The History of Aerodynamics in Aviation

Running Head: The History of Aerodynamics in Aviation 1

The History of Aerodynamics in Aviation

Joseph A Cooper #22002407

Liberty University

The History of Aerodynamics in Aviation 2

Abstract

This paper explores the roles of various men throughout history who had an impact on modern

aerodynamics. Since aerodynamics is a sub branch of physics, the paper begins with some of the

first physicists and progresses as more knowledge is attributed to mechanics, dynamics, fluid

flow, and aerodynamics respectively. The essay focuses primarily on the factors and

advancements in science, mathematics, and experimentation prior to the first powered flight by

Orville and Wilbur Wright. Thirteen articles from the congress legislated website Centennial of

Flight are referred to as separate sources. The 1998 legislated act provides no date for individual

articles thus all articles are cited with the date last updated (August 28, 2009) at the time of

research. Much research was conducted for relevant events well after the first

powered flight (1903) but was excluded from this paper for the sake of brevity.

Keywords: aerodynamics, fluid dynamics, history, aviation, pressure, viscosity, laminar


The History of Aerodynamics in Aviation

Aerodynamics, in its scientific form, is a sub-branch of mechanics. Aerodynamics only

emerged in the last 200 years as a result of scientific and technological advances. However, the

roots of aerodynamics began more than 2,000 years ago when Greek philosophers first

postulated the elements of fluid dynamics. As humanity’s curiosity and capability increased,

theorists began to discover the underlying principles that would later be the scientific foundation

of flight characteristics. From concepts to experimentation, from first flight to supersonic flight;

many men throughout history had a profound impact on what is considered today as the basis of

all flight; aerodynamics.

The primary roots of physics go back to the Greek philosopher Aristotle, who over 2,000

years ago proposed the theories of continuum and resistance (Aristotle, 199). Continuum

assumed that the mass of a fluid was not divisible, as opposed to atomic structure theory. This

would prove valuable in understanding elementary fluid flow concepts such as resistance. In the

context of a falling stone, the philosopher said that because of the nature of air, the motion of the

force impregnating the air would also produce an upward motion, what is now know as air

resistance or drag (Aristotle, 199).

Archimedes some 100 years later would utilize Aristotle’s continuum theory to postulate

on the pressures exerted by a fluid on an object. He assumed a fluid would exert an equal

pressure across an object if fully submerged. Archimedes stated in his book On Floating Bodies,

“[an object’s] parts is thrust by the fluid which is above it in a perpendicular direction if the fluid

be sunk in anything and compressed by anything else” (as cited in Heath, 1897, p. 253). Because

the fluid exerts an equal pressure on the object Archimedes was also able to consider how a


pressure gradient may force motion on an object. Though these principles are often taken for

granted today, they are the cornerstones of modern aerodynamics. The simple fact that an equal

pressure is exerted on an airfoil has a profound impact on the development of lift.

Despite numerous myths of flying men and beasts throughout history, it wasn’t

until much later in about 875 A.D. that anyone seriously considered the concept of flight. Ibn

Firnas is said to be the first man to attempt to fly the scientific way. Not much is known of the

Moorish daredevil but it is very likely that his attempts to fly with a pair of wings resembling a

bird inspired two highly influential men of aerodynamics; Otto Lilienthal and Leonardo da Vinci.

Leonardo da Vinci is infamous for his many contributions during the European

Renaissance. One of which was his treatise called “Codex on the Flight of Birds” in which he

systematically surveyed the flight and anatomy of flying creatures. Though he likely never flew,

he applied his findings to several aircraft designs. Perhaps the most important thing he

discovered was related to the physics of flight. Da Vinci said, “When a bird which is in

equilibrium throws the centre of resistance of the wings behind the centre of gravity, then such a

bird will descend with its head down” (as cited in Bradshaw, 1895, para. 4). This is an extremely

important distinguishment; the way an aircraft is able to change its direction is by altering either

the center of pressure (resistance) or center of gravity. This principle also would be highly used

by aviation pioneers in the 19th century such as Otto Lilienthal.

Before men could actually test proposals such as a center of pressure they had to

understand the more basic concepts such as air resistance. According to Johnston (2009),

Galileo Galilei expanded on Archimedes concepts in order to find that the magnitude of


resistance of a fluid on an object depends directly on the density of said fluid. Galileo also

proposed some rudimentary thoughts of inertia but they were mainly shaped by his predecessor.

The foundation of aerodynamics being rudimentarily in physics, one of the most

important physicists was Sir Isaac Newton. According to Tietjens (1934), Newton proposed

the first law of resistance. Overall the law is still applicable in context of motion

due to inertia. He developed this law in response to his momentum theorem, which

states: “the force exerted by the fluid on the body is equal to the rate of change of momentum in

the fluid due to the presence of the body” (Tietjens, 1934, p. 86). Unfortunately,

Newton’s simple formula did not adequately describe the experimental data

gathered because he assumed the fluid contained particles with no dimension yet

had mass. Since his molecular description was incorrect, man would have to wait

another hundred years before a better description of fluid flow and drag was

discovered.

Newton’s discoveries began a new era for the slowly progressing state of aerodynamics.

The primary mechanics of fluid flow were essentially understood which led to a departure of

classical physics into a new age of discovering the nuances of fluid dynamics. Daniel Bernoulli

was the first to delve deep into these nuances. It was in his book Hydrodynamica that he

published his findings on the relation between velocity and pressure of a fluid flow (Calero,

2008). It is this chapter in which the highly aviation dependent Bernoulli equations originate.

This book is also where the word “hydrodynamics” was coined (Calero, 2008). It is thanks to

Bernoulli that many aviation components exist today using the venturi such as the pitot tube,

carburetor, flight instruments, and of course, the wing.


One of Bernoulli’s old associates made some of his own contributions to fluid

dynamics. Jean le Rond d'Alembert presented a fluid flow model that incorporated

conservation of a mass and also presented that the flow of the fluid could vary in both velocity

and acceleration (Johnston, 2009). The principle which assumes a perfect fluid (no viscosity or

drag) is also named after him; D'Alembert's paradox.

Another mathematician who advanced the dynamics of lift was Pierre-Simon Laplace.

He developed an equation that would correct Euler’s equations. He also successfully calculated

the speed of sound long before the sound barrier was conceived (Johnston, 2009).

One of the most influential men in aviation long before the first flight was George

Cayley. According to Rumerman (2009), Cayley was the first person to understand and identify

the four forces of flight. He recognized the need for a propulsion system separate from the lift-

loading plane, or wing (Rumerman, 2009). In his first submission of “On Aerial Naviagation,”

Cayley (1809), said the idea of a man being able to attach wings to himself and fly was a

ridiculous proposition. This was a huge departure from the bird-inspired concept that aircraft

should have flapping wings (ornithopter). His ideas brought together the modern recognizable

shape of the airplane including elevator and rudder. Another huge advancement he discovered

was the need for a cambered wing as he observed birds curving their wings to gain more lift

(Rumerman, 2009). Additionally he found that the higher the angle of attack of a bird’s wings,

less propulsion was needed to sustain flight; in other words more lift was generated. Perhaps one

of his greatest claims was that of stability. His huge amount of research on stability led him to

discover not only oscillation of unmanned aircraft, but also the benefits of using a dihedral wing

(Cayley, 1810). Cayley also looked into and proposed solutions for longitudinal stability,

streamlining, and changing location of the center of pressure as originally proposed by da Vinci


(Rumerman, 2009). He concluded that the center of pressure is located above the wing. It was

in 1849 that his first glider took flight with a human on board; a ten year-old boy. The first flight

of an adult occurred in his triplane glider four years later, exactly 50 years before the first

powered flight of the Wright Brothers. Rumerman (2009) said, “Cayley correctly predicted that

sustained flight would not occur until a lightweight engine was developed to provide adequate

thrust and lift, an event that did not take place until the flight of Orville and Wilbur Wright in

1903” (para. 10).

At the beginning of the 19th century, Claude-Louis Navier and Sir George Stokes applied

the missing factor of friction to Euler’s description of fluid motion. The Navier-Stokes

equations, which included the effects of viscosity, were central to fluid dynamics, but were

unable to be calculated for several years (Conway, 2009). Stokes also presented his law of

resistance which integrates the Navier-Stokes equations with velocities of small Reynolds’s

numbers associated with little inertia in regard to the force of viscosity (Tietjens, 1934). These

two men set the mathematical boundaries of fluid flow in aerodynamics.

Another fluid mechanic, Gustav Kirchhoff, simplified Stoke’s Law. He proposed that a

sphere will reach equilibrium and velocity will remain constant once resistance is equal to the

weight, or force of gravity, of the sphere; this is commonly referred to as terminal velocity

(Tietjens, 1934).

In 1858, Francis Wenham began working on a multiplane glider which led

him to the conclusions that cambered wings generate most of their lift from the

front portion of the airfoil (Mid-Nineteenth Century Milestones, 2009). Wenham also

developed the first wind tunnel (Rumerman, 2009).


Osborne Reynolds’ impact on modern aerodynamics is still seen today. In

1883 his investigations of fluid motion through tubes led him to conclude

mathematically that “the transition between laminar and turbulent flow can depend only on

the dimensionless expression” (Tietjens, 1934, p. 30). Reynolds later was credited with

the law of similarity which states: “ two different motions taking place in two geometrically

similar vessels are also mechanically similar when they have the same value” (Tietjens, 1934,

p. 31). The quantitative result of the law of similarity is called the Reynolds’

number in honor of his contributions. The Reynolds’ number is what allowed a

pivotal point for many fluid flow phenomena as it explained the relation of

calculation to experimental data.

Around the 1890s is when the practical applications of fluid dynamics to aviation began.

Wilson (2001) said, “[Lilienthal bridged] the gap between those who dreamed of flying and

those who actually flew” (para. 2). Otto Lilienthal is famous for his pioneering gliding success.

By the end of his career he had designed and built over eighteen gliders and made over 2,000

flights (Lilienthal – The "Flying Man", 2009). His success, however, didn’t come without study.

He devoted himself to analyzing the flight of birds, following the footsteps of da Vinci, before he

became the first man both to fly and to land safely. He published his findings in the classic

aviation work of literature, Bird Flight as the Basis of Aviation. Noticing the twisting action of

birds’ wings he determined the amount of lift and resistance offered to the wing depending on its

camber (Lilienthal – The "Flying Man", 2009). Utilizing da Vinci and Cayley’s information of

center of gravity, Lilienthal used his body weight to change the direction of flight similar to a

hang glider. Yet instead of directly controlling the aircraft, he was merely reacting to the aircraft

to maintain stability. This imperative problem would not be solved until the Wright Brothers


entered the scene. On August 9, 1896, Otto Lilienthal’s glider stalled and he would never fly

again (Lilienthal – The "Flying Man”, 2009). The next day as he lay dying his last words were,

“Sacrifices must be made” (Lilienthal – The "Flying Man”, 2009, para. 15). According to

Wilson (2001), news of his death likely inspired the Wrights to begin their quest for the skies.

This is clearly seen when in a correspondence published in 1912, Wilbur Wright (1912) said, “Of

all the men who attacked the flying problem in the 19th century, Otto Lilienthal was easily the

most important” (para. 1).

Otto Lilienthal was not the only aviator to affect the Wrights in a profound way. Octave

Chanute noticed a major problem in the slow advancement of aerodynamics. Theorists,

physicists, and aviators were largely separated due to time and distance. Chanute took the liberty

to assemble a collection of the progress of flying experiments up to the present time (1894) in his

book called Progress in Flying Machines. After reading the highly influential book in 1899, the

Wright Brothers corresponded with Chanute and they began a mentorship over the next decade

that would prove pivotal to the success of the Wrights (Octave Chanute—A Champion of

Aviation, 2009). Some influences were the idea of a horizontal propeller, lightweight motor,

flying on the coast, and focusing primarily on attaining a way to control the aircraft and

maintaining equilibrium in flight (Chanute, 1894). In his conclusion, Chanute (1894), makes

many predictions, of which is most notable regarding aerodynamics; “the final working out of

the general problem is likely to take place through a process of evolution. The first apparatus to

achieve a notable success will necessarily be somewhat crude and imperfect. It will probably

need to be modified, reconstructed, and readventured many times before it is developed into

practical shape.” (para. 60). Despite their admirable mentorship, the Wrights grew apart from


Chanute in defense of protecting their groundbreaking findings. Nevertheless, his effect on the

Wrights was providential.

Wilbur and Orville Wright were perhaps the most academically prepared for

flight due to the material available to them, thanks primarily to Octave Chanute. They read the

works of Lilienthal and Langley and wrote to the Smithsonian Institute (The Wright Brothers'

1900 Kite and Glider Experiments, 2009). In their studies, Wilbur concluded a component was

necessary to control the longitudinal axis of their first glider. They accomplished this by using a

concept called “wing warping” where twisting the shape of the wing caused a pressure

differential producing a higher amount of lift on one wing than the other (The Wright Brothers'

1900 Kite and Glider Experiments, 2009). They also put the elevator in front of the aircraft

following Lilienthal’s designs to absorb nosedive impacts, making it a “canard” (French)

because it resembled a duck (The Wright Brothers' 1900 Kite and Glider Experiments, 2009).

Unfortunately the wing design did not produce as much lift as they were expecting based on their

calculations (The Wright Brothers' 1900 Kite and Glider Experiments, 2009).

Orville and Wilbur Wright regrouped and began working on their 1901 glider.

This time they ensured their wing camber calculations followed Otto Lilienthal’s

research (Further Gliding and Wind Tunnel Experiments – 1901, 2009). Despite their

attention to detail the second flyer performed worse. The brothers suspected

Lilienthal’s equations were not correct (Further Gliding and Wind Tunnel Experiments –

1901, 2009). They reverted to solely experimental data in a wind tunnel to ensure

real-world results. They discovered Lilienthal’s calculations inaccurately relied on

Smeaton’s Coefficient, originally used for windmill designs (Further Gliding and Wind

Tunnel Experiments – 1901, 2009). After extensively testing over 200 airfoils and


objects in a wind tunnel they moved the highest depth of the wing from half way

down the chord, as in Lilienthal’s research, to only about one fourth of the way

from the leading edge (Further Gliding and Wind Tunnel Experiments – 1901, 2009).

Another issue was that they used calculations based on a different aspect ratio than

that of their flyers.

Following their new data they added a double, fixed rudder to their 1902

glider. The brothers did this after coincidentally discovering adverse yaw ( Success!

Orville's and Wilbur's 1902 Glider Flights, 2009). Ironically, the wing warping method,

which caused more lift on the outside wing, proportionally produced more drag

causing the aircraft to yaw opposite the direction of the rolling action.

Unfortunately, the fixed rudder solution did not solve what Orville called “Well

Digging” (Success! Orville's and Wilbur's 1902 Glider Flights, 2009). Orville’s new

solution was to make one, moveable rudder to counteract the adverse yaw. As a

result, on October 8, 1902, “They had solved the key problems of flight: the lifting ability of

the wings and the perfection of three-dimensional control. The 1902 glider was, for all practical

purposes, the first true airplane” (Success! Orville's and Wilbur's 1902 Glider Flights, 2009,

para. 11).

Regarding the issue of powered flight the Wrights once again referred to

Chanute’s advice. They realized a propeller (screw) could be used in the horizontal

and that it was essentially a rotating wing (Before the First Powered Flight, 2009). Since

no motors in existence were light enough for flight they called on their associate

Charlie Taylor to design the engine for the first powered flight (Before the First

Powered Flight, 2009). With these few issues resolved, the other issues mostly fell


into place as Chanute predicted. On December 17, 1903, Orville Wright piloted the

first heavier-than-air, powered aircraft. However the real milestone was when the

rudder and roll components were separated on June 23, 1905 in order that the Flyer

III would be completely controllable in each axis (Rumerman, 2009).

Since powered aircraft first took flight aerodynamics has taken strides to

perfect the design of the airplane. A few men who have had a huge role in

aerodynamics in the last century are: Theodore von Kármán (“Father of Supersonic

Flight”), Ludwig Prandtl (explained the boundary layer and flow separation in a stall), Jakob

Ackeret, Eastman Jacobs (NACA), Adolf Buseman (swept wings), Harland D. Fowler (Fowler

flaps), Richard T. Whitcomb (NACA, transonic area rule, supercritical wing, winglets). From

2,000 year old physics, to mechanics, to fluid dynamics; without these numerous contributions

made by men throughout history aerodynamics would be inexistent. Aerodynamics is critical to

understanding the characteristics of flight. Those admirable men who tested time, finances, and

safety made considerable deliberations to study those men that went before them, eventually

leading to the aim and destiny of man; to fly.


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The History of Aerodynamics in Aviation