Ref: Drift Sight
Whilst measuring drift angle, it could also be used for a ground speed check by timing, in seconds, an object on the ground, or a wave on the sea transiting from one graticule to the other and using the computer on the LH side. Set height against time to give ground speed. Calculating an accurate ground speed was a problem as height measurement requires an accurate QNH. However a radio altimeter would have solved this problem but were not fitted to my vintage of A/C. The 'Kipper' fleet operating more or less at sea level would have made full use of the drift and groundspeed sight.
On the Hastings a/c we could check the correct alignment of the sight by checking the drift angle along the rivets on the starboard side of the airframe. On the Valetta it was checked by tying string from the pitot tube to the port wheel strut. (and removing before flight!!)
A good bit of kit if you could see the surface.
Black shoe polish on the eye piece was something the Nav had to check before using. Always caused a laugh!
Last edited by DeanoP; 30th Aug 2017 at 14:49.