Crosswind navigation - how do YOU handle drift?
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A few years ago I bought a Book at the PFA rally entitled 'Diversion Planning' (using only a stopwatch and a pencil) this gives lots of Handy Tips. It's based on RAF methods and as the author Martin Smith says if it's good enough at 400Kts it's good enough for GA. Other diversion planning books might be available. 
400 knots, 25 knot crosswind, drift is about 3½°
100 knots, 25 knot crosswind, drift is about 14½°.
The first is within most people's accuracy to fly anyhow, and should deposit you within sight of your destination. The last could put you well into controlled airspace, danger areas, and very likely not in sight of your destination if drift planning isn't done properly.
Me? Flight computer, compass, chart and stopwatch like I was taught years ago. No flight computer? draw a rough triangle of velocities on the chart and use that.
G
Joined: Oct 1999
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From: Swindon, Wilts,UK
An interesting viewpoint that.
draw a rough triangle of velocities on the chart and use that.
Actually now It's come to mind, even something as simple as map handling becomes a challenge in a small open cockpit. I think I'll have to spend some time picking the brains of my local Microlighters. Still that's another story and a whole new thread.
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Maybe I paraphrased a bit too Succinctly. What the author was trying to put across was that by using the aforementioned clock codes and other techniques you could reduce the work load in the cockpit. Lets face it at 400kts by the time you've dug out the whiz wheel you'd have run out of green stuff and be flying over the blue wavy stuff!
Ghengis is this a technique you've practised whilst airbourne in Microlights? If so I would be keen to know the finer points, as I may possibly be in a position to require this skill in the not too distant future.
Actually now It's come to mind, even something as simple as map handling becomes a challenge in a small open cockpit. I think I'll have to spend some time picking the brains of my local Microlighters. Still that's another story and a whole new thread.
Actually now It's come to mind, even something as simple as map handling becomes a challenge in a small open cockpit. I think I'll have to spend some time picking the brains of my local Microlighters. Still that's another story and a whole new thread.
The triangle of velocities is the preferred method taught on the microlight syllabus, and it works. Hardly surprising really, since what it's actually doing is no different to what the flight computer does. But, both I much prefer to do on the ground.
Speaking for myself, I have a very strong aversion to doing any more maths than necessary whilst airborne, and try to get all my planning done on the ground.
My preferred method when changing route / calculating drift / diversion planning, etc. in a microlight is something like the following:-
(1) On map, measure track from where I am now to where I want to be.
(2) Also on map, find something that I can see which which is on-track to my destination.
(3) Fly to it, visually.
(4) Whilst on the way, observe my compass heading.
(5) For as long as my heading doesn't then change by more than about 30°, and my height by more than about 500ft, assume that the difference between track and magnetic heading is then constant.
(6) If track and heading do have to change significantly (or airspeed, but en-route microlights are pretty much constant IAS aeroplanes) just repeat (1)-(5).
Whilst we're on the subject, my other favourite microlight navigation trick, which I also often extend to light aeroplanes (when flying with constant sight of surface anyhow). Mark on the chart track lines points of equal spacing - the actual spacing doesn't matter, but usually I use 6nm for microlights, 12nm for light aeroplanes. Each time you pass a marker, note the time (I write it on the chart, also I use it as a reminder to do my en-route checks). After a couple, you know that it is taking you X minutes per marker. Time to target then becomes simply a case of doing a simple multiplication (6 markers, 7 minutes per marker - I'll be at my destination in 42 minutes...)
On longer trips, I also mark the fuel state against each marker as well. Of-course, most microlights have much more accurate fuel gauges than most microlights, so you can do this - it would be a bit pointless in a PA28. That way, if I'm going to run out of fuel on a long X-country, I usually know at-least an hour in advance, and in plently of time to make a timely diversion.
G
N.B. These methods assume that (1) Your kneeboard space is limited and drafty, so having EVERYTHING on the chart is highly beneficial, (2) constant sight of surface, and (3) you can remember your times tables.
Joined: Oct 1999
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From: Swindon, Wilts,UK
(3) you can remember your times tables.
Thanks for that G
That's pretty much what they've tried to teach me over the years.
Do you use fan lines about your destination?
And does the Ju Jitsu help with the maps?
regards
WM.
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From: UK
Moderator
Joined: Feb 2000
Aviation Qualifications: CPL
Posts: 14,480
Likes: 178
From: UK
Again of-course, I do try to get all possible preparation - including map folding, done on the ground.
G
