72
Every student pilot is first taught about the four forces acting upon an aircraft in
flight: weight, lift, drag and thrust. The downward force of weight must be overcome
by an upward acting aerodynamic force called lift.
The wing lifts the aircraft by producing an air pressure above the wing which
is lower than that below the wing. This lower pressure pulls or lifts the aircraft
upward. In the 1700s a Swiss mathematician named Daniel Bernoulli discovered the
principle of a venturi, or that as the velocity of a fluid increases, the pressure it exerts
on its surroundings decreases. The basis for this is in the conservation of energy of an
airstream. The potential energy of a gas is proportional to its pressure, just like a
compressed spring. As the speed of the air is increased the kinetic energy increases,
resulting in a potential energy or pressure decrease to conserve the total energy.A
wing has a curved upper surface referred to as camber. Air molecules traveling over
the top of the wing are forced to speed up by this camber in the same way air
molecules in a venturi are sped up. The increased airstream speed over the top of the
wing decreases the air pressure and produces the lift necessary to overcome weight.
In order for the airstream to be pushed over the wing, the aircraft must be
pushed through the atmosphere. On the takeoff roll, the aircraft accelerates until
reaching a speed with sufficient airflow over the wings to produce the required lift.
Hopefully this cursory explanation has answered some basic questions about
how an aircraft flies.
12.4. EXERCISES
1. Ответьте на вопросы.
1.
Is it puzzling how an aircraft made of metal effortlessly can lift hundreds of
pas sengers miles into the sky?
2.
What are the four forces acting upon an aircraft?
3.
Who discovered the principle of a venturi?
4.
What produces the lift necessary to overcome weight?
5.
What is the conservation of energy of an airstream?
2. Переведите текст 12.5. без словаря.
12.5. Техт
McDONNEL DOUGLAS F-15E Strike Eagle
Primary Mission : Air Superiority / Deep Interdiction*
The F-15E is a two seat dual role version of the Eagle capable of performing
long-range, deep interdiction, High ordnance* , air-to ground missions by day or
night and in adverse weather, while retaining its proven air-to-air capabilities.
Production F-15Es also have front cockpit* modifications that include redesigned
‘up-front’ controls*, a wide field of view heads-up display, and three CRTs*
providing multipurpose displays for improved navigation, weapons delivery and
systems operation. For tactical missions at night and in all-weather conditions, the F-
15E has advanced radar and infra-red systems. Some 60%of the F-15s structure was
