How And Why Airplanes Fly (Instead Of Falling)

Have you ever wondered what would happen if you were flying on an airplane and all the engines stopped working?  Would you just start falling? A fear of flying is fairly common.  For some, it’s the smaller space. Others, the motion. But if you are like I was, I didn’t understand how in the world I was so high above, suspended in nothing. So if those purring engines just stopped, would I fall from the sky?  Let’s find out.

Water and air
Water and air act similarly in many ways. Not when you look at their thirst quenching abilities – water will win that one every time. But when we look at how objects move through the air, it’s characteristics are very similar to water. Even as a pilot, in my initial training, I was a little intimidated by flying.  I imagined that when I was in the air, I was just up in the nothingness. But air is not nothing.  It is very much something. And if you think of the sky like a big ocean, and standing on the ground is like standing on the bottom of the air ocean, it’ll help you understand flight.

Let’s look at water
It’s pool season, so next time you’re taking a swim, hold your arm out under water and flatten your hand (palm towards the bottom).  Spin around in a circle so your hand is moving quickly.  If you angle the front of your hand up a little, feel how your hand gets lifted towards the surface.  We call this force “lift.” Tilt the front of your hand down a little and see how the water pushes the top of your hand down, causing it to dive towards the bottom. Take note here: It is the movement of your hand through the water that creates this lifting force. If your hand is not moving, tilting it up or down doesn’t do anything to lift it.

Hand In The Wind

Now let’s look at air
Have you ever had your hand in the wind stream just outside of a car window as you rested your forearm on it? The air is a fluid – like the water – and acts like the water did in the example above. Angle the front of your hand up a bit and you’ll feel the air try to lift your hand.  Angle the front of your hand down a bit and you’ll feel the air try to push your hand down.  When the car slows down or stops, there is no lift – your hand just falls. The lift your hand felt both in the water and in the air is how a wing moving through the air feels lift as well. A little bit of angle at the front of the wing, and the air lifts the wing.  Remember how it was the motion of your hand through the fluids that made the lift?  The same is true in flying an airplane must have a certain minimum airspeed to stay flying.  And this is what the engine does – it keeps those wings flying fast enough to make lift.

 

So what happens if the engine stops?
Think about riding a bicycle on a flat street.  You have to pedal steadily to keep yourself moving. But if you find a nice downhill, you can stop pedaling and keep moving just fine. You are letting gravity keep your speed up. An airplane does the same thing, but the engine is doing the pedaling to pull the airplane along. If an airplane starts to descend “downhill” – gravity does what your engines were doing before, just like coasting on a bike.  In an airplane, those engines don’t have to run as hard when it is descending.  Even without the engines running, the airplane doesn’t have any trouble staying in the air – as long as it stays fast enough to keep the wings making lift through the air.  With no engine to keep it going, there’s only one way to keep the wings moving fast enough, and that is to go down. But here’s the catch – it doesn’t go straight down. In fact, that would be quite dangerous – it would get much too fast. Instead, like the bike rolling down a hill, it begins a descent. And you know, it doesn’t feel much different than a regular descent down to land.  This is called gliding.

Bike Tire

Each airplane has its own glide characteristics, and some planes can glide further than others, but to go back to our airplane who’s engines have stopped working, let’s look at a scenario. An typical airliner traveling at a typical cruise altitude (thirty something thousand feet) can glide for roughly a hundred miles. It would take around 20 minutes. With that sort of glide, you could order up a cold Coke and check your emails.  The pilot will use that time to select a good airport nearby and land there. They’ll probably try to figure out what’s wrong with those engines, too.

Activity Time
Let’s bring this all together with an activity. We all loved the rubber band powered balsa airplanes as a kid. Get your hands on one (Hobby Lobby is my source) and find a nice open area.

Balsa Glider Airplane Package

Wind up the propeller until there are knots all along the rubber band. Be sure to wind clockwise as you view the front. Ready? Now let go of the propeller and give it a throw!  That propeller will spin for up to ten seconds or so before the rubber band unwinds and stops. As long as that propeller is spinning, that plane’s wings are being pulled by the engine fast enough to make the wings lift and stay in the air.  Once the propeller stops, that’s like the engine quitting. Actually, it quite literally is the engine quitting for our little balsa plane. The airplane will nose over a bit and begin to glide.  The higher the airplane is when the propeller stops, the longer it can glide.  Now experiment with the configuration of the wings (slide them forwards or backwards) to try to get the best glide out of your airplane.

Balsa Glider Airplane Assembled

Glide It On Home
Now that you understand how an airplane glides, even with it’s engines inoperative, rest assured that something going wrong on your next flight won’t make you drop out of the sky like a rock.  Keep in mind that this is just a visual model.  There are many complex nuances of aerodynamics. It is, in some ways, actual rocket science.  But these basic concepts apply to both your rubber band airplane and your airline ride to your next beach trip or business meeting.  And just like a magic trick leaves you stumped until you figure out the inner workings, flight can be demystified when you realize that you aren’t just floating magically in the air as much as surfing through a fluid, much like being under water.  I don’t, however, recommend flying underwater. It scares the fish.

 

Show me your best glide! Tag your photos or videos of your rubber band airplane with #clayviation and be sure to like my Facebook page, Clayviation: Inspiring Tomorrow’s Pilot and follow me on Twitter and Instagram @clayviation. 

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