# B What is the direction of the wind based on flag direction

1. May 5, 2017

### TheWonderer1

I think it is about 90 degrees off but I never thought about wind direction too much. I guess let's say the wind is coming from the NE and there is nothing behind the flag so it's on a field. I know a windcone is 180 degrees so opposite wind direction.

2. May 5, 2017

### Orodruin

Staff Emeritus
Why do you think a flag would be any different froma windcone? And if it was not 180 degrees off, which of the two directions would it go?

3. May 5, 2017

### A.T.

How about directly upwind, like on many sail ship paintings?

4. May 6, 2017

5. May 6, 2017

### Ibix

Getting a small flag and blowing on it is also a fairly simple experiment, if you've any doubts.

6. May 8, 2017

### TheWonderer1

I figured out soon after writing it. It should be 180 degrees and found that this is true in practice.

7. May 8, 2017

To be fair, sailing ships aren't necessarily pointed directly downwind ( and in fact perform better when they aren't. They can even almost sail into the wind, called tacking. So the picture isn't really impossible by any stretch.

8. May 8, 2017

### A.T.

That picture is. Note the sails.

9. May 9, 2017

### davenn

filling in different directions LOL

10. May 9, 2017

### Orodruin

Staff Emeritus
There could be a strong velocity gradient ...

11. May 9, 2017

Staff Emeritus
I wonder if they are using the same wind we are using.

12. May 9, 2017

### Ibix

13. May 9, 2017

### Orodruin

Staff Emeritus
Also, I must say that it is not completely clear to me that the flag is flying towards the stern and the sails could very well be at an angle to the ship that is not 90 degrees. Compare to this:

14. May 9, 2017

### A.T.

That's a different type of sails. What you mean would look like this on the pirate ship above:

But this is not how that sails are set on the pirate ship image (which was just an example for an error you sometimes see, maybe not the clearest one).

15. May 16, 2017

### TheWonderer1

Eh, is the suggestion here that on a sail boat it would be different? Went away for a while but in fact, that's why I asked.

16. May 17, 2017

### A.T.

On a sail boat the flag orients down the apparent wind. At the height of the sails (like the big US one above) it's affected by the airflow diverted by the sails.