NavList:

Another way for you to measure the index error is to go down to the beach, stand with your toes in the water and measure the altitude of the horizon. Unless you are a midget or a giant it should be about minus 2.5 minutes when the horizon runs through the center of the bubble.

gl

On 9/11/2010 7:57 AM, David Harwood wrote:

Gary,
 
Thanks for the outstanding resources!  I'm out of town for a few weeks but I'll study up on what you've provided and post my results for critique as soon as I return home.
 
Dave
 
> Date: Fri, 10 Sep 2010 09:35:05 -0700
> From: glapook@pacbell.net
> To: NavList@fer3.com
> Subject: [NavList] Re: Aviation Bubble Sextant
>
> You can start here:
>
> http://www.oceannavigator.com/content/celestial-air
>
>
>
>
> If Celstaire still has any Polhemus computers you should get one because
> it makes plotting the fix in flight easy.
>
> http://www.fer3.com/arc/m2.aspx?i=105832&y=200807
>
> This shows the process:
>
> http://www.fer3.com/arc/m2.aspx?i=105846&y=200807
>
> http://www.fer3.com/arc/m2.aspx?i=105847&y=200807
>
> Here are links on how you do celnav in flight:
>
> http://www.fer3.com/arc/m2.aspx?i=105924&y=200807
>
> http://www.fer3.com/arc/m2.aspx?i=105929&y=200807
>
> http://www.fer3.com/arc/m2.aspx?i=105937&y=200807
>
> http://www.fer3.com/arc/m2.aspx?i=105938&y=200807
>
> http://www.fer3.com/arc/m2.aspx?i=105939&y=200807
>
> http://www.fer3.com/arc/m2.aspx?i=105940&y=200807
>
> http://www.fer3.com/arc/m2.aspx?i=105940&y=200807
>
>
> You can read an example of a complete flight on my website at:
>
> https://sites.google.com/site/fredienoonan/other-flight-navigation-information/in-flight-celestial-navigation
>
> To determine the index error of an A-10 you must take a number of sights
> from a known position and compare the altitudes with the computed
> altitudes and find the average error and standard deviation. Hold the
> sextant steady on a tripod or other rest. Take ten sights moving the sun
> down into the center of the bubble and then take ten more moving the sun
> up into the bubble. Calculate the index error separately for each
> series. If there is a difference between the index error for the two
> series then you have determined the amount of backlash in the mechanism,
> there will probably be some. Then, since in flight you will be moving
> the sun up and down to keep it in the bubble, average the two index
> errors to find the I.E. to use in flight.
>
> Find your location either with a GPS or Google Earth to use for
> computing the Hc. An easy way to do this calculation from you position
> is to use the Navy website at:
>
> http://www.usno.navy.mil/USNO/astronomical-applications/data-services/cel-nav-data
>
>
>
>
>
>
> You can download a copy of the current Air Force navigation manual here:
> http://www.e-publishing.af.mil/shared/media/epubs/AFPAM11-216.pdf
>
> unfortunately it is lite on celnav.
>
>
> http://www.fer3.com/arc/m2.aspx?i=105839&y=200807
>
> gl
>
>
>
>
> On 9/10/2010 6:41 AM, Dave Harwood wrote:
> >
> > Frank, I'll use this moment as my opportunity to step out of the
> > shadows and become a NavList contributor. First, some personal info:
> > I'm active duty Air Force currently stationed in Okinawa. Several
> > years ago I took an interest in Cel Nav after reading South by Sir
> > Ernest Shackleton. After reading a few books on the subject, countless
> > Google searches and a lot of time spent at the beach, I've taught
> > myself to consistently plot a fix within 4-5 miles of my known
> > position with a Davis Mark 15. I've recently completed the ASA 101 and
> > 103 (104 scheduled for Oct) sailing courses and have put some of my
> > skills to use. Up to this point I've simply been an observer of
> > NavList. Not because I intend to simply plunder its resources without
> > giving something in return, but because I didn't believe I could
> > contribute much to the conversation at my level. I've come a long way
> > and I'm ready to jump in!
> > Enough about me already, I'll get to the point:
> > My interest has now taken me into the realm of air navigation. I
> > purchased an A-10A online and, not so surprisingly, found it to be
> > seized. With the help of Bill Morris's manual I've successfully
> > restored this unit and I would like to learn more about its use. I do
> > not intend to hijack this thread, however, in their absence I'll keep
> > it going.
> > Could someone detail its proper use and the process involved in an
> > airborne fix? I have a copy of the Air Almanac (although a 2011) and
> > plenty of opportunities to use it while airborne.
> > Also, how should I go about establishing its accuracy (e.g. index error)?
> > Thanks for any help that can be offered,
> > Dave Harwood
> >
> >
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