Stability in aviation : an introduction to dynamical stability as applied to the motions of aeroplanes by Bryan George Hartley 1864-1928

Author:Bryan, George Hartley, 1864-1928
Language: eng
Format: epub, pdf
Tags: Stability of aeroplanes
Publisher: London : Macmillan
Published: 1911-03-25T05:00:00+00:00

stahility hy increasing the modulus of decay of the long oscillation. This result, which is best obtained in the first instance by algebra as is done above, is entirely in accordance with what we should expect from general considerations regarding the nature of the long and short oscillations as discussed in §§ 50—53.

Head resistance thus enables the machine to rise at a steeper angle to the horizon than would be possible if such resistance did not exist. For example, the effects of head resistance and inclination of flight path will cancel one another if

2v tan a + tan 6 + -rji con 6 = i) . . . (91)

or putting cos 6=1,

tan 6 = - 2v(tan a + ^) =. - 2.(tan « + g . velocity height) (-'^"^

If the machine is ascending at an angle 6 given by this formula, it will be as stable as it would when moving horizontally in the absence of head resistance, and generally the increased stability due to head resistance enables the tangent of the inclination of the flight path to be increased by the amount approximately given above.

ih) In all the previous work the propeller thrust has been assumed constant, but if either the horse-power or the rate of revolution of the propeller, is maintained constant the thrust will decrease when the velocity increases. In either case the effect of these variations can be represented by the addition of a positive term to X^, and will be precisely similar to that of head resistance. It will be expressible in the form of an increase in the value of V defined above, and will increase the elevation of the flight path for given stability.

The effect of such variations when the propeller thrust does not pass through the centre of gravity can be investigated if the necessity arises, but the formulae will necessarily become somewhat complicated.

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