NavList:

John H wrote: A question for all:

What precision is required when doing cel nav ?

The reason I ask is I am a pilot and when we had to do cel nav in the C-141 trying to find Canton I. or Wake we were happy to get a fix + or - 10 miles.  ( I was happy - maby my navigator was not. )

I would say that for a modern high speed, high altitude aircraft a celestial fix accuracy of ten miles was not unknown and wouldn’t have raised eyebrows.  Three miles was pretty good and less than three miles would have been thought exceptional.  Once beyond a couple of miles, the reasons for the inaccuracy was nothing to do with the accuracy of the basic mathematical formulae used to calculate the body’s altitude or the manufacturing precision of the instrument but all to do with the observers inability to correct exactly for the additional errors introduced by the use of a bubble or pendulous reference horizon, namely: Coriolis correction, rhumb line steering correction if applicable, and unintentional changes in speed and heading.  E.g. for an aircraft travelling at 480kts, a change of heading of one degree per minute during a shot would give an acceleration error of 25nm (see below).  The other thing is that, until relatively recently, over mid ocean, you had no way of checking how accurate your celestial was, because the accuracy of other long range aids to navigation, if you had them, was little better at extreme range.  It was only as you approached land and were able to use shorter range more accurate aids that you got an idea how accurate the navigation in the middle might have been.  Therefore, it’s little wonder that most aerial navigators were happy to take the tables on trust and not worry too much about the exact methods the number crunchers used to calculate them.  Flying was definitely different to sailing.  DaveP