flying machines-第13节
按键盘上方向键 ← 或 → 可快速上下翻页，按键盘上的 Enter 键可回到本书目录页，按键盘上方向键 ↑ 可回到本页顶部！
————未阅读完？加入书签已便下次继续阅读！
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； 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
