trick to avoid crosswind landing in late afternoon...

[Steve Koerner]

[repost from Arizona Soaring Assoc board where it seemed to be of interest]

I'm sure many already know this -- it's a good trick to know if you don't.

Late afternoon summer wind will very often completely stop right at sunset. If you are faced with a crosswind landing in the late afternoon, a solution is to hangout until sunset.

I've done this several times over the years at various airfields including just a few days ago flying out of Estrella. I came back about forty minutes before sunset to find an 80 degree cross of about 15 knots. The flag was whipping sharply. I probably could have landed it, but why take a chance?

There remained some very weak thermals able to sustain to about 2500 ft as is common at the end of the day. So I just hung out until the sun dropped below the distant mountains and landed in calm conditions. An added benefit is that you can see the runway after the sun drops if you are needing to land to the west as is the usual case in the southwest.

[AS]

On Wednesday, October 4, 2017 at 5:38:54 AM UTC+2, Steve Koerner wrote:
> [repost from Arizona Soaring Assoc board where it seemed to be of interest]
>
> I'm sure many already know this -- it's a good trick to know if you don't..
>
> Late afternoon summer wind will very often completely stop right at sunset. If you are faced with a crosswind landing in the late afternoon, a solution is to hangout until sunset.
>
> I've done this several times over the years at various airfields including just a few days ago flying out of Estrella. I came back about forty minutes before sunset to find an 80 degree cross of about 15 knots. The flag was whipping sharply. I probably could have landed it, but why take a chance?
>
> There remained some very weak thermals able to sustain to about 2500 ft as is common at the end of the day. So I just hung out until the sun dropped below the distant mountains and landed in calm conditions. An added benefit is that you can see the runway after the sun drops if you are needing to land to the west as is the usual case in the southwest.

Interesting idea, indeed! How long can you fly after sunset w/o nav-lights or is the sunset time much after the sun disappears behind the mountains?
Just curious,

Uli
'AS'

[Steve Koerner]

Official sunset time would be perhaps a minute or two after the sun disappears behind distant mountains. Time it right and no lights are required. I imagine last thermals would end about then anyway.

[Bruce Hoult]

On Wednesday, October 4, 2017 at 4:32:02 PM UTC+3, Steve Koerner wrote:
> Official sunset time would be perhaps a minute or two after the sun disappears behind distant mountains. Time it right and no lights are required. I imagine last thermals would end about then anyway.

No lights are required until 30 minutes after sunset.

[AM]

> No lights are required until 30 minutes after sunset.

This may vary by country. In the US, lights are required between sunset and sunrise (FAR 91.209).

[John Cochrane[_3_]]

Metorologists call it "decoulpling." When the temperature starts falling at the surface, which you can see in model soundings moving left, the air stops mixing. Much wind is mixed down from higher levels, and when the thermals stop so does the mixing. Wind at higher levels starts to flow over the lower cooler levels as it does over water. Using this knowledge to avoid a crosswind is a clever idea.

[Bob Whelan[_3_]]

On 10/4/2017 12:48 AM, AS wrote:
> On Wednesday, October 4, 2017 at 5:38:54 AM UTC+2, Steve Koerner wrote:
>> [repost from Arizona Soaring Assoc board where it seemed to be of
>> interest]
>>
>> I'm sure many already know this -- it's a good trick to know if you
>> don't.
>>
>> Late afternoon summer wind will very often completely stop right at
>> sunset. If you are faced with a crosswind landing in the late afternoon,
>> a solution is to hangout until sunset.
>>
>> I've done this several times over the years at various airfields
>> including just a few days ago flying out of Estrella. I came back about
>> forty minutes before sunset to find an 80 degree cross of about 15 knots.
>> The flag was whipping sharply. I probably could have landed it, but why
>> take a chance?
>>
>> There remained some very weak thermals able to sustain to about 2500 ft
>> as is common at the end of the day. So I just hung out until the sun
>> dropped below the distant mountains and landed in calm conditions. An
>> added benefit is that you can see the runway after the sun drops if you
>> are needing to land to the west as is the usual case in the southwest.
>
> Interesting idea, indeed! How long can you fly after sunset w/o nav-lights
> or is the sunset time much after the sun disappears behind the mountains?
> Just curious,...

I got into the habit of doing the same thing from Boulder soon after my
arrival there, for the same reason. Very useful experience gained for future
late-in-day XC's too...what's not to like?!?

Bob W.

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[kinsell]

On 10/04/2017 07:52 AM, Bruce Hoult wrote:
> On Wednesday, October 4, 2017 at 4:32:02 PM UTC+3, Steve Koerner wrote:
>> Official sunset time would be perhaps a minute or two after the sun disappears behind distant mountains. Time it right and no lights are required. I imagine last thermals would end about then anyway.
>
> No lights are required until 30 minutes after sunset.
>

30 minutes after sunset is what most states use for driving without
headlights.

I think technically you're legal to fly until the sun drops below the
horizon, if it weren't hidden by mountains.

[Mike the Strike]

On Friday, October 6, 2017 at 9:47:05 PM UTC-7, kinsell wrote:
> On 10/04/2017 07:52 AM, Bruce Hoult wrote:
> > On Wednesday, October 4, 2017 at 4:32:02 PM UTC+3, Steve Koerner wrote:
> >> Official sunset time would be perhaps a minute or two after the sun disappears behind distant mountains. Time it right and no lights are required. I imagine last thermals would end about then anyway.
> >
> > No lights are required until 30 minutes after sunset.
> >
>
> 30 minutes after sunset is what most states use for driving without
> headlights.
>
> I think technically you're legal to fly until the sun drops below the
> horizon, if it weren't hidden by mountains.

Yes, but bear in mind that most contests require you to end your flight before sunset to avoid disqualifying the flight. This includes OLC!

As the weatherman in a few contests, I always include a contest official sunset time to avoid later arguments. Land after that and you're toast!

Here in Arizona, thermals will typically start decaying in late afternoon an hour or more before sunset and you won't often need to wait that long, but Steve's suggestion is valid.

Mike