CoA. Aero Notes (1963-1975)

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Open Access
Development of a 3-component strain-gauge for use on the whirling arm
(College of Aeronautics, 1969-10) Holloway, W. G.; Kumar, P. E.; Osbourn, W.
This note covers the development of two strain-gauge balances for use on the Whirling Arm Facility of the College. The main requirements for this balance were:- (a) to withstand 700 lbs of sideload without it interfering with the lift, drag and pitching moment measurements, (b) to have a high sensitivity without too heavy a structure. The balance originally designed for this purpose proved to be unacceptable because of undue interference due to sideload and the non-repetitive nature of its calibration curves. With the information gained from this first balance a second balance of exceedingly simpler design, was manufactured and was found to give good calibration curves and sensitivity, with little interference from sideloads. A trouble free method of recording the signals from the strain-gauge bridges is being developed and should be operating within the near future. It concluded that a new model, with its c.g. lying on the transverse centre-line of the balance, will be needed if sideload interference is to be further reduced.
Open Access
Calibration of the flow in the channel of the whirling arm
(College of Aeronautics, 1969-10) Ashill, P. R.; Osbourn, E. W.
The calibration of the flow in the channel of the Whirling Arm is described and results for pitch yaw and wind speed are presented. These indicate that the flow is quite acceptable for the type of model tests envisaged.
Open Access
Some experiments with fluidic devices in aviation kerosene
(College of Aeronautics, 1969-04) Taylor, A. F.
Comparatively little has been published on ‘heavy current’ fluidic devices yet their advantages suggest that they have a place in aircraft fluid systems. As a first brief step towards assessing their value to the aircraft fuel system designer several devices were tested, singly and in pairs; in aviation kerosene. Some of the results from these experiments are given and discussed and it is considered that further work could produce some extremely worthwhile information.
Open Access
Frequency response of an aircraft as determined from transient flight tests using the fourier transformation method of analysis
(College of Aeronautics, 1967-05) Laurie-Lean, D. W.
The longitudinal dynamic response characteristics of a twin-engined propeller-driven aircraft determined from flight measurements are presented and compared with predictions based on theoretical studies. Transient responses to pilot-applied Pulsed notions of the elevator control surfaces were recorded. The transient data was then converted into frequency response form by means of the Fourier transformation and compared with predicted responses calculated from the basic equations of motion of the aircraft. In particular, detailed experience of the determination of frequency responses with regard to data sampling frequency and control input shape, using the Fourier transformation method, was obtained. Experimentally-determined transfer functions were used for the evaluation of the stability derivatives that have the greatest effect on the dynamic response of the aircraft. Some experience was also obtained with automatic data recording and processing equipment using magnetic tape, but no satisfactory frequency responses were obtained using this method. However, with further development and use of this equipment, the analysis of large quantities of flight data would be facilitated.
Open Access
The College of Aeronautics whirling arm initial development tests
(College of Aeronautics, 1967-05) Kumar, P. E.
The old Whirling Arm o-r the National Physical Laboratory has been re-erected at the College to provide a facility for the study of ground effect on wings, and other craft operating near the ground. The model is mounted on struts, which differ considerably from those used by N.P.L., and moves over an adjustable floor in a specially constructed Channel. This note covers the initial tests conducted on the arm towards making it a fully operational facility. It-is concluded that a full yaw-meter survey is necessary to define the air-flow existing in the channel, during operation of the arm, and that the instrumentation being used needs to be further developed.
Open Access
Compounded normal modes of free vibration of cantilever plates
(College of Aeronautics, 1967-04) Kirk, Colin L.
Experimental determination of the natural frequencies of a stiffened cantilever plate reveals the simultaneous excitation of two normal modes of vibration. Comparison is made between the experimental nodal pattern and the nodal pattern calculated by assuming characteristic beam functions for the vibration form of the plate.
Open Access
An advanced course in air transport engineering
(College of Aeronautics, 1966-08) Hyde, David
In 1963 K.G. Wilkinson, then Assistant Chief Engineer of British European Airways, emphasised the lack of formal engineering education in the maintenance and operation of aircraft. This report describes the nine-month postgraduate-level course in Air Transport Engineering which was started in October, 1964 at The College of Aeronautics, Cranfield, in order to help in satisfying this requirement.
Open Access
'Studies in stability and control analysis of airframes having nonlinear aerodynamic characteristics'
(College of Aeronautics, 1966-06) Christopher, P. A. T.
The problem of longitudinal stability and control of an airframe, having nonlinearity in its principal aerodynamic characteristics, is considered. It is shown that the equation describing the response in w, and thus the incidence, is a nonlinear differential equation of the fourth order. This equation, and its degenerate forms, is used as an example to demonstrate various nonlinear techniques and their shortcomings.
Open Access
'A design method for the dilution zones of gas turbine combustion chambers'
(College of Aeronautics, 1966-02) Lefebvre, Arthur Henry; Norster, E. R.
Introduction and Summary Perhaps the most important and, at the same time, most difficult Problem in the design and development of gas turbine combustion chambers, is that of achieving a satisfactory and consistent distribution of temperature in the efflux gases discharging into the turbine. In the past, experience has played a major role in the determination of dilution-zone geometry, and trial and error methods have of necessity been employed in developing the temperature-traverse quality of individual combustor designs to a satisfactory standard. Experimental investigations into dilution-zone performance carried out on actual chambers have led to useful empirical-design data, but very often it has proved difficult or impossible to distinguish the separate influences of all the variables involved. Thus although it is now generally accepted that a satisfactory temperature profile is dependent upon adequate penetration of the dilution jets, coupled with the correct number of jets to form sufficient localized mixing regions, the manner in which the total dilution-hole area is Utilized in terms of number and size of holes is still largely a matter of experience. Unfortunately, more basic studies of jet mixing do not usually yield results that can readily be expressed in the parameters which are most familiar to those concerned with combustion-chamber design. However, some of these investigations can provide a useful guide to the relationships involved. One such investigation resulted in the accumulation of a large amount of data on the mixing of cold jets when injected into hot streams under conditions where the temperature and velocity of the hot and cold streams, the injection-hole diameter, the angle of injection, and the mixing length could be accurately controlled and varied over a wide range. These data are used here, firstly to demonstrate a logical method of dilution zone design and, secondly, to provide quantitative data on the rate of exchange between temperature traverse quality and the relevant design parameters such as dilution zone length, dilution hole diameter and pressure loss factor. The effects of chamber inlet velocity and inlet velocity profile are also examined. Finally, it is proposed that the aerodynamic performance and stability of a combustion chamber may, for most practical purposes, be adequately described in terms of a parameter p which is the ratio of the flametube pressure loss to the overall pressure loss. Evidence is presented in
Open Access
Recent aeroelastic investigations at the College of Aeronautics
(College of Aeronautics, 1965-01) Johns, D. J.
Introduction Since the College of Aeronautics was founded in 1946 aeroelasticity has been the subject of much research by both students and staff in the Departments of Aircraft Design and Aerodynamics. It is not the present intention to review the entire period since 1946, but, rather, to concentrate on the period 1958/63 during which the author has been associated with the College. In this period aeroelastic research has been concentrated on four main themes, viz: (a) panel, membrane and wing instabilities; (b) investigations associated with the Morane-Saulnier M.S.760 'Paris'; (c) investigations on Design Project Studies, and (d) helicopter problems. The list of references covers the entire period up to 1963 and contains. references dealing with such related topics as flutter model construction and unsteady aerodynamics. These are included for the cake of completeness since such investigations often bear directly on the more specific problems of aeroelasticity. It should also be mentioned that there has been considerable research on vibration testing, impact loading, etc., but such references are not included. No detailed comparisons have been attempted between the research described and similar work done elsewhere - for these the appropriate references must be studied. It must be emphasised however that the research performed whilst being certainly worthwhile for its own sake also enables the students to become familiar with research methods - a primary aim of the College.
Open Access
On the flow along swept leading edges
(College of Aeronautics, 1965-10) Gaster, M.
Flight tests on the Handley Page suction wing showed that turbulence, generated at the wing root, can propagate along the leading edge and cause the whole flow to be turbulent. The flow on the attachment line of a swept wing was studied in a low speed wind tunnel with particular reference to the problem of turbulent contamination. The critical Reynolds number, R9L, of the attachment line boundary layer for the spanwise spread of turbulence was found to be about 100 for sweep angles in the range 40°- 60°. A device was developed to act as a barrier to the turbulent root flow 30 that a clean laminar flow could exist outboard. This device was shown to be effective up to an Re of at least 170. With the aid of this bump experiments were Possible on L laminar boundary layer at Reynolds numbers above the lower critical value. A spark was used to introduce spots of turbulence into the attachment line boundary layer and the propagation speeds of the leading and trailing edges were measured. The spots expanded, the leading edge moving faster than the trailing edge, at high Reynolds numbers, and contracted at low values. The behaviour of Tollmien-Schlichting waves was also investigated by exciting the flow with sound emanating from a small hole on the attachment line. Measurements of the perturbation phase and amplitude were made downstream of the source and although accurate values of wave length and propagation speed could be found no difficulties were experienced in evaluating the amplification ratio. Nevertheless, all small disturbances decayed at a sufficient distance from the source hole up to the highest Reynolds number tested of 170.
Open Access
Slender shapes offering minimum drag in free-molecular flow
(College of Aeronautics, 1965-09) Boyd, E. A.
Analytical expressions are obtained for the optimum shapes which minimise the drag of a slender axisymmetric body in free-molecular flow, provided the drag expression is simplified using the slenderness assumption. The problem is formulated as one of Mayer type in the calculus of variations and solved by using the Buler-Lagrange equations together with the transversality condition. The shapes derived are optimum subject to constraints on thickness, length, wetted area and volume. In the particular cases solved any two of these four quantities are fixed while the remaining two are free. The expression for the shape of the body when thickness is free is obtained in closed form.
Open Access
Measurement of the moments of inertia of a hawker siddeley dove Mk. 5 aircraft
(College of Aeronautics, 1965-04) Bradley, W. G.
This note describes the measurement of the moments of inertia in roll, pitch and yaw of a Hawker-Siddeley (de Havilland) Dove Mk. 5 aircraft, using a spring-restrained oscillation technique. Using the present equipment it did not prove possible to measure the product of inertia. Inertias mere measured in six different fuel conditions . The results are given in Tables I - V. A device was developed which measures the periods of oscillation of large structures, quicker and more accurately than hitherto possible. This device is described in the Appendix.
Open Access
An investigation of surface deformations occurring at the contact edges of statically loaded discs
(College of Aeronautics, 1964-09) Jones, D. A.; Reason, B. R.
An investigation has been carried out, using statically loaded steel and 'Perspex' discs, into elastic displacements occurring at the axial extremities of the Hertzian flat. By employing the technique of 'Photostress', together with optical magnification, it has been found possible to inspect in detail the disposition of strain around these points. Using a 'step grinding' technique a qualitative three-dimensional envelope of surface displacements has been constructed. The effect of these displacements is considered in relation to 'edge pitting' of discs.
Open Access
Theoretical aspects of gas turbine combustion performance
(College of Aeronautics, 1966-08) Lefebvre, A. H.
A correlating parameter for gas turbine combustion performance, based on a 'burning velocity' theory for primary zone combustion is derived using a more direct approach than that originally employed by Greenhough and Levebvre.1 The various applications of this parameter are discussed and it is shown that the shape of correlated performance curves is directly related to the combustion processes taking place in the various zones of the chamber. An alternative, more basic, theory is presented in which it is assumed that the low-pressure performance of a spray-type combustor is controlled by a balance between the separate effects of chemical reaction, fuel evaporation and mixing. It is argued that combustion efficiency is a function of p2 /M where x = 2.0, 1.7 or 1.0 depending upon whether the rate of heat release is governed by chemical reaction, fuel evaporation or mixing respectively. It is postulated that the amount by which values of x determined experimentally fall below 1.7 provides a useful practical indication of the extent to which mixing is intervening in the overall combustion process. At high pressures the mixing process predominates, x = 1, and it is shown that, for any given fuel-air ratio, the rate of heat release depends only on flame-tube geometry and mode of fuel injection, and is independent of chamber size, pressure loss factor and the operating conditions of pressure, temperature and velocity. The basic principles involved in the design of primary combustion zones for maximum volumetric heat release rate and maximum stability in terms of wide burning range are discussed.
Open Access
Tabulation of some layouts and virtual displacement fields in the theory of Michell optimum structures
(College of Aeronautics, 1964-02) Chan, H. S. Y.
In the theory of two-dimensional Michell optimum structures, there arises the problem of calculating the lines of principal stresses and the virtual displacements which are analogous to slip lines and velocities in plane plastic flow. A detailed analysis of the problem has been given in reference 1 and 2. Both analytical and numerical methods of calculation are given in reference 3.
Open Access
An investigation of vortex breakdown at Mach 2
(College of Aeronautics, 1963-11) Craven, A. H.; Alexander, A. J.
Wind tunnel tests have been made at M = 2 on a 75° swept delta wing in order to study the progressive breakdown of the leading edge vortices, which occurs at high incidence. The incidence at which vortex breakdown occurred at supersonic speeds was somewhat less than at low speeds, but the pattern of breakdown appeared to be similar, although the spiralling region of flow is much larger at supersonic speeds. Quite slender objects placed downstream of the wing had appreciable upstream effects, causing vortex breakdown to move upstream by as much as 20% of the root chord for the same incidence.
Open Access
Measurements of the moments of inertia of the Morane-Saulnier M.S.760 'PARIS' aircraft
(College of Aeronautics, 1963-11) Bradley, W. G.
This note describes the measurement of the moments of inertia, of a Morane-Saulnier M.S.760 'PARIS' aircraft. The moments of inertia in pitch, roll, and yaw were measured by the spring-constrained oscillation method. The cross-product of inertia and the inclination of the principal axis, were also determined by a variation of this method. Inertias were measured in three different fuel conditions. The results are given in Tables I - VI.
Open Access
A review of aerodynamic aspects of ram wing research
(College of Aeronautics, 1963-11) Ashill, P. R.
Theoretical and experimental research into the aerodynamics of ram wings is reviewed. The theories of two-dimensional and finite wings in ground effect are discussed and mention is made of the various experimental techniques available for ground effect tests. The possible shortcomings of each method are noted. In the final section it is concluded that there is a considerable need for research into the dynamic stability of ram wings. It is suggested that any dynamic tests should include measurements of the effect of the movement of the ground, as might be experienced when in transit. over a wavy sea.
Open Access
The teaching of aircraft design
(College of Aeronautics, 1964-03) Newell, A. F.; Howe, D.
Aircraft Design has been taught at the College of Aeronautics since 1946. The course is at postgraduate level and is of two years duration. In the first year the students are given three exercises in component design which aim to teach a logical approach and the fundamentals of the subject. During the second year each student works as a member of a team engaged in the design of a complete aircraft, which is chosen to be of a type currently being investigated by industry. The project aircraft invariably incorporates experimental features and the design work is therefore of the nature of research.