Astrocompass?

[Meatservo]

Does anyone know how much would be a reasonable price for an Astrocompass in working condition? I wish to re-familiarize myself with it (just for fun) and I want to have my own. The last company one went missing a while ago... I'm sure someone hooked it as a souvenir! Anyway, I would like to have my own. There are a couple on Ebay, but I suspect that due to their age their prices are being pushed up by the "collector" crowd... none of whom have any intention of using one.

They must be available somewhere for a reasonable price, also, does anyone calibrate and re-certify them anymore? There must be some Kenn Borek guys here who know where I can get one.

[Youngback]

Didn't check out ebay yet but it seems to get a good one with the box and manual and everything should set you back about $100. I don't think there is any need to calibrate. There is only a couple of moving parts and the bearing numbers can't move about. Might be mistaken but I've never had any issues with mine.

[Meatservo]

Yeh, I would have thought so too, I just remember they always used to have a green tag and a certification date. I'm not sure why, you're right, there's nothing on them to go out of whack.

[Conquest Driver]

http://www.celestaire.com/Compasses/Ast ... trocompass

There's where I got mine. These guys have all kinds of fun stuff.

[snoopy]

Send a PM to Just Curious .... He can set you up.

Cheers,
Kirsten B.

[Rowdy]

I had a bunch of reference material from the borek days, but alas it hath been misplaced. Lots of solid stuff out there. It really is a straightforward device once you get the basics and the hang of it. I'll keep digging

[Meatservo]

Thanks Rowdy, but I already know how to use one. My problem is I don't actually have one to monkey with as they got rid of them in our planes at work. I have seen them in Borek planes, so I assume they are still used or at least some peole stay current on them. I just want to own one for fun, and maybe to whip out now and then to practice. I'm that kind of guy. I hear the Almanacs are no longer available in printed form and need to be downloaded. Is this true?

[Youngback]

I don't know about other almanacs but I got mine from the US Naval Observatory. Only on CD format as of 2 years ago. Print off only the pages you want.

http://www.usno.navy.mil/USNO/astronomi ... s/ord-info

[Rowdy]

The almanacs are still printed. I have a copy kicking around somewhere. Good luck!

[Ref Plus 10]

Correct, Borek planes have them, and we have printed almanacs for every half year. Probably downloaded and printed a couple dozen times. Last I heard we were having trouble finding more, but honestly, the real trouble is finding people who know how they work. Give me the sun and no worries, but I can't tell the difference between a star and a planet unless I spend half an hour staring off in to space....wait, isn't that how I got my job??

Ref

[Raybanman]

Try Western Avionics in CYYC for an astrocompass, and I know for sure that they do the calibration and certification on them. Not sure what it costs, a company I worked for recently used them as the supplier. The almanacs are ordered on CD ROM, but an online version is available here: http://asa.usno.navy.mil/ if you are just messing around at home. As far as starshots are concerned, using the supplied star charts with the almanac is useless. I'd suggest buying a starwheel from a hobby shop or science store. A perfect solution if you have an iphone/ipod touch/ipad is StarMap. costs $12 but I'd reccommend it as you can move the screen to line up with what you see. Its what I've used. And it works great.

Cheers,
PP

[frozen solid]

I've noticed the military Twin Otters have a mount for these things on the "ceiling", and they hang upside-down. Any other ones I've seen are mounted right-side up. Are the military ones special, or does a MKII astrocompass work upside-down?

ISD01-6165.jpg (40.08 KiB) Viewed 2443 times

It looks like a garden-variety one to me. It surprises me that it works upside-down


PS, I stole that picture from a DND gallery, I hope it's not a big deal!

[Raybanman]

Well you should be able to use it upside down, if it was designed that way, the declination scale (the part that the sight is on) would need to be different than the ones i'm used to, as it denotes the angle up/down of the star. With the proper placarding, I see no reason why not.

This Captain needs a little more training with his though, he's got it backwards! The part of the sight with the white card and the small magnifying bit are supposed to face toward you, The open frame end with the black bar goes towards the sun/star/moon/planet. for a sunshot, the black bar creates the shadow on the white card to line up the compass, and for star-shots (planets are the same) you aim through the magnifier and line the sights up like a rifle/handgun with the star. Unless he just set it and discovered the sun is behind him.... but I'd assume you'd be smart enough to figure that out before doing sun's true bearing.

Cheers,
PP

[PanEuropean]

OMG, I knew we would forget something when we designed the Series 400 flight compartment... Do you thing it's too late, should we put it back in?

Michael

[Youngback]

I have news for you. The Astrocompass works in the southern hemisphere too. If it is "upside down" you use the red numbers and not the white ones. As long as it is oriented with the north and south pole the numbers will be correct.

[frozen solid]

I read all the previous posts over again. I didn't notice anyone wondering if it worked in the southern hemisphere. I guess I assumed that the "South Latitude" printed on it along with the red numbers had something to do with the southern hemisphere. I wasn't talking about it being upside down in the southern hemisphere along with the rest of the plane, I was talking about it being upside down IN the plane in the NORTHERN hemisphere. Thanks though.

If you're in the NORTHern hemisphere, and your compass happens to be mounted upside down in the cockpit of your plane, it seems as though you'd have to use the red "southern hemisphere" numbers. (In the northern hemisphere. I suppose you'd use the "northern hemisphere" numbers in the southern hemisphere, if your compass was mounted upside-down).

[niss]

You can order Nautical Almanac from west Marine.

http://www.westmarine.com/webapp/wcs/st ... _sku=97022

[Changes in Latitudes]

What are you looking to spend?

As far as the ebay comment, I've seen a couple on ebay go for $100 in the past, which seems reasonable. Others, out of military aircraft seem to ask higher prices. Keep your eyes open, they're out there.

[Axial Flow]

In reference to the picture of the new APEX Twin Otter panel...without the SANDEL back up slaveable DG the aircraft will not make NDA certification requirements as the APEX can not give heading when in the NDA...only GPS track.Wonder if this is just a promotional picture and not the end product...

[PanEuropean]

Hello Axial Flow:

The photo is of the end product.

The requirement for an independent gyroscopic heading device (it does not have to be a Sandel product) is unique to Canada, and unique to commercial operations carried out in the Canadian NDA. There is a 3 ATI size provision on the instrument panel to permit installation of such a device if required.

Personally, I'm not entirely convinced that an independent gyroscopic heading device is needed. As soon as the aircraft is moving at 7 knots groundspeed or more, the avionics suite will display the track made good (in either true or magnetic, whichever the pilot desires). I recently ferried a new Series 400 Twin Otter from Victoria to Europe via Rankin Inlet, Broughton Island, and Northern Iceland, and did not notice that any necessary information was missing. If the plane is stopped (not moving) on the ground, it will not display the current heading if the strength of the earth's magnetic field is less than 60 milligauss (typical in the NDA), but that's no loss - the only places that the aircraft usually comes to a complete stop are at the parking spot and (momentarily) while in position on the runway, prior to takeoff. It is very easy to confirm correct true or magnetic heading on the runway prior to takeoff by just rolling forward about 50 feet at or above 7 knots speed. There is no wind correction (drift angle correction) to be applied when taxiing, so, track will equal heading whilst on the ground.

It's possible that there is a valid reason for the operational requirement to have an independent gyroscopic heading device - I suppose it would enable the pilot to calculate winds aloft, or to calculate wind drift angle - but I'm not entirely sure that is something that is of genuine value. When operating in track mode (track made good derived from GPS velocity calcuations), the HSI displays exactly where the aircraft is, and exactly where it is going - it's like riding on a rail. I've posted a picture below that shows the aircraft carrying out an ILS approach in Iceland while in GPS derived track mode. In this particular case, the pilots have chosen to have the aircraft display magnetic track, rather than true track. I took the picture, and whilst flying the approach, I could not find any information that was "missing" as a result of not having a display of heading (as opposed to track made good, automatically converted to magnetic) displayed. Note the cyan CAS (Crew Alerting System) message on the lower middle display that says "HSI is Mag Track".

For sake of full disclosure, I need to say that I work for Viking, I am an engineering test pilot, and was involved in the specification and design of this system. I also have to apologize to the group for unintentionally knocking this discussion of the astrocompass slightly off track. I only posted the Twin Otter picture above as a humorous reference to how far our industry has come since the days of the astrocompass.

Honeywell Primus Apex - ILS Approach in 'Magnetic Track' mode