Aeroplane Tail Loads for Longitudinal Manoeuvres

Summary

This paper deals with the application of the Transfer Function-Fourier (T.F.F.) Method to the calculation of longitudinal manoeuvring tail loads for aeroplanes.

It has been found that the tail loads computed by this method agree very well with those computed by the standard method outlined in Ref. 1. The main advantages of the T.F.F. method are the time saving and the convenience in handling an arbitrary elevator input. Having once calculated the transfer function between elevator input and tail angle of attack output, it may be used repeatedly to compute the longitudinal manoeuvring tail loads for various arbitrary elevator inputs. This is done by simply expressing the input as a Fourier series and multiplying each term in the series by the value of the transfer function for the corresponding frequency. Then the resulting output series is summed at enough points to obtain a plot of the transient output. This process can be done in approximately one hour of engineering time for each arbitrary elevator input, exclusive of machine calculating time. The machine (usually I.B.M.) calculating time is about half an hour per input. On the other hand, experience has shown that the engineering time required per input by the standard method is approximately forty hours for the first input, and approximately five hours for each additional input.

It is concluded that the calculation of longitudinal manoeuvring tail loads by the T.F.F. method is accurate, dependable, especially adaptable to machine methods, and can conveniently handle arbitrary inputs.