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Looking off to the side is still ok, but looking aft will give an
error.  Flying 3 different headings was called a wind star.  It gave
not only drift but the actual wind, thus enabling you to have a
ground speed too.  We often simply estimated the ground level wind
speed from the ocean state, and applied a 90 degree CW (or was it
CCW?) correction for coriolis to get the actual wind affecting us.
This was best done below 8000 feet alt.

Ken
On Nov 19, 2009, at 6:37 PM, Gary LaPook wrote:

> Drift sights were improved over time. Chichester in 1931 didn't use
> any
> drift sight, he just estimated his drift on three different headings.
>
> See his chart to Norfolk island:
> http://www.fer3.com/arc/img/110621.chart%20to%20norfolk.pdf
>
> He plotted the arcs and rays as his method of determining drift on
> three
> headings.
>
> I have attached a photo of a pelorus/drift sight used in an open
> cockpit
> plane in 1930. It was mounted behind the cockpit looking aft.
>
> I have previously uploaded an excerpt of AFM 51-40 which discusses
> drift
> meters including the B-3 and the B-5 which is located here:
>
> http://www.fer3.com/arc/img/108625.afm%2051-40%20drift.pdf
>
> The B-3 looked straight down and was more sophisticated than the
> B-5, it
> was gyro stabilized, but it is a very large instrument about 4 or 5
> feet
> long. The B-5 looked slightly off to the side instead of straight
> down.
> If you examine WW 2 bombers you will often find the hole in the
> side of
> the plane at the nav station where the B-5 was mounted with its
> periscope tube extending through the side of the plane.
>
> I am also attaching several pictures of my B-5. The rotating computer
> dial on the left was used to compute ground speed by timing the
> movement
> of the surface object past two reticle lines but this was limited
> by the
> need to know your precise altitude.
>
> gl
>
>
>
>
> Ken Gebhart wrote:
>> Gary,  the drift sight I used in P2s looked directly below the
>> airplane, not toward the rear.  It had a capability to look rearward,
>> but that was to align it with the airplane.  Looking down, a
>> rotatable
>> grid was aligned with white caps or waves, and the drift angle read.
>>  Looking rearward to any extent would introduce an error.
>>
>> Ken Gebhart
>> On Nov 19, 2009, at 12:44 AM, Gary LaPook wrote:
>>
>
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