Browsing by Author "Johns, D. J."
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Item Open Access An analysis of an unstiffened cylindrical shell subjected to internal pressure and axial loading(College of Aeronautics, 1961-03) Houghton, D. S.; Johns, D. J.General equations are obtained for the deflections and stresses in long thin unreinforced cylinders, which are subjected to an axial load and internal pressure. By making suitable simplifying assumptions, results are presented which show the variation of the structural weight parameter with the structural axial loading index, for both pressurised and unpressurised shells. An allowance is made for the effects of shell initial eccentricities on the buckling stress coefficient K, in accordance with R. Ae.S. data sheet 04.01.01. Extreme cases are considered, in which the shell is assumed to be either fully effective (K = 0.6). 0:. completely ineffective (K = 0), in resisting axial compressive loads. For this latter case, complete pressure stabilisation of the shell is considered, and it is shown that the weight penalty involved in using this design philosophy, is negligible for a certain range of the structural loading index. A simple modification to the analysis for this case, i.e. K = 0, is made to allow for the effect of an external longitudinal bending moment.Item Open Access Buckling due to thermal stress of cylindrical shells subjected to axial temperature distributions(College of Aeronautics, 1961-05) Johns, D. J.; Houghton, D. S.; Webber, J. P. H.Thermal stress distributions in uniform circular cylindrical shells due to axial temperature distributions are investigated. The discontinuity effect due to the presence of a cooler stiffening bulkhead is considered, and the possibility of thermal buckling of the shell due to the circumferential discontinuity stress is examined. The buckling analysis is based on Donnell's shell equation, and particular attention is given to shells having clamped edges. An experimental investigation of this buckling problem is discussed, and the results obtained are seen to agree reasonably well with theory.Item Open Access The flutter of thin, plane, elliptic panels(College of Aeronautics, 1963-01) Johns, D. J.The effect of various parameters on the flutter of elliptic panels is studied by simple theoretical analyses. For clamped edge panels, compressive membrane stresses are shown to have destabilising effects. Structural damping is, in general, destabilising, except for very low values of the ratio of structural and aerodynamic damping coefficients. The addition of a concentrated mass may also have a destabilising effect, depending upon the position of the added mass. The effect of sweepback is stabilising or destabilising, depending on whether the panel aspect ratio is less than, or greater than, unity. The effect of variations in the edge conditions is shown for the case of circular panels where the difference between simply supported and fully clamped edges corresponds to a difference of 20% in critical panel thickness.Item Open Access Linear buckling of an axially reinforced pressurised cylinder(College of Aeronautics, 1960-10) Houghton, D. S.; Johns, D. J.An analysis is presented using small deflection theory for the buckling of a pressurised, axially reinforced cylinder, which is subjected to axial compression. Various approximations to the analysis are discussed and some results are presented which show the effects of internal pressure and various structural parameters on both panel buckling and overall buckling.Item Open Access Optimum design of a multicell box subjected to a given bending moment and temperature distribution(College of Aeronautics, 1958-04) Johns, D. J.The optimum geometry of a multicell box of given depth, under a given bending moment and temperature distribution, is obtained. The method is general enough to permit the skin thickness to be either specified, e.g. by stiffness requirements, or not.Item 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.Item Open Access Some design problems of thin shell structures(College of Aeronautics, 1961-09) Johns, D. J.Simplified analyses are presented which illustrate some of the design problems of typical space vehicle structures, with the emphasis on thin, circular cylindrical shells. Amongst the problems considered are panel flutter, thermal buckling and buckling under axial compression.Item Open Access Supersonic flutter of cylindrical shells(College of Aeronautics, 1960-06) Johns, D. J.The general theories of thin elastic cylindrical shells as derived by Love and Novozhilov are compared and then used in a simple binary flutter analysis which permits the existence of both axial and circumferential waves of deformation. Linear piston theory has been used and the results obtained indicate that the axi-symmetric mode of deformation is the most critical. Comparisons are then made with other published results and apparent inconsistencies in those papers are found to arise from certain assumptions made in the deformation equations used. In a further axisymmetric mode analysis the use of a travelling wave form of radial deflection is shown to give similar results as standing wave forms when applied to a shell of finite length.Item Open Access A theoretical and experimental investigation of tail unit flutter on the M.S. 760 'Paris'(College of Aeronautics, 1962) Mitchell, C. G. B.; Johns, D. J.After an incident which, it was suspected, was due to symmetric elevator flutter, had occurred on the Morane-Saulnier 760 operated by the College of Aeronautics, Cranfield, a theoretical and experimental investigation of the aircraft's flutter characteristics was undertaken. The theoretical investigation consisted of binary and ternary symmetric flutter calculations with and without the control circuit included. These showed the aircraft to be liable to flutter for mass distributions similar to that which existed at the time of the incident. The experimental work consisted of flight flutter tests using control jerk excitation with both film and magnetic tape recording. These showed that the aircraft as supplied by the makers had a critical speed for symmetric elevator flutter of 380 knots, but that this could be lowered to 240 knots by the installation of a stick force indicator combined with unfavourable distributions of fuel load and fuselage mass distribution. The tests also showed the tail unit mode excited by rudder kicks to be safe, but as doubt exists as to whether this mode is the most critical antisymmetric one, further work is needed on this aspect. A 75 c. p. s. rudder buzz was encountered that was not caused by compressibility effects. As a result of this investigation the elevator mass balance was increased and the aircraft proved to be free from elevator flutter up to at least 400 knots. A general conclusion reached in this investigation was that static balancing of control surfaces should include the effect of components of the control circuit attached to them if those components contribute to the inertia couplings induced by vibration in other elastic modes.Item Open Access Thermal stresses in thin cylindrical shells, stiffened by plane bulkheads, for arbitrary temperature distributions(College of Aeronautics, 1958-07) Johns, D. J.A study has been made of the thermal stresses reulting near the joint of a cylinder and internal bulkhead due to arbitrary temperature distributions in the configuration and to the consequent compatability forces and moments at the joint. The method is general enough to permit the inclusion of joint thermal resistance but certain limitations are placed on the form of the axial temperature distribution in the cylinder. An approximate method to determine the transient temperatures for completely general heating programmes is also proposed.