THE EXPERIMENTAL ENGINE
It will be recalled that the contract for the engine for the large
aerodrome, which had been entered into on December 12, 1898, called
for its completion on February 28, 1899. Between the time when the
engine should have been completed and May, 1900, the engine builder
had been engaged in a continuous series of changes on it, all
connected with what might be briefly called its proper functioning.
The actual mechanical construction of the more important parts had
been admirably executed, and this main portion of the constructional
work had been completed within the time called for by the contract.
The trouble was that the engine, which was of the rotary cylinder
type, would not furnish anything like the power which had been
expected of it, and which the size and number of its cylinders
indicated that it should furnish. No one who has not had practical
experience in the development of gasoline engines, can understand or
appreciate how fourteen months could be spent in changes in the minor
details of the engine with the expectation that each contemplated
change would bring success; and to anyone who has had experience in
the matter, an attempt to explain the delays would merely seem like
a history of his own experiences. It is, therefore, sufficient to
say that the delay on the engine had now reached a point where it
was necessary to bring it to a successful completion immediately or
to abandon it definitely, and either find a competent builder who
had already built engines which, while not necessarily light, were
successful, and who would undertake to construct a light one on the
same principles, or, as a last resort, to turn to steam; and even the
contemplation of this was appalling.
On May 6, 1900, the writer went to New York to see what could be done
towards assisting the engine builder to complete the large engine
and also, if possible, the small one which had been ordered for the
quarter-size model later described. He immediately made brake tests
of the engine to determine accurately just what effects were being
produced by the different changes the engine builder was making. Upon
the first test the engine was found to develop only 2.83 horse-power,
and this could not be maintained for more than a few minutes, when
without any apparent cause and without any signs of overheating the
engine would altogether cease to develop any power. After remaining
in New York for several weeks, during which time many changes were
made in the engine, he finally got it to the point where it would
develop four horse-power continuously; but, as it seemed impossible
to get any better results [p219] without an indefinite amount of
experiment, it was decided that all hope of making this engine an
immediate success would have to be abandoned.
Interest in the development of the automobile was increasing at a
rapid rate all over the world, and while the builders in this country
had not reached the stage of development which had been attained
in Europe, especially in France, yet some American builders had
succeeded in constructing cars propelled by gasoline engines which
could be depended upon to run at least a short distance, and it
was, therefore, hoped that some one of the more competent of these
builders might be found who would undertake to construct a suitable
engine. After making a most extensive but fruitless search for such
a builder in this country, it was decided that it would be best to
see what could be done in Europe, and as other administrative matters
made it necessary for Mr. Langley to go to Europe about the middle of
June, the writer accompanied him to see what could be done towards
having a suitable engine built there. Some six weeks were spent in
visiting all the important builders of gasoline engines in Europe,
and the results were very discouraging. Everywhere the builders said
that they did not care to undertake the work, and that they did
not consider it possible to construct an engine of 12 horse-power
weighing less than 100 to 150 kilograms (220 to 330 lbs.), or that,
if they had thought it possible, they would already have built it,
as they had had numerous inquiries for such engines, and also wanted
them for their own use. The last hope of securing a suitable gasoline
engine seemed to have vanished.
But, discouraging as was the refusal of the engine builders of Europe
to undertake to build the engine, and still more so their opinion
that such an engine was an impossibility, inspection of the engines
exhibited at the Paris Exposition had so strengthened the writer’s
conviction of the possibility of the undertaking that, before parting
with Mr. Langley on August 3 to return to America, he personally
assumed the responsibility of building an engine which would meet the
requirements.
Upon returning from Europe on August 13, and finding that the engine
builder in New York had made no progress whatever towards improving
the engine during his absence, the writer condemned both the large
engine and the small one. The engine builder had practically
bankrupted himself in his attempts to construct these two engines,
having spent something like $8000 or $10,000 in actual wages over
and above the contract prices for the engines, to say nothing of
remuneration for his own time or such expenses as shop rent and
power. As all of the money for the large machine and practically all
for the small one had been advanced to him at various times to assist
him over financial stringencies--such advances, however, having been
secured by suitable bonds--it was decided to take the various parts
of the two engines in [p220] payment for the money which had been
advanced, as it was hoped that some of the parts of the engines might
prove of use in experimental work.
Immediately after the writer’s return to Washington he began work
on the development of an engine. Taking some of the parts of the
engine which had been condemned and constructing others, he was able
by September 18 to have an experimental engine at work which, while
not water-jacketed, but provisionally cooled by wrapping wet cloths
around the cylinders, developed 18-1/2 horse-power on the Prony brake
at 715 R. P. M., the engine, including these wet cloths, weighing
108 pounds. Of course these wet cloths sufficed to keep the engine
cool for only a short time--three to four minutes being the maximum.
This was only a temporary expedient for enabling the engine to run
for a sufficient time to make brake tests and determine the power it
developed, but the results obtained were so very encouraging that it
was decided to make water jackets for the cylinders of this engine
and see what power it would then develop for more extended periods.
This experimental engine, which was merely a “patched-up” affair,
was first equipped with a sparking arrangement built on the
wiping-contact principle. With this sparking arrangement several
important difficulties presented themselves, among which may be
particularly mentioned the great difficulty of so adjusting the
sparking arrangements that the explosion in each cylinder occurred
at exactly the same point in its cycle that the explosions occurred
in all the other cylinders, it being necessary to secure this result
to a reasonably accurate degree in order to cause the engine to run
smoothly enough to be used in the aerodrome. Where an engine has a
large and heavy fly-wheel running at a high rate of speed, the nicety
of adjustment of the sparking arrangement is not so essential, for
the fly-wheel acts as a reservoir of energy and tends to smooth out
the rough and jerky impulses which would be otherwise introduced by
slight variations in the force of the explosions in the cylinders.
In constructing an engine for an aerodrome, however, the permissible
weight of the engine is so very small that the use of a fly-wheel
having sufficient weight to act as an energy reservoir is practically
prohibited. Another serious difficulty which was encountered with
the wiping-contact type of sparking arrangement was that of keeping
the stuffing boxes around the rotating contact rods tight enough
to prevent leakage, without at the same time binding and causing
excessive friction. Although it seemed probable that the difficulties
which have been mentioned, and other minor ones which were apparent,
could be remedied by further experiment, yet the high tension or
“jump-spark” type of sparking apparatus seemed to offer much greater
advantages. Since it had fewer moving parts, and furthermore since
the wiping-contact sparking arrangement would have to be considerably
modified in order to permit the construction of water jackets around
the cylinders, it was decided to construct a [p221] new sparking
arrangement for the engine on the jump-spark principle. After
introducing this change in the engine it was found to run very much
more smoothly and to require a minimum amount of care in adjusting it.
At the time that this engine was being developed it was practically
impossible to obtain any outside information regarding the proper way
of constructing it. The little that was then known had been learned
through laborious experience and at great cost by the experimenters
who were attempting to build automobiles, and was zealously guarded
in the hope of preventing their rivals from utilizing the results
of their labors. It was the known custom, however, of all engine
builders at this time to use a separate spark coil and a separate
contact maker for each cylinder of an engine, no matter how many
cylinders there were. This multiplication of the spark coils, which
at that time were very heavy, not only added greatly to the weight
but also had the same defect that the wipe-spark type of sparking
arrangement had of being exceedingly difficult to so adjust that
all of the contact makers would perform their functions at exactly
the same point in the cycle for each cylinder. To obviate these
difficulties, both of adjustment and of excessive weight, the writer
devised what is supposed to have been at that time a new and valuable
multiple-sparking arrangement whereby only one battery, one coil
and one contact maker were utilized for causing the spark in all
five cylinders, a small commutating arrangement in the high-tension
circuit distributing the sparks to the proper cylinders at the
proper time. This form of sparking arrangement was found upon test
to work so satisfactorily that it was afterwards adopted for the
small engine of the quarter-size model, and also for the new and
larger engine which was afterwards built and which will be described
further on. It is needless to describe in detail the many and
perplexing difficulties which were experienced in procuring suitable
spark coils, spark plugs and other appurtenances of the sparking
apparatus, all of which at this time were in a very crude state of
development, there being only a few different makes on the market,
and most of these being very unsatisfactory. One important minor
improvement connected with the spark plugs may be described, as the
beneficial effect produced by it was so very great that its use was
continued in all future spark plugs for all of the engines. This
improvement, however, is now incorporated in many of the plugs which
are on the market, and in some cases patents, covering the particular
form in which the improvement is incorporated, are exploited by
the manufacturer. Considerable difficulty was at first experienced
with the spark plugs from a coating of soot (resulting from the
incomplete combustion of the gas and oil in the cylinder at the time
of explosion) which formed on the porcelain and thereby caused a
short-circuit, preventing the plug from working properly. This was
overcome by extending the metal portion of the plug for some distance
into the cylinder, and for something like three-quarters of an
[p222] inch beyond the end of the porcelain insulator. The terminal
which passed through the insulator was also extended for something
like half an inch beyond the porcelain and bent to a proper extent
to co-act with a piece of platinum wire inserted in the interior
wall of the plug which formed the other terminal. After making this
improvement in the plugs practically no difficulty was experienced
from short-circuits caused by the soot.
In making the tests of this experimental engine it was found
practically impossible to absorb the power by a Prony brake in a
sufficiently uniform manner on account of the fact that the engine
was being run without a fly wheel. The consequent variation in
the torque and speed during each revolution caused such great
fluctuations in the reading of the scales which measured the pull of
the Prony brake that no confidence could be felt in the accuracy of
the readings and, therefore, no confidence could be placed in the
determinations of the effect which different changes in the engine
produced. A water-absorption dynamometer consisting of a number
of flat, circular discs fastened to a shaft and rotating between
other parallel flat discs arranged in a circular drum which was
filled to any desired extent with water was immediately planned,
and the construction of two of them was begun so that power could
be taken from both ends of the engine shaft, which, on account of
its necessary lightness, was apt to be injured by being twisted
when all the power was taken from one end of the shaft. In order to
continue the tests on the engine while this dynamometer was being
made it was decided to employ one of the propellers as a dynamometer.
Although no accurate tests had been made to determine just how much
power was required to drive these propellers at various speeds, yet
the fundamental law was known that under the same conditions the
power required to drive any propeller would vary as the cube of the
number of revolutions, and since the Prony-brake tests had given an
approximation as to the amount of power which the engine developed at
certain speeds, the law of the propeller, and extrapolations from the
data obtained in the tests of the smaller propellers in 1898, enabled
further approximations to be made as to the amount of extra power
which the engine developed when certain changes enabled it to drive
the propeller at increased speeds. This method had also the great
advantage that, since the power required varies as the cube of the
number of revolutions, it is practically impossible for the engine to
“run away” with the propeller and cause serious damage through the
possible excessive strains introduced by high speed. This feature is
also possessed by water-absorption dynamometers of the type which
were built and used in the later tests.
The construction of water jackets for this engine proved an
exceedingly formidable task, it being impossible to braze the jackets
directly to the walls of the cylinders without risk of ruining
them. It therefore became necessary to attach them by means of
stuffing boxes, which, on account of their large size [p223] and
the necessity for keeping the weight a minimum, was a most difficult
piece of work. The work was rendered still more difficult by the fact
that the water jackets had to be made in halves which were brazed
together after they had been fitted over the head of the cylinder.
Even when the work was done in the most careful way this method of
construction gave a great deal of trouble from the leaking of the
stuffing boxes or the jackets themselves. However, after much delay,
the water jackets were finally completed, and upon test the engine
was found to develop 21.5 horse-power at 825 R. P. M., the engine
itself weighing 120 pounds.
Further changes were made in this engine, especially in the pistons,
a new set of which were constructed which weighed 15 pounds less than
the original set. On account of the difficulty with the leakage of
the water around the stuffing boxes of the water jackets, and also
from imperfections in the brazed joints of the jackets themselves,
it was found impossible to rely on the power that the engine would
develop at any particular time, as the water leaking from the jackets
and running down on the spark plugs of the lower cylinders caused
these cylinders to work erratically, and this not only materially
reduced the power but also caused jerky impulses in the absence of
fly wheels.
It seemed so desirable to obtain as soon as possible a first test in
actual flight of the large machine that the writer offered to put
this engine in the aerodrome frame and make a test with it if the
machine were launched over the water, but with the launching track
mounted directly on the river bank. However, Mr. Langley felt it so
necessary to make the initial test from the top of the house-boat and
at an elevation of 30 feet or more that he would not consent to this,
and as the engine at its best did not develop quite 24 horse-power,
which had been calculated as the minimum which should be provided,
it was thought unwise to attempt to make the first test from the top
of the house-boat until the aerodrome had been provided with engines
that could be depended on to develop continuously not less than 24
horse-power.
It then became necessary either to build a duplicate engine and use
both of them in the aerodrome, the original plan as already explained
having been to have two engines developing the 24 horse-power
together; or, second, to construct an entirely new engine large
enough to furnish a minimum of 24 horse-power and use this single
engine.
As the construction and tests of this experimental engine had shown
many places in which the weight might be safely reduced, the writer
decided to construct an entirely new and larger single engine, and
thereby avoid the extra weight and difficulties which would be
introduced by having to use synchronizing gears where two engines
were used, it being impossible, of course, to run the two propellers
from the two engines independently without risk of serious disaster.
[p224]
It will be recalled that when the aerodrome was originally planned
in 1898 it was proposed to have two engines of 12 horse-power each,
and the contract for the single engine of 12 horse-power provided
that a duplicate was to be supplied, if desired, immediately upon
the completion and delivery of the first one. The calculations,
both from the whirling-table tests and from the results with the
steam-driven models in actual flight, indicated that 24 horse-power
would be ample for the aerodrome, which it was then expected would
not exceed 640 pounds in weight, with a supporting surface of 960
square feet. But it was found that the total weight of the machine
was rapidly increasing on account of slight increases in the various
details, which when added together made a considerable increase in
weight. Furthermore, as it had been found difficult to keep all five
of the cylinders of the experimental engine working uniformly, it was
thought best to build this new engine sufficiently large to provide
not only the extra power necessary because of the increased weight of
the aerodrome, but also to provide for further inevitable increases
in weight, and over and above all this, to provide also that the
engine would furnish all the power necessary, even though one of its
cylinders should absolutely fail to work and act as a dead load on
the others. The writer accordingly designed this new engine to give
40 horse-power when all five of the cylinders were working, and 28
horse-power even though one cylinder should act as a dead load on the
others.
The various materials for the construction of this engine were
ordered early in December, 1900, with the promise of delivery not
later than January, 1901. Owing to various causes, however, the major
portion of the materials could not be obtained until late in the
spring, and, in fact, a portion of them were not obtained until the
summer of 1901. During this period of delay, however, the engine for
the quarter-size model was completely reconstructed and further tests
were made with the experimental engine in developing accessories,
such as carburetors and spark coils.
The float-feed type of carburetor which was then coming into
prominence in automobile work proved at that stage of its development
to be totally unsuitable, as the slight but constant tremor of the
aerodrome frame, when the engine was working at high speeds under
a heavy load, caused the float to act as a pump and periodically
flood the carburetor. This resulted in an irregularity of action of
the engine which at times injured not only the transmission shafts,
gears, and frame, but the engine itself by the serious pounding
which occurred. A form was next tried in which the gasoline was fed
in through the valve seat of a lightly loaded valve which raised
whenever there was suction in the inlet pipe, the amount of gasoline
fed being regulated by a pin valve. Later there were built several
shapes and sizes of tanks filled with absorbent material, which was
saturated with gasoline and the surplus drawn off before starting
the engine. Some of these tanks were provided with a jacket through
which [p225] a portion of the exhaust gases was passed in order to
compensate for the cooling of the tank caused by the evaporation of
the gasoline. As a result of these tests it was found that a type
consisting essentially of a tank filled with small lumps of a porous
cellular wood (tupelo wood) which was initially saturated with
gasoline, and into which the gasoline was fed through a distributing
pipe as rapidly as it was taken up by the air, which was sucked
through it by the engine, gave the best results. Instead of jacketing
this tank, the cooling effect due to evaporation was compensated by
drawing the somewhat heated air from around the engine cylinders
up through the loosely packed lumps of wood. When tested in the
shop this type was found to give such a very uniform mixture that
the engine ran as smoothly and regularly as an electric motor, the
vibration in no way interfering with it, and even when the sudden
change from a state of rest to one of rapid motion through the air
was imitated by suddenly turning on the carburetor the blast of
several large electric fans from various angles, it was found to have
no appreciable effect on the running of the engine, thus indicating
that the trouble which was experienced with the model aerodrome in
the trials of 1901 was not likely to be repeated with the large
aerodrome. Somewhat more than a dozen carburetors of various forms
were constructed before this last type was devised, but this proved
so satisfactory that there were never thereafter any carburetor
troubles. In fact, as will later appear, a carburetor of this type
kept the engine on the large aerodrome running at full power not only
when the aerodrome was in a vertical position in the air, but also
after it had turned completely over on its back.
[p226]