the design of flying machines.
and bodies when inclined at various angles. It is, there-
fore, best to construct a small model of the machine, and
determine the centre of lift at any angle, by placing it in a
wind tunnel. Or a small paper glider may be made, and
the weight adjusted until the best glide is obtained. Then
we may assume that the centre of gravity of the figure
corresponds with the centre of pressure.
If, when the centre of lift has been determined, it is
found not to be in the right position relatively to the centre
of gravity, then the centre of gravity should be changed by
altering the position of the engine, or operator, etc.
The above calculations, although simple, are perhaps
of greater use to the practical man than the higher
mathematics of the aeroplane.
LABORATORY INSTRUMENTS AND APPARATUS
IT is interesting at this stage to study briefly the instru-
ments and apparatus which are used for determining
experimental data connected with the science of aeronautics.
This apparatus may be divided roughly into four
(1) Anemometers, or instruments for measuring the
speed or the distance travelled through the air.
(2) Aerodynamical balances.
(3) Propeller-testing apparatus.
(4) Wind-tunnels and whirling-tables to enable the
bodies being tested to be subjected to a current
(1) Anemometers may be divided into two types,
(a) Rotary vane, screw, or windmill type.
(6) Pressure type, in which the speed is recorded
by measuring the thrust or pressure of
(a) The rotary-vane anemometer is provided with an
extremely light aluminium vane, very delicately mounted,
so that it is rotated by the slightest motion of the air.
This vane is connected, by means of gearing with a meter,
which records the number of revolutions made by the
vane. The instrument is graduated by the makers to
record the number of feet of air passed over by the
instrument. If the distance travelled is divided by the
time taken, the resulting quotient gives the velocity.
(b) There are various types of pressure anemometers.
In the anemometer, invented by Sir Hiram Maxim
and shown in Fig. 84, two bell-crank levers are pivoted to
a weather-vane, and a spiral tension spring is connected
to the two opposing arms. A horizontal rod is pivoted
to the upper arms of the bell-crank levers, and is provided
with a vertical disc of known area. A pointer is con-
LABORATORY INSTRUMENTS AND APPARATUS.
nected to one of the bell-cranks. The instrument may be
graduated to read either the pressure or the velocity of
FIG. 84. Maxim's anemometer.
the wind, the pressure and velocity being connected by the
formula P = '003AV 2 .
A simple and extremely accurate method of measuring
the speed is by means of a Pitot tube in conjunction with
a sensitive water-gauge. The tube A (Fig. 85) has a
facing the current,
and the tube B,
for measuring the B
static pressure of
the current, has a
conical end with
small holes per-
pendicular to the
axis. The dif-
erence in pressure
= h in the two
tubes is measured
by a water-gauge.
The velocity v
is connected with the head h by the formula
FIG. 85. Pitot tube.
78 ELEMENTARY AERONAUTICS. .
where k is a constant, which does not differ greatly from
unity, (k = 1 '03, Dr Stan ton).
(2) Aerodynamic balances are of numerous types, and
may be employed for a large number of different purposes,
Thus, the variation of the lift, with the inclination of a
plane, may be determined by means of a simple piece of
apparatus due to Lord Rayleigh.
In a modification of Lord Rayleigh's apparatus, three
vanes are mounted on a frictionless spindle, each vane
being set at 120 with the other. The vanes are of equal
area, and are set at precisely the same distances from the
If two vanes are both inclined at the same angle, and
the remaining plane is set so as to tend to twist the
apparatus in the opposite direction, the angle of this plane
may be adjusted until it balances the torque of the two
A means of finding the relation between the torque
i.e., the lift- of inclined planes is thus provided.
Lord Rayleigh found that the maximum torque, or lift,
with flat planes, occurs when the inclination is about 2*7.
The same apparatus may be used to compare the
relative lifts of inclined-curved planes.
We can also determine the relative values, as regards
lift, of any two shapes of planes, by means of a similar
device, in which the two planes are balanced or weighed
against one another, a standard flat plane being used as a
Since we know, from exact experiment, the lift of the
flat plane at various angles, a very ready and reliable
means is provided of testing the lift of a certain plane by
a comparison with that of a known plane.
The drift and various other data connected with
aeroplane and aerocurves may be obtained by balancing
two planes about an axis at right angles to the direction
(3) Propellers should be tested when running (a)
without axial motion, and (6) with axial motion.
(a) The static tests may be made by suspending the
propeller and driving mechanism from above, and measuring
the deflection and horse-power consumed when running at
various speeds. The thrust may then be obtained by
finding the force required to obtain the same deflections.
To obtain the thrust on the dirigible balloon " La
LABORATORY INSTRUMENTS AND APPARATUS.
France," Colonel Renard swung the whole cage from the
roof by means of a parallel suspension, as shown in
Welner used the apparatus shown in Fig. 87.
In the Walker- Alexander tests, in which propellers of
30 feet in diameter were used, the thrust was recorded
by means of the pull on a spring balance (Fig. 88).
(6) Propellers may be tested under axially running
conditions by means of a wind tunnel or whirling-table.
In the first case, the propeller is placed in a current of
air having a known velocity, and the readings connecting
thrust, horse-power and revolutions are determined. This
method does not greatly commend
itself, in view of the fact that the
field of a propeller is considerably
greater than the diameter, and also
that it does not permit tests being
FIG. 86. Static test of propellers.
FIG. 87. Static test of
made when the propeller is not axial to the current
In the second case, the propeller is mounted in any
axial position required, at the end of a radial arm project-
ing from a rotating vertical shaft, and the readings con-
necting thrust, horse-power and revolutions are taken and
plotted. The devices for enabling these readings;- to be
obtained are numerous and ingenious.
(4) Wind tunnels and whirling tables.
The whirling table consists of a vertical rotating
shaft carrying a radial arm, at the end of which the
propellers, planes or bodies to be tested are suitably
80 ELEMENTARY AERONAUTICS.
In Sir Hiram Maxim's apparatus (Fig. 89), a fixed
vertical steel shaft a, 6 inches in diameter, was mounted in
a pedestal b, firmly grounded in concrete. This shaft was
embraced by two pine planks n, 2 inches thick, between
which were mounted the two members h of the radiating
arm. The weight of the rotating parts was carried on a
ball race u>. The members h were of Honduras mahogany
with their edges sharpened off, and were prevented from
twisting by means of. a tubej, 12 feet long, to the arms of
which bracing wires were connected. The circumference
of the circle around which the aeroplanes and propellers
travelled was exactly 200 feet. The power was trans-
FIG. 88. Static test of propellers. (Walker- Alexander.)
mitted from the engine to the propeller through a shaft /,
bevel wheels, vertical shaft, pulley and belt i running
through the arms h.
The operation was as follows : The aeroplane g to be
tested was mounted on a double parallel-motion linkage
so that its inclination to the air always remained the same
throughout the experiment. Upon starting the engine,
the propeller caused the radial arm to travel at any desired
velocity up to 90 miles per hour. The thrust of the screw
caused the screw shaft to travel longitudinally against the
action of a spring. This motion was transmitted to the
pointer o by means of a fine wire. The pointer travelled
over a graduated scale, thus enabling the thrust to be read
at sight. The lift of the aeroplanes was determined by
placing weights or shot in the pan r until the lift was
LABORATORY INSTRUMENTS AND APPARATUS.
balanced. Then the actual lift was obtained, when the
machine was stationary, by finding the pull required to
lift the aeroplane against the weight of the pan r. The
FIG. 91. Wind tunnel. (Stanton.)
speed at which the propellers and aeroplanes were travel-
ling was read by means of the centrifugal gauge p.
The power transmitted to the propellers was recorded
by means of a sensitive direct - transmission hydraulic
84 ELEMENTARY AERONAUTICS.
Thus, all the readings required, relating to aeroplanes
and propellers, could be taken.
The wind tunnel consists of a tube, passage or tunnel,
through which air may be forced or drawn by means of
rotating fans, steam jets, or tbe like.
The tunnel may be vertical or horizontal. Sir Hiram
Maxim used a horizontal tunnel (Fig. 90), in w r hich the
small part a was 12 feet long by 3 feet square inside, and
the large part was 4 feet square. Two wooden screws b
were mounted on a shaft h in the large part. The bearings
of the shaft were supported by the diagonals c. Horizontal
slats of wood d between the screws, and vertical and
horizontal slats e,f, and diagonal boards g, were provided
to prevent rotation of the air column. The lifts and drifts
of aerocurves and other bodies were measured by means
of a double system of parallel-motion linkage.
Dr Stanton used a wind tunnel (Fig. 91), in which the
current was vertical and downwards. An electrically-
driven fan, 2 feet 6 inches diameter, mounted in a box,
4 feet square, drew the air through a channel, 2 feet
diameter by 4 feet 6 inches long. The pressure of the air
on the test pieces was weighed by means of a delicate
beam provided with a jockey weight and dash-pot.
TYPES OF MACHINES
MAXIM'S first machine, which was built and experimented
with in 1893-4, was a biplane, having fore and aft control,
i.e., the longitudinal equilibrium of the machine was
maintained by means of horizontal 'rudders placed before
FIG. 92. Maxim's first biplane.
and behind the main planes. The spread of the planes
was 105 feet. These planes were in three portions. The
centre portion carried the whole of the machinery, and the
other portions were set at a dihedral angle, as shown in
Figs. 92 and 93, to give automatic lateral stability. The
total supporting area was 4000 square feet, and the weight
was between 7000 and 8000 Ibs. The machine lifted on
one occasion fully 10,000 Ibs.
Propellers (2) wood, 17 feet 10 inches diameter
driven by two compound steam-engines, each
of 1 80 horse-power.
FIG. 93. Drawings of Maxim's first biplane.
Maxim's second machine (Figs. 1 and 94) is a direct
lineal descendant of the first type. The main planes are
again divided into three portions, with the outer portions
raised so as to give lateral stability. The machine is
TYPES OF MACHINES.
provided with fore and aft biplane elevators, each
13 feet 6 inches by 3 feet. The main planes are 44 feet
spread by 6 feet 6 inches width and 6 feet 6 inches apart.
FIG. 94. Drawings of Maxim's second biplane.
There are three propellers, two 11 feet 3f inches diameter,
and one 5 feet diameter, driven by a 50 horse-power engine.
Total supporting area, 734 square feet.
The Wright machine (Fig. 95) is a biplane, having two
elevators in the front set at a negative angle with the
main plane. These elevators ride parallel to the wind
under normal conditions, and may be warped upwards or
downwards to elevate or depress the machine, Two
vertical rudders are provided at the back of the machine
for steering. The machine is controlled laterally by the
combined use of the vertical rudders and warping wings.
The rear corners of the main planes are cross connected
so that a downward motion of one corner causes an
upward motion of
the other corner.
The camber of the
main planes is 1 in
20, the maximum rise
being one-third width
from the front edge.
The total area of
the machine is 594
square feet, and the
weight in order of
flight is 1200 Ibs.
Thus, the machine
supports 2 Ibs. per
The gliding angle
is about I in
Main planes 41
feet by 6 feet
8 inches by 6
feet 2 inches
Elevators (2) 15
feet 6 inches
by 3 feet by 3
feet apart, and
10 feet 8 inches
Rudders (2) 5
feet 10 inches
FIG. 95. Drawings of the Wright biplane.
by 2 feet, and 6 feet 8 inches behind.
Propellers (2) \Vood, 8 feet 6 inches diameter,
550 revs, per min. Pitch angle, 25 degrees.
This very successful one-man biplane (Fig. 96), is
provided with fore and aft control, as in Maxim's machines.
TYPES OF MACHINES.
The front elevator is a biplane 6 feet by 2 feet, and
12 feet in front of the main planes. The back .elevator
is a single plane, 6 feet by 2 feet, and' 12 feet behind the
main planes. The main planes are 28 feet 9 inches span by
4 feet 6 inches wide by 5 feet apart. Camber 1 in 17. One
of the features of the machine is in the position of the
FIG. 96. Drawings of the Curtiss biplane.
ailerons (6 feet by 2 feet), which are mounted between the
main planes with the outer portions projecting beyond the
extremities of the main planes. The machine is steered
by a vertical triangular rudder in the front, and a fixed
vertical plane is provided at the rear, to give an anchorage
on the air for steering.
Weight in flying order = 550 Ibs.
Total supporting area = 250.
Weight supported per square foot = 2'2 Ibs.
FIG. 97. The Curtiss' machine in full flight.
One propeller, 6 feet 6 inches diameter by 5 feet
pitch, running at 1200 revolutions, and driven
by an engine of 30 horse-power.
The Wright Bros, began their experiments in 1900 by
constructing a "glider." In 1903 they applied a motor to
their machine, and made the first power flight. In 1905
they flew 24 miles in 38 minutes. These experiments,
which are now well authenticated, were conducted in secret,
and Europe was sceptical.
However, inspired by these accounts, experimenters were
busy, and in October 1906 Santos Dumont made the first
official flight. He was followed by Farman and Delagrange
using machines constructed by Voisin Freres.
The Voisin machine (Fig. 98) is a biplane having a fixed
box-tail and a front elevator. Side curtains are generally
provided between the main planes to add to the lateral
stability. Ailerons are generally not provided, the machine
being controlled laterally by means of the vertical rudder
mounted in the box-tail.
The main planes are 32 feet 10 inches span, by 6 feet
7 inches wide, by 6 feet 7 inches apart :
The tail planes are 7 feet 11 inches long, by 6 feet
7 inches wide, and are placed 13 feet 4 inches
behind the main planes.
TYPES OF MACHINES.
The front elevator is formed of two portions pivoting
together, each 6 feet 11 inches long by 3 feet
3 inches wide, and is placed 4 feet 4 inches
in front of the main planes.
The propeller is, a metal one, 7 feet 6 inches in
FIG. 98. Drawings of the Voisin biplane.
diameter, and 4 feet 7 inches pitch, and has a
central non-acting portion of about 2 feet
8 inches diameter. It is mounted directly upon
the engine shaft, and runs at about 1100 revs,
The main planes are single surfaced, and have a
camber of about 1 in 20.
92 ELEMENTARY AERONAUTICS.
The maximum rise is 2 feet from the front
edge. The elevators are doubled surfaced.
The weight in order of flight is about
The total supporting area is about 590 square feet,
FIG. 99. The Voison machine "head on" in full flight at Hheims.
giving a load 2 Ibs. per square foot of support-
ing surface. The gliding angle is between
1 in 6 and 1 in 7.
Figs. 99, 100, 101, and 102 show photographs of
this famous machine in full flight under various
FIG. 100. The Voisin machine from front right-hand side
in full flight at Juvisy.
Fia. 101. The Voison machine "broadside on " in
full flight at Rheims.
FIG. 102. The Voisin machine from rear right-hand side
in full flight at Juvisy.
The type of machine, shown in Fig. 103, built by Farman,
is a modification of the Voisin machine. It is a biplane,
having a single elevator 15 feet by 3 feet in front, and a
tail biplane in the rear. The ailerons (5 feet 9 inches by
1 foot 7 inches) are let into the outer portions of the rear
edge of the main planes, and are pulled down against the
action of the wind.
The main planes are 32 feet 6 inches span, by
6 feet 4 inches wide, by 6 feet 4 inches apart.
The tail planes are 6 feet 9 inches span, by
5 feet 9 inches wide.
Weight in flying order = 1400 Ibs.
Total supporting area = 532 square feet.
TYPES OF MACHINES.
Weight supported per square feet = 2*6 Ibs.
One propeller, 8 feet 6 inches diameter, driven by a
50 horse-power engine.
FIG. 103. Drawings of the Farman machine.
The latest type of Farman machine is provided with a
supplementary elevator at the back of the tail, thus giving
the machine fore and aft control.
M. Bleriot has been actively experimenting with
monoplanes since 1900.
The Bleriot, No. 11 (cross-Channel) type (Fig. 104),
consists of a front main plane, 28 feet span by 6 feet wide,
and a tail plane, 6 feet 1 inch by 2 feet 10 inches, having
elevators 2 feet 10 inches square at each side. The camber
of the main planes is 1 in 20. The machine is controlled
laterally by warping the main plane, and it is steered by
a vertical tail rudder, having an area of 4J square feet.
FIG. 104. Drawings of the Bleriot monoplane.
(No. II cross-Channel type.)
Weight in flying order =715 Ibs.
Total supporting area =180 square feet.
Weight supported per square foot = 4 Ibs.
The propeller is 6 feet 8 inches diameter, and is
placed in front of the main plane, and is driven
by an engine of 25-30 horse-power.
This machine is seen in full flight in Fig. 105.
TYPES OF MACHINES.
The main plane of this machine (Fig. 106) is formed of
two wings set at a dihedral angle for the purpose of giving
the machine lateral stability. The tail consists of an
approximately triangular horizontal plane with the apex
towards the main plane. It is surmounted by a triangular
vertical plane which gives the machine additional lateral
stability. The elevator consists of a triangular horizontal
FIG. 106. Drawings of the
plane placed behind the horizontal tail. The machine is
steered by triangular vertical rudders. The main plane is
46 feet span, and is 10 feet wide at the centre, and 6 feet
8 inches at the tips. The machine is controlled laterally
by warping the wings or by ailerons on the back edges.
Weight in flying order = 1300 Ibs.
Total supporting area = 420 square feet.
TYPES OF MACHINES.
FIG. 107. Latham in full flight at Rheims on an Antoinette monoplane.
Weight supported per square foot = 3*1 Ibs.
One propeller, 6 feet 10 inches diameter.
The machine is shown in Fig. 107 in full flight.
In this machine (Figs. 108 and 109) the dimensions have
been reduced to the smallest amount. Thus, the span is
only 18 feet and the length over all 20 feet. The lateral
stability is controlled by warping the wings, and the
machine is steered and elevated by a cruciform tail
mounted on a universal joint.
The main planes are 6 feet 5 inches wide, having a
camber of 1 in 19.
Weight in flying order = 41 2 Ibs.
Total supporting area = 140 square feet.
Weight supported per square foot = 2'94 Ibs.
One propeller, 6 feet 6 inches diameter, driven by a
30 horse-power engine.
THE problem of flight has been solved largely, owing to the
light and powerful motor which has been developed for
Sixteen years ago, Sir Hiram Maxim, by utilising every
appliance which experience could suggest, or modern skill
could devise, was able to produce a steam-engine of
180 brake horse-power, which weighed only 320 Ibs.
The total weight per horse-power of the whole apparatus,
complete with burner, boiler, pump, condenser, etc., was
reduced to the low value of between 8 and 9 Ibs. per horse-
power. This result was the best that had ever been done,
and appeared marvellous at the time.
Sir Hiram soon found that the great disadvantage of
the steam-engine was on account of the great quantity
and weight of water which it consumed.
In a paper which he wrote at that time, he stated this
difficulty, and said that what was required was to develop
the gasolene motor. This was done for the motor-car, and
as a result the air has been conquered.
In the early days of the motor-car, many varied and
different types of engine were proposed. These have
nearly all died out, and the engine has been reduced to the
most suitable type.
The standard type which is best suited for aeronautical
work has not yet been determined. It is, therefore, our
purpose to consider the various types which are in
Aeronautical engines may be broadly divided into
three types :
(1) Modifications of the existing motor-car types.
(2) The radial type, in which the cylinders are dis-
posed around or partly around the crank-case
(3) The rotary type, in which the shaft is fixed and
the cylinders revolve around it.
CYCLE OF OPERATIONS
Most petrol engines work on the cycle of operations
known as the Otto cycle. In this cycle there is only one
explosion for every four strokes or two revolutions.
(1) On the down or suction stroke, the inlet valve is
opened, and the air and petrol are sucked into
(2) On the back or compression stroke, the mixture
(3) At the end of the compression, it is exploded by
means of an electric spark. Then follows the
expansion or working stroke.
(4) On the back or exhaust stroke, the exhaust
valve is open, and the exploded products are
In almost all fly ing- machine engines, the ignition is
obtained by means of a high-tension magneto. The
principle of this is the
same as that of the
machine, or dynamo.
An armature, wound
with a primary or low-
tension winding, and
a secondary or high-
tension winding, is
rotated between the
poles of a permanent
magnet. The armature
consists of an iron core,
wound, as shown in
As the armature is
revolved, the numbers
of the lines of force passing through the core are varied,
and thus an electro-motive force is generated in the
FIG. 110. Diagram illustrating the principle
of the high-tension magnet.
AERONAUTICAL ENGINES. 103
primary circuit, which causes a current to flow. This
current is suddenly broken by means of the contact breaker,
and this induces a current of high potential in the secondary
circuit, from which it is led away to the distributer con-
nected to the sparking plugs.
Commercial petrol is a mixture of various lighter
liquids of the paraffin series, which have the chemical
formula of the order of Cn H 2 +2.
Commercial petrol, having a specific gravity of '72 at
15 C., is composed principally of a mixture of hexane and
heptane C 6 H 14 and C 7 H 16 .
The lightest petrol or gasolene supplied, having a
specific gravity of about "64, is composed almost wholly of
pentane C 5 H 12 . This very light petrol is now being used
for flying machines. It will be seen from its chemical
formula that it contains more energy per Ib. weight than
the others, owing to the increased proportion of hydrogen.
* Spec. Gravity Coef. of
at 15 C. Expansion, (a)
Pratt -719 -00125