NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Bubble Sextant
From: Gary LaPook
Date: 2008 Jul 13, 00:12 -0700
From: Gary LaPook
Date: 2008 Jul 13, 00:12 -0700
I've taken hundreds of sextant sights through regular aircraft windows
and have found no problem with refraction. What causes refraction in a
lack of parallel surfaces on the inside and outside of the window. As
long as the two surfaces that the ray of light passes through are
parallel to each other there will be no refraction of the ray of light,
refer to any text on optics and you will see that this is true. So when
taking sights make sure you shoot through a non curved section of the
windscreen. Domes on WW2 aircraft were curved and caused refraction
that had to be corrected with information from the dome refraction
table for the particular dome or from a standard table found in the Air
Almanac. (see attached) For example, don't take sights from the portion
of a Cessna 172 windshield up near the wing root where it is highly
curved, you can see the distortion by moving your head around while
looking through this part of the windshield. Pretty much anyplace else
is o.k. You can test your windshield by looking through it and moving
your head around and if the image wiggles avoid that part.
Get a copy of the Air Almanac, it is easier to use in flight than the Nautical Almanac, you get it on disk from the Naval Observatory, cost thirty one bucks, here is the link:
http://aa.usno.navy.mil/publications/docs/ord_info.php
Just print out the pages you need for your flight, about 7 pages of interpolation and correction tables (which don't change and only need to be printed out one time) and two daily pages for each day of your trip.
There is a MK IXA for sale on ebay right now:
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&rd=1&item=150269277288&ssPageName=STRK:MEWA:IT&ih=005
I was going to bid on it but I will leave it for you. Let me know if you aren't going to bid on it.
Here is a link to an article with a quick explanation of celnav in flight:
http://www.oceannavigator.com/ME2/dirmod.asp?sid=&nm=&type=Publishing&mod=Publications%3A%3AArticle&mid=8F3A7027421841978F18BE895F87F791&tier=4&id=6C9EECDA2E6B47FF9CED1004D3437685
gl
Greg R. wrote:
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Navigation List archive: www.fer3.com/arc
To post, email NavList@fer3.com
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Get a copy of the Air Almanac, it is easier to use in flight than the Nautical Almanac, you get it on disk from the Naval Observatory, cost thirty one bucks, here is the link:
http://aa.usno.navy.mil/publications/docs/ord_info.php
Just print out the pages you need for your flight, about 7 pages of interpolation and correction tables (which don't change and only need to be printed out one time) and two daily pages for each day of your trip.
There is a MK IXA for sale on ebay right now:
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&rd=1&item=150269277288&ssPageName=STRK:MEWA:IT&ih=005
I was going to bid on it but I will leave it for you. Let me know if you aren't going to bid on it.
Here is a link to an article with a quick explanation of celnav in flight:
http://www.oceannavigator.com/ME2/dirmod.asp?sid=&nm=&type=Publishing&mod=Publications%3A%3AArticle&mid=8F3A7027421841978F18BE895F87F791&tier=4&id=6C9EECDA2E6B47FF9CED1004D3437685
gl
Greg R. wrote:
Otherwise you're probably going to have to determine the refraction correction through the windscreen yourself (seems like I read somewhere that WWII bomber navigators had to do that themselves too (or at least confirm prior calculations), so maybe that's a starting point for your research?).
Hi and welcome to the list. I'm curious if the aircraft you fly have a dome fitted for celestial navigation (which would usually include a hook to hang the bubble sextant from). Otherwise you're probably going to have to determine the refraction correction through the windscreen yourself (seems like I read somewhere that WWII bomber navigators had to do that themselves too (or at least confirm prior calculations), so maybe that's a starting point for your research?). Good luck and keep us posted on how your project progresses. -- GregR --- bubi352 <benjaminriecken@hotmail.com> wrote:I am new to this group and new to celestial navigation. I currently work as an airline pilot and fly extensively over water at night. I have developed a keen interest in determining my position the old fashion way. Could someone tell me which bubble sextant I should buy? What should I be looking on a bubble sextant? Where can I buy one? Thank you in advance. Bubi
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Navigation List archive: www.fer3.com/arc
To post, email NavList@fer3.com
To , email NavList-@fer3.com
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