Drift Sight
The Drift Sight was a bombsight developed by Harry Wimperis in 1916 for the Royal Naval Air Service (RNAS).
The Drift Sight eliminated the need for a stopwatch to perform this calculation, as on earlier devices, and greatly eased the bomb aimer's workload.
Prior to the introduction of the Drift Sight, bombsights were generally very simple systems of very limited accuracy.
The primary pre-World War I device in RNAS service was the "Lever Sight" which had to be held out of the cockpit in one hand by the pilot while flying the aircraft with the other.
The EDS allowed the bomb run parameters to be entered once and then left the pilot free to fly the plane.
This measurement was taken prior to the bomb run, using a secondary sighting system at the rear of the main bombsight.
The timing of the drop was set by dialling in the measured air speed, which moved the entire sighting system fore or aft, carrying the two "backsights" along with it (as well as the drift bar mechanism).
At higher altitudes the indicated airspeed - being measured by pitot tube instruments - was affected by differences in outside air pressure that rendered it increasingly inaccurate.
IA was introduced for this role, including a simple adjustment between the airspeed and altitude settings that accounted for this effect.
[2] A third version was also introduced for use by Navy airships, which worked at much lower speeds and also had the advantage of being able to directly measure the windspeed by throttling their engines until they lay still over the water.
[3] Although the Drift Sight was a significant improvement over earlier designs, it still required the aircraft to fly up or downwind on the final bomb run.
For the RNAS this was a serious problem, as a submarine or ship would attempt to maneuver away if it spotted the attack, and thus upset the bomb run.
[3] The Drift Sight was introduced in 1916, and the simplicity of the device in terms of manufacture and mounting to the aircraft allowed it to quickly equip RNAS forces.
In the Equal Distance design, this movement was itself the main aiming mechanism, and could not be adjusted for ease of use as it was in the Drift Sight.
The drift bar was a metal rod that extended rearward from the sight and was pivoted so it could rotated outward, away from the aircraft fuselage.
The two raised racks are part of a Scarff ring machine gun mount and are unrelated to the Sight.
