Turns, load factor, wind shear and stall — transcript

00:00:00.400 --> 00:00:02.664 Turns, load factor and wind shear:

00:00:02.664 --> 00:00:05.964 three ways an aircraft can lose its safety margin.

00:00:06.900 --> 00:00:09.923 To turn, an aircraft banks, and its lift tilts.

00:00:09.923 --> 00:00:12.882 Part of the lift now pulls it around the turn.

00:00:14.900 --> 00:00:19.158 But the vertical part must still equal the weight, so total lift has to grow.

00:00:21.400 --> 00:00:26.122 Load factor is lift divided by weight. Level flight is one G.

00:00:26.122 --> 00:00:32.215 Thirty degrees of bank is one point one five; forty-five is one point four one.

00:00:32.800 --> 00:00:37.398 At sixty degrees, it's two G: the airframe carries twice its weight.

00:00:38.900 --> 00:00:42.426 Sharp turns, quick stops and gusts all add load to the arms,

00:00:42.426 --> 00:00:46.240 motors and propeller mounts. Fly smoothly, especially when heavy.

00:00:47.400 --> 00:00:52.024 Quick check. What load factor does a level, sixty degree banked turn produce?

00:00:53.000 --> 00:00:54.280 Two G.

00:00:55.900 --> 00:01:00.210 As you saw in Lift and Drag, a wing stalls at its critical angle of attack.

00:01:02.300 --> 00:01:06.381 In a turn, the extra lift comes from more angle of attack.

00:01:06.381 --> 00:01:09.771 So the wing reaches the stall at a higher speed.

00:01:11.400 --> 00:01:16.561 Stalling speed rises with the square root of the load factor. At sixty degrees,

00:01:16.561 --> 00:01:18.819 that's about one point four times.

00:01:20.200 --> 00:01:25.216 A wing that stalls at ten metres per second in level flight now stalls at fourteen.

00:01:26.900 --> 00:01:32.647 Slow, heavy and banking hard, like turning to land, is where a fixed-wing stalls.

00:01:32.647 --> 00:01:35.520 As weight goes up, limit the bank angle.

00:01:36.900 --> 00:01:40.363 Wind shear is a sudden change in wind speed or direction,

00:01:40.363 --> 00:01:42.333 over a short distance or height.

00:01:44.100 --> 00:01:49.298 Descending into a headwind, the wind suddenly drops. Inertia holds your groundspeed,

00:01:49.298 --> 00:01:52.172 so airspeed falls, lift is lost, and you sink.

00:01:52.900 --> 00:01:55.973 Expect it downwind of buildings, trees and hills,

00:01:55.973 --> 00:01:59.169 and near thunderstorms and fast-moving cold fronts.

00:02:00.300 --> 00:02:03.962 As a guide, stand off at least twice the obstacle's height.

00:02:03.962 --> 00:02:07.013 If the drone drops or rocks, move away and climb.

00:02:09.400 --> 00:02:14.875 On a fixed-wing in manual mode, a bank left alone can become a spiral dive.

00:02:14.875 --> 00:02:18.909 Speed builds, the bank steepens, and the G-load climbs.

00:02:19.400 --> 00:02:25.641 Recover in order: reduce power, level the wings, then gently ease the nose up.

00:02:25.641 --> 00:02:29.274 Pulling up first can overstress the airframe.

00:02:29.624 --> 00:02:35.190 Recap. Sixty degrees of bank is two G, and the stalling speed rises with it.

00:02:35.190 --> 00:02:40.538 Stand off from obstacles in wind, and recover a spiral with power, wings,

00:02:40.538 --> 00:02:41.406 then pitch.

00:02:42.124 --> 00:02:45.319 Final check. As bank angle increases in a level turn,

00:02:45.319 --> 00:02:48.159 what happens to load factor and stalling speed?

00:02:50.024 --> 00:02:51.174 Both increase.