Сборник технических текстов для домашнего чтения по английскому языку. Морозова М.А. - 17 стр.

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the best airplane for accomplishing a particular mission. Since all of these perform-
ance measurements are strongly affected by differences in the weather conditions
(that is, temperature, pressure, humidity, winds) , there are some very specific and
complex mathematical processes which are used to "standardize" these values.
One of the most important considerations in flight is the balance of forces
maintained between thrust, drag, lift, and weight.
Balance of Forces
An aircraft in flight retains energy in two forms; kinetic energy and potential
energy. Kinetic energy is related to the speed of the airplane, while potential energy
is related to the altitude above the ground. The two types of energy can be exchanged
with one another. For example when a ball is thrown vertically into the air, it ex-
changes the kinetic energy (velocity imparted by the thrower), for potential energy as
the ball reaches zero speed at peak altitude.
When an airplane is in stabilized, level flight at a constant speed, the power has
been adjusted by the pilot so that the thrust is exactly equal to the drag. If the pilot
advances the throttle to obtain full power from the engine, the thrust will exceed the
drag and the airplane will begin to accelerate. The difference in thrust between the
thrust required for level flight and the maximum available from the engine is referred
to as "excess thrust". When the airplane finally reaches a speed where the maximum
thrust from the engine just balances the drag, the "excess thrust" will be zero, and the
airplane will stabilize at its maximum speed.
Notice that this "excess thrust" can be used either to accelerate the airplane to a
higher speed (increase the kinetic energy) or to enter a climb at a constant speed (in-
crease the potential energy), or some combination of the two.
Excess Thrust Energy Exchange
There are energy exchange equations which can be used to relate the rate of
change of speed (or acceleration) to the rate of change of altitude (or rate of climb) .
(These equations are introduced later.) In this way, level flight accelerations (accels.)
at maximum power can be used to measure the "excess thrust" over the entire speed
range of the airplane at one altitude. This "excess thrust" can then be used to calculate
the maximum rate of climb capability for an aircraft.
Takeoff
The takeoff is a critical maneuver in any airplane. The airplane will usually be
carrying a payload (passengers, cargo, weapons) and often a full load of fuel. The re-
sulting heavy weight means that a high speed must be reached before the wings can
generate sufficient lift, thus a long distance must be travelled on the runway before
lift-off. After lift-off, the heavy weight will result in a relatively slow acceleration to
the speed for best angle of climb.
After lining the aircraft up on the runway, the pilot applies the brakes (accom-
plished by applying pressure to the top of the rudder pedals. - each pedal controls its
respective wheel). The throttles are then advanced to military power (100% RPM).
As the engines wind up, the engines and instruments are given a "last minute" check.
(Pilots do a lot of "checks" to ensure that everything is going OK. After all, if some-
thing were to happen, you can't just pull off to the side of the road!) When everything

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