Proceedings of the Institution of Mechanical Engineers,Part C: Journal of Mechanical Engineering Science

A novel drive train based on a simple epicyclic gear that drives a bevel combining gear through counter-rotating pinions is developed into a main gearbox for a helicopter powered by a single engine. A design with an overall speed ratio of 17.6 : 1 is compared with an advanced technology version of a production transmission.

The new design, based on an integral main shaft and bevel gear, has a dry weight of 46 kg and offers a 24 per cent reduction in weight while remaining competitive in respect of drive train losses and totals of gears and bearings.

An analysis is presented of the stiffness and damping which may be expected from a rolling element under oscillating conditions. The level of damping, which may be expected from a complete bearing plus the necessary joints, is then examined. It is shown that the assumption of no damping in the joints yields theoretical levels of damping which are substantially less than the levels measured experimentally. It is concluded that the joints are the major source of damping.

This paper concerns the response of a gyropendulum subject to vertical harmonic excitation. Instability of the Mathieu type is shown to occur, the principal region of instability lying about the nutational frequency of the system. Experimental results are presented which clearly indicate the validity of the theoretical prediction. It is also shown that an unstable gyroscopic system can be stabilized by vibrating the equipment with the proper choice of vibration parameters. In such cases, the additional stabilizing factor has been analytically derived. Based on the above analysis, practical suggestions for instrument design are also provided.

All previous analyses of slippers in axial piston pumps have assumed that the slipper running surface was perfectly flat and have all failed to explain the satisfactory performance of these bearings. It has been suggested, however, that slippers in axial piston pumps may depend, for their successful operation, on the small deviations from a perfect flat of the slipper surface. This paper examines the relationship between such a non-flatness and the minimum film thickness produced under steady operating conditions. It is shown that a very wide range of slipper non-flatnesses can lead to satisfactory slipper performance and that the minimum film thickness predicted is remarkably insensitive to the actual amount of deviation from flat.

Gear shaping cutters are provided with top-relief and rake angles. As a result of this, the profile representing the cutting edge is modified. This paper deals with the method of obtaining the effective profile on the rack-type and pinion-type cutters for spur gears. Analysis of the effective profile shows that the effective profile of the rack-type cutter is actually a straight-sided tooth form with different pressure angle and tooth thickness at the reference (pitch) line. In the case of the pinion-type cutter, tooth thinning takes place and the effective profile could not be identified with any involute form.

This paper also deals with the methods of correcting the cutter profile form so that profile close to the theoretical form can be obtained on grinding the rake face. This approach would be quite useful to the designers and manufacturers of the shaping cutters.

This paper describes a theoretical and experimental investigation of the dynamic characteristics of a capillary-compensated oil-lubricated hydrostatic bearing which has an accumulator connected to the bearing pocket via a second capillary restrictor. Results show that by careful selection of accumulator and restrictor the bearing can be tuned to give an optimum system performance. Such a facility can be of considerable use if the hydrostatic bearing is being used to support other machinery, for example in the support of journal bearings used with flexible rotors. By tuning the hydrostatic bearing dynamic characteristics, optimum rotor support impedance might be achieved thereby giving the engineer some control over system resonances and stability.

The correction that must be applied to the upstream wind velocity, when a rectangular flat plate normal to the flow direction is placed in an open jet wind tunnel, is determined and is found to be at all times equal to or greater than unity. It is also found to be dependent upon the distance of the body from the tunnel outlet, and the projected area of the body. Comparisons with previous work carried out in closed wind tunnels are made to confirm the experimental technique used.

In this paper the advantages and weak points of the analytical and vectorial methods of the derivation of equations of motion for discrete systems are considered. The analytical method is discussed especially with respect to Boltzmann-Hamel equations, as generalized Lagrange equations. The vectorial method is analysed with respect to the momentum equation and to the generalized angular momentum equation about an arbitrary reference point, moving in an arbitrary manner. It is concluded that, for the systems with complicated geometry of motion and a large number of degrees of freedom, the vectorial method can be more effective than the analytical method. The combination of the analytical and vectorial methods helps to verify the equations of motion and to avoid errors, especially in the case of systems with rather complicated geometry.

Some experimental results are presented on the influence of inherent compensation in an externally pressurized, orifice-compensated air journal bearing.

The availability of new spindle units which have hydraulically controlled variable preload bearings, means that the radial and axial deflection of bearings can be calculated more accurately than was possible when bearings had a preload set when cold and liable to change at working temperature. The present study gives the method of calculation for combined loading (i.e. axial and radial together), typical results are illustrated and the extreme cases of radial load only and of axial load only are compared with SKF's empirical formulae.