Wind Speed Calculation

[Waylander]

Hi Guys
Can anyone comment on how accurate the following estimation orf wind speed will be.

1). Fly drone to altitude required.
2). Switch to Atti mode, and watch the direction ( course ) of wind drift that occurs
3). Once the "course" has been established switch back into P-mode.
4). Flyback back along the established course to a distance say 100 feet behind your position.
5). Ensure than you stand beneath the "course" on a path that ensures the bird passes directly overhead
6). Switch back to Atti mode, and when the quad passes directly overhead start a stop watch running.
7). Allow the bird to move to a position downwind say 200 feet, ( use Go app to measure the distance)
8). When you are exactly the distance away ( eg 200 feet) that you wanted to use stop the watch.

Now carry out the folowing calculation where D = distance eg 200 feet & T = time taken eg 12 seconds

((D/T)*3600)/5280 = ((200/12)*3600)/5280 = 11.36 MPH i.e. the average wind speed

Now I know there would be some inaccuracies involved, Ie when you start the timer as the bird passes overhead, and also some vectoring will occur due to slight changes in altitude and direction, and some gusting or wind shear might be encountered, but how accurate do you think the method would be..? How could you improve on the technique.

Waylander

 

[a31burgervan]

Try UAV forecast app - tell it altitude and it will guesstimate - fine trying to calculate such things but winds tend to be variable

 

[Waylander]

Try UAV forecast app - tell it altitude and it will guesstimate - fine trying to calculate such things but winds tend to be variable

Hi yes I have that app ( and various others ) and I understand about wind speed variation, ground effect, wind shear and inversions, etc but its one thing looking at an app and another being on the ground and looking to establish a local wind speed at a particular altitude
Waylander

 

[Meta4]

Hi Guys
Can anyone comment on how accurate the following estimation orf wind speed will be.

Rather than trusting apps of dubious accuracy or complicated calculations, all you need to know is how the wind will affect your Phantom.
Simply go to the altitude you are interested in and fly upwind and note how fast you can travel against the wind.
Your Phantom should do 15 metres/sec (with object avoidance disabled).
If you can only make 5 m/s, it shouldn't take much imagination to realise how this would affect you in a long flight home.
Then keep flying further upwind and you'll have an easy flight home.

 

[N017RW]

Agreed M4.

All the calculating???...
what a buzz-kill.

 

[Waylander]

Hi All
Thanks for the responses they were all..........

Its no big deal, some of the locations I fly in are on the open moor, where the wind can be strong, I always check the general wind direction by selecting Atti mode and watching the direction of drift.

Apps like UAV forecast, Drone Buddy, Hover etc do give wind speed and direction, but the figures are for a wide area, and if you check each app in turn they all give slightly different readouts.

OK Meta4 makes a point regarding Phantom flight characteristics ( eg 15 m/sec ), but to establish local wind speed from that you still have to make some calculations, the method I suggest takes two overhead passes of the drone and a simple calculation.

Once established I enter the value in my flight log.

I do apologise if my post is... ah, em.. tiresome! perhaps some one will get something from it.

Fly Safe
Waylander

 

[N017RW]

You're entitled to your posts and flight regimes .
But in all the years (decades) of flying r/c aircraft I've never once brought my calculator with me .
The methods M4 described will do fine but again, TEHO!

 

[Waylander]

You're entitled to your posts and flight regimes .
But in all the years (decades) of flying r/c aircraft I've never once brought my calculator with me .
The methods M4 described will do fine but again, TEHO!

Yea but you do have your phone, which has a calculator on it...

 

[Waylander]

You're entitled to your posts and flight regimes .
But in all the years (decades) of flying r/c aircraft I've never once brought my calculator with me .
The methods M4 described will do fine but again, TEHO!

Yes indeed, if you only fly for a buzz... I too have flow RC for years and driven RC cars, everyone is entitled to an opinion

 

[alokbhargava]

Hi Guys
Can anyone comment on how accurate the following estimation orf wind speed will be.

1). Fly drone to altitude required.
2). Switch to Atti mode, and watch the direction ( course ) of wind drift that occurs
3). Once the "course" has been established switch back into P-mode.
4). Flyback back along the established course to a distance say 100 feet behind your position.
5). Ensure than you stand beneath the "course" on a path that ensures the bird passes directly overhead
6). Switch back to Atti mode, and when the quad passes directly overhead start a stop watch running.
7). Allow the bird to move to a position downwind say 200 feet, ( use Go app to measure the distance)
8). When you are exactly the distance away ( eg 200 feet) that you wanted to use stop the watch.

Now carry out the folowing calculation where D = distance eg 200 feet & T = time taken eg 12 seconds

((D/T)*3600)/5280 = ((200/12)*3600)/5280 = 11.36 MPH i.e. the average wind speed

Now I know there would be some inaccuracies involved, Ie when you start the timer as the bird passes overhead, and also some vectoring will occur due to slight changes in altitude and direction, and some gusting or wind shear might be encountered, but how accurate do you think the method would be..? How could you improve on the technique.

Waylander

You are calculating wind speed based on the air drag divided by the time. This will give some numbers but are not associated with the actual wind speed at all.

If you know drag for a known speed for your phantom at the same height for a given time, then you can workout the relative change in speed for the same parameters under different wind conditions.

These methods are not useful as we want to know the actual wind speed at a height even before we take off to decide about the safety of my phantom.

 

[N017RW]

Bring balloons and helium.

 

[Waylander]

Hi alokbahrgava

I see what you say but consider:-

An air balloon will asymptotically approach the wind velocity. As it gets close, the force due to drag will decrease because the apparent wind will be small, to the extent that it eventually matches the wind velocity, If the wind slows down a bit the balloon slows down to the new velocity, so there will then be a time when the balloon is moving faster than the air, but it will average out, so if the distance over which the measurements are taken is too small the the inaccuracy will be greater.

Consider that early mariners circumnavigated the earth by measuring ships speed with a length of knotted rope attached to a float and counting the knots against the time it took the sand to run out in an hour glass, they did OK.

So yes this method is not as accurate as an anemometer, but then you need take measurements at the altitude you wish to fly, which you can not do.

So yes I see that the forums consensus is that it is a waste of time..!, but then I suppose so is testing RTH at the start of a flight, many pilots do this ( I don't ), are they then also wasting their time.. ?

So then subject closed, many thanks to N017RW for his enlightened contribution.

Waylander

 

[Richard R]

Just my 2 cents worth. After having some problems with Maps Made Easy, they told me that part of my problem might be that I was flying down and up wind (turns out that wasn't the problems). So I started taking my bird up to the planned altitude and turning off GPS mode. Just watched it drift for a bit to determine both wind direction and approximate wind speed. I then adjusted my MME mission so the the flight paths were cross wind. Never flew far enough in strong wind conditions that I had to worry about wind speed and direction for the return home, but will use the same technique before starting any longer missions. As many have said, can and likely will be significant difference between winds on the ground and aloft. BTW, early on, airplane navigators had to figure winds at altitude on their own using the induced drift. One of the things that they did to help each other out was to report those estimated winds, especially high or unusual ones, to other pilots. Imagine flying across the Pacific at night with just a compass, watch and sextant (Yes, flight navigators would shoot the stars just like the ancient mariners did)! Indicated airspeed wasn't much help because they had no direct reference to relate that to ground speed.

 

[N017RW]

Hi alokbahrgava

I see what you say but consider:-

An air balloon will asymptotically approach the wind velocity. As it gets close, the force due to drag will decrease because the apparent wind will be small, to the extent that it eventually matches the wind velocity, If the wind slows down a bit the balloon slows down to the new velocity, so there will then be a time when the balloon is moving faster than the air, but it will average out, so if the distance over which the measurements are taken is too small the the inaccuracy will be greater.

Consider that early mariners circumnavigated the earth by measuring ships speed with a length of knotted rope attached to a float and counting the knots against the time it took the sand to run out in an hour glass, they did OK.

So yes this method is not as accurate as an anemometer, but then you need take measurements at the altitude you wish to fly, which you can not do.

So yes I see that the forums consensus is that it is a waste of time..!, but then I suppose so is testing RTH at the start of a flight, many pilots do this ( I don't ), are they then also wasting their time.. ?

So then subject closed, many thanks to N017RW for his enlightened contribution.

Waylander

Not my contribution...

...The first weather balloon is believed to be credited to the French in the 1700's.

NOAA has used them since about the mid-1930s in conjunction with the advent of the radiosonde.

Capable of being launched from land, sea, and air they continue today to be the Number 1 tool for meteorologists!

 

[Habanero]

Well I think I go simple after reading so much very interesting deep analysis and calculations... Great stuff . It does make sense but I'm lazy .

1). Fly drone to altitude required.
2). Switch to Atti mode, let it drift and soon will reach a max steady speed very very close to the real time wind speed.
3). switch back into P-mode , have fun .... check again as needed.

 

[Waylander]

Yep...! essentially that is what I said...

Fly Safe
Waylander

 

[ianwood]

Hang an anemometer under the drone! Done.

 

[Habanero]

That Won't work with all the turbolence coming from the props ..I think . drone already has a gps speedometer... test it with your car speedometer take the drone out for a ride while power on ...

 

[Waylander]

I Agree with Habanero, air pressure is greater below a vertically aligned propeller, or greater behind a horizontally aligned propeller, so according to Bernoulli’s Principle the down draft would cause a pressure differential on opposite sides of the blades of an anemometer, so effectively the " lift or thrust " created by the rotating blades of the anemometer would not be the same as it would in an undisturbed air stream, hence if the rotational speed of the anemometer props differ so will it's wind speed measurement. I'm sure that ianwood posted his comments for a laugh..
Waylander

 

[Habanero]

Lol I also love Star Trek ....