Aeroplanes in Gusts: Soaring Flight and the Stability of Aeroplanes by S. L. Walkden

Author:S. L. Walkden
Language: eng
Format: epub
Publisher: Spon & Chamberlain
Published: 1913-03-25T05:00:00+00:00

Fig. 47.

will assume, so quickly that the headway has not had sufficient time to increase appreciably. In position I. a pendulum, as an indicator of the direction in which things tend to weigh relative to the machine, tends to hang truly vertically, as shown, but in II. this is not the case.

Assuming—to avoid an appearance of begging the question —that the pendulum is in some non-central position A, common gravity impresses upon it an acceleration AB, or^, relative to the machine. But, on drawing AC at right angles to the trajectory, and CB parallel to the trajectory, we find CB, or ^sin a, to be the acceleration of the machine down its trajectory. Notice that no correction is yet required for head resistance, because the propeller thrust, in balancing the head resistance

at the present headway, is making the machine virtually frictionless.

Now, in having the acceleration CB, the machine is impressing upon the pendulum bob an equal and opposite acceleration BC relative to the machine. (In ordinary language, it is tending to leave the pendulum bob behind to that degree.) The resultant of AB and BC, or the " gravity " of the pendulum bob relative to the machine, is AC, which is g'cosa, and, obviously, at ri^ht angles to the machine. Thus, since the pendulum bob, and, of course, the pilot too, weigh upon the machine in the ordinary direction with respect to the floor, tilting may seem of no moment ; but suppose the pilot should dwell a little at the pose a. In this case, the machine increases its headway, and, through that, increases its head resistance and decreases its propeller thrust so that the rate of acceleration of the machine, or BC, shrinks first to Bi, then to B2, and so on, while the direction of the resultant gravity relative to the machine changes from AC, through Ai, A2, etc., to approach AB. That is to say, the pilot, if not strapped or otherwise anchored to his seat or the frame of the machine, but if at the same time gripping one of some types of control, may, before he realizes, find himself weighing forward upon the control with Ci/AB, C2/AB, etc., of his ordinary weight, and so forcing the machine into a steeper and steeper pose of increasing danger. Disaster may follow.

The remedy consists in strapping the pilot in his seat, in giving him proper abutments in the frame to take his weighty and suitably altering the method of manual control.

Though the pilot has been assumed to start the weighing upon his controls by dwelling too long in a downward pose, those who have followed the earlier parts of this book, connected with Chapter II., will easily see that a prolonged head gust, in causing a horizontal machine to be virtually travelling downhill (fig. i), may start the diving accident just as well as actual tilting.^

Since, in fig. 47, the pendulum's first tendency is to tilt with the machine into the direction AC, it will be

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