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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
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 machinesthe 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