Aerodynamics for white-knuckle fliers

Airplanes WANT to fly. They WANT to stay in the air. Fear not, my white-knuckled friend! This article is for YOU!

12
 min. read
June 22, 2021
Aerodynamics for white-knuckle fliers

A flying lesson for non-pilots.

Are you scared to fly? Does the thought of spending 2+ hours high above the ground in a metal tube that, somehow, magically floats despite physics suggesting otherwise freak you out? If humans were meant to fly, we would have wings, right? We don’t belong in the sky, right? Bad things happen up there, right?

Fear not, my white-knuckled friend! This article is for YOU! Flying is actually VERY safe. For reference, if we take all the deaths from car crashes last year and compare that number to the deaths from commercial aviation, you are 127 times MORE likely to die in your car driving than you are flying. And even if flying wanted to think about competing for more annual deaths, one Boeing 737 would need to crash, leaving no survivors, EVERY DAY for the NEXT YEAR.

But in case these numbers mean nothing to you and you still have elevated doubts, as a pilot, I want to help ease your fear of flying. Let me explain WHY flying is safe. Let me shed light on some misconceptions that strike fear into many passengers hearts.

Why does an airplane want to fly?

To begin, let’s look at how airplanes fly. Maybe by understanding why they fly will begin to help you understand why they are safe as well. Here is a crash-course (pun TOTALLY intended) in aerodynamics!

For an airplane to fly, it needs to create two unique, man-made forces that overcome two completely opposite, natural, forces.

  • Lift - Wings need to create lift to get an airplane off the ground. Lift is created when air moves over the top of the wing faster than it does the bottom, creating a lower pressure above. The lower pressure lifts, or sucks the wing up similar to how you lift liquid into your mouth through a straw. If lift is greater than gravity’s pull, the airplane is climbing. If lift is less, the airplane is descending. If lift is equal to gravity, the airplane will stay at the same altitude. If there is no lift and the airplane is off the ground, the wing stalls and the aircraft will fall…but don’t freak out just yet…we’ll get to that part later.
  • Thrust - An airplane needs to create thrust to propel it forward. Thrust is the force that moves the airplane forward, allowing air to go over the wing which, in-turn, generates lift. Thrust is accomplished by a propeller or jet engine.
  • Gravity - This is the opposite of lift. It is the pull Earth has on everything. This is the natural force lift needs to overcome to get the airplane into the sky.
  • Drag - This is the opposite of thrust. Drag is created by both thrust and lift and is the friction which prevents the airplane from going forward. It is the natural force thrust needs to overcome to get the aircraft to move forward.
Basic Aerodynamics
Four forces of flight

That is it. If you have something that creates lift and thrust, it will eventually fly. How efficiently is for another post, but all aircraft are designed to create lift and thrust and, therefore, WANT to fly. They want to avoid falling. If an airplane crashes, something usually has to go wrong.

What if something goes wrong?

Let me let you in on a little secret. Flying is relatively easy. Granted, it is more difficult than driving or riding a bike. But it is nowhere near as difficult as performing brain surgery (I’m guessing) or sitting through a never-ending office meeting. The airplane is designed to WANT to fly. As a result, once it IS flying, the plane requires very minimal input from the pilot to keep it that way. In fact, only about 20% of pilot training is learning how to fly. The other 80% is learning what to do if something goes wrong in the airplane.

I emphasize “if.” A better word might be “when.” Things go wrong in airplanes every day. In fact, there is a very high chance you have been on an airplane where something was, in fact, broken, not-working, miscalculated, misinterpreted, or just wrong.

But guess what? You are still here. The airplane and pilot knew what to do to get you and the airplane safely back on the ground.

When I was learning how to fly, a common practice maneuver involved shutting off the engine, mid-flight, to simulate an engine failure. When I tell this story to people unfamiliar with aviation, and/or who fear flying, you should see the look on their face…one of utter shock and disbelief. What wizardry have I conjured to be living to tell this story?

Remember how I said airplanes WANT to fly? Sure, shutting off the engine will decrease the thrust, but the aircraft is already going fast when we do. The wings are still getting lift…albeit, less than WITH the engine running…but the aircraft will never simply drop or fall out of the sky without an engine. It just turns into a heavy glider.

Gravity, the force we previously needed to overcome to keep us in the air is now actually helping to keep the aircraft in the sky by pulling the airplane forward, generating enough lift over the wing to keep it aloft. Without an engine, the pilot will need to find a landing spot in the near future. But the important thing is, the plane is still flying. It is not falling out of the sky. And if this doesn’t ease your concern because, well, the engine is still off, here is something that might make you feel better about the whole situation.

What if the engine breaks?

If you have flown anywhere, there is a 100% chance you were in an aircraft whose engines turned off while in-flight. Yep, you read that right. You, too, were in a very heavy glider and lived to tell the tale! …let me explain…

In order for an airplane to land, it cannot be generating lift, right? And we already learned that thrust is mostly responsible for generating the lift that overcomes Earth’s gravity, keeping the airplane in the sky. Which means, to land an aircraft, its wings need to NOT be generating lift…which further means the engine should NOT be working to move the airplane forward fast enough to generate that lift. See where this is going?

When landing, all airplanes, regardless of size, shape, or design, have their engines off. Well, for the purposes of this post, they are off…in actuality, they are still on, but not generating any meaningful thrust, ready, in case the airplane needs to “go around” or try the landing again.

Yet, despite the engines being “off,” the aircraft is still moving pretty fast…and this kinetic energy is still generating enough airflow and lift over the wing to keep the aircraft aloft. To stop this lift and land, pilots purposely stall the airplane to let it, literally, drop onto the runway.

The height from which this stall begins usually determines how much the plane “thuds” when it hits the runway. A harder landing means the plane stalled higher off the ground. A beautiful, soft landing’s stall happened only a few feet over the runway.

So, you see? YOU ALSO have been in a stalling aircraft whose engines were not working. And you are still here as well! …because aircraft are designed to fly without engines…AND without thrust.

On to debunk your next fear…the dreaded “wing falling off” scenario!

What if a wing falls off?

Let me prelude the answer to this question with a question for you. Outside military operations…so strictly commercial and general aviation…when was the last time you heard of or read about an aircraft whose wings fell off? I have been a pilot for 19 years, have been through many years of pilot training, and have many thousands of hours of flight time, and I can honestly say I have never heard of this happening.

Just after writing that last paragraph, I did a quick Google search for “airplane wing falling off.” It did return results…but not like you would think. A good majority of the first page results focus on a guy who scaled the wing of a commercial aircraft in Las Vegas and then physically fell off the wing. The wing didn’t fall off. The guy did…and was promptly arrested. The aircraft had no harm done to it as a result.

The rest of the results I found were forums discussing this very question…and mostly debunking the myth that this happens. Could it, yes. Anything can happen. Will it? It is extremely (with a strong emphasis on “extremely”) unlikely. Here’s why…

Aircraft wings are designed to flex. In fact, during a normal flight, you might see the wings bouncing around out there anywhere between 0 and 6 degrees. This is normal and expected. This flexing gives passengers a smoother ride and helps with fuel efficiency. It also helps the aircraft’s stability in turbulent flight conditions.

But, we’ve all seen the movies…an aircraft suddenly flies into clear air turbulence or inadvertently finds itself in a thunderstorm. The passengers bounce up and down. The face masks fall. The plane is shaking all over the place. Hollywood loves this stuff. That type of turbulence, the worst-possible turbulence ever, would, likely, increase that wing flex to around 10 degrees. Surely, the wings must almost break off in situations like that? Actually, the reality of the situation may surprise you.

The length of a single wing on a Boeing 787 is about 89 feet. With that number, let’s use math to see what the wings do when they flex. If you want to avoid doing math and, instead, just want to see the results, skip to the following section for an infographic. Otherwise, buckle up!

Math Time

To start, let’s assume 89 feet, the length of the wing, is the radius of a circle. Using the wing-flex angle for any given moment in flight, we can apply it to the 89-foot radius and calculate the chord length. This is the length of a line between the min and max points of flex on the wing-radius’s circle’s circumference. In the wing-flex scenario, this chord length is the flex-distance (in feet) the wing will travel for a given flex-angle.

At zero degrees, straight and level flight, the chord length is 0 feet. The wing doesn’t move at all. But during normal flight, the wing could get to 6 degrees of flex, which makes the wing tip bend about 9 feet. Seem like a lot? Maybe…but again, the airplane needs to be able to handle normal flight without any issue. So, what about a situation in non-normal flight? One in which someone might think the airplane would not be able to handle? What about the worst possible scenario? What about that movie-style turbulence?

As you remember, the flex angle for this movie-scenario is around 10 degrees, almost twice as much as normal flight conditions. When we apply 10 degrees of flex to our circle equation, the chord length measures around 15 feet…which sounds alarming, since that metal wing is bending the full height of an adult giraffe. But just like 6 degrees of flex, you might be surprised that 10 degrees is also WELL within the safe and acceptable bending limits of this airplane wing. It will not fall off.

So, how far can a wing bend safely?

To be certified for flight by the FAA, a wing needs to be able to get to 154% of its maximum load capacity AND STILL BE SAFE to fly. In the case of our 787, that amount is 17 degrees of wing flex…which, when applied to our circle, gives a chord length of 26 feet! …which further means an airplane wing can flex 7 degrees, or 11 feet, MORE than it would in a scenario that flexes that wing to THE MOST it EVER would in flight.

To paint a better picture, that airplane wing can flex to the height of a three-story building and STILL BE SAFE. See the following infographic and notice the human icon, to scale, for size reference.

Boeing 787 Wing Flex Infographic
Wing flex of a Boeing 787. Icon on wing represents a 6-foot human.

And as I mentioned, these 17 degrees of flex COULD ONLY HAPPEN in a controlled testing environment, on the ground, where engineers are trying to see how far the wings could bend before snapping. In fact, if you look at this video you will see an Airbus wing getting tested…and its wings are bending to around 30 degrees without snapping or falling off!

If math numbers are not your thing, how about statistics?

You have a greater chance of winning the lottery while getting hit by a lightning bolt for a second time in the exact same spot than you do of being in a commercial airliner when a wing falls off.

So yes, it could happen. But it probably won’t.

Mic drop.

What if my airplane hits a bird?

We’ve all probably heard about US Airways Flight 1549, the Miracle on the Hudson, which, shortly after departing LaGuardia Airport in New York City, hit a flock of birds and lost all engine power. What if that happens to you?

Let’s refer to two sections above…powerless flight and pilot training for emergencies…

So, BOOM! We hit a flock of birds and our engines go out. You know without power, the airplane will remain in flight for a period of time. It turns into a large and heavy glider. When it does, the pilots realize there is an emergency and immediately fly the airplane accordingly. All other airplanes get out of the way, per requirement. A plane in an emergency situation can literally do anything it needs to safely land.

In the case of US Air Flight 1549, the pilots needed to ditch the aircraft in the Hudson River. There were several injuries, however no casualties. Other airliners hit by birds have successfully landed as well. There have been a few crashes resulting in death, but a VERY few. So, how is this minimized?

Just like wing-flex, airplanes are designed to hit birds, to a limit, and still be able to fly. I was flying a small prop airplane that hit a bird on takeoff and could land without much incident, save a hairline crack in the prop. As for commercial jet engines, most need to be able to “ingest” a bird up to four pounds without a problem…it is a problem for the bird, though.

Most US airports also have some sort of automated bird-mitigation system in place. Because we know birds and planes do not play well together, the FAA does its best to make sure they don’t.

But should a hit happen, and they do, the likelihood of a casualty from that hit is VERY LOW…neighboring one in one billion flight hours.

To put this in a more-simple way, there are around 28,000 commercial airplanes flying now. Each one averages around 3,000 hours of flight time each year. Multiply those two numbers, and we get 84 million hours of commercial flight time every year…or roughly 8% of a billion hours. Which means if every commercial airplane on Earth flew 3,000 hours every year, starting today, it could take over 12 YEARS to have an airplane bird strike that ended in a casualty. There are so many more ways you could probably die within that timeframe than getting hit by Daffy.

What if my airplane gets struck by lightning?

If you watched the movie “The Truman Show,” you’ll remember this. Truman walks into a travel agency and is greeted by a poster on the wall showing an airplane wing getting stabbed with a raging bolt of lightning…above, text reading “It could happen to you!”

The Truman Show Scene Clip
The Truman Show, © Paramount Pictures

Yeah…that doesn’t look fun.

So, could it happen? Would this kill an airplane? Would this kill me?

Like many situations in the article, there is a good chance you were in an airplane when lightning hit it. You’re in a big metal tube flying through a charged atmosphere creating friction…this is no different from walking on carpet with socks and touching something. The airplane is that “something.” Lighting is going to hit it.

Fortunately for you, airplanes were designed with this in mind.

When lightning strikes an airplane, it is guided across the conductive outer shell of the plane and corralled back to the tail, where it dissipates back into the atmosphere through a series of small wires extending from the tail. All wiring and cables INSIDE the plane are grounded and at no time would the electricity penetrate the fuselage…which acts like a Faraday Cage, if you remember any high school physics.

What about the fuel tanks in the wing, you ask? Again, the lighting doesn’t actually penetrate the airplane, so it does not go into the fuel tanks either. The ability to safely get hit by lightning is a requirement before the FAA grants airworthy certification.

When lightning hits an aircraft, depending on how much of a surge it produces, there is the possibility it would interfere with the navigation instruments on board…albeit, temporarily in most cases. For that one time when the surge takes out a nav instrument, fortunately, aircraft have multiple, redundant instruments on board to account for any failures.

And in case you are wondering, lightning may have the ability to affect lift since it rapidly expands air in all directions from the bolt (which is what causes thunder). In the case of a direct wing hit like the poster above, the wing may experience a temporary stall, dipping shortly before recovering. Inside, it would feel like a tiny turn in the direction of the affected wing…but, again, not serious.

Let's land this thing!

Most of "life" is not 100% safe and there will always be risks with anything you do. The biggest question to ask is, "Do the rewards outweigh the risks?" When it comes to flying, one can be pretty confident in it's ability to get people from Point A to Point B with VERY minimal risk. As a method of transportation, it is, statistically, one of THE SAFEST ways to travel. And, as for reward, going from Chicago to LA in four hours rather than a 40-hour-drive is definitely a plus!