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    Re: A-10 Sextant Manual
    From: Christian Scheele
    Date: 2009 Jun 12, 12:52 +0200

    "The bigger problem is that the azimuth of the sun changes as it moves
    across the sky, not that the LOP is slightly curved. "
    
    I think I get it, and stand to be corrected in my previous email. The
    movement of the sun, in relation to changing declination and the AP,  leads
    to a non-uniform rate of change of azimuth. That's what makes it difficult
    to "keep on" the LOP, which swings around at this non-uniform rate of
    change. Thanks again.
    
    Christian Scheele
    
    ----- Original Message -----
    From: "Gary LaPook" 
    To: 
    Sent: Friday, June 12, 2009 10:14 AM
    Subject: [NavList 8635] Re: A-10 Sextant Manual
    
    
    >
    > The bigger problem is that the azimuth of the sun changes as it moves
    > across the sky, not that the LOP is slightly curved. Look at Weems
    > writings on this at
    >
    > http://www.geocities.com/fredienoonan/landfall.html
    >
    > Chichester describes the same procedure in the Observers' Book.
    >
    > The problem of shifting LOPs and curved LOPs is handled by using the
    > destination as the AP and this was the method being used by Chichester.
    > Done this way, as long he manovered the plane to keep reading the same
    > altitude from his sextant as that which would be measured at the same
    > instant of time at the destination, then he can be sure he is staying on
    > the LOP through destination, whatever the azimuth happens to be.
    > Chichester did this and took an additional sight to confirm that he was
    > staying on the LOP to Lord Howe.
    >
    > gl
    >
    >
    >
    > Christian Scheele wrote:
    >> I didn't misunderstand you.
    >>
    >> "Pointing out his
    >> plane's engine problems you say he was reckless."
    >>
    >> I then went on to discuss Chichester's navigation method on my own
    >> account:
    >>
    >> "I don't really think I'm
    >> qualified enough to judge his decision to navigate using a (his?) method
    >> iof
    >> ....precomputed D.R. ...I mean, his sun shot of course gave him only a
    >> position line, or rather, an assumed position line"
    >>
    >> I was, however, really unclear. Gary's response alerted me to this. I did
    >> not intend to argue against the concept of using LOPs, but it sure looks
    >> like it, so my apologies. In my next email, therefore, I rephrased my
    >> comment, which, in fact, concerned LOPs which are so long that they are
    >> really lines with changing gradients for plotting purposes. (Assuming
    >> nobody
    >> would bother to plot curves themselves on a Mercator chart.) If you then
    >> fly
    >> along one course because you assume from D.R. that you know which
    >> gradient
    >> or bearing applies to the part of the LOP you are on, when in fact you
    >> are
    >> on a part of  the LOP that has another bearing, then would you not fly
    >> off
    >> the LOP? If so, the real question becomes: Would you be able to use a
    >> sort
    >> of running fix to work out your position and thus rectify the problem of
    >> determining which part of the LOP you are on? I think so, what do you
    >> think?
    >> That must be quite a manoeuvre for one flying single-handed. It
    >> demonstrates
    >> how important good D.R. is.
    >>
    >> Perusing "The Lonely Sea and the Sky", I confirmed that Chichester
    >> estimated
    >> his wind speed on his flight, rather than use on a device. He also didn't
    >> want to check his compass before the flight "except against Norfolk
    >> Island".
    >> Ignoring the problem concerning long LOPs for a moment, it would seem
    >> that
    >> these navigational decisions of Chichester compounded the risk already
    >> posed
    >> by the questionable state of his plane.
    >>
    >> Christian Scheele
    >>
    >> ----- Original Message -----
    >> From: 
    >> To: 
    >> Sent: Thursday, June 11, 2009 12:17 PM
    >> Subject: [NavList 8615] Re: A-10 Sextant Manual
    >>
    >>
    >>
    >> Regarding  Sir Francis Chichester:
    >>
    >> Dr. Kolbe has it right.
    >>
    >> I was referring not his astonishing navigation for which I have the very
    >> highest regard indeed, but to the fact he was willing to put his life on
    >> the
    >> line with an aeroplane that he describes in his book already had various
    >> problems such as having fitting floats without checking if they leaked or
    >> not, and an engine that had already given him problems, and in the run-up
    >> check before leaving for Norfolk Island he says:-
    >>
    >> "I could only get 1780 revs, forty less than I expected, and my spirits
    >> sank. I should never get off with a full load with a motor like that, but
    >> said nothing to the CO about it.  The seaplane was launched. I faced her
    >> into the wind, and opened the throttle; to my surprise she left the water
    >> as
    >> easily as a sea bird..... ".
    >>
    >> The man must have been mad or very determined, or both.
    >>
    >> To cross the Tasman Sea - a nasty stretch of water notorious for bad
    >> weather, two thirds the width of the Atlantic, in a single engined float
    >> plane with engine in dubious condition is more than reckless.   But got
    >> away
    >> with it.
    >>
    >> My impression from reading his books is he was what we would call a
    >> "loose
    >> cannon" and contemptuous of any advice or authority.  From reading about
    >> him
    >> it seems he must have been a truly remarkable person but not very
    >> 'likeable'.
    >>
    >> Douglas Denny.
    >>
    >> Chichester. England.
    >>
    >>
    >>
    >>
    >> >
    >>
    >>
    >
    >
    > >
    
    
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