan‐shaped or delta wing configuration, one side being smooth and slightly concave with a well‐defined fusion crust, whilst the other side is rough, convex and possesses numerous regmaglypts. It is probable that the meteorite pentrated much of the earth's atmosphere in an aerodynamically stable orientation, typical of the stalled attitude of delta wing aircraft. The meteorite is a member of Chemical Group 1C. A comparison of the chemical composition, surface features, microstructure and location of this meteorite with the Mount Dooling meteorite confirms that the find is a larger specimen of Mount Dooling. It is possible that other fragments of the Mount Dooling meteorite may be found in the Mount Manning Range region.

The Concorde Flight Test Programme

The object of this talk is to give you a situation report on the Concorde flight test programme and to indicate the progress made to date.Two aircraft have been engaged on the programme so far, the prototypes 001 and 002 (Fig. 1). The French base for Concorde flight test operations is at Toulouse and the British flight test base is at Fairford in Gloucestershire. The two prototypes will be joined in the flight test programme next year by the two pre-production aircraft, 01 and 02.As is well-known, Concorde is a slender delta wing aircraft and it may be appropriate at this stage to state some of the considerations that led to the choice of this configuration. By virtue of a large root chord, the delta wing can overcome all the disadvantages of lack of structural stiffness and lack of wing volume associated with thin highly swept wings and yet remain aerodynamically thin.

Elastic-mode effects on the dynamics of a delta-winged aircraft

An examination is made of some effects of rigid-body elastic-mode coupling on the longitudinal dynamics of a highly-flexible delta-winged aircraft. In particular, the influence of the coupling on the automatic control system's ability to provide preselected short-period dynamics is investigated. Also, a brief check is made of the sensitivity of the dynamics to small errors in elastic-mode shape. The coupling is shown to be quite severe, precluding the establishment of approximate control element gain values with only a rigid-body dynamic analysis. In addition, very high accuracy is needed in determining elastic-mode shapes, since the strong coupling renders the dynamics objectionably sensitive to small errors in elastic-mode shape data.

Effect of rib flexibility on the vibration modes of a delta-wing aircraft

Effect of rib flexibility on the vibration modes of a delta-wing aircraft