A rocket is a vehicle or projectile that movers by exerting a direct push. The term is derived from the Italian word “rocchetta” meaning spindle. Engineers refer to the rocket as one of the three types of non-air breathing engines, the other two being the electric motor and the atomic reactor. Of these, only the rocket depends on a simple chemical reaction, namely, the combustion of a fuel. This does not require external air because the oxygen needed is taken along.
The burning of the fuel results in the generation of a large quantity of hot exhaust gases which are expelled to the rear to create a recoil similar to the recoil of a gun being fired. But whereas the latter lasts for only a fraction of second, the recoil, called the thrust lasts for a considerable time – as long a the rocket has fuel to burn.
As it was first pointed out by Sir Isaac Newton during the latter part of the 17th Century, the reaction does not depend on the surroundings of the device. Nevertheless the surroundings do have some influence. The amount of the thrust, usually expressed in pounds, depends on both the quantity of the gases generated and on the speed, relative to the rocket, with which they are expelled. Since external air exerts some pressure against the exhaust gases, it reduces the speed with which they emerge. Hence the thrust of a given rocket is higher in a vacuum than in air.
TYPES OF ROCKET FUEL
WATER ROCKETS:
Air
Water These are also similar to other rocket engines but water is used as fuel and air under high pressure is used as oxidizer. The rocket flies because of the simple law that says, “for every action, there is equal and opposite reaction”. Water under high pressure is released through a small opening at the bottom of the rocket.
Pin (removable)
Pumped used to pump air into rocket
LIQUID FUEL ROCKETS: In a liquid-fuel rocket the arrangement is more complicated because normally the fuel and the oxidizer are carried in two separate tanks. Normally the two tanks are placed above each other in a standing rocket but there have been designs in which the tank for one of the two liquids formed the core of the other tank.
If the liquid-fuel rocket is fairly small, the two liquids are forced into the combustion chamber by gas pressure. The fuel tanks have to be strong enough to withstand such pressure and are therefore quite heavy. In large rockets, tanks weight can be saved by making the tanks thin and light and adding fuel pumps to force the liquid under pressure into the combustion chamber. The normal arrangement is to have the pump for the fuel on one side, the pump for the oxidizer on the other side, and a turbine, which drives both of them, in the middle. In modern rocket engines the fuel that drives the turbine is the same fuel that propels the rocket. During the early stage of rocket development, the turbine had its separate fuel tank holding concentrated hydrogen peroxide that it was decomposed into steam to drive the turbine.
A liquid-fuel rocket then, consists of the fuel tank, oxidizer tank, fuel-pump assembly and rocket motor composed of combustion chamber and exhaust nozzle. This device may be used for assisting aircraft take-off or for propelling a rocket sled. But before it can fly, a stabilizing device, such as fins and a nose cone have to be added.
SOLID-FUEL ROCKETS
In the past the propelling charge was often fashioned into a powder stick, which was suspended with wires or metal clamps inside the tube. It was called an unrestricted burning charge because the freely suspended stick burned naturally along its whole length and all around its periphery. Since about 1950 such unrestricted burning charges are no longer used. Instead the charge completely fills the available space in the tube.
If a very powerful thrust is desired, the charge has a center hole, and it is ignited inside this hole. Naturally, it is consumed quickly, a 1, 200lb charge is used up in as little as 3 seconds. If less thrust maintained for a longer time is desired, as in rocket units assisting the take-off of an aircraft, the charge is made solid, and it burns only in cross section. Such charges are called “cigarette burners” because they burn evenly like cigarettes from one end to the other. The ignition of all solid-fuel rockets is accomplished by means of a small silk bag filled with ordinary black gunpowder. An electric igniter, a glowing wire that ignites a chemical compound similar to a match head, is located inside the bag. When the firing button is pressed the glow wire ignites the special compound, the compound ignites the black powder, and the flame of the black powder ignited the rocket charge
