How Autopilot Works, And Why Planes Don’t Fall Down – Well, now that we’ve practically got self-driving cars on the road, that means the future is here, right? And that got me thinking – if we have this sort of “autopilot” for cars, then the aviation field has been way ahead of the times for years! Autopilot: how did it come about and how does it work?
Before we get into the hows, let’s briefly talk about the why. When airplanes were first invented, they required the pilot’s undivided attention to fly safely. That is, the captain needed to keep hold of the controls the entire time. As the airplane’s range got bigger and they could travel for more hours, it got harder and harder for pilots to keep up!
People aren’t machines, after all – we need rest and breaks! That was a sign for engineers that they needed to develop something that would lift some of the weight off the pilots’ shoulders and do some of the work. Around 1912, the first autopilot was created by Sperry Corporation – a company that specialized in electronics.
The autopilot allowed the plane to fly level and straight using a compass course without the pilot constantly trying to keep it leveled manually. Later, the Royal Aircraft Establishment created an autopilot that could also move the flight controls. It was a big step forward, but still not quite where we are today!
You see, at the time, aircraft could only fly during the day and in sunny weather. But as technology progressed and the world of aviation took off, the autopilot systems improved. They became equipped with instruments, such as radio-navigation aids, which made it possible to fly in bad weather and at night with limited visibility.
What’s interesting, though, is that not all passenger planes have autopilots. For example, aircraft that are designed for private transport are to this day still only flown manually. Sometimes, even some jets might not have autopilots – instead, they have two pilots to do all the manual work. It’s usually the ones that have fewer than 20 seats, though.
With any more seats than that, international aviation regulations require that a plane have an autopilot. Ok, so what exactly is it? Well do you remember the “Otto Pilot” from the movie “Airplane”? He did some kooky stuff, and, NO, that’s not what we’re talking about here. But it was funny. Anyway. Well, what you and I call autopilot is officially known as the Automatic Flight Control System. It plays a major part in an aircraft’s avionics.
But to understand all the ins and outs of the system, you first need to know some basics about airplanes and how they can change their altitude and direction. They do that depending on which axis the aircraft turns on. Those can be yaw, pitch, and roll. Ok, back up. Let’s try to simplify that. Hold your hand out in front of you with your fingers together and your palm facing the floor.
Keep it flat, but bend your wrist so that your hand moves from left to right – that’s yaw, or vertical, axis. Now bend your wrist to lift your fingers toward the ceiling and lower them toward the floor– the up and down movement along the horizontal axis is the pitch. Finally, roll is exactly what it sounds like.
Turn your hand so that your palm faces up – congrats, you’ve just rolled along the transverse axis! You can post that on Instagram! Airplanes have different parts, or “surfaces”, to achieve those movements. The rudder, which is on the vertical part of the tail, controls the yaw axis – turn it either way, and the nose of the plane will go to the left or right.
Then, we have the elevators – they’re on the horizontal part of the tail, and they change the pitch. If they move up or down, the nose will do the same. Finally, there’s the ailerons, which are on the outer part of the wings. They also move up and down to lift either wing and roll the plane to the left or right. Ok, back to autopilots.
There are actually different types (hence the use of plural) that can control certain or all of those parts. For instance, the Single-Axis Autopilot controls the ailerons, and it’s known as the “wing-leveler”. It does exactly what it says: keeps the wings leveled. The slightly more advanced system is the Two-Axis Autopilot, which controls both the ailerons and the elevators to keep the plane level on both its horizontal and transverse axis.
Any guesses what the third kind is? Yeah, it’s the Three-Axis Autopilot, and, yes, it controls all of the above: the rudder,elevators, and ailerons. All these control surfaces on a plane have sensors inside of them, and these sensors communicate with high-speed processors to get all the information they need to control the aircraft.
And those processors are super smart too! They collect data from other systems in the plane that help them do their own thinking and act accordingly. Then, they take all that data and make their own calculation to see if it corresponds to the data given by the pilots. You see, once pilots board the plane, they enter all the control mode settings they need about the flight, like maintaining the aircraft’s altitude or direction.
Then, the smart high-speed processors sort of cross-reference their calculations to see if the plane is obeying the pilot’s orders. Basically, you can imagine the autopilot as the middleman of the flying operation, making sure the surfaces and other functions are listening to the pilots. But that’s not all!
After the processors collect all the information from the sensors, they send these signals to different servomechanism units. These things are devices that can mechanically control the surfaces. The autopilot has one servomechanism unit for each of those control surfaces. These units take orders from the computer and, using hydraulics or motors, they move those parts to make sure that the plane maintains its correct altitude and direction.
Autopilots are just one example of a control system, and like all control systems, they work in very similar ways. They act based on what they measure, and their actions impact the value of what they just measured. Uh, come again? Ok, how about another real-life example? Imagine: it’s the middle of summer, and you’re sweating buckets.
So, you decide to set your thermostat at a cool 65°F. The thermostat measures the temperature in the air and compares it to the number you set it at. If the actual temperature is higher than what you’ve requested, then the thermostat sends a message for your air conditioner to kick on. The AC, in return, does its job to lower the temperature down to 65°F.
Once it’s carried out this task, the thermostat senses the surrounding air is now at the right temperature and, thus,sends another signal to turn the AC off. This process is called a Negative Feedback Loop, and the simplest way to understand it is to take it literally – it waits for negative information before it sends feedback to the processor and corrects it.
This loop consists of a receptor (a.k.a. the thermostat), a control center, and an effect or. And that’s exactly how autopilots work! (Who knew they had so much in common with your central air, eh?) To give you an example, let’s take the simplest system: the Single-Axis Autopilot. How does it keep the airplane wings leveled?
The pilot first sets the control modes to keep the wings, well, level!But even with the slightest turbulence, the wings can change position. The gyroscopes on the wings sense that they’re being moved, so they automatically send that data to the autopilot computer. The autopilot then processes that information and understands that the wings are no longer level, so it needs to take action!
It then sends the data to the servomechanism units that control the ailerons and tells them that they need to adjust so that the wings will become level again. Now, each unit has an electric motor with a slip clutch that grips the aileron cable and moves it to make the adjustment. Then, the sensor detects that the wings are leveled and removes the autopilot command.
Right after that, the servomechanism unit stops applying pressure to the aileron cable and voila – the plane is level again! What’s even more interesting is that modern autopilots have GPS, and they can calculate the plane’s position in the air. With this type of technology, autopilots can even perform a whole flight plan!
Even though autopilots can actually land a plane in zero visibility, most landings are done manually. By the way, 100% of take-offs are manual. And get this: the autopilot does not fly the plane – pilots fly the plane through the autopilot!– mind blown! But what happens if the autopilots fail? Well, that’s when pilots come in.
You see, autopilots are designed as a fail safe – which means even if they do fail, they won’t cause any damage to other parts of the plane. In this case, the pilots will have to override the autopilot by disconnecting it. A major part of a pilot’s training is knowing how to manually operate everything in the cockpit and fly the plane without the autopilot.
Also, all planes go through a thorough check to make sure that all sensors and servo mechanism units work perfectly before a flight. But just in case they do fail, the pilots can save the day!
Well, that’s pretty the basics of autopilot, but if you know some more cool stuff about how planes work, then feel free to share your expertise down in the comments.