Construction and Operation
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Unknown >> Construction and Operation
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The beginner will need the assistance of three men.
One of these should take his position in the rear of the
machine, and one at each end. On reaching the trial
ground the aviator takes his seat in the machine and,
while the men at the ends hold it steady the one in the rear
assists in retaining it until the operator is ready. In the
meantime the aviator has started his motor. Like the
glider the flying machine, in order to accomplish the
desired results, should be headed into the wind.
When the Machine Rises.
Under the impulse of the pushing movement, and assisted
by the motor action, the machine will gradually
rise from the ground--provided it has been properly
proportioned and put together, and everything is in working
order. This is the time when the aviator requires
a cool head, At a modest distance from the ground use
the control lever to bring the machine on a horizontal
level and overcome the tendency to rise. The exact
manipulation of this lever depends upon the method of
control adopted, and with this the aviator is supposed
to have thoroughly familiarized himself as previously
advised in Chapter XI.
It is at this juncture that the operator must act
promptly, but with the perfect composure begotten of
confidence. One of the great drawbacks in aviation by
novices is the tendency to become rattled, and this is
much more prevalent than one might suppose, even
among men who, under other conditions, are cool and
confident in their actions.
There is something in the sensation of being suddenly
lifted from the ground, and suspended in the air that is
disconcerting at the start, but this will soon wear off if
the experimenter will keep cool. A few successful flights
no matter how short they may be, will put a lot of
confidence into him.
Make Your Flights Short.
Be modest in your initial flights. Don't attempt to
match the records of experienced men who have devoted
years to mastering the details of aviation. Paulhan,
Farman, Bleriot, Wright, Curtiss, and all the rest of
them began, and practiced for years, in the manner here
described, being content to make just a little advancement
at each attempt. A flight of 150 feet, cleanly and
safely made, is better as a beginning than one of 400
yards full of bungling mishaps.
And yet these latter have their uses, provided the
operator is of a discerning mind and can take advantage
of them as object lessons. But, it is not well to invite
them. They will occur frequently enough under the
most favorable conditions, and it is best to have them
come later when the feeling of trepidation and uncertainty
as to what to do has worn off.
Above all, don't attempt to fly too high. Keep within
a reasonable distance from the ground--about 25 or 30
feet. This advice is not given solely to lessen the risk
of serious accident in case of collapse, but mainly because
it will assist to instill confidence in the operator.
It is comparatively easy to learn to swim in shallow
water, but the knowledge that one is tempting death in
deep water begets timidity.
Preserving the Equilibrium.
After learning how to start and stop, to ascend and
descend, the next thing to master is the art of preserving
equilibrium, the knack of keeping the machine perfectly
level in the air--on an "even keel," as a sailor would
say. This simile is particularly appropriate as all aviators
are in reality sailors, and much more daring ones
than those who course the seas. The latter are in craft
which are kept afloat by the buoyancy of the water,
whether in motion or otherwise and, so long as normal
conditions prevail, will not sink. Aviators sail the air
in craft in which constant motion must be maintained in
order to ensure flotation.
The man who has ridden a bicycle or motorcycle
around curves at anything like high speed, will have a
very good idea as to the principle of maintaining equilibrium
in an airship. He knows that in rounding curves
rapidly there is a marked tendency to change the direction
of the motion which will result in an upset unless
he overcomes it by an inclination of his body in an opposite
direction. This is why we see racers lean well
over when taking the curves. It simply must be done
to preserve the equilibrium and avoid a spill.
How It Works In the Air.
If the equilibrium of an airship is disturbed to an
extent which completely overcomes the center of gravity
it falls according to the location of the displacement.
If this displacement, for instance, is at either end the
apparatus falls endways; if it is to the front or rear, the
fall is in the corresponding direction.
Owing to uncertain air currents--the air is continually
shifting and eddying, especially within a hundred feet or
so of the earth--the equilibrium of an airship is almost
constantly being disturbed to some extent. Even if this
disturbance is not serious enough to bring on a fall it
interferes with the progress of the machine, and should
be overcome at once. This is one of the things connected
with aerial navigation which calls for prompt,
intelligent action.
Frequently, when the displacement is very slight, it
may be overcome, and the craft immediately righted by
a mere shifting of the operator's body. Take, for illustration,
a case in which the extreme right end of the
machine becomes lowered a trifle from the normal level.
It is possible to bring it back into proper position by
leaning over to the left far enough to shift the weight
to the counter-balancing point. The same holds good as
to minor front or rear displacements.
When Planes Must Be Used.
There are other displacements, however, and these are
the most frequent, which can be only overcome by manipulation of
the stabilizing planes. The method of procedure
depends upon the form of machine in use. The
Wright machine, as previously explained, is equipped
with plane ends which are so contrived as to admit of
their being warped (position changed) by means of the
lever control. These flexible tip planes move simultaneously,
but in opposite directions. As those on one end
rise, those on the other end fall below the level of the
main plane. By this means air is displaced at one point,
and an increased amount secured in another.
This may seem like a complicated system, but its
workings are simple when once understood. It is by
the manipulation or warping of these flexible tips that
transverse stability is maintained, and any tendency to
displacement endways is overcome. Longitudinal stability
is governed by means of the front rudder.
Stabilizing planes of some form are a feature, and a
necessary feature, on all flying machines, but the methods
of application and manipulation vary according to the
individual ideas of the inventors. They all tend, however,
toward the same end--the keeping of the machine
perfectly level when being navigated in the air.
When to Make a Flight.
A beginner should never attempt to make a flight
when a strong wind is blowing. The fiercer the wind,
the more likely it is to be gusty and uncertain, and the
more difficult it will be to control the machine. Even
the most experienced and daring of aviators find there
is a limit to wind speed against which they dare not
compete. This is not because they lack courage, but
have the sense to realize that it would be silly and useless.
The novice will find a comparatively still day, or one
when the wind is blowing at not to exceed 15 miles an
hour, the best for his experiments. The machine will be
more easily controlled, the trip will be safer, and also
cheaper as the consumption of fuel increases with the
speed of the wind against which the aeroplane is forced.
CHAPTER XIII.
PECULIARITIES OF AIRSHIP POWER.
As a general proposition it takes much more power to
propel an airship a given number of miles in a certain
time than it does an automobile carrying a far heavier
load. Automobiles with a gross load of 4,000 pounds,
and equipped with engines of 30 horsepower, have travelled
considerable distances at the rate of 50 miles an
hour. This is an equivalent of about 134 pounds per
horsepower. For an average modern flying machine,
with a total load, machine and passengers, of 1,200
pounds, and equipped with a 50-horsepower engine, 50
miles an hour is the maximum. Here we have the equivalent
of exactly 24 pounds per horsepower. Why this
great difference?
No less an authority than Mr. Octave Chanute answers
the question in a plain, easily understood manner. He
says:
"In the case of an automobile the ground furnishes a
stable support; in the case of a flying machine the engine
must furnish the support and also velocity by which the
apparatus is sustained in the air."
Pressure of the Wind.
Air pressure is a big factor in the matter of aeroplane
horsepower. Allowing that a dead calm exists, a body
moving in the atmosphere creates more or less resistance.
The faster it moves, the greater is this resistance.
Moving at the rate of 60 miles an hour the resistance,
or wind pressure, is approximately 50 pounds to the
square foot of surface presented. If the moving object
is advancing at a right angle to the wind the following
table will give the horsepower effect of the resistance
per square foot of surface at various speeds.
Horse Power
Miles per Hour per sq. foot
10 0.013
15 0 044
20 0.105
25 0.205
30 0.354
40 0.84
50 1.64
60 2.83
80 6.72
100 13.12
While the pressure per square foot at 60 miles an hour,
is only 1.64 horsepower, at 100 miles, less than double
the speed, it has increased to 13.12 horsepower, or exactly
eight times as much. In other words the pressure
of the wind increases with the square of the velocity.
Wind at 10 miles an hour has four times more pressure
than wind at 5 miles an hour.
How to Determine Upon Power.
This element of air resistance must be taken into consideration
in determining the engine horsepower required.
When the machine is under headway sufficient
to raise it from the ground (about 20 miles an hour),
each square foot of surface resistance, will require nearly
nine-tenths of a horsepower to overcome the wind pressure,
and propel the machine through the air. As
shown in the table the ratio of power required increases
rapidly as the speed increases until at 60 miles an hour
approximately 3 horsepower is needed.
In a machine like the Curtiss the area of wind-exposed
surface is about 15 square feet. On the basis of this
resistance moving the machine at 40 miles an hour would
require 12 horsepower. This computation covers only
the machine's power to overcome resistance. It does
not cover the power exerted in propelling the machine
forward after the air pressure is overcome. To meet
this important requirement Mr. Curtiss finds it necessary
to use a 50-horsepower engine. Of this power, as
has been already stated, 12 horsepower is consumed
in meeting the wind pressure, leaving 38 horsepower
for the purpose of making progress.
The flying machine must move faster than the air to
which it is opposed. Unless it does this there can be no
direct progress. If the two forces are equal there is no
straight-ahead advancement. Take, for sake of illustration,
a case in which an aeroplane, which has developed a
speed of 30 miles an hour, meets a wind velocity of
equal force moving in an opposite direction. What is
the result? There can be no advance because it is a
contest between two evenly matched forces. The aeroplane
stands still. The only way to get out of the difficulty
is for the operator to wait for more favorable conditions,
or bring his machine to the ground in the usual
manner by manipulation of the control system.
Take another case. An aeroplane, capable of making
50 miles an hour in a calm, is met by a head wind of 25
miles an hour. How much progress does the aeroplane
make? Obviously it is 25 miles an hour over the ground.
Put the proposition in still another way. If the wind
is blowing harder than it is possible for the engine power
to overcome, the machine will be forced backward.
Wind Pressure a Necessity.
While all this is true, the fact remains that wind
pressure, up to a certain stage, is an absolute necessity
in aerial navigation. The atmosphere itself has very
little real supporting power, especially if inactive. If
a body heavier than air is to remain afloat it must move
rapidly while in suspension.
One of the best illustrations of this is to be found in
skating over thin ice. Every school boy knows that if
he moves with speed he may skate or glide in safety
across a thin sheet of ice that would not begin to bear
his weight if he were standing still. Exactly the same
proposition obtains in the case of the flying machine.
The non-technical reason why the support of the machine
becomes easier as the speed increases is that the
sustaining power of the atmosphere increases with the
resistance, and the speed with which the object is moving
increases this resistance. With a velocity of 12 miles
an hour the weight of the machine is practically reduced
by 230 pounds. Thus, if under a condition of absolute
calm it were possible to sustain a weight of 770 pounds,
the same atmosphere would sustain a weight of 1,000
pounds moving at a speed of 12 miles an hour. This
sustaining power increases rapidly as the speed increases.
While at 12 miles the sustaining power is figured at
230 pounds, at 24 miles it is four times as great, or 920
pounds.
Supporting Area of Birds.
One of the things which all producing aviators seek
to copy is the motive power of birds, particularly in their
relation to the area of support. Close investigation has
established the fact that the larger the bird the less is
the relative area of support required to secure a given
result. This is shown in the following table:
Supporting
Weight Surface Horse area
Bird in lbs. in sq. feet power per lb.
Pigeon 1.00 0.7 0.012 0.7
Wild Goose 9.00 2.65 0.026 0.2833
Buzzard 5.00 5.03 0.015 1.06
Condor 17.00 9.85 0.043 0.57
So far as known the condor is the largest of modern
birds. It has a wing stretch of 10 feet from tip to tip, a
supporting area of about 10 square feet, and weighs 17
pounds. It. is capable of exerting perhaps 1-30 horsepower.
(These figures are, of course, approximate.)
Comparing the condor with the buzzard with a wing
stretch of 6 feet, supporting area of 5 square feet, and a
little over 1-100 horsepower, it may be seen that, broadly
speaking, the larger the bird the less surface area (relatively)
is needed for its support in the air.
Comparison With Aeroplanes.
If we compare the bird figures with those made possible
by the development of the aeroplane it will be
readily seen that man has made a wonderful advance in
imitating the results produced by nature. Here are the
figures:
Supporting
Weight Surface Horse area
Machine in lbs. in sq. feet power per lb.
Santos-Dumont . . 350 110.00 30 0.314
Bleriot . . . . . 700 150.00 25 0.214
Antoinette. . . . 1,200 538.00 50 0.448
Curtiss . . . . . 700 258.00 60 0.368
Wright. . . . .[4]1,100 538.00 25 0.489
Farman. . . . . . 1,200 430.00 50 0.358
Voisin. . . . . . 1,200 538.00 50 0.448
[4] The Wrights' new machine weighs only 900 pounds.
While the average supporting surface is in favor of
the aeroplane, this is more than overbalanced by the
greater amount of horsepower required for the weight
lifted. The average supporting surface in birds is about
three-quarters of a square foot per pound. In the average
aeroplane it is about one-half square foot per pound.
On the other hand the average aeroplane has a lifting
capacity of 24 pounds per horsepower, while the buzzard,
for instance, lifts 5 pounds with 15-100 of a horsepower.
If the Wright machine--which has a lifting power of 50
pounds per horsepower--should be alone considered the
showing would be much more favorable to the aeroplane,
but it would not be a fair comparison.
More Surface, Less Power.
Broadly speaking, the larger the supporting area the
less will be the power required. Wright, by the use of
538 square feet of supporting surface, gets along with an
engine of 25 horsepower. Curtiss, who uses only 258
square feet of surface, finds an engine of 50 horsepower
is needed. Other things, such as frame, etc., being equal,
it stands to reason that a reduction in the area of
supporting surface will correspondingly reduce the weight
of the machine. Thus we have the Curtiss machine with
its 258 square feet of surface, weighing only 600 pounds
(without operator), but requiring double the horsepower
of the Wright machine with 538 square feet of surface
and weighing 1,100 pounds. This demonstrates in a
forceful way the proposition that the larger the surface
the less power will be needed.
But there is a limit, on account of its bulk and
awkwardness in handling, beyond which the surface area
cannot be enlarged. Otherwise it might be possible to
equip and operate aeroplanes satisfactorily with engines
of 15 horsepower, or even less.
The Fuel Consumption Problem.
Fuel consumption is a prime factor in the production
of engine power. The veriest mechanical tyro knows in
a general way that the more power is secured the more
fuel must be consumed, allowing that there is no difference
in the power-producing qualities of the material
used. But few of us understand just what the ratio of
increase is, or how it is caused. This proposition is one
of keen interest in connection with aviation.
Let us cite a problem which will illustrate the point
quoted: Allowing that it takes a given amount of gasolene
to propel a flying machine a given distance, half the
way with the wind, and half against it, the wind blowing
at one-half the speed of the machine, what will be
the increase in fuel consumption?
Increase of Thirty Per Cent.
On the face of it there would seem to be no call for
an increase as the resistance met when going against the
wind is apparently offset by the propulsive force of the
wind when the machine is travelling with it. This, however,
is called faulty reasoning. The increase in fuel
consumption, as figured by Mr. F. W. Lanchester, of the
Royal Society of Arts, will be fully 30 per cent over
the amount required for a similar operation of the machine
in still air. If the journey should be made at right
angles to the wind under the same conditions the increase
would be 15 per cent.
In other words Mr. Lanchester maintains that the work
done by the motor in making headway against the wind
for a certain distance calls for more engine energy, and
consequently more fuel by 30 per cent, than is saved by
the helping force of the wind on the return journey.
CHAPTER XIV.
ABOUT WIND CURRENTS, ETC.
One of the first difficulties which the novice will
encounter is the uncertainty of the wind currents. With a
low velocity the wind, some distance away from the
ground, is ordinarily steady. As the velocity increases,
however, the wind generally becomes gusty and fitful
in its action. This, it should be remembered, does not
refer to the velocity of the machine, but to that of the
air itself.
In this connection Mr. Arthur T. Atherholt, president
of the Aero Club of Pennsylvania, in addressing the
Boston Society of Scientific Research, said:
"Probably the whirlpools of Niagara contain no more
erratic currents than the strata of air which is now immediately
above us, a fact hard to realize on account
of its invisibility."
Changes In Wind Currents.
While Mr. Atherholt's experience has been mainly
with balloons it is all the more valuable on this account,
as the balloons were at the mercy of the wind and their
varying directions afforded an indisputable guide as to
the changing course of the air currents. In speaking of
this he said:
"In the many trips taken, varying in distance traversed
from twenty-five to 900 miles, it was never possible
except in one instance to maintain a straight course.
These uncertain currents were most noticeable in the
Gordon-Bennett race from St. Louis in 1907. Of the
nine aerostats competing in that event, eight covered a
more or less direct course due east and southeast, whereas
the writer, with Major Henry B. Hersey, first started
northwest, then north, northeast, east, east by south, and
when over the center of Lake Erie were again blown
northwest notwithstanding that more favorable winds
were sought for at altitudes varying from 100 to 3,000
meters, necessitating a finish in Canada nearly northeast
of the starting point.
"These nine balloons, making landings extending from
Lake Ontario, Canada, to Virginia, all started from one
point within the same hour.
"The single exception to these roving currents occurred
on October 21st, of last year (1909) when, starting
from Philadelphia, the wind shifted more than eight
degrees, the greatest variation being at the lowest altitudes,
yet at no time was a height of over a mile reached.
"Throughout the entire day the sky was overcast, with
a thermometer varying from fifty-seven degrees at 300
feet to forty-four degrees, Fahrenheit at 5,000 feet, at
which altitude the wind had a velocity of 43 miles an
hour, in clouds of a cirro-cumulus nature, a landing finally
being made near Tannersville, New York, in the
Catskill mountains, after a voyage of five and one-half
hours.
"I have no knowledge of a recorded trip of this distance
and duration, maintained in practically a straight
line from start to finish."
This wind disturbance is more noticeable and more
difficult to contend with in a balloon than in a flying
machine, owing to the bulk and unwieldy character of
the former. At the same time it is not conducive to
pleasant, safe or satisfactory sky-sailing in an aeroplane.
This is not stated with the purpose of discouraging
aviation, but merely that the operator may know what to
expect and be prepared to meet it.
Not only does the wind change its horizontal course
abruptly and without notice, but it also shifts in a vertical
direction, one second blowing up, and another
down. No man has as yet fathomed the why and wherefore
of this erratic action; it is only known that it exists.
The most stable currents will be found from 50 to 100
feet from the earth, provided the wind is not diverted
by such objects as trees, rocks, etc. That there are
equally stable currents higher up is true, but they are
generally to be found at excessive altitudes.
How a Bird Meets Currents.
Observe a bird in action on a windy day and you will
find it continually changing the position of its wings.
This is done to meet the varying gusts and eddies of the
air so that sustentation may be maintained and headway
made. One second the bird is bending its wings, altering
the angle of incidence; the next it is lifting or depressing
one wing at a time. Still again it will extend
one wing tip in advance of the other, or be spreading or
folding, lowering or raising its tail.
All these motions have a meaning, a purpose. They
assist the bird in preserving its equilibrium. Without
them the bird would be just as helpless in the air as a
human being and could not remain afloat.
When the wind is still, or comparatively so, a bird,
having secured the desired altitude by flight at an angle,
may sail or soar with no wing action beyond an occasional
stroke when it desires to advance. But, in a
gusty, uncertain wind it must use its wings or alight
somewhere.
Trying to Imitate the Bird.
Writing in _Fly_, Mr. William E. White says:
"The bird's flight suggests a number of ways in which
the equilibrium of a mechanical bird may be controlled.
Each of these methods of control may be effected by
several different forms of mechanism.
"Placing the two wings of an aeroplane at an angle of
three to five degrees to each other is perhaps the oldest
way of securing lateral balance. This way readily occurs
to anyone who watches a sea gull soaring. The
theory of the dihedral angle is that when one wing is
lifted by a gust of wind, the air is spilled from under it;
while the other wing, being correspondingly depressed,
presents a greater resistance to the gust and is lifted
restoring the balance. A fixed angle of three to five degrees,
however, will only be sufficient for very light puffs
of wind and to mount the wings so that the whole wing
may be moved to change the dihedral angle presents
mechanical difficulties which would be better avoided.
"The objection of mechanical impracticability applies
to any plan to preserve the balance by shifting weight
or ballast. The center of gravity should be lower than
the center of the supporting surfaces, but cannot be
made much lower. It is a common mistake to assume
that complete stability will be secured by hanging the
center of gravity very low on the principle of the
parachute. An aeroplane depends upon rapid horizontal motion for
its support, and if the center of gravity be far
below the center of support, every change of speed or
wind pressure will cause the machine to turn about its
center of gravity, pitching forward and backward dangerously.
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