Assessing wind from the air

[Sam Rutherford]

When landing without clear ground indicators - how do you assess wind direction and strength?

Hoping for a couple of 'tricks of the trade'!

Cheers, Sam.

[TomD]

A couple of things I was taught to look for in float flying are the water and the leaves on the trees ( no help in evergreen forest or the winter).

The leeward side of a shore or tree line will have slick water, the higher the obstruction the longer the slick water. Pop over to the seaplane bb and there are a couple of charts that have what wind speed creates waves, whitecaps etc.

Deciduous trees will turn the lighter colored bottoms up in heavier winds. You can get a feel of the direction from which way the wave of lighter green is showing, obviously white side to windward. If you see waves of lighter green you are probably looking a pretty brisk wind. I will let wiser heads give you some guesses on speeds.

Pick up trucks and small animals blowing across the landing area would probably mean a tricky landing.

TD

[Skystrider]

Here is a link to a great chart that will help you assess wind speed.

http://www.unc.edu/~rowlett/units/scales/beaufort.html

[rjb]

A Garmin 76CS is in my flight bag and a Garmin 250 and Garmin 430 are in my plane; a look approaching the airport at indicated and ground speed is generally sufficient although I do use the 430 calculator enroute to verify that 25 knots of the 26 knot wind is a headwind.

[YELLOWMAULE]

Horses stand with their arses to the wind

[DavidCaswell]

Hi Sam,

I find that wind info is mostly a matter of situational awareness.

There are always signs of what the wind is doing, but they pop up at odd moments - when a truck goes by on a dirt road, when you cross a pond or a bunch of trees, when you see some smoke, etc. - i.e there isn't always a wind sign right when you need it. So what I've found is that if I devote a few mental cycles to continualy looking for signs of what the wind is doing on the ground then I build up a pretty good sense of the wind that I can use when I need it. It takes a little work at first, but it quickly becomes second nature. Obviously there are situations where local terrain makes your wind sense inaccurate - but I really haven't found too many of those.

David

[UP-M5]

water never lies. like tomD says. go get a seaplane checkout, and you will become very aware of what the water is telling you about the wind speed/direction.

secondly- GPS. if you are looking at a strip or "area" to land, fly it slow and low to look for obstructions and check your ground speed vs airspeed at several points along the landing area. when you are low and slow you will notice any crosswind by the crab you are keeping to parallel the landing area. and a groundspeed higher than your airspeed means you should try it in the other direction, if possible. if its a one-way strip, you need to assess if you have enough real estate to get in with the tailwind.

[akloon]

Go back to your basics. Pick a point and fly around it using a constant bank angle. If you hold a steady bank and trim your reference point will drift upwind and when you finish a 360 you draw a line back to it for your wind line. Don't be in a hurry if you don't know the wind.
"Sometimes you gotta slow down to go fast"

[Kirk]

I'll second the technique of looking at water and spotting the glassy areas in the lee side of trees etc. I do that in every descent even if I have an ATIS/AWOS etc. The technique may have limited utility in places like Libya though...

The observer doors really help with my backup technique. I overfly perpendicular to the runway and note the crab of the aircraft as I am inspecting the runway. If the runway or winds are questionable, I'll then fly down the runway in the direction of intended landing, again noting crab.

I've been amazed in desert locations like some of the places you fly, how much wind can be blowing down there without a single visual cue except which way the aircraft is crabbing.

Kirk

[Sam Rutherford]

Indeed, it's for Libya I'm asking. When I last flew there about a year ago there were ZERO indicators. At one stage I had to make a 20kt full crosswind landing - it was difficult just taxiing, but even with all that almost no indication on the ground (clearly, it was obvious in flight that we were a long way from still air!). Took off in under 200ft from the ramp!

But, I digress...

This time (in 2 weeks time) we're looking to make some off-pavement landings, hence the question. I do like the 360 idea, will give that a shot as well as the usual GPS comparisons.

Cheers, Sam.

[UtahMaule]

By always paying attention to indicated vs. GPS you should pretty well know what the wind is doing at all times. But at a landing area I like to fly a small square pattern and double check those speeds in four directions and can usually land, get out, and the wind is exactly as predicted by the pattern comparison. Checking the wind close to the ground is preferable, around here sometimes we get one direction at ground level and a few hundred feet up it can be 180 degrees different.

We have heard of water around here, but never seen much

[maules.com]

If the wind is blowing but the sand is showing no indication, either drop a partial toilet roll, a bag of flour in burstable bag, a smoke flare, surveyor flagging with rock or weight tied to one end, paper bag or balloon tied to a rock or weight,( paint the rock or fasten colour to it) then fly over and check it out. There is always something in the plane.
Or, fly over the place you want to land as if landing and check drift across ground while holding a specific heading. Do this in three directions over your chosen site and you will know the favourable direction and have a good idea of the wind speed/effect on your landing site.
Now make a landing but don't stop, go around after feeling the surface.
Fly back over to see the tyre marks, depth crust or softness.

[Kirk]

Desert winds are problematic. Low level winds are common near sunset/sunrise so getting down low for a check is well advised.

This all reminds me of another desert hazard I encountered while flying relief in the Sudan in the late 80s. We were supplying a refugee camp in the western part of the country. Flat desert scrub about 15 miles north of the low mountains on the southwest border.

A Cessna Caravan reported the strip as very muddy. The strip was a stretch of dry riverbed in an area that only gets about 3" of rain annually. We suspended operations for a week until the Ground Coordinator reported the strip as dry.

I launched up there based on that report. (Flying civil registered C-130). On arrival overhead, we observed livestock running off the runway kicking up dust; looked very dry indeed.

On landing as soon as the nosewheel was touching down and we were going into full reverse, mud/dirt erupted from the nose, flamed out the 2 inboard engines and we were stuck after about an 800 foot ground roll.

Turns out, the runway was a dry crust about 6" thick on top of soupy mud. On questioning the Ground Cooordinator he commented that although the runway had not seen rain in over a week, the distant hills had rain every day. The underground flow of the river was not noticeable.

Several hours of about 30 tribesman digging and scooping mud from the intakes we were offloaded and managed to taxi along the edge of the wash far enough to get room for a takeoff run. Broke through several times on takeoff roll but had the nose up and staggered off about 40 knots below VMC.

Moral of the story, water is hard to find in the desert, but it really can be lurking just below the surface. Driving a stake down into the surface is a good part of runway survey.

Kirk

[Green Hornet]

I agree with Jeremy. In Vietnam when landing a Huey in some tough areas to get into we used good old reliable smoke grenades. The cost is $22.00 for two grenades but that is cheap if you are going to take on 25kt crosswinds in a Maule! in a unknown strip. I also agree with Kirk if you can survey the strip a head of landing.

http://www.amazon.com/M18-Smoke-Grenade ... B0007W7126

[TomD]

Que, "Flight of the Valkyrie"