Hot, high, heavy and windy — transcript

00:00:00.400 --> 00:00:04.710 Hot, high, heavy and windy: how much performance margin do you have left?

00:00:05.900 --> 00:00:10.085 Performance margin is what's left after hovering, climbing, turning,

00:00:10.085 --> 00:00:14.573 wind and the trip home. It's a moving margin, not one flight time number.

00:00:16.400 --> 00:00:19.147 In a hover, total thrust equals weight.

00:00:19.147 --> 00:00:22.580 More weight needs more thrust to hover and climb,

00:00:22.580 --> 00:00:26.013 so a heavy payload eats straight into the margin.

00:00:27.400 --> 00:00:32.170 Propellers push on air. Hot air is thinner, and so is air at a high site.

00:00:32.170 --> 00:00:37.327 Thinner air means less thrust for the same propeller speed, and a slower climb.

00:00:39.900 --> 00:00:43.218 Worst case: a high site, a hot day and low pressure.

00:00:43.218 --> 00:00:46.348 The standard day is fifteen degrees at sea level,

00:00:46.348 --> 00:00:50.166 and every ten degrees above it costs noticeable performance.

00:00:51.900 --> 00:00:52.614 For example,

00:00:52.614 --> 00:00:58.822 forty degrees at an inland site could leave you ten to fifteen percent less thrust than a cool day at sea level.

00:01:01.400 --> 00:01:05.762 Quick check. Same drone, same payload. Which day leaves the least margin?

00:01:06.600 --> 00:01:08.507 Hot, high, and low pressure.

00:01:09.900 --> 00:01:14.912 Now wind. Airspeed is speed through the air; groundspeed is speed over the ground.

00:01:14.912 --> 00:01:21.133 Forty kilometres an hour into a fifteen kilometre an hour headwind gives a groundspeed of twenty-five.

00:01:22.900 --> 00:01:27.107 Battery use follows airspeed; distance follows groundspeed. Into wind,

00:01:27.107 --> 00:01:31.076 the drone uses the same power each minute, but covers less ground.

00:01:33.400 --> 00:01:36.679 So plan for the worst leg. If the trip home is into wind,

00:01:36.679 --> 00:01:40.636 keep enough battery for it. Most apps show groundspeed, not airspeed.

00:01:43.400 --> 00:01:46.995 The outbound leg flew with the wind and felt easy.

00:01:46.995 --> 00:01:51.576 Now the drone is coming home into it: slower, with less battery.

00:01:53.400 --> 00:01:58.407 Watch for the warning signs: a slow climb, fighting the wind, sounding loaded,

00:01:58.407 --> 00:02:02.020 running hot, or a battery draining faster than expected.

00:02:03.900 --> 00:02:08.932 Test hover before you commit. Poor climb after launch is a useful warning.

00:02:08.932 --> 00:02:12.756 Lighten the load, simplify the job, and come back early.

00:02:14.900 --> 00:02:19.169 Recap. Hot, high and heavy shrink the margin. Battery follows airspeed,

00:02:19.169 --> 00:02:23.259 distance follows groundspeed. Test hover, and keep reserve for home.

00:02:25.400 --> 00:02:28.664 Final check. Airspeed forty kilometres an hour,

00:02:28.664 --> 00:02:33.289 with a fifteen kilometre an hour tailwind. What's your groundspeed?

00:02:33.800 --> 00:02:36.073 Fifty-five. The tailwind adds to it.