Gen Nav

[The Otter's Pocket]

From yesterdays Gen NAv Exam
What is a small circle? Also How many points can a small circle join?
Its been bugging me all night.
Any help would be greatly appreciated.

[bfato]

I thought a small circle was any circle around the earth that was not a great circle. e.g. lines of lattitude other than the equator would be small circles. If I'm correct, then surely there could be any number of 'points' lying on that circle.

Anyone else?

[The Otter's Pocket]

I thought that it could be any number of points, however isn't the Equator a Great Circle and a Rhumb Line depending on the projection, or is that my bum talking again?
I thought with a small cirle there is only one point.

[High Wing Drifter]

Strange questions:

1) A small circle is an intersection of a sphere whose circumference is less than the sphere's. In geographic terms all parallels except for the equator are small circles. Meridians are not as they are the same circumference as the Earth (assuming the Earth is a sphere of course). So only some rhumb lines are small circles .

2) One. A circle ends where it starts! Why do I think that isn't the answer though?

[Send Clowns]

A small circle is defined as any circle on the surface of a sphere that is not a great circle. However HWD's definition is also correct, and since a sphere can always be chosen that can be drawn through a given 4 points then the answer is 4 points - with the exception that if they are all on a great circle then it cannot be done (as the great circle is, by definition, not a small circle!).

Send Clowns
Former Gen Nav instructor, BCFT

[bolty_1000]

guys.....any further tips on the exam? im set to take it in Feb and this is the subject that i reckon is going to kill me!!!
the rumour i have heard is that you are pushed for time....did you have enough time to complete it??

[High Wing Drifter]

Bolty,
Did you have enough time to complete it??
Yes, I had fifteen minutes to spare which was the least remaining time of all the exams by a long way. Just enough to cover some of my unsure questions before collection time.

From my experience, these things kill time in the Gnav exam:
1) Spending time working out problems using Pythagoras (or other relatively complex problems) when the correct answer is logically aparent just by looking at the alternatives.

2) The CPR-5 work: You absolutely essentially must just practice your CRP knowledge. I was asked to work out all sorts of things. 1/3rd of the questions were CRP based and they used up more than 1/3rd of the available time!

3) Make sure your plotting is good: If I recall correctly, there were quite a few points up for grabs there.

4) Be efficient, if you are stuck on a 1 pointer, mark it to come back later and move one.

[aztec25]

Agree totally with HWD's points.

This was the only exam where I found time was a problem. I went into the exam thinking that Gen Nav was one of my strongest subjects along with Met. I came out thinking I'd blown it (luckily I still got 86%) BUT I ran out of time with three questions not done and one of them was a 3 pointer (unforgiveable); lousy exam techinique on my part escpecially as the guys at BGS had drummed into us - 'find the 2 & 3 point questions first!' the 2 & 3 point questions are not any harder they just take up a little more time.

As HWD says you will save loads of time if you are totally comfortable with the CRP5 and read the questions very carefully - the questions look similar but they are often asking for different things: like asking for HDG/GS when you wouldn't apply drift and Track/GS when you would apply drift etc.

In any exam with numerous questions if I can't answer the Q straight off or do the calculation in 2 minutes I make a note of the question number and come back to it at the end. You will find that you often come back to a number of questions with more time left than you think - pressure off!

Having said that - if you know your stuff the Gen Nav paper isn't hard just watch the time. One guy did the paper with me, finished with 45 mins to go and scored 98%!!

Good luck.

[The Otter's Pocket]

Thank You all for the responses. I had only ever heard of a small circle once before and I must admit that HWD answer was the same conclusion I came too. I sketched a drawing and trip many possibilities, the opposite to a great circle. I came to the conclusion that there is only One.

With regard to this months exam I must admit that it was a great deal more manageable than I had thought it would be. I failed it in the summer as I was rushed for time, forgot my protractor, was hot and sweaty and just didn't spark in the exam. This time I was comfortable with the questions and felt prepared.
I finished with over half an hour to go! Yet my friends struggled to finish in December. Unfortunatly it is pure luck of the draw. There was only one question on plotting which was a shame as that is easy points, and one on time and four on INS from the question bank.

Good luck in Feb. Use the databases of questions, they are invaluable.

[greengage22]

Are we quite sure that that was the question? Someone who sat the GN exam yesterday told me that he remembered the question as: How many small circles can be drawn through 2 points on the earth's surface? and he thought that the options were : None, one, two, many.

Obviously it makes a difference if the question has not been accurately recalled. Does anyone else who sat the paper yesterday remember what the wording actually was?

[Charlie Zulu]

Funny you should mention that aztec but I also left the exam room with just over half an hour left on the clock. This was after double checking everything. In hindsight if I took another five minutes or so on a Lamberts Conformal theory question then I would have got 100% (I am pretty sure that was the question I had wrong). In reality I was happy with the 99% that dropped through the door.

It isn't difficult. Nor is it particularly time constrained if you are very familiar with the CRP-5. Also with the runway hw/cw questions use the calculator, it is a lot quicker than the CRP-5.

Know GC's and RL's and how to calculate them quickly.

Be very careful when it comes to variation / deviation etc etc... easy to subtract / add the wrong way around and hey presto choosing the incorrect answer that the CAA have very handily supplied as an option.

There is usually a nice easy question that looks complicated at first but if you draw it out you'll find it is a right angled triangle with two equal sides so the answer is normally 45/135/225/315 degree relative bearing to / from the aircraft (usually a VOR or something).

The plotting is usually centred over Ireland. So know the E(LO)1 chart well.

Also INS/IRS and Compass questions crop up near the end. The IRS question usually has three waypoints with an autopilot flying between each of them in turn. The Lat/Long's are given and they want the number of degrees the aircraft would turn at the second waypoint to reach waypoint three. This is usually a two marker (maybe a three but I might be wrong).

Know the formula's well. "No two C's together" will tell you that Convergency and Cos can't go together so it must be Convergency and Sin. Cos must therefore be Departure.

Anyway if I think of any specific examples I'll post them here.

[taxitoalpha]

Are we quite sure that that was the question? Someone who sat the GN exam yesterday told me that he remembered the question as: How many small circles can be drawn through 2 points on the earth's surface? and he thought that the options were : None, one, two, many.
Obviously it makes a difference if the question has not been accurately recalled. Does anyone else who sat the paper yesterday remember what the wording actually was?

I sat it this week and recall it being as you defined here, so I came to the conclusion that it was many as did my instructor but my head was a little fuzzy when I left gen nav so could be mistaken!

[Keith.Williams.]

We could consider a small circle to be made up of an infinitely large number of infinitely small points each touching the next. This means that a small circle can touch an infinite number of points.

If the question asked how many small circles can join two points the answer once again is an infinite number. All we need to do is select a slightly different radius for each circle.

If however the question asked at how many points a small circle can cross any given great circle then the answer is not more than 2