The "wind problem"

[PeteM]

Usually my P4 flies in waypoints mode and usually my flights have a duration "in the air" of about 15 minutes, so adding a few minutes for takeoff and landing I can complete the whole mission with about 30% of remaining battery.

But... it often happens to arrive on the spot and find some moderate wind, with or without gusts, and not knowing whether to take off or not for fear of battery life.

Are there any precise decision making parameters, not based on pilot's sensations ?

 

[With The Birds]

Fly manually- put your phantom up where it will be flying the mission, flick to ATTI mode and watch how fast it drifts (as displayed in the GO app) and the direction (without any stick inputs). That will give you a really good sense of what you are dealing with.

 

[PeteM]

This procedure consumes battery and does not give me the answer I'm looking for.

The problem is not the flight stability since I did some tests and I saw that the Phantom 4 can fly very stably and safely even with winds in the order of 7 or 8 m/s.

My fear is that the increased consumption of battery, due to the wind, bring down the battery level below the safety threshold when the drone is still making the last strips...

Is there a way to estimate the increased consumption based on wind speed ?

 

[With The Birds]

This procedure consumes battery and does not give me the answer I'm looking for.

The problem is not the flight stability since I did some tests and I saw that the Phantom 4 can fly very stably and safely even with winds in the order of 7 or 8 m/s.

My fear is that the increased consumption of battery, due to the wind, bring down the battery level below the safety threshold when the drone is still making the last strips...

Is there a way to estimate the increased consumption based on wind speed ?

When you have a better means of establishing what the actual wind speed and direction might be at the altitude you propose to fly your waypoint mission please let us know.

You can’t make any estimate of increased consumption absent knowing what the wind speed is. The consumption calculation itself is trivial in comparison.

Good luck...

 

[PeteM]

When you have a better means of establishing what the actual wind speed and direction might be at the altitude you propose to fly your waypoint mission please let us know.

Something like wind at 8 m/s with some gusts at 10 m/s.

You can’t make any estimate of increased consumption absent knowing what the wind speed is. The consumption calculation itself is trivial in comparison.

In all the flights I have done (very similar for speed and characteristics) there is a fairly clear relationship between km traveled and the remaining battery. In the absence of moderate winds, I can predict with how much battery I land.

In estimation, however, I can not understand how to handle the variable wind when its present in a relevant way...

 

[Waylander]

Hi With the Birds

Well over a year ago, I proposed the same thing as you suggest, Fly to mission altitude directly overhead, hover check your distance from home point ( 1 or maybe 2 mtrs what ever the display says), switch to atti mode allow the aircraft to drift with the wind, time the duration for the bird to drift 50 mtrs from home point, make your wind speed calculation.

Assuming zero drag, then this formula can be used :- Distance over speed *time, or Speed = Distance / time,
eg distance = 50 mtrs, time = 15 seconds so speed = 50/15= 3.33 mtrs/second
To convert this into Knots multiply Speed in Mtrs/sec by a factor of 1.9 therefor 3.33 mtrs/sec = 3.33*1.9 = 6.3 Knots

So this is only a rough guide because we are ignoring the drag coefficient and initial inertia of the drone, but the longer the time allowed to cover the measured distance the less the drag factors will effect the answer. So qualified pilots, if this calculation is wrong or some other factor needs to be include please post...

PS WTBirds when I posted this proposal the first time many OP's, poo pooed it, saying it was a waste of time, but you don't want to be tearing off until your battery has warmed up any way, so use this exercise to warm up your battery, or move down wind of your mission and allow the wind to carry the bird to the first waypoint....

Waylander

 

[PeteM]

To measure the wind speed (in terms of order of magnitude) you just need a few dollars anemometer.

Ok... I know that the wind speed in the air is not equal to the wind speed on the ground, but in the open field I dont think that a few tens of meters of altitude can introduce significant variations...

The problem is not knowing the wind speed with maximum precision, but having an idea of "how much" it is and how it can affect the duration of the flight...

 

[With The Birds]

To measure the wind speed (in terms of order of magnitude) you just need a few dollars anemometer.

Ok... I know that the wind speed in the air is not equal to the wind speed on the ground, but in the open field I dont think that a few tens of meters of altitude can introduce significant variations...

The problem is not knowing the wind speed with maximum precision, but having an idea of "how much" it is and how it can affect the duration of the flight...

A few tens of metres can, and often does, make a big difference. When I flew this morning it was basically calm at ground level. 20 metres up it was 6ms and at 80m altitude it was over 12ms. The Mavic handled it fine however a hyper lapse would have been out of the question.

Your anemometer is probably only slightly more reliable than sticking a moistened finger in the air when it comes to understanding what is going on past arms length.

What does tend to be very useful and reliable is a subscription to UAV forecast. It is very close to the mark in most cases.

 

[With The Birds]

Hi With the Birds

Well over a year ago, I proposed the same thing as you suggest, Fly to mission altitude directly overhead, hover check your distance from home point ( 1 or maybe 2 mtrs what ever the display says), switch to atti mode allow the aircraft to drift with the wind, time the duration for the bird to drift 50 mtrs from home point, make your wind speed calculation.

Assuming zero drag, then this formula can be used :- Distance over speed *time, or Speed = Distance / time,
eg distance = 50 mtrs, time = 15 seconds so speed = 50/15= 3.33 mtrs/second
To convert this into Knots multiply Speed in Mtrs/sec by a factor of 1.9 therefor 3.33 mtrs/sec = 3.33*1.9 = 6.3 Knots

So this is only a rough guide because we are ignoring the drag coefficient and initial inertia of the drone, but the longer the time allowed to cover the measured distance the less the drag factors will effect the answer. So qualified pilots, if this calculation is wrong or some other factor needs to be include please post...

PS WTBirds when I posted this proposal the first time many OP's, poo pooed it, saying it was a waste of time, but you don't want to be tearing off until your battery has warmed up any way, so use this exercise to warm up your battery, or move down wind of your mission and allow the wind to carry the bird to the first waypoint....

Waylander

You can avoid all the mathematics and simply look at the depicted airspeed in the GO app....

 

[umanbean]

What does tend to be very useful and reliable is a subscription to UAV forecast. It is very close to the mark in most cases.

Glad to hear you feel that way about UAV Forecast, given your expertise. That's what I use also for wind prediction. I don't need the extra features a subscription offers so just use the 'free' version. I wouldn't mind donating a few dollars for the app, but a $25 subscription is a little steep for hobby use.

 

[PeteM]

Ok... let's say that thanks to these services I can get to know the speed of the wind at certain altitude.

How do I decide whether to fly or not ? How can I tell if with "that 8 m/s" I'll land safely or my battery will die during flight ?

 

[bdooley]

Not sure there is an easy way to accurately calculate that. Too many variable. But can't you just monitor the battery and how far you are into the mission and determine if you need to abort?