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Thanks to Microsoft for the use of this text.
WHY IT ALL WORKS
Lift
Lift is the upward force produced by a wing as it moves through the air. It's the same force that counteracts the gravity of an aircrafts weight.
- How a wing works Ask engineers how a wing works and they'll go on about circulation theory, the shape of the wing, and "Bernoulli's Theorem." They'll talk your ear off but the most useful information for a combat pilot learning to fly in a hurry is admittedly simplistic: A wing keeps an airplane up by deflecting the air down.
- The angle that matters most The angle at which a wing meets the air is called the angle of attack or AOA. This is not the angle between the airplane's nose and the horizon. It's the difference between where your wing is pointing and where it's actually going.
- Changing the amount of lift You can control the amount of lift a wing generates by adjusting two things: speed and AOA. To produce a certain amount of lift at low speeds, the air must be deflected using a large angle of attack. To produce the same amount of lift at high speeds, the air must be deflected using a small angle of attack. If the speed is very low, the angle of attack you'll need to maintain lift, will be so large at a certain point(critical angle of attack) that the air cannot flow smoothly over the wing, and the wing will stall.
You can also add lift by extending the flaps, which increases the curvature of the wing. With the flaps extended, more air is deflected downward, so there is more lift. Flaps also cause an increase in drag.
Weight opposes lift - it's the downward force caused by gravity pulling an airplane toward the center of the earth.
For your ship to fly, the wings must develop enough lift to counteract it's weight. The "real" weight of your aircraft changes only as fuel and ammunition are used up. But changes in "apparent gravity" (measured in G-forces) are caused by maneuvering. For example, a level turn with a 60-degree bank puts a 2-G load on the plane and it's pilot. Both seem to weigh twice as much as they do when in straight-and-level flight - and in a way they do - because of the increase in "apparent gravity."
- Compensating for G-forces During maneuvers, you have to adjust the amount of lift to compensate for the changes in weight caused by G-forces. To stay level during a steeply banked turn, for example, you'll need to raise the nose slightly (increase the AOA) and add more power (thrust) to produce more lift to balance you out.
- Blackout and redout Most maneuvers create only slight, brief G-forces. But combat maneuvers produce strong, rapidly changing G-forces that can be uncomfortable, or even incapacitating.
- Positive Gs Rapid pull-ups and steeply banked, level turns creat positive G-forces that act toward your feet. As the blood circulation to your brain decreases, your visual field narrows and you may experience "blackout:: you'll loose color vision and eventually lose consciousness.
- Negative Gs Rapid pushovers and certain aerobatic maneuvers create negative G-forces that act toward your head. As the forces increase, you'll experience discomfort, headache, "redout" caused by excessive blood flow to your eyes, and even unconsciousness. Most pilots have a harder time handling negative Gs than positive Gs.
Thrust is the forward force provided by an airplanes propeller, and is opposed by drag (the resistance of the air as the airplane moves through it).
An airplanes propeller creates thrust in the same way it's wings create lift: air is deflected backward, so the propeller (and the aircraft) move forward. The more powerful the engine (and bigger the propeller), the greater the thrust, and the faster the airplane can fly. Thrust is also the most important factor in determining a planes ability to climb.
Drag
Drag is the rearward-pulling force that opposes thrust, and has two components: "parasitic drag" and "induced drag".
- Parasitic Drag Parasitic drag is caused by friction between the air and an airplane's structure. The more things there are sticking out into the airflow (antennas, landing gear, bombs, drop tanks, and yes, even rivets), the higher the parasitic drag. Your plane is designed to have as little parasitic drag as possible, but the faster you go, the more there will be.
- Induced Drag As the angle of attack increases, lift pulls an airplane upward and backward. The upward component of lift is called "effective lift"; the backward component is called "induced drag". Effective lift counteracts weight to keep the airplane flying. Induced drag counteracts thrust and slows the airplane down. The slower you go (the bigger the angle of attack), the greater the induced drag. Eventually you'll need to add more power to generate the lift necessary to remain aloft.
"Torque" is a catch-all term used to describe your planes tendancy to yaw and bank in either one direction or the other at certain power settings. A fighter's powerful engine and big propeller make the effect very pronounced, especially when the throttle's on high, but the airspeed is low (as during takeoff). To counter these turning tendancies you'll need to use the rudder and ailerons, although torque can be used to your advantage in a dogfight.
What causes torque? Four phenomena:
- Reactive force When the powerful engine of a fighter plane turns the propeller in one direction, there is an "equal and opposite force" that makes the plane roll in the other direction. When your throttles high but your airspeeds low (as during takeoff), the plane will roll in a direction opposite to the rotation of the prop. This effect is most pronounced during acceleration.
- Spiraling slipstream A propellers sprialing slipstream (the air mass that the propeller "propels" behind it) hits one side of the tail and causes the nose of the plane to yaw> (rotate left or right around the vertical axis) in the same direction the reactive force causes it to roll. The result? An even stronger tendency to turn.
- Gyroscopic precession Because it's big and spins rapidly, your planes propeller behaves like a gyroscope. This makes it subject to the effects of "gyroscopic precession". When a force acts on a gyroscope, the gyroscope behaves as if the force were applied at a point 90 degrees to the direction of rotation. If your planes propeller turns clockwise (viewed from cockpit), then when the tail comes up on the take-off run the nose goes down - and the gyroscopic precession makes the plane swerve to the left.
- P factor A propeller is a bunch of small wings moving around a crankshaft. Each propeller blade produces a certain amount of thrust. When an airplane is flying at a high angle of attack, the downward-moving proeller blades have higher angles of attack and produce more thrust than the upward-moving blades. The result is "P factor" - asymmetric propller loading that creates a yawing motion.