BALLOONS.
As far as the actual navigation of the air is concerned, balloonists
have had everything to themselves until quite recently, but we find that
at the present moment, experimenters are dividing their attention about
equally between balloons or machines lighter than the air, and true
flying machines or machines heavier than the air. In all Nature, we do
not find any bird or insect that does not fly by dynamic energy alone,
and I do not believe that the time is far distant when those now
advocating machines lighter than the air, will join the party advocating
machines heavier than the air, and, eventually, balloons will be
abandoned altogether. No matter from what standpoint we examine the
subject, the balloon is unsuitable for the service, and it is not
susceptible of much improvement. On the other hand, the flying machine
is susceptible of a good deal of improvement; there is plenty of scope
for the employment of a great deal of skill, both mechanical and
scientific, for a good many years to come.
I do not know that I can express myself better now than I did when I
wrote an article for the Engineering Supplement of the _Times_, from
which I quote the following:--
“The result of recent experiments must have convinced every thinking man
that the day of the balloon is past. A balloon, from the very nature of
things, must be extremely bulky and fragile.
“It has always appeared to the writer that it would be absolutely
impossible to make a dirigible balloon that would be of any use, even in
a comparatively light wind. Experiments have shown that only a few
hundred feet above the surface of the earth, the air is nearly always
moving at a velocity of at least 15 miles an hour, and more than
two-thirds of the time at a velocity considerably greater than this. In
order to give a balloon sufficient lifting power to carry two men and a
powerful engine, it is necessary that it should be of enormous bulk.
Considered as a whole, including men and engine, it must have a mean
density less than the surrounding air, otherwise it will not rise.
Therefore, not only is a very large surface exposed to the wind, but the
whole thing is so extremely light and fragile as to be completely at the
mercy of wind and weather. Take that triumph of engineering skill, the
‘Nulli Secundus,’ for example. The gas-bag, which was sausage-shaped and
30 feet in diameter, was a beautiful piece of workmanship, the whole
thing being built up of goldbeater’s skin. The cost of this wonderful
gas-bag must have been enormous. The whole construction, including the
car, the system of suspension, the engine and propellers, had been well
thought out and the work beautifully executed; still, under these most
favourable conditions, only a slight shower of rain was sufficient to
neutralise its lifting effect completely--that is, the gas-bag and the
cordage about this so-called airship absorbed about 400 lbs. of water,
and this was found to be more than sufficient to neutralise completely
the lifting effect. A slight squall which followed entirely wrecked the
whole thing, and it was ignominiously carted back to the point of
departure.
“We now learn that the War Office is soon to produce another airship
similar to the ‘Nulli Secundus,’ but with a much greater capacity and a
stronger engine. In the newspaper accounts it is said that the gas-bag
of this new balloon would be sausage-shaped and 42 feet in diameter,
that it is to be provided with an engine of 100 horse-power, which it is
claimed will give to this new production a speed of 40 miles an hour
through the air, so that, with a wind of 20 miles an hour, it will still
be able to travel by land 20 miles an hour against the wind. Probably
the writer of the article did not consider the subject from a
mathematical point of view. As the mathematical equation is an extremely
simple one, it is easily presented so as to be understood by any one
having the least smattering of mathematical or engineering knowledge.
The cylindrical portion of the gas-bag is to be 42 feet in diameter; the
area of the cross-section would therefore be 1,385 feet. If we take a
disc 42 feet in diameter and erect it high in the air above a level
plain, and allow a wind of 40 miles an hour, which is the proposed speed
of the balloon, to blow against it, we should find that the air pressure
would be 11,083 lbs.--that is, a wind blowing at a velocity of 40 miles
an hour would produce a pressure of 8 lbs. to every square foot of the
disc.[3] Conversely, if the air were stationary, it would require a push
of 11,083 lbs. to drive this disc through the air at the rate of 40
miles an hour.
[3] Haswell gives the pressure of the wind at 40 miles an hour as 8
lbs. per square foot, and this is said to have been verified by the
United States Coast Survey. Molesworth makes it slightly less; but the
new formula, according to most recent experiments (Dr. Stanton’s
experiments at the National Physical Laboratory and M. Eiffel’s at
Eiffel Tower), is P = 0·003 V², which would make the pressure only 4·8
lbs. per square foot, and which would reduce the total H.P. required
from 472 to 283, where P represents pounds per square foot and V miles
per hour.
“A speed of 40 miles an hour is at the rate of 3,520 feet in a minute of
time. We therefore have two factors--the pounds of resistance
encountered, and the distance through which the disc travels in one
minute of time. By multiplying the total pounds of pressure on the
complete disc by the number of feet it has to travel in one minute of
time, we have the total number of foot-pounds required in a minute of
time to drive a disc 42 feet in diameter through the air at a speed of
40 miles an hour. Dividing the product by the conventional horse-power
33,000, we shall have 1,181 horse-power as the energy required to propel
the disc through the air. However, the end of the gas-bag is not a flat
disc, but a hemisphere, and the resistance to drive a hemisphere through
the air is much less than it would be with a normal plane or flat disc.
In the ‘Nulli Secundus’ we may take the coefficient of resistance of the
machine, considered as a whole, as 0·20--that is, that the resistance
will be one-fifth as much as that of a flat disc. This, of course,
includes not only the resistance of the balloon itself, but also that of
the cordage, the car, the engine, and the men.
“Multiplying 1,181 by the coefficient ·20, we shall have 236; therefore,
if the new balloon were attached to a long steel wire and drawn by a
locomotive through the air, the amount of work or energy required would
be 236 horse-power--that is, if the gas-bag would stand being driven
through the air at the rate of 40 miles an hour, which is extremely
doubtful. Under these conditions, the driving wheels of the locomotive
would not slip, and therefore no waste of power would result, but in the
dirigible balloon we have a totally different state of affairs. The
propelling screws are very small in proportion to the airship, and their
slip is fully 50 per cent.--that is, in order to drive the ship at the
rate of 40 miles an hour, the screws would have to travel at least 80
miles an hour. Therefore, while 236 horse-power was imparted to the ship
in driving it forward, an equal amount would have to be lost in slip,
or, in other words, in driving the air rearwards. It would, therefore,
require 472 horse-power instead of 100 to drive the proposed new balloon
through the air at the rate of 40 miles an hour.
“It will be seen from this calculation that the new airship will still
be at the mercy of the wind and weather. Those who pin their faith on
the balloon as the only means of navigating the air may dispute my
figures. However, all the factors in the equation are extremely simple
and well known, and no one can dispute any of them except the assumed
coefficient of resistance, which is given here as ·20. The writer feels
quite sure that, after careful experiments are made, it will be found
that this coefficient is nearer ·40 than ·20, especially so at high
speeds when the air pressure deforms the gas-bag. Only a slight bagging
in the front end of the balloon would run the coefficient up to fully
·50, and perhaps even more.”--_Times_, Feb. 26, 1908.
[Illustration: Fig. 73.--The enormous balloon, “Ville de Paris,” of the
French Government. This balloon is a beautiful piece of workmanship, and
is said to be the most practical balloon ever invented, not excepting
the balloon of Count Zeppelin. Some idea of its size may be obtained by
comparing it with the size of the men who are standing immediately
underneath.]
Since writing the _Times_ article, a considerable degree of success has
been attained by Count Zeppelin. According to newspaper accounts, his
machine has a diameter of about 40 feet, and a length of no less than
400 feet. It appears that this balloon consists of a very light
aluminium envelope, which is used in order to produce a smooth and even
surface, give rigidity, and take the place of the network employed in
ordinary balloons. It seems that the gas is carried in a large number of
bags fitted in the interior of this aluminium envelope. However, by
getting a firm and smooth exterior and by making his apparatus of very
great length as relates to its diameter, he has obtained a lower
coefficient of resistance than has ever been obtained before, and as his
balloon is of great volume, he is able to carry powerful motors and use
screw propellers of large diameter. It appears that he has made a
circuit of considerable distance, and returned to the point of departure
without any accident. A great deal of credit is, therefore, due to him.
His two first balloons came to grief very quickly; he was not
discouraged, but stuck to the job with true Teutonic grit, and has
perhaps attained a higher degree of success than has ever been attained
with a balloon. However, some claim that the French Government balloon,
“La Patrie” is superior to the Zeppelin balloon at all points. When we
take into consideration the fact that the Zeppelin machine is 400 feet
long and lighter than the same volume of air, it becomes only too
obvious that such a bulky and extremely delicate and fragile affair will
easily be destroyed. Of course ascensions will only be made in very
favourable weather, but squalls and sudden gusts of wind are liable to
occur. It is always possible to start out in fine weather if one waits
long enough, but if a flight of 24 hours or even 12 hours is to be
attempted, the wind may be blowing very briskly when we return, and an
ordinary wind will not only prevent the housing of Count Zeppelin’s
balloon, but will be extremely liable to reduce it to a complete wreck
in a few minutes.[4]
[4] Shortly after this was written, the Zeppelin machine was
completely demolished by a gust of wind.
I am still strongly of the opinion that the ultimate mastery of the air
must be accomplished by machines heavier than the air.
APPENDIX I.
MAJOR BADEN-POWELL’S DEMAND.
(_From our own Correspondent._)
BERLIN, Friday.
Germany’s fleet of “air cruisers,” or dirigible airships, will, it is
proudly announced to-day, presently number six:--
Count Zeppelin’s III., rigid type.
Count Zeppelin’s IV., rigid type, which has done a twelve-hour flight
and will be taken over by the Government, with No. III., for £100,000,
after a twenty-four-hour test.
Major Gross’s Army airship, half rigid.
Motor Airship Study Society’s old airship, non-rigid.
Major von Parseval’s non-rigid ship building for the above society.
New airship, of which details are kept secret, nearly ready at the
works of the Siemens-Schuckert Electric Company.
The first announcement of the last-named airship was given in _The Daily
Mail_ several months ago. The company has engaged a celebrated military
aeronaut, Captain von Krogh, as commander of the vessel. The Study
Society’s new non-rigid ship will be sold to the War Office as soon as
she has completed her trial trips.
The Army will then possess three dirigibles, each representing one of
the three opposed types of construction--rigid, half-rigid, and
non-rigid--with a view to arriving at a conclusion on their merits.
* * * * *
“Only a year or so ago, our authorities were talking of aerial
navigation in its relation to war as ‘an interesting and instructive
study.’ Now we must reckon it as the gravest problem of the moment. The
cleverest aeronauts in England should be called upon at once to design
an airship, not only as efficient as that of Count Zeppelin’s, but
possessed of even greater speed. (His average was said to be about 34
miles an hour.) In speed will lie the supremacy of the air when it comes
to actual warfare. Of two opposing airships, the faster will be able to
outmanœuvre its adversary and hold it at its mercy.”--_Daily Mail_, July
11, 1908.
COMMAND OF THE AIR.
GERMANY AS THE AERIAL POWER.
TEUTONIC VISION.
A LANDING OF 350,000 MEN.
Herr Rudolph Martin, author of books on war in the air and “Is a
World-War Imminent?” points out how England is losing her insular
character by the development of airships and aeroplanes.
“In a world-war,” he said to me, “Germany would have to spend two
hundred millions sterling in motor airships, and a similar amount in
aeroplanes, to transport 350,000 men in half an hour during the night
from Calais to Dover. Even to-day the landing of a large German army in
England is a mere matter of money. I am opposed to a war between Germany
and England, but should it break out to-day, it would last at least two
years, for we would conclude no peace until a German army had occupied
London.
“In my judgment it would take two years for us to build motor airships
enough simultaneously to throw 350,000 men into Dover _via_ Calais.
During the same night, of course, a second transport of 350,000 men
could follow. The newest Zeppelin airship can comfortably carry fifty
persons from Calais to Dover. The ships which the Zeppelin works in
Friedrichshafen will build during the next few months are likely to be
considerably larger than IV., and will carry one hundred persons. There
is no technical reason against the construction of Zeppelin airships of
1,100,000 or even 1,700,000 cubic feet capacity, or twice or three times
the capacity of IV. (500,000 cubic feet).
“I am at present organising a German ‘Air Navy League,’ to establish
air-traffic routes in Germany. Aluminium airships could carry on regular
traffic between Berlin and London, Paris, Cologne, Munich, Vienna,
Moscow, Copenhagen, and Stockholm. In war time these ships would be at
the disposal of the German Empire.
“The development of motor airship navigation will lead to a perpetual
alliance between England and Germany. The British fleet will continue to
rule the waves, while Germany’s airships and land armies will represent
the mightiest Power on the Continent of Europe.”--_Daily Mail_, July 11,
1908.
It is needless to say that the above was written before the wreck of
Zeppelin’s machine.
* * * * *
For many years scientific mechanicians and mathematicians have told us
that the navigation of the air was quite possible. They have said it is
only a question of motive power; “Give us a motor that is sufficiently
light and strong, and we will very soon give you a practical flying
machine.” A domestic goose weighs about 12 lbs., and it has been
estimated that it only exerts about one-twelfth part of a horse-power in
flying--that is, it is able to exert one man-power with a weight of only
12 lbs., which seems to be a very good showing for the goose. However,
at the present moment, we are able to make motors which develop the
power of ten men--that is, one horse-power--with less than the weight of
a common barnyard fowl. Under these conditions it is quite evident that
if a machine can be so designed that it will not be too wasteful in
power, it must be a success. It is admitted by scientific men that all
animals, such as horses, deer, dogs, and also birds, are able to develop
much more dynamic energy for the carbon consumed than is possible with
any thermodynamic machine that we are able to make. It may be said that
many animals are able to develop the full dynamic energy of the carbon
they consume, whereas the best of our motors do not develop more than 10
per cent. of the energy contained in the combustibles that they consume;
but, as against this, it must be remembered that birds feed on grass,
fruit, fish, etc., heavy and bulky materials containing only a small
percentage of carbon, whereas with a motor we are able to use a pure
hydrocarbon that has locked up in its atoms more than twenty times as
much energy per pound as in the ordinary food consumed by birds. I
think, in fact I assert, that the time has now arrived, having regard to
the advanced state of the art in building motors, when it will be quite
a simple and safe affair to erect works and turn out successful flying
machines at less cost than motor cars; in fact, there is nothing that
stands in the way of success to-day. The value of a successful flying
machine, when considered from a purely military standpoint, cannot be
over-estimated. The flying machine has come, and come to stay, and
whether we like it or not, it is a problem that must be taken into
serious consideration. If we are laggards we shall, unquestionably, be
left behind, with a strong probability that before many years have
passed over our heads, we shall have to change the colouring of our
school maps.
* * * * *
As the newspaper accounts that we receive from the Continent give all
weights and measures in the metric system, it is convenient to have some
simple means at hand to convert their values into English weights and
measures. I therefore give the following, which will greatly simplify
matters both for French and English measurements:--
One metre = 39·37 inches.
„ decimetre = 3·937 „
„ centimetre = ·3937 inch.
„ millimetre = ·03937 „
In order to convert
Metres into inches, multiply by 39·37.
„ feet, „ „ 3·28.
„ yards, „ „ 1·09.
„ miles, „ „ ·00062138.
Cubic metres into cubic yards, multiply by 1·30802.
„ „ feet, „ „ 35·31658.
Miles per hour into feet per minute, multiply by 88.
„ „ „ second, „ „ 1·46663.
„ „ kilometres per hour, „ „ 1·6093.
„ „ metres per second, „ „ ·44702.
Miles per minute into feet per second, „ „ 88.
Pounds into grammes, multiply by 453·5926.
„ „ kilogrammes, „ „ ·45359.
Pounds pressure per sq. inch into atmospheres, multiply
by ·06804.
British thermal units into
Pounds of water, 1° C., multiply by ·55556.
Kilogramme-calories, „ „ ·252
Joules (mechanical equivalent), multiply by 1047·96.
Foot-pounds, multiply by 778.
Pounds of water into pints, multiply by ·8.
„ „ „ cubic feet, „ ·016046.
„ „ „ litres, „ ·454587.
„ „ „ cubic centimetres, multiply by 454·656.
Gallons of water into pounds, multiply by 10.
„ „ „ cubic feet, „ „ ·16057.
„ „ „ kilogrammes, „ „ 4·5359.
„ „ „ litres, „ „ 4·54586.
Litres of water into cubic inches, multiply by 61·0364.
„ „ „ pounds, „ „ 2·20226.
„ „ „ gallons, „ „ ·21998.
Air, 1 cubic foot weighs at 62° 532·5 grains.
Air, cubic feet into pounds, 32° F., multiply by ·08073.
Pounds of dry air into cubic feet, „ „ 13·145.
Kilogramme-calories into British thermal units,
multiply by 3·9683.
„ „ „ gramme-calories, „ „ 1000.
„ „ „ mechanic equivalent in
foot-lbs., multiply by 3065·7.
APPENDIX II.
RECAPITULATION OF EARLY EXPERIMENTS.
[Illustration: Fig. 74.--Photograph of a model of my machine, showing
the fore and aft horizontal rudders and the superposed aeroplanes.]
In my early “whirling table”[5] experiments, the aeroplanes used were
from 6 inches to 4 feet in width. They were for the most part made of
thin pine, being slightly concave on the underneath side and convex on
the top, both the fore and aft edges being very sharp. I generally
mounted them at an angle of 1 in 14[6]--that is, in such a position that
in advancing 14 feet they pressed the air down 1 foot. With this
arrangement, I found that with a screw thrust of 5 lbs. the aeroplane
would lift 5 × 14, or 70 lbs., while if the same plane was mounted at an
angle of 1 in 10, the lifting effect was almost 50 lbs. (5 × 10). This
demonstrated that the skin friction on these very sharp, smooth and
well-made aeroplanes was so small a factor as not to be considered.
When, however, there was the least irregularity in the shape of the
aeroplane, the lifting effect, when considered in terms of screw thrust,
was greatly diminished. With a well-made wooden plane placed at an angle
of 1 in 14, I was able to carry as much as 113 lbs. to the H.P., whereas
with an aeroplane consisting of a wooden frame covered with a cotton
fabric (Fig. 75), I was only able to carry 40 lbs. to the H.P.[7]
[5] A name given by Professor Langley to an apparatus consisting of a
long rotating arm to which objects to be tested are attached.
[6] I found it more convenient to express the angle in this manner
than in degrees.
[7] The actual power consumed by the aeroplane itself was arrived at
as follows:--The testing machine was run at the desired speed without
the aeroplane, and the screw thrust and the power consumed carefully
noted. The aeroplane was then attached and the machine again run at
the same speed. The difference between the two readings gave the power
consumed by the aeroplane.
[Illustration: Fig. 75.--The fabric-covered aeroplane experimented with.
The efficiency of this aeroplane was only 40 per cent. of that of a
well-made wooden aeroplane.]
[Illustration: Fig. 76.--The forward rudder of my large machine, showing
the fabric attached to the lower side. The top was also covered with
fabric. This rudder considered as an aeroplane had a very high
efficiency and worked very well indeed.]
These facts taken into consideration with my other experiments with
large aeroplanes, demonstrated to my mind that it would not be a very
easy matter to make a large and efficient aeroplane. If I obtained the
necessary rigidity by making it of boards, it would be vastly too heavy
for the purpose, while if I obtained the necessary lightness by making
the framework of steel and covering it with a silk or cotton fabric in
the usual way, the distortion would be so great that it would require
altogether too much power to propel it through the air. I therefore
decided on making a completely new form of aeroplane. I constructed a
large steel framework arranged in such a manner that the fore and aft
edges consisted of tightly drawn steel wires. This framework was
provided with a number of light wooden longitudinal trusses, similar to
those shown in Fig. 76. The bottom side was then covered with balloon
fabric secured at the edges, and also by two longitudinal lines of
lacing through the centre. It was stretched very tightly and slightly
varnished, but not sufficiently to make it absolutely air-tight. The top
of this framework was covered with the same kind of material, but
varnished so as to make it absolutely airtight. The top and bottom were
then laced together forming very sharp fore and aft edges, and the top
side was firmly secured to the light wooden trusses before referred to.
Upon running this aeroplane, I found that a certain quantity of air
passed through the lower side and set up a pressure between the upper
and lower coverings. The imprisoned air pressed the top covering upward,
forming longitudinal corrugations which did not offer any perceptible
resistance to the air, whereas the bottom fabric, having practically the
same pressure on both sides, was not distorted in the least. This
aeroplane was found to be nearly as efficient as it would have been had
it been carved out of a solid piece of wood. It will be seen by the
illustration that this large or main aeroplane is practically octagonal
in shape, its greatest width being 50 feet, and the total area 1,500
square feet.
EXPERIMENTS WITH A LARGE MACHINE.
Upon running my large machine over the track (Fig. 77) with only the
main aeroplane in position, I found that a lifting effect of 3,000 to
4,000 lbs. could be obtained with a speed of 37 to 42 miles an hour. It
was not always an easy matter to ascertain exactly what the lifting
effect was at a given speed on account of the wind that was generally
blowing. Early in my experiments, I found if I ran my machine fast
enough to produce a lifting effect within 1,000 lbs. of the total weight
of the machine, that it was almost sure to leave the rails if the least
wind was blowing. It was, therefore, necessary for me to devise some
means of keeping the machine on the track. The first plan tried was to
attach some very heavy cast-iron wheels weighing with their axle-trees
and connections about 1-1/2 tons. These were constructed in such a
manner that the light flanged wheels supporting the machine on the steel
rails could be lifted 6 inches above the track, leaving the heavy wheels
still on the rails for guiding the machine. This arrangement was tried
on several occasions, the machine being run fast enough to lift the
forward end off the track. However, I found considerable difficulty in
starting and stopping quickly on account of the great weight, and the
amount of energy necessary to set such heavy wheels spinning at a high
velocity. The last experiment with these wheels was made when a head
wind was blowing at the rate of about 10 miles an hour. It was rather
unsteady, and when the machine was running at its greatest velocity, a
sudden gust lifted not only the front end, but also the heavy front
wheels completely off the track, and the machine falling on soft ground
was soon blown over by the wind.
I then provided a safety track of 3 × 9 Georgia pine placed about 2 feet
above the steel rails, the wooden track being 30 feet gauge and the
steel rails 9 feet gauge (Fig. 77). The machine was next furnished with
four extra wheels placed on strong outriggers and adjusted in such a
manner that when it had been lifted 1 inch clear of the steel rails,
these extra wheels would engage the upper wooden track.[8]
[8] Springs were interposed between the machine and the axle-trees.
The travel of these springs was about 4 inches; therefore, when the
machine was standing still, the wheels on the outriggers were about 5
inches below the upper track.
[Illustration: Fig. 77.--View of the track used in my experiments. The
machine was run along the steel railway which was 9 feet gauge, and was
prevented from rising by the wooden track which was 35 feet gauge.]
[Illustration: Fig. 78.--The machine on the track tied up to the
dynamometer.]
[Illustration: Fig. 79.--Two dynagraphs, one for making a diagram of the
lifting effect off the main axle-tree, and the other for making a
diagram of the lift off the front axle-tree. By this arrangement, I was
able to ascertain the exact lifting effect at all speeds, and to arrange
my aeroplanes in such a manner that the center of lifting effect was
directly over the center of gravity. The paper-covered cylinders made
one rotation in 2,000 feet.]
When fully equipped, my large machine had five long and narrow
aeroplanes projecting from each side. Those that are attached to the
sides of the main aeroplanes are 27 feet long, thus bringing the total
width of the machine up to 104 feet. The machine is also provided with a
fore and an aft rudder made on the same general plan as the main
aeroplane. When all the aeroplanes are in position, the total lifting
surface is brought up to about 6,000 square feet. I have, however, never
run the machine with all the planes in position. My late experiments
were conducted with the main aeroplane, the fore and aft rudders, and
the top and bottom side planes in position, the total area then being
4,000 square feet. With the machine thus equipped, with 600 lbs. of
water in the tank and boiler and with the naphtha and three men on
board, the total weight was a little less than 8,000 lbs. The first run
under these conditions was made with a steam pressure of 150 lbs. to the
square inch, in a dead calm, and all four of the lower wheels remained
constantly on the rails, none of the wheels on the outriggers touching
the upper track. The second run was made with 240 lbs. steam pressure to
the square inch. On this occasion, the machine seemed to vibrate between
the upper and lower tracks. About three of the top wheels were engaged
at the same time, the weight on the lower steel rails being practically
nil. Preparations were then made for a third run with nearly the full
power of the engines. The machine was tied up to a dynamometer (Fig.
78), and the engines were started with a pressure of about 200 lbs. to
the square inch. The gas supply was then gradually turned on with the
throttle valves wide open; the pressure soon increased, and when 310
lbs. was reached, the dynamometer showed a screw thrust of 2,100
lbs.,[9] but to this must be added the incline of the track which
amounts to about 64 lbs. The actual thrust was therefore 2,164 lbs. In
order to keep the thrust of the screws as nearly constant as possible, I
had placed a small safety valve--3/4-inch--in the steam pipe leading to
one of the engines. This valve was adjusted in such a manner that it
gave a slight puff of steam at each stroke of the engine with a
pressure of 310 lbs. to the square inch, and a steady blast at 320 lbs.
to the square inch. As the valves and steam passages of these engines
were made very large, and as the piston speed was not excessive, I
believed if the steam pressure was kept constant that the screw thrust
would also remain nearly constant, because as the machine advances and
the screws commence to run slightly faster, an additional quantity of
steam will be called for and this could be supplied by turning on more
gas. When everything was ready, with careful observers stationed on each
side of the track, the order was given to let go. The enormous screw
thrust started the machine so quickly that it nearly threw the engineers
off their feet, and the machine bounded over the track at a great rate.
Upon noticing a slight diminution in the steam pressure, I turned on
more gas, when almost instantly the steam commenced to blow a steady
blast from the small safety valve, showing that the pressure was at
least 320 lbs. in the pipes supplying the engines with steam. Before
starting on this run, the wheels that were to engage the upper track
were painted, and it was the duty of one of my assistants to observe
these wheels during the run, while another assistant watched the
pressure gauges and dynagraphs (Fig. 79). The first part of the track
was up a slight incline, but the machine was lifted clear of the lower
rails and all of the top wheels were fully engaged on the upper track
when about 600 feet had been covered. The speed rapidly increased, and
when 900 feet had been covered, one of the rear axle-trees, which were
of 2-inch steel tubing, doubled up (Fig. 80), and set the rear end of
the machine completely free. The pencils ran completely across the
cylinders of the dynagraphs and caught on the underneath end. The rear
end of the machine being set free, raised considerably above the track
and swayed. At about 1,000 feet, the left forward wheel also got clear
of the upper track and shortly afterwards, the right forward wheel tore
up about 100 feet of the upper track. Steam was at once shut off and
the machine sank directly to the earth imbedding the wheels in the soft
turf (Figs. 81 and 82) without leaving any other marks, showing most
conclusively that the machine was completely suspended in the air before
it settled to the earth. In this accident, one of the pine timbers
forming the upper track went completely through the lower framework of
the machine and broke a number of the tubes, but no damage was done to
the machinery except a slight injury to one of the screws (Fig. 83).
[9] The quantity of water entering the boiler at this time was so
great as to be beyond the range of the feed-water indicator.
[Illustration: Fig. 80.--The outrigger wheel that gave out and caused an
accident with the machine.]
[Illustration: Fig. 81.--Shows the broken planks and the wreck that they
caused. It will be observed that the wheels sank directly into the
ground without leaving any track.]
[Illustration: Fig. 82.--The condition of the machine after the
accident. One of the broken planks that formed the upper track is shown.
It will be observed that the wheels have sunk directly into the ground
without leaving any tracks, showing that the machine did not run along
the ground, but came directly down when it stopped.]
In my experiments with the small apparatus for ascertaining the power
required to perform artificial flight, I found that the most
advantageous angle for my aeroplane was 1 in 14, but when I came to make
my large machine, I placed my aeroplanes at an angle of 1 in 8 so as to
be able to get a great lifting effect at a moderate speed with a short
run. In the experiments which led to the accident above referred to, the
total lifting effect upon the machine must have been at least 10,000
lbs. All the wheels which had been previously painted and which engaged
the upper track were completely cleaned of their paint and had made an
impression on the wood, which clearly indicated that the load which they
had been lifting was considerable.[10] Moreover, the strain necessary to
double up the axle-trees was fully 1,000 lbs. each, without considering
the lift on the forward axle-trees which did not give way but broke the
upper track.
[10] The latest form of outrigger wheels for engaging the upper track
is shown in Fig. 84.
[Illustration: Fig. 83.--This shows the screw damaged by the broken
planks; also a hole in the main aeroplane caused by the flying
splinters.]
The advantages arising from driving the aeroplanes on to new air, the
inertia of which has not been disturbed, are clearly shown in these
experiments. The lifting effect of the planes was 2·5 lbs. per square
foot. A plane loaded at this rate will fall through the air with a
velocity of 22·36 miles per hour, according to the formula √(200 × P) =
V. But as the planes were set at an angle of 1 in 8, and as the machine
travelled at the rate of 40 miles an hour, the planes only pressed the
air downwards 5 miles an hour (40 ÷ 8 = 5). A fall of 5 miles an hour
without advancing would only exert a pressure of ·125 lb. per square
foot, according to the formula (V² × ·005 = P).[11]
[11] This is the old formula used by Haswell. The account of this
experimental work was written in the autumn of 1894 and Haswell’s
formula was used. I have thought best to make no changes.
[Illustration: Fig. 84.--This shows a form of outrigger wheels which
were ultimately used.]
Engineers and mathematicians who have written to prove that flying
machines were impossible have generally computed the efficiency of
aeroplanes moving through the air, on the basis that the lifting effect
would be equal to a wind blowing against the plane at the rate at which
the air was pressed down by the plane while being driven through the
air. According to this system of reasoning, my 4,000 square feet of
aeroplanes would have lifted only ·125 lb. per square foot, and in order
to have lifted 10,000 lbs. they would have to have had an area twenty
times as great. This corresponds exactly with the discrepancy which
Professor Langley has found in the formula of Newton.
With aeroplanes of one-half the width of those I employed, and with a
velocity twice as great, the angle could be much less, and the
advantages of continually running on to fresh air would be still more
manifest. With a screw thrust of 2,000 lbs., the air pressure on each
square foot of the projected area of the screw blades is 21·3 lbs.,
while the pressure on the entire discs of the screws is 4 lbs. per
square foot, which would seem to show with screws of this size, that
four blades would be more efficient than two.
[Illustration: Fig. 85.--One pair of my compound engines. This engine
weighed 310 lbs. and developed 180 H.P., with 320 lbs. of steam per
square inch.]
The engines, as before stated, are compound (Fig. 85). The area of the
high-pressure piston is 20 square inches, and that of the low-pressure
piston is 50·26 square inches. Both have a stroke of 12 inches. With a
boiler pressure of 320 lbs., the pressure on the low-pressure piston is
125 lbs. to the square inch. This abnormally high pressure in the
low-pressure cylinder is due to the fact that there is a very large
amount of clearance in the high-pressure cylinder to prevent shock in
case water should go over when the machine pitches; moreover, the steam
in the high-pressure cylinder is cut off at three-quarters stroke, while
the steam in the low-pressure cylinder is cut off at five-eighths
stroke. If we should compute the power of these engines with the steam
entering at full stroke, without any friction, and with no back pressure
on the low-pressure cylinder, the total horse-power would foot up to
461·36 horse-power at the speed at which the engines were run--namely,
375 turns per minute. If we compute the actual power consumed by the
screws, by multiplying their thrust, which is probably 2,000 lbs. while
they are travelling, by their pitch, 16 feet, and this by the number of
turns which they make in a minute, and then divide the product by
33,000,
2,000 × 16 × 375
---------------- = 363·63,
33,000
we find that we have 363·63 horse-power in actual effect delivered on
the screws of the machine, which shows that there is rather less than 22
per cent. loss in the engines, due to cutting off before the end of the
stroke, to back pressure, and to friction. The actual power applied to
the machine being 363·63 horse-power, it is interesting to know what
becomes of it. When the machine has advanced 40 miles (which it would do
in an hour), the screws have travelled 68·1 miles (375 × 16 × 60/5,280)
= 68·1; therefore, 150 horse-power is wasted in slip, and 213·63
horse-power consumed in driving the machine through the air. Now, as the
planes are set at an angle of 1 in 8, the power actually used in lifting
the machine is 133·33, and the loss in driving the body of the machine,
its framework and wires through the air is 90·30 horse-power.
Power lost in screw slip, 150 H.P.
„ „ driving machinery and framework, 80·30 „
„ actually consumed in lifting the machine, 133·33 „
------
Total power delivered by the engines, 363·63 „
THE ADVANTAGES AND DISADVANTAGES OF VERY NARROW PLANES.
[Illustration: Fig. 86.--The path that the air has to take in passing
between superposed aeroplanes in close proximity to each other. By this
arrangement the drift is considerably increased.]
My experiments have demonstrated that relatively narrow aeroplanes lift
more per square foot than very wide ones; but as an aeroplane, no matter
how narrow it may be, must of necessity have some thickness, it is not
advantageous to place them too near together. Suppose that aeroplanes
should be made 1/4-inch thick, and be superposed 3 inches apart--that
is, at a pitch of 3 inches--one-twelfth part of the whole space through
which these planes would have to be driven would be occupied by the
planes themselves, and eleven-twelfths would be air space (Fig. 86). If
a group of planes thus mounted should be driven through the air at the
rate of 36 miles an hour,[12] the air would have to be driven forward at
the rate of 3 miles an hour, or else it would have to be compressed, or
spun out, and pass between the spaces at a speed of 39 miles an hour. As
a matter of fact, however, the difference in pressure is so very small
that practically no atmospheric compression takes place. The air,
therefore, is driven forward at the rate of 3 miles an hour, and this
consumes a great deal of power; in fact, so much that there is a
decided disadvantage in using narrow planes thus arranged.
[12] The arrows in the accompanying drawings show the direction of the
air currents, the experiments having been made with stationary planes
in a moving current of air.
In regard to the curvature of narrow aeroplanes, I have found that if
one only desires to lift a large load in proportion to the area, the
planes may be made very hollow on the underneath side; but when one
considers the lift in terms of the screw thrust, I find it advisable
that the planes should be as thin as possible, and the underneath side
nearly flat. I have also found that it is a great advantage to arrange
the planes after the manner shown in Fig. 87. In this manner the sum of
all the spaces between the planes is equal to the whole area occupied by
the planes; consequently, the air neither has to be compressed, spun
out, nor driven forward. I am, therefore, able by this arrangement to
produce a large lifting effect per square foot, and, at the same time,
to keep the screw thrust within reasonable limits.
[Illustration: Fig. 87.--The position of narrow aeroplanes arranged in
such a manner that the air has free passage between them, and this
arrangement has been found superior to arranging one above the other
after the manner of a Venetian blind.]
A large number of experiments with very narrow aeroplanes have been
conducted by Mr. Horatio Philipps at Harrow, in England. Fig. 88 shows a
cross-section of one of Mr. Philipps’ planes. Mr. Philipps is of the
opinion that the air, in striking the top side of the plane, is thrown
upwards in the manner shown, and a partial vacuum is thereby formed over
the central part of the plane, and that the lifting effect of planes
made in this form is therefore very much greater than with ordinary
narrow planes. I have experimented with these “sustainers” (as Mr.
Philipps calls them) myself, and I find it is quite true that they lift
in some cases as much as 8 lbs. per square foot,[13] but the lifting
effect is not produced in the exact manner that Mr. Philipps seems to
suppose. The air does not glance off in the manner shown. As the
“sustainer” strikes the air two currents are formed, one following the
exact contour of the top, and the other that of the bottom. These two
currents join and are thrown downwards, as relates to the “sustainer,”
at an angle which is the resultant of the angles at which the two
currents meet. These “sustainers” may be made to lift when the front
edge is lower than the rear edge, because they encounter still air, and
leave it with a downward motion.
[13] In my early experiments I lifted as much as 8 lbs. per square
foot with aeroplanes which were only slightly curved, but very thin
and sharp.
[Illustration: Fig. 88.--The very narrow aeroplanes, or sustainers,
employed by Mr. Philipps. It has been supposed that the air in striking
at A was deflected in the manner shown, but such is not the case. The
air in reality follows the surface, as shown in the dotted line in the
second illustration.]
In my experiments with narrow superposed planes, I have always found
that with strips of thin metal made sharp at both edges and only
slightly curved, the lifting effect, when considered in terms of screw
thrust, was always greater than with any arrangement of the wooden
aeroplanes used in Philipps’ experiments. It would, therefore, appear
that there is no advantage in the peculiar form of “sustainer” employed
by this inventor.
If an aeroplane be made perfectly flat on the bottom side and convex on
the top, and be mounted in the air so that the bottom side is exactly
horizontal, it produces a lifting effect no matter in which direction it
is run, because, as it advances, it encounters stationary air which is
divided into two streams. The top stream being unable to fly off at a
tangent when turning over the top curve, flows down the incline and
joins the current which is flowing over the lower horizontal surface.
The angle at which the combined stream of air leaves the plane is the
resultant of these two angles; consequently, as the plane finds the air
in a stationary condition, and leaves it with a downward motion, the
plane itself must be lifted. It is true that small and narrow aeroplanes
may be made to lift considerably more per square foot of surface than
very large ones, but they do not offer the same safeguard against a
rapid descent to the earth in case of a stoppage or breakdown of the
machinery. With a large aeroplane properly adjusted, a rapid and
destructive fall to the earth is quite impossible.
THE EFFICIENCY OF SCREW PROPELLERS, STEERING, STABILITY, &c.
Before I commenced my experiments at Baldwyn’s Park, I attempted to
obtain some information in regard to the action of screw propellers
working in the air. I went to Paris and saw the apparatus which the
French Government employed for testing the efficiency of screw
propellers, but the propellers were so very badly made that the
experiments were of no value. Upon consulting an English experimenter,
who had made a “life-long study” of the question, he assured me that I
should find the screw propeller very inefficient and very wasteful of
power, and that all screw propellers had a powerful fan-blower action,
drawing in air at the centre and discharging it with great force at the
periphery. I found that no two men were agreed as to the action of screw
propellers. All the data or formulæ available were so confusing and
contradictory as to be of no value whatsoever. Some experimenters were
of the opinion that, in computing the thrust of a screw, we should only
consider the projected area of the blades, and that the thrust would be
equal to a wind blowing against a normal plane of equal area at a
velocity equal to the slip. Others were of the opinion that the whole
screw disc would have to be considered; that is, that the thrust would
be equal to a wind blowing against a normal plane having an area equal
to the whole disc, and at the velocity of the slip. The projected area
of the two screw blades of my machine is 94 square feet, and the area of
the two screw discs is 500 square feet. According to the first system of
reasoning, therefore, the screw thrust of my large machine, when running
at 40 miles an hour with a slip of 18 miles per hour, would have been,
according to the well-known formula,
V² × ·005 = P
18² × ·005 × 94 = 152·28 lbs.
If, however, we should have considered the whole screw disc, it would
have been 18² × ·005 × 500 = 810 lbs. However, when the machine was run
over the track at this rate, the thrust was found to be rather more than
2,000 lbs. When the machine was secured to the track and the screws
revolved until the pitch in feet, multiplied by the turns per minute,
was equal to 68 miles an hour, it was found that the screw thrust was
2,164 lbs. In this case, it was of course, all slip, and when the screws
had been making a few turns they had established a well-defined
air-current, and the power exerted by the engine was simply to maintain
this air current. It is interesting to note that, if we compute the
projected area of these blades by the foregoing formula, the thrust
would be--68² × ·005 × 94 = 2,173·28 lbs., which is almost exactly the
observed screw thrust.
When I first commenced my experiments with a large machine, I did not
know exactly what sort of boiler, gas generator, or burner I should
finally adopt; I did not know the exact size that it would be necessary
to make my engines; I did not know the size, the pitch, or the diameter
of the screws which would be the most advantageous; neither did I know
the form of aeroplane which I should finally adopt. It was, therefore,
necessary for me to make the foundation or platform of my machine of
such a character that it would allow me to make the modifications
necessary to arrive at the best results. The platform of the machine is,
therefore, rather larger than is necessary, and I find if I were to
design a completely new machine, that it would be possible to greatly
reduce the weight of the framework, and, what is still more, to greatly
reduce the force necessary to drive it through the air.
[Illustration: Fig. 89.--One of the large screws being hoisted into
position. Its size may be judged by comparison with the man.]
At the present time, the body of my machine is a large platform, about 8
feet wide and 40 feet long. Each side is formed of very long trusses of
steel tubes, braced in every direction by strong steel wires. The
trusses which give stiffness are all below the platform. In designing a
new machine, I should make the trusses much deeper and at the same time
very much lighter, and, instead of having them below the platform on
which the boiler is situated, I should have them constructed in such a
manner as to completely enclose the boiler and the greater part of the
machinery.[14] I should make the cross-section of the framework
rectangular and pointed at each end. I should cover the outside very
carefully with balloon material, giving it a perfectly smooth and even
surface throughout, so that it might be easily driven through the air.
[14] This arrangement of the framework is now common to all successful
machines.
In regard to the screws, I am at the present time able to mount screws
17 feet 10 inches in diameter (Fig. 89). I find, however, that my
machine would be much more efficient if the screws were 24 feet in
diameter and I believe with such very large screws, four blades would be
much more efficient than two.
My machine may be steered to the right or to the left by running one of
the propellers faster than the other. Very convenient throttle valves
have been provided to facilitate this system of steering. An ordinary
vertical rudder placed just after the screws may, however, prove more
convenient if not more efficient.
The machine is provided with fore and aft horizontal rudders, both of
which are connected with the same windlass.
In regard to the stability of the machine, the centre of weight is much
below the centre of lifting effect; moreover, the upper wings are set at
such an angle that whenever the machine tilts to the right or to the
left the lifting effect is increased on the lower side and diminished on
the higher side. This simple arrangement makes it automatic as far as
rolling is concerned. I am of the opinion that whenever flying machines
come into use, it will be necessary to steer in a vertical direction by
means of an automatic steering gear controlled by a gyroscope. It will
certainly not be more difficult to manœuvre and steer such machines than
it is to control completely submerged torpedoes.
When the machine is once perfected, it will not require a railway track
to enable it to get the necessary velocity to rise. A short run over a
moderately level field will suffice. As far as landing is concerned, the
aerial navigator will touch the ground when moving forward, and the
machine will be brought to a state of rest by sliding on the ground for
a short distance. In this manner very little shock will result, whereas
if the machine is stopped in the air and allowed to fall directly to the
earth without advancing, the shock, although not strong enough to be
dangerous to life or limb, might be sufficient to disarrange or injure
the machinery.
THE COMPARATIVE VALUE OF DIFFERENT MOTORS.
So far I have only discussed the navigation of the air by the use of
propellers driven by a steam engine. The engines that I employ are what
is known as compound engines--that is, they have a large and a small
cylinder. Steam at a very high pressure enters the high-pressure
cylinder, expands and escapes at a lower pressure into a larger cylinder
where it again expands and does more work. A compound engine is more
economical in steam than a simple engine, and therefore requires a
smaller boiler to develop the same horse-power, so that when we consider
the weight of water and fuel for a given time, together with the weight
of the boiler and the engine, the engine motor with a compound engine is
lighter than a simple engine. However, if only the weight of the engine
is to be considered then the simple engine will develop more power per
unit of weight than the compound engine. For instance, if, instead of
allowing the steam to enter the small cylinder, and the exhaust from
this cylinder to enter the large or low-pressure cylinder--which
necessitates that the high-pressure piston has to work against a back
pressure equal to the full pressure on the low-pressure cylinder--I
should connect both cylinders direct with the live steam, and allow both
to discharge their exhaust directly into the air, I should then have a
pair of simple engines, and instead of developing 363 H.P. they would
develop fully 500 H.P., or nearly 1 H.P. for every pound of their
weight. I mention this fact to show that the engines are exceedingly
light, and that when compared with simple engines their power should be
computed on the same basis. It will, therefore, be seen that if we do
not take into consideration the steam supply or the amount of fuel and
water necessary, the simple steam engine is an exceedingly light motor.
But, as before stated, great improvements have recently been made in oil
engines. I have thought much on this subject, and am of the opinion that
if one had an unlimited supply of money, a series of experiments could
be very profitably conducted with a view of adapting the oil engine for
use on flying machines. If we use a steam engine, it is necessary to
have a boiler, and at best a boiler is rather a large and heavy object
to drive through the air. If we use an oil engine, no boiler is
necessary, and the amount of heat carried over in the cooling water will
only be one-seventh part of what is carried over in the exhaust from a
steam engine of the same power. Therefore, the condenser only need be
one-seventh part the size, and consequently should be made lighter with
the tubes placed at a greater distance apart, and thus reduce the amount
of power necessary to drive the machine through the air. Moreover, the
supply of water necessary will be greatly reduced, and a cheaper and
heavier oil may be employed, which is not so liable to take fire in case
of an accident. It is then only a question as to whether an oil engine
can be made so light as to keep its weight within that of a steam motor;
that is, an oil engine in order to be available for the purpose must be
as light, including its water supply, as a complete steam motor, which
includes not only the engine, but also the boiler, the feed pumps, the
water supply, the burner, the gas generator, and six-sevenths of the
condenser. It requires a very perfect steam engine and boiler, not using
a vacuum, to develop a horse-power with a consumption of 1-1/2 lbs. of
petroleum per hour; but there are many oil engines which develop a
horse-power with rather less than 1 lb. of oil per hour. It will,
therefore, be seen that, as far as fuel is concerned, the oil engine has
a decided advantage over the more complicated steam motor. Moreover,
with an oil engine, the cooling water is not under pressure, so that the
waste of water would be much less than with a steam engine, where the
pressure is so high as to cause a considerable amount of waste through
joints and numerous stuffing-boxes.
The great advances that have been made of late years in electrical
science and engineering have led many to believe that almost any knotty
scientific question may be solved by the employment of electrical
engineering, and a great deal has been written and said in regard to
navigating the air by flying machines driven by electric motors.
Before I commenced my experiments, I made enquiries of all the prominent
electrical engineering establishments where there was any likelihood of
obtaining light and efficient electric motors, and found that it was
impossible to obtain one that would develop a horse-power for any
considerable time that would weigh less than 150 lbs. Since that time,
notwithstanding that a great deal has appeared in the public prints
about the efficiency and lightness of electric motors, I am unable to
learn of any concern that is ready to furnish a complete motor,
including a primary battery, which would supply the necessary current
for two hours at a time, at a weight of less than 150 lbs. per
horse-power, and as far as I have been able to ascertain from what I
have myself seen, I cannot learn that there are any motors in practical
use which do not weigh, including their storage batteries, at least 300
lbs. per horse-power. The last electric motor which I examined was in a
boat; it was driven by a primary battery which weighed over 1,000 lbs.
to the horse-power. From this I am of the opinion that we cannot at
present look to electricity with any hope of finding a motor which is
suitable for the purpose of aerial navigation.
ENGINES.
There is no question but what birds, and for that matter all animals,
when considered as thermo-dynamic machines, are very perfect motors;
they develop the full theoretical amount of energy of the carbon
consumed. This we are quite unable to do with any artificial machine,
but birds, for the most part, have to content themselves with food which
is not very rich in carbon. It is quite true that a bird may develop
from ten to fifteen times as much power from the carbon consumed as can
be developed by the best steam engine, but, as an off-set against this,
a steam engine is able to consume petroleum, which has at least twenty
times as many thermal units per pound as the ordinary food of birds. The
movement of a bird’s wings, from long years of development, has without
doubt attained a great degree of perfection. Birds are able to scull
themselves through the air with very little loss of energy. To imitate
by mechanical means, the exact and delicate motion of their wings would
certainly be a very difficult task, and I do not believe that we should
attempt it in constructing an artificial flying machine. In Nature it is
necessary that an animal should be made all in one piece. It is,
therefore, quite out of the question that any part or parts should
revolve. For land animals there is no question but what legs are the
most perfect system possible, but in terrestrial locomotion by
machinery, not necessarily in one piece, wheels are found to be much
more effective and efficient. The swiftest animal can only travel for a
minute of time at half the speed of a locomotive, while the locomotive
is able to maintain its much greater speed for many hours at a time. The
largest land animals only weigh about 5 tons, while the largest
locomotives weigh from 60 to 80 tons. In the sea, the largest animal
weighs about 75 tons, while the ordinary Atlantic liner weighs from
4,000 to 14,000 tons. The whale, no doubt, is able to maintain a high
speed for several hours at a time, but the modern steamer is able to
maintain a still higher speed for many consecutive days.
As artificial machines for terrestrial and aquatic locomotion have been
made immensely stronger and larger than land or water animals, so with
flying machines, it will be necessary to construct them much heavier and
stronger than the largest bird. If one should attempt to propel such a
machine with wings, it would be quite as difficult a problem to solve as
it would be to make a locomotive that would walk on legs. What is
required in a flying machine is something to which a very large amount
of power can be directly and continuously applied without any
intervening levers or joints, and this we find in the screw propeller.
* * * * *
When the Brayton gas engine first made its appearance, I commenced
drawings of a flying machine, using a modification of the Brayton motor
which I designed expressly for the purpose; but even this was found to
be too heavy, and it was not until after I had abandoned the vertical
screw system that it was possible for me to design a machine which, in
theory, ought to fly. The next machine which I considered was on the
kite or aeroplane system. This was also to be driven by an oil engine.
Oil engines at that time were not so simple as now, and, moreover, the
system of ignition was very heavy, cumbersome, and uncertain. Since that
time, however, gas and oil engines have been very much improved, and the
ignition tube which is almost universally used has greatly simplified
the ignition, so that at the present time, I am of the opinion that an
oil engine might be designed which would be suitable for the purpose.
In 1889 I had my attention drawn to some very thin, strong, and
comparatively cheap tubes which were being made in France, and it was
only after I had seen these tubes that I seriously considered the
question of making a flying machine. I obtained a large quantity of them
and found that they were very light, that they would stand enormously
high pressures, and generate a very large quantity of steam. Upon going
into a mathematical calculation of the whole subject, I found that it
would be possible to make a machine on the aeroplane system, driven by a
steam engine, which would be sufficiently strong to lift itself into the
air. I first made drawings of a steam engine, and a pair of these
engines was afterwards made. These engines are constructed, for the most
part, of a very high grade of cast steel, the cylinders being only 3/32
of an inch thick, the crank shafts hollow, and every part as strong and
light as possible. They are compound, each having a high-pressure piston
with an area of 20 square inches, a low-pressure piston of 50·26 square
inches, and a common stroke of 1 foot. When first finished, they were
found to weigh 300 lbs. each; but after putting on the oil cups,
felting, painting, and making some slight alterations, the weight was
brought up to 320 lbs. each, or a total of 640 lbs. for the two engines,
which have since developed 362 horse-power with a steam pressure of 320
lbs. per square inch. A photograph of one of these engines is shown in
Fig. 85.
* * * * *
When first designing this engine, I did not know how much power I might
require from it. I thought that in some cases it might be necessary to
allow the high-pressure steam to enter the low-pressure cylinder direct,
but as this would involve a considerable loss, I constructed a species
of an injector. This injector may be so adjusted that when the steam in
the boiler rises above a certain predetermined point, say 300 lbs. to
the square inch, it opens a valve and escapes past the high-pressure
cylinder instead of blowing off at the safety valve. In escaping through
this valve, a fall of about 200 lbs. pressure per square inch is made to
do work on the surrounding steam and to drive it forward in the pipe,
producing a pressure on the low-pressure piston considerably higher than
the back pressure on the high-pressure piston. In this way a portion of
the work which would otherwise be lost is utilised, and it is possible,
with an unlimited supply of steam, to cause the engines to develop an
enormous amount of power.
* * * * *
=Boiler Experiments.=--The first boiler which I made was constructed
something on the Herreshoff principle, but instead of having one simple
pipe in one very long coil, I used a series of very small and light
pipes, connected in such a manner that there was a rapid circulation
through the whole--the tubes increasing in size and number as the steam
was generated. I intended that there should be a pressure of about 100
lbs. more on the feed water end of the series than on the steam end, and
I believed that this difference in pressure would be sufficient to
ensure a direct and positive circulation through every tube in the
series. This first boiler was exceedingly light, but the workmanship, as
far as putting the tubes together was concerned, was very bad, and it
was found impossible to so adjust the supply of water as to make dry
steam without overheating and destroying the tubes.
[Illustration: Fig. 90.--Steam boiler employed in my experiments. With
this boiler, I had no trouble in producing all the steam that I could
possibly use, and at any pressure up to 400 lbs. to the square inch.]
[Illustration: Fig. 91.--The burner employed in my steam experiments.
This produced a dense and uniform blue purple flame 20 inch deep.]
Before making another boiler I obtained a quantity of copper tubes,
about 8 feet long, 3/8 inch external diameter, and 1/50 of an inch
thick. I subjected about 100 of these tubes to an internal pressure of 1
ton per square inch of cold kerosine oil, and as none of them leaked I
did not test any more, but commenced my experiments by placing some of
them in a white-hot petroleum fire. I found that I could evaporate as
much as 26-1/2 lbs. of water per square foot of heating surface per
hour, and that with a forced circulation, although the quantity of water
passing was very small but positive, there was no danger of
over-heating. I conducted many experiments with a pressure of over 400
lbs. per square inch, but none of the tubes failed. I then mounted a
single tube in a white-hot furnace, also with a water circulation, and
found that it only burst under steam at a pressure of 1,650 lbs. per
square inch. A large boiler, having about 800 square feet of heating
surface including the feed-water heater, was then constructed. It is
shown in Fig. 90. This boiler is about 4-1/2 feet wide at the bottom, 8
feet long and 6 feet high. It weighs with the casing, the dome, the
smoke stack and connections, a little less than 1,000 lbs. The water
first passes through a system of small tubes--1/4 inch in diameter and
1/60 inch thick--which were placed at the top of the boiler and
immediately over the larger tubes--not shown in the cut. This feed-water
heater is found to be very effective. It utilises the heat of the
products of combustion after they have passed through the boiler proper
and greatly reduces their temperature, while the feed-water enters the
boiler at a temperature of 250° F. A forced circulation is maintained
in the boiler, the feed-water entering through a spring valve, the
spring valve being adjusted in such a manner that the pressure on the
water is always 30 lbs. per square inch in excess of the boiler
pressure. This fall of 30 lbs. in pressure acts upon the surrounding hot
water which has already passed through the tubes, and drives it down
through a vertical outside tube, thus ensuring a positive and rapid
circulation through all the tubes. This apparatus is found to work
extremely well. A little glass tube at the top provided with a moving
button, indicates exactly how many pounds of water per hour are passing
into the boiler. By this means, the engineer is not only enabled to
ascertain at a glance whether or not the pumps are working, but also to
what degree they are working.
Water may be considered as 2,400 times as efficient as air, volume for
volume, in condensing steam. When a condenser is made for the purpose of
using water as a cooling agent, a large number of small tubes may be
grouped together in a box, and the water may be pumped in at one end of
the box and discharged at the other end through relatively small
openings; but when air is employed, the tubes or condensing surface must
be widely distributed, so that a very large amount of air is
encountered, and the air which has struck one tube and become heated
must never strike a second tube.
In order to accomplish this, I make my condenser something in the form
of a Venetian blind, the tubes being made of very thin copper and each
tube in the form of a small aeroplane. These were driven edgewise
through the air, so that the actual volume of air passing between them
is several thousand times greater than the volume of water passing
through a marine condenser. I find that with such a condenser I can
recover the full weight of the copper tubes in water every five minutes,
and if I use aluminium, in half that time. Moreover, experiments have
shown that a condenser may be made to sustain considerably more than its
own weight and the weight of its contents in the air, and that all the
steam may be condensed into water sufficiently cool to be pumped with
certainty.
I find that the most advantageous position for the condenser is
immediately after the screw propellers. In this case, if the machine is
moving through the air at the rate of 50 miles an hour, and the slip of
the screws is 15 miles an hour, it follows that the air will be passing
through the condenser at the rate of 65 miles an hour. At this velocity,
the lifting effect on the narrow aeroplanes forming the condenser is
very great, and at the same time the steam is very rapidly condensed.
The tubes are placed at such an angle as to keep them completely drained
and prevent the accumulation of oil, the steam entering the higher end
and the water being discharged at the lower end.
. . . . . . . . .
EXPERIMENTS WITH SMALL MACHINES ATTACHED TO A ROTATING ARM.
These experiments demonstrated most conclusively that as much as 133
lbs. could be sustained and carried by the expenditure of one
horse-power, and that a screw was a fairly efficient air propeller. They
also demonstrated that a well made aeroplane, placed at an angle of 1 in
14, would lift practically fourteen times the thrust required to drive
it through the air, and that the skin friction on a smooth and well
finished aeroplane or screw was so small as not to be considered. A
large number of aeroplanes were experimented with, and it was found that
those which were slightly concave on the underneath side and convex on
the top, both edges being very sharp and the surface very smooth and
regular, were the most efficient; also that with small screw propellers,
two blades having slightly increasing pitch were the most efficient.
* * * * *
Since writing the foregoing, great progress has been made with flying
machines, and great disasters have happened to airships or balloons.
Count Zeppelin’s gigantic airship encountered a squall or thunder
shower, and the work of years, which had cost over £100,000, was reduced
to scrap metal in a few minutes. Similar disasters have happened to
other balloons.
The British Dirigible No. 2 has not attempted a long flight, but the
Wright Brothers, Farman, and De la Grange have all met with a certain
degree of success.
A few months ago, the remarkable feats of the Wright Brothers in the
States were discredited in Europe. It was claimed that “the accounts
were not authentic,” “too good to be true,” etc., but recent events have
shown that the Wright Brothers are able to outdo anything that was
reported in the American Press. On many occasions they have remained in
the air for more than an hour, and have travelled at the rate of 30 to
40 miles an hour; in fact, the remarkable success of the Wright Brothers
has placed the true flying machine in a new category.
It can no longer be ranked with the philosopher’s stone or with
perpetual motion. Success is assured, and great and startling events may
take place within the next few years.
[Illustration: Fig. 92.--Count Zeppelin’s aluminium-covered airship
coming out of its shed on Lake Constance.]
[Illustration: Fig. 93.--Count Zeppelin’s airship in full flight.]
[Illustration: Fig. 94.--The new British war balloon “Dirigible” No 2.]
[Illustration: Fig. 95.--The Wright aeroplane in full flight.]
GENERAL INDEX.
PAGE
Accident to my large machine, 138
Action of aeroplanes and power required, 100
Adjustment of birds’ wings, 19
Admiralty specification for a steamship, 48
Advantages of driving aeroplanes on to new air, 140
Advantages and disadvantages of very narrow planes, 143
Aeroplanes:--
Action of, 31, 32, 100
Advantageous angle of, 139
Advantages and disadvantages of very narrow, 143
„ arising from driving aeroplanes on to new air, 140
Curvature of, 145
Evolution of a wide aeroplane, 102
Experiments with, 49-59
Fabric covered, 131
Lifting effect of, 141
Lifting surface of, 103
Philipps’ sustainers, 146
Reduction of projected horizontal area, 3, 4
Shape and efficiency of, 99
Superposed, 144, 146
Testing fabrics for, 50
The paradox aeroplane, 88
Air currents and the flight of birds, 11
„ Conclusions regarding, 21
„ Alpes Maritimes, 17
„ Mediterranean, 18
„ Mid-Atlantic, 16
„ 2,000 feet above the earth’s surface, 22
„ witnessed at Cadiz, 20
Angles and degrees compared, 115
Antoinette motor, The, 89
Balloons, 120
„ spiders, 27
Birds as thermo-dynamic machines, 153
„ Two classes of, 23
Bleriot’s machine, 113
Boiler experiments, 156
Brayton’s gas engine, 154
British war balloon, 159, 162
Building up of my large screws, 41
Burner employed in my experiments, 157
Character of text-books recently published, 1
Circulation of air produced by differences in temperature, 27
Cody’s kite, 28, 30
Comparative value of different motors, 151
Conclusions regarding air currents, 21
Condensers, Testing of, 52
Condenser tubes, 60
Continental flying machines, 9
Crystal Palace experiments, 72-76
Darwin on the flight of condors, 11
Deflection of air coming in contact with aeroplanes, 2
De la Grange machine, The, 110
“Dirigible” No 2, 159, 162
Drift at various distances from center to center, Table of, 58
Dynagraphs, 136
Dynamic energy of animals, 127
Eagles, Flight of, 19
Efficiency of screw propellers, 147
„ screws in steamships, 47
Energy developed by a bird, 13
Engines, 153
Equivalent inclinations, 115
„ velocities, 116
Experiments of Count Zeppelin, 124
„ Horatio Philipps, 9, 118, 119, 145
„ Lord Rayleigh in reference to Newton’s Law, 6
„ Professor Langley, 9, 62, 99, 109
„ Wright Bros., 109
Experiments to show efficiency of Screw propellers, 33
„ with apparatus attached to rotating arm, 62
„ „ boiler, 156
„ „ hard rolled brass aeroplane, 3
„ „ my large machine, 10, 133
„ „ rotating arm, 64-72
„ „ small machines attached to rotating arm, 159
Fabric covered screw, 40
Farman’s machine, 110
Flying of kites, 25, 28, 29
Forced circulation used by me, 158
Formulæ unsupported by facts, 3
French and English measurements, 128, 129
Gulls, 20, 21
Gyroscope apparatus, 93
„ Steering by means of, 92
Hawks and Eagles, 13
Hélicoptère machine, 82
Hints as to the building of flying machines, 77-91
Horizontal movement of the air, 14
Hub for flying machine, New form of, 45
Interstellar temperature, 15
Introductory, 1
Kites, 21, 22, 25, 26, 28, 29
„ Behaviour of, 26
„ Flying of, 25, 28, 29
Langley, Experiments of, 9, 62, 99, 109
„ on the flight of birds, 11, 22
„ on the power exercised by birds, 12
“La Patrie,” 124
Lifting effect of aeroplanes, 5
„ surface of aeroplanes, 103
Low temperature of space, 15
Major Baden Powell’s demand, 125
Mistral, The, 21
Motors, Development of, 31
Motor, The Antoinette, 89
My compound engines, 142
„ experiments with aeroplanes, 7
„ „ large machine, 10, 133
„ steam engines, 155
Newton’s Law, 2, 6
“Nulli Secundus,” 28, 121
Oil engines, 154
Philipps’ experiments, 9, 118, 119, 145
„ sustainers, 145
Pneumatic buffer, 90
Position of screw, 49
Power exerted by a land animal, 13
„ required, 100
Principally relating to screws, 31
Rayleigh’s experiments in reference to Newton’s law, 6
Recapitulation of early experiments, 130
Recent machines, 109
Relative value of woods for flying machines, 85
Reserve energy necessary in flying machines, 30
Resistance encountered by various shaped bodies, 52
Rotating arm experiments, 64-72
Santos Dumont’s flying machine, 113
Screw blade on Farman’s machine, 41
„ blades, Testing of, 36
„ „ used by the French Government, 39
„ „ with radial edges, 43
„ Fabric-covered, 40
„ Position of, 49
„ propeller made of sheet metal, 41
„ propellers, Efficiency of, 33, 147
Screws, 8, 31, 35, 36, 40, 41, 46, 47, 49
„ Building up of my large, 40
„ their efficiency in steamships, 47
Shape and efficiency of aeroplanes, 99
Skin friction, 41, 48
Spider’s webbing down from the sky, 27
Spirit lamp and ice box, 62
Stability of flying machines, 147, 150
Steam engines used by me, 155
Steering, 147, 149
Superposed aeroplanes, 144
System of splicing and building up wooden members, 86
Tables:--
Equivalent inclinations, 115
„ velocities, 116
French and English measurements, 128, 129
Philipps’ experiments, 119
Relative value of different woods, 85
Showing the relative power exerted by different birds, 24
Velocity and pressure of the wind, 114
„ „ thrust corresponding with various horse-powers, 117
Testing aeroplanes, condensers, etc., 52
Teutonic vision of aerial power, 126
Velocity and pressure of wind, 114
„ „ thrust corresponding with various horse-powers, 117
“Ville de Paris,” 123
Wright Bros.’ experiments, 109, 159, 162
Zeppelin’s experiments, 124, 159, 161
BELL AND BAIN, LIMITED, PRINTERS, GLASGOW.
Transcriber’s Notes:
Inconsistent spelling and hyphenation in the original work have been
retained.
Depending on the hard- and software used to read this text and their
settings, not all characters and symbols may display as intended.
Changes made to the text:
Illustrations and tables have been moved out of the text, and
footnotes have been moved to directly under the paragraph or table
they refer to.
Obvious punctuation and typographical errors have been corrected
silently.
In some formulas × has been inserted for consistency; brackets
have been added for clarity where necessary.
Page vii: battaillons Kommandeur changed to Bataillonskommandeur
Page x: 1 in 20 changed to 1 in 10 (as discussed in the remainder of
the paragraph)
Page 24, table: ·64 changed to 7·64
Page 73: all the air effected changed to all the air affected
Page 110: Hargraves’ changed to Hargrave’s
Page 128: over estimated changed to over-estimated.
End of Project Gutenberg's Artificial and Natural Flight, by Hiram S. Maxim