WAFS + which wind direction/speed

[Cessna 172S Skyhawk]

I am having trouble with my pre flight navigation and hope someone can help.
I am looking at the WAFS to get the wind direction and strength at altitude. I will be flying at 2000'.

Here is the what is showing for today.

2000ft CALM PS05

As it says calm, what wind direction/strength do you use. Say for example the ground wind is 250/08 and the wind at 5000' is 340/15. What wind do I put into the Whiz Wheel?

[BackPacker]

If the predicted wind is "calm" then why would you use anything other than "calm" in your trip calculation?

As for how to calculate that on the whizz wheel - well if there is no wind then there's no need for a wind compensation calculation. GS is TAS and TH is TT. So you don't use the wheel for that part. You just need to take into account variation and deviation.

[Cessna 172S Skyhawk]

So in essence, "Calm" is the ideal scenario for flying a navigation.
I am still a little confused though, while I complete comprehend what you are saying, does Calm not encompass any wind direction or any wind speed?

[dublinpilot]

I've idea what you're looking at, but presume it's a ground report.

Go here and register for the UK Met Office (it's free). (http://www.metoffice.gov.uk/aviation/ga)

Then log in and in the top left corner you'll see a link for Form F214.

This will give you the predicted wind at altitude for various different altitudes in various different locations. Your instructor will take you through using and understanding this.

You can also register for the Irish Met Office here. (https://briefing.met.ie/) After registering, switch to "Local" and scroll down to the bottom and you'll find the wind charts. They are similar to the F214 mentioned above.

dp

[dublinpilot]

Calm=no wind speed (or less than 2kts if I remember correctly). If there is no wind speed, then there can't be any wind direction.

But I believe that you're looking at a ground report, not a forecast winds aloft. It would be unusual in the extreme to have wind calm at all levels. It's quite common at ground level, but less so as you move up in the athmosphere.

[Cessna 172S Skyhawk]

Hi DublinPilot,
I am also from Dublin, going out to Weston to do Nav Training later, if the vis holds up.

I am using the Low Level Winds & Temp Chart on briefing.met.ie
For today at 12:00 at 2000ft, is is Calm PS05.

I will be flying my short local Nav, Weston to Enfield to Trim to Kinnegad to Enfield to Weston.

I am trying to get the pre flight planning done, and as the winds are Calm (I hear what you are saying about less than 2kts) I take it that as our esteemed colleague from Amsterdam indicated that GS=TAS and TT=HT

As it is likely to be about 250/08 on the ground, at 2000ft, it reads no wind and no wind direction? Or am I completely off the wall with that rationale?

[dublinpilot]

Ok. I see what you're at now. Indeed the wind at 2000 is forecast to be calm. In that case you make no correction for wind because there s no wind to blow you off course!

The surface wind is irrelevant to your flight at 2000ft so don't worry about it.

So as bp say..groundspeed is same as true airspeed and magnetic heading is the same as magnetic track.

Having said that I don't think you'll be going too far today unless the weather clears up!

[Cessna 172S Skyhawk]

At the moment I think I may be restricted to the circuit only, it might even give me a chance to do some solo circuits. But it looks like it might get a little better, I'm not flying till 1400.

[BackPacker]

So in essence, "Calm" is the ideal scenario for flying a navigation.

Personally I prefer a stonking but steady tailwind on all my legs, and a moderate non-gusting headwind just down the runway for my take-offs and landings. And the last remains of a cold front just moving away as I start my engine.

So far I have not flown in those conditions though. At least not on days where everything came together.

Furthermore, dead calm conditions, particularly this time of year, typically mean a lot of morning ground fog which burns off, or lifts, relatively slowly as there's not a lot of mixing in the atmosphere. Particularly as those dead-calm conditions often mean you're in the center of a low or high pressure area.