This application is not of great practical use (a mechanical slip ball is unlikely to fail), and was written mostly just to confirm that it would work (it does). The slip ball graphic could be included in the Pilot assist display.
The picture here has the three accelerometer readings shown at the top, while the fourth line shows the current accelerometer maximum scale (the device can work to 2g or 6g) and smoothing (in this case, over 8 (23) readings). The slip ball graphic is at the bottom, which has a full-scale deflection of 10° and where the partial vertical lines indicate 5°.
Theory & practice
Accelerometer readings are smoothed over eight readings to reduce jitter (a new reading is taken at the slowest-possible rate, 40 times a second). Only the x-axis is used for the slip reading: a value of 0.174 corresponds to full-scale deflection of the ball (sin(10°) = 0.174). If acceleration is to the right (positive x) then the ball moves to the left.
The x↔y axes should be normalized to allow for reductions due to pitch (z) values, but the slip ball is rarely relevant when the pitch of the aircraft is significant, so this correction is not currently applied.
Accelerometer scale is not corrected for, so if 6g is selected (by pressing the joystick) the full-scale reading is extended beyond 10° (to about 31.5°).
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This page was last edited on 2010-09-23 by mfc.