Saturday, August 30, 2008
Rocket-powered aircraft
(see Experimental rocket powered aircraft were developed by the Germans as early as World War IIMe 163 Komet), and about 29 were manufactured and deployed. The first fixed wing aircraft to break the sound barrier in level flight was a rocket plane- the Bell X-1. The later North American X-15 was another important rocket plane that broke many speed and altitude records and laid much of the groundwork for later aircraft and spacecraft design. Rocket aircraft are not in common usage today, although rocket-assisted takeoffs are used for some military aircraft. SpaceShipOne is the most famous current rocket aircraft, being the testbed for developing a commercial sub-orbital passenger service; another rocket plane is the XCOR EZ-Rocket; and there is of course the Space Shuttle. Bell X-1A in flight
Jet aircraft
Jet aircraft make use of turbines for the creation of thrust. These engines are much more powerful than a reciprocating engine. As a consequence, they have greater weight capacity and fly faster than propeller driven aircraft. One drawback, however, is that they are noisy; this makes jet aircraft a source of noise pollution. However, turbofan jet engines are quieter, and they have seen widespread usage partly for that reason.
The jet aircraft was developed in Germany in 1931. The first jet was the Heinkel He 178, which was tested at Germany's Marienehe Airfield in 1939. In 1943 the Messerschmitt Me 262, the first jet fighter aircraft, went into service in the German Luftwaffe. In the early 1950s, only a few years after the first jet was produced in large numbers, the De Havilland Comet became the world's first jet airliner. However, the early Comets were beset by structural problems discovered after numerous pressurization and depressurization cycles, leading to extensive redesigns.
Most wide-body aircraft can carry hundreds of passengers and several tons of cargo, and are able to travel for distances up to 17,000 km. Aircraft in this category are the Boeing 747, Boeing 767, Boeing 777, the upcoming Boeing 787, Airbus A300/A310, Airbus A330, Airbus A340, Airbus A380, Lockheed L-1011 TriStar, McDonnell Douglas DC-10, McDonnell Douglas MD-11, Ilyushin Il-86 and Ilyushin Il-96.
Jet aircraft possess high cruising speeds (700 to 900 km/h, or 400 to 550 mph) and high speeds for take-off and landing (150 to 250 km/h). Due to the speed needed for takeoff and landing, jet aircraft make use of flaps and leading edge devices for the control of lift and speed, as well as thrust reversers to direct the airflow forward, slowing down the aircraft upon landing.
Propeller aircraft
Smaller and older propeller aircraft make use of reciprocating internal combustion engines that turns a propeller to create thrust. They are quieter than jet aircraft, but they fly at lower speeds, and have lower load capacity compared to similar sized jet powered aircraft. However, they are significantly cheaper and much more economical than jets, and are generally the best option for people who need to transport a few passengers and/or small amounts of cargo. They are also the aircraft of choice for pilots who wish to own an aircraft.
Turboprop aircraft are a halfway point between propeller and jet: they use a turbine engine similar to a jet to turn propellers. These aircraft are popular with commuter and regional airlines, as they tend to be more economical on shorter journeys.
Gliders
Gliders or sailplanes are aircraft designed for unpowered flight. Most gliders are intended for use in the sport of gliding and so have high aerodynamic efficiency. Lift-to-drag ratios may exceed 70 to 1. After launch, the energy for sustained gliding flight is obtained through the skillful exploitation of rising air in the atmosphere. Glider flights of thousands of kilometers at average speeds over 200 km/h have been achieved. The glider is most commonly launched by a tow-plane or by a winch. Some gliders, called motor gliders, are equipped with engines (often retractable) and some are capable of self-launching. Military gliders have been used in war to deliver assault troops, and specialized gliders have been used in atmospheric and aerodynamic research. The most numerous class of gliders are hang gliders; hang gliders generally are slower, less massive, and less expensive than sailplanes; hang gliders are generally categorized into a default use of the term "hang glider" for hang gliders that have considerable stiffening and the fully-flexible non-sparred-winged hang gliders called "paragliders".
Aircraft instruments
Instruments provide information to the pilot. They may operate mechanically from the pitot-static system, or they may be electronic, requiring 12VDC, 24VDC, or 400 Hz power systems.[3] An aircraft that uses computerized CRT or LCD displays almost exclusively is said to have a glass cockpit.
Basic instruments include:
- An airspeed indicator, which indicates the speed at which the aircraft is moving through the surrounding air.
- An altimeter, which indicates the altitude of the aircraft above the ground or above mean sea level.
- An attitude indicator, sometimes called an artificial horizon, which indicates the exact orientation of the aircraft about its pitch and roll axes.
Other instruments might include:
- A Turn coordinator, which helps the pilot maintain the aircraft in a coordinated attitude while turning.
- A rate-of-climb indicator, which shows the rate at which the aircraft is climbing or descending
- A horizontal situation indicator, shows the position and movement of the aircraft as seen from above with respect to the ground, including course/heading and other information.
- Instruments showing the status of each engine in the aircraft (operating speed, thrust, temperature, and other variables).
- Combined display systems such as primary flight displays or navigation displays.
- Information displays such as on-board weather radar displays.
Control duplication
On an aircraft with a pilot and copilot, or instructor and trainee, the aircraft is made capable of control without the crew changing seats. The most common arrangement is two complete sets of controls, one for each of two pilots sitting side by side, but in some aircraft (military fighter aircraft, some taildraggers and aerobatic aircraft) the dual sets of controls are arranged one in front of the other. A few of the less important controls may not be present in both positions, and one position is usually intended for the pilot in command (e.g., the left "captain's seat" in jet airliners). Some small aircraft use controls that can be moved from one position to another, such as a single yoke that can be swung into position in front of either the left-seat pilot or the right-seat pilot.
Aircraft that require more than one pilot usually have controls intended to suit each pilot position, but still with sufficient duplication so that all pilots can fly the aircraft alone in an emergency. For example, in jet airliners, the controls on the left (captain's) side include both the basic controls and those normally manipulated by the pilot in command, such as the tiller, whereas those of the right (first officer's) side include the basic controls again and those normally manipulated by the copilot, such as flap levers. The unduplicated controls that are required for flight are positioned so that they can be reached by either pilot, but they are often designed to be more convenient to the pilot who manipulates them under normal condition.
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