Construction and Operation
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Placing of the Motor.
As on other points, aviators differ widely in their
ideas as to the proper position for the motor. Wright
locates his on the lower plane, midway between the front
and rear edges, but considerably to one side of the exact
center. He then counter-balances the engine weight by
placing his seat far enough away in the opposite direction
to preserve the center of gravity. This leaves a
space in the center between the motor and the operator
in which a passenger may be carried without disturbing
the equilibrium.
Bleriot, on the contrary, has his motor directly in
front and preserves the center of gravity by taking his
seat well back, this, with the weight of the aeroplane,
acting as a counter-balance.
On the Curtiss machine the motor is in the rear, the
forward seat of the operator, and weight of the horizontal
rudder and damping plane in front equalizing the
engine weight.
No Perfect Motor as Yet.
Engine makers in the United States, England, France
and Germany are all seeking to produce an ideal motor
for aviation purposes. Many of the productions are
highly creditable, but it may be truthfully said that
none of them quite fill the bill as regards a combination
of the minimum of weight with the maximum of
reliable maintained power. They are all, in some respects,
improvements upon those previously in use, but
the great end sought for has not been fully attained.
One of the motors thus produced was made by the
French firm of Darracq at the suggestion of Santos Dumont, and on
lines laid down by him. Santos Dumont
wanted a 2-cylinder horizontal motor capable of developing
30 horsepower, and not exceeding 4 1/2 pounds per
horsepower in weight.
There can be no question as to the ability and skill
of the Darracq people, or of their desire to produce a
motor that would bring new credit and prominence to
the firm. Neither could anything radically wrong be
detected in the plans. But the motor, in at least one
important requirement, fell short of expectations.
It could not be depended upon to deliver an energy
of 30 horsepower continuously for any length of time.
Its maximum power could be secured only in "spurts."
This tends to show how hard it is to produce an ideal
motor for aviation purposes. Santos Dumont, of undoubted
skill and experience as an aviator, outlined definitely
what he wanted; one of the greatest designers
in the business drew the plans, and the famous house of
Darracq bent its best energies to the production. But
the desired end was not fully attained.
Features of Darracq Motor.
Horizontal motors were practically abandoned some
time ago in favor of the vertical type, but Santos Dumont
had a logical reason for reverting to them. He
wanted to secure a lower center of gravity than would
be possible with a vertical engine. Theoretically his
idea was correct as the horizontal motor lies flat, and
therefore offers less resistance to the wind, but it did not
work out as desired.
At the same time it must be admitted that this Darracq
motor is a marvel of ingenuity and exquisite workmanship.
The two cylinders, having a bore of 5 1-10
inches and a stroke of 4 7-10 inches, are machined out
of a solid bar of steel until their weight is only 8 4-5
pounds complete. The head is separate, carrying the
seatings for the inlet and exhaust valves, is screwed onto
the cylinder, and then welded in position. A copper
water-jacket is fitted, and it is in this condition that the
weight of 8 4-5 pounds is obtained.
On long trips, especially in regions where gasolene is
hard to get, the weight of the fuel supply is an important
feature in aviation. As a natural consequence flying
machine operators favor the motor of greatest economy
in gasolene consumption, provided it gives the necessary
power.
An American inventor, Ramsey by name, is working
on a motor which is said to possess great possibilities
in this line. Its distinctive features include a connecting
rod much shorter than usual, and a crank shaft located
the length of the crank from the central axis of the
cylinder. This has the effect of increasing the piston
stroke, and also of increasing the proportion of the
crank circle during which effective pressure is applied
to the crank.
Making the connecting rod shorter and leaving the
crank mechanism the same would introduce excessive
cylinder friction. This Ramsey overcomes by the location
of his crank shaft. The effect of the long piston
stroke thus secured, is to increase the expansion of the
gases, which in turn increases the power of the engine
without increasing the amount of fuel used.
Propeller Thrust Important.
There is one great principle in flying machine propulsion
which must not be overlooked. No matter how
powerful the engine may be unless the propeller thrust
more than overcomes the wind pressure there can be
no progress forward. Should the force of this propeller
thrust and that of the wind pressure be equal the result
is obvious. The machine is at a stand-still so far
as forward progress is concerned and is deprived of the
essential advancing movement.
Speed not only furnishes sustentation for the airship,
but adds to the stability of the machine. An aeroplane
which may be jerky and uncertain in its movements, so
far as equilibrium is concerned, when moving at a slow
gait, will readily maintain an even keel when the speed
is increased.
Designs for Propeller Blades.
It is the object of all men who design propellers to
obtain the maximum of thrust with the minimum expenditure
of engine energy. With this purpose in view
many peculiar forms of propeller blades have been
evolved. In theory it would seem that the best effects
could be secured with blades so shaped as to present a
thin (or cutting) edge when they come out of the wind,
and then at the climax of displacement afford a maximum
of surface so as to displace as much air as possible.
While this is the form most generally favored
there are others in successful operation.
There is also wide difference in opinion as to the
equipment of the propeller shaft with two or more
blades. Some aviators use two and some four. All
have more or less success. As a mathematical proposition
it would seem that four blades should give more
propulsive force than two, but here again comes in one
of the puzzles of aviation, as this result is not always
obtained.
Difference in Propeller Efficiency.
That there is a great difference in propeller efficiency
is made readily apparent by the comparison of effects
produced in two leading makes of machines--the Wright
and the Voisin.
In the former a weight of from 1,100 to 1,200 pounds
is sustained and advance progress made at the rate of
40 miles an hour and more, with half the engine speed
of a 25 horse-power motor. This would be a sustaining
capacity of 48 pounds per horsepower. But the actual
capacity of the Wright machine, as already stated, is 50
pounds per horsepower.
The Voisin machine, with aviator, weighs about 1,370
pounds, and is operated with a so-horsepower motor.
Allowing it the same speed as the Wright we find that,
with double the engine energy, the lifting capacity is
only 27 1/2 pounds per horsepower. To what shall we
charge this remarkable difference? The surface of the
planes is exactly the same in both machines so there
is no advantage in the matter of supporting area.
Comparison of Two Designs.
On the Wright machine two wooden propellers of
two blades each (each blade having a decided "twist")
are used. As one 25 horsepower motor drives both propellers the
engine energy amounts to just one-half of
this for each, or 12 1/2 horsepower. And this energy is
utilized at one-half the normal engine speed.
On the Voisin a radically different system is employed.
Here we have one metal two-bladed propeller with a
very slight "twist" to the blade surfaces. The full energy
of a 50-horsepower motor is utilized.
Experts Fail to Agree.
Why should there be such a marked difference in
the results obtained? Who knows? Some experts
maintain that it is because there are two propellers on
the Wright machine and only one on the Voisin, and
consequently double the propulsive power is exerted.
But this is not a fair deduction, unless both propellers
are of the same size. Propulsive power depends upon
the amount of air displaced, and the energy put into the
thrust which displaces the air.
Other experts argue that the difference in results may
be traced to the difference in blade design, especially
in the matter of "twist."
The fact is that propeller results depend largely upon
the nature of the aeroplanes on which they are used.
A propeller, for instance, which gives excellent results
on one type of aeroplane, will not work satisfactorily on
another.
There are some features, however, which may be safely
adopted in propeller selection. These are: As extensive
a diameter as possible; blade area 10 to 15 per cent
of the area swept; pitch four-fifths of the diameter;
rotation slow. The maximum of thrust effort will be thus
obtained.
CHAPTER X.
PROPER DIMENSIONS OF MACHINES.
In laying out plans for a flying machine the first thing
to decide upon is the size of the plane surfaces. The
proportions of these must be based upon the load to be
carried. This includes the total weight of the machine
and equipment, and also the operator. This will be a
rather difficult problem to figure out exactly, but
practical approximate figures may be reached.
It is easy to get at the weight of the operator, motor
and propeller, but the matter of determining, before they
are constructed, what the planes, rudders, auxiliaries,
etc., will weigh when completed is an intricate proposition.
The best way is to take the dimensions of some
successful machine and use them, making such alterations
in a minor way as you may desire.
Dimensions of Leading Machines.
In the following tables will be found the details as to
surface area, weight, power, etc., of the nine principal
types of flying machines which are now prominently before
the public:
MONOPLANES.
Surface area Spread in Depth in
Make Passengers sq. feet linear feet linear
feet
Santos-Dumont . . 1 110 16.0 26.0
Bleriot . . . . . 1 150.6 24.6 22.0
R. E. P . . . . . 1 215 34.1 28.9
Bleriot . . . . . 2 236 32.9 23.0
Antoinette. . . . 2 538 41.2 37.9
No. of Weight Without
Propeller
Make Cylinders Horse Power Operator
Diameter
Santos-Dumont. . 2 30 250 5.0
Bleriot. . . . . 3 25 680 6.9
R. E. P. . . . . 7 35 900 6.6
Bleriot. . . . . 7 50 1,240 8.1
Antoinette . . . 8 50 1,040 7.2
BIPLANES.
Surface Area Spread in Depth
in
Make Passengers sq. feet linear feet linear
feet
Curtiss . . . 2 258 29.0
28.7
Wright. . . . 2 538 41.0
30.7
Farman. . . . 2 430 32.9
39.6
Voisin. . . . 2 538 37.9
39.6
No. of Weight Without
Propeller
Make Cylinders Horse Power Operator
Diameter
Curtiss . . . 8 50 600 6.0
Wright. . . . 4 25 1,100 8.1
Farman. . . . 7 50 1,200 8.9
Voisin. . . . 8 50 1,200 6.6
In giving the depth dimensions the length over all--
from the extreme edge of the front auxiliary plane to
the extreme tip of the rear is stated. Thus while the
dimensions of the main planes of the Wright machine
are 41 feet spread by 6 1/2 feet in depth, the depth over
all is 30.7.
Figuring Out the Details.
With this data as a guide it should be comparatively
easy to decide upon the dimensions of the machine required.
In arriving at the maximum lifting capacity the
weight of the operator must be added. Assuming this
to average 170 pounds the method of procedure would be
as follows:
Add the weight of the operator to the weight of the
complete machine. The new Wright machine complete
weighs 900 pounds. This, plus 170, the weight of the
operator, gives a total of 1,070 pounds. There are 538
square feet of supporting surface, or practically one
square foot of surface area to each two pounds of load.
There are some machines, notably the Bleriot, in which
the supporting power is much greater. In this latter
instance we find a surface area of 150 1/2 square feet
carrying a load of 680 plus 170, or an aggregate of 850
pounds. This is the equivalent of five pounds to the
square foot. This ratio is phenomenally large, and
should not be taken as a guide by amateurs.
The Matter of Passengers.
These deductions are based on each machine carrying
one passenger, which is admittedly the limit at present
of the monoplanes like those operated for record-making
purposes by Santos-Dumont and Bleriot. The biplanes,
however, have a two-passenger capacity, and this adds
materially to the proportion of their weight-sustaining
power as compared with the surface area. In the following
statement all the machines are figured on the
one-passenger basis. Curtiss and Wright have carried
two passengers on numerous occasions, and an extra 170
pounds should therefore be added to the total weight
carried, which would materially increase the capacity.
Even with the two-passenger load the limit is by no
means reached, but as experiments have gone no further
it is impossible to make more accurate figures.
Average Proportions of Load.
It will be interesting, before proceeding to lay out the
dimension details, to make a comparison of the proportion
of load effect with the supporting surfaces of various
well-known machines. Here are the figures:
Santos-Dumont--A trifle under four pounds per square
foot.
Bleriot--Five pounds.
R. E. P.--Five pounds.
Antoinette--About two and one-quarter pounds.
Curtiss--About two and one-half pounds.
Wright--Two and one-quarter pounds.
Farman--A trifle over three pounds.
Voisin--A little under two and one-half pounds.
Importance of Engine Power.
While these figures are authentic, they are in a way
misleading, as the important factor of engine power
is not taken into consideration. Let us recall the fact
that it is the engine power which keeps the machine in
motion, and that it is only while in motion that the machine
will remain suspended in the air. Hence, to attribute the support
solely to the surface area is erroneous.
True, that once under headway the planes contribute
largely to the sustaining effect, and are absolutely essential
in aerial navigation--the motor could not rise without
them--still, when it comes to a question of weight-
sustaining power, we must also figure on the engine
capacity.
In the Wright machine, in which there is a lifting
capacity of approximately 2 1/4 pounds to the square foot
of surface area, an engine of only 25 horsepower is used.
In the Curtiss, which has a lifting capacity of 2 1/2
pounds per square foot, the engine is of 50 horsepower.
This is another of the peculiarities of aerial construction
and navigation. Here we have a gain of 1/4 pound in
weight-lifting capacity with an expenditure of double
the horsepower. It is this feature which enables Curtiss
to get along with a smaller surface area of supporting
planes at the expense of a big increase in engine power.
Proper Weight of Machine.
As a general proposition the most satisfactory machine
for amateur purposes will be found to be one with
a total weight-sustaining power of about 1,200 pounds.
Deducting 170 pounds as the weight of the operator,
this will leave 1,030 pounds for the complete motor-
equipped machine, and it should be easy to construct one
within this limit. This implies, of course, that due care
will be taken to eliminate all superfluous weight by using
the lightest material compatible with strength and safety.
This plan will admit of 686 pounds weight in the
frame work, coverings, etc., and 344 for the motor,
propeller, etc., which will be ample. Just how to distribute
the weight of the planes is a matter which must
be left to the ingenuity of the builder.
Comparison of Bird Power.
There is an interesting study in the accompanying
illustration. Note that the surface area of the albatross
is much smaller than that of the vulture, although the
wing spread is about the same. Despite this the albatross
accomplishes fully as much in the way of flight
and soaring as the vulture. Why? Because the albaboss is quicker
and more powerful in action. It is
the application of this same principle in flying machines
which enables those of great speed and power to get
along with less supporting surface than those of slower
movement.
Measurements of Curtiss Machine.
Some idea of framework proportion may be had from
the following description of the Curtiss machine. The
main planes have a spread (width) of 29 feet, and are
4 1/2 feet deep. The front double surface horizontal rudder
is 6x2 feet, with an area of 24 square feet. To the
rear of the main planes is a single surface horizontal
plane 6x2 feet, with an area of 12 square feet. In connection
with this is a vertical rudder 2 1/2 feet square.
Two movable ailerons, or balancing planes, are placed
at the extreme ends of the upper planes. These are 6x2
feet, and have a combined area of 24 square feet. There
is also a triangular shaped vertical steadying surface in
connection with the front rudder.
Thus we have a total of 195 square feet, but as the
official figures are 258, and the size of the triangular-
shaped steadying surface is unknown, we must take it
for granted that this makes up the difference. In the
matter of proportion the horizontal double-plane rudder
is about one-tenth the size of the main plane, counting
the surface area of only one plane, the vertical rudder
one-fortieth, and the ailerons one-twentieth.
CHAPTER XI.
PLANE AND RUDDER CONTROL.
Having constructed and equipped your machine, the
next thing is to decide upon the method of controlling
the various rudders and auxiliary planes by which the
direction and equilibrium and ascending and descending
of the machine are governed.
The operator must be in position to shift instantaneously the
position of rudders and planes, and also to control
the action of the motor. This latter is supposed to
work automatically and as a general thing does so with
entire satisfaction, but there are times when the supply
of gasolene must be regulated, and similar things done.
Airship navigation calls for quick action, and for this
reason the matter of control is an important one--it is
more than important; it is vital.
Several Methods of Control.
Some aviators use a steering wheel somewhat after
the style of that used in automobiles, and by this not
only manipulate the rudder planes, but also the flow of
gasolene. Others employ foot levers, and still others,
like the Wrights, depend upon hand levers.
Curtiss steers his aeroplane by means of a wheel, but
secures the desired stabilizing effect with an ingenious
jointed chair-back. This is so arranged that by leaning
toward the high point of his wing planes the aeroplane
is restored to an even keel. The steering post of the
wheel is movable backward and forward, and by this
motion elevation is obtained.
The Wrights for some time used two hand levers, one
to steer by and warp the flexible tips of the planes, the
other to secure elevation. They have now consolidated
all the functions in one lever. Bleriot also uses the
single lever control.
Farman employs a lever to actuate the rudders, but
manipulates the balancing planes by foot levers.
Santos-Dumont uses two hand levers with which to
steer and elevate, but manipulates the planes by means
of an attachment to the back of his outer coat.
Connection With the Levers.
No matter which particular method is employed, the
connection between the levers and the object to be manipulated
is almost invariably by wire. For instance, from
the steering levers (or lever) two wires connect with opposite
sides of the rudder. As a lever is moved so as to
draw in the right-hand wire the rudder is drawn to the
right and vice versa. The operation is exactly the same
as in steering a boat. It is the same way in changing
the position of the balancing planes. A movement of
the hands or feet and the machine has changed its
course, or, if the equilibrium is threatened, is back on
an even keel.
Simple as this seems it calls for a cool head, quick
eye, and steady hand. The least hesitation or a false
movement, and both aviator and craft are in danger.
Which Method is Best?
It would be a bold man who would attempt to pick
out any one of these methods of control and say it was
better than the others. As in other sections of aeroplane
mechanism each method has its advocates who dwell
learnedly upon its advantages, but the fact remains that
all the various plans work well and give satisfaction.
What the novice is interested in knowing is how the
control is effected, and whether he has become proficient
enough in his manipulation of it to be absolutely dependable
in time of emergency. No amateur should attempt
a flight alone, until he has thoroughly mastered
the steering and plane control. If the services and advice of an
experienced aviator are not to be had the
novice should mount his machine on some suitable supports
so it will be well clear of the ground, and, getting
into the operator's seat, proceed to make himself well
acquainted with the operation of the steering wheel and
levers.
Some Things to Be Learned.
He will soon learn that certain movements of the
steering gear produce certain effects on the rudders. If,
for instance, his machine is equipped with a steering
wheel, he will find that turning the wheel to the right
turns the aeroplane in the same direction, because the
tiller is brought around to the left. In the same way
he will learn that a given movement of the lever throws
the forward edge of the main plane upward, and that the
machine, getting the impetus of the wind under the concave
surfaces of the planes, will ascend. In the same
way it will quickly become apparent to him that an opposite
movement of the lever will produce an opposite
effect--the forward edges of the planes will be lowered,
the air will be "spilled" out to the rear, and the machine
will descend.
The time expended in these preliminary lessons will
be well spent. It would be an act of folly to attempt to
actually sail the craft without them.
CHAPTER XII.
HOW TO USE THE MACHINE.
It is a mistaken idea that flying machines must be
operated at extreme altitudes. True, under the impetus
of handsome prizes, and the incentive to advance scientific
knowledge, professional aviators have ascended to
considerable heights, flights at from 500 to 1,500 feet being
now common with such experts as Farman, Bleriot,
Latham, Paulhan, Wright and Curtiss. The altitude
record at this time is about 4,165 feet, held by Paulhan.
One of the instructions given by experienced aviators
to pupils, and for which they insist upon implicit obeyance, is:
"If your machine gets more than 30 feet high,
or comes closer to the ground than 6 feet, descend at
once." Such men as Wright and Curtiss will not tolerate
a violation of this rule. If their instructions are
not strictly complied with they decline to give the offender
further lessons.
Why This Rule Prevails.
There is good reason for this precaution. The higher
the altitude the more rarefied (thinner) becomes the air,
and the less sustaining power it has. Consequently the
more difficult it becomes to keep in suspension a given
weight. When sailing within 30 feet of the ground sustentation
is comparatively easy and, should a fall occur,
the results are not likely to be serious. On the other
hand, sailing too near the ground is almost as objectionable
in many ways as getting up too high. If the craft
is navigated too close to the ground trees, shrubs, fences
and other obstructions are liable to be encountered.
There is also the handicap of contrary air currents
diverted by the obstructions referred to, and which will
be explained more fully further on.
How to Make a Start.
Taking it for granted that the beginner has familiarized
himself with the manipulation of the machine, and especially
the control mechanism, the next thing in order
is an actual flight. It is probable that his machine will
be equipped with a wheeled alighting gear, as the skids
used by the Wrights necessitate the use of a special
starting track. In this respect the wheeled machine is
much easier to handle so far as novices are concerned
as it may be easily rolled to the trial grounds. This,
as in the case of the initial experiments, should be a
clear, reasonably level place, free from trees, fences,
rocks and similar obstructions with which there may be
danger of colliding.
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