Full Slip Research Articles

Second Paper: Analysis of Spin/Roll Conditions and the Frictional-Energy Dissipation in Angular-Contact Thrust Ball Bearings

In current analyses of the contact conditions in angular-contact ball bearings it is assumed that sliding occurs in all regions where tangential surface tractions are operative. Other work in similar rolling-contact situations has, however, demonstrated that some of this slip requirement may be accommodated by the elastic surface deformations. This type of analysis leads to areas of sliding and sticking coexisting within the contact areas. These concepts are here applied to angular-contact thrust ball bearings and lead to some interesting deviations from the results obtained using the complete slip analysis. In particular, these concepts of microslip enable the determination of the spin/roll ratio at each race contact. Detailed calculations for conical ball thrust bearings illustrate the main discrepancy of the full slip analysis in over-estimating the frictional-energy losses, such discrepancies being most marked with decreasing contact angle, increasing pitch/ball radii, and increasing coefficient of sliding friction.

Notes on induction motor losses

The data obtained from numerous tests on induction motors, check the losses as given by the Standardization Rules with the exception of the fixed and stray losses. The tests show that both losses are less than would be obtained by the Institute method. The true fixed loss should be taken as the power input, when the motor is running at rated voltage and without load, minus the stator copper loss produced by the magnetizing current. This copper loss is appreciable in slow speed motors. With stator cores built up of well varnished punchings and without drifting or filing of the slots, the stray loss in the magnetic materials is negligible. The stray or eddy current loss in the stator copper is proportional to the stator copper loss, the percentage loss depending upon the degree of lamination of the conductor. The average stray loss of the test for both 25-and 60-cycle machines is approximately 6 per cent of the stator copper loss. The writer is not aware of any satisfactory commercial method of determining the stray loss in induction motor stators. It therefore seems desirable that an average value of the stray loss in per cent of the stator copper loss be adopted as standard. In squirrel cage motors and small wound-rotor motors, where the slip is usually greater than 2 per cent, the total rotor loss should be determined from the slip reading when operating at full load. The rotor loss should be taken as the copper I <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> r loss from resistance measurements in large wound-rotor motors where the slip of less than 2 per cent and a full load slip reading cannot be readily obtained.

Mechanical Principles of the Helicopter

In spite of the rapid development of aeroplanes there are many experimenters interested in the helicopter; it will perhaps be useful to consider a few theoretical points in connection with this type of machine upon which recent research has thrown a stronger light.Propeller Thrust with Full Slip.—The principal question that concerns us is the possible value of the propeller thrust, and it should, at once be noted that it is probable that much larger values are obtainable for this than is possible in the case of the propellers of an aeroplane. Each horse-power employed by the propeller produces 550 ft.-lbs. of work per second.