Share Info About Wind Effects and Buildings/ Bridges

[Alex Folds]

I was wondering if anyone could share information/ links about the effects of wind shadows from buildings, and wind shears, and anything else good and technical about wind that might be applicable to us phantom fliers. I would like to be as prepared as possible if I am going to be flying around bridges, beaches, lakes, buildings, or in city downtown areas either above or between buildings.

I think the information be good to be in a collected place for reference as I think its an important education point on drone flying. The other information I have found online doesn't really go deep enough in its explanation from what I have found. Mabey one of you studied wind in their University studies and knows a thing or two in detail.

I plan on flying in many cities and over lots of water in October and November in the NYC, Orlando/ Miami, Chicago, San Francisco, Los Angeles, Palm Springs, and Denver areas. If I remember correctly, October and November are windy months on the eastern part of the country right? My flight is scheduled to land in NYC right as Hurricane Joaquin is going to hit, we will see how that goes.

 

[Alex Folds]

This has the equation for windshear and some common variable values: Wind Shear

Wind moving across the Earth's surface is slowed by obstructions like buildings, trees and similar and the wind velocity increases with altitude.

The wind shear can be expressed as
v / vo = (h / ho)α (1)
where
v = the velocity at height h (m/s)
vo = the velocity at height ho (m/s)
α = the wind shear exponent
The wind shear exponent varies with the terrain. and in the link it gives sample values. Very helpful from a physics point of view.

 

[Alex Folds]

A reason to love the FAA https://www.faasafety.gov/files/gsl...7/FAA P-8740-40 WindShear[hi-res] branded.pdf

 

[GadgetGuy]

More important than wind around the obstructions you describe is the blocking of the transmitter signal! Between buildings, you could experience a complete loss of signal for more than 3 seconds which would trigger a RTH. Flying over buildings usually maintains the LOS of the signal and is much safer. Always remember to fly against the wind on your outward leg, so your return will be downwind, and hope that the wind direction doesn't change in midflight! If you ever notice you are flying downwind (extremely fast flying speed), turn around when you reach 70% remaining battery, because you will need twice as much battery power to return home, as you used up, getting there!

 

[ianwood]

Never had a loss of signal in any city. Always VLOS. As for wind, it'll ruin your shots. Have fun in Chicago. Gimbals hate the cold. Or at least DJI ones do. I shot a bunch of stuff in the bitter cold of November in Chicago. Never again.

The issue with wind and buildings is it's turbulent and blustery. In other words, unpredictable. I don't think I ever was at risk of losing control, but then again, there are many days I opted out of filming. The good news is sunny days tend to be less windy than cloudy ones. Except for Chicago. It's always windy in Chicago. Uggh.

And filming on cloudy days is a complete waste of time. Looks like crap. Don't do it.

 

[Alex Folds]

Good advice. Have anything from the cold In Chicago you could share so I could see ( I know you probably want to forget the experience) I think that is going to be the most challenging part of the trip.

So the gimbal motors and electronics slow their responses in the cold? Shame I wanted to film really nice snowboarding in Colorado shots.

 

[GadgetGuy]

Batteries are especially sensitive to cold, so you could experience a sudden drop in remaining battery capacity. As long as you keep an eye on your battery cell readouts, and stay within VLOS, you should be fine. High winds force the aircraft to tip at extreme angles to maintain position, which can lead to gimbal guard contact and props appearing in the frame, neither of which help the videography. Have plenty of spare batteries on hand for the cold.

 

[RoyVa]

Also remember the more wind the more it uses battery power against it. Don't get caught with your pants down er battery down that is. She autolands at critical battery level and makes no difference where she is or what's under her, down she comes.

 

[Ti22]

Great point about battery life. Lipoly is very sensitive to minor drops in temperature.

Store your packs at room temp or above (next to your body) before placed into service. If they start out warm, IR (internal resistance) will likely generate enough heat internally to help avoid a major change in performance.

Spend enough time in NYC and other major cities with tall buildings you’ll learn about the “tunnel” or “plenum” effect. It’s really like a huge ductwork funneling strong winds down the “canyons” between buildings. Look up venturi effect…

On any rainy, blustery day in NYC you’ll see many umbrellas in the trash cans. This is because people have let their guard down as they step around the corner of a building and get blasted by strong gusts of wind.

Gotta be aware of the prevailing wind strength and direction. Use that information to better anticipate when you may suffer a severe change in wind direction and in some cases, velocity.

 

[SilverStone641]

This is a great thread with a ton of information. Thanks very much! I just got my P3P yesterday and have been eye-balling some of the bridges around Dallas for some premo video. I've been nervous about doing it ever since I saw someone drive an Inspire into the pavement in downtown. He was showing off a bit and came around the side of a building, caught an unexpected gust and down he went. That was a spectacular crash!

 

[GadgetGuy]

Go big or go home! At least if you crash spectacularly, you'll have a terrific crash video, and might get enough YouTube viewers to replace your aircraft!