Friday, May 4, 2012

3.1 UNDERSTANDING PRESSURE

  •  Pressure is defined as force per unit area. therefore, the smaller the area, the higher the pressure.
  • The SI units for pressure are Newtons per square metre (N/m2), now called Pasals (Pa) ( 1 N/m2 = 1 Pa). 
  • You can also use Newtons per square cm (N/cm2).
  • The pressure between two solid surfaces depends on two things:
                (a) the force between the surfaces
                (b) the area of contact between the two surfaces.

  • The greater the force or the smaller the area the greater the pressure.
  • The pressure of a given force increases as the surface area decreases.


Thursday, May 3, 2012

3.1 UNDERSTANDING PRESSURE : APPLICATION

APPLICATION INVOLVING HIGH PRESSURE
  • Increasing the pressure by reducing the area
  • A sharp knife has a very small surface area on its cutting edge so that high pressure can be exerted 
  • The studs on a football boot have only a small area of contact with the ground. The pressure under the studs is high enough for them to sink into the ground, which gives extra grip. 
APPLICATION INVOLVING LOW PRESSURE
  • Reducing the pressure by increasing the area
  • Skis have a large area to reduce the pressure on the snow so that they do not sink in too far.
  • A tractor moving on soft ground has wide tires to reduce the pressure on the ground so that they will not sink into the ground

Sunday, January 8, 2012

THRUST VECTOR CONTROL (TVC)


(AKSI SUKHOI MALAYISA DI UDARA: Half Loop Tumble Yaw, TVC Flat Spin, Tail Slide Maneuver, TVC Power Wind dan Spin Roll dan patukan ular tedung, Cobra)

Thrust vector control or TVC, is the ability of an aircraft, rocket or other vehicle to manipulate the direction of thethrust from its engine or motor in order to control the attitude or angular velocity of the vehicle.

In rocketry and and ballistic missiles that fly outside the atmosphere, aerodynamic control surface are ineffective, so thrust vectoring is the primary means of attitude control.

For aircraft, the method was originally envisaged to provide upward vertical thrust as a means to give aircraft vertical (VTOL) or short (STOL) takeoff and landing ability. Subsequently, it was realized that using vectored thrust in combat situations enabled aircraft to perform various maneuvers not available to conventional-engined planes. To perform turns, aircraft that use no thrust vectoring must rely on aerodynamic control surfaces only, such as ailerons or elevator; craft with vectoring must still use control surfaces, but to a lesser extent.

Thrust vectoring methods

Rockets and missiles

Thrust vectoring for many liquid rockets is achieved by gimballing the rocket engine. This often involves moving the entire combustion chamber and outer engine bell, or even the entire engine assembly including the related fuel and oxidizer pumps. Such a system was used on the saturn V and was employed on the space shuttle.

Another method of thrust vectoring used on early solid propellant ballistic missiles was liquid injection, in which the rocket nozzle is fixed, but a fluid is introduced into the exhaust flow from injectors mounted around the aft end of the missile. If the liquid is injected on only one side of the missile, it modifies that side of the exhaust plume, resulting in different thrust on that side and an asymmetric net force on the missile.

A later method developed for solid propellant ballistic missiles achieves thrust vectoring by deflecting the rocket nozzle using electric servomechanisms or hydraulic cylinders. The nozzle is attached to the missile via a ball joint with a hole in the center, or a flexible seal made of a thermally resistant material, the latter generally requiring more torque and a higher power actuation system. The Trident C4 and D5 systems are controlled via hydraulically actuated nozzle.

Some smaller sized atmospheric tactical missiles, such as the AIM-9X sidewinder, eschew flight control surfaces and instead use mechanical vanes to deflect engine exhaust to one side.