
NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Cessna CN Summary
From: Gary LaPook
Date: 2010 Jan 13, 14:56 -0800
From: Gary LaPook
Date: 2010 Jan 13, 14:56 -0800
But CN is a "position finding" system, not a "position keeping" system
so the accuracy of a celestial fix is completely independent of prior
fixes or DR errors. You can start with three observations and know
only that you are on the planet Earth and in only three iterations come
up with a fix of normal accuracy. Noonan could have paddled a canoe
across the Pacific to Howland and the final LOP used to find the island
would be of normal accuracy. Dead reckoning , INS and Doppler are
"position keeping" systems so they acquire errors or uncertainty as
time goes by. CN, GPS, LORAN, CONSOL, DECCA, VOR, visual bearings, and
radio bearings are all "position finding" systems. Interestingly,
OMEGA has characteristics of both. OMEGA gives you an LOP within a
"lane" but you must keep account of crossing the lanes to place the LOP
within the correct lane. The normal way to do a single LOP landfall is
to use the destination as the AP so if you want to plot the LOPs (which
is not really necessary) then the LOPs get more accurate as you
approach the island. The only impact of deterioration of the DR on a
long leg is that one must aim off farther to the side to intercept the
LOP through destination so that you can be certain on what side of the
destination you intercept the LOP. Noonan would have known when he had
his last fix and would have allowed for DR uncertainty commensurate
with the length of the DR leg.
gl
Greg R. wrote:
gl
Greg R. wrote:
a very experienced flight navigator, such as Fred Noonan, should have been able to find anl island, such as Howland.True enough - and while not wanting to disagree with your analysis, I'm not sure it's a valid comparison. Your flights had the benefit of a very recent and very close known position (i.e. Oxnard or Santa Paula airports, depending on where you departed from) that Earhart and Noonan didn't after 20-some hours over the open ocean. I would certainly hope that any halfway-decent navigator would be able to find an island (or at least an LOP through it) that's only a few tens of miles offshore with that as a starting point... ;-) -- GregR --- On Wed, 1/13/10, Gary LaPook <glapook@pacbell.net> wrote:From: Gary LaPook <glapook@pacbell.net> Subject: [NavList] Re: Cessna CN Summary To: NavList@fer3.com Date: Wednesday, January 13, 2010, 12:55 PM Even first timer flight navigators taking sights achieved the accuracy needed to find an island. So,a very experienced flight navigator, such as Fred Noonan, should have been able to find anl island, such as Howland. gl gregrudzinski@yahoo.com wrote:Three Flights Completed Five Sun observations performed using a two minuteaverager( Intercepts of 2A, 3A, 8A, 10A, 18A ) Six individual observations performed with fourconsecutively averaged.( Average of four 9A, Individual from back seat 22T,Individual from front seat 19T )First Impression- The Bubble moves a great deal eventhough the plane seems to be level and steady. This was most apparent when the horizon prism was flipped in on the MK 5 where the bubble movement could be seen relative to the horizon. In spite of this reasonable accuracy was still obtained. Clearly there would have been no problem finding an island such as Anacapa (6NM long) with or without an averager but given the choice I would go with the averager.Greg Rudzinski----------------------------------------------------------------NavList message boards and member settings:www.fer3.com/NavListMembers may optionally receive posts by email. To cancel email delivery, send a message toNoMail[at]fer3.com----------------------------------------------------------------Linked File: http://www.fer3.com/arc/imgx/IMG_5123.JPG