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An examination of the methods of mixing peroxides into polythene to form polymer networks
No full textIn the production of peroxide cross-linked polyethylenes it is
customary to introduce the organic peroxide by the hot milling process.
Inevitably some peroxide is lost by volatilization and the process is,
therefore, difficult to standardize.
In this paper, the efficiencies of the processes in which the
peroxide is introduced by wet and dry powder mixing are compared with
the efficiency of the normal method of mill mixing. It is shown that
in both the wet and dry processes the loss of peroxide is avoided, but
that the dry mixed material shows inhomogeneities in the cross-linked
state
Diffraction gratings - their principles and applications to machine tools
No full textThe use of diffraction gratings as measuring elements on machine
tools is nowadays an accepted procedure. Part I of this paper therefore
sets out to give a brief understanding of the principles of diffraction
gratings, and the ways in which they have been utilised commercially.
In addition, comparisons are made with other reference elements and some
consideration is given to manufacturing techniques.
Part II of the paper deals in more detail with the pure theory of
crossed diffraction gratings
Investigation into the possibility of applying lubrication theory to the selection of optimum clearance fits for plain hydrodynamically lubricated bearings
No full textBS1916 limits and fits for engineering is based on ISA bulletin 25
which was first issued in 1921 and designed for use with the metric system.
It provides a wide range of tolerances for holes and shafts from which it
is possible by suitable selection to satisfy a wide range of engineering
requirements.
The basic principle underlying the system is the allocation of letters
to signify the magnitude of the displacement of that part of the tolerance
zone which is nearest to the basic size and a number to indicate the
magnitude of the tolerance. Capital letters are used for holes, small
letters for shafts. The numbers referred to as fundamental tolerances
are common to holes and shafts.
In applying the system to inch sizes care was taken to ensure that
fit combinations (H6/k4) would provide the same type of fit in the inch
system as was established in the metric system throughout the whole of the
Size range. It was also recommended that a unilateral hole basis be
adopted in which the hole is the standard member and the tolerance specified
as a value from nominal to plus an amount determined.by the number signifying
the magnitude of the tolerance. Different types of fit are obtained by selecting from the standard shafts available the one whose fundamental deviation from basic size is considered to be the most suitable and
:allocating to it a suitable standard tolerance
When ISA bulletin 25 was issued great care was taken in selecting
the disposition of the sizes allocated to standard shafts so that when one
standard shaft was used with one standard hole it would provide a fit which
-mould be functionally similar throughout the complete range of sizes.
The decision of I.S.O. and B.S.I. to extend the size range from 20 inches
to 200 inches caused reasonable doubts to exist about the reliability of
this simple rule that one fit combination would be functionally similar
throughout the whole of the extended size range. As this problem was
examined in more detail cases were found where the above rule was not
satisfactory over the extended or the smaller size range covered by the
original standard (0.040” to 20”).
In considering the possibility of applying theoretical analysis to
this problem it was clear that the most difficult section was that concerned
with the selection of clearance fits for hydrodynamically lubricated plain
'beatings. The present paper is a preliminary survey into this problem and
the detailed analysis is restricted to the application of lubrication theory
to the selection of what appear to be optimum clearance fits for hydrodynamically
lubricated bearings and the means that may be used for comparing
these results with the recommendations of I.S.A. bulletin 25 and BS1916.
Figure 1 is a simplified representation of a plain bearing operating under conditions of hydrodynamic lubrication
Investigating the PIO-susceptibility of the F-4C
No full textPilot Induced Oscillations are still a serious safety problem in aviation. Especially in regard of the
continuous evolution of modern fly-by-wire flight control systems, PIOs seem to occur more
frequently. Although test pilots, flight test engineers and handling qualities specialists have dealt with
this phenomenon over the past three decades, it still is difficult to apprehend and all too often it
catches pilots as well as engineers by surprise. This report gives a brief overview of the mechanisms
and the contributing factors in pilot behaviour, in aircraft dynamics and in the environment that lead to
a PIO-condition.
A great effort has been made over the years to develop reliable tools, analytically as well as
experimentally, which are capable of identifying PIO-prone and PIO-resistant configurations. Five of
the most acknowledged, state-of-the-art frequency and time domain criteria for evaluating PIO-susceptibility, based on linear aircraft dynamics, are introduced and compared. These are the Neal and
Smith Criterion (original definition), the Bandwidth/Pitch-Rate Overshoot Criterion, the Smith-Geddes Criterion, the Gibson Phase Rate Criterion and the Gibson Dropback Criterion. These Criteria
are applied to two selected flight conditions of a linearised, small perturbations model of the F-4C (Phantom II) aircraft, based on the longitudinal equations of motion. The responses of the
mathematical aircraft model, which is developed for this purpose using the state space method, are
examined and verified with the MATLAB software package and the applicability/suitability of the
criteria for this configuration is assessed. Finally, similarities and differences in the application of the
criteria, the utilised criterion parameters and the obtained results are discussed. The objective of this
exercise is to provide a consolidated review of current criteria for longitudinal PIO-evaluation.Cranfield Universit
Control jet-slender body performance characteristics at hypersonic speeds
No full textThe jet control effectiveness of a 5 deg semi-angle cone has been tested at hypersonic speeds. The study has been
carried out in the Cranfield hypersonic gun tunnel facility at a Mach number of 8.2, and a Reynolds number based on
base diameter of 3.788 x 10(5). Under those conditions, the initial boundary layer in the absence of the jet was laminar.
The jet was injected normal to the cone surface at sonic speed. Both sharp and blunted cones were used. The
Jet/flowfield interaction, including boundary-layer separation and its influence upon aerodynamic coefficients was
determined. Pressure and force measurements were made in the incidence range of -15 deg to 15 deg. The forces were
measured with a 3-component balance equipped with semi-conductor strain gauges. The flow structure was studied
using high speed schlieren photography. Jet penetration distances have been compared with theoretical estimates.The Universit
Computer-aided conceptual aircraft design (CACAD) for transport aircraft
No full textCACAD is capable to optimise the size, and configurations of turbofab-powered transport aircraft. The synthesis sizes aircraft from the low-capacity short range Fokker F-100 class to the long range medium-capacity Airbus A-340 class. It has an optimisation capability, with the objective function being direct operating cost in which, maintenance costs is extensively sub-divided according to ATA chapters. The objective of this report is to present the listing, the user's guide on how to run the program, as well as the description of the formulation used within the program. There are flow charts, table of nomenclatures included in this report. The floppy disc that contains the programme listings will be made available on request from the office of Department of Aerospace Technology, College of Aeronautics, Cranfield University, Cranfield, Bedford, UK, MK43 0ALThe Universit
Multi-dimensional WAF-type schemes for model conservation laws
No full textWe explore how the Weighted Average Flux (WAF) approach can be used to generate first and second order accurate finite volume schemes in one, two and three space dimensions. The derived schemes have multidimensional upwinding aspects and good stability properties. We construct oscillation-free methods that are second order accurate in smooth flow by making use of one-dimensional limiter functions. Some numerical results are presented.The Universit
TVD regions for the weighted average flux (WAF) method as applied to a model hyperbolic conservation law
No full text
The Linearised small perturbation equations of motion for an airship
No full textOriginally published July 1987, revised January 199