Showing papers by "Vaughn College of Aeronautics and Technology published in 1996"

Automatic liquid crystal thermography for transient heat transfer measurements in hypersonic flow

Abstract: A technique has been developed to measure surface heat transfer on windtunnel models in hypersonic flow based on the colour response of encapsulated thermochromic liquid crystals. The method supplies results of a superior spatial resolution at experimental uncertainties comparable to traditional methods. The approach is different from other liquid crystal applications in several key areas. It combines the calibration of the liquid crystal coating with the actual mesurement and therefore allows for an efficient experiment. The method is automated in most steps involved. Results are shown for the flow over an axisymmetric compression corner at Mach 5 and compared with surface thermocouple measurements.

Quasi-Steady Structures in the Two-Dimensional Initiation of Detonations

Abstract: Two regimes of reflected-shock-induced ignition of explosive gases are known to exist, referred to as strong and weak (or mild) ignition. Experimental studies have shown that the former is manifested by the early appearance of a plane shock wave of chemical activity near the back wall of the shock tube and the whole strong-ignition process is a nominally one-dimensional phenomenon. When small distinct regions of increased chemical activity exist near the wall from which the incident wave reflects, localized thermal runaway leads directly to detonations that are multidimensional in character; this is the situation in what is called mild ignition. Although both strong and weak modes have been studied experimentally (in the 1960s and 1970s) and visualized by means of streak-camera and stroboscopic-laser-schlieren techniques, up to now most studies which use the methods of computational fluid dynamics have concentrated on the one-dimensional case. Previous analytical/numerical studies have shown how the three-dimensional structure of detonations can appear as a consequence of the instability of an initially ideal planar Zeldovich-von Neumann-Doring detonation. The latter is subject to some small-amplitude disturbances, and subsequent events lead to the eventual appearance of triple points along the front. In this paper some of the transient phenomena that take place in the first few microseconds after incident shock reflection from the closed end of a shock-tube are examined by means of a number of numerical simulations. A small hot-spot is assumed to exist in one of the corners between the reflective end plate and the walls of the shock tube. Evolution of the flow is followed, from the time of incident shock reflection, through the genesis of curved reaction waves, on to the appearance of an `explosion within the explosion' ending with the creation of a nearly plane detonation wave and its gradual contamination by triple-shock-wave features. The events portrayed in this way are recognizable stages in the story that the experimental studies revealed 25 years ago. The all-important region between reflective wall and reflected shock, within which intense chemical activity begins and which, because of its small geometric extent, is not well resolved in the schlieren photographs, is here replaced by high resolution images of the primitive variables of the flow. The wealth of data provided by these simulations is subsequently correlated to reveal the existence of quasi-steady structures in the form of reaction waves (specifically, weak detonations and fast flames or deflagrations), which previously have been shown to be part of the evolutionary processes only in strictly one-dimensional phenomena.

Woodland area estimation by spectral mixing: applying a goodness-of-fit solution method

Abstract: A goodness-of-fit solution method for spectral mixture modelling is applied to Landsat Multi-Spectral Scanner (MSS) data. The modelled pixel proportions are compared against independent validation data obtained by aerial photographic interpretation. A goodness-of-fit parameter is found to provide an objective means of investigating the impact of both the number of ground-cover components and spatial averaging on the mixture solution.

Aircraft parameter identification using an estimation-before-modelling technique

Abstract: Abstract This paper describes a comparative evaluation of two data smoothing algorithms for use in a two step estimation-beforemodelling procedure for aircraft parameter identification. A simple fixed lag smoother is compared with the usual, and more complex, modified-Bryson-Frazier smoother in the first, state estimation, step of the aircraft parameter identification procedure. The comparison is illustrated by application to the analysis of the Dutch Roll motion of the Embraer EMB-312 Tucano. Both algorithms were found to give results of comparable accuracy although the fixed lag smoother is computationally more efficient. It was concluded that the fixed lag smoother algorithm is an acceptable alternative to the modified-Bryson-Frazier algorithm in aircraft parameter identification applications.

Research into the factors influencing survival in aircraft accidents

Abstract: The factors influencing survival in aircraft accidents can be classified into configurational, environmental, procedural or behavioural. New methodologies which have been developed in order to simulate emergency behaviour are introduced. A series of experimental programmes in which the new behavioural techniques are applied to configurational, environmental and procedural changes in the cabin are described. The results suggest that the techniques provide the behavioural and statistical data required for the assessment of design options or safety procedures for use in aircraft emergencies.

Hypersonic control flap effectiveness

Abstract: The effects of flap deflection, configuration incidence and leading edge bluntness on boundary layer separation and transition have been studied experimentally. A quasi two-dimensional flat plate equipped with a full span trailing edge control flap has been employed for these tests. The studies have been carried out in a hypersonic gun tunnel at M∞ = 8·2 and Re∞/cm = 9·0 × 104. The flap deflection angles studied were in the range 0° ≤ β ≤ 30°. The incidence range was from zero to α = 10° (positive α is nose down). Leading edge bluntness effects were simulated by the introduction of a hemi-cylindrical leading edge. The flow structure was studied using high speed Schlieren photography as well as surface pressure and heat transfer measurements. Liquid crystals were employed to study the threedimensionality of the flow structure for selected configurations. Analytical theories have been developed to estimate the flap pressure and heat transfer levels for the sharp and blunt configurations. These are compared against experimental measurements.

Reliability, maintainability and development cost implications of variable camber wings

Abstract: A computer assisted conceptual aircraft design methodology (CACAD) has been developed to size turbofan powered transport aircraft. New modules for predicting the maintenance costs of each airframe system and subsection of structure, were developed and incorporated into CACAD. Many aspects of variable camber wing technology (VCW) were modelled. These included different types of drag saving due to chordwise, as well as spanwise camber variation. Models were also derived for mass, maintenance cost, and extra development cost increments for wing trailing edge devices, flight control, and hydraulic systems. These were incorporated into CACAD, and then a multidisciplinary trade-off study resulted in predicted savings of up to 3·5% in direct operating cost (DOC). The technology was evaluated for DOC improvement against a number of existing, future, and derivative aircraft, under different sensitivity conditions. Reliability, maintainability, and development (R, M&D) predictions were shown to be decisive in determining the feasibility of VCW technology. The study showed that long range, low to medium capacity, derivative aircraft are the most suitable applications for VCW technology.

Oct-tree terrain modelling methods for terrain reference navigation systems

Abstract: This paper describes the use of oct-trees to represent digitised terrain elevation data (DTED) in terrain reference navigation (TRN) systems. Oct-trees provide a regular method to represent digitised terrain data where the level of detail of the terrain is encoded in the tree structure. The use of oct-trees also provides a basis for a significant reduction in the on-line storage requirement for DT-EDs. A method of encoding using Morton ordering is introduced which allows DTEDs to be accessed as oct-trees and quad-trees where the tree structures are represented as pointerless structures. Algorithms to construct and access terrain oct-trees are presented which form a set of access primitives for tree operations required in TRN applications. The paper concludes with examples to illustrate the efficiency of the methods described in the paper for two DTEDs, in terms of performance of the tree access operations and reductions in storage.

The Qualification of Safety Critical Structures by Finite Element Analytical Methods

Abstract: The paper introduces the concept of certifying or qualifying structures in a safety critical situation using the finite element method. Error control and error treatment methods for this purpose are discussed together with the associated role of testing. The underlying methodology follows the principles laid down in the SAFESA (SAFE Structural Analysis) method which is described in outline.

An experimental investigation into yaw control at high alpha on a chined forebody using slot blowing

Abstract: Abstract Results are presented from low-speed windtunnel tests on an isolated generic chined forebody with pneumatic methods of yaw control at high alpha. Measurements of forces and moments were made on the forebody at angles of attack in the range 0° ≤ ɑ ≤ 60°. Slot blowing through the chine edge at various angles and upper surface tangential blowing have been compared, and optimum configurations have been identified. The effects of forebody cross-sectional shape have also been investigated and have been found to be highly critical in determining blowing effectiveness. Limited flowfield visualisation is also presented in order to gain some understanding of the flow field characteristics.

Turning performance in a moving airstream

Abstract: This paper develops the theory of turning flight in a moving air mass to explain some of the problems encountered in making downwind turns, particularly in light aircraft. Although the basic mechanics of flight and aerodynamics of the aircraft are well understood, the methods used by the pilot to control the aircraft in turning flight are less well established and can be critical in maintaining a safe flight path. In this paper the effect of the control strategy likely to be employed by a pilot flying close to the ground is used to show how the energy loss during a turn can lead to an unsafe flight path.

The structural design of an advanced short take‐off vertical landing combat aircraft — part 1

Abstract: Reports on the MSc group design project of students at the College of Aeronautics, aerospace vehicle design in 1995. The students worked on advanced short take‐off and vertical landing of a combat aircraft. Details the project showing aircraft dimensions and design. Full assessment of the results is pending, but outlines a number of problems faced by the students.

Natural formulation of the random choice method for two–dimensional inert high–speed flow fields

Abstract: The random choice method has now been shown to be successfully extendible from the original one-dimensional unsteady formulation to inert high-speed flow fields which are steady and two-dimensional using Cartesian, axisymmetric and Lagrangian formulations. This paper deals with the description of a new implementation of the random choice method formulated for natural co-ordinates based on streamlines and normals. Comparisons between theoretical and computed results for several different physical configurations are presented.