directional gyros Flashcards
directional gyro principles of operation
horizontally tied so provides datum for measuring heading
gyro first aligned to a known datum
heading found by comparing aircrafts axis with gyros axis
has 2 gimbals so 2 deg of freedom
2 types of DGI gyro erection
pneumatic and electric
DG pneumatic erection
coarse erection with air jet
fine erection with wedge plate
air driven gyros limited to 55°in pitch and roll
DG erection and alignment
requires slow rate of precession to compensate for RW, ER, TW
have caging mechanisms to realign gyro to tied alignment
should resynchronise every 10 minutes
DG gimbolling errors
occurs when gimbal and gyro not at right angles
due to turning
may also have topple errors
error increases with increasing bank angle
electric erection
higher RPM therefore more rigid
pitch and roll limits 85°
gimballing errors
occur whenever 2 gimbals are not at right angles to each other
turns- increases with bank angle
drift error
apparent wander( & real wander
total drift =
ER+TD+RD+LN
can’t calculate RD or TD
random drift RD
no way to calculate
call it ‘mechanically perfect’
ER earth rotation
drift due to rotation
indicated heading decreases by amount of degrees earths rotated (northern hem)
increase in southern
+/- 15 x Sin(lat)
LN latitude nut
nut causes gyro to undergo real drift at a rate equal and opposite to the drift caused by earth rotation
15 x sin(lat)
use latitude set on the nut not the lat where the aircraft is
sign has to be opposite sign to ER to oppose it
TD transport drift
similar to ER but now flying round the world
drift east or west but get none going north or south
greatest near poles
questions will say travelling north/south or locally as don’t need to calculate it
