Ver.04.29.93*END*
Aeroplanes
by J. S. Zerbe
Scanned by Charles Keller with OmniPage Professional OCR software
AEROPLANES
This work is not intended to set forth the exploits of aviators
nor to give a history of the Art. It is a book of instructions
intended to point out the theories of flying, as given by the
pioneers, the practical application of power to the various
flying structures; how they are built, the different methods of
controlling them; the advantages and disadvantages of the types
now in use; and suggestions as to the directions in which
improvements are required.
It distinctly points out wherein mechanical flight differs
from bird flight, and what are the relations of shape, form, size
and weight. It treats of kites, gliders and model aeroplanes,
and has an Interesting chapter on the aeroplane and its uses In
the great war. All the illustrations have been specially prepared
for the work.
Every Boy's Mechanical Library
AEROPLANES
BY
J. S. ZERBE, M. E.
Author of Automobiles--Motors
COPYRIGHT, 1915, BY
CUPPLES & LEON COMPANY
NY
CONTENTS
INTRODUCTORY
CHAPTER I. THEORIES AND FACTS ABOUT FLYING
The "Science" of Aviation. Machine Types. Shape
or Form not Essential. A Stone as a Flying Machine.
Power the Great Element. Gravity as Power. Mass
and Element in Flying. Momentum a Factor. Resistance.
How Resistance Affects Shape. Mass and Resistance.
The Early Tendency to Eliminate Momentum.
Light Machines Unstable. The Application of
Power. The Supporting Surfaces. Area not the Essential
Thing. The Law of Gravity. Gravity. Indestructibility
of Gravitation. Distance Reduces Gravitational
Pull. How Motion Antagonizes Gravity. A
Tangent. Tangential Motion Represents Centrifugal
Pull. Equalizing the Two Motions. Lift and Drift.
Normal Pressure. Head Resistance. Measuring Lift
and Drift. Pressure at Different Angles. Difference
Between Lift and Drift in Motion. Tables of Lift and
Drift. Why Tables of Lift and Drift are Wrong.
Langley's Law. Moving Planes vs. Winds. Momentum
not Considered. The Flight of Birds. The
Downward Beat. The Concaved Wing. Feather Structure
Considered. Webbed Wings. The Angle of Movement.
An Initial Movement or Impulse Necessary. A
Wedging Motion. No Mystery in the Wave Motion.
How Birds Poise with Flapping Wings. Narrow-
winged Birds. Initial Movement of Soaring Birds.
Soaring Birds Move Swiftly. Muscular Energy
Exerted by Soaring Birds. Wings not Motionless.
CHAPTER II. PRINCIPLES OF AEROPLANE FLIGHT
Speed as one of the Elements. Shape and Speed.
What "Square of the Speed" Means. Action of a
"Skipper." Angle of Incidence. Speed and Surface.
Control of the Direction of Flight. Vertical Planes.
CHAPTER III. THE FORM OR SHAPE OF FLYING MACHINES
The Theory of Copying Nature. Hulls of Vessels.
Man Does not Copy Nature. Principles Essential, not
Forms. Nature not the Guide as to Forms. The Propeller
Type. Why Specially-designed Forms Improve
Natural Structures. Mechanism Devoid of Intelligence.
A Machine Must Have a Substitute for Intelligence.
Study of Bird Flight Useless. Shape of
Supporting Surface. The Trouble Arising From Outstretched
Wings. Density of the Atmosphere. Elasticity
of the Air. "Air Holes." Responsibility for
Accidents. The Turning Movement. Centrifugal Action:
The Warping Planes.
CHAPTER IV. FORE AND AFT CONTROL
The Bird Type of Fore and Aft Control. Angle and
Direction of Flight. Why Should the Angle of the
Body Change. Changing Angle of Body not Safe. A
Non-changing Body. Descending Positions by Power
Control. Cutting off the Power. The Starting Movement.
The Suggested Type. The Low Center of Gravity.
Fore and Aft Oscillations. Application of the
New Principle. Low Weight not Necessary with Synchronously-
moving wings.
CHAPTEB V. DIFFERENT MACHINE TYPES AND THEIR CHARACTERISTICS
The Helicopter. Aeroplanes. The Monoplane. Its
Advantages. Its Disadvantages. The Bi-plane. Stability
in Bi-planes. The Orthopter. Nature's Type
not Uniform. Theories About Flight of Birds. Instinct.
The Mode of Motion. The Wing Structure.
The Wing Movement. The Helicopter Motion.
CHAPTER VI. THE LIFTING SURFACES OF AEROPLANES
Relative Speed and Angle. Narrow Planes Most Effective.
Stream Lines Along a Plane. The Center of
Pressure. Air Lines on the Upper Side of a Plane.
Rarefied Area. Rarefaction Produced by Motion. The
Concaved Plane. The Center of Pressure. Utilizing
the Rarefied Area. Changing Center of Pressure.
Plane Monstrosities. The Bird Wing Structure.
Torsion. The Bat's Wing. An Abnormal Shape. The
Tail as a Monitor.
CHAPTER VII. ABNORMAL FLYING STUNTS AND SPEEDS
Lack of Improvements in Machines. Men Exploited
and not Machines. Abnormal Flying of no Value.
The Art of Juggling. Practical Uses the Best Test.
Concaved and Convex Planes. How Momentum is a
Factor in Inverted Flying. The Turning Movement.
When Concaved Planes are Desirable. The Speed
Mania. Uses of Flying Machines. Perfection in Machines
Must Come Before Speed. The Range of its
Uses. Commercial Utility.
CHAPTER VIII. KITES AND GLIDERS
The Dragon Kite. Its Construction. The Malay
Kite. Dihedral Angle. The Common Kite. The Bow
Kite. The Box Kite. The Voison Bi-plane. Lateral
Stability in Kites, not Conclusive as to Planes. The
Spear Kite. The Cellular Kite. Tetrahedral Kite.
The Deltoid. The Dunne Flying Machine. Rotating
Kite. Kite Principles. Lateral Stability in Kites.
Similarity of Fore and Aft Control. Gliding Flight
One of the Uses of Glider Experiments. Hints in
Gliding.
CHAPTER IX. AEROPLANE CONSTRUCTION
Lateral and Fore and Aft. Transverse. Stability
and Stabilization. The Wright System. Controlling
the Warping Ends. The Curtiss Wings. The Farman
Ailerons. Features Well Developed. Depressing the
Rear End. Determining the Size. Rule for Placing
the Planes. Elevating Plane. Action in Alighting.
The Monoplane. The Common Fly. Stream Lines.
The Monoplane Form.
CHAPTER X. POWER AND ITS APPLICATION
Features in Power Application. Amount of Power
Necessary. The Pull of the Propeller. Foot Pounds
Small Amount of Power Available. High Propeller
Speed Important. Width and Pitch of Blades. Effect
of Increasing Propeller Pull. Disposition of the
Planes. Different Speeds with Same Power. Increase
of Speed Adds to Resistance. How Power Decreases
with Speed. How to Calculate the Power Applied.
Pulling Against an Angle. The Horizontal and the
Vertical Pull. The Power Mounting. Securing the
Propeller to the Shaft. Vibrations. Weaknesses in
Mounting. The Gasoline Tank. Where to Locate the
Tank. The Danger to the Pilot. The Closed-in Body.
Starting the Machine. Propellers with Varying Pitch.
CHAPTER XI. FLYING MACHINE ACCESSORIES
The Anemometer. The Anemograph. The Anemometrograph.
The Speed Indicator. Air Pressure Indicator.
Determining the Pressure From the Speed.
Calculating Pressure From Speed. How the Figures
are Determined. Converting Hours Into Minutes.
Changing Speed Hours to Seconds. Pressure as the
Square of the Speed. Gyroscopic:Balance. The Principles
Involved. The Application of the Gyroscope.
Fore and Aft Gyroscopic Control. Angle Indicator.
Pendulum Stabilizer. Steering and Controlling
Wheel. Automatic Stabilizing Wings. Barometers.
Aneroid Barometer. Hydroplanes. Sustaining Weight
of Pontoons. Shape of the Pontoon.
CHAPTER XII. EXPERIMENTAL WORK IN FLYING
Certain Conditions in Flying. Heat in Air. Motion
When in Flight. Changing Atmosphere. "Ascending
Currents." "Aspirate Currents." Outstretched Wings.
The Starting Point. The Vital Part of the Machine.
Studying the Action of the Machine. Elevating the
Machine. How to Practice. The First Stage. Patience
the Most Difficult Thing. The Second Stage.
The Third Stage. Observations While in Flight. Flying
in a Wind. First Trials in a Quiet Atmosphere.
Making Turns. The Fourth Stage. The Figure 8.
The Vol Plane. The Landing. Flying Altitudes.
CHAPTER XIII. THE PROPELLER
Propeller Changes. Propeller Shape. The Diameter.
Pitch. Laying Out the Pitch. Pitch Rule. Laminated
Construction. Laying up a Propeller Form.
Making Wide Blades. Propeller Outline. For High
Speeds. Increasing Propeller Efficiency.
CHAPTER XIV. EXPERIMENTAL GLIDERS AND MODEL AEROPLANES
The Relation of Models to Flying Machines. Lessons
From Models. Flying Model Aeroplanes. An
Efficient Glider. The Deltoid Formation. Racing
Models. The Power for Model Aeroplanes. Making
the Propeller. Material for the Propeller. Rubber.
Propeller Shape and Size. Supporting Surfaces.
CHAPTER XV. THE AEROPLANE IN THE GREAT WAR
Balloon Observations. Changed Conditions in Warfare.
The Effort to Conceal Combatants. Smokeless
Powder. Inventions to Attack Aerial Craft. Functions
of the Aeroplane in War. Bomb-throwing Tests.
Method for Determining the Movement of a Bomb.
The Great Extent of Modern Battle Lines. The Aeroplane
Detecting the Movements of Armies. The Effective
Height for Scouting. Sizes of Objects at Great
Distances. Some Daring Feats in War. The German
Taube. How Aeroplanes Report Observations. Signal
Flags. How Used. Casualties Due to Bombs
From Aeroplanes.
GLOSSARY
INTRODUCTORY
In preparing this volume on Flying Machines
the aim has been to present the subject in such a
manner as will appeal to boys, or beginners, in
this field of human activity.
The art of aviation is in a most primitive state.
So many curious theories have been brought out
that, while they furnish food for thought, do not,
in any way, advance or improve the structure of
the machine itself, nor are they of any service
in teaching the novice how to fly.
The author considers it of far more importance
to teach right principles, and correct reasoning
than to furnish complete diagrams of the details
of a machine. The former teach the art, whereas
the latter merely point out the mechanical
arrangements, independently of the reasons for
making the structures in that particular way.
Relating the history of an art, while it may be
interesting reading, does not even lay the foundations
of a knowledge of the subject, hence that
field has been left to others.
The boy is naturally inquisitive, and he is interested
in knowing WHY certain things are
necessary, and the reasons for making structures in
particular ways. That is the void into which
these pages are placed.
The author knows from practical experience,
while experimenting with and building aeroplanes,
how eagerly every boy inquires into details.
They want the reasons for things.
One such instance is related to evidence this
spirit of inquiry. Some boys were discussing the
curved plane structure. One of them ventured
the opinion that birds' wings were concaved on the
lower side. "But," retorted another, "why are
birds' wings hollowed?"
This was going back to first principles at one
leap. It was not satisfying enough to know that
man was copying nature. It was more important
to know why nature originated that type of formation,
because, it is obvious, that if such structures
are universal in the kingdom of flying creatures,
there must be some underlying principle
which accounted for it.
It is not the aim of the book to teach the art
of flying, but rather to show how and why the
present machines fly. The making and the using
are separate and independent functions, and of
the two the more important is the knowledge how
to make a correct machine.
Hundreds of workmen may contribute to the
building of a locomotive, but one man, not a
builder, knows better how to handle it. To
manipulate a flying machine is more difficult to
navigate than such a ponderous machine, because
it requires peculiar talents, and the building is
still more important and complicated, and requires
the exercise of a kind of skill not necessary
in the locomotive.
The art is still very young; so much is done
which arises from speculation and theories; too
much dependence is placed on the aviator; the
desire in the present condition of the art is to exploit
the man and not the machine; dare-devil exhibitions
seem to be more important than perfecting
the mechanism; and such useless attempts as
flying upside down, looping the loop, and characteristic
displays of that kind, are of no value to
the art.
THE AUTHOR.
AEROPLANES
CHAPTER I
THEORIES AND FACTS ABOUT FLYING
THE "SCIENCE" OF AVIATION.--It may be
doubted whether there is such a thing as a "science
of aviation." Since Langley, on May 6,
1896, flew a motor-propelled tandem monoplane
for a minute and an half, without a pilot, and the
Wright Brothers in 1903 succeeded in flying a
bi-plane with a pilot aboard, the universal opinion
has been, that flying machines, to be successful,
must follow the structural form of birds, and
that shape has everything to do with flying.
We may be able to learn something by carefully
examining the different views presented by
those interested in the art, and then see how they
conform to the facts as brought out by the actual
experiments.
MACHINE TYPES.--There is really but one type
of plane machine. While technically two forms
are known, namely, the monoplane and the
bi-plane, they are both dependent on outstretched
wings, longer transversely than fore and aft, so
far as the supporting surfaces are concerned, and
with the main weight high in the structure, thus,
in every particular, conforming to the form
pointed out by nature as the apparently correct
type of a flying structure.
SHAPE OR FORM NOT ESSENTIAL.--It may be
stated with perfect confidence, that shape or form
has nothing to do with the mere act of flying. It
is simply a question of power. This is a broad
assertion, and its meaning may be better understood
by examining the question of flight in a
broad sense.
A STONE AS A FLYING MACHINE.--When a stone
is propelled through space, shape is of no importance.
If it has rough and jagged sides its speed
or its distance may be limited, as compared with
a perfectly rounded form. It may be made in
such a shape as will offer less resistance to the air
in flight, but its actual propulsion through space
does not depend on how it is made, but on the
power which propelled it, and such a missile is a
true heavier-than-air machine.
A flying object of this kind may be so constructed
that it will go a greater distance, or require
less power, or maintain itself in space at
less speed; but it is a flying machine, nevertheless,
in the sense that it moves horizontally through the
air.
POWER THE GREAT ELEMENT.--Now, let us examine
the question of this power which is able to
set gravity at naught. The quality called energy
resides in material itself. It is something within
matter, and does not come from without. The
power derived from the explosion of a charge of
powder comes from within the substance; and so
with falling water, or the expansive force of
steam.
GRAVITY AS POWER.--Indeed, the very act of the
ball gradually moving toward the earth, by the
force of gravity, is an illustration of a power
within the object itself. Long after Galileo
firmly established the law of falling bodies it began
to dawn on scientists that weight is force.
After Newton established the law of gravitation
the old idea, that power was a property of each
body, passed away.
In its stead we now have the firmly established
view, that power is something which must have
at least two parts, or consist in pairs, or two elements
acting together. Thus, a stone poised on
a cliff, while it exerts no power which can be
utilized, has, nevertheless, what is called potential
energy. When it is pushed from its lodging place
kinetic energy is developed. In both cases,
gravity, acting in conjunction with the mass of
the stone, produced power.
So in the case of gunpowder. It is the unity of
two or more substances, that causes the expansion
called power. The heat of the fuel converting
water into steam, is another illustration of the
unity of two or more elements, which are necessary
to produce energy.
MASS AN ELEMENT IN FLYING.--The boy who
reads this will smile, as he tells us that the power
which propelled the ball through the air came
from the thrower and not from the ball itself.
Let us examine this claim, which came from a real
boy, and is another illustration how acute his mind
is on subjects of this character.
We have two balls the same diameter, one of
iron weighing a half pound, and the other of cotton
weighing a half ounce. The weight of one
is, therefore, sixteen times greater than the other.
Suppose these two balls are thrown with the
expenditure of the same power. What will be the
result! The iron ball will go much farther, or,
if projected against a wall will strike a harder
blow than the cotton ball.
MOMENTUM A FACTOR.--Each had transferred
to it a motion. The initial speed was the same,
and the power set up equal in the two. Why this
difference, The answer is, that it is in the
material itself. It was the mass or density which accounted
for the difference. It was mass multiplied
by speed which gave it the power, called, in
this case, momentum.
The iron ball weighing eight ounces, multiplied
by the assumed speed of 50 feet per second, equals
400 units of work. The cotton ball, weighing 1/2
ounce, with the same initial speed, represents 25
units of work. The term "unit of work" means
a measurement, or a factor which may be used to
measure force.
It will thus be seen that it was not the thrower
which gave the power, but the article itself. A
feather ball thrown under the same conditions,
would produce a half unit of work, and the iron
ball, therefore, produced 800 times more energy.
RESISTANCE.--Now, in the movement of any body
through space, it meets with an enemy at every
step, and that is air resistance. This is much
more effective against the cotton than the iron
ball: or, it might be expressed in another way:
The momentum, or the power, residing in the
metal ball, is so much greater than that within the
cotton ball that it travels farther, or strikes a
more effective blow on impact with the wall.
HOW RESISTANCE AFFECTS THE SHAPE.--It is because
of this counterforce, resistance, that shape
becomes important in a flying object. The metal
ball may be flattened out into a thin disk, and now,
when the same force is applied, to project it forwardly,
it will go as much farther as the difference
in the air impact against the two forms.
MASS AND RESISTANCE.--Owing to the fact that
resistance acts with such a retarding force on an
object of small mass, and it is difficult to set up a
rapid motion in an object of great density, lightness
in flying machine structures has been considered,
in the past, the principal thing necessary.
THE EARLY TENDENCY TO ELIMINATE MOMENTUM.--
Builders of flying machines, for several
years, sought to eliminate the very thing
which gives energy to a horizontally-movable
body, namely, momentum.
Instead of momentum, something had to be
substituted. This was found in so arranging the
machine that its weight, or a portion of it, would
be sustained in space by the very element which
seeks to retard its flight, namely, the atmosphere.
If there should be no material substance, like
air, then the only way in which a heavier-than-air
machine could ever fly, would be by propelling it
through space, like the ball was thrown, or by
some sort of impulse or reaction mechanism on
the air-ship itself. It could get no support from
the atmosphere.
LIGHT MACHINES UNSTABLE.--Gradually the
question of weight is solving itself. Aviators are
beginning to realize that momentum is a wonderful
property, and a most important element in
flying. The safest machines are those which have
weight. The light, willowy machines are subject
to every caprice of the wind. They are notoriously
unstable in flight, and are dangerous even
in the hands of experts.
THE APPLICATION OF POWER.--The thing now to
consider is not form, or shape, or the distribution
of the supporting surfaces, but HOW to apply
the power so that it will rapidly transfer a machine
at rest to one in motion, and thereby get
the proper support on the atmosphere to hold it
in flight.
THE SUPPORTING SURFACES.--This brings us to
the consideration of one of the first great problems
in flying machines, namely, the supporting
surfaces,--not its form, shape or arrangement,
(which will be taken up in their proper places), but
the area, the dimensions, and the angle necessary
for flight.
AREA NOT THE ESSENTIAL THING.--The history
of flying machines, short as it is, furnishes many
examples of one striking fact: That area has
but little to do with sustaining an aeroplane when
once in flight. The first Wright flyer weighed
741 pounds, had about 400 square feet of plane
surface, and was maintained in the air with a 12
horse power engine.
True, that machine was shot into the air by a
catapult. Motion having once been imparted to it,
the only thing necessary for the motor was to
maintain the speed.
There are many instances to show that when
once in flight, one horse power will sustain over
100 pounds, and each square foot of supporting
surface will maintain 90 pounds in flight.
THE LAW OF GRAVITY.--As the effort to fly
may be considered in the light of a struggle to
avoid the laws of nature with respect to matter,
it may be well to consider this great force as a
fitting prelude to the study of our subject.
Proper understanding, and use of terms is very
desirable, so that we must not confuse them.
Thus, weight and mass are not the same. Weight
varies with the latitude, and it is different at various
altitudes; but mass is always the same.
If projected through space, a certain mass
would move so as to produce momentum, which
would be equal at all places on the earth's surface,
or at any altitude.
Gravity has been called weight, and weight
gravity. The real difference is plain if gravity
is considered as the attraction of mass for mass.
Gravity is generally known and considered as a
force which seeks to draw things to the earth.
This is too narrow.
Gravity acts in all directions. Two balls suspended
from strings and hung in close proximity
to each other will mutually attract each other.
If one has double the mass it will have twice the
attractive power. If one is doubled and the other
tripled, the attraction would be increased six
times. But if the distance should be doubled the
attraction would be reduced to one-fourth; and
if the distance should be tripled then the pull
would be only one-ninth.
The foregoing is the substance of the law,
namely, that all bodies attract all other bodies
with a force directly in proportion to their mass,
and inversely as the square of their distance from
one another.
To explain this we cite the following illustration:
Two bodies, each having a mass of 4
pounds, and one inch apart, are attracted toward
each other, so they touch. If one has twice the
mass of the other, the smaller will draw the larger
only one-quarter of an inch, and the large one
will draw the other three-quarters of an inch,
thus confirming the law that two bodies will attract
each other in proportion to their mass.
Suppose, now, that these balls are placed two
inches apart,--that is, twice the distance. As
each is, we shall say, four pounds in weight, the
square of each would be 16. This does not mean
that there would be sixteen times the attraction,
but, as the law says, inversely as the square of
the distance, so that at two inches there is only
one-sixteenth the attraction as at one inch.
If the cord of one of the balls should be cut, it
would fall to the earth, for the reason that the
attractive force of the great mass of the earth is
so much greater than the force of attraction in
its companion ball.
INDESTRUCTIBILITY OF GRAVITATION.--Gravity
cannot be produced or destroyed. It acts between
all parts of bodies equally; the force being
proportioned to their mass. It is not affected by
any intervening substance; and is transmitted
instantaneously, whatever the distance may be.
While, therefore, it is impossible to divest matter
of this property, there are two conditions
which neutralize its effect. The first of these is
position. Let us take two balls, one solid and
the other hollow, but of the same mass, or density.
If the cavity of the one is large enough to receive
the other, it is obvious that while gravity is still
present the lines of attraction being equal at
all points, and radially, there can be no pull which
moves them together.
DISTANCE REDUCES GRAVITATIONAL PULL.--Or
the balls may be such distance apart that the attractive
force ceases. At the center of the earth
an object would not weigh anything. A pound
of iron and an ounce of wood, one sixteen times
the mass of the other, would be the same,--absolutely
without weight.
If the object should be far away in space it
would not be influenced by the earth's gravity;
so it will be understood that position plays an
important part in the attraction of mass for mass.
HOW MOTION ANTAGONIZES GRAVITY.--The second
way to neutralize gravity, is by motion. A
ball thrown upwardly, antagonizes the force of
gravity during the period of its ascent. In like
manner, when an object is projected horizontally,
while its mass is still the same, its weight is less.
Motion is that which is constantly combating
the action of gravity. A body moving in a circle
must be acted upon by two forces, one which tends
to draw it inwardly, and the other which seeks to
throw it outwardly.
The former is called centripetal, and the latter
centrifugal motion. Gravity, therefore, represents
centripetal, and motion centrifugal force.
If the rotative speed of the earth should be retarded,
all objects on the earth would be increased
in weight, and if the motion should be accelerated
objects would become lighter, and if sufficient
speed should be attained all matter would fly off
the surface, just as dirt dies off the rim of a
wheel at certain speeds.
A TANGENT.--When an object is thrown horizontally
the line of flight is tangential to the earth,
or at right angles to the force of gravity. Such
a course in a flying machine finds less resistance
than if it should be projected upwardly, or directly
opposite the centripetal pull.
_Fig 1. Tangential Flight_
TANGENTIAL MOTION REPRESENTS CENTRIFUGAL
PULL.--A tangential motion, or a horizontal
movement, seeks to move matter away from the
center of the earth, and any force which imparts
a horizontal motion to an object exerts a centrifugal
pull for that reason.
In Fig. 1, let A represent the surface of the
earth, B the starting point of the flight of an object,
and C the line of flight. That represents a
tangential line. For the purpose of explaining
the phenomena of tangential flight, we will assume
that the missile was projected with a sufficient
force to reach the vertical point D, which
is 4000 miles from the starting point B.
In such a case it would now be over 5500 miles
from the center of the earth, and the centrifugal
pull would be decreased to such an extent that the
ball would go on and on until it came within the
sphere of influence from some other celestial
body.
EQUALIZING THE TWO MOTIONS.--But now let us
assume that the line of flight is like that shown
at E, in Fig. 2, where it travels along parallel
with the surface of the earth. In this case the
force of the ball equals the centripetal pull,--or,
to put it differently, the centrifugal equals the
gravitational pull.
The constant tendency of the ball to fly off at
a tangent, and the equally powerful pull of
gravity acting against each other, produce a
motion which is like that of the earth, revolving
around the sun once every three hundred and
sixty-five days.
It is a curious thing that neither Langley, nor
any of the scientists, in treating of the matter of
flight, have taken into consideration this quality
of momentum, in their calculations of the elements
of flight.
_Fig. 2 Horizontal Flight_
All have treated the subject as though the
whole problem rested on the angle at which the
planes were placed. At 45 degrees the lift and
drift are assumed to be equal.
LIFT AND DRIFT.--The terms should be explained,
in view of the frequent allusion which
will be made to the terms hereinafter. Lift
is the word employed to indicate the amount
which a plane surface will support while in flight.
Drift is the term used to indicate the resistance
which is offered to a plane moving forwardly
against the atmosphere.
_Fig. 3. Lift and Drift_
In Fig. 3 the plane A is assumed to be moving
forwardly in the direction of the arrow B. This
indicates the resistance. The vertical arrow C
shows the direction of lift, which is the weight
held up by the plane.
NORMAL PRESSURE.--Now there is another term
much used which needs explanation, and that is
normal pressure. A pressure of this kind
against a plane is where the wind strikes it at
right angles. This is illustrated in Fig. 4, in
which the plane is shown with the wind striking
it squarely.
It is obvious that the wind will exert a greater
force against a plane when at its normal. On the
other hand, the least pressure against a plane is
when it is in a horizontal position, because then
the wind has no force against the surfaces, and
the only effect on the drift is that which takes
place when the wind strikes its forward edge.
_Fig. 4. Normal Air Pressure_
_Fig. 5. Edge Resistance_
HEAD RESISTANCE.--Fig. 5 shows such a plane,
the only resistance being the thickness of the
plane as at A. This is called head resistance,
and on this subject there has been much controversy,
and many theories, which will be considered
under the proper headings.
If a plane is placed at an angle of 45 degrees
the lift and the drift are the same, assumedly, because,
if we were to measure the power required
to drive it forwardly, it would be found to equal
the weight necessary to lift it. That is, suppose
we should hold a plane at that angle with a heavy
wind blowing against it, and attach two pairs of
scales to the plane, both would show the same
pull.
_Fig. 6. Measuring Lift and Drift_
MEASURING LIFT AND DRIFT.--In Fig. 6, A is the
plane, B the horizontal line which attaches the
plane to a scale C, and D the line attaching it to
the scale E. When the wind is of sufficient force
to hold up the plane, the scales will show the same
pull, neglecting, of course, the weight of the
plane itself.
PRESSURE AT DIFFERENT ANGLES.--What every
one wants to know, and a subject on which a
great deal of experiment and time have been expended,
is to determine what the pressures are at
the different angles between the horizontal, and
laws have been formulated which enable the pressures
to be calculated.
DIFFERENCE BETWEEN LIFT AND DRIFT IN MOTION.--The
first observation is directed to the differences
that exist between the lift and drift,
when the plane is placed at an angle of less than
45 degrees. A machine weighing 1000 pounds
has always the same lift. Its mass does not
change. Remember, now, we allude to its mass,
or density.
We are not now referring to weight, because
that must be taken into consideration, in the
problem. As heretofore stated, when an object
moves horizontally, it has less weight than when
at rest. If it had the same weight it would not
move forwardly, but come to rest.
When in motion, therefore, while the lift, so
far as its mass is concerned, does not change, the
drift does decrease, or the forward pull is less
than when at 45 degrees, and the decrease is less
and less until the plane assumes a horizontal position,
where it is absolutely nil, if we do not consider
head resistance.
TABLES OF LIFT AND DRIFT.--All tables of Lift
and Drift consider only the air pressures. They
do not take into account the fact that momentum
takes an important part in the translation of an
object, like a flying machine.
A mass of material, weighing 1000 pounds while
at rest, sets up an enormous energy when moving
through the air at fifty, seventy-five, or one hundred
miles an hour. At the latter speed the movement
is about 160 feet per second, a motion which
is nearly sufficient to maintain it in horizontal
flight, independently of any plane surface.
Such being the case, why take into account only
the angle of the plane? It is no wonder that
aviators have not been able to make the theoretical
considerations and the practical demonstrations
agree.
WHY TABLES OF LIFT AND DRIFT ARE WRONG.--
A little reflection will show why such tables are
wrong. They were prepared by using a plane
surface at rest, and forcing a blast of air against
the plane placed at different angles; and for determining
air pressures, this is, no doubt, correct.
But it does not represent actual flying conditions.
It does not show the conditions existing
in an aeroplane while in flight.
To determine this, short of actual experiments
with a machine in horizontal translation, is impossible,
unless it is done by taking into account
the factor due to momentum and the element
attributable to the lift of the plane itself due to its
impact against the atmosphere.
LANGLEY'S LAW.--The law enunciated by
Langley is, that the greater the speed the less the
power required to propel it. Water as a propelling
medium has over seven hundred times
more force than air. A vessel having, for instance,
twenty horse power, and a speed of ten
miles per hour, would require four times that
power to drive it through the water at double the
speed. The power is as the square of the speed.
With air the conditions are entirely different.
The boat submergence in the water is practically
the same, whether going ten or twenty miles an
hour. The head resistance is the same, substantially,
at all times in the case of the boat; with the
flying machine the resistance of its sustaining
surfaces decreases.
Without going into a too technical description
of the reasoning which led to the discovery of the
law of air pressures, let us try and understand
it by examining the diagram, Fig. 7.
A represents a plane at an angle of 45 degrees,
moving forwardly into the atmosphere in the
direction of the arrows B. The measurement
across the plane vertically, along the line B,
which is called the sine of the angle, represents
the surface impact of air against the plane.
In Fig. 8 the plane is at an angle of 27 degrees,
which makes the distance in height across the line
C just one-half the length of the line B of Fig. 7,
hence the surface impact of the air is one-half that
of Fig. 7, and the drift is correspondingly decreased.
_Fig. 7. Equal Lift and Drift in Flight._
_Fig. 8. Unequal Lift and Drift._
MOVING PLANES VS. WINDS.--In this way Boisset,
Duchemin, Langley, and others, determined
the comparative drift, and those results have been
largely relied upon by aviators, and assumed to
be correct when applied to flying machines.
That they are not correct has been proven by
the Wrights and others, the only explanation being
that some errors had been made in the calculations,
or that aviators were liable to commit errors
in observing the true angle of the planes
while in flight.
MOMENTUM NOT CONSIDERED.--The great factor
of momentum has been entirely ignored, and it is
our desire to press the important point on those
who begin to study the question of flying machines.
THE FLIGHT OF BIRDS.--Volumes have been
written concerning observations on the flight of
birds. The marvel has been why do soaring birds
maintain themselves in space without flapping
their wings. In fact, it is a much more remarkable
thing to contemplate why birds which depend
on flapping wings can fly.
THE DOWNWARD BEAT.--It is argued that the
downward beat of the wings is so much more
rapid than the upward motion, that it gets an action
on the air so as to force the body upwardly.
This is disposed of by the wing motion of many
birds, notoriously the crow, whose lazily-flapping
wings can be readily followed by the eye, and the
difference in movement, if any, is not perceptible.
THE CONCAVED WING.--It is also urged that the
concave on the under side of the wing gives the
quality of lift. Certain kinds of beetles, and particularly
the common house fly, disprove that theory,
as their wings are perfectly flat.
FEATHER STRUCTURE CONSIDERED.--Then the
feather argument is advanced, which seeks to
show that as each wing is made up of a plurality
of feathers, overlapping each other, they form a
sort of a valved surface, opening so as to permit
air to pass through them during the period of
their upward movement, and closing up as the
wing descends.
It is difficult to perform this experiment with
wings, so as to show such an individual feather
movement. It is certain that there is nothing in
the structure of the wing bone and the feather
connection which points to any individual feather
movement, and our observation is, that each
feather is entirely too rigid to permit of such an
opening up between them.
It is obvious that the wing is built up in that
way for an entirely different reason. Soaring
birds, which do not depend on the flapping motion,
have the same overlapping feather formation.
WEBBED WINGS.--Furthermore, there are numerous
flying creatures which do not have
feathered wings, but web-like structures, or like the
house fly, in one continuous and unbroken
plane.
That birds which fly with flapping wings derive
their support from the air, is undoubtedly true,
and that the lift produced is due, not to the form,
or shape, or area of the wing, is also beyond question.
The records show that every conceivable
type of outlined structure is used by nature; the
material and texture of the wings themselves differ
to such a degree that there is absolutely no
similarity; some have concaved under surfaces,
and others have not; some fly with rapidly beating
wings, and others with slow and measured
movements; many of them fly with equal facility
without flapping movements; and the proportions
of weight to wing surface vary to such an extent
that it is utterly impossible to use such data as a
guide in calculating what the proper surface
should be for a correct flying machine.
THE ANGLE OF MOVEMENT.--How, then, it may
be asked, do they get their support? There must
be something, in all this variety and diversity of
form, of motion, and of characteristics, which
supplies the true answer. The answer lies in the
angle of movement of every wing motion, which
is at the control of the bird, and if this is examined
it will be found that it supplies the correct
answer to every type of wing which nature has
made.
AN INITIAL IMPULSE OR MOVEMENT NECESSARY.--
Let A, Fig. 9, represent the section of a bird's
wing. All birds, whether of the soaring or the
flapping kind, must have an initial forward movement
in order to attain flight. This impulse is
acquired either by running along the ground, or
by a leap, or in dropping from a perch. Soaring
birds cannot, by any possibility, begin flight,
unless there is such a movement to change from a
position of rest to one of motion.
_Fig. 9. Wing Movement in Flight._
In the diagram, therefore, the bird, in moving
forwardly, while raising the wing upwardly, depresses
the rear edge of the wing, as in position
1, and when the wing beats downwardly the rear
margin is raised, in relation to its front margin,
as shown in position 2.
A WEDGING MOTION.--Thus the bird, by a
wedge-like motion, gives a forwardly-propelling
action, and as the rear margin has more or less
flexure, its action against the air is less during its
upward beat, and this also adds to the upward lift
of the body of the bird.
NO MYSTERY IN THE WAVE MOTION.--There is
no mystery in the effect of such a wave-like motion,
and it must be obvious that the humming
bird, and like flyers, which poise at one spot, are
able to do so because, instead of moving forwardly,
or changing the position of its body horizontally,
in performing the undulatory motion of
the wing, it causes the body to rock, so that at the
point where the wing joins the body, an elliptical
motion is produced.
_Fig. 10. Evolution of Humming-Bird's Wing._
HOW BIRDS POISE WITH FLAPPING WINGS.--This
is shown in Fig. 10, in which eight successive positions
of the wing are shown, and wherein four
of the position, namely, 1, 2, 3, and 4, represent
the downward movement, and 6, 7, 8, and 9, the
upward beat.
All the wing angles are such that whether the
suspension point of each wing is moving downwardly,
or upwardly, a support is found in some
part of the wing.
NARROW-WINGED BIRDS.--Birds with rapid flapping
motions have comparatively narrow wings,
fore and aft. Those which flap slowly, and are
not swift flyers, have correspondingly broader
wings. The broad wing is also typical of the
soaring birds.
But how do the latter overcome gravitation
without exercising some sort of wing movement?
INITIAL MOVEMENT OF SOARING BIRDS.--Acute
observations show that during the early stages
of flight, before speed is acquired, they depend
on the undulating movement of the wings, and
some of them acquire the initial motion by flapping.
When speed is finally attained it is difficult
for the eye to note the motion of the wings.
SOARING BIRDS MOVE SWIFTLY.--Now, the first
observation is, that soaring birds are swiftly-
moving creatures. As they sail overhead
majestically they seem to be moving slowly. But
distance is deceptive. The soaring bird travels
at great speeds, and this in itself should be sufficient
to enable us to cease wondering, when it is
remembered that swift translation decreases
weight, so that this factor does not, under those
conditions, operate against flight.
MUSCULAR ENERGY EXERTED BY SOARING BIRDS.
--It is not conceivable that the mere will of the
bird would impel it forwardly, without it exerted
some muscular energy to keep up its speed. The
distance at which the bird performs this wonderful
evolution is at such heights from the observer
that the eye cannot detect a movement.
WINGS NOT MOTIONLESS.--While the wings appear
to be absolutely motionless, it is more reasonable
to assume that a slight sinuous movement,
or a rocking motion is constantly kept up, which
wedges forwardly with sufficient speed to compel
momentum to maintain it in flight. To do so requires
but a small amount of energy. The head
resistance of the bird formation is reduced to a
minimum, and at such high speeds the angle of
incidence of the wings is very small, requiring but
little aid to maintain it in horizontal flight.