Page 327 - NS-2 Textbook

322 NAUTICAL SCIENCES

constant, if one element in any system of streamlined
fluid flmv is decreased, another must increase to COlU\-
terbalance it. 111is is called Benzoulli's principle. Air flow-
Angle of ing past the fuselage or over the wing of a guided missile
Attack
or aircraft forms a system to V\Thich this theorem can be
applied.
When air passes over the streamlined convex wing
of an aircraft, it must travel a greater distance than air
passing under it. Since the two parts of the airstream
reach the trailing edge of the wing at the same time, the
air that flmvs over the -wing must move faster than the air
Trailing that flows under it. According to Bernoulli's theorem,
Edge this results in a lower pressure on the top than on the bot-
tom surface of the wing. This pressure difference tends to
force the wing upward, thereby giving it lift. Since most
missiles use flat wings rather than the curved wings of
conventional aircraft they must get the necessary lift en-
An illustration of an angle of attack between the inclination of an tirely from the angle of attack.
airfoil and the oncoming airstream.
Here is an example. Consider an airplane taking off
from a runway. Before it starts rolling, its speed is zero,
Each of the forces described above is a vector quantity, and there is no drag. When its brakes are released, the
meaning something that has both magnitnde (length or force of tluust developed by its engines at full power is
size) and direction. All forces acting on a body can be unbalanced, and as a result, the plane begins to acceler-
mathematically combined by adding their vectors to form ate rapidly down the runway, in accordance with New-
the resultant or net force. The net force determines the ton's second law. As its speed increases, the lift force
motion of the body, in accordance with Newton's laws. grows rapidly by Bemoulli's theorem.
In the 1700s Daniel Bernoulli (1700-1782) postulated As its takeoff run progresses, the plane's forward ac-
that since the total energy in any isolated system remains celeration gradually decreases -while speed increases, be-

I POWERED (GUIDEO'C--<'il ... -::::::===~~B:A:Ll~':STIC I FREE-FALL) ------.-11
~ PHASE PHASE
00'
./ SECOND STAGE
/" SEPARATION
APOGEE
j1 <J NOSE FAIRING SEPARATION
/ AND JETIISONING REENTRY BODY

f FIRST STAGE SEPARATION
I __ ~ "., ~m.

---------1---------- +

ATMOSPHERE -... ......... -...
~
ARST STAGE IGNITION
LAUNCH y-: REENTRr
PHASE PHASE
~ ~[JEcnON _____ EARTH
a
!
:;;>
c=-'
\1<.>-----------4000 NAUTICAL MILES----------+j
Typical trajectory (flight path) of a sea-launched ICBM. A ballistic missile is affected by several aerodynamic forces during its flight phases
through Earth's atmosphere. While in space it is subject primarily to gravitational and inertial forces.