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"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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