|From:||R Andrew Hayden <rahayden@*****.WEEG.UIOWA.EDU>|
|Date:||Sat, 30 Jan 93 22:13:49 CET|
(c) 1990 Grolier Electronic Publishing, Inc.
The development of the airplane and other heavier-than-air craft has
had the most far-reaching effects of any 20th-century invention. Although
many scientific disciplines are involved in the rapid advances in aviation
technology, none is as important as the aircraft itself. In this article
the anatomy of an airplane is examined along with recent developments in
such unconventional aircraft as helicopters. Basic principles of flight
can be found in AERODYNAMICS; the history of airplane development and a
description of contemporary air transportation are the subjects of
AVIATION and AIRPORT. Lighter-than-air craft are discussed in AIRSHIP.
The first powered, controllable aircraft, Orville and Wilbur WRIGHT's
flying machine, demonstrated in its structure the same basic principles of
flight as do today's high-flying jets. The wings, or airfoils, of the
original 1903 Wright Flyer resembled a box kite. A small pair of wings,
called a canard, was located forward of the main wings and provided
control about the pitch axis, allowing the aircraft to climb or descend.
The canard performed the same function as the elevators that are attached
to the horizontal stabilizers on most modern aircraft (and the device is
increasingly used again today on small, experimental aircraft).
Controlled, coordinated turns in the air were achieved through a method
called "wing warping," which deflected the rear, or trailing, edges of the
wing and rudder. With no cockpit, the pilot lay prone over the wing in a
cradle arrangement and moved his body from side to side to actuate the
controls that effected wing warping and changed the plane's direction.
The Wright Flyer was an extremely difficult aircraft to fly because
it was statically unstable: it could not "fly by itself" but had to be
constantly controlled by the pilot. European inventors believed that an
aircraft should be inherently stable, and they soon improved upon the
Wright brothers' design by developing dynamically stable and controllable
aircraft that were safer and easier to fly. The concept of static
stability has carried over to virtually all aircraft designs--although
recent developments in fighter aircraft, such as the General Dynamics
F-16, show that aerodynamically unstable aircraft have some advantages in
The success of any one of the thousands of different craft made since
the Wright brothers' first flying machine depended on the quality of
research, design, engineering, and manufacturing used to produce it. By
the time World War II began, the aviation industry had accumulated enough
experience in aerodynamics, materials, and structures to ensure uniformity
in aircraft development. As a result, most modern aircraft exhibit many
structural similarities. They are almost always monoplanes--single-
rather than double-winged. They are made of metal, are powered by one to
four jet or reciprocating engines, and are supported on the ground by
retractable landing gear.
ANATOMY OF THE AIRPLANE
The main structural components of modern aircraft are the fuselage;
wings; empennage, or tail surfaces; power plant; and landing gear, or
The fuselage is the main body structure to which the wings, tail,
landing gear, and power plants are attached. It contains the cockpit or
flight deck, passenger compartment, cargo compartment, and--in the case of
fighter aircraft--the engines and fuel tanks.
The wing is the most important lift-producing element of an aircraft.
Wing designs vary, depending on the aircraft type and purpose.
Propeller-driven aircraft normally have an all-metal straight wing with a
thick camber, or curvature. Jet transports have swept-back wings of
medium camber that lower aerodynamic drag and improve performance at high
airspeeds. Both straight and swept-wing aircraft normally have ailerons
attached to the outermost trailing edges of the wing. These ailerons
raise and lower in opposition to one another, to increase or decrease lift
on their respective wing in order to facilitate turning the aircraft. The
wing also has flaps along the trailing edge, inboard of the ailerons.
Flaps increase aerodynamic lift and drag and are used during takeoff and
landing to increase lift at low speeds. Modern swept-wing transport
aircraft also have high lift devices called leading-edge slats, which
extend in conjunction with the flaps to further increase the lifting
capability of the wing.
An aircraft flies when the lift, or upward force generated by the
wing, increases to a value larger than the aircraft's total weight. The
most critical element in a wing's ability to produce lift is its
cross-sectional shape. Early aerodynamic research on kites and gliders
indicated that a flat plate would produce lift, but even more lift could
be produced if the plate was inclined slightly into the wind. If the
leading edge of the flat plate was rounded and the trailing edge tapered
to streamline the wing, drag could be reduced. By increasing the camber
of the top surface of the wing, while flattening the lower surface, lift
could be dramatically improved. Wind tunnels, which are used extensively
in airfoil research, have facilitated the compilation of a large amount of
data on airfoil types and design.
The tail, or empennage, provides stability and control for the
aircraft and is mounted on the aft portion of the fuselage. It consists
of two main parts: the vertical stabilizer, or fin, to which the rudder
is attached; and the horizontal stabilizer, to which the elevator is
connected. The rudder is used in conjunction with the ailerons to make
coordinated turns, while the elevator is used to climb or descend. The
horizontal stabilizer is sometimes mounted high on the vertical
stabilizer, as is the case with the DC-9 and Boeing 727. The new Boeing
757 and 767 have the horizontal stabilizer attached to the rear section of
The many aircraft propulsion systems include those which drive a
PROPELLER, primarily reciprocating and turbine (turboprop) engines; and
propellerless systems that use the energy of rapidly expanding gases as a
propulsive force (see JET PROPULSION). The turbojet and the turbofan--a
turbojet modification--are the most widely used commercial jet engines,
and the reciprocating engine is still used extensively in light general
aviation aircraft. Jet engines are normally attached to the wing or aft
fuselage on pylons, but occasionally they are imbedded in the wing root
next to the fuselage. On many fighter-bomber aircraft they are mounted in
the fuselage in order to reduce aerodynamic drag and improve performance.
Engine-propeller combinations on single-engine aircraft are usually
located in the nose, or forward-most, section of the fuselage and pull the
aircraft through the air. When two or more engine-propeller combinations
are used, they are mounted on the wing, but forward of the leading edge.
"Pusher"-type aircraft have the engine mounted in the rear section of the
fuselage. Several aircraft designs utilize two engines, one pushing and
With respect to performance, turbojet engines operate most
efficiently at high altitudes (above 7,600 m/25,000 ft); turboprops at mid
altitudes (4,500-7,600 m/15-25,000 ft); and reciprocating engines at low
altitudes (sea level to 4,500 m/15,000 ft).
Fixed gear consists of a simple design of struts, wheels, and brakes
that is not retractable into the wings or fuselage. It is usually found
on light aircraft of simple design. The static nature of fixed gear
reduces the probability of landing gear problems, but it creates increased
drag on a plane in flight. Retractable gear is used on more complex
aircraft. Since it reduces drag, it increases range significantly.
The relatively simple controls on a light, general aviation airplane
govern the speed of the craft and its direction, both on the ground and in
the air. The control wheel at which the pilot sits may be pushed forward
or pulled back to move the tail elevators; pushing forward causes the
plane to nose down. The control wheel also alters the position of the
ailerons. The movements of the rudder are controlled from foot pedals in
front of the pilot's seat; the pedals activate the wheel brakes when the
plane is on the ground. Wing flap controls are usually powered, either
hydraulically or by electric motors. Engine thrust, and thus airplane
speed, is controlled by a throttle.
Many of today's new craft are heralded as innovations, although some
are old, reliable concepts wrapped in new packaging. Hang gliders, for
example, operate on the same principles as the early gliders developed by
such 19th-century aerodynamicists as Sir George Caley and Otto LILIENTHAL.
The wood frames and heavy fabric coverings of the original gliders have
been replaced by lightweight aluminum, fiberglass, and synthetic fibers.
Design of the modern hang glider was evolved from research at the National
Aeronautics Space Administration (NASA) into spacecraft reentry.
The GLIDER, or sailplane, has the same basic structure as other
"heavier than air" machines but does not use a power plant. Instead, it is
towed into the air by another aircraft and released at an altitude that
permits it to soar along the "thermals," the columns of warm air that help
keep it aloft. Gliders normally have a thin fuselage and very long wings
with a narrow width, or chord. Many of the aerodynamic characteristics of
the glider have been incorporated into high altitude reconnaissance
aircraft, such as the U-2 and the RB-57 operated by the U.S. Air Force.
Research into glider aerodynamics continues today at NASA and military
Short takeoff and landing aircraft (see STOL) have gained popularity
in recent years as air transportation has changed its emphasis from speed
to efficiency. De Havilland Aircraft in Britain has developed the DHC-7,
a four-engine STOL aircraft that requires only a very short runway for
takeoff and landing. It utilizes advanced light-weight structural
materials, new improved engines, and high lift devices to give it its STOL
capability. An economical airplane to operate, it is used by many small
commuter and local service airlines around the world.
VTOL and V-STOL Aircraft.
Vertical takeoff and landing aircraft (see VTOL), which include
HELICOPTERS, are still being developed for commercial and military use.
For many years the military has utilized helicopters with great success on
a variety of missions: medical evacuation, supply, troop transport,
reconnaissance, attack. Industrial helicopters transport materials and
personnel to and from areas where no landing strip is available to
accommodate a fixed-wing aircraft. Some aircraft combine vertical and
short takeoff and landing (V/STOL) capabilities. The propellers, the
craft's power plants, or the wings themselves can tilt upward for takeoff
and landing, but reverse to a horizontal position for flight. The
Harrier, a British fighter plane, achieves vertical takeoff by rotating
the exhaust nozzles of its jet engines downward in what is called a
Airships, or Blimps.
The high price of aircraft fuel has inspired a new interest in
lighter-than-air AIRSHIPS, which use relatively little fuel and offer the
promise of great economy. Some analysts feel that 10 to 15 small,
effective airships could be built for the price of one jumbo jet. One of
these craft might be capable of airlifting 1,000 tons of cargo or a
passenger load greater than that of a jumbo jet, at speeds of up to 200
miles per hour. It could operate at one-third the cost of a passenger
liner and would not require a large airport for takeoff and landings. In
addition, the airship is a quiet craft, and--unlike the jet--its exhausts
are comparatively nonpolluting.
Supersonic and Hypersonic Planes.
Supersonic transports, or SSTs, aircraft that can fly faster than the
speed of sound, have been used by the military for many years. Commercial
supersonic flight has been limited to the CONCORDE, built by the British
and French in 1976, which has proved to be a commercial failure in large
part because of the vast amounts of fuel it consumes. The Russians have
also built an SST, the TU-144, but it was not a successful design and was
withdrawn from service after several disastrous crashes.
Occasionally, aviation futurists speak of developing a hypersonic
transport that would travel beyond the stratosphere at speeds in excess of
8,000 km/h (5,000 mph); given the price of fuel, however, it is doubtful
that this type of aircraft will be developed in the near future.
Small aircraft made from ultralight, superstrong materials are
increasing the range of present-day aeronautical technology. The current
interest in ultralight planes began with the surge in popularity of the
hang glider; a hang glider equipped with a small golf-cart engine and a
propeller (1976) was the first member of this new generation of aircraft.
The enthusiasm for ultralights came originally from a few engineers who
manufactured make-it-yourself kits for home builders, and from the kit
buyers who found that they could make their own planes for a cost as low
as a few thousand dollars.
Some of the new ultralights resemble the earliest experimental
aircraft. Others incorporate the most advanced aerodynamic
shapes--achieved by computer modeling--and the newest materials: carbon
fiber, kevlar, fiberglass-and-epoxy laminates, plastic foams. Design
innovations include the rebirth of the Wright brothers' canard, which now
takes the form of a second wing and acts to maintain lift; "winglets,"
vertical fins on the wing ends that increase wing efficiency; and
rear-mounted, or tail, propellers that provide greater speed and
stability. Ultralights range in cruising speed from 50 to upward of 320
km/h (30 to 200 mph). Some can reach altitudes of 4,300 m (14,000 feet).
World records achieved by ultralights include the 1986 triumph of the
Voyager, whose hollow plastic body holds four tons of fuel. With two
pilots, the Voyager flew around the world nonstop in nine days.
Ultralight airplanes also figure in experiments with human
powered-flight (see FLIGHT, HUMAN-POWERED), first successfully achieved in
1977 by the 35-kg (77-lb) Gossamer Condot.
Map reading and "dead reckoning"--manual speed and distance
calculations--were the principal methods of navigation during the pioneer
days of aviation, when a sudden change in weather combined with inadequate
charts or maps could result in a forced landing or crash. One of the
first reliable radio navigation aids was the Non-Directional Beacon, a
radio signal that could be picked up by a cockpit device and used as a
checkpoint to verify that the aircraft was on course. VOR (Very High
Frequency Omni Directional Range) and TACAN (Tactial Air Navigation) were
developed by the military and combined into the present-day VORTAC system
that provides the majority of checkpoints that mark today's airway system,
although increased airway congestion will necessitate a modernization of
Among the new navigation technologies that are or will soon be used
by commercial aviation, Area-Navigation, or R-Nav, is an on-plane system
using computers, dopplers, and inertial navigation to produce a
self-contained navigational system that needs no ground-based signals as
reference points. Omega, developed originally for ships, uses Very Low
Frequency radio beam sent out by eight ground-based stations located
across the globe. The signals can be picked up by any plane equipped with
Omega receivers. The Global Positioning Satellite system uses a number of
earth-orbiting satellites to provide two- or three-dimensional fixes
(including altitude). Although confined to military planes at present,
GPS will be operational for civilian use in the near future and will allow
pinpoint navigational accuracy at any location in the sky.
All of these new systems permit the pilot to do his or her own
navigation, so that navigation officers are no longer needed for most
commercial and military flights.
Fifty percent of all fatal air accidents occur during the approach
and landing phase of flight, and it is imperative that the most precise
navigational aids be utilized during this critical period. The ILS, or
Instrument Landing System, is the best navigational aid available. An
airport ILS transmits several electronic signals to the pilot of an
approaching plane. These define the approach course and glide slope--the
angle of descent that must be used. The MLS, or Microwave Landing System
now being installed at many airports, is similar to the ILS but allows
curved approaches to be flown to the runway, alleviating the noise and
congestion problems that plague the modern jet airport.
RADAR is used by an airport's Air Traffic Control to separate
aircraft and vector them to the airport for landing. Aircraft may utilize
radar as a navigation aid, and new radars now being used on some
commercial aircraft also have the capability of detecting turbulence.
Power, performance, and navigational instruments are used by the
pilot to evaluate the well-being of the aircraft and to check its course.
The power instruments check engine performance, power output, and
airspeed. The TACHOMETER is the basic power-indicating instrument. Jet
aircraft use engine-pressure ratio gauges to determine thrust output. On
piston-powered aircraft manifold pressure gauges measure the pressure
under which the fuel-air mixture is supplied to the engine. Turboprop
aircraft measure power output on a torque gauge that monitors the power
available at the prop shaft. All aircraft have instruments that check oil
temperature and pressure and fuel flow. The electrical and hydraulic
systems are also monitored with gauges and caution lights.
Performance instruments show how well and at what altitude the
aircraft is flying. They include the artificial horizon, a
gyroscope-mounted device that shows the pilot the plane's relation to the
real horizon; the altimeter and vertical velocity gauges, which indicate
height above mean sea level and the rate of climb or descent; and the
airspeed indicator. A turn-and-bank indicator and an accelerometer, or G
meter, keep the pilot informed as to the direction of turn and the
loading, or strain, on the aircraft. (On some military aircraft,
accelerometers are also used in inertial guidance systems to detect
The location of all these instruments in the cockpit is vital to the
pilot's ability to assess craft conditions quickly and accurately.
Instrument design and location is a science in itself and is constantly
undergoing study. The "electronic cockpitm" or EFIS (Electronic Flight
Information System), a computerized instrumentation array that includes
the presentation of flight information via television screens, is
revolutionizing the way flight instruments are used. Its introduction has
caused some difficulty because it requires a change in habit patterns; in
the long run, however, it will simplify cockpit design and enable the
pilot to make better decisions in critical situations involving mechanical
failure, weather avoidance, or navigaitonal problems. The new Boeing 757,
the 767, and the European Airbus A-310 are all being equipped with the
J. Michael Jobanek
Anderson, John D., Jr., Introduction to Flight: Its Engineering and
History (1978); Bowers, Peter M., Unconventional Aircraft (1984);
Coombs, Charles, Ultralights: The Flying Featherweights (1984); Jerram,
M., Classic Aircraft (1981); Markowski, Michael A., Ultralight Aircraft
(1981); Montgomery, M. R., A Field Guide To Airplanes of North America
(1984); Nayler, J. L., Aviation: Its Technical Development; (1965);
Stinton, Darrol, The Anatomy of the Aeroplane (1980); Swanborough, Gordon,
Civil Aircraft of the World, rev. ed. (1980); Taylor, J. W. R., ed.,
Jane's All the World's Aircraft (annual).
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