HOUSE-BOAT AND LAUNCHING APPARATUS
The use of a house-boat seemed to Mr. Langley so indispensable in
former years in making open-air tests of the models that he decided
from the outset, though advised by the writer against doing so, to
use the same plan on a much larger scale in connection with the
large aerodrome. Aside from its supposed utility as a convenient
and apparently safe place from which to launch the aerodrome, the
house-boat was valuable as a portable workshop for making necessary
repairs and as a temporary storehouse for the apparatus, thereby
saving much packing and unpacking. It also provided sleeping quarters
for the workmen.
It was early seen that this plan would require a boat at least 60
by 40 feet, which could be built only at a large initial cost. But
as the experience with models had so firmly convinced Mr. Langley
that it was necessary not only that the aerodrome be launched over
the water, but also at a considerable height above it, and from a
station that commanded all points of the compass, he decided to adopt
this plan for the large aerodrome, and designs for such a boat were
accordingly made in the latter part of 1898.
In order to insure the completion of this house-boat by the time the
aerodrome was expected to be ready for trial, it was built under
contract. Immediately after its delivery in May, 1899, work was
begun on the superstructure which carried the launching track. This
superstructure was a considerable undertaking, involving a turn-table
weighing about 15 tons, supported on a double circular track, and
this track in turn was supported entirely from the side walls of
the house to avoid having columns in the middle of the floor. From
the photographs, Plate 38, Figs. 1, 2 and 3, it will be seen that
the entire superstructure was supported by three trussed girders
extending across the boat above the roof and carried by vertical
posts built into the side walls of the house. The turn-table was 48
feet square and the launching track carried by it was 5 feet gauge by
80 feet long.
[Illustration: PL. 38
FIG. 1.
FIG. 2.
FIG. 3.
HOUSE-BOAT AND LAUNCHING APPARATUS, 1899]
In making tests of the models, it had been the practice to carry
the main body of the aerodrome up a ladder to the upper works of
the boat, the wings being also carried up in the same manner. As
the large aerodrome was expected to weigh at least 640 pounds, of
which 350 pounds would be the steel frame with its undetachable
parts, such as the engine and its appurtenances, it was seen that
something more effective than a ladder would need to be provided for
getting the aerodrome from the interior of the boat to the launching
track [p157] above. It was therefore decided to place the upper
works of the boat rather nearer the rear end than the front, thus
leaving a space over the front end of the house through which a large
trap-door might be cut in the roof, and it was thought that in this
way the aerodrome might be passed up to the launching track by the
use of suitable ropes and pulleys. The upper works were so arranged,
and a sliding trap-door was provided in the roof, but more intimate
knowledge of the difficulties of handling so large and heavy a frame
made it certain, even before the aerodrome was ever placed upon the
house-boat, that it would be impossible to transport it to the upper
works by passing it through the trap-door. A different plan was then
resorted to. A very large door was constructed at the rear end of the
house, through which the completely assembled frame could be carried
in a level position and placed upon a large raft, consisting of a
lattice flooring over pontoons, moored at the rear end of the boat,
as clearly seen in Plate 38. In order to raise the aerodrome frame
from the raft to the upper works, a large, but light, mast and boom,
with suitable stays were provided. As the wings, when mounted in
their proper position on the aerodrome, would be interfered with by
such a mast, the mast and boom were so devised as to be capable of
rapid erection and dismounting, only five minutes being necessary for
either operation. In Plate 38 the mast and boom are seen in position
in Fig. 3, while in Figs. 1 and 2 they have been dismounted.
The construction of the launching track and car was begun in
November, 1899, but their completion was long delayed, as they were
frequently put aside for the more immediately important parts of
the work. Moreover, the arrangement of the struts and clutch of
the launching car depended entirely on the form and dimensions of
the frame of the aerodrome, which could not be entirely decided
until a proper engine had been secured and tested in the frame to
determine what modifications of it were necessary. In the spring of
1902, however, the launching car was entirely finished and a number
of tests of the large engine were made in the shop with the frame
mounted in position on the car.
From the description of the “overhead” launching apparatus (Part
I, Chapter X) which had proved so successful in the tests of the
models, both in 1896 and in the later experiments of 1899, it will be
recalled that the essential features of it were a track and a light
car with three hinged struts which extended below the body of the
car, and against which suitable co-acting bearing points attached to
the frame of the aerodrome were tightly drawn by means of a clutch
which gripped a special fitting fastened to the aerodrome frame near
the central point of its length. After the engine of the aerodrome
had been started and got to running at full speed, the car was
released and moved forward along its track by the combined force of
the thrust of the propellers and the pull of the coiled launching
springs. Just before the car reached the forward end of the track, a
cam at this point caused the clutch to open and release [p158] the
aerodrome, which immediately dropped slightly, as it had purposely
not quite reached a speed sufficient to cause it to soar. This slight
drop of the aerodrome, even if it were only a fraction of an inch,
made it possible for the hinged struts, against which it had been
held by the clutch, to be folded up by their special springs against
the floor of the car, thus leaving the aerodrome free in the air
without danger of entanglement.
The struts referred to above were three in number, two being placed
near the rear and one at the center of the front of the car. The use
of three points of support had the advantage of furnishing a rather
rigid foundation against which the frame could be tightly drawn by
means of the clutch-hook without risk of straining it. In designing
the “underneath” launching apparatus, which was very thoroughly
tested in the experiments with the models in the summer of 1899, the
plan of having three struts with the aerodrome drawn tightly against
them by means of a central clutch-hook was continued with most
satisfactory results.
When the position of the struts on this launching apparatus had been
changed so as to permit it to be used for the quarter-size model,
it was found, in making shop tests of the engine with the aerodrome
mounted on the launching car, that, owing to the greater vibration
produced by the gasoline engine, the three points of suspension
did not hold the model in a sufficiently rigid manner. It became
necessary, therefore, to use four struts, the two rear ones being
left as before, and the single one in front being replaced by two
interconnected ones arranged similarly to those in the rear. After
making this change no difficulty was found in holding the aerodrome
rigidly against the struts, and this modification was therefore
immediately introduced in the designs for the large launching car
which was already under construction.
[Illustration: PL. 39
METHOD OF ATTACHING GUY-WIRES TO GUY-POSTS TO RELIEVE TORSIONAL
STRAIN]
Experience, both with models 5 and 6, and with the quarter-size
model, had also demonstrated the necessity of providing some means
whereby the aerodrome frame would be relieved of the torsional
strains produced upon it by a side wind striking the under surface of
the wings when the aerodrome was mounted on the car preparatory to a
test. The means for preventing these torsional strains in the case of
the models, when “overhead” type of launching car was used, has been
described in Chapter X of Part I. However, with the “underneath” type
of launching car, a different means was necessary. A plan, in which
outriggers projected from the body of the car and wires running from
these outriggers up to the main ribs of the wings, with means for
releasing the wires just before the car reached the end of the track,
was used with the “underneath” car in the tests of models 5 and 6 in
the summer of 1899, but the outriggers were frequently deranged by
the sudden stopping of the car at the end of the run and they were
replaced by a simpler arrangement. In this plan the torsional strains
were relieved by providing, at the forward and rear ends [p159] of
the car, smaller hinged uprights furnished in their upper part with a
small slot into which a pin projected from the bottom of the forward
and rear guy-posts, respectively. The guy-wires from wings being
connected to the lower ends of the guy-posts the torsional strain
produced by a side wind was immediately transmitted from the wings
through the guy-wires to the guy-post, whence it was transmitted to
the car itself, and thus prevented from acting on the metal frame of
the aerodrome, as shown in Plate 39. These additional short struts
for taking up the torsional strain were first added to the small
launching car in 1901, and in the succeeding tests made with the
quarter-size model no trouble of any kind was indicated as likely to
be caused by them. As it was these extra struts which were directly
responsible for the accident in the launching of the large aerodrome
October 7, 1903, at the time of its first trial, and possibly also
for that on December 8, 1903, at the time of the second trial,
special attention is here called to them.
The length of travel which could be provided for the launching
car in the case of the large aerodrome, as well as in that of the
models was necessarily very limited, owing to the fact that the
track had to be constructed on the top of the house of the boat. It
was therefore necessary, in order that the aerodrome might attain
a speed sufficient for soaring before being launched, to keep the
weight of the launching car as small as possible, a given spring
tension being capable of accelerating a given mass a definite amount
in a given length of travel. With a heavier launching car the spring
tension would have to be increased. Moreover, since the blow which
would be struck when the car was suddenly stopped at the end of the
track, would depend on its mass as well as its velocity, there was an
additional reason for trying to keep the weight of the car as small
as possible.
While it was found perfectly feasible to keep the weight of the
launching car for the model low enough for practical purposes, in
designing the launching car for the large aerodrome it was only by
eliminating all flooring of the car and providing merely a box frame
with necessary cross-braces, that its weight was kept within what
appeared reasonable limits. Even then the blow which it would strike
when it reached the end of the track was found by calculation to be
exceedingly formidable.
Referring to the drawings of Plate 40, Figs. 1, 2 and 3, it will
be seen that the large launching car consisted essentially of two
parallel longitudinal side members 6 inches deep by 1.5 inches thick
by 19 feet long, connected by three main sets of cross-members:
one set near the rear, at the point at which the rear struts for
supporting the aerodrome were mounted; a second rather heavier set
about the middle of its length, at the point where the strut which
carried the clutch-hook was mounted; and a third near the front,
at the point where the front struts were mounted. Projecting from
the forward end of each of the [p160] longitudinal side members
were piston rods, on which were mounted leather-cup pistons, which
co-acted with buffer cylinders fixed at the extreme front of the
track to absorb the blow when the car reached them at the end of its
travel. The car was supported on each side by means of four hangers
(Figs. 4 and 5) which carried grooved wheels having ball-bearings
and running on a steel track consisting of flat plates fastened on
the side of the timbers of the launching track. On the extreme lower
point of these hangers were small guide pulleys, so placed as to be
just below and out of contact with a guard rail on the side of the
launching track, thus preventing any possibility of the launching car
being raised from the track either during its forward motion or by a
side wind striking underneath the wings.
[Illustration: PL. 40
‹Aerodrome “A.”›
‹General Plan & Details of Launching Car›.
(‹Details 1/3 Full Size›)
GENERAL PLAN AND DETAILS OF LAUNCHING-CAR]
[Illustration: PL. 41
FIG. 1.
FIG. 2.
FIG. 3.
AERODROME ON LAUNCHING-CAR]
[Illustration: PL. 42
‹Aerodrome “A”›
‹Details of Clutch Post for Launching Car›.
‹Scale 1/3 Full Size›
DETAILS OF CLUTCH POST FOR LAUNCHING-CAR]
[Illustration: PL. 43
FRONT END OF TRACK JUST PREPARATORY TO LAUNCHING AERODROME]
On the large launching car the arrangement of the struts against which
the bearing points of the frame were tightly drawn by the clutch was
similar in all respects to that used on the model car, there being only
slight differences in details. The details of the uprights on which the
bearing points of the aerodrome frame rested are clearly shown in Figs.
6, 7, 8, and 9 of Plate 40. From the photographs (Plate 41, Figs. 1,
2, and 3) which show the large frame mounted on the launching car, the
general arrangement of the struts and the clutch-hook can be readily
seen; and from Plate 42, Figs. 1, 2, and 3, which show in detail most
of the important features of the clutch-post and its clutch, a very
good idea of the size of the different parts may be had by observing
that the distance from the fulcrum of each half of the hook to the pin
by which it was connected through the universal joint to the vertical
rods is five inches. As previously stated, this clutch-hook gripped the
lower pyramid and pulled the bearing points of the frame firmly against
the forward and rear struts of the launching car, and in launching the
aerodrome the triggers arranged on the bottom of the car, which at the
proper time pull on the vertical rods and thereby force the two halves
of the clutch-hook apart, are so arranged that they strike a cross-beam
at the front end of the track one inch before the triggers, which keep
the struts from being pulled down by their springs, which tend to
fold them up and force them down against the car. The triggers, which
prevent the struts from being folded down, strike a cross-beam in the
track one foot before the buffer pistons on the end of the car begin to
enter the buffer cylinders at the end of the track, and, consequently,
one foot before the folding prop, which supports the front end of the
track, is knocked out by the car striking a special trigger which
allows this folding prop to swing forward when the front end of the
track folds down to insure that the aerodrome will not become entangled
with the car, even though the aerodrome be not quite up to soaring
speed at the moment of launching. The manner in which this front end
of the track folds down can be very readily seen by comparing Plate 43
with Plate 95 of Chapter XII, the former showing the front end of the
track in horizontal position, with [p161] the aerodrome at the
extreme rear end just preparatory to launching, and the latter showing
the front end of the track folded down with the hinged prop standing
outward in its downward path and the aerodrome just launched. These
photographs will be more particularly referred to later, but attention
is here called to them so that the description immediately following
may be more easily understood.
Although this method of launching the aerodrome seemed to Mr.
Langley, both theoretically and from the experience with the models,
to be a satisfactory and feasible plan, there were two very important
respects in which it seemed from the very first open to objection.
In the first place, it was necessary that the aerodrome should be
launched as nearly at its soaring speed as possible, because either
an excess or deficiency of speed interfered to some extent with the
equilibrium of the machine. So many factors were involved in the
determination of what this final velocity should be that it seemed
almost impossible to be sure of the results until at least one test
of the aerodrome had been made. In the second place it was not known
whether the rapid acceleration of the car would seriously interfere
with the equilibrium of the aviator.
In reference to the first question it was, of course, known that
a freely falling body acquires a speed of 32 feet per second at
the end of the first second after having fallen a distance of 16
feet. It was proposed to launch the aerodrome at approximately 35
feet per second; and, since the distance over which the car would
pass in acquiring this speed was approximately 60 feet, the rate of
acceleration would, of course, be less than that for a freely falling
body. The conditions in the two cases, however, are quite different.
In the case of the freely falling body there is the constant force of
gravity which causes the acceleration. In the case of the aerodrome
the car is initially standing still but ready to be acted upon by
the combined force of the thrust of the propellers and the tension
of the springs. The propeller thrust is approximately 450 pounds
at the moment of releasing the car, while the spring tension adds
approximately 400 pounds more pull, giving a total pull of 850
pounds acting on the car at the start. The weight of the aerodrome
including the aeronaut being approximately 850 pounds, and the
weight of the car being approximately 450 pounds, the total weight
to be accelerated is 1300 pounds. The resistance of the car and the
aerodrome is zero at the moment the car is released, and increases
approximately as the square of the velocity until it reaches
approximately 300 pounds at the soaring speed of the aerodrome;
while on the other hand the spring tension decreases uniformly from
400 pounds at the start to approximately 76 pounds at the end of
the track, and the thrust due to the propellers decreases from 450
pounds at the start to approximately 250 pounds at the moment of
launching. Consequently, it is in a general way clear that the rate
of acceleration of the aerodrome and car decrease, probably in a
geometric ratio, the rate of acceleration [p162] at the moment of
launching the aerodrome being much less than that of a freely falling
body. Since so many factors enter into the problem no confidence was
felt in calculations as to what the rate of acceleration would be. It
was, therefore, decided to determine it experimentally at the same
time that tests were made on the car to determine what spring tension
would be necessary to enable the aerodrome and car to acquire soaring
speed by the time they reached the end of the track.
It was obviously impossible to make this initial test with the
aerodrome mounted on the launching car, as the aerodrome would
certainly wreck both itself and the car were it allowed to remain
fastened when the car was stopped at the end of the track. It was,
therefore, decided to make the tests by mounting on the car boards
which would have a head resistance equal to that of the aerodrome.
In order to minimize as much as possible the blow due to the car
striking the buffers at the end of the track, the car had been made
as light as possible. On this account it was felt to be unwise to
risk adding to it a weight of 850 pounds to represent the aerodrome,
and supplying an additional spring tension to represent the thrust of
the propellers, as the total effect of the added weight and the added
pull would certainly completely demolish the car. By calculation it
was found that the omission of the 850 pounds weight of the aerodrome
and the spring tension to represent the thrust of the propellers
would practically counterbalance each other; and that if sufficient
spring tension were provided to cause the car, with the light boards
representing the head resistance of the aerodrome, to reach the
soaring speed by the time it arrived at the end of the track, it
would be safe to assume that this spring tension would be sufficient
for use in launching the aerodrome.
The method of measuring the final speed of the launching car for
the models consisted in fastening a strip of smoked paper to the
launching car in such a position that it was drawn past a stylus
fastened to the end of a vibrating tuning fork placed at the end
of the track. This had proved perfectly successful, but it gave a
record merely of the final speed attained by the car at the moment
of launching the aerodrome. In the case of the large aerodrome it
was desirable to have a record of the speed of the car during the
first few feet, and also at several other points in its travel down
the launching track, and the more numerous these points the better.
Short strips of copper were accordingly placed every twelve inches
along the length of the track, and these were connected by a wire
to one terminal of a small electric battery. Mounted on the car, in
such a way that it would be drawn across these contact strips, was a
copper brush arranged to make continuous contact with another wire
stretched along the track, this second wire being connected to the
other terminal of the electric battery and having in its circuit
the magnet which actuated a pen on a chronograph. Since the rate of
revolution of the chronograph barrel was known, the [p163] distance
between the marks which the magnet would cause the pen to make when
its circuit was closed by the brush on the car passing across the
contact strips on the track would give correct measures of the time
consumed by the car in passing over each twelve inches of its travel.
Upon test, however, it was found impossible to get the chronograph
magnets to work rapidly enough to respond to the very rapid opening
and closing of the circuit after the car had passed over the first
one-quarter of its length of travel. As a large part of the slowness
of action seemed to be due to the weight of the fountain pens, they
were replaced by small glass tubes drawn out to a fine point and
containing a small amount of ink. These seemed, however, to be still
too heavy to respond to the rapid closing of the circuit unless
the contacts were made unduly long. The contacts were finally made
three inches long and placed only every three feet along the track,
but just as these contacts were completed and placed in position
the clock-work of the chronograph itself became deranged. Before it
could be repaired, the tests were discontinued, as everything was in
readiness for the boat to proceed down the river where the actual
tests in free flight were to be made. Tests of the final speed of the
car were, however, made by the tuning-fork method, and the springs
were adjusted until their tension was sufficient to cause the car to
attain a speed of thirty-five feet a second at a point three inches
in front of the point at which the aerodrome would be released from
the car.
[p164]