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Author
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Topic: Artificial Horizons
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cmoller
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posted July 05, 2014 08:02 AM
David,
On page 35 of your plastic sextant book you refer the reader to "the References for cautions on the altitude corrections when using upper and lower limbs and a few other nuances." Are the references included as Further Reading and Resources? Since there are many readings listed I was not sure which one to try to read. I bought the Davis AH. The instructions simply say: make the index correction to your initial reading, then divide the result in half to apply all the other corrections except for dip. I assume this means to apply the altitude correction. I also assume this means using the halved value as the Apparent Altitude and lower limb if the double reflected image is brought into coincidence with the top of the image on the liquid. No?
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David Burch
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posted July 05, 2014 10:02 AM
Thanks for noting the typo. References should be Further Reading as you state. we will fix that in the next printing.
the reference referred to is our textbook, section 11.15. A search of this discussion forum and the text book brings up discussion of AH use.
Another way to find many articles on this topic is to search the full starpath website from the home page.
There are many examples. I am not sure i follow your proposed procedure. Can you please post a numerical example of all values you refer to.
There is a chance we discuss mostly the method we propose and not so much on other options.
Steve has a lot of experience with these sights and can address specific points.
From: Starpath, Seattle, WA
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cmoller
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posted July 05, 2014 11:56 AM
Sorry about not being careful with the way I wrote my question. On rereading I got mixed up myself.
Basically I am wanting to practice using my sextant. I bought a Davis artificial horizon for this purpose since I live far from a body of water. This morning I wanted to try it out and in reading through various documents, especially the Plastic Sextant book, I got the impression that there may be special considerations for its use. In any case I did use the device with my sextant and got several lines of position an hour apart which crossed within a half mile of my actual location. I will do this again in the late afternoon to hopefully get a better cut angle on the morning lines. This exercise also gave me an opportunity to practice the Fit-Slope averaging technique.
After reading your answer I found the extensive discussion in section 11.15 of the Cel Nav Home Study Course Text and of course everything is discussed there.Fortunately I was using the correct reductions and as mentioned above got good results.
Thanks
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David Burch
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posted July 05, 2014 06:29 PM
Excellent. Sounds like you have the procedure sorted out and are getting good data.
and yes, the fit slope could well improve your results.
As for the davis AH, these are neat, well made devices, but you can also use a plate of molasses. One of the articles we have describes this in some detail.. and there is a blog post called the eatable artificial horizon.
We have not tried putting molasses in the davis unit. maybe not a good idea, but you could use old black motor oil.
From: Starpath, Seattle, WA
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cmoller
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posted July 06, 2014 11:51 AM
I couldn't bring myself to motor oil because I didn't like thinking about the clean up. I stole some cheap olive oil from the cooking cabinet which did the job nicely. I did see the smart man's pan of molasses in 11.15 which reminded me that you are a physicist probably of the school that honored transforming ph
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cmoller
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posted July 06, 2014 11:54 AM
I hit the wrong button before the sentence finished...transforming physical principles with stuff you could buy at the hardware store!
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David Burch
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posted July 06, 2014 01:52 PM
I just realized that this conversation is taking place in the wrong discussion group.
I will move this to the student discussion forum and we can carry on there.
Anyone registered in a course is best to use the Student Discussion Forum. it is monitored by the instructors and you get a quicker response.... it is also the data base with the most extensive records of related matters, dating back some 15 years.
From: Starpath, Seattle, WA
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Topic Closed
