Small gimmick, big effect....

[nigelb]

;-)

As stated approximately 2 inches above....

That's what I get for not reading the rest of the thread before responding!

[Tom Clayton]

;-)

As stated approximately 2 inches above....

That's what happens when you get to the bottom of page 1 and don't notice that there's a second page!

[Kevin]

Hobby wrote:

I recall reading somewhere that Francis Chichester flew a Moth of some kind to New Zealand in the 1930s and worked on the principle that objects were more easily identified at an angle rather than seeeking to aim straight at them. On his flight to NZ he deliberately flew a track across the sea such that his landfall was not directly overhead his intended destination. I cannot recall whether he flew at a height in excess of the highest expected land in the area - and in any case after a long, relatively slow over-water flight how would he know what pressure to set on his altimeter?

Any real navigators or pilots care to comment on the above navigation technique?

Almost right, but the real technique that Chichester developed was this:

Suppose you are navigating from any place to a very small island far away and you are limited to using pre-radio navigational techniques. For clarity of example, we will also suppose that you are flying east-west or west-east, although it works for any track.

First, you calculate your course and track using your best estimates for wind, etc, such that under ideal circumstances you would arrive dead overhead the island if there were no flying errors and winds were exactly as calculated.

This idealised situation is of course not generally achievable, so that the usual technique prior to Chichester's was that when your watch/sextant told you that you should be at the island (eg viewing the Sun at sunrise when flying east), you would then be faced with searching along a north-south line without knowing whether you were starting from N or S of the island. This of course led to a 50/50 chance of spending search time (and fuel) flying away from the island; this distance would then have to be retraced (more fuel) before starting to make good the distance to the island. Furthermore, the pilot/navigator will be tempted to broaden his search as time goes by and he loses confidence. People have become lost this way.

Chichester's technique, at once both simple and powerful, is to 'build-in' a deliberate offset to ensure that, when all the reasonably possible errors are factored in, the track flown will always end up (say, in this example) north of the island. This means that the navigator applies all the precalculated deviations/errors in one direction. In modern parlance, you would take the 3-sigma error and apply it.

The result is that when you arrive at the N-S position line for the island, you merely turn 90 degrees to the south and fly directly to it.

This technique, published by Francis Chichester in his book in the 1930's, works for both aerial and marine navigation. Even today, if all your modern navaids have gone out, this will work with just a map, watch and compass.

Cheers,

Kevin

[speedbird591]

Thanks for that insight, Kevin. Such a simple idea and virtually foolproof that it makes you wonder why it hasn't always been established practice. Very interesting.

On the same subject - navigation - I read a fascinating book a couple of years back called Longitude by Dava Sobel. It's the history of how a British clockmaker solved the problem of how to accurately measure longitude which had puzzled men for hundreds of years. http://www.amazon.co.uk/Longitude-Dava- ... F8&s=books

As one sailed on a long voyage, the primitive clocks of the day would become increasingly inaccurate and taking the position of the sun at midday became guesswork. The movement of the ship and the effects of the heat, cold or humidity also affected the delicate instruments. Hundreds of ships and thousands of men were lost becuse of the inability to navigate accurately.

The book traces the histories of navigation and clockmaking and contains entertaining insights into the men and the politics of the day. It's a cracking read and was in the best-sellers chart for a long time. A good stocking filler?

Ian

[hobby]

Thank you Kevin for the detailed and interesting description of the correct method Chichester used. That method would be of interest to pilots and navigators today if they suffered total electrical supply failure on a long ferry flight.

I recall that during the last couple of years a twin engined GA aircraft and the two crew members were lost at sea during a flight from Iceland to the UK. Perhaps due to electrical failure? But then aren't standby GPS systems, of which I have no practical experience, powered by their own batteries to guard against such an eventuality?

Many thanks to Dan for his directions for FS9 stars.dat. I am just off to attend to that.

[hobby]

Just followed Speedbird and Dan's directions and found the original FS9 stars.dat file that I have now replaced with rlstar04.zip. Then went to Basra (ORMM) at night and the sky contained an extraordinary number of stars. Well worth the small amount of time spent on downloading, enquiries here and changing the original FS9 stars.dat. Once again many thanks.

[petermcleland]

Well I have FSX and I have looked at the stars, I still can't find evidence that they are accurately placed but I remember a video interview with one of the FSX development team where he said that the stars are accurate.

Im not really familiar with the skies though so I wouldn't notice alot!

If you look at Orion in FSX you will see that one of the "Belt" stars is badly misplaced. There is apparently more attempt at colour in the FSX stars but I still prefer FS9.1 + "Stars" which has great accuracy and more stars but no attempt at colour. The Moon phases are corrected in FSX as the lit portion in FS9 did not align correctly to point at the Sun.

[flugkapitan]

Thanks for the info about the real stars file. I had remembered reading something about it quite some time ago, but never got around to downloading and installing it. That is the first priority when I get home from work shortly

Regards,
Scott
KJMS (or thereabouts)