Reciprocals

[peter2407]

If i have a lighthouse to my immediate left, it is 090 degrees from me to it, therefore 270 from it to me? Assuming i am facing north (does that matter?)

What is the equivalent regarding the face of a clock? Reason for asking (apart from the obvious of confirming my maths (not math, our colonial chums ..) - picked up the PBO skippers handbook thingy and one page 64 it talks about "talking in" a resue helicopter by telling it where you in relation to it, from its perspective.

 

[davidej]

Just add 180 degrees if you start in the 0-180 range or subtract 180 if you start in the 181 -360 range

If a clock - do something similar with 6hrs

 

[Deleted member 36384]

You just state the reference point i.e 3 o-clock from helicopter.

 

[theoldsalt]

If you are facing north and the lighthouse is to your immediate left then it is at 270 (west) not 090 (east).

The reciprocal is that you are due east of the lighthouse.......or have I misunderstood you?

 

[Athene V30]

Reciprocals - add 200 subtract 20 or subtract 200 add 20.

 

[MoodySabre]

If i have a lighthouse to my immediate left, it is 090 degrees from me to it, therefore 270 from it to me? Assuming i am facing north (does that matter?)

What is the equivalent regarding the face of a clock? Reason for asking (apart from the obvious of confirming my maths (not math, our colonial chums ..) - picked up the PBO skippers handbook thingy and one page 64 it talks about "talking in" a resue helicopter by telling it where you in relation to it, from its perspective.

Surely you have to know the heading of the helicopter to tell it you were at Xo'clock. I suppose a guess followed by a guess etc until it was close would do.

 

[pampas]

Doesn't matter which way you are facing, one should give your position as the bearing from the object (In this case the lighthouse), then the pilot or navigator simply lays in the course and steers to intersect you, (IF you also have given an approx. distance )

 

[VicMallows]

If you are facing north and the lighthouse is to your immediate left then it is at 270 (west) not 090 (east).

The reciprocal is that you are due east of the lighthouse.......or have I misunderstood you?

I agree with you.

 

[Rigger Mortice]

Alternatively. Just read the reciprocal off the compass.

 

[Giblets]

The direction in which the helicopter is travelling would always be towards twelve o'clock from it's perspective regardless of it's actual compass heading. Therefore if it is heading due west and you are due north of it you would be at three o'clock in relation to it.

 

[duncan99210]

I was always taught that when talking to a helicopter that you could see and where the helicopter was not aware of your exact location you should use the clock system. 12 o'clock is the front of the helicopter: 6 o'clock is directly behind it, 3 o'clock is off to its right and 9 o'clock is off to its left. Then add in your estimated distance: just off the right side of the aircraft and three hundred metres away would be "300 metres at your one o'clock".

Bearings: just add 180 to the bearing, remembering to only count up to 360. Always found it fairly easy to. Equally, using a Portland Plotter, just dial in the bearing, lay it on the chart so that it crosses the object and your position is somewhere along that line. Take a second bearing and plot that in the same fashion and you have your position(ish).

 

[nigelmercier]

If i have a lighthouse to my immediate left, it is 090 degrees from me to it, therefore 270 from it to me?

The relative bearing of the lighthouse from you is 270°, the relative bearing of you from the lighthouse is undefined. The absolute bearings depend on your direction; if you are heading North, they are 270° and 90° respectively.

 

[alahol2]

The relative bearing of the lighthouse from you is 270°, the relative bearing of you from the lighthouse is undefined. The absolute bearings depend on your direction; if you are heading North, they are 270° and 90° respectively.

No, the relative bearing is dependent on the direction of travel. The absolute bearing is dependent on the instantaneous position.

 

[Buck Turgidson]

The direction in which the helicopter is travelling would always be towards twelve o'clock from it's perspective regardless of it's actual compass heading. Therefore if it is heading due west and you are due north of it you would be at three o'clock in relation to it.

No, the direction of travel is irrelevant. It the heading that defines 12 o'clock.
Unless you can clearly see the aircraft then you cannot use the clock system to describe your position but a compass bearing will always work. I say this having spent a considerable amount of time in a large aircraft surrounded by small aircraft all wanting to probe me ;-)

 

[Giblets]

Sorry, I forgot that helicopters can fly sideways & backwards as well!

It's always intrigued me. How do in-flight tankers take payment? Would it be a "Customer Not Present" transaction?

 

[prv]

The relative bearing of the lighthouse from you is 270°, the relative bearing of you from the lighthouse is undefined. The absolute bearings depend on your direction; if you are heading North, they are 270° and 90° respectively.

No, the relative bearing is dependent on the direction of travel. The absolute bearing is dependent on the instantaneous position.

You two are agreeing with each other, except that Nigel is forgetting that the OP specified that he's facing North, and Alahol is forgetting that the OP started with "a lighthouse to my left".

Pete

 

[zzyyxx]

If i have a lighthouse to my immediate left, it is 090 degrees from me to it, therefore 270 from it to me? Assuming i am facing north (does that matter?)

What is the equivalent regarding the face of a clock? Reason for asking (apart from the obvious of confirming my maths (not math, our colonial chums ..) - picked up the PBO skippers handbook thingy and one page 64 it talks about "talking in" a resue helicopter by telling it where you in relation to it, from its perspective.

As I recall, it mentions that you should state your position as the distance and bearing from the lighthouse i.e. In the boat you take a bearing and the lighthouse is 270 say 5 miles, you would state your position as 90 degrees 5 miles from the lighthouse.

That is you tell people where the moving object is relative to a fixed charted point.

 

[alant]

Doesn't matter which way you are facing, one should give your position as the bearing from the object (In this case the lighthouse), then the pilot or navigator simply lays in the course and steers to intersect you, (IF you also have given an approx. distance )

Reading the OP & others, it seems there can be some confusion, so why, does a casualty when in extremis & under stress, have to do 'difficult sums' when calling for help? The simplest method surely, is for the casualty to give a bearing to an object then let the man in a nice calm/warm/dry CG watchroom, work out the bearing from the object, for the helicopter to fly along.

 

[Oldhairy]

it seems there can be some confusion, so why, does a casualty when in extremis & under stress, have to do 'difficult sums

Your observation is indeed logical, but long established emergency and standard navigation procedures dictate bearings from land marks etc. Imperative if there is any chance of language difficulty.

 

[alant]

it seems there can be some confusion, so why, does a casualty when in extremis & under stress, have to do 'difficult sums

Your observation is indeed logical, but long established emergency and standard navigation procedures dictate bearings from land marks etc. Imperative if there is any chance of language difficulty.

Is 'strain' a language then?

Presumably, that practice was established, when mainly ships were in distress, not multitudes of amateur yotties, up to their armpits in water in a F8.