User Guide

63
Flight Instruction
62
Flight Instruction
ADVANCED AERONAUTICS:
A CLOSER LOOK AT LIFT
In the main part of this chapter, we’ve explained that lift not
only supports, but also steers, an airplane. A little more detail
about how lift is produced (and what happens if and when that
production quits!) can be very valuable - and it’ll increase your
understanding of all the airplanes simulated in FLY!
IT’S ALL IN THE CURVES:
We’ve already learned that to hold the airplane up, the wing
has to push down against the air with an equal force...but if we
look closely, it’s not really “pushing.” In fact, that’s the error made
by the first would-be flyers, who tried to use simple flat surfaces -
boards!—as wings. It wasn’t until pioneers like Lilienthal and the
Wright brothers examined the wings of birds that they realized that
the secret was in their curved shapes. Actually, Leonardo da Vinci
had figured that one out four hundred years earlier...but he was a
theorist rather than an experimenter.
It wasn’t long after da Vinci that another European, Daniel
Bernoulli, discovered that the faster a fluid moves (whether it’s air
or water), the lower its pressure will be. Here’s a simple experi-
ment: take a sheet of typing paper and hold it, by its two top cor-
ners, just below your mouth. Now blow gently over the top of the
paper. You’ll notice that it floats up to the horizontal, even though
you’re blowing across the top rather than underneath it. Why? Be-
cause the fast-moving air over the top of the paper is at low pres-
sure compared to the air underneath.
A wing works the same way: it’s not so much “pushing”
down the air below it as it’s “pulling” on the air above its upper
surface. This is why its curved surface is so important. The dis-
tance from the front of the wing to the rear (from its leading
edge to its trailing edge) is longer around the curved top than
along the relatively straight bottom. Air flowing around the
wing has to speed up over the top, thus creating lower pressure
and generating lift.
WHAT DO THE CONTROLS DO?
All fixed-wing airplanes have three primary flight controls:
ailerons, elevator, and rudder.
The ailerons are what
make the airplane bank left
and right. They’re small flaps
hinged to the rear of the wing,
near the tips (in fact, their
name means “little wings” in French), and they work in opposi-
tion: when one goes up, the other goes down. They’re connected
to the cockpit controls so that they’re operated by sideways (left-
right) movement of the stick or yoke.
The elevator is the movable portion of the horizontal tail,
and its name is something of a misnomer: although it indirectly
can affect the altitude at which an airplane flies, what it controls
directly (and very effectively) is nothing more than our old friend
angle of attack. It’s operated by forward-backward movement of
the stick or yoke: pull the control back toward you, and angle of
attack increases; push it away, and angle of attack decreases.
Note that I purposely haven’t said “the nose goes up,” “the
airplane gets slower,” or anything similar, since that depends
entirely on the initial position, or attitude, of the airplane. For
example, in the unlikely event of your being upside down, pulling
the controls would bring the nose down toward the ground while
increasing the airspeed alarmingly. A considerably more common
situation would be a steeply-banked turn; pulling the stick or yoke
would tighten the turn, but wouldn’t have much direct effect on
your altitude or speed (at least at first).
Finally, the rudder is the movable portion of the vertical tail. A
common misconception is that this is what turns the airplane. In
fact, it’s the lift from the banked wing that makes the turn; the func-
tion of the rudder is mainly to ensure that the airplane is pointed the
same way it’s going, rather like the feathers on an arrow. In an actu-
al airplane, it’s controlled by the foot pedals. Don’t worry too much
if you don’t have a set of rudder pedals for FLY!; the program can be
configured to handle rudder chores automatically. In fast, high-per-
formance airplanes, the rudder isn’t as important as in slower ones.
Most jets, such as the Hawker 800XP in FLY!, are flown “feet on the
floor” except during takeoff, landing, or engine failures.
Rudder
Aileron
Elevator