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steerable； except to a limited extent； and moves only in
one directionagainst the wind。 Besides this its power
of flotationsuspension in the airis circumscribed。
Larger Surface Area Required。
The real flying machine is the glider enlarged； and
equipped with motor and propeller。 The first thing to
do is to decide upon the size required。 While a glider
of 20 foot spread is large enough to sustain a man it
could not under any possible conditions； be made to rise
with the weight of the motor； propeller and similar
equipment added。 As the load is increased so must the
surface area of the planes be increased。 Just what this
increase in surface area should be is problematical as
experienced aviators disagree； but as a general proposition
it may be placed at from three to four times the area of
a 20…foot glider。＇3＇
＇3＇ See Chapter XXV。
Some Practical Examples。
The Wrights used a biplane 41 feet in spread； and 6 1/2
ft。 deep。 This； for the two planes； gives a total surface
area of 538 square feet； inclusive of auxiliary planes。
This sustains the engine equipment； operator； etc。； a total
weight officially announced at 1；070 pounds。 It shows
a lifting capacity of about two pounds to the square
foot of plane surface； as against a lifting capacity of
about 1/2 pound per square foot of plane surface for the
20…foot glider。 This same Wright machine is also reported
to have made a successful flight； carrying a total
load of 1；100 pounds； which would be over two pounds
for each square foot of surface area； which； with auxiliary
planes； is 538 square feet。
To attain the same results in a monoplane； the single
surface would have to be 60 feet in spread and 9 feet
deep。 But； while this is the mathematical rule； Bleriot
has demonstrated that it does not always hold good。
On his record…breaking trip across the English channel；
July 25th； 1909； the Frenchman was carried in a
monoplane 24 1/2 feet in spread； and with a total sustaining
surface of 150 1/2 square feet。 The total weight of
the outfit； including machine； operator and fuel sufficient
for a three…hour run； was only 660 pounds。 With
an engine of （nominally） 25 horsepower the distance of
21 miles was covered in 37 minutes。
Which is the Best？
Right here an established mathematical quantity is
involved。 A small plane surface offers less resistance
to the air than a large one and consequently can attain
a higher rate of speed。 As explained further on in this
chapter speed is an important factor in the matter of
weight…sustaining capacity。 A machine that travels one…
third faster than another can get along with one…half the
surface area of the latter without affecting the load。 See
the closing paragraph of this chapter on this point。 In
theory the construction is also the simplest； but this is
not always found to be so in practice。 The designing
and carrying into execution of plans for an extensive
area like that of a monoplane involves great skill and
cleverness in getting a framework that will be strong
enough to furnish the requisite support without an undue excess
of weight。 This proposition is greatly simplified
in the biplane and； while the speed attained by the latter
may not be quite so great as that of the monoplane； it
has much larger weight…carrying capacity。
Proper Sizes For Frame。
Allowing that the biplane form is selected the construction
may be practically identical with that of the
20…foot glider described in Chapter V。； except as to size
and elimination of the armpieces。 In size the surface
planes should be about twice as large as those of the
20…foot glider； viz： 40 feet spread instead of 20； and 6 feet
deep instead of 3。 The horizontal beams； struts； stanchions；
ribs； etc。； should also be increased in size proportionately。
While care in the selection of clear； straight…grained
timber is important in the glider； it is still more important
in the construction of a motor…equipped flying
machine as the strain on the various parts will be much
greater。
How to Splice Timbers。
It is practically certain that you will have to resort to
splicing the horizontal beams as it will be difficult； if not
impossible； to find 40…foot pieces of timber totally free
from knots and worm holes； and of straight grain。
If splicing is necessary select two good 20…foot pieces；
3 inches wide and 1 1/2 inches thick； and one 10…foot long；
of the same thickness and width。 Plane off the bottom
sides of the 10…foot strip； beginning about two feet back
from each end； and taper them so the strip will be about
3/4 inch thick at the extreme ends。 Lay the two 20…foot
beams end to end； and under the joint thus made place
the 10…foot strip； with the planed…off ends downward。
The joint of the 20…foot pieces should be directly in the
center of the 10…foot piece。 Bore ten holes （with a 1/4…
inch augur） equi…distant apart through the 20…foot
strips and the 10…foot strip under them。 Through these
holes run 1/4…inch stove bolts with round； beveled heads。
In placing these bolts use washers top and bottom； one
between the head and the top beam； and the other between
the bottom beam and the screw nut which holds
the bolt。 Screw the nuts down hard so as to bring the
two beams tightly together； and you will have a rigid
40…foot beam。
Splicing with Metal Sleeves。
An even better way of making a splice is by tonguing
and grooving the ends of the frame pieces and enclosing
them in a metal sleeve； but it requires more mechanical
skill than the method first named。 The operation of
tonguing and grooving is especially delicate and calls
for extreme nicety of touch in the handling of tools； but
if this dexterity is possessed the job will be much more
satisfactory than one done with a third timber。
As the frame pieces are generally about 1 1/2 inch in
diameter； the tongue and the groove into which the
tongue fits must be correspondingly small。 Begin by
sawing into one side of one of the frame pieces about 4
inches back from the end。 Make the cut about 1/2 inch
deep。 Then turn the piece over and duplicate the cut。
Next saw down from the end to these cuts。 When the
sawed…out parts are removed you will have a 〃tongue〃
in the end of the frame timber 4 inches long and 1/2 inch
thick。 The next move is to saw out a 5/8…inch groove in
the end of the frame piece which is to be joined。 You
will have to use a small chisel to remove the 5/8…inch bit。
This will leave a groove into which the tongue will fit
easily。
Joining the Two Pieces。
Take a thin metal sleevethis is merely a hollow tube
of aluminum or brass open at each end8 inches long；
and slip it over either the tongued or grooved end of one
of the frame timbers。 It is well to have the sleeve fit
snugly； and this may necessitate a sand…papering of the
frame pieces so the sleeve will slip on。
Push the sleeve well back out of the way。