Celestial Nav.
- Thread starter ppragman
- Start date
Got a few Nav winged guys in my unit who were "table-Nav's" in the -135 and the -130. I posed the question to them and they said it was like riding a bike, so far as remembering how to use one.
ppragman
FLIPY FLAPS!
Yeah, that's what I've heard, it's kind of a pointless exercise in time wasting when even the average VFR only airplane has ten types of GPS, a VOR, an ADF etc. It is interesting however. It's kind of a lost art.
fish314
Well-Known Member
Yeah, even fix to fix direct off a VOR, or dead reckoning off the ground are going away. Cell Nav is pretty much gone. From what I hear they don't even teach it in NAV school anymore.
Cessnaflyer
Wooooooooooooooooooooooooooooooo
I've always wanted to do that. Where did you get you sextant at?
You're right, they don't. I can remember being at the old Mather AFB in Sacremento, where they had this IMAX-type theatre that showed outer space, and where they'd teach stars, constellations, etc and celestial nav. I believe they stopped teaching it 3 years ago or so.
ppragman
FLIPY FLAPS!
I bought a non-leveling practice plastic sextant from western marine.
http://www.westmarine.com/webapp/wc...11?&cid=chanintel&ci_src=14110944&ci_sku=1611
granlistillo
Well-Known Member
Hey buddy,
Glad to hear your interest in a dying art. As I understand it they don't even teach it to military navigators anymore, which Im not convinced is a good idea. GPS can be jammed or attacked. Nothing will jam cel, except a vast area of high overcast.
Pretty much impossible to get a good height observed of a cel body with a marine sextant (that would be useful for navigation). You would need to have a sextant with a bubble to give an artificial horizon.
Using a marine sextant from a boat, you can do a easy horizon calculation for your small height above the surface, not so in a plane. Also aerial sextants allow for an averaged observation and have some sort of mounting to hold it steady.
If you wanted to practice on the ground, and could get one, I would recommend the older sextants that they used in the astrodomes of old airplanes. In the Navy I had to use a periscopic sextant, which would be useless for your purposes.
I would love to get back into it if I ever have time to do some sailing, and it was probably the most challenging thing I ever did in aviation.
granlistillo
Well-Known Member
I met a nav 3 yrs ago that never went through it and I think he was a 02 or 03. Really don't see the point in having a Nav with all the FMS and EFIS stuff out there.
If they want to have old school capabilities for a contigency, fine then train for it. I remember getting 1st gen GPS retrofit in our planes, but we still had to shoot a celestial line of position, and take cel heading check every flight for proficiency.
ppragman
FLIPY FLAPS!
Could I just glue a couple of levels onto the body of the instrument, and match the bubbles up and then shoot my sight? Not really useful in the airplane, nor will I probably ever use celnav in the airplane, but still, a curiosity. I've been reading a lot about it, and damn that stuff is cool. Pressure nav is pretty cool too.
Orange Anchor
New Member
Here you go. http://tinyurl.com/degav8
ASpilot2be
Qbicle seat warmer
How do you plan to use it with all the cloudy weather around here?
Of course the sun is out now that you get it.
Of course the sun is out now that you get it.
granlistillo
Well-Known Member
I guess so...
The bubble also acts as the horizon. It creates a level plane so you put the star, planet, son or moon in the center of the bubble and dont see the actually horizon.
We used the intercept method for shooting and plotting the LOP. I think this is different from what sailors do.
Pressure Nav????
How long would it take to get all the levels lined up for you to shoot your star and also mark the time you took your observation? The longer it takes you your accuracy/precision of your celestial fix will suffer - but the upshot is that you'll get better the more you work with it.
Even on the surface side of it - the Navy uses a program called STELLA now where you put in your estimated position at the time you intend to take your observation - the program then tells you which stars to use and relieves you of having to go through the Air Almanac.
I never thought of the differences required for an aerial observation and a surface observation. At least on the surface side if you didn't have a visible horizon you couldn't take a celestial fix. It was interesting to hear about the bubble level.
ppragman
FLIPY FLAPS!
Pressure Pattern Navigation:
From this airfroce document I found.
Though I doubt I could calculate it.
granlistillo
Well-Known Member
Modern aerial sextants used a mechanical averager as you kept moving the height adjuster dial for two minutes, one each side of fix time. Trying to take an instantaneous observation at fix time would be avpretty tall order.
The calculating of an EP or assumed position, and then comparing the height calculated vs height observed of the body, is known as the intercept method. It was mandatory for a periscopic sextant, as you had to calculate the rough position of the star to find it in the viewer. You then just zeroed in on in with the dial. Maybe an aircraft with an astrodome could use something like Pat's equipment.
granlistillo
Well-Known Member
My head hurts just thinking about it.
fish314
Well-Known Member
I have a book somewhere that gave a little plug and chug formula based on pressure pattern nav. The author took the Altimeter settings at the departure and destination airfields, and based on the difference between the two came up with an average drift correction for the entire flight. He wasn't exactly navigating off of the pressure patterns, but it was more like a way to fly VFR without having to make any heading changes.
See if I can find it tonight.
Pub 9 you mean? or Bowditch as it's called in the Navy - that's what's used in the Navy. Lots of good info in there about coastal piloting, open ocean nav, also discusses radio propagation - HF, LF stuff and radar navigation. Though the celestial nav in there can be a little confusing if you've never seen/used the stuff before.
Aboard ship, when you took your round of star shots, it was usually a two person deal - one person shot the star and did the time hack - the other person marked the exact time for each shot and recorded the observation. Then in was back into the pilothouse to plot the LOPs to fix the ship's position and reset the ship's DR (dead reckoning) plot. and then you compared your celestial fix with your GPS fix.
