Construction and Operation
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Unknown >> Construction and Operation
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Frequently somebody asks why the ribs should be
curved. The answer is easy. The curvature tends to
direct the air downward toward the rear and, as the air
is thus forced downward, there is more or less of an impact
which assists in propelling the aeroplane upwards.
CHAPTER VI.
LEARNING TO FLY.
Don't be too ambitious at the start. Go slow, and
avoid unnecessary risks. At its best there is an element
of danger in aviation which cannot be entirely eliminated, but it
may be greatly reduced and minimized by
the use of common sense.
Theoretically, the proper way to begin a glide is from
the top of an incline, facing against the wind, so that
the machine will soar until the attraction of gravitation
draws it gradually to the ground. This is the manner in
which experienced aviators operate, but it must be kept
in mind that these men are experts. They understand
air currents, know how to control the action and direction
of their machines by shifting the position of their
bodies, and by so doing avoid accidents which would be
unavoidable by a novice.
Begin on Level Ground.
Make your first flights on level ground, having a couple
of men to assist you in getting the apparatus under
headway. Take your position in the center rectangle,
back far enough to give the forward edges of the glider
an inclination to tilt upward very slightly. Now start
and run forward at a moderately rapid gait, one man at
each end of the glider assisting you. As the glider cuts
into the air the wind will catch under the uplifted edges
of the curved planes, and buoy it up so that it will rise
in the air and take you with it. This rise will not be
great, just enough to keep you well clear of the ground.
Now project your legs a little to the front so as to shift
the center of gravity a trifle and bring the edges of the
glider on an exact level with the atmosphere. This, with
the momentum acquired in the start, will keep the machine
moving forward for some distance.
Effect of Body Movements.
When the weight of the body is slightly back of the
center of gravity the edges of the advancing planes are
tilted slightly upward. The glider in this position acts
as a scoop, taking in the air which, in turn, lifts it off the
ground. When a certain altitude is reached--this varies
with the force of the wind--the tendency to a forward
movement is lost and the glider comes to the ground.
It is to prolong the forward movement as much as possible
that the operator shifts the center of gravity slightly,
bringing the apparatus on an even keel as it were by
lowering the advancing edges. This done, so long as
there is momentum enough to keep the glider moving, it
will remain afloat.
If you shift your body well forward it will bring the
front edges of the glider down, and elevate the rear ones.
In this way the air will be "spilled" out at the rear, and,
having lost the air support or buoyancy, the glider comes
down to the ground. A few flights will make any ordinary
man proficient in the control of his apparatus by his
body movements, not only as concerns the elevating and
depressing of the advancing edges, but also actual steering. You
will quickly learn, for instance, that, as the
shifting of the bodily weight backwards and forwards
affects the upward and downward trend of the planes, so
a movement sideways--to the left or the right--affects
the direction in which the glider travels.
Ascends at an Angle.
In ascending, the glider and flying machine, like the
bird, makes an angular, not a vertical flight. Just what
this angle of ascension may be is difficult to determine.
It is probable and in fact altogether likely, that it varies
with the force of the wind, weight of the rising body,
power of propulsion, etc. This, in the language of physicists,
is the angle of inclination, and, as a general thing,
under normal conditions (still air) should be put down as
about one in ten, or 5 3/4 degrees. This would be an ideal
condition, but it has not, as vet been reached. The force
of the wind affects the angle considerably, as does also
the weight and velocity of the apparatus. In general
practice the angle varies from 23 to 45 degrees. At
more than 45 degrees the supporting effort is overcome
by the resistance to forward motion.
Increasing the speed or propulsive force, tends to
lessen the angle at which the machine may be successfully
operated because it reduces the wind pressure.
Most of the modern flying machines are operated at an
angle of 23 degrees, or less.
Maintaining an Equilibrium.
Stable equilibrium is one of the main essentials to
successful flight, and this cannot be preserved in an
uncertain, gusty wind, especially by an amateur. The
novice should not attempt a glide unless the conditions
are just right. These conditions are: A clear, level
space, without obstructions, such as trees, etc., and a
steady wind of not exceeding twelve miles an hour. Always
fly against the wind.
When a reasonable amount of proficiency in the handling
of the machine on level ground has been acquired
the field of practice may be changed to some gentle
slope. In starting from a slope it will be found easier
to keep the machine afloat, but the experience at first is
likely to be very disconcerting to a man of less than iron
nerve. As the glider sails away from the top of the
slope the distance between him and the ground increases
rapidly until the aviator thinks he is up a hundred miles
in the air. If he will keep cool, manipulate his apparatus
so as to preserve its equilibrium, and "let nature take its
course," he will come down gradually and safely to the
ground at a considerable distance from the starting place.
This is one advantage of starting from an elevation--
your machine will go further.
But, if the aviator becomes "rattled"; if he loses control
of his machine, serious results, including a bad fall
with risk of death, are almost certain. And yet this
practice is just as necessary as the initial lessons on
level ground. When judgment is used, and "haste made
slowly," there is very little real danger. While experimenting
with gliders the Wrights made flights innumerable
under all sorts of conditions and never had an accident
of any kind.
Effects of Wind Currents.
The larger the machine the more difficult it will be to
control its movements in the air, and yet enlargement is
absolutely necessary as weight, in the form of motor,
rudder, etc., is added.
Air currents near the surface of the ground are diverted
by every obstruction unless the wind is blowing
hard enough to remove the obstruction entirely. Take,
for instance, the case of a tree or shrub, in a moderate
wind of from ten to twelve miles an hour. As the wind
strikes the tree it divides, part going to one side and
part going to the other, while still another part is directed
upward and goes over the top of the obstruction.
This makes the handling of a glider on an obstructed
field difficult and uncertain. To handle a glider successfully
the place of operation should be clear and the wind
moderate and steady. If it is gusty postpone your flight.
In this connection it will be well to understand the velocity
of the wind, and what it means as shown in the
following table:
Miles per hour Feet per second Pressure per sq. foot
10 14.7 .492
25 36.7 3.075
50 73.3 12.300
100 146.6 49.200
Pressure of wind increases in proportion to the square
of the velocity. Thus wind at 10 miles an hour has four
times the pressure of wind at 5 miles an hour. The
greater this pressure the large and heavier the object
which can be raised. Any boy who has had experience
in flying kites can testify to this, High winds, however,
are almost invariably gusty and uncertain as to direction,
and this makes them dangerous for aviators. It
is also a self-evident fact that, beyond a certain stage,
the harder the wind blows the more difficult it is to
make headway against it.
Launching Device for Gliders.
On page 195 will be found a diagram of the various
parts of a launcher for gliders, designed and patented
by Mr. Octave Chanute. In describing this invention
in Aeronautics, Mr. Chanute says:
"In practicing, the track, preferably portable, is
generally laid in the direction of the existing wind and
the car, preferably a light platform-car, is placed on the
track. The truck carrying the winding-drum and its motor
is placed to windward a suitable distance--say from
two hundred to one thousand feet--and is firmly blocked
or anchored in line with the portable track, which is
preferably 80 or 100 feet in length. The flying or gliding
machine to be launched with its operator is placed on
the platform-car at the leeward end of the portable track.
The line, which is preferably a flexible combination
wire-and-cord cable, is stretched between the winding-
drum on the track and detachably secured to the flying
or gliding machine, preferably by means of a trip-hoop,
or else held in the hand of the operator, so that the
operator may readily detach the same from the flying-
machine when the desired height is attained.
How Glider Is Started.
"Then upon a signal given by the operator the engineer
at the motor puts it into operation, gradually increasing
the speed until the line is wound upon the drum
at a maximum speed of, say, thirty miles an hour. The
operator of the flying-machine, whether he stands upright and
carries it on his shoulders, or whether he sits
or lies down prone upon it, adjusts the aeroplane or
carrying surfaces so that the wind shall strike them on
the top and press downward instead of upward until
the platform-car under action of the winding-drum and
line attains the required speed.
"When the operator judges that his speed is sufficient,
and this depends upon the velocity of the wind as well
as that of the car moving against the wind, he quickly
causes the front of the flying-machine to tip upward, so
that the relative wind striking on the under side of the
planes or carrying surfaces shall lift the flying machine
into the air. It then ascends like a kite to such height
as may be desired by the operator, who then trips the
hook and releases the line from the machine.
What the Operator Does.
"The operator being now free in the air has a certain
initial velocity imparted by the winding-drum and line
and also a potential energy corresponding to his height
above the ground. If the flying or gliding machine is
provided with a motor, he can utilize that in his further
flight, and if it is a simple gliding machine without
motor he can make a descending flight through the air
to such distance as corresponds to the velocity acquired
and the height gained, steering meanwhile by the devices
provided for that purpose.
"The simplest operation or maneuver is to continue
the flight straight ahead against the wind; but it is possible
to vary this course to the right or left, or even to
return in downward flight with the wind to the vicinity
of the starting-point. Upon nearing the ground the
operator tips upward his carrying-surfaces and stops his
headway upon the cushion of increased air resistance
so caused. The operator is in no way permanently
fastened to his machine, and the machine and the operator
simply rest upon the light platform-car, so that
the operator is free to rise with the machine from the
car whenever the required initial velocity is attained.
Motor For the Launcher.
"The motor may be of any suitable kind or construction,
but is preferably an electric or gasolene motor.
The winding-drum is furnished with any suitable or customary
reversing-guide to cause the line to wind smoothly
and evenly upon the drum. The line is preferably a
cable composed of flexible wire and having a cotton or
other cord core to increase its flexibility. The line
extends from the drum to the flying or gliding machine.
Its free end may, if desired, be grasped and held by the
operator until the flying-machine ascends to the desired
height, when by simply letting go of the line the operator
may continue his flight free. The line, however, is preferably
connected to the flying or gliding machine
directly by a trip-hook having a handle or trip lever
within reach of the operator, so that when he ascends
to the required height he may readily detach the line
from the flying or gliding machine."
CHAPTER VII.
PUTTING ON THE RUDDER.
Gliders as a rule have only one rudder, and this is in
the rear. It tends to keep the apparatus with its head to
the wind. Unlike the rudder on a boat it is fixed and
immovable. The real motor-propelled flying machine,
generally has both front and rear rudders manipulated
by wire cables at the will of the operator.
Allowing that the amateur has become reasonably expert
in the manipulation of the glider he should, before
constructing an actual flying machine, equip his glider
with a rudder.
Cross Pieces for Rudder Beam.
To do this he should begin by putting in a cross piece,
2 feet long by 1/4x3/4 inches between the center struts,
in the lower plane. This may be fastened to the struts
with bolts or braces. The former method is preferable.
On this cross piece, and on the rear frame of the plane
itself, the rudder beam is clamped and bolted. This
rudder beam is 8 feet 11 inches long. Having put these
in place duplicate them in exactly the same manner and
dimensions from the upper frame The cross pieces on
which the ends of the rudder beams are clamped should
be placed about one foot in advance of the rear frame
beam.
The Rudder Itself.
The next step is to construct the rudder itself. This
consists of two sections, one horizontal, the other vertical.
The latter keeps the aeroplane headed into the wind,
while the former keeps it steady--preserves the equilibrium.
The rudder beams form the top and bottom frames of
the vertical rudder. To these are bolted and clamped
two upright pieces, 3 feet, 10 inches in length, and 3/4
inch in cross section. These latter pieces are placed about
two feet apart. This completes the framework of the
vertical rudder. See next page (59).
For the horizontal rudder you will require two strips
6 feet long, and four 2 feet long. Find the exact center
of the upright pieces on the vertical rudder, and at this
spot fasten with bolts the long pieces of the horizontal,
placing them on the outside of the vertical strips. Next
join the ends of the horizontal strips with the 2-foot
pieces, using small screws and corner braces. This done
you will have two of the 2-foot pieces left. These go in
the center of the horizontal frame, "straddling" the
vertical strips, as shown in the illustration.
The framework is to be covered with cloth in the
same manner as the planes. For this about ten yards
will be needed.
Strengthening the Rudder.
To ensure rigidity the rudder must be stayed with
guy wires. For this purpose the No. 12 piano wire is
the best. Begin by running two of these wires from the
top eye-bolts of stanchions 3 and 4, page 37, to rudder
beam where it joins the rudder planes, fastening them
at the bottom. Then run two wires from the top of the
rudder beam at the same point, to the bottom eye-bolts
of the same stanchions. This will give you four diagonal
wires reaching from the rudder beam to the top
and bottom planes of the glider. Now, from the outer
ends of the rudder frame run four similar diagonal wires
to the end of the rudder beam where it rests on the
cross piece. You will then have eight truss wires
strengthening the connection of the rudder to the main
body of the glider.
The framework of the rudder planes is then to be
braced in the same way, which will take eight more
wires, four for each rudder plane. All the wires are
to be connected at one end with turn-buckles so the
tension may be regulated as desired.
In forming the rudder frame it will be well to mortise
the corners, tack them together with small nails, and
then put in a corner brace in the inside of each joint.
In doing this bear in mind that the material to be thus
fastened is light, and consequently the lightest of nails,
screws, bolts and corner pieces, etc., is necessary.
CHAPTER VIII.
THE REAL FLYING MACHINE.
We will now assume that you have become proficient
enough to warrant an attempt at the construction of a
real flying machine--one that will not only remain suspended
in the air at the will of the operator, but make
respectable progress in whatever direction he may desire to go.
The glider, it must be remembered, is not
steerable, except to a limited extent, and moves only in
one direction--against the wind. Besides this its power
of flotation--suspension in the air--is 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 sleeve--this is merely a hollow tube
of aluminum or brass open at each end--8 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. Cover the
tongue thoroughly with glue, and also put some on the
inside of the groove. Use plenty of glue. Now press
the tongue into the groove, and keep the ends firmly
together until the glue is thoroughly dried. Rub off the
joint lightly with sand-paper to remove any of the glue
which may have oozed out, and slip the sleeve into place
over the joint. Tack the sleeve in position with small
copper tacks, and you will have an ideal splice.
The same operation is to be repeated on each of the
four frame pieces. Two 20-foot pieces joined in this
way will give a substantial frame, but when suitable
timber of this kind can not be had, three pieces, each 6
feet 11 inches long, may be used. This would give 20
feet 9 inches, of which 8 inches will be taken up in the
two joints, leaving the frame 20 feet 1 inch long.
Installation of Motor.
Next comes the installation of the motor. The kinds
and efficiency of the various types are described in the
following chapter (IX). All we are interested in at
this point is the manner of installation. This varies
according to the personal ideas of the aviator. Thus one
man puts his motor in the front of his machine, another
places it in the center, and still another finds the rear of
the frame the best. All get good results, the comparative
advantages of which it is difficult to estimate. Where
one man, as already explained, flies faster than another,
the one beaten from the speed standpoint has an advantage
in the matter of carrying weight, etc.
The ideas of various well-known aviators as to the
correct placing of motors may be had from the following:
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