A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: A-10 Sextant Manual
From: Christian Scheele
Date: 2009 Jun 12, 12:52 +0200
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. >> >> >> >> >> > >> >> > > > > --~--~---------~--~----~------------~-------~--~----~ Navigation List archive: www.fer3.com/arc To post, email NavList@fer3.com To unsubscribe, email NavListemail@example.com -~----------~----~----~----~------~----~------~--~---