Thomasso

How do GA pilots know the wind when performing maneuvers?

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Hello,

I'm studying the AFH from FAA at the moment (yes, for simming purposes, I am that weird... Although I plan on doing a PPL in Europe in a few years :) ). There's this thing that keeps bugging me. I'm currently reading the chapter "Ground reference maneuvers" which is a lot about wind corrections.

But the book anticipates that I have perfect knowledge of surrounding wind speed and direction at all times. Also the wind usually is either perpendicular or parallel to the airplane. 

How do GA pilots deal with this in the real world? Usually the wind isn't exactly perpendicular or parallel, its speed and direction changes, there are gusts etc... And when I fly 100 nm and decide to practice ground reference maneuvers, how am I supposed to know the winds? 

Every tip will be appreciated :-)

Thanks,
Tomas

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You look out the windshield? I've only flown a real plane once, but in my experience with that, prior to take-off, my friend was telling me what reference points on the ground we were using for the flight, like smokestacks or another airport and what not. Once we got airborne, it was a matter of looking out the windshield and finding that reference point on the ground.

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6 minutes ago, Captain Kevin said:

You look out the windshield? I've only flown a real plane once, but in my experience with that, prior to take-off, my friend was telling me what reference points on the ground we were using for the flight, like smokestacks or another airport and what not. Once we got airborne, it was a matter of looking out the windshield and finding that reference point on the ground.

Hi, thanks for the reply.

I'm not sure that I follow. How are these reference points gonna help you determine wind speed & direction? By seeing whether you drift to/away from them?

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Exactly, you can decide how much to correct by how much you drift. It is an essential skill to develop and you need to get an eye for it.

For planning purposes you obtain winds aloft data and then you measure your actual performance by timing how long it takes to get from point to point against your plan.

Ground reference is not about using winds aloft data as much. You know where the prevailing winds will be from, but you'll be fairly low and the winds aloft data is not available near the surface. You must learn to maneuver with "reference" to points on the ground. You do what is required to correct your course. It sounds difficult at first, but with practice it isn't so bad.

With fancier equipment you can get derived wind vector data, but I ignore it when flying in VFR conditions. I can see and estimate speed and direction fairly well at 1000 feet and down. Above 1000 feet it is more difficult to measure drift over the ground and you can calculate it using an E6B or equivalent.

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Hi Tomas,

It all starts with a good preflight - any real flight planner will provide you with the prevailing winds - so you should know what they should be before you leave... 

Once in the air - you could call Flight Services "Radio" for an updated brief on what the winds are doing at different altitudes - I've done that multiple times on windy trips to determine best altitudes while enroute...

A quick look at your airspeed vs groundspeed will give you some information...

Any GPS will give you the winds - even if you manually have to input the information... Just punch in your numbers and it will spit out the winds...

Ground reference maneuvers are normally performed at lower altitudes - below 3000 feet - so yep - just line up on a straight piece of anything - road - tracks - field edge - and see what the wind does - anything less than 5 knots is calm and you won't even notice in your ground reference maneuver - so you're looking at substantial changes or crab angles...

Regards,
Scott

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1 minute ago, Oracle427 said:

Exactly, you can decide how much to correct by how much you drift. It is an essential skill to develop and you need to get an eye for it.

For planning purposes you obtain winds aloft data and then you measure your actual performance by timing how long it takes to get from point to point against your plan.

Ground reference is not about using winds aloft data as much. You know where the prevailing winds will be from, but you'll be fairly low and the winds aloft data is not available near the surface. You must learn to maneuver with "reference" to points on the ground. You do what is required to correct your course. It sounds difficult at first, but with practice it isn't so bad.

So basically I just start the maneuver, see where the wind takes me and correct for that. Right? :) 

Thanks for explaining.

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If you are lucky enough to have a gps which shows wind direction and speed then you are all set. 

Otherwise its map, pencil and e6b time......

http://www.mye6b.com/e6b.html#_windDS

 

This is more for cross country work though. If you are 3000-4000 feet with plenty of visual reference it should be pretty obvious what you need to correct to. 

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1 hour ago, ThomassoCZ said:

Hi, thanks for the reply.

I'm not sure that I follow. How are these reference points gonna help you determine wind speed & direction? By seeing whether you drift to/away from them?

Do you need to know the exact wind speed and direction? When I flew that flight, I had a general idea of the winds (which I admittedly forgot right after I got in the plane), but ultimately, I just flew towards where I needed to go. First visual reference was smokestacks. Look out the windshield, find the smokestacks, fly towards them. Next one was an airport. Look out the windshield, find the airport, fly towards it. You just see where you're going and make whatever corrections you need to make to get there.

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Just now, Captain Kevin said:

Do you need to know the exact wind speed and direction? When I flew that flight, I had a general idea of the winds (which I admittedly forgot right after I got in the plane), but ultimately, I just flew towards where I needed to go. First visual reference was smokestacks. Look out the windshield, find the smokestacks, fly towards them. Next one was an airport. Look out the windshield, find the airport, fly towards it. You just see where you're going and make whatever corrections you need to make to get there.

Yeah but I was asking about ground reference maneuvers, not a simple A to B flight :) But thanks anyway...

 

Thank you everybody for very good explanations! :)

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Depending on the altitude and weather, there are a number of things you can look for, that is if you only want to determine the wind speed and direction yourself rather than with an ATC reference, although this can help too, and you should as a rule have an idea of that before you take off, since the windsock will provide that to you. A windsock will give you the speed and direction even if ATC do not, since a windsock is gauged and calibrated -  each orange/white division which is blowing out horizontal indicates 3 knots of wind speed - so a windsock which is fully horizontal will indicate a wind speed of at least 15 knots (about 17mph). Most windsocks are divided visually into five segments, and even if they aren't, you can simply 'guesstimate it' by dividing the windsock's length into five. This is true in FS as well as in real life by the way.

If you tune an ATIS frequency for a nearby airport, providing the air mass is not going to change significantly, that will give you a good average to start with, your airport will give you a good visual clue too when you take off, since the airfield usually has its runways aligned with the typical prevailing wind for the region; this is often westerly, which is why many runways are 27/09, since they are usually constructed to be into the wind on an average day. Needless to say, when you turn up at the airfield, it is common sense to read a weather briefing, and of course if it says NOSIG on it, then you will know it is good for quite a while since that means there is no significant change is expected, similarly, you can check online for that kind of thing too.

Having done all of that, you will have a pretty good idea of the average windspeed and direction for the region and if it is likely to stay that way or not, and can then ally that with what you observe in flight, since weather forecasts are exactly that, a forecast and not a fact.

A good indicator for wind speed and direction is cloud shadows, which can be observed moving across the terrain; these will give you a fairly accurate indication if you are familiar with what things look like at various heights. For example, if you fly in an area familiar to you, then you will have a good idea of the size and distance between various landmarks, and from that, if you see cloud shadows moving between these and time them for fifteen seconds, you can multiply that by four and you will have how long it is taking things to move a certain distance over a minute, and if you times that number by 60, can determine the approximate wind speed in mph and its direction. One knot is 1.15 mph, so you can work out knots from mph too, and if you need to do so very quickly, just add a bit over ten percent to mph and it will be close enough.

A nice trick is to go on google earth and have a look at where you expect to fly, then observe from the distance ruler how big the average field is, this will allow you to take a good guess at how fast clouds are moving by observing their shadows, however, do not fly along transfixed on this when flying VFR, simply use the clock to note the position of a cloud shadow, then look back where it is a minute later, in this way you can maintain your VFR observation.

Here is an example I might use when flying over my home town: At about four miles from the threshold of Manchester Airport's runway 23R, you pass over the large brick railway viaduct which crosses the river Mersey in the centre of Stockport. This is easy to spot since it is 109 feet tall, so it can be seen from miles away, in fact right when you turn for the localiser from 15 miles away when on finals for EGCC; that viaduct is approximately one third of a mile long, so if you observed a cloud shadow moving near it which took about 20 seconds to travel a distance over the ground which appeared similar to around one quarter of its length, you would then know that shadow took 20 seconds to cover about 1/12th of a mile, which means it would take it 240 seconds to traverse a mile, which is four minutes. If something is taking four minutes to cover a mile, then it is doing about 15 miles per hour, which is about 17 knots, and you sussed that from a 20 second observation and a quick bit of basic maths. It's not perfect, but it is okay for starters in the absence of any other clue.

Smoke from chimneys of factories and steam from power stations are always good wind direction indicators, as are flags on buildings, ripples on lakes, or over the grass or crops in fields although much of this is not available in a flight sim, which is why the cloud shadows in P3D are good (or the DX10 fixer cloud shadows in FSX).

Note that cumulous clouds form in lines, known as cloud streets. Typically that means sunlight will be shining on a surface, heating it, then air will be rising from it and the moisture in that rising air will be condensing at an altitude near the inversion layer height. Busy roads, towns, dark surfaces, ploughed fields, large expanses of tarmac or concrete etc are all sources that will kick up such thermals which eventually condense into clouds downwind of such ground features, and this can show you the prevailing wind direction and give you a (very rough) indication of wind speed too, as well as a reasonable indication of where turbulence will be. Lenticular clouds on the downwind side of hills will indicate the wind direction low down and will also show where there is likely to be windshear and downdrafts which might be hazardous.

Note that wind is a function of the air mass in high pressure areas flowing into low pressure areas, so observing longer range weather maps and the pressure values can help to determine where the wind is likely to blow and you can also sort of figure that out by tuning several ATIS frequencies, since these always give the local air pressure; there is a decent chance wind will be blowing from the location of a high pressure area to a lower pressure area, although this is not always true, but in the absence of any other info, such as night time when you won't see cloud shadows, it is at least something.

What can you do with such observations? Well, if you know the windspeed and you know its direction, you can use an E6B to calculate the amount of drift for a specific course at a specific speed, and from that you would know how much to offset your course, although if you don't want to do that, and you are VFR, you can simply aim off a reference point on the horizon until it remains stationary in your view, and that'll do it too. If there is no suitable landmark and no suitable cloud shadows, you can use your aircraft's own shadow to determine drift too, since you can fly along a road and see how much you drift off it by observing your aeroplane's shadow.

What is worth doing for that kind of rough guess, if you fly a certain aeroplane type regularly, is learning how large things look against certain points on the windows from certain altitudes, you can do that by flying over a known object at a specific height and making note of how big it looks. For example, a football pitch might look like it covers a third of the window sill's length when you're at 1,500 feet or some such, or you might know your home runway is one mile long and so you could see how big that looks against the window at circuit height etc. You do get used to that sort of thing when flying regularly and it is useful to be able to gauge the size of things since you might one day have to pick a field to make a forced landing in, and so knowing roughly how long fields are, is useful for emergencies as well as for guessing wind speeds.

 

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54 minutes ago, ThomassoCZ said:

Yeah but I was asking about ground reference maneuvers, not a simple A to B flight :) But thanks anyway...

When you said ground reference maneuvers, I assumed you meant finding a reference point on the ground and flying towards it. I just used the smokestacks and the airport as examples because that's what we used as reference points when we flew our flight. We didn't actually land at the airport that we overflew.

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18 hours ago, Chock said:

 

Wow, thanks for a very detailed explanation! :) Very cool.

Edited by n4gix
Removed excessive quote. Please don't quote a "wall of text" for a one sentence reply!

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One other cool thing to try, to get a feel for observing the ground, is to cover the altimeter and then try to guess how high up you are, and you can do this just as well in a flight sim as you can in real life (look at the size of cars, houses, animals in fields etc). One of my old instructors used to do this with me, and I was rubbish at it at first, but I got better with practice and it's useful to develop that skill because if you don't have a pressure update and the weather changes significantly, your altimeter will not be reading accurately at all, but that will give you a fairly good guide to your height AGL.

Check this out. Have a look at this website link below and you will see it shows Manchester airport from above. Now, even if you did not know Manchester's two runways were 10,000 feet long, you could quickly determine that from observing the markers on the runway, which are spaced every 500 feet. So, you've got a very speedy reference for what 500 feet looks like for the surrounding area (these markers are the same for every runway). From this, you could quickly determine that the average size of a field in the surrounding area near this location is coincidentally, about 500 feet long. And since you know there are just over 5,000 feet in a mile, you could very quickly determine how fast the wind speed was by watching a cloud shadow pass over a field, and from that you could also work out which would be a good choice for a wheels up emergency landing, and which way you should come into, it if you had to.

This is a pretty useful thing to know when piloting a single engine aeroplane, and it's a really useful thing to know when flying a glider. I've had cause to make use of that a few times in one of those (golf courses are good for impromptu forced landings incidentally, although trust me, you will upset the golfers if you do that, because driving a towing vehicle with a glider trailer onto the fairways makes a right mess of them, but I say it serves them right for wearing those stupid golfing outfits lol).

https://www.flightradar24.com/53.35,-2.28/15

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Hi Folks,

I always thought it was cool when you did your 360's properly on a calm day - you would hit your own wake turbulence when completing the circle - even a little C172 can feel the bump...

Regards,
Scott

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