Rule of thumb for winds aloft?

[Oscar Kilo]

All,

When I was learning to fly I remember I was taught some sort of "rule of thumb" for calculating winds aloft based on the wind at surface level, for cross country planning purposes. In my 6 years of fun flying since, I can't quite remember what the rule was!! When I'm planning a cross country I tend to take the surface wind and add a bit to the direction and double the strength, eg 210/10 would become about 230 at 20 at 3000 feet.

My approach works to a degree but is only based on "gut feel" - Does anyone have a good "rule of thumb" for this (like the one I am ashamed to admit I have long since forgotton!).

Grateful for your thoughts....

- Andy.

[IO540-C4D5D]

That's probably as close as you will get in reality, for that sort of altitude.

For a 100-150kt plane the resulting error in the heading required to hold a particular desired track is smaller than a human can hold a heading for extended periods, anyway!

This is why I can't see why they still teach the stupid slide rule for wind calcs. It's far more precise than the data you've got.

[drauk]

During my IMC training I was taught add 30 degrees and double it.

I'd agree with IO540-C4D5D that the whole business is generally over stated, but I wouldn't go quite so far with it - 20knt of wind on the ground, doubled gives 40knts. Then max wind correction angle at 100knts is 25deg. I'd hope I can hold a 25deg heading change for tracking a beacon or whatever.

As for the slide rule for wind calculations in the PPL, I'd certainly agree with that - using a WindProtractor is so much easier, quicker and plenty accurate enough. And at least it is feasible to use it in the air - good for diversion planning.

[Barney_Gumble]

A while ago I bought a little plastic disk called a Knightsun(?), just a protractor with concentric circles representing different winds aloft. It is all I tend to use for planning and gives reasonably accurate heading and 6 minute distances which I mark on the map. Plenty good enough. I must admit my flight computer hasn't seen much light since then.

I did a little validation exercise on the ground where the flight computer V disk heading given the same track and winds were identical to a degree or so and as mentioned I can't hold that accurate a heading by hand anyway.

Barney

[IO540-C4D5D]

Drauk

"I'd agree with IO540-C4D5D that the whole business is generally over stated, but I wouldn't go quite so far with it - 20knt of wind on the ground, doubled gives 40knts. Then max wind correction angle at 100knts is 25deg. I'd hope I can hold a 25deg heading change for tracking a beacon or whatever."

I was referring to the error in estimating the wind drift, not to the magnitude of the wind drift.

With a rough guess you might get a 25deg heading offset from the track. With a precise calculation you might get 30deg. But the error in the actual wind, transferred into the error in the heading, is likely to be as much as 5deg or more.

That's why the rule of thumb is good enough and the slide rule is rather pointless. I have never used mine since the exams.

Also if you are tracking a beacon you will see any drift and will compensate as you go. Same on an ILS - you have to suss it out pretty quick there.

[drauk]

Sorry IO540-C4D5D, I misunderstood your original post. I agree completely with what you said.

I also agree that you'll "see" the drift when tracking a navaid, but I do like to have a rough idea in mind before I start.