How the Airplane Remains Airborne?
We often use mechanical equipment without completely understanding how it works.
As a young bachelor, my parents gave me a vacuum cleaner for my birthday. Several months later, Mom called and asked, "Are you having trouble finding bags for your vacuum cleaner?" I said, "Bags? What bags?"
How was I to know the thing needed bags?
Technological ignorance has its advantages, but not when you're up in the air. You don't need a Ph.D. in
aerodynamics to be a pilot, but a moderate-to-decent understanding of why an airplane stays airborne will prove helpful and life-sustaining. That's why this first ground school class is the longest. Don't worry; you won't need to have your eyeballs recapped after reading it. But I do want you to read it all the way through. In order to fly a plane, you must first fill your brain (with a little bit of information, at least). This class is the place to start. Read, and be happy because this is an investment that will pay off big-time.
May the Four Forces Be With You
No, the four forces isn't a 1960s rock group. These forces are actually the things that pull and push on an airplane in flight. The four forces—lift, weight, thrust, and drag—are present any and every time a plane is airborne. Look at Figure 1-1, which shows the action of the four forces.
Figure 1-1 The four forces acting on an airplane in flight.
1-Lift, 2-Thrust, 3-Weight, and 4-Drag
Of course, enormous arrows don't really protrude from the airplane. I know this will disappoint those of you who still expect the states to be colored blue and red and have lines drawn around their borders as you fly over them, but you'll get used to it. The arrows do serve to show that what we've got here is a highly competitive new game—four way tug-of-war. Your job as pilot is to manage the resources available in order to balance these forces. Let's see what they're all about.
Lift
Lift is the upward-acting force created when an airplane's wings move through the air. Forward movement produces a slight difference in pressure between the wings' upper and lower surfaces. This difference becomes lift. It's lift that keeps an airplane airborne.
I discovered how lift works at four years of age during my first visit to church. The collection plate passed in front of me, and I picked out a few shiny items. My grandfather chased me around the pew, and I thought, "Wow, church is fun!" Picking me up by my sweater, Grandpa held me suspended four feet off the ground and toted me outside. It was the lift from Grandpa's arm, precisely equaling my weight, that kept me airborne. Wings do for the airplane what Grandpa's arm did for me—provide the lift to remain aloft.
Weight
Weight is the downward-acting force. It's the one force pilots control to some extent by choosing how they load the airplane. With the exception of fuel burn, the airplane's actual weight is difficult to change in flight. Once airborne, you should not be burning cargo or acquiring extra passengers (or losing them for that matter). Unexpected discharge of passengers while in flight is a violation of some FAA rule, so please don't do it.
In unaccelerated flight (when the airplane's speed and direction are constant), the opposing forces of lift and weight are in balance.
Thrust and Drag
Thrust is a forward-acting force produced by an engine-spun propeller. For the most part, the bigger the engine (meaning more horsepower), the greater the thrust produced and the faster the airplane can fly—up to a point. Forward movement always generates an aerodynamic penalty called drag. Drag pulls rearward on the airplane and is simply the atmosphere's molecular resistance to motion through it. In plain English (which pilots and engineers rarely use), it's wind resistance. Few things are free with Mother Nature. As a buddy of mine likes to say: "If you're getting something for nothing, you're not using your own credit card."
Thrust causes the airplane to accelerate, but drag determines its final speed. As the airplane's velocity increases, its drag also increases. Due to the perversity of nature, doubling the airplane's speed actually quadruples the drag. Eventually, the rearward pull of drag equals the engine's thrust, and a constant speed is attained.
My high school Volkswagen Beetle knew these limits well. The Bug's forward speed is limited by its engine size. With four little cylinders (only three of which worked at any one time), this VW simply wouldn't go faster than 65 mph. Figure 1-2 shows the results of maximum thrust meeting the equal and rearward pull of drag at this speed.
Figure 1-2 An automobile's 1-Thrust, produced by engine power
and 2-Drag,caused by resistance of air molecules
Maintaining a slower speed requires less power, since less drag exists. At any speed less than the maximum forward speed of the car, excess thrust (horsepower) is available for other uses, such as accelerating around other cars or perhaps powering a portable calliope if you are so inclined.
The same is true of airplanes. At less-than-maximum speed in level flight, there's power (thrust) to spare. Excess thrust can be applied to perform one of aviation's most important maneuvers—the climb.
With this introduction complete, I think it's time for you to learn a little about the airplane's flight controls.
Flight Controls
If you're ready-made pilot material, you've been patiently licking your chops waiting for the discussion on flight controls. Gandhi would applaud your patience (but Gandhi isn't here, so I will). Figure 1-3 shows the three imaginary axes of the airplane.
Figure 1-3 The three axes of an airplane.
1-Vertical Axis (Yaw), 2-Longitudinal Axis (Roll), 3-Lateral Axis (pitch)
By use of the flight controls, the airplane can be made to rotate about one or more of these axes. The longitudinal, or long, axis runs through the centerline of the airplane from nose to tail. Airplanes roll, or bank, about their longitudinal axis. A good way to remember which way the longitudinal axis runs is to remember that it's a long (as in longitudinal) way from the nose to the tail of an airplane.
A sideways pass in football is called a lateral pass. Similarly, the lateral axis runs sideways through the airplane from wingtip to wingtip. Airplanes pitch about their lateral axis.
The vertical axis of the airplane runs up and down from the cockpit to the belly. Airplanes yaw about their vertical axis. Think of yawing motion as yawning motion. In the morning, you yawn by standing and stretching vertically, rotating right and left, waiting for those vertebrae to kick in.
Now we're ready to examine each of the three main flight controls that cause an airplane to move about its axes.
Ailerons
Ailerons are the moveable surfaces on the outer trailing edges of the wings. Their purpose is to bank the airplane in the direction you want to turn. When the control wheel is turned to the right, as shown in Figure 1-4, the ailerons simultaneously move in opposite directions (this doesn't mean they're broken, either).
Figure 1-4 Banking to the right. How ailerons bank the airplane.
1-More lift with a lowered aileron, 2-Less lift with a raised aileron.
When the control wheel is turned to the left, as shown in Figure 1-5, the left wing aileron raises, decreasing the lift on the left wing.
Figure 1-5 Banking to the left. How ailerons bank the airplane
1-Less lift with a raised aileron. 2-More lift with a lowered aileron.
The right wing aileron lowers, increasing the lift on the right wing. This causes the airplane to bank to the left.
Ailerons allow one wing to develop more lift and the other to develop less. Differential lift banks the airplane, which tilts the total lifting force in the direction you want to turn.
Elevator
The elevator is the moveable horizontal surface at the rear of the airplane. Its purpose is to pitch the airplane's nose up or down (Figure 1-6)
Figure 1-6 How the Elevator Control changes the airplane's pitch
Tail moves down (1) because the elevator (2) moves up.
What the Heck is "Back Pressure?"
you'll be giving your instructor some sort of in-flight massage (as nice an idea as that may be). Rather, it
refers to the action when a pilot pulls back—gently—on the airplane's control wheel. The phrase probably
came about as the result of an instructor who realized that novice students have a tendency to take the
phrase "pull back on the wheel" a little too literally and yanked the wheel back hard… a maneuver I don't
recommend.
The elevator control works on the same aerodynamic principle as the aileron. Applying back pressure on the control wheel of the airplane, as shown in Figure 1-6, deflects the elevator surface upward.
Lower pressure is created on the underside of the tail, which moves it downward, and the nose of the airplane
pitches up.
Figure 1-7 How the Elevator Control changes the airplane's pitch
Tail moves up (1) because the elevator (2) moves down.
There's also a third flight control, the rudder, which controls yaw around the vertical axis. We'll discuss this later on, but for now, I want to make sure you know I didn't forget about it.
Now that you've acquired a basic idea of how the flight controls work, let's put our brain in the plane and discuss how to perform a useful flight maneuver: straight-and-level flight.
Straight-and-Level Flight
You're about to practice straight-and-level flight, one of aviation's most fundamental maneuvers. Does this sound like two separate maneuvers instead of one? Well, it is. Straight flight means the airplane's nose remains pointed in one direction and the wings are parallel to the earth's horizon. Level flight means the airplane doesn't gain or lose altitude.
Figure 1-8 shows what straight-and-level flight looks like from the left seat where you, the pilot, normally sit.
Figure 1-8
Don't worry if the picture shows us headed for a distant mountain. I'm with you, and I'm good at avoiding
mountains. In fact, it's my specialty.
How to Tell You're Going Straight?
Okay, how do you know you're actually flying straight and level? The easiest way to tell is to look over the
instrument panel and out the windscreen (the front window), as shown in Figure 1-8. It appears that the top portion of the instrument panel is approximately parallel with the earth's distant horizon. This implies that your wings are not banked, which means you're flying straight ahead and not turning.
There is, however, another way to tell if you're flying straight. You can press the hat switch on your joystick. (The hat switch is the button that sticks straight up out of the middle, near your thumb) If you look out the left or right window, as shown in Figure 1-9, you'll notice the position of each wing relative to the earth's horizon.
Figure 1-9
In straight flight, both wings should be the same distance above the horizon (refer to the horizon, not themountains).
Having the Right Attitude
In real airplanes, I prefer that my students almost strip the gears in their neck by looking right and left out the
windows. This helps them check the wing's position and keeps their eyes focused out the cockpit looking for traffic. No, I don't mean automobile traffic, either. I mean airplane traffic. In the simulator, however, it's inconvenient to keep shifting views to the left and to the right. So you'll use the attitude indicator to help maintain straight-andlevel flight. The attitude indicator is located at the top of the six main flight instruments directly in front of you (Figure 1-10).
Figure 1-10
indicator displays the airplane's attitude (its upward or downward pitch and the bank the wings make with the
horizon). The upper half of the attitude indicator is blue (like the real sky, unless, of course, you fly in Los Angeles), the bottom half is brown (like the surface below us). The thin white line between these colors is the artificial horizon line. Pilots use the attitude indicator when they can't see the earth's horizon because of restrictions to visibility or when it's inconvenient to look at the wing tips (which will usually be your situation when flying the simulator).
By moving the joystick to the left, the airplane banks to the left, which dips the left wing downward toward the ground, as shown in Figure 1-11A.
Fig. 11-11A |
Fig. 11-11B |
Fig. 11-11C |
This is how you begin a left turn. Notice that the miniature (orange-winged) airplane in the attitude indicator also appears to dip its left wing toward the ground. Mechanically speaking, it's really the background of the attitude indicator that moves and creates a picture of the airplane's attitude. Nevertheless, you can always tell which way you're banking by determining which one of the small orange wings in the attitude indicator dips toward the ground. (This is easy since you only have two choices).
By gently moving the joystick to the right in the same manner just described, the attitude indicator will indicate a right turn. Now the orange-winged plane's right wing dips toward the ground, as shown in Figure 1-11B. Moving the joystick to the right or left until both of the miniature plane's wings are parallel to the artificial horizon line returns the joystick to its center (default) position and returns the airplane to straight flight, as shown in Figure 1-11C. After all, if the wings aren't banked, the airplane isn't turning.
Know Where You're Heading
There is one more way to know if you're flying straight. This involves using the airplane's heading indicator, as
shown in Figure 1-12.