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What is the fuselage?
Can you please explain the different parts of an aircraft, such as the wing, horizontal tail, vertical tail, and fuselage? Let's start by first looking at a very basic schematic of a traditional aircraft layout, and we will add more complexity as we go. 1) Basic Components:  Basic components of an aircraft fuselage: The fuselage is that portion of the aircraft that usually contains the crew and payload, either passengers, cargo, or weapons. Most fuselages are long, cylindrical tubes or sometimes rectangular box shapes. All of the other major components of the aircraft are attached to the fuselage. Empennage is another term sometimes used to refer to the aft portion of the fuselage plus the horizontal and vertical tails. wing: The wing is the most important part of an aircraft since it produces the lift that allows a plane to fly. The wing is made up of two halves, left and right, when viewed from behind. These halves are connected to each other by means of the fuselage. A wing produces lift because of its special shape, a shape called an airfoil. If we were to cut through a wing and look at its cross-section, as illustrated below, we would see that a traditional airfoil has a rounded leading edge and a sharp trailing edge.  Definition of an airfoil engine: The other key component that makes an airplane go is its engine, or engines. Aircraft use several different kinds of engines, but they can all be classified in two major categories. Early aircraft from the Wright Flyer until World War II used propeller-driven piston engines, and these are still common today on light general aviation planes. But most modern aircraft now use some form of a jet engine. Many aircraft house the engine(s) within the fuselage itself. Most larger planes, however, have their engines mounted in separate pods hanging below the wing or sometimes attached to the fuselage. These pods are called nacelles. horizontal stabilizer: If an aircraft consists of only a wing or a wing and fuselage, it is inherently unstable. Stability is defined as the tendency of an aircraft to return to its initial state following a disturbance from that state. The horizontal stabilizer, also known as the horizontal tail, performs this function when an aircraft is disturbed in pitch. In other words, if some disturbance forces the nose up or down, the horizontal stabilizer produces a counteracting force to push the nose in the opposite direction and restore equilibrium. When in equilibirum, we say that an aircraft is in its trim condition. The horizontal tail is essentially a miniature wing since it is also made up of an airfoil cross-section. The tail produces a force similar to lift that balances out the lift of the wing to keep the plane in equilibrium. To do so, the tail usually needs to produce a force pointed downward, a quantity called downforce. vertical stabilizer: The vertical stabilizer, or vertical tail, functions in the same way as the horizintal tail, except that it provides stability for a disturbance in yaw. Yaw is the side-to-side motion of the nose, so if a disturbance causes the nose to deflect to one side, the vertical tail produces a counteracting force that pushes the nose in the opposite direction to restore equilibrium. The vertical tail is also made of an airfoil cross-section and produces forces just like a wing or horizontal tail. The difference is that a wing or horizontal tail produces lift or downforce, forces that are pointed up or down from the aircraft. Meanwhile the vertical tail produces a force pointed to one side of the aircraft. This force is called side-force. 2) Basic Control Surfaces: In addition to the wing and tail surfaces, aircraft need some additional components that give the pilot the ability to control the direction of the plane. We call these items control surfaces.  Aircraft control surfaces and axes of motion elevator: The elevator is located on the horizontal stabilizer. It can be deflected up or down to produce a change in the downforce produced by the horizontal tail. The angle of deflection is considered positive when the trailing edge of the elevator is deflected upward. Such a deflection increases the downforce produced by the horizontal tail causing the nose to pitch upward. rudder: The rudder is located on the vertical stabilizer. It can be deflected to either side to produce a change in the side-force produced by the vertical tail. The angle of deflection is usually considered positive when the trailing edge of the rudder is deflected towards the right wing. Such a deflection creates a side-force to the left which causes the nose to yaw to the right. aileron: Ailerons are located on the tips of each wing. They are deflected in opposite directions (one goes trailing edge up, the other trailing edge down) to produce a change in the lift produced by each wing. On the wing with the aileron deflected downward, the lift increases whereas the lift decreases on the other wing whose aileron is deflected upward. The wing with more lift rolls upward causing the aircraft to go into a bank. The angle of deflection is usually considered positive when the aileron on the left wing deflects downward and that on the right wing deflects upward. The greater lift generated on the left wing causes the aircraft to roll to the right. The effects of these control surfaces and the conventions for positive deflection angles are summarized in the following diagram.  Aircraft control surfaces and positive deflection angles 3) Additional Components: We've already seen the major parts of a typical plane, but a few important items were left out for simplicity. Let's go back and discuss a few of these items.  Components of an aircraft flap: Flaps are usually located along the trailing edge of both the left and right wing, typically inboard of the ailerons and close to the fuselage. Flaps are similar to ailerons in that they affect the amount of lift created by the wings. However, flaps only deflect downward to increase the lift produced by both wings simultaneously. Flaps are most often used during takeoff and landing to increase the lift the wings generate at a given speed. This effect allows a plane to takeoff or land at a slower speed than would be possible without the flaps. In addition to flaps on the trailing edge of a wing, a second major category is flaps on the leading edge. These leading-edge flaps, more often called slats, are also used to increase lift. More information on slats and flaps is available here. cabin & cockpit: Sometimes these two terms are used synonymously, but most of the time the term cockpit is applied to a compartment at the front of the fuselage where the pilots and flight crew sit. This compartment contains the control yolks (or sticks) and equipment the crew use to send commands to the control surfaces and engines as well as to monitor the operation of the vehicle. Meanwhile, a cabin is typically a compartment within the fuselage where passengers are seated. nose & main gear: The landing gear is used during takeoff, landing, and to taxi on the ground. Most planes today use what is called a tricycle landing gear arrangement. This system has two large main gear units located near the middle of the plane and a single smaller nose gear unit near the nose of the aircraft. trim tab: The above diagram illustrates a "trim tab" located on the elevator. These control tabs may be located on other surfaces as well, such as a rudder control tab or a balance tab on the aileron. Nonetheless, the purpose of all these tabs is the same. In the previous section, we discussed that the horizontal stabilizer and elevator are used to provide stability and control in pitch. In order to keep a plane in a steady, level orientation, the elevator usually has to be deflected by some small amount. Since it would be very tiring for a pilot to physically hold the control stick in position to keep the elevator at that deflection angle for an entire flight, the elevator is fitted with a small "tab" that creates that elevator deflection automatically. The trim tab can be thought of almost as a "mini-elevator." By deflecting the tab up or down, it increases or decreases the downforce created by the elevator and forces the elevator to a certain position. The pilot can set the deflection of the trim tab which will cause the elevator to remain at the deflection required to remain trimmed. Jet Engine Types Can you explain how various jet engines work, including the turbojet, turbofan, turboprop, and turboshaft? In particular, what is the difference between a turbojet and a turbofan and which is more efficient? The term "jet engine" is often used as a generic name for a variety of engines, including the turbojet, turbofan, turboprop, and ramjet. These engines all operate by the same basic principles, but each has its own distinct advantages and disadvantages. All jet engines operate by forcing incoming air into a tube where the air is compressed, mixed with fuel, burned, and exhausted at high speed to generate thrust. The key to making a jet engine work is the compression of the incoming air. If uncompressed, the air-fuel mixture won't burn and the engine can't generate any thrust. Most members of the jet family employ a section of compressors, consisting of rotating blades, that slow the incoming air to create a high pressure. This compressed air is then forced into a combustion section where it is mixed with fuel and burned. As the high-pressure gases are exhausted, they are passed through a turbine section consisting of more rotating blades. In this region, the exhausting gases turn the turbine blades which are connected by a shaft to the compressor blades at the front of the engine. Thus, the exhaust turns the turbines which turn the compressors to bring in more air and keep the engine going. The combustion gases then continue to expand out through the nozzle creating a forward thrust. The above explanation describes a simple turbojet, as illustrated below. 
Diagram of an axial-flow turbojet
The turbojet (and the turbofan) can also be fitted with an afterburner. An afterburner is simply a long tube placed in between the turbine and the nozzle in which additional fuel is added and burned to provide a significant boost in thrust. However, afterburners greatly increase fuel consumption, so aircraft can only use them for brief periods. 
Comparison of a turbojet and a turbojet with an afterburner
A further variation on the turbojet is the turbofan. Although most components remain the same, the turbofan introduces a fan section in front of the compressors. The fan, another rotating series of blades, is also driven by the turbine, but its primary purpose is to force a large volume of air through outer ducts that go around the engine core. Although this "bypassed" air flow travels at much lower speeds, the large mass of air that is accelerated by the fan produces a significant thrust (in addition to that created by the turbojet core) without burning any additional fuel. Thus, the turbofan is much more fuel efficient than the turbojet. In addition, the low-speed air helps to cushion the noise of the jet core making the engine much quieter.  Comparison of a low-bypass turbofan with long ducts and a high-bypass turbofan with short ducts Turbofans are typically broken into one of two categories--low-bypass ratio and high-bypass ratio--as illustrated above. The bypass ratio refers to the ratio of incoming air that passes through the fan ducts compared to the incoming air passing through the jet core. In a low-bypass turbofan, only a small amount of air passes through the fan ducts and the fan is of very small diameter. The fan in a high-bypass turbofan is much larger to force a large volume of air through the ducts. The low-bypass turbofan is more compact, but the high-bypass turbofan can produce much greater thrust, is more fuel efficient, and is much quieter. A concept similar to the turbofan is the turboprop. However, instead of the turbine driving a ducted fan, it drives a completely external propeller. Turboprops are commonly used on commuter aircraft and long-range planes that require great endurance like the P-3 Orion and Tu-95.  Schematic of a turboprop engine The turboprop is attractive in these applications because of its high fuel efficiency, even greater than the turbofan. However, the noise and vibration produced by the propeller is a significant drawback, and the turboprop is limited to subsonic flight only. In a typical turboprop, the jet core produces about 15% of the thrust while the propeller generates the remaining 85%. Another noteworthy variation on the turbojet is the ramjet. The idea behind this type of engine is to remove all the rotary components of the engine (i.e. fans, compressors, and turbines) and allow the motion of the engine itself to compress incoming air for combustion.  Simple schematic of a ramjet However, the price of this simplicity is that the ramjet can only produce thrust when it is already in motion. Instead of using a compressor to draw in air and compress it for combustion, the ramjet relies on the motion of the aircraft to ram air into the engine at high enough speed that it is already sufficiently compressed for combustion to occur. Since ramjets typically cannot function until reaching about 300 mph (485 km/h) at sea level, they have been rarely used on manned aircraft. However, the ramjet is more fuel efficient than turbojets or turbofans starting at about Mach 3 making them very attractive for use on missiles. Such missiles are typically launched using rocket motors that accelerate the vehicle to high-subsonic or low-supersonic speeds where the ramjet is engaged. Finally, let us talk briefly about the turboshaft, a version of the jet engine that powers nearly every helicopter built today. As the below image illustrates, the turboshaft utilizes many of the same components as a turbojet.  Schematic of a turboshaft engine Air is drawn in through an inlet, compressed by low- and high-pressure compressor blades, mixed with fuel and burned in a combustion chamber, passed through turbine blades, and exhausted through a nozzle. The key difference between the turboshaft and previously discussed engines is that the turbine not only drives the compressors, but the shaft is also connected to a gear box that drives a helicopter's rotor blades. Although the engine shaft rotates about the horizontal, the gear box contains a sequence of gears that transform that motion to a rotation about the vertical axis as required by a helicopter main rotor. Helicopters also typically operate at much lower altitudes than aircraft where dust, sand, and other debris can easily be sucked into the engine. To address this problem, most turboshaft engines are equipped with a particle separator that filters out and expels the unwanted dust before the air flow reaches the compressor.  Schematic of a turboshaft engine particle separator While the turboprop is still popular on aircraft where low fuel consumption is vital, nearly all aircraft today employ some version of the turbofan, usually high-bypass turbofans. The high thrust, low fuel consumption, and low noise levels of these engines make them well-suited to both military and commercial applications. Today, about the only use for turbojets and ramjets is in missiles. Air-breathing, long-range, subsonic missiles like the Tomahawk use turbojets since these are small, relatively low-cost systems that provide much greater range than is possible with a rocket of comparable size. Ramjets find applications on air-breathing, long-range, supersonic missiles for similar reasons. Turboshafts, of course, have displaced the piston engine as the primary powerplant used on helicopters. |