Thread by @alexbloor, Navigation : the way we need to learn to pass a test, [...]

Navigation : the way we need to learn to pass a test, but which nobody in real life would ever do. A thread.

First we draw on our way points and link them. In this case the VOR/DMEs at Ockham and Midhurst and the towns of Petworth and Petersfield.

1/several

Now start to fill out the Plog.

Now measure distances. Yes, with a ruler. Like in school.

This completes the distance. In miles. But not ordinary miles like on the road. Nautical miles. And definitely not metric. Because fuck progress.

Now we use the iso to clean the pen marks off the protractor, yes a protractor like in geometry at school again! The cleaning spray and sheet of kitchen towel is vital gear.

Now we rattle through and measure our track angles. Re marking the protractor we just cleaned off.

Only one mistake.

But to err is human, which is why this whole process should and could he automated but anachronistically remains.

So now I have distances and track angles. If there was zero wind, this could end here, more or less.

Having clearly demonstrated that computers shouldn't be trusted - which seems to be the idiotic raison d'etre for this, what I now need is to get are 214 and 215s from the Met Office.

I will do this using a conductive ink weather fax printer presumably? Ah no, a... computer.

Homer voice : "computers can do that?!"

I'm going to use this bit of the chart. Arguably I maybe should average the values between two adjacent tables. But, I'm already terminally bored.

And the interesting line is
02 190 05 +03

Which means at 2000 ft, the wind will be coming from 190 (roughly from south) at 5kts.

For gross error reasons I like to draw it on the chart. I mean, not like. But... You know. It means if I'm flying south I will expect my ground speed to be lower, and when flying back north I'll expect my ground speed to be higher.

Now we mark our antique turning the wheel to 190 and drawing a line and arrow representing the 5kts.

Ah also our aim for airspeed is 90 on a cessna 152. So I can fill that in too.

And move the dot to that on the antique.

Now we dial in our first track 205. OK so that has caused a drift. The arrow head looks to be about one degree off. So we compensate for that. Not worth another photo because the difference is too small to see. But we'll call it 204.

Also note the lower ground speed about 85kts.

Next 170. Drift looks to be about 2. As expected similarly reduced g/s due to headwind. 5kts headwind: 5kts lower g/s. Good.

Next 278.almost total sidewind. Again conforms to gross check. No reduction or benefit to ground speed. But a drift to compensate for.

Actually, a little loss in g/s and a 5 degree compensation for drift.

79 degrees. Wind behind us now, so expect faster g/s and a more noticeable compensation for drift.

Finally 25 degrees. Almost entirely tail wind, so g/s higher by pretty much the full amount of then windspeed. And perhaps a one degree drift. Probably above the accuracy possible in practice.

So this is almost filled out now.

See the big 13?

That is a tallest land or obstacle in that bit of the map. We go 500 ft above that for safe alt, and because of airspace stuff can't really go above that.

So filling in the plan/safe alts.

Also for completeness fill in the wind column all 190/5

Now to calculate leg times based on this distance speed and time triangle. Which I hate.

So starting with 17 miles at 85kts.... 12 mins.

Gross error check :

First leg should take a bit longer than last leg, because same distance but first has headwind and last has tailwind.

Yes. Good.

Finally assume a start time of 12.30 let's do expected ETAs over each way point.

And that's exactly why GA examination hasn't kept up to date with the real world.

Can you believe the syllabus has this in it BUT not GPS, skydemon or any other moving map stuff?!

Here is what skydemon makes of it. This took me 2 minutes to ask it to do.

They aren't all quite the same but they are all pretty close. Skydemon for the win. Sliderule for the suxx.

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