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 For example, using the page from the Air
Almanac found on page 206, a day when the H.P is 60', and an altitude
of 36� we find the parallax in altitude correction to be 48' and this
would be the correction to use with a bubble sextant. (Page 206 of
AFPAM 11-216.)

Additionally, formulas for these correction are found on pages 393 and
394 of the same manual.

gl

On Jul 28, 5:24 am, glap...@pacbell.net wrote:
> One more thing to discuss before giving an example of in flight celnav
> is corrections to sights taken in flight. We discussed this back on
> December 14, 2007 in the thread "additional corrections... (just
> search "additional corrections") which include an excerpt from AFPAM
> 11-216. You should download the entire manual 
here:http://www.e-publishing.af.mil/shared/media/epubs/AFPAM11-216.pdf
>
> Review chapters 10 through 13.
>
> I want to add to the manual on this.
>
> Coriolis can be handled in a number of ways. You can move the A.P. to
> the right (northern hemisphere) 90� to the course (track) prior to
> plotting the LOPs by the amount of coriolis correction shown in the
> table in the Air Almanac and in H.O. 249 (previously posted). Or you
> can move the final fix the same way. Or, the most complicated way, is
> to make a correction to each Hc by multiplying the coriolis correction
> by the sine of the relative Zn, the Polhemus makes this relatively
> painless.
>
> Rhumb line correction is avoided by steering by directional gyro
> during the two minute shooting period and this is what is normally
> done anyway.
>
> Wander correction is small at low airspeeds and it can be avoided by
> making sure the heading is the same at the end of the shot as it was
> at the beginning of the shot. It doesn't matter how the heading
> changes during the shot (within reason) as the errors will average
> out.
>
> Ground speed correction can also be avoided by making sure the
> airspeed is the same at the end as at the beginning, any changes in
> between will also average out.
>
> Auto pilots do a good job of maintaining airspeed and heading for the
> two minute shooting period so eliminating the need for the above
> corrections.
>
> The AFPAM states you must figure the refraction correction based on
> the actual Hs as opposed to using the refraction correction based upon
> the Hc but this is a needless refinement and keeps you from completing
> the pre computation prior to the shot. Look at the refraction table in
> H.O. 249 (previously posted) and you will see for altitudes exceeding
> 10� that the brackets are at least two degrees wide. So only in the
> rare cases where the altitude is almost exactly at the break point
> could you come up with a different refraction correction using Hc
> rather than Hs and even then it could only be a difference of one
> minute of altitude. For example the break point between a 5'
> correction and a 4' refraction correction is 12� so if Hs were 11� 50'
> and Hc were 12� 15' then using Hc would get you a 4' correction and
> using Hs would get you a 5' correction. This is actually only 1/2 of a
> minute error because the corrections are rounded to the nearest full
> minute.
>
> The parallax in altitude correction for the moon is printed on each
> page of the Air Almanac based upon the horizontal parallax (H.P.) for
> the moon on that particular day. This parallax varies with the
> distance to the moon and moves in lock step with the S.D. since they
> are both related to the distance to the moon. The H.P varies from 54'
> to 61' during the year. For example, using the page from the Air
> Almanac found on page 206, a day when the H.P is 60', and an altitude
> of 36� we find the parallax in altitude correction to be 48' and this
> would be the correction to use with a bubble sextant. If using a
> marine sextant and shooting the lower limb we would add the S.D. of
> 16' to produce a total correction (but not including refraction yet)
> of 64'. Subtract the refraction correction of 1' gives the total
> correction of 63'. Using the correction table in the Nautical almanac
> for the identical parameters you get 63.5'. The Nautical Almanac moon
> correction table includes a procedure for using it with a bubble
> sextant and what this does is just backs out the S.D. correction which
> is included in the correction table and not needed for a bubble
> observation. Using this procedure produces a correction for a bubble
> observation of 47.2' which compares with the 48' from the Air Almanac.
>
> Remember to reverse the signs of these corrections and apply them to
> Hc to produce Hp (pre computed altitude) which you then compare
> directly with Hs to compute intercept.
>
> gl
>
> On Jul 25, 7:48 pm, Gary LaPook  wrote:
>
> > We can also use the Polhemus computer to calculate the MOO adjustment.
> > We do this by setting the ground speed  in the setting window and read
> > out the MOO in the "ZN-TR" window adjacent  to the relative Zn. (See
> > Pol1.jpg) (Zn-TR is another way of saying "relative Zn" since you
> > calculate relative Zn by subtracting Track from Zn.) Looking at the top
> > of the TR-ZN window where the relative Zn of 000� is adjacent to "5" in
> > the MOO window showing that the aircraft moves 5NM per minute which
> > causes the altitude to also change 5' every minute when the body is
> > directly ahead of or directly behind the aircraft. This MOO is
> > equivalent to the MOO table at page 6 of the original PDF which
> > tabulates the MOO adjustment per minute. Multiplying this 5' times the
> > same eight minute period gives the same 40' adjustment we got from the
> > MOO table on page 4 of the PDF. You will also find that the adjustment
> > is 2.5' adjacent to the relative Zn of 60� which multiplied by eight
> > minutes gives the 20' adjustment we found in the table on page 4.
>
> > The Polhemus makes it easy to figure the relative Zn. You place the "SET
> > TRACK" pointer on the track of the aircraft ,130�  as shown in the
> > attached image. (see Pol2.jpg) Look at the next image (Pol3.jpg) for the
> > second case, a track of 70� and you find the relative Zn, 60� on the
> > inner scale.
>
> > The Polhemus also makes it easy to figure the sign to use for the
> > adjustment, if the relative Zn is on the white scale, meaning the body
> > is ahead, then the sign is minus and if found on the black scale (the
> > body is behind) then the sign is plus when these adjustments are made to
> > Hc, the normal method. This same pattern is revealed in the two MOO
> > tables, the top of the tables show the body ahead and the bottom has the
> > body behind.
>
> > gl
>
> > glap...@pacbell.net wrote:
> > > Now let's talk about the "motion of the observer" (MOO) adjustment.
> > > Every fix in the air is a running fix because the aircraft moves a
> > > considerable distance between the first and last sight. Assuming the
> > > normal eight minute spacing between the first and last shot, a slow
> > > airplane, say 100 knots, will have traveled 14 NM while a 450 knot
> > > plane will have traveled 60 NM. In marine practice the navigator will
> > > advance the earlier LOPs to cross them with the last shot. The MOO
> > > adjustment accomplishes the same thing.
>
> > > As an example of how this works consider a sun shot taken at 1000Z
> > > resulting in an observed altitude, Ho, of 35� 55'. After doing the
> > > normal sight reduction you end up with an Hc of 35� 45' at the chosen
> > > A.P and a Zn of 130�. This results in an intercept of 10 NM toward the
> > > body, 130�. To plot this LOP you draw the azimuth line from the A.P
> > > and measure off the 10 NM intercept toward the sun and plot the LOP
> > > perpendicular to the Zn.
>
> > > Then, two hours later at 1200Z you take another altitude of the sun
> > > and to obtain a 1200Z running fix you must advance the 1000Z sun line
> > > to cross the 1200Z line. There are three ways to advance the LOP.
> > > First, you can pick any spot on the LOP and lay off a line in the
> > > direction of travel of the vessel, measure off the distance traveled
> > > along that line, make a mark there and then draw a line through that
> > > mark that is parallel  to the existing LOP and label the advanced LOP
> > > "1000-1200Z SUN." A second way is to advance each end of the LOP and
> > > then just draw a line through these two points, this avoids having to
> > > measure the azimuth when laying down the advanced line. The third way
> > > is to advance the original A.P and then from the ADVANCED A.P. plot
> > > the LOP using the ORIGINAL intercept and Zn. Any of these methods will
> > > produce the same advanced LOP.
>
> > > Now let's consider a simple case. Suppose the vessel's course is the
> > > same as the Zn, in this case, 130� and the vessel's speed is 20 knots
> > > meaning it has traveled 40 NM in the two hour period. In this simple
> > > case we can just extend the Zn line an additional 40 NM and then plot
> > > the advanced LOP at that point. So,  the LOP is now 50 NM from the
> > > original A.P., the original 10 NM intercept plus the additional 40 NM
> > > that the vessel has traveled on the same course as the azimuth. Since
> > > we have no interest in actually plotting the 1000Z LOP, as we are just
> > > planning on having the 1200Z running fix, we can skip drawing the
> > > earlier LOP and just plot the advanced LOP by adding the distance
> > > traveled to the original intercept to get a total intercept now of 50
> > > NM and using that adjusted intercept to plot the advanced LOP using
> > > the ORIGINAL A.P. This method also creates the exact same advanced LOP
> > > as the other three methods. This last described procedure is how the
> > > MOO table is used.
>
> > > Look now at the MOO table, page 4 of the PDF in my original post.
> > > Assume now we are in 300 knot airplane and the first sight is taken at
> > > 1152Z, eight minutes prior to the planned fix time. At the top of the
> > > column marked "300" knots ground speed you find the number "20"
> > > showing that the plane will travel 20 NM (and so the altitude of the
> > > body should change by 20 minutes of arc) in a 4 minute period. Also
> > > notice that the top row of values are marked for a relative Zn of 000�
> > > meaning the body is directly ahead, as in our example. The plane will
> > > obviously travel 40M in the normal 8 minute period from the first to
> > > the last shot of a three star fix. The sign convention is the same as
> > > that for the MOB table so simply draw a horizontal line
>
> ...
>
> read more �
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