Construction and Operation
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Wrights--In rear of machine and to one side.
Curtiss--Well to rear, about midway between upper
and lower planes.
Raich--In rear, above the center.
Brauner-Smith--In exact center of machine.
Van Anden--In center.
Herring-Burgess--Directly behind operator.
Voisin--In rear, and on lower plane.
Bleriot--In front.
R. E. P.--In front.
The One Chief Object.
An even distribution of the load so as to assist in
maintaining the equilibrium of the machine, should be
the one chief object in deciding upon the location of the
motor. It matters little what particular spot is selected
so long as the weight does not tend to overbalance the
machine, or to "throw it off an even keel." It is just
like loading a vessel, an operation in which the expert
seeks to so distribute the weight of the cargo as to keep
the vessel in a perfectly upright position, and prevent a
"list" or leaning to one side. The more evenly the cargo
is distributed the more perfect will be the equilibrium of
the vessel and the better it can be handled. Sometimes,
when not properly stowed, the cargo shifts, and this at
once affects the position of the craft. When a ship
"lists" to starboard or port a preponderating weight of
the cargo has shifted sideways; if bow or stern is unduly
depressed it is a sure indication that the cargo has shifted
accordingly. In either event the handling of the craft
becomes not only difficult, but extremely hazardous.
Exactly the same conditions prevail in the handling of a
flying machine.
Shape of Machine a Factor.
In placing the motor you must be governed largely by
the shape and construction of the flying machine frame.
If the bulk of the weight of the machine and auxiliaries
is toward the rear, then the natural location for the motor
will be well to the front so as to counterbalance the
excess in rear weight. In the same way if the
preponderance of the weight is forward, then the motor
should be placed back of the center.
As the propeller blade is really an integral part of the
motor, the latter being useless without it, its placing
naturally depends upon the location selected for the
motor.
Rudders and Auxiliary Planes.
Here again there is great diversity of opinion among
aviators as to size, location and form. The striking
difference of ideas in this respect is well illustrated in
the choice made by prominent makers as follows:
Voisin--horizontal rudder, with two wing-like planes,
in front; box-like longitudinal stability plane in rear,
inside of which is a vertical rudder.
Wright--large biplane horizontal rudder in front at
considerable distance--about 10 feet--from the main
planes; vertical biplane rudder in rear; ends of upper
and lower main planes made flexible so they may be
moved.
Curtiss--horizontal biplane rudder, with vertical damping
plane between the rudder planes about 10 feet in
front of main planes; vertical rudder in rear; stabilizing
planes at each end of upper main plane.
Bleriot--V-shaped stabilizing fin, projecting from rear
of plane, with broad end outward; to the broad end of
this fin is hinged a vertical rudder; horizontal biplane
rudder, also in rear, under the fin.
These instances show forcefully the wide diversity of
opinion existing among experienced aviators as to the
best manner of placing the rudders and stabilizing, or
auxiliary planes, and make manifest how hopeless would
be the task of attempting to select any one form and
advise its exclusive use.
Rudder and Auxiliary Construction.
The material used in the construction of the rudders
and auxiliary planes is the same as that used in the main
planes--spruce for the framework and some kind of
rubberized or varnished cloth for the covering. The
frames are joined and wired in exactly the same manner
as the frames of the main planes, the purpose being to
secure the same strength and rigidity. Dimensions of
the various parts depend upon the plan adopted and the
size of the main plane.
No details as to exact dimensions of these rudders and
auxiliary planes are obtainable. The various builders,
while willing enough to supply data as to the general
measurements, weight, power, etc., of their machines,
appear to have overlooked the details of the auxiliary
parts, thinking, perhaps, that these were of no particular
import to the general public. In the Wright machine, the
rear horizontal and front vertical rudders may be set
down as being about one-quarter (probably a little less)
the size of the main supporting planes.
Arrangement of Alighting Gear.
Most modern machines are equipped with an alighting
gear, which not only serves to protect the machine and
aviator from shock or injury in touching the ground, but
also aids in getting under headway. All the leading
makes, with the exception of the Wright, are furnished
with a frame carrying from two to five pneumatic rubber-
tired bicycle wheels. In the Curtiss and Voisin
machines one wheel is placed in front and two in the
rear. In the Bleriot and other prominent machines the
reverse is the rule--two wheels in front and one in the
rear. Farman makes use of five wheels, one in the,
extreme rear, and four, arranged in pairs, a little to the
front of the center of the main lower plane.
In place of wheels the Wright machine is equipped
with a skid-like device consisting of two long beams
attached to the lower plane by stanchions and curving
up far in front, so as to act as supports to the horizontal
rudder.
Why Wood Is Favored.
A frequently asked question is: "Why is not aluminum,
or some similar metal, substituted for wood."
Wood, particularly spruce, is preferred because, weight
considered, it is much stronger than aluminum, and this
is the lightest of all metals. In this connection the following
table will be of interest:
Compressive
Weight Tensile Strength Strength
per cubic foot per sq. inch per sq. inch
Material in lbs. in lbs. in lbs.
Spruce . . . . 25 8,000 5,000
Aluminum 162 16,000 ......
Brass (sheet) 510 23,000 12,000
Steel (tool) 490 100,000 40,000
Copper (sheet) 548 30,000 40,000
As extreme lightness, combined with strength,
especially tensile strength, is the great essential in flying-
machine construction, it can be readily seen that the
use of metal, even aluminum, for the framework, is
prohibited by its weight. While aluminum has double the
strength of spruce wood it is vastly heavier, and thus
the advantage it has in strength is overbalanced many
times by its weight. The specific gravity of aluminum
is 2.50; that of spruce is only 0.403.
Things to Be Considered.
In laying out plans for a flying machine there are five
important points which should be settled upon before
the actual work of construction is started. These are:
First--Approximate weight of the machine when finished
and equipped.
Second--Area of the supporting surface required.
Third--Amount of power that will be necessary to
secure the desired speed and lifting capacity.
Fourth--Exact dimensions of the main framework
and of the auxiliary parts.
Fifth--Size, speed and character of the propeller.
In deciding upon these it will be well to take into
consideration the experience of expert aviators regarding
these features as given elsewhere. (See Chapter X.)
Estimating the Weights Involved.
In fixing upon the probable approximate weight in
advance of construction much, of course, must be assumed.
This means that it will be a matter of advance
estimating. If a two-passenger machine is to be built
we will start by assuming the maximum combined
weight of the two people to be 350 pounds. Most of
the professional aviators are lighter than this. Taking
the medium between the weights of the Curtiss and
Wright machines we have a net average of 850 pounds
for the framework, motor, propeller, etc. This, with
the two passengers, amounts to 1,190 pounds. As the
machines quoted are in successful operation it will be
reasonable to assume that this will be a safe basis to
operate on.
What the Novice Must Avoid.
This does not mean, however, that it will be safe to
follow these weights exactly in construction, but that
they will serve merely as a basis to start from. Because
an expert can turn out a machine, thoroughly equipped,
of 850 pounds weight, it does not follow that a novice
can do the same thing. The expert's work is the result
of years of experience, and he has learned how to construct
frames and motor plants of the utmost lightness
and strength.
It will be safer for the novice to assume that he can
not duplicate the work of such men as Wright and Curtiss
without adding materially to the gross weight of
the framework and equipment minus passengers.
How to Distribute the Weight.
Let us take 1,030 pounds as the net weight of the machine
as against the same average in the Wright and
Curtiss machines. Now comes the question of distributing
this weight between the framework, motor, and
other equipment. As a general proposition the framework
should weigh about twice as much as the complete
power plant (this is for amateur work).
The word "framework" indicates not only the wooden
frames of the main planes, auxiliary planes, rudders,
etc., but the cloth coverings as well--everything in fact
except the engine and propeller.
On the basis named the framework would weigh 686
pounds, and the power plant 344. These figures are
liberal, and the results desired may be obtained well
within them as the novice will learn as he makes progress
in the work.
Figuring on Surface Area.
It was Prof. Langley who first brought into prominence
in connection with flying machine construction the
mathematical principle that the larger the object the
smaller may be the relative area of support. As explained
in Chapter XIII, there are mechanical limits as
to size which it is not practical to exceed, but the main
principle remains in effect.
Take two aeroplanes of marked difference in area of
surface. The larger will, as a rule, sustain a greater
weight in relative proportion to its area than the smaller
one, and do the work with less relative horsepower. As
a general thing well-constructed machines will average
a supporting capacity of one pound for every one-half
square foot of surface area. Accepting this as a working
rule we find that to sustain a weight of 1,200 pounds
--machine and two passengers--we should have 600
square feet of surface.
Distributing the Surface Area.
The largest surfaces now in use are those of the
Wright, Voisin and Antoinette machines--538 square
feet in each. The actual sustaining power of these machines,
so far as known, has never been tested to the
limit; it is probable that the maximum is considerably
in excess of what they have been called upon to show.
In actual practice the average is a little over one pound
for each one-half square foot of surface area.
Allowing that 600 square feet of surface will be used,
the next question is how to distribute it to the best
advantage. This is another important matter in which
individual preference must rule. We have seen how
the professionals disagree on this point, some using
auxiliary planes of large size, and others depending upon
smaller auxiliaries with an increase in number so as to
secure on a different plan virtually the same amount of
surface.
In deciding upon this feature the best thing to do is
to follow the plans of some successful aviator, increasing
the area of the auxiliaries in proportion to the increase
in the area of the main planes. Thus, if you use 600
square feet of surface where the man whose plans you
are following uses 500, it is simply a matter of making
your planes one-fifth larger all around.
The Cost of Production.
Cost of production will be of interest to the amateur
who essays to construct a flying machine. Assuming
that the size decided upon is double that of the glider
the material for the framework, timber, cloth, wire, etc.,
will cost a little more than double. This is because it
must be heavier in proportion to the increased size of
the framework, and heavy material brings a larger price
than the lighter goods. If we allow $20 as the cost of
the glider material it will be safe to put down the cost
of that required for a real flying machine framework
at $60, provided the owner builds it himself.
As regards the cost of motor and similar equipment
it can only be said that this depends upon the selection
made. There are some reliable aviation motors which
may be had as low as $500, and there are others which
cost as much as $2,000.
Services of Expert Necessary.
No matter what kind of a motor may be selected the
services of an expert will be necessary in its proper
installation unless the amateur has considerable genius
in this line himself. As a general thing $25 should be
a liberal allowance for this work. No matter how carefully
the engine may be placed and connected it will be
largely a matter of luck if it is installed in exactly the
proper manner at the first attempt. The chances are
that several alterations, prompted by the results of trials,
will have to be made. If this is the case the expert's bill may
readily run up to $50. If the amateur is competent to do this
part of the work the entire item of $50 may, of course, be cut
out.
As a general proposition a fairly satisfactory flying machine,
one that will actually fly and carry the operator with it, may be
constructed for $750, but it will lack the better qualities which
mark the higher priced machines. This computation is made on
the basis of $60 for material, $50 for services of expert, $600
for motor, etc., and an allowance of $40 for extras.
No man who has the flying machine germ in his system will be long
satisfied with his first moderate price machine, no matter how
well it may work. It's the old story of the automobile "bug"
over again. The man who starts in with a modest $1,000 automobile
invariably progresses by easy stages to the $4,000 or $5,000
class. The natural tendency is to want the biggest and best
attainable within the financial reach of the owner.
It's exactly the same way with the flying machine
convert. The more proficient he becomes in the manipulation
of his car, the stronger becomes the desire to fly
further and stay in the air longer than the rest of his
brethren. This necessitates larger, more powerful, and
more expensive machines as the work of the germ progresses.
Speed Affects Weight Capacity.
Don't overlook the fact that the greater speed you
can attain the smaller will be the surface area you can
get along with. If a machine with 500 square feet of
sustaining surface, traveling at a speed of 40 miles an
hour, will carry a weight of 1,200 pounds, we can cut
the sustaining surface in half and get along with 250
square feet, provided a speed of 60 miles an hour can
be obtained. At 100 miles an hour only 80 square feet
of surface area would be required. In both instances the
weight sustaining capacity will remain the same as with
the 500 square feet of surface area--1,200 pounds.
One of these days some mathematical genius will
figure out this problem with exactitude and we will have
a dependable table giving the maximum carrying capacity
of various surface areas at various stated speeds,
based on the dimensions of the advancing edges. At
present it is largely a matter of guesswork so far as
making accurate computation goes. Much depends upon
the shape of the machine, and the amount of surface
offering resistance to the wind, etc.
CHAPTER IX.
SELECTION OF THE MOTOR.
Motors for flying machines must be light in weight,
of great strength, productive of extreme speed, and
positively dependable in action. It matters little
as to the particular form, or whether air or
water cooled, so long as the four features named are
secured. There are at least a dozen such motors or
engines now in use. All are of the gasolene type, and
all possess in greater or lesser degree the desired qualities.
Some of these motors are:
Renault--8-cylinder, air-cooled; 50 horse power;
weight 374 pounds.
Fiat--8-cylinder, air-cooled; 50 horse power; weight
150 pounds.
Farcot--8-cylinder, air-cooled; from 30 to 100 horse
power, according to bore of cylinders; weight of smallest,
84 pounds.
R. E. P.--10-cylinder, air-cooled; 150 horse power;
weight 215 pounds.
Gnome--7 and 14 cylinders, revolving type, air-cooled;
50 and 100 horse power; weight 150 and 300 pounds.
Darracq--2 to 14 cylinders, water cooled; 30 to 200
horse power; weight of smallest 100 pounds.
Wright--4-cylinder, water-cooled; 25 horse power;
weight 200 pounds.
Antoinette--8 and 16-cylinder, water-cooled; 50 and 100
horse power; weight 250 and 500 pounds.
E. N. V.--8-cylinder, water-cooled; from 30 to 80
horse power, according to bore of cylinder; weight 150
to 400 pounds.
Curtiss--8-cylinder, water-cooled; 60 horse power;
weight 300 pounds.
Average Weight Per Horse Power.
It will be noticed that the Gnome motor is unusually
light, being about three pounds to the horse power
produced, as opposed to an average of 4 1/2 pounds per
horse power in other makes. This result is secured by
the elimination of the fly-wheel, the engine itself revolving,
thus obtaining the same effect that would be produced
by a fly-wheel. The Farcot is even lighter, being
considerably less than three pounds per horse power,
which is the nearest approach to the long-sought engine
equipment that will make possible a complete flying
machine the total weight of which will not exceed one
pound per square foot of area.
How Lightness Is Secured.
Thus far foreign manufacturers are ahead of Americans
in the production of light-weight aerial motors, as
is evidenced by the Gnome and Farcot engines, both of
which are of French make. Extreme lightness is made
possible by the use of fine, specially prepared steel for
the cylinders, thus permitting them to be much thinner
than if ordinary forms of steel were used. Another big
saving in weight is made by substituting what are
known as "auto lubricating" alloys for bearings. These
alloys are made of a combination of aluminum and magnesium.
Still further gains are made in the use of alloy steel
tubing instead of solid rods, and also by the paring away
of material wherever it can be done without sacrificing
strength. This plan, with the exclusive use of the best
grades of steel, regardless of cost, makes possible a
marked reduction in weight.
Multiplicity of Cylinders.
Strange as it may seem, multiplicity of cylinders does
not always add proportionate weight. Because a 4-
cylinder motor weighs say 100 pounds, it does not necessarily
follow that an 8-cylinder equipment will weigh
200 pounds. The reason of this will be plain when it
is understood that many of the parts essential to a 4-
cylinder motor will fill the requirements of an 8-cylinder
motor without enlargement or addition.
Neither does multiplying the cylinders always increase
the horsepower proportionately. If a 4-cylinder
motor is rated at 25 horsepower it is not safe to take
it for granted that double the number of cylinders will
give 50 horsepower. Generally speaking, eight cylinders,
the bore, stroke and speed being the same, will give
double the power that can be obtained from four, but
this does not always hold good. Just why this exception
should occur is not explainable by any accepted rule.
Horse Power and Speed.
Speed is an important requisite in a flying-machine
motor, as the velocity of the aeroplane is a vital factor
in flotation. At first thought, the propeller and similar
adjuncts being equal, the inexperienced mind would
naturally argue that a 50-horsepower engine should
produce just double the speed of one of 25-horsepower.
That this is a fallacy is shown by actual performances.
The Wrights, using a 25-horsepower motor, have made
44 miles an hour, while Bleriot, with a 50-horsepower
motor, has a record of a short-distance flight at the rate
of 52 miles an hour. The fact is that, so far as speed
is concerned, much depends upon the velocity of the
wind, the size and shape of the aeroplane itself, and the
size, shape and gearing of the propeller. The stronger
the wind is blowing the easier it will be for the aeroplane
to ascend, but at the same time the more difficult
it will be to make headway against the wind in a horizontal
direction. With a strong head wind, and proper
engine force, your machine will progress to a certain
extent, but it will be at an angle. If the aviator desired
to keep on going upward this would be all right, but
there is a limit to the altitude which it is desirable to
reach--from 100 to 500 feet for experts--and after that
it becomes a question of going straight ahead.
Great Waste of Power.
One thing is certain--even in the most efficient of
modern aerial motors there is a great loss of power between
the two points of production and effect. The
Wright outfit, which is admittedly one of the most effective
in use, takes one horsepower of force for the raising
and propulsion of each 50 pounds of weight. This,
for a 25-horsepower engine, would give a maximum lifting
capacity of 1250 pounds. It is doubtful if any of the
higher rated motors have greater efficiency. As an 8-
cylinder motor requires more fuel to operate than a 4-
cylinder, it naturally follows that it is more expensive
to run than the smaller motor, and a normal increase in
capacity, taking actual performances as a criterion, is
lacking. In other words, what is the sense of using an
8-cylinder motor when one of 4 cylinders is sufficient?
What the Propeller Does.
Much of the efficiency of the motor is due to the form
and gearing of the propeller. Here again, as in other
vital parts of flying-machine mechanism, we have a wide
divergence of opinion as to the best form. A fish makes
progress through the water by using its fins and tail;
a bird makes its way through the air in a similar manner
by the use of its wings and tail. In both instances the
motive power comes from the body of the fish or bird.
In place of fins or wings the flying machine is equipped
with a propeller, the action of which is furnished by the
engine. Fins and wings have been tried, but they don't
work.
While operating on the same general principle, aerial
propellers are much larger than those used on boats.
This is because the boat propeller has a denser, more
substantial medium to work in (water), and consequently
can get a better "hold," and produce more propulsive
force than one of the same size revolving in the air.
This necessitates the aerial propellers being much larger
than those employed for marine purposes. Up to this
point all aviators agree, but as to the best form most of
them differ.
Kinds of Propellers Used.
One of the most simple is that used by Curtiss. It
consists of two pear-shaped blades of laminated wood,
each blade being 5 inches wide at its extreme point,
tapering slightly to the shaft connection. These blades
are joined at the engine shaft, in a direct line. The propeller
has a pitch of 5 feet, and weighs, complete, less
than 10 pounds. The length from end to end of the two
blades is 6 1/2 feet.
Wright uses two wooden propellers, in the rear of his
biplane, revolving in opposite directions. Each propeller
is two-bladed.
Bleriot also uses a two-blade wooden propeller, but
it is placed in front of his machine. The blades are each
about 3 1/2 feet long and have an acute "twist."
Santos-Dumont uses a two-blade wooden propeller,
strikingly similar to the Bleriot.
On the Antoinette monoplane, with which good records
have been made, the propeller consists of two spoon-
shaped pieces of metal, joined at the engine shaft in
front, and with the concave surfaces facing the machine.
The propeller on the Voisin biplane is also of metal,
consisting of two aluminum blades connected by a forged
steel arm.
Maximum thrust, or stress--exercise of the greatest
air-displacing force--is the object sought. This, according
to experts, is best obtained with a large propeller
diameter and reasonably low speed. The diameter is the
distance from end to end of the blades, which on the
largest propellers ranges from 6 to 8 feet. The larger
the blade surface the greater will be the volume of air
displaced, and, following this, the greater will be the
impulse which forces the aeroplane ahead. In all centrifugal
motion there is more or less tendency to disintegration
in the form of "flying off" from the center, and
the larger the revolving object is the stronger is this
tendency. This is illustrated in the many instances in
which big grindstones and fly-wheels have burst from
being revolved too fast. To have a propeller break
apart in the air would jeopardize the life of the aviator,
and to guard against this it has been found best to make
its revolving action comparatively slow. Besides this
the slow motion (it is only comparatively slow) gives
the atmosphere a chance to refill the area disturbed by
one propeller blade, and thus have a new surface for
the next blade to act upon.
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