Celestial Navigation

[Jacques]

I finally have enough time on my hands to try and really understand this form of navigation using Kronzky's port-over of the Bubble sxtant to FSX. I have it installed in the stratocruiser, and I've made a few short journeys in daylight taking random shots just to familiarize myself with the procedure. I don't really feel as if I'm using it correctly. Mainly, I feel I'm over-thinking the process. So, my first question would be: assuming a North Atlantic flight, how do you go about selecting the stars to use for your shots? I know from looking at the USNO celestial tables:

http://aa.usno.navy.mil/data/docs/celnavtable.php

that the only two columns necessary in the sim are Hc (for elevation) and Zn (for Azimuth). How do you use that information to choose suitable stars? And then, do you need to put the sxtant in a window actually facing the stars, or is the information you put into the worksheet good enough ( if not realistic, you should point in the direction at least, but do you truly need to do so? )



Any help would be greatly appreciated!

JP



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[robert41]

Hello JP.
A few basics.
The s-- tant in FSX is greatly simplified, but there is still some skill needed to make an accurate position/fix. You do not need to position the s--tant, in the aircraft, to take a shot.

Looking at the usno site, enter a position, and we see the columns of stars.
Note the colors.
Red is for the sun and our local planets.
Green is for the north star Polaris and Aries. Polaris is exceptional because it moves very little from north.
Blue are the usable stars.
Black are non usable stars.
In order for a star/sun/planet to be usable it must be between 15 and 60 degrees in elevation, Hc.

Ideally, we want to shoot at least one good north or south star and one good east or west star for the assumed position, AP.
Good meaning as close to, north 360deg. or south 180deg. and west 270deg. or east 90deg. azimuth Zn, as possible.
From these 2 shots, we will get 2 lines of position. Where they cross is where we are relative to the AP.
The north or south shot will give us a latitude or how far north or south we are to the AP.
The east or west shot will give us a longitude or how far east or west we are to the AP.

It is also important to know, when entering the assumed position in the s--tant,
north degrees are positive
south degrees are negative
west degrees are negative
east degrees are positive.

OK. now you need to plan your route in FSX. Then go to the FSX map, and you will find the pink line that is your flight path. Drag your plane to a point on the pink line about 100 to 200nm from the starting airport, after some time this will be easy to guess how far to go. Write down the latitude and longitude at that point. And do this all the way to the destination airport. these positions are the assumed positions you will take shots of.

In flying the North Atlantic, we will always use Polaris for our north/south shot. Giving us a north or south position.
Then we just have to find a good east/west star for our east or west position.

Remember we cannot see the stars in daylight, so we can only use the sun for a shot. This gives us only one line of position to use. Normally this will be a longitude, east/west position. Except at high noon. The sun will give us a perfect latitude, north/south position. And of course it needs to be within 15 to 60deg in elevation.

Corrected a couple of directions.

[Jacques]

Hey Robert,
So, if you are flying West to East, for your speed line, you are looking for a star that roughly corresponds to your average heading, or 180 degrees off of your average heading at a planned assumed position, correct? OK, just as an example, today I put the Stratocruiser at Gander (CYQX), the course I've planned to EGPK is roughly 85 degrees.

Looking at the USNO info for today at 0030 GMT, Vega had an azimuth of 82 degrees. So I chose that as my speed line, since it was the closest to the heading I was going to fly. Then I chose Dubhe with an azimuth of 312 for one of my course lines and I chose Saturn with an azimuth of 174 as another course line. After reading your post, I realize that using Saturn was okay since its elevation was 24.34. I set my assumed position at N50.28 W50.28 which figured out to be 183 nm from Gander. When I ran the shots, and moved the green position circle to the intersection of all three shots, I was within a few nm miles of my actual position. Man, this is so cool I don't know if I'm going to be able to sleep tonight!

Robert, HUGE thanks for coming in with your knowledge! I can easily see making the transition from following the pink line to physically charting my progress across the map! I will probably have a lot more questions, if you're willing! I realize that this is a highly simplified simulation of celestial navigation, but I feel like I've grabbed hold of the reins of history, and I am in for a hell of a ride!


JP



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[robert41]

That is essentially how to do it.
I like to use one good north/south star and one good east/west star.
I have been using the s--tant since back in the FS9 days.
I have gotten very used to navigating with it. But some flights still end up with a few surprises.
Fire away with any questions.

[Jacques]

Hi Robert,

How are you plotting and/or keeping track of your progress? Do you use a paper chart, straight edge, pencil and compass to plot your course, or do you use another online source or even FSX? I think I am edging towards using the paper chart method, although I haven't had the best luck finding charts that copy easily off a web page. I guess I could use Plan G ( an online flight planning, mapping program) and just not link it to FSX. I would have my proposed course and waypoints on the map and could plot current position with each shot. What is your routine, though?

JP


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[robert41]

I use paper and pencil. First, plan the route in FSX. Find the coordinates for the assumed positions. I do not have a printer, so I just draw a simple map, (not to scale) with the start and end airports. I mark the assumed positions along the course. After taking the star shots, I mark roughly where Iam, and make small heading adjustments as needed.
One could use a plotting chart also, but the s--tant comes with a pretty good chart for this.

[dacamp66]

what I often do is to take a kitchen timer, and set it to 20-30 minutes; when it rings, i pop up the map and check my position compared to my desired course, with this information, i then determine whether i need to turn 5 deg. left, 5 deg. right, or maintain present course. the purpose of this is to simulate my (pretend) navigator feeding me a position fix and a recommended course. the timer is to simulate the time it takes for him to "work up" a fix. i do not look at the map at all in between "fixes"

[robert41]

I have been recreating Amelia Earhart's round the world flight in FSX using the s--tant. Flying the FSDB L10E with FSX upgrades.
This weekend was the Lae to Howland leg. Very long flight.
I have flown this leg many times in FS9 and FSX with some interesting results, and this flight was no different.
Starting at 1100am local Lae time. North to New Britain, then on course to Buka, in the Solomons. Then the long trek to the Gilberts.
Next the equator and date line. Crossing the equator is no problem, but crossing the date line can be quite interesting. In the RW, we go back one day. In FSX, several things can happen. The day can change or stay the same, and the time can change or stay the same. On this flight, the date stayed the same, but the time went back two hours.
Not certain what this does to the s--tants' chronometer, but at my final fix, the sun is coming up, and I can see a small island right on course, great, here we are. So I thought, after reaching this island, similar size, but it is not Howland (I have some scenery installed for Howland Island). Now the sun is up and I cannot use the stars anymore. After some thought, I think this is maybe the island to the south of Howland, way south, and I go back to my last east/west fix and steer straight north. After a bit, I pick up the NDB at Howland, now I can breath again.
Fortunate the weather was clear with light winds.

[Jacques]

That is an amazing story, Robert. I think it perfectly underscores why I have been trying to understand this form of navigation! I've a route planned and hope to give it a try this coming week.
If FSX changes the time and/or date arbitrarily at the dateline, could you go into the FSX menu and reset that information to what it should be? Or does that somehow make a bad situation worse, or do you just not want to interrupt the flow of the flight!

JP


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[robert41]

Not sure if changing the time or date in FSX would help or hurt. Have not tried this. As far as I can tell, the s--tant seems to keep with FSX time. And does this FSX time/date change agree with the USNO times and readings? This is something that I will have to check out further.

[robert41]

I ran a number of flight tests, changing dates and times. Seems to have no effect on using the s--tant. As long as you use the current date/time in the s--tant, all is good.

Just finished the Howland to Hawaii leg. Pretty uneventful except for about a 1 hour part through some stormy weather. Unable to take any star shots. After clearing the weather, I found I was right on course. Not bad. Sometimes better to be lucky. One more to go. The long trip back to California.

[Jacques]

Ok, Robert, thats good information! Thanks for doing the extra work!


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[robert41]

Made it to California. A very loooooong flight. Pretty uneventful till about 700nm out. Then the winds started shifting all over the place. Flying at 10000ft, just above the clouds. Great for taking star shots. Once the sun came up, it was sun shots and DR only, with 600 and some nm to go. At 50nm out, descended through the clouds. Right down to 1000ft before finally being able to see anything. And land ho. Picked up the SF NDB, slightly right of course, not a big deal, just glad to be here. Made my way to the bay, flew past the GG bridge, sighted Oakland, landed without any problems.

[Japo32]

Hi!

I wanted to reflote this topic because I want to make more or less the Amelia world tour but with the A2A P51 Civ one. So I have to make it through the south with the biggest jump from Pascua Island to Robinson Crusoe Island. It can be done as I tested the distance without winds.
BUT I don't want to use the GPS. I want to use the S..tant.

Something I saw in the instrument is that you don't point to the right stars directly (I don't know how to do it with different stars. Would be interesting to see a youtube tutorial, but I didn't see anyone). So in any position you aim the s..tant is ok. Always it is going to appear the sun or the stars (if you are inside of those 300nm of the AP)
What I would like to find is a instrument that let me aim the star I choose (so I have to identify it visually) or the Sun.. and tell me the azimuth and elevation that is. Something from the internal VC and appear in the shift+z menus for example...
Do you know any instrument like that?

[robert41]

Hello Japo.
No such instrument is available that I know of.
It might not be practical.
The sky (stars, sun, moon) was made back in 2004 or so. So we are always viewing that one particular time. And I do not know just how accurate it is to the real world sky.
Having to change the stars for every day/night, in the sim, would be a huge undertaking.
Good luck on your flight round the world.