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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 Weight Without
Propeller
Make Cylinders Horse Power Operator
Diameter
Curtiss 。 。 。 8 50 600 6。0
Wright。 。 。 。 4 25 1；100 8。1
Farman。 。 。 。 7 50 1；200 8。9
Voisin。 。 。 。 8 50 1；200 6。6
In giving the depth dimensions the length over all
from the extreme edge of the front auxiliary plane to
the extreme tip of the rear is stated。 Thus while the
dimensions of the main planes of the Wright machine
are 41 feet spread by 6 1/2 feet in depth； the depth over
all is 30。7。
Figuring Out the Details。
With this data as a guide it should be comparatively
easy to decide upon the dimensions of the machine required。
In arriving at the maximum lifting capacity the
weight of the operator must be added。 Assuming this
to average 170 pounds the method of procedure would be
as follows：
Add the weight of the operator to the weight of the
complete machine。 The new Wright machine complete
weighs 900 pounds。 This； plus 170； the weight of the
operator； gives a total of 1；070 pounds。 There are 538
square feet of supporting surface； or practically one
square foot of surface area to each two pounds of load。
There are some machines； notably the Bleriot； in which
the supporting power is much greater。 In this latter
instance we find a surface area of 150 1/2 square feet
carrying a load of 680 plus 170； or an aggregate of 850
pounds。 This is the equivalent of five pounds to the
square foot。 This ratio is phenomenally large； and
should not be taken as a guide by amateurs。
The Matter of Passengers。
These deductions are based on each machine carrying
one passenger； which is admittedly the limit at present
of the monoplanes like those operated for record…making
purposes by Santos…Dumont and Bleriot。 The bi