Hi all,

Got an aviation question, but couldn't take a picture to describe it, so please bear with me...

Spent the weekend at a seminar, office building opposite a hospital with a helicopter landing platform.

On the platform, two windsocks - equally high poles and equally large fabric for each, but one of the poles on a slightly higher base of the building than the other, the other a little lower and closer to the landing deck. I guess only about max 10m separate and not more than 5m lower.

Highest building around, no others close by. Parts of the building higher than the platform. Windsocks misaligned by as much as 50 or 60 degress to each other, pretty well inflated.

So I'm really left wondering:

Why have two?

Why two separate readings?

Possible that one indicates turbulence caused by the building itself?

Lots of weird winds around buildings.

Helicopters try to land with the nose into the wind whenever possible, buildings can cause wind direction shifts (Wind tunneling) which can be dangerous if the pilot does not know about it. It significantly changes the game at and near hover speeds. When doing a vertical takeoff or landings it can be pretty critical to know exactly what the wind is doing.

I used to hear about a lot of crashes of small helicopters wrangling tuna in the pacific. The boat captains refused to turn the boats into the wind for the returning pilots, time is money was the thinking. The guy would have to land on a pitching deck with a tailwind, plus all the webbing on the deck. Dangerous stuff. Not sure if this is still an issue but it was claiming a few pilots every year.

It's not just buildings - windsocks at regular airports can disagree with each other in significant ways.

At my little Talladega airport there are actually three and a half.

There is the "true" windsock between the taxiways with the segmented circle around it. It's the most honest of all of them, as it's stuck right out there with no obstructions.

There are two smaller one about a quarter of the way down each end, but they're about 50 yards from the treeline. I refer to them as "useless, lying little bastages," as that is what they are.

The "half" of a windsock is the American flag on a pole on top of the FBO building. The building itself, though it's just a small one, does some funky stuff with how the wind acts with it, and it can be 50 or 60 degrees off the "true" one.

Now, then, the runway is a bit less than a mile long, and brother the wind can change from one end of it to the other!

There is also wind shear, so having multiple windsocks help to indicate that. I've had to land where the windsock on one end of the runway was completely different from that on the other end of the runway, so I knew to prepare for wind shear during the landing which could be dangerous. Ask Harrison Ford, heh.

v6,
boNes