Now you are probably thinking that helicopters do not need to move forward in order to fly, and you are right.
This is because helicopters are "rotary wing aircraft," meaning that the rotor which is turned around rapidly by the engine s is shaped like a narrow wing and provides the Lift necessary to overcome the Weight of the aircraft. This is different than a "fixed wing" aircraft where the wings are attached to the fuselage fixed and the Thrust of the engine s moves the plane forward to generate Lift.
Tilting the rotor allows the helicopter to move forward and backward or side-to-side. Propeller Driven Planes - Propeller driven airplanes use a propeller that is turned by some type of engine. Propellers are shaped just like the wings, and also generate lift, except that the lift is forward instead of up and is called thrust.
Each propeller is made up of two or more blades. The first propellers were made of wood, but now most propellers now are made of metal. The F4U Corsair is a propeller driven aircraft. Jet Planes - Jet planes do not have propellers. Instead, they have jet engines that move the airplane forward through another physical principal discovered by Sir Isaac Newton - The resulting heat forces the gases out of the back of the tube at high speed.
In accordance with Newton's Law, an equal force is applied in the forward direction, moving the engine and the plane it is attached to forward. These are simple explanations, and the real systems are complicated machines that are designed by specially trained engineers.
Some jets also have inertial navigation systems onboard to help pilots find their way. These computer-based systems calculate the plane's position from its point of departure, by closely tracking its heading, speed and other factors after it leaves the gate.
Some aircraft also are capable of using signals from a constellation of satellites to pinpoint their position. This is known as the Global Positioning System. Commercial aircraft are increasingly using it. GPS enables aircraft to operate, with the permission of Air Traffic Control, to operate safely off predetermined airways.
This capability makes for more efficient operations and adds capacity to the aviation system. Pilots control and steer aircraft in flight by manipulating panels on the aircraft wings and tail. Those control surfaces are described in greater detail later in this chapter. In this phase of a flight, the pilot gradually brings the aircraft back toward the ground, by reducing engine power and speed, and thus the force of the lift.
The so-called final approach begins several miles from the airport. By this point, Air Traffic Control has put the aircraft in a sequence to land, carefully separating it from all other aircraft headed for, or leaving, the same airport.
The landing gear is lowered, slowing the plane further. In addition, panels at the trailing edge of the aircraft's wings, known as flaps, are manipulated to increase drag and thus reduce speed and altitude. Other panels, known as elevators, and the rudder are used as they are throughout the flight to steer the plane and keep it on the localizer heading and glideslope glidepath , the continuous radio signals the flight crew will follow to the end of the runway.
Airline aircraft generally are traveling at about miles per hour relative to the ground when they touch down. The flight crew then slows the aircraft quickly with several actions: pulling back on the throttles, raising yet another set of panels on the top of the wings, called spoilers, that disrupt airflow and increase wind resistance, reversing the thrust of the engines, and, of course, applying the brakes.
The final phase of a flight is a reverse of the first phase. The aircraft is driven at slow speed under its own power onto the taxiway and from there to a gate. Since most gates are equipped with moveable jetways, or covered ramps, aircraft generally are parked under their own power. This is the main body of an aircraft, exclusive of its tail assembly, wings and engines.
The term derives from a French word, fusele, meaning tapered, because the fuselage is the shape of a long cylinder with tapered ends. It is made of aluminum sections that are riveted together, and inside are three primary sections: the cockpit, the cabin which often is subdivided into two or three sections with different seating arrangements and different classes of service and the cargo hold.
The cockpit is the most forward part of the fuselage and contains all the instruments needed to fly the plane. Sometimes referred to as the flight deck, the cockpit has seats for the pilot and co-pilot; a flight engineer, on some planes; and seats for one or two observers that could be from the airline itself, or from FAA. The cockpit is off limits to passengers during flight and to flight attendants during takeoffs and landings. The cabin is the section of the fuselage behind and below in the case of the double-deck Boeing the cockpit, where an airline carries passengers, freight, or both, in the case of a combination carrier.
A typical passenger cabin has galleys for food preparation; lavatories; one or more seating compartments, closets and overhead bins, for stowing baggage, coats, and other things carried onto the plane by passengers; and several doors to the outside, most of which are used only for emergency evacuations. The number of exits is determined by the number of seats. Small jets carry about 60 passengers, the larger ones like the Boeing can carry more than This is the area of the fuselage below the passenger deck where cargo and baggage are carried.
It is basically the lower half of the fuselage cylinder. It is pressurized, along with the rest of the fuselage, and has heating systems for areas designated for the carriage of live animals. Aircraft also have ventilation systems that force air into these areas.
Access to the cargo holds is through doors in the belly of the aircraft. There is no access from the cabin area. The wings are the airfoil that generates the lift necessary to get and keep, an aircraft off the ground. Like the fuselage to which they are attached, they are made of aluminum alloy panels riveted together. The point of attachment is the aircraft's center of gravity, or balance point.
Most jet aircraft have swept wings, meaning the wings are angled back toward the rear of the plane. Swept wings produce less lift than perpendicular wings, but they are more efficient at high speeds because they create less drag. Wings are mostly hollow inside, with large compartments for fuel. On most of the aircraft in service today, the wings also support the engines, which are attached to pylons hung beneath the wings.
Wings are designed and constructed with meticulous attention to shape, contour, length, width and depth, and they are fitted with many different kinds of control surfaces, which are described below. The empennage is the tail assembly of an aircraft, consisting of large fins that extend both vertically and horizontally from the rear of the fuselage.
Their primary purpose is to help stabilize the aircraft, much like the keel of a boat. In addition, they also have control surfaces built into them that help the pilots steer the aircraft. The control surfaces attached to an aircraft's wings and tail alter the equilibrium of straight and level flight when moved up and down or left and right.
They are manipulated from controls in the cockpit. In some planes, hydraulic lines connect the cockpit controls with these various exterior panels. In others, the connection is electronic. The rudder is a large panel attached to the trailing edge of a plane's vertical stabilizer in the rear of the plane. It is used to control yaw, which is the movement of the nose left or right. The rudder is used mostly during takeoffs and landings to keep the nose of an aircraft on the centerline of the runway.
It is manipulated via foot pedals in the cockpit. To take advantage of these pressure differences, Einstein proposed an airfoil with a bulge on top such that the shape would increase airflow velocity above the bulge and thus decrease pressure there as well.
Einstein probably thought that his ideal-fluid analysis would apply equally well to real-world fluid flows. He brought the design to aircraft manufacturer LVG Luftverkehrsgesellschaft in Berlin, which built a new flying machine around it. Contemporary scientific approaches to aircraft design are the province of computational fluid dynamics CFD simulations and the so-called Navier-Stokes equations, which take full account of the actual viscosity of real air.
Still, they do not by themselves give a physical, qualitative explanation of lift. In recent years, however, leading aerodynamicist Doug McLean has attempted to go beyond sheer mathematical formalism and come to grips with the physical cause-and-effect relations that account for lift in all of its real-life manifestations.
McLean, who spent most of his professional career as an engineer at Boeing Commercial Airplanes, where he specialized in CFD code development, published his new ideas in the text Understanding Aerodynamics: Arguing from the Real Physics. Considering that the book runs to more than pages of fairly dense technical analysis, it is surprising to see that it includes a section 7. I was never entirely happy with it. Where these clouds touch the airfoil they constitute the pressure difference that exerts lift on the airfoil.
The wing pushes the air down, resulting in a downward turn of the airflow. In addition, there is an area of high pressure below the wing and a region of low pressure above. It is as if those four components collectively bring themselves into existence, and sustain themselves, by simultaneous acts of mutual creation and causation. There seems to be a hint of magic in this synergy. And what causes this mutual, reciprocal, dynamic interaction?
McLean says no: If the wing were at rest, no part of this cluster of mutually reinforcing activity would exist. But the fact that the wing is moving through the air, with each parcel affecting all of the others, brings these co-dependent elements into existence and sustains them throughout the flight.
Soon after the publication of Understanding Aerodynamics , McLean realized that he had not fully accounted for all the elements of aerodynamic lift, because he did not explain convincingly what causes the pressures on the wing to change from ambient.
In particular, his new argument introduces a mutual interaction at the flow field level so that the nonuniform pressure field is a result of an applied force, the downward force exerted on the air by the airfoil.
There are reasons that it is difficult to produce a clear, simple and satisfactory account of aerodynamic lift. Some of the disputes regarding lift involve not the facts themselves but rather how those facts are to be interpreted, which may involve issues that are impossible to decide by experiment.
Nevertheless, there are at this point only a few outstanding matters that require explanation. Lift, as you will recall, is the result of the pressure differences between the top and bottom parts of an airfoil. We already have an acceptable explanation for what happens at the bottom part of an airfoil: the oncoming air pushes on the wing both vertically producing lift and horizontally producing drag. The upward push exists in the form of higher pressure below the wing, and this higher pressure is a result of simple Newtonian action and reaction.
Things are quite different at the top of the wing, however. A region of lower pressure exists there that is also part of the aerodynamic lifting force. We know from streamlines that the air above the wing adheres closely to the downward curvature of the airfoil. This is the physical mechanism which forces the parcels to move along the airfoil shape. A slight partial vacuum remains to maintain the parcels in a curved path. This drawing away or pulling down of those air parcels from their neighboring parcels above is what creates the area of lower pressure atop the wing.
But another effect also accompanies this action: the higher airflow speed atop the wing. But as always, when it comes to explaining lift on a nontechnical level, another expert will have another answer.
But he is correct in everything else. The problem is that there is no quick and easy explanation. Drela himself concedes that his explanation is unsatisfactory in some ways. So where does that leave us? In effect, right where we started: with John D.
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