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-   -   How to Navigate visually?? (https://www.pprune.org/pacific-general-aviation-questions/83935-how-navigate-visually.html)

squall 10th Mar 2003 00:18

How to Navigate visually??
 
Hi all,

Just wondering if some kind people could give me some tips on how to find a needle in the haystack which is required for the CPL. I always get in the general area but am finding it hard to narrow it down to the actual location. Often because there are more roads than appear on the map or something like that. Please give me some advice so that I can find a house or mineshaft or whatever the first time around. It is incredibly frustrating having to do this sort of naviagtion after having completed my instrument rating. I am after some set procedures to ensure that I stay on track after take-off to ensure that I get there the first time around. Eg take-off set course, note time etc.

Thanks for all your help as I really need it with visual nav. In theory it sounds very easy. Maintain Hdg and note time etc but I find that nine times out of ten I am off track.

Please help me !!:confused:

Keg 10th Mar 2003 02:18

When preparing the nav I used to put 'ten mile markers' on each leg and then work out ETAs based on flight plan. I could then check off beside them how I was going and whether I was up or down on ground speed. Heading and time works if you know the wind but you will need to adapt that if the wind isn't as accurate as you would've liked. The ten mile markers also help you know more instinctively where you are on the map. (Hugh Jarse may be able to comment some more on that as he was one of the instructors at my school when I learnt that one.)

I assume that you've got a pencil notched with ten mile markers in them too? Always good for working out easily and quickly how far off track I am! :eek:

Lastly, a good instructor to teach you and practise, practise, practise!!!

Arm out the window 10th Mar 2003 02:40

Hope this doesn't sound too much like telling you how to suck eggs:
Go clock to map to ground.

Orientate the map so that the direction you're going is at the top.

Use big dog's balls features to lead your eyes into the small ones.
Use funnel features if there are any, like roads, rivers, railway lines.

Plan for pinpoints at convenient positions along track legs; obvious features, so you get an accurate picture early on of what the wind's doing to you, with respect to both timing and track.

Either work out your groundspeed to revise ETAs, or use proportional nav - ie, I'm 2 minutes late 1/3 of the way along the leg, so I should be 6 minutes late at the end.

Know your usual cruise TAS in nm/min to work out where you should be along track at any particular time (I usually adjust for wind by using a percentage method - ie if I cruised at 140 KTAS and there's about a 10 kt headwind, I should be doing 130 kt over the ground, or 2 miles a minute plus (roughly) 10 percent. So if I've been on the leg for say 16 minutes, I should have gone about 32 + 3.2 nm along track, call it 35 miles.

Know how to use the 1 in 60 rule (or whatever you want to use) to give you accurate heading adjustments for wind - eg at a pinpoint, you find you're 2 miles off track after 40 miles along. That's 3 in 60, therefore change heading 3 degrees to parallel track. To get back on track in, say, 20 miles, you need to make up 2 miles across track in 20 which equates to 6 in 60, so change heading another 6 degrees to start converging back to track. Total heading change required 9 degrees. Then when you're back on track, the 'parallel track' heading should work.

Have a cruise nav cycle planning for a pinpoint every 15 - 20 minutes, or whatever time interval you want.

Do a standard check at every turn point - something like FCLEAR - Fuel, Compass(es), Log, Engine, Altimeter, Radio (Calls, airspace etc.)

Apologies for preaching if it's stuff you already do!

Lodown 10th Mar 2003 03:21

In addition to the above. You obviously have a bit of experience and I apologise if I am writing in simplistic terms.
My tip is don't just rely on one item. If you see a road that is expected at a particular time, don't just assume it is THE road you are looking for. The WACs are updated once about every four years, unlike your IFR charts. New features like roads and airports are added that are not shown on the chart. Many small features aren't depicted because they'd clutter the chart.
You need to confirm your position with a series of checks. The road should match the direction that is printed on the chart and the orientation with your track. Utilise surrounding landmarks like towns, mountain ranges, spot heights, powerlines and other features on the chart for confirmation. You should never be flying en route without occasionally checking your approximate position anyway. The turning or end point should simply be a confirmation of good en route navigation. Even if you aren't directly over your turning point at the end of a leg, don't get your knickers in a knot. If you've been navigating (even a little) en route, you won't be far off. A quick look around will usually result in a confirmation. Then, if that fails, you should know which direction to turn to get you to a point over which you can confirm your position, then work out a new track.
Low level navigation is demanding because instead of say ten or more features to confirm position, you're now down to one or two with gaps between confirmations. In this case, you're concentrating on confirming position at every possible reference on your track.
I think I was only once ever unsure of my position for an uncomfortable period of time (outside of my instructional period getting a CPL). It was many years ago in the stupidity of my youth and my passenger wanted to navigate to a farm strip, which was just a lat and long on the chart garnished from a phone call, and I inappropriately let him have the chart. (I should mention I was familiar with 95% of the route and we were in the middle of nowhere.) When we couldn't find the strip where he said it would be, I took the WAC back, made a few crosschecks with terrain and a town about 20 miles away, recalculated our position and then flew direct to the strip.
These are just my tips. Other people are far more knowledgeable than me.
Probably the best tip I have is that VFR is fun. It's not that hard. Don't sweat it. Get out and enjoy it. It's a heck of a lot more fun than IFR. IFR is for work. VFR is all FUN!

High Altitude 10th Mar 2003 04:26

Look out the window...;) ;) ;)

heypilut 10th Mar 2003 05:58

Wnen u know where your going drive there the day before and put coordinates in GPS.If your having trouble around the capital cities god help u in the tanami dessert in a clapped out 206.:eek:

Hugh Jarse 10th Mar 2003 07:40

I think Keg, Lodown and Arm have the good oil here, Squall.

There are a couple of schools of thought on markers along your track. Some say 10 miles, others 6 minutes. Both work fine, but my preference is 10 miles. Use what suits you best. 10 miles are a constant, but 6 mins depends on your groundspeed and may vary from nav to nav or even leg to leg. Use what you're comfortable with. When I was taught, we only used 1/2 way markers, which made it much easier to miss the key feature/s associated with that point. Far less accurate than the abovementioned.

Read map to ground (unless uncertain of your position), using the markers described above. Try to have a key feature picked out for each marker.

As for features, work from large to small. The larger features are gonna be easier to pick out when it all turns pear-shaped.

Remember, big to small.

And have fun!:}

TurboOtter 11th Mar 2003 01:10

I remember one of first navs, I had to find a road junction with a house, something stupid like that.
I flew to a point and looked at the ground and said to the intructor I felt the place was a few miles to the west, he said that I was wrong and pointed to a place a mile or two to the east and said that was it, and then proceeded to tell me how I had made my mistake.:confused:

We then had to fly in an westerly direction for the next leg of the nav and believe it or not the silly little place was where I said it was.:D
The instructor then mumbled something along the lines of "smartarse" :O

Visual navigation - the art of finding map makers mistakes and compensating for them!!:cool:

Mile High Society 11th Mar 2003 01:23

Where I learnt, we were taught to make at least one point along track which would give a positive fix. Dont wait to see something along the track to get a fix.

When planning the flight, pick one feature at least per leg (a town or dam or something visible which is more likely to be on the map and on the ground) reducing the distance between positive fixes reduces the amount you get off track before its too late.

Use the positive fix to do a 1 in 60, at least one per leg... unless of course it is a very short leg.

Also remember that 1 in 60's rely on having had a very constant heading. Pick a command heading and stick to it. If you wonder from your heading too often, you are inserting a variable which your flight plan does not allow for.

I am sorry if this seems all to simple, and perhaps a litle condescending but it is not intended that way. I am trying to emphasise the point that VFR nav is in fact just a formula. Heading + groundspeed gives a result, if it is not the desired result, take the corrective action. It is all simple maths. Just apply the method and reduce variables as best you can.

All of the above info is excellent as well.

Where I learnt, we were given our maps and flightplans for several minutes at the start of any given leg. After setting a command heading and giving our instructor an estimate for our 1 in 60 point, he/she would take everything back off us so that we would concentrate purely on flying accurately. 5 minutes before our estimate for the 1 in 60 point we would get our flight plans back just long enough to do a 1 in 60 and revise our estimate and then it was all taken away again and given back a few minutes before we were due to reach the waypoint.

This emphasises the point that VFR is for fun. Concentrate on flying accurately, and keep your head up. Looking at the maps for long durations actually works against you.

The last peice of advice I can give is to make sure you do a windcheck with your wizz wheel every now and then. Dont just go off the forecast as we all know they are not always right. Reduce the variables as much as you can.

Good luck and Happy Flying.... :)

Boomerang 11th Mar 2003 07:49

Before you depart, try to plot 10 minute markers on forecast wind. Then as soon as you can, identify a fix on track, or close to and abeam, circle it and write a time, continue to do so every 5, 10 or so minutes. Then, if you've held a constant heading (very important, you will be able to do a grounspeed check using a plotter and your CR-2/wizzwheel. Then recalcualte from your present, known position. Then if as you say you do, get in the general area, and still can't see it, perhaps get down lower to identify smaller features, read the road signs, or stop and ask directions :)

Good luck, alternatively contact Casio (?) for one of their GPS watches :)

gaunty 11th Mar 2003 08:12

Hmmm

I was given a little bit of advice from a wise old bird, that held me in good stead under the right circumstances and that was to fly track for heading after departure, you find out pretty quickly what is "actually" happening "now"and you can proceed from there, rather than waiting to find out later.

Has anybody else used that technique??

BTW don't try this at home folks, untill you are pretty confident of your nav.

squall 11th Mar 2003 08:52

Thanks for all the help. None of it was too basic as I need all the help and ideas I can get.

Were any of you nervous about having to find a remote feature on the map??? This is the most nerve racking part of the CPL test for me. I am worried that I may not find that homestead or mine shaft or whatever straight away.

Any tips for diversions at all??

All help much appreciated!!

RENURPP 11th Mar 2003 08:59

Re the needle in the hay stack.
If at all possible flight plan to an easily identifiable position, even if it is slightly off track, however still close to your needle, which will give you a short leg to the needle.
Navigating over a short leg should make it alot easier to find your needle, especially at low level..

Maybe give us a scenario and we can offer some suggestions.

As for 10 mile 10 min etc I beieve it depends on the type of terrain you are flying over.
I prefer 10nm markers myself, however they are at their most uselful over terrain with regular features.
Over feature less terrain you might find proportional markers more use. i.e. 1/2 1/3 etc.

Arm out the window 11th Mar 2003 10:00

For the diversion, here's a couple of points:

You should have a few minutes to plan it, so don't be tempted to turn onto some random heading off the cuff; plan a point you will divert from (ideally an easily identifiable spot a little bit up track from where you are now). That will give you some time to work out a decent heading and ETI for a starter.

If an immediate divert is required, pick what you think is a good heading, turn onto it and note the time and the heading on the map. Then when the confusion dies down a bit, you will be able to plot where you started the diversion leg from on your previous track, if you haven't had time to before turning.

Always consider FUEL and airspace, as well as the terrain you've chosen to divert over (obviously a vital issue for IFR because of revised LSALTS, but also for VFR if you start heading over tiger country without thinking about it first).

Get a lot of practice at estimating tracks off the map by eye, and check yourself with the protractor. Also get used to drawing the new track in whilst flying, one-armed paper hanging, but you should be able to get a decent straight line on the map without too much trouble. You can then measure off the track and distance. Some people I know fold their maps on the line from divert point to destination and run a pencil along the fold, that draws a straight line for you.

A rough checklist could be something like this:
1. Where to divert from.
2. Where to divert to.
3. New track, heading and distance.
4. Estimated time interval for the new leg, and select an appropriate altitude for the new track.
5. Have you got enough fuel? If not, better come up with an alternative plan (go somewhere else, find nearest suitable...)
6. Figure out your radio call to ATC or flightwatch if required, or other means of having SAR coverage. Make the call.
7. At the divert point or time, turn onto new heading.
8. FCLEAR check.
9. Plan for a pinpoint or two on the new leg, and familiarise yourself with the features you should see along track and at subsequent turn points.
10. Navigate normally, just like on your planned legs.
11. When you have a spare minute, check your work.
12. Expect the (unexpected) engine failure!

liquid_gold 11th Mar 2003 10:31

Gaunty,

Spent most of my VFR time in the NT pre GPS and would have to agree with your statement. As a general rule I would set HDG as TRK and plan on G/S as TAS. Quick check during climb, then at TOPC and again at 1/4, 1/2 and 3/4 of total distance. Some checks were 100+ miles apart, so would start to 'track crawl' with the chart if in doubt. Seemed to keep me out of trouble ...... except for this one occasion when there was overcast at 1000' going from nowhere to somewhere in the middle of nowhere ..... all a learning experience. :)

Lodown 11th Mar 2003 22:07

Agree with Gaunty and Liquid Gold. All these 10 mile/6 minute markers, or whatever, take a lot of time to prepare and are no more accurate than a nice simple straight line track and fly heading for track and work on TAS as GS.

Tinstaafl 11th Mar 2003 23:24

For a start, accept & expect that you will get off track. The trick is to recognise it & be able to correct.

Somethings you can do to minimise the problem:


1. Use funnel features to 'lead you in' to the destination.

2. If funnel features aren't available (or allowed in the test :p ) think about how you can use line features.

a. Is there one that crosses track for G/S checks?
b. Or parallels track for drift checks?
c. Running through the destination? If so, perhaps a deliberate off track error is appropriate ie ensure you track enough to one side or another to arrive definitely off-side. You'll at least know which way to turn. The possibility otherwise is for there to be some doubt about which way to turn.

3. Sometimes it's just as important to know what will tell you you're NOT where you wish to be, as it is to know what features show you that your destination. These could be lfeatures to the left or right of TR, or beyond that would show you've gone too far eg line features , significant terrain, towns, lakes etc etc etc.

4. Definitely use Clock to map to ground. Orient the chart to suit your HDG. Remember that you could be a bit left or right of track so don't presume an object to one side of track on the chart may not be to the same side of the nose.

5. Large BIG, BIG objects before trying to locate less obvious things eg. The coastline is a great feature to start with if visible... :p

6. If going to somewhere that might be awkward to find eg only a small feature then plan to track to a more easily found feature nearby THEN to the final destination. You might use clock & compass as usual OR even track crawl using minor features. Tr. crawling is handy to find a particular river bend/road junction/stock fence etc AS LONG AS you start from a known position and have reasonable features to follow. You must still use TIME to check for the reasonableness of progress. It's very easy to miscount creek junctions etc...

7. Hold headings accurately. Even if the DI. doesn't match the compass, the constant error will allow a good 1:60 to correct your track.

Similarly to Gaunty, I use Tr. as Hdg. If I *know* that there is a significant crosswind then I'll use 5 or 10 deg as a guesstimate. Doesn't really matter since I'll be doing a 1:60 anyway.

I look for a fix ASAP at or near TOPC then base my TMG on that.

Drift during climb is usually different to CRZ so I treat my TOPC fix as the start of my en-route tracking. If off track at that point I base my 1:60 on the now offset parallel. No good using departure point since speed (& therefore drift) is different between climb & crz.

Sometimes I do a 1:60 half way through the climb instead. Depends on how much I feel like working & how much drift has been obvious.

Nothing wrong with doing multiple 1:60s along a track, not just one at the mid-point.

8. Use a search pattern if the place just can't be found. Make sure you log the time & start point though! It takes a long time to do if you're a fair way from the target.

9. If you're having trouble seeing how the depictions on the WAC relate to the ground features, try holding the chart at arms length or so. The shading will help you see what's a valley or ridge.

10. Don't underestimate the use of cross bearings to get a Line of Position. A couple of crossing LoPs will give you a fix. Some ways to get a LOP:

a. As you fly between two recognisable points they'll give a LoP when you're between them. eg a couple of towns or lakes or mountains etc in some combination. Draw a line on your chart between those points & you're somewhere on that line. If you can estimate distance from one of the features then you have a fix.
b. If not between two points then two that line up away from from eg a lake + a mountain. Again draw
c. A line feature as mentioned earlier. Perhaps you can see a straight road or railway in the distance that will or does point at you before it bends. Extend a line on your chart from the straight section to make a LoP.
d. Navaids: DME, VOR, NDB. Don't forget the DME will be a curved LoP centred on the DME transmitter.

Hope this helps...

Best of luck!

gaunty 12th Mar 2003 00:34

squall

WOW

Wish there had been a PPRuNe when I were a lad.

There is more concentrated pearls of wisdom on the one page here, than I have seen in a lifetime.

Be careful to get your head right and decide on whatever method with which you are most comfortable and have experience and stick to it.

Don't fall for the, "well that doesn't seem to be working I'd better try something else" syndrome.

Relax,...................:cool: you're not going fast enough (unless you're AOTW perhaps :D) to get far enough out of wack that it can't be salvaged simply and easily.

Unless you do something really stupid or there is a serious crosswind, just how far off track and time can you get at 140KTS in ten minutes or so, even 30 minutes.
As an exercise do the math on where you would end up using average winds calculated on flying TRK for HDG and TAS for GS, as if you hadn't made any corrections for winds and then draw a circle around the destination or checkpoint of a radius equivalent to the worst case.
You will see that you you wont be all that far away and if a little altitude is available you should be able to see it.
The radius of the circle shouldn't change all that much, regardless of your TAS as the effect of wind is proportionate.
This should only be used as a confidence boosting exercise to show you that the worst case, subject to serial stupidity, is not all that bad.

Macro nav, look at the big picture out there, coz thats what's on the map then home in from there.

Look at the fence rather than trying to count the pickets, then go go on from there.

Had occasion to "find" an "uncertain of my position" chap between Leonora and The Rock, who was scuttling around in circles at dot feet trying to get a handle on it by looking for the "hills and lakes":rolleyes: as landmarks on the chart.
It only took as long as it took to him to climb to altitude and tell me about the huge salt lakes in every direction that looked just like those on the chart, to put him within a couple of miles. Sounds simple, but it really is.

I will admit to confusing myself on the odd occasion and not being able to positively identify enroute features and resorted at the end to just flying my plan and hey presto the pinpoint or destination had a habit of turning up more or less where it should. It would be easy to get lured away from that plan, which if properly and carefully prepared will invariably get you there.
I reckon 90% of the success of the flight, is the time spent in preparation, the execution is the easy and fun part.

Good luck and as they all say have fun.

clear to land 12th Mar 2003 04:26

Track as Hdg and TAS as GS works. I also cut my teeth pre GPS in the NT, and this method definately works. You can make an edumacated guess as to any likely drift by the forecast wind, comnined with cloud movement and windsock, bushfire smoke etc. If going somewhere with few fixes then also consider deliberate track error ie deliberately going L or R of track so you know what direction to turn when tha appropriate time is up. Get to be able to judge reasonably well GS by looking at the ground rate of movement. Calibrate your eyeballs by going to a known point and looking at fixed distance points from different altitudes ie know where 15nm miles is on the windscreen at 1000ft, 5000ft and 10000ft. Another alternative is to track crawl. Pick obvious physical features:hills, ridges, spotheights if you are desperate, and fly to them. Note the HDG required to get there and this will give you a good idea of drift. Plus you always have a positive fixe at least every 20nm or so. Good nav cycle is essential. For diversions calculate estimates using LAT lines on WAC (1 deg=60nm) and reference ETAs to 2-3 nm min depending on what you are flying. KISS. :) The more you do it the easier it gets. Expect to make mistakes but DON'T PANIC!. Use circles of probability: fix + time + GS and HDG. Go back to last + fix if in doubt. Have a good log. Have fun, its more fun than the procedural stuff later.

wherethehellarewe 13th Mar 2003 02:05

Thank for the excellent posts. Been navigating for 45 years after RAAF instruction without getting lost too often but have still picked up some new ideas from the posts. Have summarised and abridged the posts for our flying club's newsletter.

Aussiebert 13th Mar 2003 04:56

clearos, and lots of em!

i only skimmed some of the logner replies so apologies if i repeat something allready said...

if you can, do go track as heading and use a navaid to work out your wind correction. VOR's preferably, if theres one handy.

navaids are there to be used. Of course chances are you'll have them switched off quickly so make trhe most of them while you have them

and clock to map to ground is VITAL.

Ascend Charlie 13th Mar 2003 07:48

I assume you are in an aeroplane, which is stable, trimmed, and wants to hold its heading. This is not the case in a helicopter, which wants to bounce all over the place and jiggle that stupid magnetic compass out of its bowl.

So, try this:

1. Over your first point, turn onto the TRACK for the leg, hold it steady, and look ahead. You will be drifting with the wind while shooting this sight line, so don't take too long.

2. Pick 3 features that are lined up on this track - maybe a shed, or distinctive treeline, or a funny hill, and REMEMBER them. (Don't fall for a shadow, as it is moving)

3. Now set up your planned heading, and check that it is taking you along the sight line. If it isn't, fix it. And write the new heading down.

4. As you pass over one sight point, pick another in the distance, still in line with the remaining 2.

IT WORKS!!

squall 13th Mar 2003 11:51

Thanks guys and gals for all the useful input. I am very impressed and you have all given me motivation to go out there and try some of them to see how well they work.

Keep them coming!! I think not only I am learning something here.

Very interesting stuff. Much appreciated!!

SQUALL

Tinstaafl 13th Mar 2003 17:15

Some other stuff I just thought of...

** Fold your chart so that there is still a decent amount showing to the L & right of track and beyond your destination. Large features in those areas are useful for basic orientation.

** Make sure you're comfortable with some form of track correction calculation. This could be 1:60 (my preference), pre-drawn drift lines or whatever.

I like 1:60 because it's so flexible. It can be done in your head very quickly to an acceptable accuracy by memorising about 4 numbers:

If the distance run (or to run) is anywhere 60 nm then multiply the distance off track by 1 to get Track Error or Closing Angle. eg 57 miles since last fix. 5 miles off track = 5 deg TE. 68 nm to desired on track position = another 5 deg. Total HDG change = 10 deg.

If ~30 nm run/to run, multiply dist. off track by 2. eg 35 nm run, 3 off = 6 deg TE

If ~20 then x3

If ~15 then x4

If ~45 then x 1.5 --> this is an interpolation but good enough. After all, the whole of the 1:60 method is based on approximations!

If 120 nm then dist. off x a half.


** A fix or DR position isn't proven until the next anticipated fix occurs.


** Use a navigation log. That's a key part of navigating to somewhere that's unknown.

It doesn't have to be on some sort of form. Your map itself makes a very good log device. That's what I use.

Use the correct nav. symbols on your chart to remind you later in the flight about what sort of fix or position line you were able to get earlier. This helps tell you how much you can rely on that particular 'fix'/DR position.

Important things are Times, Headings & Groundspeed. TAS too if you're varying it a lot.


The common symbols include:

A dot with a little circle around it: a pinpoint ie you can prove you're over that position. Still subject to my earlier comment though :p .

A dot with a little square around it: This is an AIR position ie where you would be having held HDG & TAS for xx mins. There is no wind effect in this.

If you add wind effect for that period time then you get:

A dot with a little triangle around it: this is a DR position ie where you THINK you are based on calculation eg have held xx HDG for yy mins @ zz TAS with this much wind effect therefore I should be 'here'.

A line with an arrow at each end: This marks a line of position. You're somewhere on that line. Two of these lines crossing give you a FIX. Use common sense about how long you draw the line. :O

This next is a bit more complicated & not often used. That said, I've happily used it a number of times before. It's just another tool to add to your box of tricks...

A dotted line with an arrow at each end. This is a 'running line of position' or a 'transferred LoP. It's analagous to a DR or air position's relationship to a pinpoint. You can use a couple of these + a 'proper' line of position to give you a fix. Quite handy if there is only a single navaid somewhere to the left or right of track since it enables you to get a fix.

You would get a line of position while the aid was ahead & to the side of your track, then a second LoP when you were abeam it then a 3rd LoP when it's behind & to the side.

Transfer (hence the name) the first two LoPs using known or estimated TMG & G/S over the time from taking each of them to when the 3rd LOP was done. Where they cross is where you are. If they don't cross exactly (usual case) then you're in the middle of the 'cocked hat' triangle they form. If TMG &/or G/S isn't known then use HDG &/or TAS.

Some people (erm.....like me :rolleyes: ) love navigation. You may or may not want to go into such detail. Nevertheless it all adds up to helping get from A to B since you can choose the best method for the various conditions.

Hope your flight goes well.

T.

proxus 13th Mar 2003 17:44

Can anyone explain a little better the 1:60 rule. I am not yet a CPL so please explain.

Arm out the window 13th Mar 2003 22:48

The 1 in 60 rule is based on similar right-angled triangles, but don't let that put you off!
Basically, imagine a long skinny right-angled triangle with the two sides at right angles being 60 units and 1 unit long respectively.
It so happens that the angle formed between the long side and the hypotenuse is 1 degree.
Now make the short side 2 units long; the angle becomes 2 degrees, and so on. This works for smaller angles, say less than about 15 degrees or so.
The similar triangles part goes like this: Using a triangle with long side 60 units and short side 4 units, the angle as described above would be 4 degrees. Say your long side was then 30 units and the short side 2 units, that would still be a 4 degree angle, and so on for all the other similar triangles – long 120, short 8 etc.
In flying terms, it means that if you have drifted 1 mile across track for 60 along, your track angle error is 1 degree. You would use it like this:

Say you departed on track overhead an airfield and flew your planned heading (let’s say 090). If the wind was exactly as forecast, you should stay right on track.
You take a pinpoint after 40 miles along track and find you’re 2 miles left of track.
2 in 40 is the same as 3 in 60 (just using the same proportion) or 3 degrees, so you have actually made good a track 3 degrees to the left of your planned track.
To parallel your planned track, you would turn right 3 degrees onto 093.
However, you’re still 2 miles left of track. To get back to track, you use the 1 in 60 rule again.
From the ‘parallel track heading’, you want to change heading further right to go back to track, and it depends on how quickly you want to get back as to how big a change you make.
To get back on in 60 miles, 2 in 60 is 2 degrees, so turn right a further 2 deg onto 095.
To get back on in 30 miles, 2 in 30 is 4 in 60, so turn 4 degrees further, onto 097.
You can pick any distance you like – if there was a good feature on track in 37 miles, I’d say something like this to myself – 37 is very close to 40. 2 in 40 equals 3 in 60, so I’ll turn right 3 degrees more from the parallel track heading, onto 096.
That’s basically it – do a bunch of practice ones of these on paper using different distances flown, miles off track, and distance to go to get back on track. Very useful once you get the hang of it; happy mental DR-ing.

PS Gaunty, 90 kts is about my speed these days, not that I ever went that quick previously – only ever had a joyride in those fast pointy things...

proxus 14th Mar 2003 03:39

Thanks for the clarification

fruitbatflyer 18th Mar 2003 05:11

Ascend Charlie's method is not only good for a chopper, it works well in any aeroplane when you are stuck low down below cloud if you do a bit of preflight preparation with your chart. It's really just a variation on a theme long used by mariners when in coastal areas.
Look for features on your chart along track that may be lined up, e.g. a small lake with a prominent hill or small town behind it, and also look for features that will line up to form these so-called 'transit' lines cutting across your track at 30 to 90 degree angles. Rule them in on your chart in pencil so that they cross each other. Not too many as you don't want to get confused, just obvious ones or ones you hope will be obvious. Where transits intersect is exactly where you are and even if you can't get them to line up conveniently with your track, you will soon get the idea that any transit, if properly identified, is as accurate as any radio-aid derived line of position.
Don't panic if you occasionally can't see what you expect once in the air - some features on WAC charts just don't show up too well.
Keep ticking off the 10nm marks as well, and if you miss one, just keep the DR going.
Also, the advice to build in a deliberate offset is good, but take into account the sun - you don't want to be looking into the sun for your destination.

RENURPP 18th Mar 2003 23:13

just to pick up on some ones comment above re wind direction.

Be very careful there, don't jump to conclusions. Looking at smoke is only useful in determining wind direction if you are down low.
Using cloud shadows is only useful in determining wind direction if you are around the level of the cloud.

The wind can and does change direction very quickly with altitude at times. An example is dry season in the territory, strong easterly wind on the ground and by the time you get to 10,000 ft it can be a strong westerly !


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