Meteorology question PLEASE HELP ME!!!!

[The green baron]

Hi folks,
im currently using the Thom books and cant find a valauabel piece of info and thought you might help. Whats the general rule of thumb for calculating wind speeds (in the northen hemisphere).

If the wind speed on the ground is 15 Knots at 250 degrees whats the rule of thumb for calculating the wind speed and direction at say 1000 or 2000 feet?

Many Thanks for the help in advance!
The Baron.

[aluminium persuader]

For 2000' wind...

Double the speed & add 30 degrees.

When you're planning, though, bear in mind that upper winds provided by met are forecast and not measured. It can be totally different to the forecast. You also get gusts up there just as you do on the ground.

Here's a tip; if you're flying from or near an airport with commercial airliner operations, when there's an airliner (or bizjet) on frequency ask ATC to ask them for a "spot wind" as they pass the level you're interested in.

Obviously, such a request would be of lower priority than doing the ATC, but as an ATCO myself I would certainly do my best to help.

ap:ok:

[IO540]

Add 20 and 20 seems to work, as close as any human pilot can fly the resulting wind corrected heading :)

So surface wind of 220/30 would be 240/50 at 1000-2000ft. Very rough.

But then F214 is very rough too. It's only when you fly with a GPS which allows the wind aloft to be worked out exactly that you realise just how bad F214 can be.

SFC wind of 220/15G35 will probably be 240/40 i.e. the top of the gust, plus a little bit, indicates the wind aloft.

[mad_bear]

I was taught:

At 1000 ft: Add 20% and 20 degrees
At 2000 ft: add 50% and 25 degrees

These, FWIW, are the figures that the PPL confuser uses. Of course, if you're cruising at around 100 kt, then the difference between adding 20 kt, and adding 20%, is insignificant.

[foxmoth]

Of course, if you're cruising at around 100 kt, then the difference between adding 20 kt, and adding 20%, is insignificant.

You are adding to the wind speed not your cruising speed - so a 20kt w/s at ground level becomes either 40 kts or 24kts - a significant difference at 100 kts cruise speed! :=

[mad_bear]

Doh! I had a hard day yesterday. What an embarrassing mistake :\ Sorry.

[Piltdown Man]

IO540 - I like your 20/20. For real life that is as good as you can get, however (when is a post not complete without a "however") in addition to a GPS you also have to have the means of calculating instantaneous TAS. So in addition to a GPS, either a wizz-wheel or an ADC is also required!

PM

[IO540]

Not sure I understand you, PM.

If you really want to know your TAS, then at piston speeds you can use the adjustable subscale on the ASI.

An air data computer doesn't do any more than take the OAT and the altitude and use that to correct the IAS to get TAS. You pay 5000 quid for that :) I actually wrote to Shadin once with this assertion and they were unable to disagree.

I find I never need to know my TAS. All that matters is the GS; that is what will determine how much fuel I will have at the destination, assuming current flow rate etc. And GS can be had from a GPS, or from a DME if flying more or less directly to/from it.

In radio navigation, whether it is GPS or VOR/DME, TAS is superfluous.

The only time, in the piston context, one really needs to know TAS is for checkrides ;)

(To be more correct, knowing TAS and therefore knowing the exact wind, is handy for working out the wind profile with height during a climb to cruise, allowing you to choose the best level at which to request a stop-climb).

[Piltdown Man]

It's not the speed that matters, it's the altitude and temperature that cause the differences. Admittedly, most piston engined aircraft don't get high enough to generate a significant errors but there again the need for accuate information in these levels is less important as well. But to accurately calculate the wind you have to have a valid TAS and the sliding subscale, let's face it, is a bit "Noddy".

[tiggermoth]

I was taught:

At 1000 ft: Add 20% and 20 degrees
At 2000 ft: add 50% and 25 degrees


Yes, I saw that in the PPL Confuser too, but didn't see it in the Trev Thom book either...

[tiggermoth]

By the way, if it's any consolation, I'm studying for Met at the moment, and I'm finding it horrible. For some reason it's a subject matter that I find very difficult to learn from a book.