Drift, wind velocity and crosswind — transcript

00:00:00.400 --> 00:00:06.016 Drift, wind velocity and crosswind: how wind changes where your drone really goes.

00:00:06.900 --> 00:00:11.949 Heading is where the nose points. Track is the path over the ground.

00:00:11.949 --> 00:00:16.779 Fly zero nine zero with wind from the north, and you slide south.

00:00:16.779 --> 00:00:18.316 That angle is drift.

00:00:19.400 --> 00:00:23.948 To hold the track, turn the nose into wind: about zero eight zero.

00:00:23.948 --> 00:00:28.360 How much depends on wind strength, direction, and your airspeed.

00:00:29.800 --> 00:00:33.917 From the RePL Guide: a road running zero nine two.

00:00:33.917 --> 00:00:39.165 Wind drifts the drone ten degrees left, so you fly one zero two.

00:00:39.165 --> 00:00:44.977 The photos come out skewed: yaw the gimbal, or let the software fix it.

00:00:45.500 --> 00:00:48.120 GPS usually holds the track for you. Fly manually,

00:00:48.120 --> 00:00:50.124 and holding off the drift is your job.

00:00:53.100 --> 00:00:57.624 Wind velocity is direction and speed. Two seven zero at fifteen: from the west,

00:00:57.624 --> 00:01:01.696 at fifteen knots, about seven point seven metres per second. Into wind,

00:01:01.696 --> 00:01:04.411 groundspeed drops and the battery works harder.

00:01:05.700 --> 00:01:11.499 Quick check. The wind is one eight zero at twenty. Which way is it blowing?

00:01:11.900 --> 00:01:13.598 Towards the north. It comes from the south.

00:01:14.900 --> 00:01:18.144 Now compare the wind with your track or runway.

00:01:18.144 --> 00:01:23.212 The part blowing across is the crosswind component. At forty-five degrees,

00:01:23.212 --> 00:01:24.226 it's not half.

00:01:25.500 --> 00:01:29.132 Crosswind is wind speed times the sine of the angle.

00:01:29.132 --> 00:01:33.929 Thirty degrees gives fifty percent. Forty-five, about seventy. Sixty,

00:01:33.929 --> 00:01:36.602 about eighty-seven. Ninety: all of it.

00:01:37.800 --> 00:01:42.013 Twenty knots at thirty degrees: half, so ten knots across.

00:01:42.013 --> 00:01:47.726 If your aircraft's crosswind limit is ten knots, you're at the limit. Postpone,

00:01:47.726 --> 00:01:48.798 or reposition.

00:01:49.400 --> 00:01:53.837 On site, hold a handheld anemometer at head height, facing the wind,

00:01:53.837 --> 00:01:57.696 and read it for thirty to sixty seconds to catch the gusts.

00:01:57.696 --> 00:02:01.876 Compare it with your aircraft's limit. And at four hundred feet,

00:02:01.876 --> 00:02:03.741 the wind is likely stronger.

00:02:04.800 --> 00:02:09.683 Recap: heading isn't track. Wind is named for where it comes from.

00:02:09.683 --> 00:02:13.473 Crosswind follows the sine. Measure before you fly.

00:02:14.200 --> 00:02:17.697 Final check. Twenty knots, sixty degrees off your track.

00:02:17.697 --> 00:02:19.477 About how much is crosswind?

00:02:20.200 --> 00:02:21.584 About seventeen knots.