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

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


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.

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


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


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