The Wright Brothers' Airplane Compared to Insect Flight Design
Published in Creation Research Society Quarterly, June 2003
vol. 40 (1): 1-7
Arthur L. Manning, M.S. *
Abstract
The Wright brothers' activities in inventing the airplane are set forth.
They include library research, conscious imagining of a solution to
flight's demands, kite experiments, communication with experts, glider
experiments, experiments with a wind tunnel, and propeller design. Then
the aerodynamics of insect flight are considered, demonstrating their
superb sophistication. It is concluded that since human flight was in
fact the result of such a high degree of intelligent planning, certainly
the Creator's design is even more directly obvious in the origin of
insect flight.
Introduction
This year, 2003, marks the one hundredth anniversary of powered,
controlled, manned flight. It is probably commonly believed that the
invention of the airplane by the Wright brothers was the result of a
couple of ordinary men (bicycle mechanics) tinkering around and somehow
putting together a simple machine that managed to fly. In reality,
however, their achievement was the result of a highly controlled
scientific enterprise. Part I of this article provides an historical
overview of the Wright brothers' accomplishment and Part II gives a
description of the highly complex flight design features found in
insects.
Part I: The Wright Brothers
The Process of the Invention of the Airplane
As far as we know, before 1903 no one in all of the history of mankind
had ever succeeded in devising a heavier-than-air machine capable of
carrying a man in sustained, powered, controlled flight. Before the
Wright brothers achievement the greatest minds had failed to conquer this
frontier.
After reading about Otto Lilienthal's gliding experiments in Germany,
Wilbur and Orville Wright developed an interest in manned flight; and in
the years 1896 through about 1899 they started reading everything they
could on the subject. Through this research they learned much from the
experiences of others (Kelly, 1989, pp. 46-48).
After realizing how much a problem others had experienced in aircraft
stability and that no one had succeeded in solving it, Orville devised a
technique based on controlling the inclination of the wing tips.
Then Wilbur devised another technique based on wing warping (Kelly, 1989,
pp. 48-50). These inventions showed ingenuity on the part of the
brothers. In August, 1899 they built a biplane kite and conducted their
own experiments on it. They found that they could control it by extra
cords attached so as to enable them to warp the wings (Kelly, 1989, pp.
50-51). Thus, the brothers commenced a long process of scientific
experimentation.
In May, 1900, Wilbur Wright wrote a letter to Octave Chanute (who had
experience in gliding), communicating his plans for experimenting with a
man-carrying kite (Kelly, 1989, p. 52). This practice of communicating
with experts in the field of study is an important part of the scientific
method. In addition, it is in keeping with the Biblical wisdom of using a
"multitude of counselors" ( Proverbs 15:22).
Next the Wrights invented an elevator (a device for controlling the
airplane's tilt up or down) superior to previous designs (Kelly, 1989, p.
54). Then they built and experimented with a man-carrying glider. First
they worked with it as a kite, and then they actually flew it as a
glider. These experiments, conducted in the fall of 1900 at Kitty Hawk,
North Carolina, were highly successful (Kelly, 1989, pp. 64-66).
In 1901 the brothers returned to Kitty Hawk and continued their
experiments with a larger glider. They began to change the camber of the
wing. It is this camber, or height of the wing's curve, which determines
the amount of lift that a wing can provide. Camber is actually the height
of the wing divided by the distance from front to back. They then
adjusted the camber to a ratio of 1 to 18, which improved the glider's
performance. Also, during that year, by experimentation they learned more
about the center of pressure on a curved surface (Kelly, 1989, p.71).
During the latter months of 1901 the brothers built a wind-tunnel and
used it to test more than 200 types of wing surfaces (Kelly, 1989, p.76).
In 1902 the Wrights added a tail to the glider consisting of two vertical
veins (Kelly, 1989, p.79). The success of these flights demonstrated that
they were justified in disregarding the tables of air pressures used by
their predecessors and building their gliders in accordance with the data
obtained from their own wind-tunnel experiments (Kelly, 1989, p.80). This
demonstrated the Wright's quest for and reliance upon empirical data
rather than tradition and authority. This aspect of proper scientific
research is also in accordance with the biblical admonition to "prove all
things" ( I Thess. 5:21).
Before the Wrights experimented with powered flight they built their own
motor and devised a highly efficient propeller (Kelly, 1989, pp. 85-89).
On December 17, 1903 the brothers finally made their historic first
powered flight, followed by three others, each successively longer, that
same day. According to Orville Wright: "...faith in our calculations and
the design of the first machine, based upon our table of air pressures,
obtained by months of careful laboratory work, and confidence in our
system of control developed by three years of actual experiences in
balancing gliders in the air, had convinced us that the machine was
capable of lifting and maintaining itself in the air, and that, with a
little practice, it could be safely flown" (Kelly, 1989, p.99).
The Product
To produce a flying machine the Wright brothers skillfully brought
together wings, propellers, an engine, and a pilot. These all had to be
of a specific design and composition. In addition, it was essential to
have control mechanisms. First of all, it was necessary to control the
wings so that there would not be any rotation about a central axis
running from the front to the rear of the airplane. This type of rotation
is called "roll". This control was accomplished by what the Wrights
called "wing warping".
A second mechanism was necessary to control the movement of the plane's
nose in a vertical dimension. This direction of movement is called
"pitch". Orville Wright was able to control pitch by designing an
elevator (Wright, 1953, p. 14).
A third mechanism was necessary to control the plane's nose from moving
right or left, a movement that is called "yaw". The device used to
control this movement was a vertical rudder in the rear of the plane
which was originally controlled by being connected by wires to the cables
that caused wing warping. Later this was changed so that the operator
could control the rudder separately (Wright, 1953, p. 19).
This brief analysis of the use of design and controlling devices by the
Wright brothers shows that they left little or nothing to "chance" in
their labors. A study of insect flight will likewise show amazing
evidence for design.
Part II: Insect Flight
Introduction
More than 99.9 % of all insect species exhibit flight (Dudley, 2000, p.
10). There are more than one million winged insect species described and
they can be found "... in essentially all terrestrial ecosystems, and on
all continental land masses, including Antarctica" (Dudley, 2000, p. 3).
Some insects are phenomenal fliers. Horseflies are said to be able to fly
at speeds up to 30 mph (Dalton, 1975, p.26). Some dragonflies and
hawkmoths can attain speeds of up to about 38 mph (Brackenbury, 1992, p.
118). The housefly can travel 250 body lengths per second, compared to 80
for diving swifts, and only 5 or 6 for humans (Brackenbury, 1992, p.
118). "Swarms of locusts occasionally make landfall in the Caribbean
islands after being carried from breeding grounds in North Africa,
several thousand miles to the east" (Brackenbury, 1992, p. 120). Monarch
butterflies migrate 4,000 miles from Canada to Mexico (Brackenbury, 1992,
p. 120). Acceleration rates of up to 9 times the force of gravity (g's)
have been observed in some dragonflies and "acceleration at the
transition from hovering to forward flight in hover flies and in bee
flies reaches... up to 18 g's" (Brodsky, 1994, p. 71). ",,,[A]bout 23
million wingbeats were obtained in a tethered simulation of long-duration
flight using a single Drosophila melanogaster (fruit fly)" (Dudley, 2000,
p. 59). In order for insects to have such amazing capabilities, it is
evident that they are, indeed, not the product of chance; but, in the
words of the Psalmist, are "...fearfully and wonderfully made" ( Psalm
139:14).
The flight of insects is very different from the flight of the Wright
brothers' airplane. But the same basic features are present in both: a
means of power (muscles instead of an engine), a means of translating
that power into thrust (moving wings instead of a propeller), aerodynamic
structures to provide lift (flexible wings instead of fixed wings),
control mechanisms (for controlling flight in three dimensions), and
control ( an insect's nervous system instead of that of a human pilot).
Muscles, fuel, and oxygen
The Wright brothers' "Flyer" was powered by an engine which used fuel,
burned in the presence of oxygen. The power for insect flight is provided
by muscles which use a different kind of fuel, consumed with oxygen,
also. Unlike vertebrate flying animals, insects have no muscles in their
wings (Dalton, 1975, p. 19). Their flight muscles are in the thorax. The
base of each wing is attached to the thorax by an axillary apparatus,
which includes sclerites, small bodies which act as fulcrums. In some
cases the muscles pull directly on the wing base and sclerites (direct
muscles), but in other cases the muscles pull on the thorax itself,
changing its shape and causing it to pull on the wings (indirect
muscles). The muscles function on both the down- and the upstroke. "Wing
elevation in all insect orders is primarily attained through action of
indirect dorsoventral muscles" (Dudley, 2000, p.44). As muscles
connecting the interior dorsal and ventral aspects of the thorax are
contracted, they pull these surfaces together, levering the wings upward.
The muscles themselves are similar in insects and in birds; but insect
muscles can generate far more force than those in birds or bats, since
they can contract many more times per second, making them "...the most
powerful muscle known in any animal" (Brackenbury, 1992, p. 36).
In insects, the fuel is either fats or carbohydrates. Fats are best for
long distance flying, such as in locust migrations; while carbohydrates
are best for fast, short distance flights, such as those made by bees.
The fuel is delivered to the muscles by the blood (Brackenbury, 1992, p.
36). Flight muscle contraction not only enables insects to fly, it also
accelerates the insect blood circulation, bringing fuel to the muscles
more efficiently when it is most needed (Dudley, 2000, p. 163).
Insects need an enormous amount of oxygen when flying -- up to 400 times
the amount they need at rest (Brackenbury, 1992, p.43). "...[T]he
thoracic muscles of insects in flight exhibit the highest known
mass-specific rates of oxygen consumption for any locomotor tissue"
(Dudley, 2000, p. 159). In insects, oxygen is not delivered to the
muscles by the blood (as is the case in birds and bats), but through a
system of air tubes (called tracheae) which bring in air from the outside
through openings called spiracles. An insect can move its abdomen in such
a way as to cause minute balloon-like sacs in certain regions of the
tracheae to expand and act like a bellows, pumping air through the tubes
(Brackenbury, 1992, p. 43). In addition, the thoracic muscle pumping
during flight contributes to air flow through the tracheal system by
compressing and expanding various tracheal tubes and tracheoles (the ends
of tracheal tubes) (Dudley, 2000, p. 162). When the air sacs in some
insects expand, the anterior spiracles open and the posterior spiracles
shut. Then when the air sacs are compressed, the anterior spiracles close
and the posterior spiracles open. The result is a one-way movement of air
through the body, bringing in fresh air and expelling stale air
(Brackenbury, 1992, p.43). Complex, coordinated systems, such as this
one, are hardly what one would expect to come about by chance mutations
and natural selection. At the tracheoles, oxygen leaves the respiratory
system and enters into the muscle cells where it is needed. The thickness
of the tracheole walls is important for the diffusion of oxygen through
them. Dudley comments perceptively that "... structural design would
appear in this instance to closely approximate the optimal value for
effective oxygen transport" (Dudley, 2000, p. 161). Even a tiny detail,
like the thickness of the tracheole wall, contributes to making insect
flight feasible and appears to be the work of a Master Designer.
Wing movement
According to Dalton, insect wing movement in flying is more complex than
that of birds (1975, p. 22). When a bird flaps its wings it changes their
length by flexing and extending joints in the shoulder, elbow, and wrist.
Insects cannot change the length of their wings, and in this respect are
more similar to airplanes. But insects can deform the contour of their
wings and rotate them about the longitudinal axis to a much greater
degree than can birds (Dudley, 2000, p. 333). Torkel Weis-Fogh "...points
out that as insects move their wings in an extremely complicated way,
they produce fluctuating and unsteady airflow by means of a variety of
novel aerodynamic mechanisms" (Dalton, 1975, p. 24). I think that such
extreme complexity points to an extremely intelligent Designer. "[A]s
soon as flapping starts and a flow of air passes around them, [the wings]
change shape and become cambered into more efficient airfoils" (Dalton,
1975, p. 24). Brodsky lists four different wing deformations (1994, pp.
44-46). As the wing moves up and down it twists first one way, then the
other. A fly's wing moves in an ellipse or a figure eight and this
creates a "...current of air backward and downward, providing both lift
and thrust" ( Dalton, 1975, p. 25).
Some rates of wing beats for different insects in wing beats (up and
down) per second are as follows: medium butterflies: 8-12, large
dragonflies: 25-40, bumblebees: 130, houseflies: 200, honeybees: 225,
mosquitos: 600, and gnats: 1,000 (Dalton, 1975, p. 26). As for the
extremely high rate of wingbeat of gnats, Dalton reveals that: "...there
are peculiar aerodynamic problems at these speeds that make the normal
properties of airfoils change. In these conditions the insect is not
flying in an aerodynamic sense at all, but rowing its its way through the
air....A very sophisticated method of propulsion indeed" (p. 48).
Dragonflies can make their forward and rear wings beat in unison,
completely out of phase, or anything in between, depending on their need.
They can make such changes instantly while in flight (Brackenbury, 1992,
p. 142). Dragonflies' four wings each functions independently, enabling
these insects to perform complex maneuvers (Brackenbury, 1992, p. 115).
Members of order Diptera (flies) also have independent movement of wings
on opposite sides (they only have two wings), but the mechanism
responsible for this is different from that in dragonflies (Brodsky,
1994, p. 186). These three common insects -- gnats, dragonflies, and
house flies -- are phenomenal illustrations of God's handiwork.
We do not fully understand all that takes place in the insect body which
contributes to flight. Dudley explains that this is because of a high
number of interacting structures, such as the 16 muscles used to control
a fly's wing, resulting in complex mechanics (2000, p. 50). Of course,
all of human history (including the Wright brother's achievement) teaches
us that complex mechanics is the product of master mechanics.
Wing and Thorax Morphology
Insect wings are not modified limbs, as is the case in flying
vertebrates. The wings consist of two thin layers of chitin, strengthened
by a network of hollow veins (Dalton, 1975, p. 18). Wing strength and
flexibility are essential to flight. These qualities come from
"...polysaccharide chitin microfibers embedded in a protein matrix...[
which makes it]... the finest zoological example of this mechanical
design" (Dudley, 2000, p. 36). The wing's flexibility actually imparts
considerable strength to it (Brackenbury, 1992, p.102). Dudley describes
a gradient of wing stiffness from base to tip and also from leading edge
to trailing edge (p. 55).
In addition, extra strength is imparted to insect wings by pleating.
Pleating in insect wings not only enables them to be folded away but
produces extra strength needed to resist the stresses of flight
(Brackenbury, 1992, p. 85). Most insect wings only weigh a few millionths
of a gram (Brackenbury, 1992, p. 82). The ratio of wing mass to body mass
varies from 0.5% to 10% (Dudley, 2000, p. 55). It is important that
insect wings are so light because when they are flapped so rapidly their
inertia produces a great increase in resistance (Brackenbury, 1992, p.
82).
Other structural features which enhance wing performance include
microscopic hairs (which prevent turbulent eddies from forming)
(Brackenbury, 1992, p. 142); small vein-supporting brackets; spines;
scales; and sensory structures (Dudley, 2000, p. 57). Finally, the
hemolymph (insect blood) pumped through the wing veins apparently helps
to keep the wings from drying out and becoming too fragile for flight.
Anteriorly within the wings, circulation is caused by pressure induced by
the heart; but posteriorly, circulation is caused by accessory pumping
organs located at the base of the wings (Dudley, 2000, p. 53). So we see
that even the complex wings themselves plus the structures required to
produce their complex movements are apparently insufficient to produce
flight. Additional organs are necessary, increasing the complexity of the
entire flight system, and decreasing the already remote likelihood of its
origin by chance.
In addition to complex wings, insects also have a specialized thorax to
enable them to fly: "The thorax of the insect, to which the wings are
attached, is a complex of flight muscles and mechanisms so utterly
sophisticated as to boggle an aircraft designer's imagination. The thorax
enables an insect in flight to carry out just about any maneuver, to
loop, swoop, climb vertically, fly upside down, sideways, backwards, to
hover, and to vary between all of these in a fraction of a second"
(Dalton, 1975, p. 19).
The wings are attached to the thorax by a series of couplings which allow
movement in any direction, much like a ball-and-socket joint (Dalton,
1975, p. 19). As already mentioned, within the thorax are sclerites --
hard, small, peg-like outgrowths from the wall of the thorax which serve
as a fulcrum for the movement of the wing and also as points of
attachment for small muscles that alter the angle of attack of the wing
during flight (Brackenbury, 1992, p. 16). There are also "...many
elastic, rubber-like elements in the flexible wing base... to absorb the
repeated shocks and reduce the frictional stresses..." (Brackenbury,
1992, p. 17). Extra chitin reinforces the wall of the thorax to help the
wing pivot to withstand the stresses of rapid flapping (Brackenbury,
1992, p. 20). Since dragonflies use dorsoventral muscles for both upward
and downward flapping, this causes additional stress on the thorax which
is alleviated by an internal projection called an apodeme (Dudley, 2000,
p. 49). If all of this complexity within the insect's thorax would boggle
an aircraft designer's imagination, it must be the product of One with an
even greater imagination.
Control Mechanisms
Attached to the sclerites, insects have small muscles that alter the
angle of attack of the wing during flight (Brackenbury, 1992, p. 16).
Flies have a total of eighteen such muscles (Dudley, 2000, p. 45).
Locusts can use their flexible abdomens as a rudder (Brackenbury, 1992,
p. 131). Some insects can turn in flight by extending a hind leg in the
direction they wish to turn. This interferes with the motion of the hind
wing on that side resulting in a turn in that direction since the
opposite wing then produces a greater relative force (Brackenbury, 1992,
p. 131). Some insects obtain aerodynamic control by structurally
determined changes of the wing shape during flapping; but in dragonflies
the wing shape is altered by a small muscle located at the wing base
(Dudley, 2000, p. 61).
Control of Flight
"...[S]o advanced and automatic is the flight adjustment mechanism of
most insects that they are incapable of falling from the air, enjoying a
perfection of flying ability to make most pilots loop with envy" (Dalton,
1975, pp. 23-24). The nervous impulse to fly begins in the thoracic or
abdominal ganglia "...and is regulated by a complex network of ganglial
interneurons" (Dudley, 2000, p. 174). In one type of flight muscle
(called synchronous) the neurons regulate the frequency and amplitude of
contraction (Dudley, 2000, p. 172). The other type of insect muscle
(called asynchronous) requires only one nervous impulse in order to
contract over and over again (Dudley, 2000, p.175). This explains how
some insects can attain such phenomenal wing beat rates as those
previously mentioned. Such high rates of flapping would not be possible
if the muscles had to contract and recover from each impulse. The nervous
system enables flying insects to rapidly and continuously sense and
correct any instability by a wide variety of compensatory, asymmetric
wing motions (Dudley, 2000, p. 204).
The greatest sensory input is through the eyes. In all insects the region
of the brain involved in vision is the largest. In dragonflies this
region comprises about 80% of the total brain volume. Compound eyes
provide much information to the insect, not only ahead, but substantially
laterally, above, and below (Dudley, 2000, p. 205). It is apparent that
the insect visual system must be able to rapidly evaluate the nature of
the changing environment in order for flight to be controlled (Dudley,
2000, pp. 205-206). One reason for the success of insects in meeting this
challenge is the fact that they are capable of resolving light impulses
at a much higher frequency than even vertebrates -- some flies and bees
about ten times as fast (Dudley, 2000, p. 206).
Other sense organs are also involved in flight. Ocelli (simple eyes) are
probably used in maintaining stable flight (Dudley, 2000, p. 213). All
winged insects have a specialized structure (Johnston's organ), located
in the second segment of each antenna, which monitors its bending during
flight (Dudley, 2000, p. 213). "On wings, arrays of campaniform sensillae
(dome-shaped mechanoreceptors) monitor the rate and extent of local
bending" (Dudley, 2000, p. 215). Dragonflies have four beds of hairs
between the head and body that send information to the brain about the
orientation of the body (Dalton, 1975, p. 29). Flies have a pair of
halteres instead of a second pair of wings. These small knob-like
structures oscillate at the same frequency as the wings, and are said to
serve as gyroscopes (Dudley, 2000, p. 217).
In addition to having nervous control of flight, insects exhibit behavior
which, though not itself flight, relates to flying. Some of these
behaviors are quite complex, including placing the feet in the best
position under the body, and orienting the body towards the wind in order
to experience lift (Brackenbury, 1992, p. 45). Some species have
elongated hind legs which they use to leap into flight (Brackenbury,
1992, p.46). Some jumping insects have additional structures to help them
get air-borne:
"[M]any jumping insects ... overcome the physiological deficiencies in
their leg muscles by cranking up a spring that is then held ready to be
released at high speed at the appropriate moment. They can thus catapult
their bodies into the air at far greater speeds than could ever be
achieved by muscle contraction. The principle is ingenious, and the
hardware to make it work involves remarkable innovations of design"
(Brackenbury, 1992, p. 59).
Grasshoppers use a similar strategy with a stretch of elastic cuticle on
the outside of the femur-tibia joint of the hind leg. When the cuticle
has been fully stretched it is held by a catch until the moment when all
the power is released at once (Brackenbury, 1992, p. 59). Our Creator has
designed other "remarkable innovations" as well.
There is evidently much more to insect flight than just wing flapping. We
see that sensing and rapidly and accurately responding to a wide variety
of environmental stimuli through ingenious structures and complex
behaviors takes place in these miniature organic machines we call
insects, resulting in the marvels of flight that we can observe right in
our back yards. What we see is far more sophisticated than not only the
Wright brothers' airplane, but any airplane ever built by man's
intelligence. "The heavens declare the glory of God..." (Psalm 19:1), but
flying insects mightily declare His wisdom.
The Origin of Insect Flight
The following are quotations from previously cited sources regarding
their views of the origin of insect flight:
"Assuming that the ability to fly arose somewhere between the Devonian
and the Carboniferous, 20 million years of the evolutionary development
of winged insects are shrouded in mystery" (Brodsky, 1994, p. 79).
"Unfortunately, the evolutionary origins of flight in insects are not
well known. Paleontological records of transitional forms are absent, and
the likely selective forces acting on early winged morphologies can only
be surmised, precluding any paleobiological interpretation of this major
event in metazoan evolution" (Dudley, 2000, p. 261).
"The paleontological history of winged insects starts from the Upper
Carboniferous (Namurian). Namurian insects were represented by three
clearly distinct groups" (Brodsky, 1994, p. 88).
"We do not know how and when the three main lines of evolution of winged
insects diverged..." (Brodsky, 1994, p. 98).
"As impressive as insect diversity is today, even more remarkable is the
fact that most major morphological innovations and indeed insect orders
were present before the Mesozoic [245-65 million years ago]" (Dudley,
2000, pp. 8-9).
"The dragonfly provides an excellent example of the perfection of ancient
flight; they have changed very little from their ancestors ... about 300
million years ago" (Brodsky, 1994, p. 66).
"Odonata [dragonflies] is the oldest surviving order of flying insects,
and ... the aerial equipment of the dragonfly has remained essentially
unchanged" (Dalton, 1975, p. 28).
So not only do the complex, ordered flight systems of insects make
foolish the notion that they are the product of mutations and natural
selection; but the fossil record also offers no support for such a
notion.
Conclusion
The Wright brothers' airplane was capable of flying because it had an
intelligence controlling many specifically designed features which all
had to be in place before it could fly. The anatomy of flying insects
likewise meets all of the requirements for flight. It has been shown that
each of these insect structures required for flight is a highly complex
system (composed of specific materials). The logical conclusion is that
insect flight is also the result of deliberate design. Furthermore, there
is no evidence for a gradual evolution of insect flight. Indeed, without
all of the above requirements being met, an insect could not experience
flight. Even the evolutionist, Maynard Smith, agreed with this assessment
when he is quoted as stating that flight control is "...a prerequisite
for the initial evolution and subsequent elaboration of flight" (Dudley,
2000, pp. 203-204). If only one of the requirements for flight were
satisfied, the insect would not fly, and even that particular innovation
would be selected against because of the disadvantage involved in
carrying around useless structures. The more requirements that might be
satisfied, the greater would be the selective disadvantage, unless all
were satisfied. The only logical solution is that these exceedingly
complex flying insects would have to have been initially formed complete.
This is clearly antithetical to evolution and supportive of creation.
When one compares insect flight to human flight, the vast superiority of
the former requires a vastly superior intelligence. Wherever there are
people flying insects exist and their "message" of intelligent design is
so clear that no man anywhere has an excuse for denying the existence of
their Designer (see Romans 1:20).
Acknowledgments
I wish to thank Dr. George Howe for his editorial assistance and Rick
Herr for drawing the sketches in the published article.
References
-
Brackenbury, J. 1992. Insects in flight. Blandford, London.
- Brodsky, A. 1994. The evolution of insect flight. Oxford University
Press, New York, NY.
- Dalton, S. 1975. Borne on the wind. Reader's Digest Press, New York, NY.
- Dudley, R. 2000. The biomechanics of insect flight. Princeton University
Press, Princeton, NJ.
- Kelly, Fred C. 1989. The Wright brothers - A biography. Dover
Publications, Mineola, NY.
- Wright, Orville. 1953. How we invented the airplane. Dover Publications,
Mineola, NY.
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