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Lounge / Jail Pinjra => Knowledge => Topic started by: garaarι ѕιngн on June 28, 2015, 09:03:55 AM

Title: Engineering World ( how stuffs works)
Post by: garaarι ѕιngн on June 28, 2015, 09:03:55 AM

                  A JET ENGINE
 A jet engine is a machine for turning fuel into thrust (forward motion). The thrust is produced by action and reaction—a piece of physics also known as Newton's third law of motion. The force (action) of the exhaust gases pushing backward produces an equal and opposite force (reaction) called thrust that powers the vehicle forward. Exactly the same principle pushes a skateboard forward when you kick backward with your foot. In a jet engine, it's the exhaust gas that provides the "kick". Let's have a look inside the engine...

How a jet engine works

1. For a jet going slower than the speed of sound, the engine is moving through the air at about 1000 km/h (600 mph). We can think of the engine as being stationary and the cold air moving toward it at this speed.

2. A fan at the front sucks the cold air into the engine.

3. A second fan called a compressor squeezes the air (increases its pressure) by about eight times. This slows the air down by about 60 percent and it's speed is now about 400 km/h (240 mph).

4. Kerosene (liquid fuel) is squirted into the engine from a fuel tank in the plane's wing.

5. In the combustion chamber,just behind the compressor, the kerosene mixes with the compressed air and burns fiercely, giving off hot exhaust gases. The burning mixture reaches a temperature of around 900°C (1650°F).

6. The exhaust gases rush past a set of turbine blades, spinning them like a win turbine blades are connected to a long axle  that runs the length of the engine. The compressor and the fan are also connected to this axle. So, as the turbine blads spin, they also turn the compressor and the fan.

8. The hot exhaust gases exit the engine through a tapering exhaust nozzle. The tapering design helps to accelerate the gases to a speed of over 2100 km/h (1300 mph). So the hot air leaving the engine at the back is traveling over twice the speed of the cold air entering it at the front—and that's what powers the plane. Military jets often have an after burner that squirts fuel into the exhaust jet to produce extra thrust. The backward-moving exhaust gases power the jet forward. Because the plane is much bigger and heavier than the exhaust gases it produces, the exhaust gases have to zoom backward much faster than the plane's own speed.

Title: Re: Engineering World ( how stuffs works)
Post by: Blaze in the Northern Sky on June 29, 2015, 04:41:35 AM

Good post for an overview of how a jet engine functions.
Thanks for sharing.

Just to add, the speed of sound is 1225 km/h or 761.2 m/h (661.5 knots), so an engine producing a speed more than that of the sound is supersonic.

Jet engines producing a flow velocity of 1.2–5.0 Mach come under the supersonic regime.

You can try posting something about the radial piston engines that were used in the old propeller passenger aircrafts and also the fighter aircrafts used during the World War era.These engines too produced enough thrust.

Cheerio!

Title: Re: Engineering World ( how stuffs works)
Post by: garaarι ѕιngн on June 29, 2015, 09:48:25 AM

Radial engine or rotary engines works same as a simple internal combustion engine works which in used in vehicles, so everybody is aware of it how it works
Radial engines are used in planes during WWI nd WWII
 The radial engine idea is very simple -- it takes the pistons and arranges them in a circle around the crankshaft The radial engine has the same sort of pistons, valves and spark plugs that any four-stroke engine has. The big difference is in the crankshaft.

Instead of the long shaft that's used in a multi-cylinder car engine, there is a single hub -- all of the piston's connecting rods connect to this hub. One rod is fixed, and it is generally known as the master rod. The others are called articulating rods. . They mount on pins that allow them to rotate as the crankshaft and the pistons move.
Earlier during WWI carburetor is not used in engines, but later is a part of fuel system in radial engines
In planes like B17 there r nine cylinders displaces 1,800 cubic inches (29.5 liters) and produces 1,200 horsepower.
Radial engines have a relatively low maximum rpm so they can often drive propellers without any use of reduction gearing.

Title: Re: Engineering World ( how stuffs works)
Post by: Blaze in the Northern Sky on June 30, 2015, 03:00:16 AM

Well the reason why I mentioned piston aviation engines was because not many people may know that the same principle and mechanism used for putting a vehicle into motion is/was also used for putting an aircraft in the air.

Radial engines came later, prior to that they used inline engines (similar to the ones used in cars) for the aircrafts.Infact some of these engines were also turbocharged, depending on the requirement.

All in all, a good insight on the radial engines and its differentiation from the inline or column engines with respect to the crankshaft.

Title: Re: Engineering World ( how stuffs works)
Post by: garaarι ѕιngн on June 30, 2015, 09:36:00 PM

                                   BULLETS

 Bullets are a bit like fireworks and they are arranged in three sections: the primer, the propellant, and the bullet proper. At the back, the primer (or percussion cap) is like the fuse of a firework: a small fire that starts a bigger one. The next section of the bullet, effectively its "main engine," is a chemical explosive called a propellant. Its job is to power the bullet through the air from the gun to the target. The front part of the bullet is a tapering metal cylinder that hits the target at high speed. It tapers to a point to help it penetrate through metal, flesh, or whatever else the target may be made from.

What happens when you fire?

Bullets are designed to be (relatively) safe until the moment when you fire them. When you pull the trigger of a gun, a spring mechanism hammers a metal firing pin into the back end of the bullet, igniting the small explosive charge in the primer. The primer then ignites the propellant—the main explosive that occupies about two thirds of a typical bullet's volume. As the propellant chemicals burn, they generate lots of gas very quickly. The gas shoots from the back of the bullet, increasing the pressure behind it, and forcing it down the gun barrel at extremely high speed (300 m/s or 1000 ft/s is typical in a handgun).

The propellant chemicals in a handgun bullet are not designed to explode suddenly, all at once: that would blow the whole gun open and very likely kill the person firing it. Instead, they are supposed to start burning relatively slowly, so the bullet moves off smoothly down the gun. They burn faster as the bullet accelerates down the barrel, giving it a maximum "kicking" force just as it comes out of the end. As the bullet emerges, the whole gun recoils (leaps backward) because of a basic law of physics called "action and reaction" (or Newton's third law of motion). When the gas from the explosion shoots the bullet forwards with force, the whole gun jolts backwards with an equal force in the opposite direction. The explosion that fires a bullet happens in the confined space of the gun barrel. As the bullet flies out of the gun, the pressure of the explosion is suddenly released. That's what makes a gun go BANG! It's a bit like uncorking a bottle of wine at much higher speed and pressure. Some bullets also make noise because they go so quickly. The fastest bullets travel at around 3000 km/h (over 1800 mph) —about three times the speed of sound. Like a supersonic (faster-than-sound) jet fighter, these bullets make shock waves as they roar through the air.

How bullets travel

Gun barrels have spiraling grooves cut into them that make bullets spin around very fast as they emerge. A spinning bullet is like a gyroscope: a sort of "stubborn" spinning wheel that always tries to keep turning the same way. If you try to tilt a gyroscope while it's spinning, it will try to resist whatever force you apply and, if you let go, it will soon tilt back the other way. This is why, when things are spinning, they are very hard to deflect from their path. We call this idea gyroscopic inertia or stability. A bullet behaves in exactly the same way: once it's spinning, it follows a straighter path as it goes through the air, so it's harder to deflect and much more likely to reach its target.

We think of bullets flying in perfectly straight lines—but nothing could be further from the truth. Several different forces act on a bullet as it goes through the air. Over very short distances, bullets do follow more or less a straight line. Over longer distances, they follow a slight downward curve because gravity tugs them toward the ground as they go along. Air resistance and the spinning, gyroscopic motion of a bullet complicate things too. Usually, because of recoil, the person firing wobbles the gun slightly when the bullet emerges. When all these factors—the bullet's motion, gravity, air resistance, recoil, and spinning—add together, they make a bullet follow a very complicated corkscrew path as it flies through the air.

Why bullets do damage

A moving object has momentum,which is the product of its mass and its velocity. The faster something moves and the heavier it is, the more momentum it has. A truck trundling along slowly has a lot of momentum because it weighs so much. Even though bullets are tiny, they have lots of momentum because they go so fast. And because they go fast, they also have huge amounts of kinetic energy, which they get from the chemical energy of the burning propellant. (Remember that kinetic energy is related to the square of an object's velocity—so if it goes twice as fast, it has four times the energy.)

Bullets do damage when they transfer their energy to the things they hit. The faster something loses its momentum, the more force it produces. (One way to define force is as the rate at which an object's momentum changes.) A rifle bullet coming to a stop in a tenth of a second produces as much force as a heavy, slow moving truck coming to rest in 10 seconds.