Sextant Video Tutorial

The "Queen of the Skies"
Stearmandriver
Senior Airman
Posts: 174
Joined: 12 Mar 2017, 22:33

Sextant Video Tutorial

Post by Stearmandriver »

Hey all,

Since some folks seemed interested in my recent post about celestial nav with the sextant gauge, I made a video tutorial about it. If anyone's interested, it's here:

https://youtu.be/1Es9Qi8z4is

TreeTops
Master Sergeant
Posts: 1086
Joined: 07 Apr 2010, 06:13

Re: Sextant Video Tutorial

Post by TreeTops »

Thanks for the awesome tutorial mate. Pretty concise and covered enough to now give it a go, even adding at the end how celestial bodies can be used. Well done.
I spent the afternoon getting the gauge installed, decompiling the manual so I could read it and going through your Johnson Atoll to Christmas island flight to piece it all together, which is what your video backed nicely. Cleared up some of the mystery for sure.
If you feel so inclined to do another one, talking through the thought processes as the flight proceeded would be interesting.
You touched on the first shot being just a speed check only, which was fine, and proceeding to 2 and 3 shot locations. Allowing for the sextant level of accuracy, how far off course and also being ahead or behind position before correcting the aircraft track and airspeed calculations? Obviously wind direction and strength changes across large distances of 500+nm comes into play.
Thanks again mate. It was a huge help.
Cheers
Trev
Cheers
Trev

Stearmandriver
Senior Airman
Posts: 174
Joined: 12 Mar 2017, 22:33

Re: Sextant Video Tutorial

Post by Stearmandriver »

TreeTops wrote:Thanks for the awesome tutorial mate. Pretty concise and covered enough to now give it a go, even adding at the end how celestial bodies can be used. Well done.
I spent the afternoon getting the gauge installed, decompiling the manual so I could read it and going through your Johnson Atoll to Christmas island flight to piece it all together, which is what your video backed nicely. Cleared up some of the mystery for sure.
If you feel so inclined to do another one, talking through the thought processes as the flight proceeded would be interesting.
You touched on the first shot being just a speed check only, which was fine, and proceeding to 2 and 3 shot locations. Allowing for the sextant level of accuracy, how far off course and also being ahead or behind position before correcting the aircraft track and airspeed calculations? Obviously wind direction and strength changes across large distances of 500+nm comes into play.
Thanks again mate. It was a huge help.
Cheers
Trev

Hey Trev,

Glad to hear it helped! I actually was thinking I'd make one more video like you suggested, detailing my next pacific flight (I'm thinking from Christmas Island to Bora Bora). I figure I'll pre-plan everything and talk a bit about my planning methodology at the start, then cut the video and use time compression between fixes, filming video at every checkpoint to show the sextant shots and how to figure out any necessary corrections. That's probably a few weeks off though, considering my April schedule.

As far as methodology for off-course corrections, I've been waiting until I've got corroborating data from a couple different fixes before introducing a course correction; as you said, the accuracy level of the sextant is such that you want to be sure before changing heading. I've planned carefully and so haven't ended up more than 15 miles or so off course before correcting, but I guess if I got a single fix showing me significantly off course, I wouldn't wait until the next checkpoint - I'd grab another 3 shots for a new fix right away. If it agreed, I'd correct.

There is a dead reckoning calculation for off-course correction; it's avaliable at that website I use for calculations:
http://www.luizmonteiro.com/
Aviation calculations --> miscellaneous calculations --> off course problems. I've used this calculator and it works... but I'm not sure it isn't easier and just as effective to say "I'm left of course. Let's try 5 right and see how that looks at next checkpoint".

TreeTops
Master Sergeant
Posts: 1086
Joined: 07 Apr 2010, 06:13

Re: Sextant Video Tutorial

Post by TreeTops »

Great to hear you are thinking about another video. Myself and I guess many others will appreciate it.
Next thing you will have is a competition to see who is the most accurate for a given flight.

One thing I wish PlanG had was the ability to plot enroute aircraft position and generate an actual flight plan using all the features currently available to plan a route. ie Initial flight plan table and actual flight plan table.
Cheers
Trev

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Paul K
Technical Sergeant
Posts: 962
Joined: 20 Jun 2010, 08:44
Location: Norwich U.K.

Re: Sextant Video Tutorial

Post by Paul K »

Stearmandriver wrote:Hey all,

Since some folks seemed interested in my recent post about celestial nav with the sextant gauge, I made a video tutorial about it. If anyone's interested, it's here:

https://youtu.be/1Es9Qi8z4is
A first class tutorial, thank you ! :)

Hobart Escin

Re: Sextant Video Tutorial

Post by Hobart Escin »

Stearmandriver wrote:Hey all,

Since some folks seemed interested in my recent post about celestial nav with the sextant gauge, I made a video tutorial about it. If anyone's interested, it's here:

https://youtu.be/1Es9Qi8z4is
Wow Stearman, you've put in an enormous amount of time and effort into both your original post, and now by providing this EXCELLENT video tutorial. Thank you for all your hard work, and the personal time it took for you to put all of this together. This is so much fun to learn and implement in the sim!

From the best of my understanding IRL though, it's not possible to actually get a sun fix (two intersecting LOPs at right angles) by just using one celestial body as a reference is it? In other words, I think only a single LOP can be derived at a time using this technique, but exact longitude can be determined once a day at noontime with a sun only shot, and there is another technique called 'advancing sun lines' which sort of compliments solid dead reckoning but does not determine an exact fix. The only way to achieve a daytime fix IRL is to do a 'Sun/Moon' shot at times of the day and month that the moon is visible during daylight hours. So, your technique illustrated in your video would essentially be Sun/Moon intersecting LOP fix I think IRL?

Fun damn stuff and again, thank you so much for your very hard work with this.

DaveR
Airman Basic
Posts: 5
Joined: 23 Mar 2017, 08:48

Re: Sextant Video Tutorial

Post by DaveR »

Thanks Stearmandriver! I was not aware of the celestial nav capability in FSX before this. Time to brush up on some old skills and give it a try.

TreeTops
Master Sergeant
Posts: 1086
Joined: 07 Apr 2010, 06:13

Re: Sextant Video Tutorial

Post by TreeTops »

Hobart, you are correct that a single celestial body will not give you a fix but only a line of position (LOP)
See Stearman's thread from last year showing using sun shots to give a progress check only, and using 1:10 rule to take care of the track.
http://www.flightsim.com/vbfs/showthrea ... Tiny-Atoll
Cheers
Trev

Stearmandriver
Senior Airman
Posts: 174
Joined: 12 Mar 2017, 22:33

Re: Sextant Video Tutorial

Post by Stearmandriver »

TreeTops wrote:One thing I wish PlanG had was the ability to plot enroute aircraft position and generate an actual flight plan using all the features currently available to plan a route. ie Initial flight plan table and actual flight plan table.
Agreed. This is why I've been using Google Earth - it's the only digital charting application I know of that lets you plot lines on the chart, measuring distance and true course. It would be nice to use something purpose-built for navigation, but Earth actually works nicely.

Stearmandriver
Senior Airman
Posts: 174
Joined: 12 Mar 2017, 22:33

Re: Sextant Video Tutorial

Post by Stearmandriver »

Hobart Escin wrote:From the best of my understanding IRL though, it's not possible to actually get a sun fix (two intersecting LOPs at right angles) by just using one celestial body as a reference is it? In other words, I think only a single LOP can be derived at a time using this technique, but exact longitude can be determined once a day at noontime with a sun only shot, and there is another technique called 'advancing sun lines' which sort of compliments solid dead reckoning but does not determine an exact fix. The only way to achieve a daytime fix IRL is to do a 'Sun/Moon' shot at times of the day and month that the moon is visible during daylight hours. So, your technique illustrated in your video would essentially be Sun/Moon intersecting LOP fix I think IRL?

Fun damn stuff and again, thank you so much for your very hard work with this.
Correct. My example shots were daytime shots for simplicity, and to show two important ideas: the ideal geometry of a two-shot fix (LOPs at right angles) and a three-shot fix (LOPs at right angles with another crossing at a 45), and the fact that this gauge doesn't actually care about current position of celestial bodies. You can shoot any azimuth you want, at any time. As you point out, this isn't realistic but I was trying not to scare folks off with an extra layer of realism (and complexity) that isn't necessary to use the gauge. I do talk at the end about looking up and using celestial objects in the positions that would actually be available, but I don't blame you if you didn't make it that far through. I got babbling at the end ;-)

You're correct though, during the day all you can count on is the sun. Like you say, you may be able to get the moon too, but the LOPs are never going to make nice right angles like we had in our example ;-).

TreeTops
Master Sergeant
Posts: 1086
Joined: 07 Apr 2010, 06:13

Re: Sextant Video Tutorial

Post by TreeTops »

I put in a request on the Plan-G forum. See if Tim can come up with something.
Cheers
Trev

Hobart Escin

Re: Sextant Video Tutorial

Post by Hobart Escin »

Stearmandriver wrote:
Hobart Escin wrote:From the best of my understanding IRL though, it's not possible to actually get a sun fix (two intersecting LOPs at right angles) by just using one celestial body as a reference is it? In other words, I think only a single LOP can be derived at a time using this technique, but exact longitude can be determined once a day at noontime with a sun only shot, and there is another technique called 'advancing sun lines' which sort of compliments solid dead reckoning but does not determine an exact fix. The only way to achieve a daytime fix IRL is to do a 'Sun/Moon' shot at times of the day and month that the moon is visible during daylight hours. So, your technique illustrated in your video would essentially be Sun/Moon intersecting LOP fix I think IRL?

Fun damn stuff and again, thank you so much for your very hard work with this.
Correct. My example shots were daytime shots for simplicity, and to show two important ideas: the ideal geometry of a two-shot fix (LOPs at right angles) and a three-shot fix (LOPs at right angles with another crossing at a 45), and the fact that this gauge doesn't actually care about current position of celestial bodies. You can shoot any azimuth you want, at any time. As you point out, this isn't realistic but I was trying not to scare folks off with an extra layer of realism (and complexity) that isn't necessary to use the gauge. I do talk at the end about looking up and using celestial objects in the positions that would actually be available, but I don't blame you if you didn't make it that far through. I got babbling at the end ;-)

You're correct though, during the day all you can count on is the sun. Like you say, you may be able to get the moon too, but the LOPs are never going to make nice right angles like we had in our example ;-).
Hi Stearman,

My bad for not digesting all of your information properly! You actually explained everything VERY thoroughly in your video, but I was confused about how the gauge actually works in the sim vs. real life, and I was trying to reconcile my understanding of everything. What I wasn't getting is that the sextant gauge actually does all the calculations AUTOMATICALLY after you take a shot (DUH moment for me :P ) and returns the distance offset value which you use to plot a LOP. You explained earlier that the sextant gauge in the sim doesn't really know or care about the actual positions of celestial objects in the Flightsim sky itself, but rather acts like a trigonometric calculator using the assumed position data and observation angles you input into it. I'm finally grasping this concept (yay). You are using the tables just as you would IRL for a sextant shot in terms of expected position data for a celestial object, and after you input this data into the gauge it automatically performs the calculations right away instead of the user having to cross reference actual table data and making manual calculations. The sextant gauge is doing all the grunt work at this point to yield the value you need (again, as you explained earlier). Everything is finally soaking in, despite my protective layers that normally keep new information from getting into my brain. :lol:

Seriously though, this is opening up a whole new avenue for me to enjoy simming on a whole different level of immersion. THANK YOU again for sharing all of this information with us!!!!

Hobart Escin

Re: Sextant Video Tutorial

Post by Hobart Escin »

TreeTops wrote:Hobart, you are correct that a single celestial body will not give you a fix but only a line of position (LOP)
See Stearman's thread from last year showing using sun shots to give a progress check only, and using 1:10 rule to take care of the track.
http://www.flightsim.com/vbfs/showthrea ... Tiny-Atoll
Aha, now THIS is realistic. Thanks for the pointing me to that thread!

TreeTops
Master Sergeant
Posts: 1086
Joined: 07 Apr 2010, 06:13

Re: Sextant Video Tutorial

Post by TreeTops »

Yes, there is so many combinations available depending of the flight taken and whether there are any Nav aids in range or recognisable land features.
In this case it was accurate westing but only dead reckoning with the course drift.

I am planning my first big flight from Hobart, Tasmania to Dunedin, New Zealand which is 1000nm. I am plotting to make landfall on the southern tip of New Zealand where I can avoid the mountains on the west coast and then pick up an NDB where I can be confident of letting down safety if the weather is bad.
Cheers
Trev

Stearmandriver
Senior Airman
Posts: 174
Joined: 12 Mar 2017, 22:33

Re: Sextant Video Tutorial

Post by Stearmandriver »

Hobart Escin wrote: What I wasn't getting is that the sextant gauge actually does all the calculations AUTOMATICALLY after you take a shot (DUH moment for me :P ) and returns the distance offset value which you use to plot a LOP. You explained earlier that the sextant gauge in the sim doesn't really know or care about the actual positions of celestial objects in the Flightsim sky itself, but rather acts like a trigonometric calculator using the assumed position data and observation angles you input into it. I'm finally grasping this concept (yay). You are using the tables just as you would IRL for a sextant shot in terms of expected position data for a celestial object, and after you input this data into the gauge it automatically performs the calculations right away instead of the user having to cross reference actual table data and making manual calculations. The sextant gauge is doing all the grunt work at this point to yield the value you need (again, as you explained earlier)
Yup. Glad it's making sense. Practically speaking, this isn't complex, but even though the gauge documentation is very good, I agree it can be confusing until you see it in action a couple times. I was hoping a video would help.

One thing your comment makes me I feel like I should have emphasized in the video - while I believe the gauge DOES do the calculations immediately as you say, the distance offset it returns for a result at the end very much DOES depend on your accuracy at aligning the bubble with the star. That part isn't for fun or for show - every mouse wheel click you are off changes the distance offset returned by 5nm. And it does take some practice - sometimes it'll feel like the sweet spot is between two possible positions, probably because it is. The designers did a great job with this.

Anyway, just wanted to make sure that part was clear. I've been emphasizing how easy and automated the gauge is, and all the ways it lowers workload by doing the grunt work for you, but I want to make sure you understand THAT part is important. A sloppy shot will yeild a less accurate result for sure.

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