How Airplanes Work
All the things that freak you out about flying, explained by a reformed pilot from an aviation-obsessed family.
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Alright, onto the good stuff.
The Flying Public and Knowledge of Airplanes
First, some stats:
There are roughly 338 million people in the United States.
Roughly 720,000 of them hold a pilot certificate of some kind from the FAA (data here).
Of that 720,000, only about 430,000 (60%) are certified to fly on their own. The rest hold “student” pilot certificates, which is sort of like a bunch of people holding learner’s permits. Lots of people are learning to fly at any given time but…flying is expensive and people go on hiatus a lot.
Of that 430,000, ~268,000 of them (62%) - hold some sort of high-level certificate (commercial or airline-transport) that allows them to get paid to fly.
Thus, a grand total of…
0.21% of the country has any idea how to fly
0.12% of the country can fly on its own
0.08% of the country can get paid to fly
To give you an idea of proportion, there were 1,062,205 physicians actively practicing medicine in the USA as of late 2021, meaning that pilots allowed to fly on their own are more than twice as rare as doctors.
So, to say that aviation knowledge in the general public is rare is an understatement. Thus, there are a lot of people that are afraid of flying. Some are true acrophobes (fear of heights) but most just don’t understand what’s happening around them. It causes a lot of people - that otherwise wouldn’t based on their education, expertise, or intelligence - to react irrationally to commonplace events, often leading to anxiety, agitation, or even violence.
Sidebar: I once heard a couple of middle-aged men in the car-rental elevator at Orlando Int’l Airport talk about how the pilot - who was simply following the landing pattern - didn’t know where he was going and that “they all have GPS telling them what to do nowadays” (GPS wasn’t in airliners at the time). These guys looked and sounded like upper-middle-class professionals, too.
But I digress.
My Background + Why I Care
First, I was born in the Minneapolis metro area to a pilot and flight attendant of then-Northwest Orient Airlines, which became Northwest and is now Delta. My brother flies for Delta. I’ve flown on airliners my entire life.
My career arc has been interesting but diverse and informative. It didn’t seem it at the time I chose to change careers but I think, overall, it’s helped me in the longer term. I’m an IT project manager in healthcare today but I entered the real world aspiring to be a commercial-airline pilot (shocking, I know - it’s almost a genetic trait).
Life as a pilot doesn’t require any sort of special degree, so I elected to get a BS in Aerospace Engineering Sciences - as an interesting and useful backup education - from the University of Colorado at Boulder.
I became a Certified Flight Instructor (CFI) and Airline Transport Pilot (ATP) not long after I graduated from CU in 2000, and these are high-level certifications given by the FAA. I’d been flying since 1994. Either way, I’ve used these certifications to log just over 3,800 hours of flight time, all in small aircraft (nearly all produced by Cessna, Piper, Mooney, and Diamond). If you want proof, look me up in the FAA Airmen Certification registry (it’s public). I spent 4 1/2 years teaching college students how to fly. After deciding against a career in commercial aviation, I spent ~3 years managing flight instructors, and ~5 years as a planner & scheduler for the department.
I also used to teach aviation courses in the classroom and online, and I even got an ex-girlfriend to lose her fear of flying.
All of this, together, gives me a pretty solid background to tell you all about airplanes and why you should learn to love the simplicity (honestly) of them and enjoy the ride.
All Airplanes are the Same
OK, not exactly. The meals on a Delta 767 are better than those I used to serve in a Cessna 172 when I was teaching in Florida (which was none).
But, it’s important to note, the physics are the same, regardless of the size of the aircraft. Mostly, we have the Godfather, Daniel Bernoulli, to thank:
No, Bernoulli didn’t invent the airplane (that was the Wright Brothers). He didn’t conceive of it, either (that was Leonardo da Vinci, about 250 years prior). What he did do, however, is pioneer the field of fluid dynamics mathematically and established what became known as Bernoulli’s Principle, published in 1738. Specifically:
In fluid dynamics, Bernoulli's [P]rinciple states that an increase in the speed of a fluid occurs simultaneously with a decrease in static pressure or a decrease in the fluid's potential energy.
In English, this means that if you move a fluid - let’s call this one air - over a surface, the pressure measured on that surface drops as the speed of the air increases over it.
Huh?
Maybe an experiment will help. Take a loose sheet of paper and hold it at the top with both hands, letting it hang from your fingertips. Then place your lips just above the paper and blow air “down the hill”, so to speak, along the top of the sheet of paper. The paper rises. I remember learning this at age 6. Mind. Blown.
Feel dumb doing this on your own? Watch this physics professor at Washington State demonstrate it:
In effect, moving the air along the top of the paper “sucks” the paper upward. This seems like an important piece of the whole “flying” process.
Bernoulli - Not Just for Wings
There are many uses of this principle, too. For example, for those of you older than 20 - or those that work on small engines - you remember carburetors (the predecessor to fuel injection). They use the physics behind Bernoulli’s Principle to pull gasoline into it and combine it with air before sending the mixture into cylinders to be burned for power. They’re still used pretty regularly in small engines, such as those used on gas-powered lawnmowers. This dude does a great job explaining it.
There are other applications but I’ll skip those for this post. The short version is that Bernoulli’s Principle is not complicated and it’s used in lots of low-tech applications.
Bernoulli, Meet Euler
Although Bernoulli deduced that pressure decreases when the flow speed increases, it was Leonhard Euler in 1752 who derived Bernoulli's equation in its usual form.
What is Bernoulli’s equation?
“How does this even remotely apply to flying, Jeff?”
This way:
The pressure difference between the flatter under side of the wing and the more-curved top effectively pulls the wing upward. This force is called lift and, if you make enough of it, you can get the object off the ground. It doesn’t even matter how large the object is. If you can make more force pointing upward than you do pointing downward (basically weight), it will take off. What determines how much lift you create? The Lift Equation:
L = Lift
CL = Coefficient of Lift
ρ (Greek rho) = Air Density
V = Velocity of Air
S = Surface Area of the Wing
In English:
Make a better wing (smoother, nice curvature) or increase the angle of attack (basically pitch the nose up), get more lift (CL)
Get into more-dense air (lower altitude/higher air pressure, colder day, drier air), get more lift (ρ)
Go faster, get more lift (V)
Make a bigger wing, get more lift (S)
How do you get a 747 off the ground (weight: 875,000 lbs)? Basically, give it big enough engines to accelerate it to a similar takeoff speed as for any other large aircraft…and give it effective, huge wings. It works.
“Jeff, Why Does it Look Like There are Clouds Over its Wings?”
This doesn’t always happen but, if it does, there’s an easy explanation. Again, the diagram from above but just the wing itself:
As air flows over the wing, its pressure drops. As the air pressure drops, so does the temperature. Why? Let’s go back to your high-school chemistry class. Yup, it’s the Ideal Gas Law:
If the left side decreases (i.e.: P drops), the right side must decrease (i.e.: T drops) in order to keep the equation balanced if the air volume is constant.
But that’s just temperature. Why the clouds? It’s all about the dew point.
The dew point is the temperature the air needs to be cooled to (at constant pressure) in order to achieve a relative humidity (RH) of 100%.
Air goes over the wings, drops in pressure, cools down, and brings the air temperature down to its dew point, making fog/clouds. You typically only see this in humid temperatures, however, so it’s common to see it in the morning in the American Southeast or even on cool spring or fall days in the Upper Midwest, Pacific Northwest, or Northeast.
“Madam Captain, Why Can’t We Take Off With a Broken Oven?”
I explain this in my Flowcharts are Cool article.
Why Do the Engines Look Like That?
If It Has “Jets”…
They’re turbofans. You see these on nearly every modern airliner. Here’s a Boeing 767-400:
Here’s how they work:
They use the same steps as your garden-variety internal-combustion engine (ICE) - intake, compression, combustion, exhaust - but they execute them in a line instead of in a time sequence. Your car “pulsates” as the pistons do their jobs, hitting their power “stroke” every couple of oscillations. Turbofan engines do not have this same characteristic. Turbofans make a high-pitched whining noise from its constant rotation, which is basically the same noise a car’s turbocharger makes.
If It Has “Props”…
They’re turboprops. You see these on smaller aircraft that fly shorter routes. For example, here’s a Horizon Air Bombardier Q400, which often flies between Seattle and Portland:
Here’s how they work:
These also use the same steps as your garden-variety internal-combustion engine (ICE) - intake, compression, combustion, exhaust - and execute them in a line instead of in a sequence (same as a turbofan). However, the engine basically operates backward, with the intake near the back of the engine and the exhaust near the front. The turbine (where the power is created) drives the propeller…which is in front of the engine. It’s a little convoluted, but it works.
These turboprops differ from, say, a Cessna 172 Skyhawk…
…which actually has a large, 4-cylinder engine under the hood (like an old car). Here’s an explainer from my old employer, Embry-Riddle Aeronautical University (and I know the dudes that made it):
Aside from the fact that both airplanes have propellers attached to their engines, however, they’re nothing the same. If you listen to them, you can tell. The Q400 has a propeller but with that whining jet sound. The Skyhawk has the propeller with the pulsating piston sound. If you look under the hoods, they’re from different planets.
In the End…
…every airplane on which you fly, save only a small number in special areas of the world, has a jet engine at its core, regardless of what you see out your window. Jet engines are highly reliable and efficient and you should feel confident in their use in mass transportation. In fact, the Cessna engines are great, too. Airplanes are quite safe on their own.
What is Jet Fuel?
It’s basically diesel but with some anti-freeze additives to keep it from freezing at 35,000’. Honestly. That’s all it is.
OK, So It’s Flying. How Do We Not Pass Out?
The air inside the cabin is pressurized, usually to the equivalent pressure you’d experience in a city such as Aspen or Breckenridge, CO, which are a mile and a half high. The Boeing 787 Dreamliner is pressurized to just over a mile high, which is a marginal improvement in comfort. Either way, this cabin “altitude” is why you’re often sleepy - and why you dry out a bit - while flying. You’re in an environment of lower air (and thus oxygen) pressure, which can both leave you wanting for a bigger breath and dehydrate you.
But We’re Way Up High. Where Do We Get High-Pressure Air?
The engines, mainly.
Do you know what turbojets do? They pressurize the air. Why? So they can mix it with jet fuel to make lots of power to make the airplane zoom through the sky. The pressurization system taps a little of that pressurized air via bleed-air valves and routes some of it into the cabin. No, it’s not exhaust. It’s tapped before it’s burned.
Since it enters the cabin via vents, the aircraft is getting a constant flow of pressurized air. Of course, an aircraft is rigid. If you keep filling it with high-pressure air, it’ll explode. That’s no good. So, the cabin works kind of like a leaky balloon that you have to keep inflated to a certain PSI, except that you let it leak on purpose. High-pressure air keeps getting pumped in but, since you don’t want the cabin to rupture, you let some out the other side via a regulator valve. The balance between air in and air out determines the cabin air pressure. If the system malfunctions - which is super uncommon but not impossible - that’s when those oxygen masks fall from the ceiling and you need to get to a lower altitude.
Sidebar: This is why airplanes are actually not COVID-19 factories. They have a constant flow of air coming into and leaving the cabin. That air is cycled out pretty quickly, kind of like driving with your windows cracked open. The airborne virus doesn’t “build up” throughout the flight. I’d guess this is why few, if any, outbreaks have been traced back to airline flights.
Why Do Parts of the Wings Move?
If the front of the wing extends, those are called slats. If the back of the wing extends, those are called flaps. Both work to make the wing more curvalicious, giving it a higher Coefficient of Lift (CL - see above) and making it able to create more lift at a slower speed. They let you slow down without the otherwise-inevitable consequence of descending more quickly…or they let you take off at a slower speed, meaning you need less runway.
TL;DR (“too long; didn’t read” for those of you not up on the lingo) - You can do everything at a slower speed. This is why you see them at takeoff and landing.
Why Can’t I Screw With the Lavatory Smoke Detector?
If you have to ask…ugh. But, basically, if something is on fire in flight, you’ll want to know. Remember this pilot mantra:
You’d rather be down there, wishing you were up here, than be up here, wishing you were down there.
A fire at the airport is a concern and an inconvenience. A fire on the airplane is an outright emergency, so you want to know when something is on fire ASAP. That’s why you’re not allowed to screw with them to have a smoke.
What Are All Those Noises?
Probably easiest in bullets:
That ding-dong-ding as you climb or descend?
That’s the pilot telling the cabin crew that you’ve gone above/below 10,000’ and they can let the passengers use their electronic devices…or that they have to put them away.
That loud thud that you hear shortly after takeoff and before landing?
That’s probably the landing-gear doors closing or opening.
That prolonged, whiny sound you hear before takeoff, after takeoff, or before landing?
If before takeoff or landing, it’s probably the flaps and/or slats extending on the wings.
If after takeoff, it’s probably the flaps retracting.
Why Can’t We Take Off Right After the Aircraft in Front of Us?
Two possible reasons:
There’s an aircraft about to land and it’d be unsafe/inconvenient to try to take off ahead of it, just in case there’s a delay in your takeoff.
The aircraft ahead of you needs to be a certain distance ahead of you to keep you from being disrupted by wingtip vortices, which are basically little horizontal tornadoes that form off the edges of wings creating lift (has to do with the pressure difference between the top and bottom of the wing - see above). These dissipate quickly but need a few minutes.
They look cool but you don’t want to end up flying through them. An American Airlines aircraft crashed after encountering them after departing New York-Kennedy in November 2001.
Is Flying Actually Hard?
Flying? No. Landing? Sure can be, especially in lousy weather. Taking off? Depends on the airport and weather, but generally not. My dad always said:
Flying is 3 hours of boredom surrounded by 30 minutes of sheer terror.
My dad has a flair for the hyperbolic but his sentiment is basically correct.
How Can Pilots See Through the Clouds?
They can’t.
However, their flight instruments sure can. Most aircraft use either ground-based radio navigation signals or, in newer aircraft, satellite-based ones (GPS) to guide the pilots - or the autopilot - along the flight path or to the runway. Pilots are specifically trained, from early in their careers in small planes, to operate flight-navigation instruments so that they’re not limited by the weather (within reason). It turns out humans are pretty lousy at acting like birds, so these systems are built to help pilots tune out their instincts and “follow the science”, so to speak, to keep your aircraft upright and get it on the ground.
For smaller aircraft or old airliners, here are my friends at ERAU again:
Some airplanes even have autoland capabilities! Here’s the cockpit view of a 737 executing one into Geneva, Switzerland:
Why Do We Make a Bunch of Turns Right Before Landing After Flying Straight for Hours?
All aircraft “enter the traffic pattern”, regardless of the size, prior to landing. You don’t just fly straight at the airport and then fall onto the runway. You have to, basically, line up…and you and many others are trying to do the same thing, so there’s a standard way of doing it. Those turns are getting you set up to enter that pattern, or they’re done while in the pattern.
While the altitudes and aircraft are different, my friend Joey Maxwell of ERAU Special VFR Productions goes through the basics in this video. The reality for airliners is that this all happens at higher altitudes and speeds than are shown here (this video is for student pilots)…but watch out the window next time you fly and you’ll see the similarities.
Why Do We Have to Wait on the Taxiway After Landing Sometimes?
Busy airports are operated like hotels. As you can imagine, there isn’t a gate assigned to every airplane that could possibly fly in at any time. Each flight is given a “slot” at the airport, where you reserve it for a window of time, not unlike a hotel room. As you probably know, if you show up to the hotel 5 hours ahead of check-in time, the hotel often hasn’t cleaned your room yet and, due to its current occupancy, doesn’t have a suitable room to give you in its place. So, you wait in the lobby or get a cup of coffee next door.
No different for airplanes. It just so happens there’s nowhere to go get a cup of coffee while you wait.
Aren’t Pilots Just Glorified Bus Drivers?
First, I will fight you.
Second, there’s a ton of mechanical, aerodynamic, and meteorological information that you need to learn to truly understand what’s happening all over the plane…and what might happen if something goes south. Commercial pilots have to be given “recurrent” training every 6-12 months (depends on what they fly) to keep them fresh. This just isn’t true for any other vehicle operator.
Third, as mentioned throughout this article, everything is a big deal when you’re not on terra firma. Your safety margin is a lot smaller, as is your list of options. A problem on the bus? Your options:
You ignore it and report it when you get back to the garage.
You get to the end of the line and then call it in and get a replacement.
You pull over, get another bus to pick up your passengers, and fix the bus.
A problem on the airplane? You have none of these options. You get to fix or work around it in flight, or figure out - or execute - Plan B, often under some degree of duress. Plan B might be equivalent to #2 above…but your plan had better enable you to get to the end of the line.
Alright, That’s Enough!
If you have any flying-specific questions that you want me to answer, drop a comment below and I’ll be happy to answer it! Thanks for reading :)