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
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
Farcot--8-cylinder, air-cooled; from 30 to 100 horse
power, according to bore of cylinders; weight of smallest,
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
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
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
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
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.
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
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
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
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
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
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
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