She sits next to you on the plane, gripping the arm rests, her chest rising and falling with each laboured breath. Her eyes are closed, so you chance a sneaky glance at her face. She’s beautiful. A light sheen of sweat clings to her forehead and her hair cascades in blonde tresses down her neck. The airplane comes to a brief halt as the pilot waits for the runway to clear. It clears and the engines begin to roar. Her breathing gets faster and faster with every mile per hour the plane accelerates. The cabin is vibrating, the industrial scenery is whipping past, but all you notice is the pained expression on her face and the fact that her eyes are screwed shut…
A fear of flying is not uncommon. In fact, most first-timers or even frequent fliers will experience a degree of nervousness, if not downright crippling anxiety. Having said that, a fear of flying is much like a fear of sharks: you are much more likely to be killed by something else, so it doesn’t make any sense to stink up the cabin with your fear sweat.
In theory, this fear is totally understandable, as you are hurtling through the thin upper troposphere in an aluminium tube held aloft by nothing more than a couple of clunky-looking wings fashioned from, surprise, metal. The cool thing is, if you understand the dynamics behind flight and therefore what is likely to send you spiralling Earth-bound in a plume of smoke and flame, you can provide your buxom neighbour with an insight that just might get you a first class ticket to the mile high club.
Everyone knows that we as creatures are most vulnerable when we are anxious or scared. With a brief lecture on the physics of flight and some careful massaging, I mean, assuaging of her fears, you could face the somewhat challenging task of cramming two bodies into an aircraft toilet. Alternatively, there are always those free blankets they hand out on some of those long haul flights: they’re great for camouflaging iniquitous activities. Not that I would know.
So, how is it possible? How can something that weighs, on its own, in excess of 400 tonnes lift you, hundreds of passengers, thousands of kilograms worth of luggage, countless bottles of duty-free liquor and the occasional spoilt first-class pet into the air? The dynamics behind it all are quite elementary my dear Watson.
Air is a Fluid, Physically Speaking
We like to think that air is nothingness, emptiness, vacuous and that it doesn’t really consist of anything. But physicists know better. Just grab a mouthful of air and, closing your oesophagus, try compressing it against your palate with your tongue. You can’t. Without an exit route, that air may as well we a block of concrete. That’s how NOT nothingness air is and moving air is exactly what allows an airplane to leave the runway to infinity and beyond.
Air is classed as a fluid. A very airy fluid, but it behaves just like a liquid in the way it moves and flows. So, whether you’re talking about the air, water or any other fluid for that matter, the physical laws that govern the way they behave are the same. As such, it can be said that fish fly through the air and airplanes swim through the atmosphere. Physically speaking.
Thrust, Drag, Lift and Weight
Photo Credit: National Aeronautics and Space Administration
These concepts may sound like they belong in the gym (or the bedroom), but the delicate dance between thrust, drag, lift and weight is responsible for getting something that weighs hundreds of metric tonnes into the air. Let’s take a closer look at the four forces that play such an important role in flight and how they contribute to getting you to your domestic and international destinations…
Thrust and Drag
“Thrust” and “drag” may be your camp gay friend’s two most favouritest words, like ever, but they’re also fundamental in flight. Thrust is the aerodynamic force that propels something forward. An aeroplane gets its thrust from an engine or from a propeller. Since air in not nothingness and consists of gazillions of molecules, it exerts a counter force on any body hurtling through it. That force is called drag. If you want to feel drag, stick your hand out of a moving car window or ask your sister for some of her old dresses.
Drag is essentially air resistance and it is caused by all those air (or water) molecules crashing into the molecules that make up, for example, your hand when you stick it out the window of a moving car. The greater the surface area of the object moving through the fluid, the greater the drag or resistance. This is why, when your hand is turned edge on into the wind, you don’t feel much resistance. Then, when your hand is flat and palm open towards the rushing air, it feels as though you’re being high-fived by the invisible man. Having said all this, drag cannot exist if BOTH the object and the air are stationary. There has to be a difference in relative speed.
The concept of minimizing drag in the manufacture of things designed to go fast is called aerodynamics and it applies to a mind-boggling number of everyday technology. Fast cars and trains are manufactured in such a manner so as to promote the flowing of air over their bodies. This reduces drag and allows them to go faster. A square car would be about as efficient on the racetrack as a baboon with a Sudoku puzzle.
The nose of the bullet train has been specially designed to channel airflow over its top so as to reduce drag and maximise speed.
Airplanes are also made to be extremely aerodynamic. At speeds of 1,000 km/hr. anything sticking out would be subject to such intense drag forces that they’d likely be ripped right off the fuselage (the main body of the plane). This is why the landing gear is retracted after take off. This is also why you should not repeat the hand-out-the-window experiment on an airplane or else your entire arm would not accompany you to your final destination.
In order for a plane to take off, the thrust must be at least the same as or greater than the force of drag. You’ll notice that when your plane comes in for landing, the pilot lifts the flaps on the wings of the plane, effectively increasing the surface area of the wing facing the rushing air and therefore the drag. At this stage, drag is greater than thrust and the plane slows down. I can only imagine that landing a plane at cruising altitude wouldn’t be very much fun for anyone on board.
Weight and Lift
You should know what weight is. Your bathroom scale groans with it every morning. Weight is the force any object exerts on the ground and is a product of its mass and gravity, conveyed in the unit Newton according to the following equation:
Weight = Mass (kg) x Gravitational constant (on Earth it’s 9.8 m/s2)
A 60 kg woman on planet Earth is not only a bitch; she is a 588,6 Newton bitch. On the planet Mercury, she is a 217,8 Newton (dead) bitch. The greater your mass, the more you weigh. The larger the planet you stand on, the greater its gravitational pull on you and therefore, the more you will weigh. So you can imagine that a standard Boeing airliner full of passengers and luggage will weigh a considerable amount, even on Mercury. That’s okay because this is where lift makes its glorious stage entrance.
Lift is the opposite force of weight in effect and just like drag, it cannot exist if the object in question is not moving or if the air (or fluid) around it is still. As long as there is a difference in the relative speed of the object and the surrounding air, lift and drag can be achieved. This explains why kites, which don’t make use of any source of thrust to fly, can stay in the air as long as it’s windy, but will dive-bomb you like a kamikaze bat should the wind cease. It also explains why airplanes, which make use of jet engines or propellers for thrust, can fly on windless days.
So now you know the difference between thrust, drag, weight and lift. But, how does this explain how 400+ tonne airplane gets in and stays in the air?
The Mechanics of Flight
When a moving fluid, be it water or air, encounters an obstacle, it seeks a path around it. In the case of aeronautics, the wings (or airfoils as they are known in the industry) are the obstacles and the air is the fluid. The wings of the plane split the air into two pathways: one flows over the top of the wing and the other flows beneath it. The wings of airplanes are specifically shaped so as to promote the faster flow of air over the top of the wing than the underside. The slower flow of air underneath the wing causes a build-up of pressure beneath the wing, while the faster flow of air on top causes a localized decrease in air pressure.
This region of high pressure caused by the faster flowing air exerts a greater force on the underside of the wing than the air on the opposing side and this creates lift. In other words, the high pressure beneath the wing is physically pushing it upwards (see the rather useful diagram below). By adjusting the angle at which the wing faces the oncoming air, a pilot can control the difference in air pressure above and beneath the wing, thus controlling lift.
How does a pilot do this?
While you are distracted by the pretty airhostesses and are desperately trying not to miss the free snack and drinks cart, tiny green gremlins abseil down the fuselage, dismantle the take-off wings and replace them with specially shaped cruise wings. This is why, without a cloud in sight and at 10,000m in the air, the plane goes through patches of turbulence. It’s those damn gremlins playing around with the airfoils.
In a more realistic scenario, the pilot controls the shape of the wing using flaps and slats. When cruising, these lie flush against the wings thus having no effect on flight speed or altitude. When opened, flaps and slats serve to decrease speed and lift, allowing the plane to descend and land safely. Or at least land. The safely part is up to the skill of the pilot.
Class Dismissed: Your Take-Home Message
So there you have it! Next time you’re seated on a plane next to a nervous blonde, or anxious brunette, distract him or her with your supreme knowledge of the physics of flight. Calm their nerves by explaining how elementary the concepts behind getting an immensely heavy hunk of metal into the air are and that once in the air the chances of things going wrong are highly unlikely. It’s times like this that you REALLY don’t want to be one in a million.
If you ever do manage to get seated next to someone attractive and takes things so far as a conversation on aeronautics, please do let me know all about it. I’ve been on too many flights to recall and the kind of people I have sat next to have included a 6 foot something Russian (who took a nap on my shoulder without buying me a drink first), a young gentleman with flatulence issues, a 50-something pianist with a severe case of verbal diarrhoea and a woman whose butt took up more than its fair share of seating.
Remember, if you are lucky enough to be in the right place at the right time, put the “naughy” in aeronautics and take one for the team!