Category Flying and Gliding

As I hinted earlier, there’s a little more to it than that. A Swiss mathematician named Daniel Bernoulli was working on complex formulas that explained changing pressure caused by flowing masses of water when he derived a formula, now called the Bernoulli equation, that explains lift. Here’s what Bernoulli discovered, and what gave birth to a million aerodynamic equations: When a fluid accelerates past an obstruction, like the surface of a wing, its pressure decreases. To be precise, a special case of Bernoulli’s equation says that [pressure + (Density+2 (velocity)2)] equals a constant value—at least in an open, continuous flow of fluid. In other words, increased velocity results in decreased pressure.

Actually, the principle can be explained pretty simply. Wings are shaped with an upper surface that is curved, or “cambered” (to use the aviation term), and a lower surface that is much less curved. When an airplane is in flight, some air is going over the top, curved surface, and some is going under the bottom, flatter surface. Because the air moving over the top, curved part of the wing must move faster to cover more surface than the air moving under the bottom, flat part of the wing, the pressure of the air on top drops slightly.

That small pressure difference is the key to creating lift, because high school physics tells us that an area of high pressure tends to move toward an area of low pressure. In flight, that means the higher pressure below the wing tries to move toward the lower pressure above. Because the body of the wing is in the way, the high – pressure air takes the wing along with it, lifting it as it goes.

In brief, that’s the concept that put magic in the smooth curve of an airplane’s wing. Together with Newton’s law of action and reaction, Bernoulli’s equation provides the explanation of the physics of flight.

Four opposing forces act on a plane during flight: lift, weight, thrust, and drag. When an airplane is flying straight and level, lift works upward and is opposed by weight, which acts toward the earth. Thrust is the propelling force that gives an airplane the

speed required to stay aloft, and it is opposed by drag, the force which tends to slow down an airplane. Let’s examine each of these forces a little more closely.

Lift: The Gift of Newton and Bernoulli

Lift is the force that makes flight possible for any aircraft that relies on an airfoil, including airplanes, gliders, and helicopters. (You’ll learn in Chapter 11, “Up, Up, and Away: Hot-Air Balloons,” that balloon and blimp flights are made possible by buoyancy.) Simply put, lift is the force that pushes an airplane upward.

Lift is not produced by a single force or property. Instead, it is a combination of two forces that work together. We’ll look at one component of lift that can be characterized by a law of physics first written down by Newton, and another, more subtle form that was the brainchild of a lesser-known physicist named Daniel Bernoulli.

For Every Action…

Sir Isaac Newton, the eighteenth-century philosopher, mathematician, physicist, and man for all seasons, put down in writing one of the laws of motion that explains the first element of lift. To paraphrase, Newton wrote that every action causes a reaction of equal force and in an opposite direction.

To understand what this means in terms of airplane flight, think of a wing as a simple flat metal plate. If we place that flat plate in a steady stream of moving air, such as in a wind tunnel, and position the plate so that it is perfectly streamlined in the wind, the air above and below the plate will flow past at the same speed and no lift will be created. But if we tilt the plate upward in the air stream, some of the air will strike the bottom of the plate and deflect downward. In Newton’s words, the plate has “acted” on the air stream by changing its direction. The “reaction” is a force pushing in the opposite direction, upward. Voila—lift.

In This Chapter

► Pitch, roll, and yaw

Lift: the key to flying an airplane V Drag: an unavoidable cost of flying >• Thrust: the driving force in airplanes >■ The turn: one maneuver, many forces

In the last chapter we discussed the components that make up the airplane. In this chapter, we’ll learn how those components work together to enable an airplane to fly.

Pivot Points: Pitch, Roll, and Yaw

When the pilot controls the ailerons, Haps, elevators, and rudder surfaces, he brings the three axes of motion into play.

Imagine a small toy airplane. If you imagine a wooden dowel or a metal wire running the length of the airplane from the tip of the propeller to the tip of the tail (the point where the vertical and horizontal stabilizers meet), you’re visualizing the “longitudinal axis.” Rotation around the longitudinal axis is accomplished by using the ailerons, and is called “roll.” The pilot controls roll by turning the control column, or “steering wheel,” left and right.

Now imagine a wire running from one wingtip to the other. This is roughly the position of the “lateral axis.” The airplane pivots around this axis as a result of moving the elevators, and such pivoting is called “pitch.” The pilot controls pitch by pushing the control column in and out.

Finally, imagine the place where the longitudinal and lateral axes meet. If you were to run a wire vertically through that point, that would represent the “vertical axis,” which the pilot controls using the rudder. Movement around the vertical axis is called “yaw.” The pilot controls yaw by using the foot pedals.

To sum up:

•The aileron control surfaces located on the wings, and moved by turning the control column left and right, cause roll around the longitudinal axis.

•The elevator control surfaces located on the horizontal stabilizers, and moved by pushing the control column in and out, cause pitch around the lateral axis.

•The rudder control surfaces located on the vertical stabilizers, and moved using the foot pedals, cause yaw around the vertical axis.

The three airplane axes meet at a single point called the “center of gravity,” which is also the point where airplane designers consider the aerodynamic forces of flight to be concentrated. The center of gravity is a significant factor in such areas as calculating the stability and the maneuverability of an airplane, though that is a factor we generally leave to the engineers.

As we’ll learn in the next chapter, anything that protrudes from an airplane into the air stream can slow it down. To make airplanes fly faster, engineers sometimes equip them with retractable gear that can be mechanically pulled up after takeoff. With the wheels tucked away, the airplane’s exterior is smoother, and when you’re talking about aerodynamics, smoother means faster.

But not every airplane has retractable gear. The main reason is that the hydraulics and motors that help pull up the gear are heavy and complicated. Heavy airplanes can carry less cargo, and complicated airplanes cost more to manufacture, maintain, and insure. So, smaller airplanes and those that put a premium on carrying cargo are usually equipped with fixed landing gear.

And there you have it: the major parts of a plane that enable it to fly. In the next chapter, we’ll see how these parts work together with the pivot points and the four opposing forces on a plane to produce the magic of flight.

The last major component that makes up an airplane is the landing gear. Landing gear generally comes in two types: tricycle configuration or the more traditional conventional pattern.

Tricycle Gear

Tricycle gear is so named because its wheel configuration resembles that of a child’s tricycle—that is, it has one lead wheel near the plane’s nose and two main wheels behind it under the wings. Tricycle gear has become the most popular configuration in most planes rolling off of modern assembly lines because they make landing easier. The technical reason is that the airplane’s “center of gravity,” the point at which the plane would balance like a seesaw if placed on a fulcrum, rests between the main gear and the nose gear in a tricycle – gear airplane.

In practical terms, it means that tricycle-gear airplanes are more stable during landing, and any swerving caused by wind or poor control technique would tend to stabilize when the pilot steps on the brakes.

Tricycle gear also makes for better forward visibility when the airplane is taxiing on the ground, having a more level attitude than the conventional type.

Plane Talk

Airplanes are equipped with other types of landing gear besides wheels. For example, some airplanes can be transformed from a land plane to a seaplane simply by removing the nose wheel or tail wheel and attaching floats in place of the main gear. For flying into snow – and ice-covered terrain, pilots can attach skis to the gear. Even tires are versa­tile: Normal narrow tires are good for landing on paved runways and fat "balloon" tires are ideal for landing on grass.

Conventional Gear.

As its name suggests, conventional gear is the older style that was a tradition in aviation until the past few decades. In addition to the main wheels under the wings, this configuration features a third wheel under the airplane’s tail. The tail-down attitude caused by conventional gear makes the nose stick up high enough to obscure the pilots view while she’s taxiing. It also demands extra skill from a pilot during landing, especially in a crosswind.

In a conventional-gear airplane, the center of gravity is located behind the main landing gear, a less stable setup than in the tricycle-gear airplane. The result is an airplane that (as old-timers joke) the pilot has to keep flying “until it’s parked and the wheel chocks are in place.”

Because conventional gear reminds a lot of pilots of the “good old days,” conventional-gear airplanes are still popular. Some pilots won’t even consider buying anything other than a “tail dragger,” even if they are somewhat more demanding to fly.

Flaps are familiar to anyone who has flown in a jetliner and watched the wings closely during the approach to landing. There was a point at which the trailing edge of the wing seemed almost to come apart, as enormous slabs of metal moved backward and downward in a curve until the wing seemed to have nearly doubled its size. Those flaps, called Fowler flaps, are the most complex of all the varieties available to designers. Small airplanes use simpler hinged flaps that are much lighter than Fowler flaps. Remember, small airplanes can’t afford too much in the way of complex systems because of the weight restriction.

Simply put, flaps help an airplane fly slower. That’s why you see them used mostly during landing, when a pilot wants to slow the plane as much as possible. The slower the plane is flying when it touches down for landing, the less the brakes have to work to bring it to a stop, allowing the plane to land on a shorter runway and to touch down at a slower, safer speed.

The Empen-What?

Another major structural component of the airplane is the “empennage” (pronounced EM-puh-nazh). The word empennage comes from the French word for putting feathers on the end of an arrow. The empennage is largely responsible for stabilizing the plane in flight.

The primary surfaces making up the empennage of most planes are a horizontal stabilizer and a vertical stabilizer.

The Horizontal Stabilizer

The horizontal stabilizer resembles two miniature wings attached to the back end of the airplane. On the trailing edge of the horizontal stabilizers are hinged surfaces called “elevators,” which the pilot controls by pushing the control column forward and backward in the cockpit.

By a show of hands, how many believe the horizontal stabilizers produce upward lift just like the wings do? If you raised your hand, you’d be wrong. In fact, the horizontal stabilizers create a force that is downward in most flight conditions. We’ll examine why in the next chapter when we talk about the effects of weight on the way an airplane flies.

The vertical stabilizer helps keep the airplane from slipping through the air in a sort of sideways slouch. Think of what happens when your car door is slightly ajar while you’re driving down the highway. When you try to open it in order to pull it closed, you notice how difficult it is to open. As you already understand instinctively, the pressure of the blowing air against the surface of the door tends to keep it streamlined in a closed position. When you push it out into the air stream, the air pressure resists.

The same principle is at work on the vertical stabilizer. When some force pushes the airplane into a slight sideways angle to the wind, whether that force comes from an errant gust of wind or an intentional input by the pilot, the vertical stabilizer tends to push the tail back into line. The airplane is most “comfortable,” meaning its opposing forces are most in equilibrium, when the tail is exactly in line with the center of the propeller.

The empennage seems to have more than its fair share of surprises. First we learn that the horizontal stabilizer creates lift toward the ground instead of toward the sky. Now, we’ll see that the vertical stabilizer is attached to the airplane askew, and it’s done on purpose. During flight, and especially during a climb to a higher altitude, the airplane tends to turn toward the left. This is due to a complex combination of factors mostly connected to the torque produced by the engine and the peculiar aerodynamics of a propeller. (For more detail on torque, see Chapter 8, “How Airplanes Fly, Part 2: The Aerodynamics of Flight") One thing that engineers do to try to offset an airplane’s left-turning tendency is to attach the rudder to the vertical stabilizer at an angle that produces a permanent right­turning effect If you stand behind a small airplane on the airport ramp, you can see the very small offset angle.

Attached to the trailing edge of the vertical stabilizer is the rudder, a hinged surface that is controlled by the pilot using two foot pedals on the floor of the cockpit. These pedals are located roughly in the same position as the brake and accelerator pedals in a car, but are larger and sturdier.

Rudders play a large but mostly unnoticed role in making a flight comfortable. It is the sideways, fishtail motion of a plane that creates airsickness in passengers. A heavy-footed pilot who misuses the rudders can make passengers feel sick faster than a case of ptomaine poisoning. By the same token, a pilot with deft touch on the rudders can tame even the most unruly and turbulent atmosphere.

The “cowling” is an important part of the powerplant, even though it doesn’t produce any horsepower at all. The cowling is the curved metal covering over the engine. It’s not there just to give the airplane a stylish flair. Its most important function is to smooth the surface around the engine.

As we’ll see in greater detail shortly, air flows better over a smooth surface than a rough one. Without some kind of covering to smooth the way, the surface of an engine diverts air into any number of crevices and hiding places. Because it hides the rough edges, the cowling, which is usually made of lightweight sheet aluminum or molded Fiberglas, actually enables airplanes to fly faster—not to mention make a fashion statement!

That portion of the airplane that houses pilot and passenger is called the “fuselage” (pronounced FYOO-suh-lazh). The fuselage contains the cockpit, the passenger cabin, and the baggage compartment in most small airplanes. The fuselage also shelters the airplane’s sensitive instruments.

The fuselage also anchors the rest of the airplane’s structure: wings, tail, and landing gear. In single-engine planes, the fuselage anchors the engine with the help of a “firewall.” Don’t let the name worry you; the firewall acts more as a barrier for airflow and noise than for fire, which is an extremely rare occurrence in flying. But in the offhand chance that a fire does occur, the stainless steel firewall is there to protect you and your passengers.

In the front part of the fuselage is the cockpit—the area reserved in large planes for pilots and in small planes for a single pilot and perhaps a passenger.

The cockpit features a control panel of instruments and dials that help the pilot keep on top of navigation, communications, the condition of the engine or engines, and a host of other flight details.

The control panel includes a cluster of flight instruments directly in front of the pilot. We’ll discuss most of the important instruments on the control panel in Part 3, “In the Cockpit.” But in brief, the flight instruments include the attitude indicator, the directional gyro, the altimeter, the vertical speed indicator, the turn coordinator, and the airspeed indicator. The panel also features the dials and readouts of navigation radios, as well as communications radios.

Finally, the control panel includes a set of engine instruments that range from such basic readings as engine temperature and oil pressure to the more detailed readouts describing the conditions deep inside a jet engine—for example, the temperature of the gas as it leaves the exhaust nozzle.

The cockpit also houses the “steering wheel” that the pilot uses to control the attitude of the airplane. (Except don’t call it a steering wheel—it sounds too much like what you’d find on bus, and airline pilots are touchy about being compared to bus drivers.) The big black wheel is called the “control column,” and it is connected to surfaces in the wing and in the tail. As you might have seen in movies, the control column is pushed and pulled to help control whether the airplane’s nose points up or down, and it can be turned left or right to bank the wings in one direction or another

Putting Wings on It.

In low-wing airplanes—airplanes whose wings are beneath the cockpit rather than above it—the bottom of the fuselage provides the wings anchor points. Of course, in high-wing airplanes, the anchors are in the fuselage ceiling. Through this section run the cables and electric wires that connect to the wing control surfaces and lights.

On the trailing edge of each wing are two control surfaces—the ailerons and flaps. The ailerons (pronounced AlL-ur-rahnz, which is French for “little wings”) are movable surfaces attached near the outboard tip of the wing’s trailing edge. They are controlled from the cockpit and help turn the plane. Also attached to the wing’s trailing edge are flaps, hinged panels that are similar to ailerons but larger and attached closer in toward the fuselage. The flaps help control an airplane’s speed.

The ailerons move in opposite directions from each other when the pilot turns the control column. For example, if a pilot wants to bank toward the right, he would turn the control column to the right. The aileron on the right wing would rise slightly, causing the wind to strike it with a downward force. (W e’ll get into the aerodynamics of the turn in the next chapter.)

At the same time, the aileron on the left wing would dip slightly, causing an upward reaction. Together, the dipping of one wing and the raising of the other create a bank, and therefore a turn.

Airplanes are made up of thousands of parts, from the simplest assemblies of sheet aluminum and rivets to the most complex system of gyroscopes or radio navigation receivers. No two airplanes are exactly alike, of course, but they all have certain very basic features in common:

•The powerplant

•The fuselage

•The wings

•The tail, or empennage •The landing gear

Let’s examine these common components and the role they play in producing flight.

The Powerplant

The propeller, engine, and cowling together comprise the airplane’s powerplant.

The Engine

Powerplants can consist of a number of different types of engines with varying capabilities of power, durability, and capability to perform at high altitude.

Reciprocating engines, the type of engine you have in your car, are familiar to most of us, and the engines in airplanes are not a lot different from those in cars. In many ways, airplane engines are simpler than car engines. Many of them use carburetors, which in automobiles have been replaced by fuel injection systems. One major difference between the two engines is that airplane engines are typically air-cooled,

because radiators, water pumps, and the rest of the mechanical components that go along with the water-cooled engine of a car are too heavy for an airplane to carry.

An airplane with just one engine is called, quite logically, a single-engine airplane, while those with two or more engines are called twin-engine or multiengine airplanes. In a single-engine airplane, the cockpit and cabin that house the pilot and passengers rests behind the engine. In a twin-engine airplane the engines generally are mounted on each wing about a third of the distance outward from the cabin.

A common misconception is that twin-engine airplanes are neces­sarily more powerful than single­engine ones. Simply counting engines isn’t enough to judge engine power. The Cessna Caravan cargo plane has only one engine, while a Piper Seminole has two engines. But the Caravan’s single engine is capable of churning out 675 horsepower, while the Seminole engines combined can manage only 360 horsepower. Sometimes, one really beefy engine is a bet­ter choice than two lightweight ones.

Twin-engine airplanes can fly at higher speeds than a plane with just one engine, assuming the engines are of comparable power. However, because drag increases with speed, a principle we’ll explore in greater detail in the next chapter, twice as many horsepower doesn’t translate into twice as much speed.

Also, twin-engine airplanes offer a backup engine in case one fails. That’s reassuring to some pilots, but it must be said that flying some small twin-engine airplanes with only one operating engine is very demanding, and more than one pilot has crashed because he wasn’t up to the task.

Even some jetliners, such as the twin-engine Boeing 737, are notoriously difficult to handle in the event of the failure of one of its engines. Because of the difficult one – engine handling characteristics of some twin-engine planes, simply having two engines sometimes adds to the complications that can arise from the failure of one engine.

The Propeller

Powerplants can feature propellers with a host of characteristics. They can range from the simplest carved wood-and-lacquer prop that drives some older, smaller airplanes to the massive, four-bladed metal-and-composite propellers able to shed ice and to automatically adjust theirpitch during flight. These “constant speed” propellers turn faster or slower during different segments of flight, almost like an airborne version of an automobile transmission.

The small airplanes that most private pilots use for flying lessons are equipped with the simpler fixed-pitch propellers. Their shortcomings in not being able to adjust to different speeds during flight—fastest rotation during takeoff and slowest rotation during cruise—is more than made up for in simplicity.

When a student pilot is learning how to control and maneuver an airplane, simplicity in a prop becomes a virtue. A fixed-pitch eliminates one thing the pilot must think about. Later, when he is more experienced, the pilot can more easily transition to a more complicated airplane, including one with an efficient constant-speed propeller.

When asked what makes an airplane fly, I’m often tempted to answer, “magic. ” To me, the forces of aerodynamics are that marvelous and awe-inspiring. But as aweinspiring as these physical forces are, they are easily understood, and can be applied to every invention of aviation.

Part 2 introduces you not only to airplanes, gliders, helicopters, and hot-air balloons, but to the aerodynamic forces that enable them to fly. You’ll even get a look at some of the oddities of aviation, including a jet that behaves like a helicopter.

Chapter 7

How Airplanes Fly, Part 1: The Parts of a Plane

In This Chapter

^ Identify the basic parts of an airplane V The powerplant ^ The fuselage >- The wings ^ The empennage ^ The landing gear

We’ve already seen that airplanes are far from the only kind of aircraft available to the recreational aviator. But there’s something about the fixed-wing engine-driven airplane that makes it the most popular form of flying among pilots in the United States. (Gliding is also gaining in popularity. We’ll look at the differences between flying airplanes and gliders in Chapter 9, “Soaring on Silent Wings: Gliding.”)

The attraction that airplanes hold for many of us is rooted in nostalgia. The image of the dashing barnstormers of the 1920s and 1930s is deeply ingrained in our culture. The silk scarf and the swagger of those daring pilots have become part of an archetype that is purely American in origin; we see the barnstormers who pioneered the skies as direct descendents of the pioneers who tamed the Great Plains and the Rocky Mountains.

Maybe it’s simpler than that, though. Maybe some of us love flying airplanes because they allow us to master an element that is foreign to us, though good pilots eventually learn that mastery of flight only comes with acknowledging its potential dangers and backing down when they are overmatched.

Airplanes give us the ability to break the two-dimensional restraints that bind us to the ground and enable us to view the earth from a lofty perspective where the fumes of traffic and the constant reminders of responsibility grow less important with distance, and where the elemental demands of the sky and the airplane occupy all our attention.

With that bit of hangar philosophy, let’s begin to examine the delightful details of how an airplane flies. In this chapter we’ll take a look at how the airplane is put together, and in the next chapter we’ll examine the forces that keep it in the sky.

And you thought Oshkosh was only a label on your toddler’s overalls! Actually, Oshkosh, a small town in Wisconsin, is to aviation what Indianapolis is to car racing. Every summer, beginning in the last week of July, this town of about 60,000 is overrun by more than 700,000 swarming aviation fanatics from all over the world. Visitors look at giant jets, secretive ultra-modern military planes, and small, racy propeller planes of all descriptions. But mostly, they are there to be a part of an aviation event that every pilot feels drawn to attend at least once.

So why have few people heard of Oshkosh, while the Indianapolis 500 is a national institution? For one thing, the Indy 500 was first held in 1909, while the Oshkosh festival marked only its 47th anniversary in 1999. For another, as long as more people drive cars than fly planes, auto racing will continue to receive more television coverage than events such as Oshkosh and the Reno Air Races (see Chapter 4, “Great Flyers of the World Wars”).

But to the sport pilot and aviation buff, Oshkosh, a six-day event that the sponsoring Experimental Aircraft Association has dubbed AirVenture Oshkosh, is a kind of rite of passage. Once you’ve been there, you’ve always got a story to tell on a rainy day at the airport when you and your flying friends are hanging around the airport and doing a little bit of hangar flying.

The thousands of airplanes that fly into Oshkosh each summer turn the town’s Wittman Regional Airport into one of the busiest in the nation. The Federal Aviation Administration staffs a temporary control tower that, for a few days, handles as many arrivals and departures as some of the world’s busiest airports while ground workers lead hundreds of airplanes to parking areas that surround the airport. Cessnas, Pipers, and Beechcraft make up the majority of planes at Oshkosh, though there are dozens of other great airplane lines represented, from the Grumman Tiger (the beloved model that endured terrible abuse from me as I was learning to fly) to the sleek-waisted Mooneys that look fast even when they’re parked on the airport ramp.

Each year, pilots of Cessnas, Pipers, Mooneys, Beechcraft, and the hundreds of other models and variations of planes that can be found at America’s airports find one common meeting point: Oshkosh.

The Least You Need to Know

V Sport flying is not only increasing in popularity, it’s also getting safer.

>■ Cessnas and Pipers are the most popular, and least expensive, airplanes in America.

Beechcrafb and Mooneys are not as affordable as Pipers and Cessnas, but they’re popular airplanes with wildly loyal fans.

>• The Oshkosh festival is a pilgrimage every small-plane pilot should make at least once.