Aircraft
Analyses
Most people are familiar with the Standard Configuration, the most common
airplane design. However, recent revelations in both military and general
aviation have shown at least a slight movement toward different arrangements of
an airplane’s lift and control surfaces. These variations in aircraft structure
include the canard configuration and the flying wing. First, we must understand
the basic principles of flight before any different configurations of lift
surfaces can be discussed. In order for any object to gain lift, it must have a
force pushing it upwards which is greater than its weight. This force, called
lift, results from the differing pressures on the upper and lower surfaces of
the wing. The air that hits the leading edge of the wing separates. Part goes
over the wing, and part travels underneath it. The top of the wing curves, or is
cambered, causing the air passing over the top of the wing to go faster than the
air passing under the wing. The lower surface of the wing is relatively flat, so
air travels at, or near, its normal speed. Bernoulli’s Law says that as the
speed of gas or fluid increases its pressure decreases (Pappas 2). Therefore,
there is a greater air pressure under the wing than there is above the wing.
This greater pressure under the wing pushes the plane up. When this force
exceeds the pull of gravity on the aircraft, flight is achieved. Two other
forces affect an aircraft’s movement through the air: thrust and drag. Thrust is
the force provided by an aircraft’s power plant which pushes or pulls it forward
through the air. Drag, which counteracts thrust, is the force of wind resistance
against the aircraft. It is supplemented by various appendages on the aircraft,
such as the wings, stabilizers, and the fuselage. The less drag there is on an
aircraft, the faster and more economically it can fly. Drag can be reduced by
eliminating items which disrupt airflow. The wing, horizontal stabilizer and
vertical stabilizer of an aircraft have, at their trailing edges, control
surfaces which change the direction of flight by altering the lift
characteristics of the surface which house them. The flaps, which are designed
to increase the lift of the wings on take-off and landing, are lowered. The
increased camber of the upper surface causes the air flowing across the wing’s
upper surface to move even faster, decreasing the air pressure on the upper
surface. This increases the force on the bottom of the wing and increases the
lift. The ailerons, which control the rolling motion of the plane, shift in
opposite directions. When the airplane is to turn to the right, the aileron on
the left wing lowers, increasing the lift on that wing. At the same time, the
aileron on the right wing is raised, which creates an opposite-lift effect, and
the aircraft “rolls” to the right. The opposite is true for a left
turn. The rudder works similarly: to yaw to the right, the rudder swings right,
creating a greater pressure on the right side of the vertical stabilizer. This
causes the tail of the plane to shift to the left, and the plane pivots about
the vertical axis, pointing the nose right. The opposite is true for left yaw.
Elevators, which control the pitch of the plane, work differently for each
configuration. They will be discussed separately. Today, the Standard
Configuration is the most prevalent design of personal, commercial and military
airplanes. The main wing is located about a third- or half-way from the nose of
the aircraft, close to the center of gravity, and serves as the lateral axis.
The empennage at the tail of the plane consists of the horizontal stabilizer and
the vertical stabilizer. The horizontal stabilizer provides lateral stability
and houses the elevator, which controls the pitch of the aircraft. In the
Standard Configuration, because the horizontal stabilizer and the elevator are
aft of the lateral axis. A downward motion of the elevator increases the lift of
the airplane’s tail. As the tail rises, the plane pivots on the lateral axis,
and the nose points downward. An upward motion of the elevator decreases the
lift of the tail, pushing it downward. The aircraft pivots in the opposite
direction, causing the plane to climb. The vertical stabilizer gives
longitudinal stability and houses the rudder, which controls the aircraft’s
bearing, or yaw. The Standard Configuration is the most common and most popular
design “because a relatively small and light surface can be made to provide
control and stability over a fairly wide range of centers of gravity, with
economy of effort and a fairly modest penalty in weight (Stinton 389). The
Canard Configuration, a second arrangement of aircraft lift and stabilizing
surfaces, is named for the canard, or “forward-wing,” which is the
basis of its design. After nearly forty years of more-of-the-same aircraft
design, general aviation is suddenly breaking the mold and racing into the
future with new planes that challenge traditional thinking (Popular Science 74).
The tail-first idea is not new. Many of the gliders built and flown by aviation
pioneers such as Lilienthal and the Wrights were built on the Canard
Configuration (Stinton 151). This configuration has not been used much in the
past, but we may see more aircraft manufacturers moving to this design. The
operation of the elevators is opposite that in the Standard Configuration.
Because the elevators are forward of the lateral axis, they directly alter the
lift on the forward section of the aircraft. Down-elevator increases lift on the
nose of the airplane, which causes the plane to climb. Up-elevator has the
opposite effect. This design is being seen more and more in personal and
business aviation, mostly in the radical designs of aeronautical engineer Burt
Rutan. It is especially attractive for short-field operation because it has
better acceleration and thrust in shorter distances than Standard Configuration
aircraft with the same weight, wing, and power loadings. All of Rutan’s designs
feature a high-aspect-ratio, cambered, high-lift canard. The canard replaces the
empennage, decreases the mass and weight of the aircraft, and provides stall and
spin resistance (Rollo 32). In a stall situation, because the horizontal
stabilizer is placed forward, it stalls before the main wing does (Stinton 151).
When the horizontal stabilizer, or canard, stalls, the aircraft automatically
pitches nose-down. This causes the plane to un-stall and return to controlled
flight (Mondey 91). The canard configuration employs two lift surfaces, instead
of a single lift surface, the wing, and a tail which provides a balancing
downforce (Beechcraft 2). This downforce is subtracted from the lift on the
aircraft. The canard, however, adds to the lift of the wing (Stinton 151).
Probably the best known canard aircraft is the Beechcraft Starship, a new
corporate aircraft designed by Rutan. Gates and Rinaldo Piaggio are jointly
creating another canard corporate aircraft to provide Gates with a new aircraft
with “learjet performance and quality but costing less,” (Popular
Science 143). They decided to put the main wing aft to give more walking space
in the cabin. They used a canard design to avoid the weight of a huge tail
(Popular Science 143). General aviation is not the only field that has been
introduced to the Canard Configuration. The United States Air Force is exploring
a canard trainer, the T-46. The Navy is exploring a new breed of
fighters–post-stall aircraft–and the X-31, the first in this field employs,
among many other advanced features, a canard (Schefter 59). NASA, as well, is
exploring the efficiency of a canard on a modified A-3B Sky Warrior (Popular
Science 143). With a conventional tail, there would be a downward vector, which
reduces aircraft performance. But by putting a canard and control surfaces out
front, you get an upward force vector to balance out the nose-down moment. The
name of the game is to get as much lift as you can so you can carry as much
weight as possible (Popular Science 143). Results from the NASA research are
expected to influence both military and commercial-jet design of this decade and
the future. “The industry has been conservative for years–now we’re
pushing. These airplanes will be better than anything that exists today”
(Popular Science 143). The Canard Configuration, though it has many physical,
economical and safety advantages over the Standard Configuration, it has its
shortcomings. To cope with a center of gravity that is further aft, more keel
surface is needed for directional stability. Also, the tail weight is increased
by placing the main wing aft (Stinton 152). Essentially, the Canard
Configuration is attractive because the removal of an empennage reduces the
mass, weight, and drag of an aircraft. The canard, more importantly, provides
stall and spin resistance by providing an additional lift surface (Rollo 32).
Another airplane design that has been seen a lot lately in powered flight is the
Flying Wing. The Flying Wing design is not new, either. Hang gliders and kites
are merely smaller, un-powered versions of a flying wing design. As early as
1910, the world had seen a successful tailless airplane–the D-10, designed by
author, soldier, pilot and designer William Dunne of Britain (Wooldridge 40).
However, now that “Stealth” aircraft has become a serious need of
military forces, we have seen and heard a lot more of the “all-wing”
concept. As the name suggests, the Flying Wing is the airplane distilled to its
essence, the wing. The lack of various appendages found on conventional aircraft
greatly reduces drag (Wooldridge 39). Everything necessary for flight is
contained in a huge wing: engines, cockpit, landing gear, and all control
surfaces, as well as armament on a military aircraft. What benefit does this
have? Jack Northrop, an aeronautical engineer in the 1920’s and -30’s believed
that a flying wing “could carry any load faster, farther, and more
economically than a conventional plane,” (Hallion 93). The flying wing
functions much like a conventional aircraft. Two moving surfaces at each
trailing edge for lateral and longitudinal control and landing flaps are located
beneath the center section (Wooldridge 45). Longitudinal stability is achieved
by building decalage into the wing. That is, portions lying ahead of the center
of gravity (CG) have a larger angle of incidence than trailing portions. Because
the flying wing design is used most in military aircraft, an important question
to address is: Why is the Flying Wing design attractive for military
“Stealth” aircraft? The fact that all components are contained within
a streamlined surface contributes to a successful “Stealth” Aircraft.
There are no appendages to reflect radar beams, and the engines are recessed
within the wing with small openings. This lessens the heat produced and escapes
infrared sensors. These attributes, combined with radar-absorbing materials help
planes such as the B-2 Stealth Bomber escape radar and infrared detection at any
altitude. This paper discusses differences between three airfoil configurations.
The Standard Configuration has a main wing and its empennage aft. The Canard
Configuration adds or replaces the empennage with a forward-wing. This airfoil
reduces parasite drag by adding lift. This additional lift and reduced drag
makes a canard aircraft hard or impossible to stall. The Flying Wing is a large
self-contained wing, containing everything necessary for controlled flight
within a streamlined surface.
Bibliography
Hallion, Richard P. The Epic of Flight: Designers and Test Pilots.
Alexandria: Time-Life Books, Inc. 1983. Rollo, Vera Foster, PhD. Burt Rutan:
Reinventing the Airplane. Lanham, MD: Maryland Historical Press. 1991. Schefter,
Jim. “Hot New Shapes–Passenger Planes That Will Revolutionize
Aviation.” pp. 74-77, 143. Popular Science. June, 1984. Schefter, Jim.
“X-31: How They’re Inventing a Radical New Way to Fly.” pp 58-64.
Popular Science. February, 1989. Wooldridge, E. T. “Flying Wing.” pp
58-64. Aviation Heritage. November, 1991. The Design of the Aeroplane Hallion,
Richard P. The Epic of Flight: Designers and Test Pilots. Alexandria: Time-Life
Books, Inc. 1983. Rollo, Vera Foster, PhD. Burt Rutan: Reinventing the Airplane.
Lanham, MD: Maryland Historical Press. 1991. Schefter, Jim. “Hot New
Shapes–Passenger Planes That Will Revolutionize Aviation.” pp. 74-77, 143.
Popular Science. June, 1984. Schefter, Jim. “X-31: How They’re Inventing a
Radical New Way to Fly.” pp 58-64. Popular Science. February, 1989.
Wooldridge, E. T. “Flying Wing.” pp 58-64. Aviation Heritage.
November, 1991. The Design of the Aeroplane Hallion, Richard P. The Epic of
Flight: Designers and Test Pilots. Alexandria: Time-Life Books, Inc. 1983. Rollo,
Vera Foster, PhD. Burt Rutan: Reinventing the Airplane. Lanham, MD: Maryland
Historical Press. 1991. Schefter, Jim. “Hot New Shapes–Passenger Planes
That Will Revolutionize Aviation.” pp. 74-77, 143. Popular Science. June,
1984. Schefter, Jim. “X-31: How They’re Inventing a Radical New Way to
Fly.” pp 58-64. Popular Science. February, 1989. Wooldridge, E. T.
“Flying Wing.” pp 58-64. Aviation Heritage. November, 1991. The Design
of the Aeroplane Hallion, Richard P. The Epic of Flight: Designers and Test
Pilots. Alexandria: Time-Life Books, Inc. 1983. Rollo, Vera Foster, PhD. Burt
Rutan: Reinventing the Airplane. Lanham, MD: Maryland Historical Press. 1991.
Schefter, Jim. “Hot New Shapes–Passenger Planes That Will Revolutionize
Aviation.” pp. 74-77, 143. Popular Science. June, 1984. Schefter, Jim.
“X-31: How They’re Inventing a Radical New Way to Fly.” pp 58-64.
Popular Science. February, 1989. Wooldridge, E. T. “Flying Wing.” pp
58-64. Aviation Heritage. November, 1991. The Design of the Aeroplane Hallion,
Richard P. The Epic of Flight: Designers and Test Pilots. Alexandria: Time-Life
Books, Inc. 1983. Rollo, Vera Foster, PhD. Burt Rutan: Reinventing the Airplane.
Lanham, MD: Maryland Historical Press. 1991. Schefter, Jim. “Hot New
Shapes–Passenger Planes That Will Revolutionize Aviation.” pp. 74-77, 143.
Popular Science. June, 1984. Schefter, Jim. “X-31: How They’re Inventing a
Radical New Way to Fly.” pp 58-64. Popular Science. February, 1989.
Wooldridge, E. T. “Flying Wing.” pp 58-64. Aviation Heritage.
November, 1991. The Design of the Aeroplane Hallion, Richard P. The Epic of
Flight: Designers and Test Pilots. Alexandria: Time-Life Books, Inc. 1983. Rollo,
Vera Foster, PhD. Burt Rutan: Reinventing the Airplane. Lanham, MD: Maryland
Historical Press. 1991. Schefter, Jim. “Hot New Shapes–Passenger Planes
That Will Revolutionize Aviation.” pp. 74-77, 143. Popular Science. June,
1984. Schefter, Jim. “X-31: How They’re Inventing a Radical New Way to
Fly.” pp 58-64. Popular Science. February, 1989. Wooldridge, E. T.
“Flying Wing.” pp 58-64. Aviation Heritage. November, 1991. The Design
of the Aeroplane Hallion, Richard P. The Epic of Flight: Designers and Test
Pilots. Alexandria: Time-Life Books, Inc. 1983. Rollo, Vera Foster, PhD. Burt
Rutan: Reinventing the Airplane. Lanham, MD: Maryland Historical Press. 1991.
Schefter, Jim. “Hot New Shapes–Passenger Planes That Will Revolutionize
Aviation.” pp. 74-77, 143. Popular Science. June, 1984. Schefter, Jim.
“X-31: How They’re Inventing a Radical New Way to Fly.” pp 58-64.
Popular Science. February, 1989. Wooldridge, E. T. “Flying Wing.” pp
58-64. Aviation Heritage. November, 1991.
