CoA. Reports

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Open Access
Addendum to type record. Avro "Lancaster" Mk.1 P. A. 474 Type record No. 1/P1/Lancaster. Investigation of boundary layer conditions on wings. M.O.S. Contract No.6/Aircraft/9807/C. B. 6(a)
(College of Aeronautics, 1956-01) College of Aeronautics, Department of Aircraft Design
Introduction The investigation involves, briefly, the mounting of a wing of 45' sweep-back in a dorsal position on the fuselage of 'Lancaster' P.A.474 such that wing incidence will be variable in flight over a 20 range, i.e. ± 100. A ‘partial chord’ technique for swept wings has been established by the College using a similar wing mounting configuration on an Avro 'Anson' Aircraft and this technique has been applied to the current investigation.
Open Access
The elastic stability of sandwich plates
(College of Aeronautics, 1949-03) Hunter-Tod, J. H.
This paper treats the elastic stability of supported rectangular plates of sandwich construction with isotropic and aeolotropic fillings under compression and shear loading. Formulae are developed for critical stresses for flat and curved panels in compression and flat panels in shear for the buckling of the whole panel, also for the wrinkling or local failure of the faces of flat panels in compression. A method is indicated for calculating the critical load of a cylinder in pure bending. It is established that for a wide range of conditions the critical stress for panels buckling in compression is independent of the form of the filling providing it is symmetrical about the normal; of the elastic constants of the filling only the transverse shear is of concern. As a result a simple extension of the equivalent plate theory of greatly improved accuracy is developed enabling the use of equations treating the plate as a whole.
Open Access
Measurement of the derivative 'ZW' for an oscillating aerofoil
(College of Aeronautics, 1950-06) Buchan, A. L.; Harris, K. D.
This report presents the results of experimental measurements of the damping derivative coefficient zw for constant chord rigid wings of various aspect ratios having sweepback angles of zero and 450. The results for the rectangular wings Flow substantial agreement with the unsteady aerofoil theory developed by TI.P. Jones $2) The dependence of Zvi upon frequency parameter is as given by theory and is much less than for two dimensional flow, but the numerical results are approximately 10 per cent below the theoretical. This is attributed to the large trailing edge angle 22° of the N.A.C.A. 0020 section used for the model aerofoils. The effect of sweepback is to decrease the numerical value of z , but this effect is much less pronounced, for low than for high aspect ratios. For aspect ratios 5 and 3 the numerical value is greater than would be given by a factor of proportionality equal to the cosine of the angle of sweepback. The measurements were corrected for tunnel interference by a method based on the theoretical work of 7.P.Jones.(1)
Open Access
Laplace plane GeoSAR feasibility study: summary of the group design project MSc in astronautics and space engineering 2014-15, Cranfield University
(Cranfield University, 2015-10-07) Hobbs, Stephen
Students of the MSc course in Astronautics and Space Engineering 2014-15 at Cranfield University performed a feasibility study of a geosynchronous radar mission for their group project. This report summarises the students' work and their findings. The report consists of an overview and discussion of the technical work of the project and a compilation of the executive summaries which describe the special contributions of each student. The mission studied is a geosynchronous synthetic aperture radar Earth observation mission using the Laplace orbit plane to reduce station-keeping propulsion demand. User applications are drawn from a wide range of sectors (agriculture, meteorology, geohazards, etc.) and are translated into system design requirements. The proposed mission design uses satellites with 13 m diameter antennas and a total electrical power demand of 6 kW. The mission seems feasible, although further study is recommended especially for the areas of _ orbit selection with respect to user requirements, imaging performance and orbit maintenance, _ mass budget (driven largely by the propulsion system), _ user requirements, imaging performance and operational imaging modes, _ opportunities for improved imaging with a constellation.
Open Access
Generic regional aircraft flying qualities for the approach and landing task
(Cranfield University, 1997-08) Gautrey, Jim
Many changes have occurred in the past 20 years in aircraft manufacture and development. New technologies have appeared, spanning the entire aircraft design environment, such as new production methods, new materials and new avionics systems. These new methods have been developed for two reasons. For military aircraft, they have arisen through the need to improve performance. However, for civil aircraft they have arisen through the need to reduce the overall cost. This report considers one aspect of these technologies for civil aircraft: fly-by-wire. This technology uses electrical signalling in place of conventional heavy mechanical control runs. In addition, flyby- wire generally permits improvements to be made in aircraft flying and handling qualities. This requirement has originated from two main sources; a need to make improvements in the light of an increasing amount of experience, and a requirement to cope with aerodynamic modifications which have been implemented to improve aerodynamic efficiency, but which have a deleterious effect on the aircraft's flying and handling qualities. Both of these adverse effects have come about from a desire to reduce costs for the end aircraft user, i.e. the airlines. The aircraft used for these evaluations is a Generic Regional Aircraft, of about 100 seats and a weight of 90,000 lbs. Only a limited portion of the flight envelope was considered since these evaluations primarily concentrate on the approach and landing flight phase. These evaluations are being carried out as part of a joint Avro International Aerospace — Cranfield University Engineering Doctorate programme researching advanced flight control system design for a Generic Regional Aircraft. The overall aim of this programme is to produce a control law design which gives aircraft in question excellent handling qualities. The evaluations described here comprise the first in a series of three planned studies, and consider solely the approach and landing flight phase.
Open Access
On a theory of sandwich construction
(College of Aeronautics, 1948-03) Hemp, W. S.
The theory of sandwich construction developed in this paper proceeds from the simple assumption that the filling has only transverse direct and shear stiffnesses, corresponding to its functional requirements (§1). This supposition permits integration of the equilibrium equations for the filling (§2). The resulting integrals are used to study the compression buckling of a flat sandwich plate (§3). The formulae obtained are complex, but may be simplified in practical cases (§4). A second approach to sandwich problems is made in §5, where a theory of "bending" of plates is outlined. This generalises the usual theory, making allowance for flexibility in sheer. This approach is applied to overall compression buckling of a plate in §6, and agreement with the previous calculations is found. This suggests the possibility of calculating buckling loads for curved sandwich shells. A simple example, the symmetrical buckling of a circular cylinder in compression is worked out in §7. The theory developed would seem applicable to all cases of buckling of not too short a wave length (§8).
Open Access
Note on the limits to the local Mach number on an aerofoil in subsonic flow
(College of Aeronautics, 1948-10) Young, A. D.
Open Access
Note on the limits to the local Mach number on an aerofoil in subsonic flow
(College of Aeronautics, 1948-04) Young, A. D.
It has been noted in some experiments that the local Mach number just ahead of a shock wave on an aerofoil in subsonic flow is limited, values of the limit of the order of 1.4 are usually quoted. This note presents two lines of thought indicating how such a limit may arise. The first starts with the observation that the pressure after the shock will not be higher than the rain stream pressure. Fig.1 shows the calculated relation between local Mach number ahead of the shock (M„ 1 ), shock inclination (S), mainstream Mach number (M1) and pressure coefficient just aft of the shock. • (Cp) It is noted that, for given M1 , Cp and .5 ,two shocks are possible in general, a strong one for which Ms , > 1.48, and a weak one for which MS1 < 1.48, and it is argued that the latter is the more likely. The second approach is based on the fact that a relation between stream deflection (8) and Mach number for the flow in the limited supersonics regions on a number of aerofoils has been derived from some. experimental data. Further analysis of experimental data is required before this relation can be accepted as general. If it is accepted, however, then it indicates that the Mach numbers increase above unity for a given deflection is about one-third of that given by simple wave theory (Fig.2). An analysis of the possible deflections on aerofoils of various thicknesses (Fig.3) then indicates that deflections corresponding to local Mach numbers of the order of 1,5 or higher are unlikely except at incidences of the order of5 ° or more, and may then be more likely for thick wings than for thin wings. Flow breakaway will make the attainment of such high local Mach numbers less likely.
Open Access
Temperature effects on material characteristics
(College of Aeronautics, 1960-08) Murphy, A. J.; Kennedy, A. J.
Some of the physical properties of the main elements of interest in high temperature technology are reviewed. Some general trends emerge when these properties are viewed as a function of melting point, but there are a few notable exceptions. Titanium, zirconium, niobium and tantalum all have disappointingly low moduli; chromium is excellent in many ways, but has a limited ductility at lower temperatures; molybdenum oxidises catastrophically above about 700° C, and niobium suffers from severe oxygen embrittlement. Beryllium and carbon (in the graphitic form) both stand out as exceptional materials, both have very low densities, beryllium a very high modulus but an unfortunately low ductility, while graphite has a relatively low strength at the lower temperatures, although at temperatures of 2000° C and above it emerges as a quite exceptional (and probably as the ultimate) high temperature material. Some of the fundamental factors involved in high temperature material development are examined, in the light, particularly, of past progress with the nickel alloys. If a similar progress can be achieved with other base elements then a considerable margin still remains to be exploited. Protection from oxidation at high temperatures is evidently a factor of major concern, not only with metals, but with graphite also. Successful coatings are therefore of high importance and the questions they raise, such as bonding, differential thermal expansion, and so on, represent aspects of an even wider class covered by the term “composite structures". Such structures appear to offer the only serious solution to many high temperature requirements, and their design, construction and utilization has created a whole series of new exercises in materials assessment. Matters have become so complex, that a very radical and fundamental reassessment is required if we are to change, in any very significant way, the wasteful and ad hoc methods which characterise so much of present-day materials engineering.
Open Access
Boundary layers with suction and injection a review of published work on skin friction
(College of Aeronautics, 1960-09) Craven, A. H.
Available data on the effects of suction and injection on skin friction are summarised and compared. It is shown that injection into a turbulent boundary layer can produce a skin friction coefficient lower than the laminar value at trio same Reynolds number on an impermeable plate.
Open Access
Skin friction in the laminar boundary layer in compressible flow
(College of Aeronautics, 1948) Young, A. D.
Open Access
Multi-objective Tabu Search 2: first technical report
(Cranfield University, 2015-06) Tsotskas, Christos; Kipouros, Timoleon; Savill, Mark A.
The purpose of this document is to describe Multi-Objective Tabu Search 2 (MOTS2), which is a native mutli-objective optimiser. It has been developed to tackle a variety of real-world problems of engineering interest. The design and implementation are presented, followed by verification, validation and user instructions. At a glance, it involves introduction to the algorithm, explains configuration settings and structure, and results interpretation. Then, the optimiser is tested against a series of mathematical test functions in order to verify its functionality. The main goal is to demonstrate and assess the performance and applicability of the optimiser. The next step is to use MOTS2 on a real-world case, where the performance of optimising a 2D airfoil is validated and illustrated.
Open Access
Ignoration of distortional co-ordinates in the theory of stability and control
(College of Aeronautics, 1946-12) Duncan, W. J.
Gates and Lyon have proposed to treat theoretically the stability and control of deformable aircraft by a method in which the distortion co-ordinates are ignored and the influence of distortion is allowed for by suitable modifications of the derivatives and other coefficients. in the 'present paper an exact method for eliminating the distortion co-ordinates is given and the conditions in which the true eliminant conforms with the simplification of Gates and Lyon are examined. In general the simplification is not justified mathematically, but in certain circumstances it provides an acceptable approximation. it will not be practically valid unless the structural distortions occur so relatively slowly that the associated inertia forces are negligible, i.e. the distortions must be quasi-static.
Open Access
Experimental investigation on a cropped delta wing with edge blowing
(College of Aeronautics, 1963-06) Alexander, A. J.
Low speed wind tunnel tests have been made on a 70° cropped delta wing with edge blowing both in the plane of the wing and at a downward deflection angle of 30°. The tests include six-component force and moment measurements, the distribution of static pressure at four chordwise stations, and quantitative measurements of the flow in the leading edge vortex. At a constant incidence, blowing increases the size and strength of the leading edge vortices and moves the vortex cores outwards and upwards. Blowing also tends to suppress the secondary separation due to the entrainment effect of the jet. Blowing from the streamwise tips and trailing edge was relatively ineffective and most of the tests were made with blowing from the swept leading edges only, with tips and trailing edge sealed.
Open Access
Experiments on a delta wing using leading edge blowing to remove the secondary separation
(College of Aeronautics, 1963-05) Alexander, A. J.
It is found that the entrainment effect of a thin jet emerging from the leading edge of a delta wing is sufficient to remove the secondary separation. The minimum jet momentum required is small, but increases with incidence. Tests made without blowing, and with minimal blowing, include balance measurements, pressure plotting and tuft studies, over the range of incidence α = 0[degrees] - 20[degrees] . It is concluded that the presence of the secondary separation does not affect the lift or the vortex height appreciably, but is at least partly responsible for the large discrepancy between theory and experiment with regard to the spanwise position of the vortex.
Open Access
Statistical parameters in planning aero-engine production
(College of Aeronautics, 1963-02) Atkinson, A. H.; Harris, J. T.
This report considers the estimation of statistical parameters and their application to production planning in the aero-engine industry. A similar pattern of behaviour to that already recognised as existing in the airframe industry is found to operate, though there are indications of quantitative differences. The build-up time to the planned peak rate of production in a particular situation is found to be about eighteen months but with variation between firms. The reduction in operator performance time, which occurs with repetition during the build-up period and afterwards, is discovered to be present in machining as well as assembly, but to a lesser extent. The logarithmic function generally descriptive of such a tendency is found to fit the actual man-hour content values rather than the cumulative average ones. The relationship between the logistic of output and the logarithmic function is established and made use of to estimate labour requirements from the commencement of production onwards. In addition to the above consideration of production variables, examples are given of the use of engine performance ratings to estimate costs. Finally, because of the importance of planning to productivity, a typical production programme has been included.
Open Access
On the application of boundary layer control to a slender wing supersonic airliner cruising at M = 2.2
(College of Aeronautics, 1962-04) Craven, A. H.; Hopkins, H. L.
The use of suction or injection to reduce the drag of a supersonic airliner is considered. It is shown that injection gives no reduction in operating costs. With suction applied to an M =2.2 aircraft on the London - New York route, the basic operating cost of 13.30d per short ton statute mile is expected to be reduced by 0.5d for the same payload assuming no change in configuration. If the theoretical maximum skin friction reduction could be obtained the payload could be increased by 4750 lb. and the direct operating cost could be reduced to 10.63d per short ton statute mile.
Open Access
The effect of curvature on the stress concentrations around holes in shells
(College of Aeronautics, 1962-05) Houghton, D. S.; Rothwell, A.
An experimental investigation has been carried out to investigate the effect of curvature on the stress concentrations around holes in shell structures. Two methods have been employed: - (I) Araldite cylinders, containing holes of various shapes, subjected to axial tension, internal pressure and torsion were examined by the photoelastic frozen stress technique. (2) Aluminium alloy curved panels and hemispheres were used in conjunction with miniature electrical strain gauges. The results are compared with the theoretical solutions and suggest that the curvature effect can be significant, particularly for the case of shear or biaxial loading.
Open Access
The compressible laminar boundary layer with foreign gas injection
(College of Aeronautics, 1962-01) Craven, A. H.
The equations of the steady compressible two-dimensional laminar boundary layer with foreign gas injection through a porous wall are solved, using an extended form of Lighthill's approximate method, for arbitrary main stream pressure gradient, wall temperature and injection velocity. The wall shear stress and heat transfer rate are obtained in the form of equations suitable for iteration. It is shown that substantial reductions in skin friction and heat transfer rate can be obtained by the injection of a light gas instead of air.
Open Access
The analysis of reinforced circular and elliptical cutouts under various loading conditions
(College of Aeronautics, 1961-07) Houghton, D. S.; Rothwell, A.
The effect of reinforced cutouts in a plane sheet under various loading conditions is considered, and a number of experimental results are given for circular and elliptical cutouts with a uniform plate reinforcement, subjected to various systems of biaxial tension and pure shear. These experiments were conducted using a plane loading frame, and the results are compared with the theoretical plane stress solution. For the circular cutout the effect of neglecting the bending stiffness of the reinforcement is considered. Some additional experiments were carried oUt on a 60 in. diameter pressurised cylinder containing an elliptical hole reinforced according •to Mansfield's neutral hole theory. The strains in the sheet in the region of the neutral hole are .compared with the corresponding strains in the uncut sheet. The experimental results obtained generally show a good agreement with the theory.