Search results

The purpose of this paper is to present an analytical approximate solution of the nonlinear mathematical model of the bifilar pendulum.

First, the equation of motion derived based on the classical dynamics law by only an angular oscillation assumption and vertical oscillation is neglected. The energy balance method is applied to solve an established model and an analytical formulation has been obtained for the nonlinear frequency of the bifilar pendulum.

A comparison of results with those obtained by a numerical solution of the exact model (without any simplifications) shows the precise accuracy even for a large amplitude of oscillation.

The proposed model and solution are relatively simple and can be applied instead to a linear model for achieving accurate results.

Aerial refuelling, which was introduced operationally as a temporary means of extending the range of the U.S.A.F.'s long‐range bomber force is now an accepted and important part of military operations. Most combat aircraft are now required to incorporate provisions for aerial refuelling, and it is expected that it will continue to play an important role in Air Force operations until such time as other means are found to extend the range of military aircraft. In addition to the range extension possibilities of aerial refuelling other uses are for increasing payload and decreasing take‐off distance by take‐off with partial fuel load and completion of the fuelling operation in the air. The use of aerial refuelling for these latter purposes is expected to become more important in the future.

Continuing the series on technical subjects in secondary schools, the writer describes a course now starting in his school, and the thinking and planning behind it.

THE experimental determination of the moment of inertia of a body is frequently required to confirm a calculated value or to eliminate the tedious work involved in the calculation. This is normally done by integrating the body into a vibrating system, such as a pendulum.

THE serious nature of difficulties which might be encountered in tail spins, was brought forcibly to the attention of the Material Division of the U.S. Army Air Corps, in the Spring of 1926, when Lieutenant E. H. Barksdale lost his life in attempting to determine the cause of difficult recovery from spins in a military aeroplane being flight tested at Dayton, Ohio. Trouble in recovery from spins had been encountered in several instances in foreign countries, and one or two cases had occurred in the United States: however, the problem was not considered as one generally applicable to all aeroplanes, because, in most cases of previous trouble, the aeroplanes concerned possessed unusual design features which were thought to be mainly responsible for their abnormal behaviour. Prior to this time, general conjectures had been made, regarding probable reasons for difficult recovery from spins, but very little in the nature of systematic investigation had been attempted, consequently no generally applicable principles had been determined. Numerous studies had been made in wind tunnels, and it was recognised that the normal aerofoil would rotate automatically under certain conditions, but the magnitude of the forces involved, and therefore the ability of an aeroplane to recover a normal attitude by use of the controls, could not be readily determined by wind tunnel tests. A few flight tests had indicated that the centre of gravity location, with respect to the resultant air force vector on the lifting surfaces, influenced the type of spin and the case of return to a normal attitude.

Under this heading are published regularly abstracts of all Reports and Memoranda of the Aeronautical Research Committee, Reports and Technical Notes of the U.S. National Advisory Committee for Aeronautics, and publications of other similar research bodies as issued

Experiments with Modified Tail Units.—Experiments have been performed with 1/15th scale models of the original single‐seater fighter and 1/20th scale models of the Bristol Fighter with a view to improving their spinning properties by redesigning the tail unit. The experiments with the fighter models were mainly directed at investigating the spinning characteristics of the original and deepened models to see whether the overall effects of the deepened fuselage and raised tail plane would bear out the encouraging conclusions drawn from the wind tunnel work. The scope of the experiments was somewhat limited, but all results indicated that slower and steeper spins and very much more rapid recoveries might be expected from the deepened fighter.