EXPERIMENTS WITH APPARATUS ATTACHED TO A ROTATING ARM.
From what information I have at hand, it appears that Prof. Langley made
his first experiments with a small apparatus, using aeroplanes only a
few inches in dimensions which travelled round a circle perhaps 12 feet
in diameter. With this little apparatus, he was able to show that the
lifting effect of aeroplanes was a great deal more than had previously
been supposed. After having made these first experiments, he seems to
have come to the conclusion that Newton’s law was erroneous. Shortly
after Langley had made these experiments on what he called a whirling
table, which, however, was not a very appropriate name, I made an
apparatus myself, but very much larger than that employed by Prof.
Langley. I reckoned the size of my aeroplanes in feet, where he had
reckoned his in inches. The circumference of the circle around which my
aeroplanes were driven was exactly 200 feet, and shortly after this
Langley constructed another apparatus, the same dimensions as my own.
From an engraving which I have before me, it appears that he constructed
an extremely large wooden scale beam supported by numerous braces, but
free to be tilted in a vertical direction after the manner of all other
scale beams. As this apparatus was of great weight and offered enormous
resistance to the air, I do not understand how it was possible to obtain
any very correct readings, especially as it was in the open and subject
to every varying current of air.
[Illustration: Fig. 32.--Machine with a rotating arm, 31·8 feet long, to
which is attached the object to be experimented with. Professor Langley
had a similar machine and called it a “whirling table.”]
[Illustration: Fig. 33.--A screw and fabric covered aeroplane in
position for testing.]
[Illustration: Fig. 34.--The rotating arm of the machine with a screw
and aeroplane attached.]
In constructing my apparatus, which is shown in the photographs, and
also in a side elevation (Fig. 32), I aimed at making the apparatus very
light and strong, avoiding as far as possible atmospheric resistance. In
the drawing, _a_, is a thick seamless steel pipe 6 inches diameter; _b_,
is a cast-iron pedestal firmly bolted to _d_, and connected to a large
cast-iron spider embedded in hydraulic cement; by this means great
rigidity and stiffness were obtained. _n_, _n_ was formed of strong
Georgia pine planks 2 inches thick, and strongly bolted together. The
two members of the long radial arm _h_, _h_, were made of Honduras
mahogany, an extremely strong wood, and had their edges tapered off as
shown at _y_, _y_. The power was transmitted from a small steam engine
provided with a sensitive governor through the shaft _f_, _f_. In the
base _c_, of the casting _b_, was placed a pair of tempered steel bevel
gears, giving to the vertical shaft a high velocity. From a pulley on
the top of this shaft, the belt _i_, was run through the arms _h_, _h_,
as shown in section _y_, _y_. This gave a rapid rotation to the screw
shaft in a very simple manner. The operation of the machine was as
follows:--the aeroplane _g_, to be tested was secured to a sort of
weighing apparatus which is shown in detail (Fig. 36), and the screw
attached to the shaft. Upon starting the engine, a very rapid rotation
was given to the screw which caused the radial arm to travel at a high
velocity, the whole weight resting on a ball bearing at _w_. The radial
arms and all of their attachments were balanced by a cigar-shaped lead
weight _s_, which was secured to a sliding bar so as to make it easily
adjustable. The thrust of the screw caused the screw shaft to travel
longitudinally, and this was opposed by a spring connected by a very
thin and light wire to the pointer of the index _o_. As the apparatus
rotated rather slowly on account of its great diameter, it was quite
possible to observe the lift while the machine was running at its
highest speed. The aeroplanes were mounted after the manner of the tray
of a grocer’s scales (see Fig. 36), and the lift of the aeroplane was
determined by what it would lift at _r_--that is, while the machine was
running at a given speed, iron or lead weights were placed in the pail
_r_, until the lift of the aeroplane was exactly balanced, and then, in
order to ascertain exactly what the lift was, the aeroplane was placed
under what might be called a small crane, and a cord, running over a
pulley, attached. The amount of weight necessary to lift the plane into
the same position that it occupied while running was taken as its true
lift. In order to facilitate experiments the gauge _p_, was provided.
This gauge consisted of a large glass tube and the index _p_, with a
quantity of red water at _q_. The centrifugal force of rotation caused
the red water to rise in the tube. This was easily seen, so that if
experiments were being tried, we will say at 50 miles an hour, it was
always possible to turn on steam until the red liquid mounted to 50.
This device was very simple and effective, and saved a great deal of
time. In order to prevent the twisting of the radial arm, a piece of
stiff oval steel tube 12 feet long was secured between the arms at _j_,
and on each end of this tube were attached the wires _u_, _u_. This not
only effectually supported the end of the arm, but at the same time
prevented twisting and made everything extremely stiff. Of course, while
the machine was running at a high velocity, centrifugal force had to be
dealt with, and in order to prevent this from causing friction in the
articulated joints of the weighing apparatus (Fig. 36), thin steel wires
_k_, _k_ were provided. As this apparatus was in the open, it was found
that the slightest movement of the air greatly interfered with its
action. On one occasion when a fabric covered aeroplane, 4 feet long by
3 feet wide, was placed in position, the four corners being held down by
the wires _v_, _v_, and the apparatus driven at a high velocity, a
sudden gust of wind snapped two of the wires, broke the aeroplane, and
the flying fragments smashed the screw, and this notwithstanding that
each of the four wires was supposed to be strong enough to resist at
least four times any possible lifting that the whole aeroplane might be
subjected to.
[Illustration: Fig. 35.--The little steam engine used by me in my
rotating arm experiments; the tachometer and dynamometer are distinctly
shown.]
In order to ascertain the force and direction of the wind, I made an
extremely simple and effective apparatus which is fully shown (see Fig.
38). Whilst conducting these experiments it occurred to me, when a large
aeroplane was used, that after it had been travelling for a considerable
time, it would impart to the air in the path of its travel, a downward
motion, and that the lifting effect would be greatly reduced on this
account. In order to test this, I provided four light brass screws and
mounted them, as shown at _x_, on a hardened polished steel point much
above their centre of gravity, so that they balanced themselves. On
account of the absence of friction, they were easily rotated, and
responded to the least breath of air that might be moving. One morning
when there was a dead calm, I placed four of these screws equidistant
around the whole circle. Some of them rotated very slowly in one
direction and some in another; some alternated, but all their motions
were extremely slow. However, upon setting the machine going with a
large aeroplane and a powerful screw, I found after a few turns that the
air was moving downwards around the whole circle at a velocity of about
2 miles an hour, but as the screw was a considerable distance below the
aeroplane, I estimated that the actual downward velocity of the air in
which the aeroplane was travelling was about 4 miles an hour. The result
of my experiments are clearly shown in an unpublished paper which I
wrote at the time, and as it is of considerable historical interest, I
have placed it in the appendix, notwithstanding that there may be
certain repetitions.
[Illustration: Fig. 36.--The machine attached to the end of the rotating
shaft--_a_, _a_, the body of the machine; _b_, _b_, four-legged spider
secured to _a_, _a_; _c_, _c_, parallel bars; _d_, _d_, vertical member
to which the aeroplane _g_, _g_ is attached; _h_, _h_, the screw; _f_,
_f_, wires for preventing distortion of the aeroplane.]
[Illustration: Fig. 37.--Marking off the dynamometer. In order to
ascertain the actual amount of power consumed in driving the propeller,
a brake was put on in place of the screw, a weight applied, and the
engine run at full speed. In this way all the uncertain and unknowable
factors were eliminated.]
In Fig. 36, _a_, _a_ is the body of the apparatus, partly of gunmetal
and partly of wood. It is provided with a steel shaft to which the screw
_h_, is attached, and also with a cylindrical pulley for taking the
belt. The thrust of the screw pushes the shaft inwards and records the
lift at _o_ (Fig. 32). The corners of the aeroplane _g_, _g_, are
attached by wires to the steel plate _e_. _b_, _b_, is a four-arm
spider for holding the ends of the parallel bars _c_, _c_, and _d_, _d_,
show vertical steel bars to which all devices to be tested are attached.
In testing aeroplanes, weights may be placed at _e_, sufficient to
balance the lifting effect, and then by adding the weight to the upward
pull of the aeroplane, the true lift of the aeroplane is obtained. It is
also possible to attach an aeroplane at _e_, that is, the machine was
made to test superposed aeroplanes if required. In these experiments, I
naturally assumed that the best position for a screw was at the rear and
in the path of the greatest resistance, but as some experimenters with
navigable balloons placed the screw in front in order to pull the
apparatus along instead of to push it, I made experiments to see what
the relative difference might be. In order to do this, I wound a large
amount of rope one-half inch in diameter around the whole apparatus
forward of the screw, converting it into an irregular mass well
calculated to offer atmospheric resistance. Upon starting the engine, I
was rather surprised to see how little retardation these ropes gave to
the apparatus. It appeared to me that nearly all of the energy consumed
in driving the ropes through the air was recovered by the screw. I then
removed the right-hand screw and replaced it by a left-hand screw of the
same pitch and dimensions (Fig. 37_a_). I then found that the blast of
the screw blowing against the tangle of ropes greatly retarded the
travel; in fact, with the same number of revolutions per minute, the
velocity fell off 60 per cent. I think that these experiments ought to
show that there is but one place for the screw, and that is at the
stern, and in the direct path of the greatest atmospheric resistance.
[Illustration: Fig. 37_a_.--Right- and left-hand four-blade screws used
in my experiments for ascertaining the comparative efficiency between
screws placed in front and in the rear of the machine.]
[Illustration: Fig. 38.--Apparatus for indicating the force and velocity
of the wind direct without any timing, counting, or mathematical
calculations.]
Fig. 38 shows an original apparatus which I designed and made for my own
use; with ordinary anemometers it is necessary to count the number of
turns per minute in order to ascertain the velocity of the wind. I
wanted something that would indicate the velocity and the direction of
the wind without any figures or formulæ. I therefore made the apparatus
shown in the drawing, in which _a_, _a_, is a metallic disc 13·54 inches
in diameter, giving it an area of exactly 1 square foot. This is
attached to the horizontal bar _b_, and the whole mounted on two bell
crank levers as shown. When the wind is not blowing, the long arms of
these two levers assume a vertical position, and the spiral spring _h_,
is in exact line with the pivots on which these levers are mounted, and
has no effect except to hold the levers in a vertical position. As the
spring has very little tension in this position, and as it requires a
considerable movement in order to give it tension, the arms _c_, _c_,
and the bar _b_, _b_, are very easily pushed backwards, but as the
distance through which they travel increases, the angle of the lever
changes and the tension of the spring increases at the same time, so
that when the disc is pushed backwards to any considerable distance, a
strong resistance is encountered. Had I made this apparatus so that the
pressure acted directly on the spiral spring, the spaces on the index
indicating low velocities would have been very near together, while
those indicating high velocities would have been widely separated, but
with this device properly designed, the spacing on the index became
regular and even. The index being very large enabled one to read it at a
considerable distance, and at the same time, it acted as a tail and kept
the apparatus face to the wind. The spaces of the dial were not laid off
with a pair of dividers, but each particular division was marked by an
actual pull on the bar _b_, through the agency of a cord and easily
running pulley and weight. The markings, however, were not correct,
because Haswell’s formula was employed in which the pressure of the wind
against the normal plane is considerably greater than with the more
recent formula, which is now known to be correct. Haswell’s formula was
V² × ·005 = P, and the recent formula P = 0·003 × V², where P = pressure
in lbs. per square foot and V = velocity in miles per hour. In my
experiments, I also employed a very well made and delicate anemometer by
Negretti & Zambra.
[Illustration: Fig. 39.--Apparatus for testing the lifting effect of
aeroplanes at a low angle and extremely high velocity. _a_, _a_, the
aeroplane; _b_, lead weight; _c_, long and slender pine rod; _d_, tail
for keeping the apparatus head on and ensuring its travelling straight
through the air; _e_, the point of suspension, also the centre of
gravity. When this apparatus was travelling at the rate of 80 miles an
hour, it gave a lifting effect of about 36 lbs., which is about 7 lbs.
per square foot.]
CRYSTAL PALACE EXPERIMENTS.
Having fully satisfied myself that aeroplanes flying around a circle 200
feet in circumference had their lifting effect reduced to no
insignificant degree by constantly engaging air which had already had
imparted to it a downward movement by a previous revolution, I
determined to make some experiments where this trouble could not occur,
but the opportunity did not present itself until after the large
roundabout, erroneously described as “a captive flying machine,” was put
up at the Crystal Palace. This presented a fine opportunity for making
experiments at an extremely high velocity around a very large circle. I
will only refer to a few of these experiments. To a prolongation of one
of the long arms, I attached a thin steel wire rope about 60 feet above
the platform; I then attached to this wire rope the little device shown
(Fig. 39), in which _a_, is an aeroplane, 5 feet long and 1 foot wide,
placed at an inclination of 1 in 20. Great care was used in preparing
this aeroplane to see that it was free from blemish, smooth, and without
any irregularities. Both edges were sharp and the curvature was about
one-eighth of an inch on the underneath side. It was made relatively
thick in the middle where it was attached to the bar _c_, and thinner
at the ends. _b_, shows a lump of lead just heavy enough to balance the
bar _c_, and the tail; _d_, was a light but strong wooden frame, all the
edges being thin and sharp, and covered with a special silk that Mr.
Cody had found to be best for such purposes. The wire rope _e_, was
attached to the long arm which I referred to. The great length of the
bar _c_, and the accuracy with which the whole was made and balanced
caused the aeroplane to travel straight through the air adjusting itself
to all the shifting currents. Upon starting the machine on a very calm
day, this apparatus mounted as high as the point of support, sometimes
going 10 or more feet higher and sometimes 8 or 10 feet lower. However,
as a rule, it carried its own weight at a velocity of 80 miles an hour
around a circle 1,000 feet in circumference. Under these conditions, of
course, there could be no downward motion of the air as all the air
affected would be removed long before it could be struck the second time
by the aeroplane. I had no means of ascertaining exactly how much this
plane did actually lift, because the air was always moving to some
extent, and it was not an easy matter to ascertain whether it was above
or below the point of support. I am sure, however, that it was as much
as 36 lbs., or rather more than 7 lbs. to the square foot, and this is
just what it should have lifted, providing that we consider the results
obtained by smaller planes placed in an air blast of 40 miles an hour
and at the same angle. When these experiments were finished, I made a
very small apparatus having only about 25 square feet of lifting
surface, and this carried the weight of a man, in fact several gentlemen
came up from London and went round on it themselves. I saw, however,
that it was a dangerous practice, because if the wind was blowing at
all, the apparatus would mount very much above the point of support
while travelling against the wind, only to drop much below the point of
support on the other side of the circle where it was travelling with the
wind; in fact, on one occasion the apparatus shown (Fig. 39) mounted in
a high wind fully 20 feet above the point of support and came down with
such a crash on the other side that it broke the wire rope. In
connection with this, it is interesting to note that when I erected the
first so-called “captive flying machine” on my own grounds at Thurlow
Park, I intended that instead of ordinary boats such as were ultimately
employed, each particular boat should be fitted with an aeroplane, that
the engine should be of 200 H.P., and that the passengers should
actually be running on the air, each boat being provided with a powerful
electric motor in addition to the motive power that drove the shaft. Had
this been carried out as was originally designed, it would have removed
the apparatus altogether from the category of vulgar merry-go-rounds,
but such was not to be. Unforeseen circumstances were against me. I had
some of these boats fitted up with aeroplanes and running on my grounds,
and two of the engineers of the London County Council came out to see
the apparatus before it was put up for public use. On that occasion the
wind was blowing a perfect gale of 40 miles an hour, and as the boats
travelled at the rate of 35 miles an hour, they, of course, encountered
a wind of 75 miles an hour when passing against the wind, and a minus
velocity of 5 miles an hour when travelling with the wind on the other
side of the circle. The aeroplanes, although of considerable size, were
small in relation to weight. I had neglected to put any weight in the
boats, and when three of us were studying the eccentric path through
which the boats were travelling, suddenly one of them in passing to the
windward, raised very much above the point of support and plunged down
with great force on the other side; in fact, the shock was so great that
it made everything rattle, but nothing was broken. Nevertheless, the
engineers said at once, it would not do to run the boats with those
aeroplanes; it was too dangerous. This would not, however, have occurred
if the boats had been loaded, or the velocity of the wind had been less.
It, however, demonstrated what a tremendous lift may be obtained from a
well-made aeroplane passing at a high velocity through the wind at a
sharp angle. These aeroplanes were only about 12 feet long and 5 feet
wide, having, therefore, 60 square feet of surface. They were, however,
strong, well-made, and perfectly smooth, both top and bottom. I would
say right here that I am not a success as a showman--previous long years
of rubbing up against honest men have disqualified me altogether for
such a profession. I was extremely anxious to go on with my experiments.
I appreciated fully that I had made a machine that lifted 2,000 lbs.
more than its own weight, and I knew for a dead certainty if I took the
matter up again, got rid of my boiler and water tank, and used an
internal combustion engine, such as I thought I could produce, that
mechanical flight would soon be a _fait accompli_. I had already spent
more than £20,000, and was looking about for some means of making the
thing self-supporting. I believed that the so-called “captive flying
machine” would be very popular, and bring in a lot of money, and it
would have done so, if it had been put up as originally designed. I
proposed to use my share of the profits for experimental work on real
flying machines. That I was not far wrong in believing that such a
machine would be a success, is witnessed by the fact that just about the
same time, an American inventor thought of the same thing, put up some
three or four machines the first year, and the next year about 50. They
were highly profitable, and there are fully 140 of them running at the
present time in the U.S.A. It is a fact that nothing in the way of
side-shows at exhibitions or public resorts has ever had the success of
this machine in the U.S.A., and even the little machine at Earl’s Court
took £325 10s. in one day and £7,500 in a season. However, this little
attempt to make one hand wash the other cost me no less than £10,400,
not to mention more than a year of very hard work. This sum would have
been amply sufficient to have enabled me to continue my experiments
until success was assured.