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in the area of the main planes。 Thus； if you use 600
square feet of surface where the man whose plans you
are following uses 500； it is simply a matter of making
your planes one…fifth larger all around。
The Cost of Production。
Cost of production will be of interest to the amateur
who essays to construct a flying machine。 Assuming
that the size decided upon is double that of the glider
the material for the framework； timber； cloth； wire； etc。；
will cost a little more than double。 This is because it
must be heavier in proportion to the increased size of
the framework； and heavy material brings a larger price
than the lighter goods。 If we allow 20 as the cost of
the glider material it will be safe to put down the cost
of that required for a real flying machine framework
at 60； provided the owner builds it himself。
As regards the cost of motor and similar equipment
it can only be said that this depends upon the selection
made。 There are some reliable aviation motors which
may be had as low as 500； and there are others which
cost as much as 2；000。
Services of Expert Necessary。
No matter what kind of a motor may be selected the
services of an expert will be necessary in its proper
installation unless the amateur has considerable genius
in this line himself。 As a general thing 25 should be
a liberal allowance for this work。 No matter how carefully
the engine may be placed and connected it will be
largely a matter of luck if it is installed in exactly the
proper manner at the first attempt。 The chances are
that several alterations； prompted by the results of trials；
will have to be made。 If this is the case the expert's bill may
readily run up to 50。 If the amateur is competent to do this
part of the work the entire item of 50 may； of course； be cut
out。
As a general proposition a fairly satisfactory flying machine；
one that will actually fly and carry the operator with it； may be
constructed for 750； but it will lack the better qualities which
mark the higher priced machines。 This computation is made on
the basis of 60 for material； 50 for services of expert； 600
for motor； etc。； and an allowance of 40 for extras。
No man who has the flying machine germ in his system will be long
satisfied with his first moderate price machine； no matter how
well it may work。 It's the old story of the automobile 〃bug〃
over again。 The man who starts in with a modest 1；000 automobile
invariably progresses by easy stages to the 4；000 or 5；000
class。 The natural tendency is to want the biggest and best
attainable within the financial reach of the owner。
It's exactly the same way with the flying machine
convert。 The more proficient he becomes in the manipulation
of his car； the stronger becomes the desire to fly
further and stay in the air longer than the rest of his
brethren。 This necessitates larger； more powerful； and
more expensive machines as the work of the germ progresses。
Speed Affects Weight Capacity。
Don't overlook the fact that the greater speed you
can attain the smaller will be the surface area you can
get along with。 If a machine with 500 square feet of
sustaining surface； traveling at a speed of 40 miles an
hour； will carry a weight of 1；200 pounds； we can cut
the sustaining surface in half and get along with 250
square feet； provided a speed of 60 miles an hour can
be obtained。 At 100 miles an hour only 80 square feet
of surface area would be required。 In both instances the
weight sustaining capacity will remain the same as with
the 500 square feet of surface area1；200 pounds。
One of these days some mathematical genius will
figure out this problem with exactitude and we will have
a dependable table giving the maximum carrying capacity
of various surface areas at various stated speeds；
based on the dimensions of the advancing edges。 At
present it is largely a matter of guesswork so far as
making accurate computation goes。 Much depends upon
the shape of the machine； and the amount of surface
offering resistance to the wind； etc。
CHAPTER IX。
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 qualities。
Some of these motors are：
Renault8…cylinder； air…cooled； 50 horse power；
weight 374 pounds。
Fiat8…cylinder； air…cooled； 50 horse power； weight
150 pounds。
Farcot8…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。
Gnome7 and 14 cylinders； revolving type； air…cooled；
50 and 100 horse power； weight 150 and 300 pounds。
Darracq2 to 14 cylinders； water cooled； 30 to 200
horse power； weight of smallest 100 pounds。
Wright4…cylinder； water…cooled； 25 horse power；
weight 200 pounds。
Antoinette8 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。
Curtiss8…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 sacri