For the making of the cylinders two fishing rod ferrules, known as
female ferrules, are required. And for the heads of the cylinders, two
male ferrules are required. Such ferrules can be secured at most any
sporting goods store. The female ferrules should be filed down to a
length of 2″, cut down on one side a distance of ³⁄₄ of the diameter,
then cut in from the end as shown in Figure 7. When this has been done
the two male ferrules should be cut off a distance of ¹⁄₈″ from the top
as shown in Figure 7-a, to serve as heads for the cylinders.
[Illustration: Diagram 16]
A hole ¹⁄₈″ in diameter should be drilled in the center of each head
so as to enable the connecting of the intake pipes. By the use of soft
wire solder the heads should be soldered into the ends of the cylinders
as shown in Figure 1-d.
The pistons should now be made; for this purpose two additional male
ferrules are required. These should be made to operate freely within
the cylinders by twisting them in a rag which has been saturated with
oil and upon which has been shaken fine powdered emery. When they have
been made to operate freely they should be cut down one-half inch
from the closed end as shown in Figure 5-a. For the connecting rods,
2 pieces of brass tubing, each ¹⁄₈″ in diameter by 1¹⁄₄″ long, are
required, and, as illustrated in Figure 6, should be flattened out at
either end and through each end a hole ³⁄₃₂″ in diameter should be
drilled. For the connecting of the piston rods to the pistons, studs
are required, and these should be cut from a piece of brass rod ¹⁄₄″ in
diameter by ¹⁄₂″ in length. As two studs are necessary, one for each
piston, this piece should be cut in half, after which each piece should
be filed in at one end deep enough to receive the end of the connecting
rod. Before soldering the studs to the heads of the pistons, however,
the connecting rods should be joined to the studs by the use of a steel
pin which is passed through the stud and connecting rod, after which
the ends of the pin are flattened, to keep it in position as shown in
Figure 5-a.
For the outside valve mechanism and also to serve in the capacity as a
bearing for the crankshaft, a piece of brass tubing ¹⁄₄″ in diameter by
1¹⁄₂″ long is required. Into this should be drilled three holes, each
¹⁄₈″ in diameter, and each ¹⁄₂″ apart as shown in Figure 4. Next, for
the valve shaft and also propeller accommodation, secure a piece of
³⁄₁₆″ drill rod 2″ long. On the left hand side of the valve shaft, as
shown in Figure 3, a cut ¹⁄₃₂″ deep by ¹⁄₂″ in length is made 1″ from
the end. Another cut of the same dimensions is made on the right side
only; this cut is made at a distance of ³⁄₈″ from the stud end.
As shown in Figure 1-f, the crank throw consists of a flat piece of
steel, ³⁄₃₂″ thick, ³⁄₈″ in length by ¹⁄₄″ in width. At each end of the
crank throw a hole ³⁄₁₆″ in diameter should be drilled, the holes to
be one-half inch apart. Into one hole a piece of steel drill rod ³⁄₃₂″
in diameter by ¹⁄₄″ long is soldered, to which the connecting rods are
mounted, as shown in Figure 1-f. Into the other hole the stud end of
the crank throw is soldered.
[Illustration: Schober pusher type compressed air driven monoplane]
[Illustration: Schober compressed air driven biplane]
Before making the tank it is most desirable to assemble the parts of
the engine, and this may be done by first fitting the pistons into the
cylinders as shown in Figure 1-b, after which the cylinders should be
lapped one over the other and soldered as shown in Figure 1-a. When
this has been done a hole one-fourth of an inch in diameter should be
drilled half way between the ends of the cylinders, and into this hole
should be soldered one end of the valve casing shown in Figure 4. For
the inlet pipes as shown in Figure 1-c secure two pieces of ¹⁄₈″ brass
tubing and after heating until soft, bend both to a shape similar
to that shown in Figure 1-c. When this has been done solder one end to
the end of the cylinder and the other in the second hole of the valve
shaft casing. The valve shaft should now be inserted in the valve shaft
casing and the connecting rods sprung onto the crank throw as shown
in Figure 1-d. To loosen up the parts of the engine which have just
been assembled it should be filled with oil and by tightly holding the
crankshaft in the jaws of a drill the engine can be worked for a few
minutes.
The tank is made from a sheet of brass or copper foil 15″ long by
¹⁄₁₀₀₀″ thick. This is made in the form of a cylinder, the edges of
which are soldered together as shown in Figure 2. Sometimes this seam
is riveted every one-half inch to increase its strength, but in most
cases solder is all that is required to hold the edges together. For
the caps, or ends, the tops of two small oil cans are used, each can
measuring 2¹⁄₂″ in diameter. To complete the caps two discs of metal
should be soldered over the ends of the cans where formerly the spouts
were inserted, the bottoms of the cans having been removed. The bottom
edges of the cans should be soldered to the ends of the tank as shown
in Figure 2. Into one end of the completed tank a hole large enough
to receive an ordinary bicycle air valve should be drilled. Figure 2.
Another hole is drilled into the other end of the tank, into which is
soldered a small gas cock to act as a valve. Figure 2. This should be
filed down where necessary, to eliminate unnecessary weight. To connect
the tank with the engine, a piece of ¹⁄₈″ brass tubing 3″ long is
required, the ends of which are soldered into the holes in the valve
shaft casing nearest the cylinders, as shown in Figure 1-ee. As shown
in Figure 1-ee, a hole ¹⁄₈″ in diameter is drilled in one side of this
piece, but not through, in the end nearest the tank. Another piece of
brass tubing ¹⁄₈″ in diameter is required to connect the tank with
the engine, one end of which is soldered to the cock in the tank, the
other in the hole in the pipe which leads from the engine to the tank,
illustrated in Figure 1-ee, thus completing the engine.
In conclusion it is suggested that the builder exercise careful
judgment in both the making and assembling of the different parts
of the engine in order to avoid unnecessary trouble and secure
satisfactory results. After having constructed an engine as has just
been described, the constructor may find it to his desire to construct
a different type of engine for experimental purposes. The constructor
therefore may find the descriptions of satisfactory compressed air
engines in the following paragraphs of suggestive value.
COMPRESSED AIR DRIVEN MODELS
The development of the compressed air engine has given an added impetus
to model making, necessitating more scientific experimenting and
developing the art of model flying along lines of greater value to
those who may eventually take up the work of building our future air
fleets.
THE DART COMPRESSED AIR DRIVEN MODEL
In the accompanying illustration is shown a model aëroplane of
monoplane type driven by a three-cylinder rotary engine which was
constructed by Edward Willard Dart of South Norwalk, Connecticut.
The engine was constructed after several months of patient labor.
Careful judgment was exercised in the drafting of the plane and
likewise in the assembling of the engine for it is absolutely
essential that all parts be properly fitted as to enable the engine to
run smoothly. In designing the wings every detail was taken into
consideration to insure good flying.
[Illustration: Model by Edward Willard Dart]
The main wing has a spread of 58″ and 7″ in chord. The elevator
measures 23″ in spread and 6″ in chord. In the construction of both
wings bamboo ribs are used, the frames being covered over with China
silk and coated with celluloid solution. The main wing is made in two
sections to facilitate quick adjustment to the fuselage.
THE MCMAHON COMPRESSED AIR DRIVEN MONOPLANE
One of the latest developments in the field of model flying is the
McMahon compressed air driven monoplane. This model was built to be
used as either a tractor or pusher, but in view of its ability to
balance more easily as a pusher most of the experiments have been
carried out on this machine as a pusher. The machine in itself is
simple and inexpensive to construct, the chief portion of the expense
being involved in the making of the engine. By using the machine as a
pusher a great deal of protection is afforded both the propeller and
engine, and this protection helps to avoid damaging the propeller or
engine, which would mean an additional expenditure for repairs, thus
minimizing the cost of flying the model.
The frame has been made to accommodate both the tank and engine, and
this is done by using two 30″ strips of spruce, each ¹⁄₄″ wide by ³⁄₈″
deep, laid side by side, a distance of three inches apart, up to within
10″ of the front, as shown in the accompanying photograph. No braces
are used on the frame, as the tank, when securely fastened between the
frame, acts in that capacity.
The wings are made in two sections, each section measuring 24″ in span
by 8″ in chord, consisting of two main spars, ³⁄₁₆″ in diameter, one
for the entering edge and one for the trailing edge. To these edges, at
a distance of three inches apart, are attached bamboo ribs, 18 in all,
each measuring 8″ in length by ¹⁄₈″ in width by ¹⁄₁₆″ thick. The wings
are round at the tips, and have a camber of approximately one-half
inch, but they are not set at an angle of incidence. Light China silk
is used for covering and after being glued over the top of the wing
frame is given two coats of dope to shrink and fill the pores of the
fabric. A good “dope” for the purpose can be made from celluloid
dissolved in banana oil. The wing sections are attached to the frame
and braced by light wire. The forward wing or “elevator” is made in the
same manner as the main wing, but should measure only 18″ × 3″. Instead
of being made in two sections as the main wing, the forward wing is
made in one piece.
The chassis is made by forming two V struts from strong steel wire
sufficiently large enough so that when they are attached to the frame
of the model the forward part will be 9″ above the ground. One V strut
is securely fastened to either side of the frame, at a distance of 8″
from the front. A 7″ axle is fastened to the ends of these struts. On
the axle are mounted two light wheels, each about 2″ in diameter. The
chassis is braced by light piano wire.
The rear skid is made in the same manner as the forward skid, only
that the ends of the struts are brought together and a wheel 1 inch in
diameter is mounted at the bottom ends by means of a short axle. The
struts are not more than 7¹⁄₂″ long, thus allowing a slight angle to
the machine when it is resting upon the ground.
[Illustration: John McMahon and his compressed air driven monoplane]
[Illustration: Frank Schober preparing his model for flight. Gauge to
determine pressure of air may be seen in photograph]
The machine complete does not weigh over 7 ounces. The power plant
used in connection with this model is of the two cylinder opposed
engine type, with tank such as has just been described in the foregoing
chapter.
The tank is mounted in the frame by drilling a ¹⁄₁₆″ hole through
either end of the tank, through which a drill rod of this diameter can
be inserted. About ³⁄₄ths of the drill rod should extend out on each
side of the tank, to permit the fastening of the tank to the frame
side members. This method of mounting the tank serves two purposes to
a satisfactory degree. First, it permits secure fastening; second, as
the rods are passed through the side and cap of the tank they help
materially in preventing the caps from being blown off in the event of
excessive pressure.
THE MCMAHON COMPRESSED AIR DRIVEN BIPLANE
In the McMahon model we find a very satisfactory type of compressed
air driven model. On several occasions this model has made flights of
over 200 feet with a duration of between 10 and 15 seconds, and the
indications are that by the use of a more powerful engine the model can
be made to fly a greater distance, with a corresponding increase of
duration. The engine used in connection with the model is of the two
cylinder opposed type, such as described in the foregoing paragraphs.
The tank, however, is somewhat different in design from that just
described, it having been made of 28 gauge sheet bronze, riveted every
one-half inch. The two long bolts that hold the steel caps on either
end of the tank also serve as attachments for the spars that hold the
tank to the engine bed, as shown in diagram 17. The tank has been
satisfactorily charged to a pressure of 200 lbs. per square inch, but
only a pressure of 150 lbs. is necessary to operate the engine. The
tank measures 10″ in length by 3″ in diameter and weighs 7 ounces.
The wings of this machine are single surfaced and covered with fiber
paper. The top wing measures 42″ in span by 6″ in chord. The lower
wing is 24″ by 6″. The wings have a total surface of 396 square inches
and are built up of two ³⁄₁₆″ dowel sticks, flattened to streamline
shape. Only two sets of uprights separate the wings, thus adding to the
streamline appearance of the machine.
Both tail and rudder are double surfaced and are built entirely of
bamboo for lightness, the tail being made in the form of a half circle
measuring 12″ by 8″. Steel wire is used on the construction of the
landing chassis, the chassis being so designed as to render it capable
of withstanding the most violent shock that it may possibly receive
in landing. The propeller used in connection with the model is 14″ in
diameter and has an approximate pitch of 18″.
[Illustration: Diagram 17]
COMPRESSED AIR ENGINES
THE WISE COMPRESSED AIR ENGINE
Although of peculiar construction, the Wise rotary compressed air
engine offers a very interesting design from a viewpoint of ingenuity.
This engine embodies a number of novel features not hitherto employed
in the construction of compressed air engines, and in view of the fact
that the majority of compressed air engines are made on the principle
of the opposed type, this engine suggests many possibilities for the
rotary type engine.
The engine consists of five cylinders and weighs four ounces, including
the propeller and mounting frame. On a pressure of 15 lbs. the engine
will revolve at a speed of 1000 r.p.m. The connecting rods are fastened
to the crankshaft by means of segments and are held by two rings,
making it possible to remove any one piston without disturbing the
others. This is done by simply removing a nut and one ring. The crank
case is made from seamless brass tubing, into which the cylinders are
brazed. The valve cage and cylinder heads are also turned separately
and brazed. One ring only is used in connection with the pistons. The
cylinders have a bore of ¹¹⁄₃₂″, with a piston stroke of ⁷⁄₁₆″. In
view of the fact that pull rods show a greater tendency to overcome
centrifugal force, they are used instead of push rods to operate the
valves. The crankshaft has but one post, which is uncovered in turn by
each inlet pipe as the engine revolves. The “overhang” method is used
to mount this engine to the model. With the exception of the valve
springs, the entire engine, including the mounting frame and tank, is
made of brass.
[Illustration: Wise five cylinder rotary compressed air engine]
THE SCHOBER-FUNK COMPRESSED AIR ENGINE
Two of the most enthusiastic advocates of the compressed air engine
for use in model aëroplanes are Messrs. Frank Schober and Rudolph
Funk, both members of the Aëro Science Club. For a number of months
both these gentlemen have experimented with compressed air engines of
various designs, until they finally produced what is perhaps one of
the most satisfactory rotary engines now in use, from a standpoint of
simplicity and results.
[Illustration: Schober-Funk three cylinder rotary engine]
As can be seen from the accompanying illustration, this little
engine is remarkably simple in appearance. The engine complete, with
equipment, weighs at the most but 14 ounces. The cylinders, three in
all, are stamped from brass shells for strength and lightness. The
pistons are made from ebony fiber. The cylinders have a bore of ⁵⁄₈″,
with a piston stroke of ¹⁄₂″. The crank case is built up from a small
piece of brass tubing and is drilled out for lightness. The crankshaft
is hollow, and is supported at the rear by a special bearing which
acts as a rotary valve, admitting the intake through the crankshaft
and permitting the exhaust to escape through a specially constructed
bearing.
The tank is constructed of 30 gauge sheet bronze, wire wound, and
fitted at the ends with spun brass caps. The actual weight of the
engine alone is 2¹⁄₂ ounces, the tank and fittings weighing 11¹⁄₂
ounces, making the total weight of the complete power plant 14 ounces.
THE SCHOBER FOUR CYLINDER OPPOSED ENGINE
Another interesting type of compressed air engine that has been
developed in America is the Schober four cylinder opposed engine.
While this engine is different in appearance from most compressed air
engines, it has been made to work satisfactorily and is consistent with
the same high class construction that is displayed in most all of Mr.
Schober’s engines. The accompanying diagram 18 illustrates the method
of operation of the four cylinder engine.
[Illustration: Diagram 18]
The crank case is constructed from four pieces of 24 gauge spring
brass, substantially connected in the form of a rectangle, the top and
bottom being left open. The front and rear walls have flanges which
engage the inside of the side walls and are secured thereto by four
small screws on each side, thereby making it an easy matter to take the
crank case apart.
The four cylinders are made from drawn brass shells and have a bore of
¹⁄₂″ and stroke of ¹⁄₂″. The pistons are made of solid red fiber. The
two-throw crankshaft is built up of steel with brass webs. The bearings
are of steel. The valves, being overhead, are driven by a gear mounted
at the end of the crankshaft, the gear driving the valve shaft by means
of a gear on that shaft, with which the crankshaft gear meshes. The
valve arrangement, as shown in diagram 18, consists of four recesses
cut into the valve shaft, two of which allow the air to pass from the
inlet pipes, which lead into the valve chamber at the center of same,
to two of the cylinders at once, while the other two recesses allow the
exhaust to pass from openings in the sides of the valve chamber.
The cylinders are secured to the side plates of the crank case so
that when those side plates are removed, the cylinders are removed with
them. The pipes are detachable at their centers; small pipes running to
the heads of the cylinders extending into the larger pipes which run
to the valve chamber. This arrangement is shown in the end view of the
engine. A 17″ propeller is used in connection with this engine.
GASOLINE ENGINES
THE JOPSON 1 H. P. GASOLINE ENGINE
FOR MODEL AËROPLANES
During the past few years several attempts have been made, both in this
country and abroad, to produce a reliable gasoline engine for model
aëroplane work, but mostly without any degree of success. The reason
for this inability, no doubt, is due to the scarcity of small working
parts sufficiently light and at the same time reliable. The engine
described herewith, designed by Mr. W. G. Jopson, a member of the
Manchester Aëro Club, England, is one of the few that have been made to
work satisfactorily.
[Illustration]
[Illustration: The interesting horizontal-opposed Jopson gasoline
engine for model aëroplanes. The top photograph shows the half-speed
shaft and the arrangement of the valve mechanism. This engine is
air cooled, develops 1 h.p. at 1,500 r.p.m., and weighs 7¹⁄₂ lbs.,
including gasoline tank and propeller. The bottom view shows the engine
with propeller _in situ_. Courtesy _Flight_.]
As the accompanying diagrams 19 and 20 and photograph show, the engine
is of the four-cycle, horizontal opposed type, having two cast-iron
cylinders of 1¹⁄₄″ bore and 1³⁄₈″ stroke. Each cylinder is cast in
one piece, and as the engine is air cooled, they are cast with
radiating fins. One h.p. is developed at 1500 r.p.m. The total weight
of the engine, gasoline tank and propeller is 7¹⁄₂ lbs. In preparing
the design of this engine, the designs of similar full-sized aëro
engines were followed as far as possible. The pistons are similar to
those used on large aëro engines and are fitted with two rings; the
crankshaft is turned out of two inch special bar steel, and is carried
in two phosphor-bronze bearings. There is no special feature about the
connecting rods, these being of the standard type, but very strong and
light. To enable the two cylinders to be exactly opposite one another,
the connecting-rods are offset in the pistons and are connected to
the latter by gudgeonpins. The aluminum crank case is extremely
simple, being cylindrical and vertically divided. The inlet valves are
automatic, the exhaust valves being mechanically operated; the camshaft
is driven from the main shaft by two-to-one gearing.
[Illustration: Diagram 19
Sectional elevation of the 1 h.p. Jopson gasoline engine for
models. The disposition of the gasoline tank and wick carburettor
is particularly noteworthy. It will be seen that metal journals are
provided for the crankshaft, which is turned out of 2-inch bar steel.
Courtesy _Flight_.]
To assist the exhaust, and also the cooling, small holes are drilled
round the cylinder in such a position that when the piston is at the
inner end of its stroke, these holes are uncovered, thus permitting
the hot exhaust to escape, and so relieve the amount passing through
the exhaust valves. The commutator is also driven off the camshaft, as
shown in the drawing. No distributor is fitted to the commutator, as
small ones are somewhat troublesome and very light coils are obtainable
at a reasonable price.
The gasoline tank is made of copper in streamline form, and is usually
fitted to the back of the crankcase, thus reducing the head resistance,
but if desired it can be fitted in any other position. The action of
the carburetor can be easily seen from the drawings; it is of the
surface type and much simpler, lighter and quite as efficient as the
spray type. Specially light and simple spark plugs are used, that give
very little trouble. The propeller used in connection with this engine
is somewhat out of the ordinary, having been specially designed for
this engine, and patented. The propeller is made entirely of aluminum
and has a variable pitch, this being easily obtainable, as the blades
are graduated so that any desired pitch, within certain limits, may be
given at once. The results of a series of tests on a 30 inch propeller
are shown on the accompanying chart, and from it the thrust as certain
speeds with a certain pitch can be obtained. Taking the engine running
at 1540 r.p.m. with a pitch of 15″, the thrust comes out at 9¹⁄₂ lbs.,
or more than the weight of the engine and accessories.
[Illustration: Diagram 20
Diagram of results obtained from tests of the 1 h.p. Jopson model
gasoline engine, showing the thrust in pounds at varying speeds with
propellers of different pitch. Courtesy _Flight_.]
THE MIDGET AËRO GASOLINE ENGINE
Although numerous model constructors in America are experimenting with
model gasoline engines, the Midget Gasoline Engine, the product of
the Aëro Engine Company, Boston, Massachusetts, is perhaps the most
satisfactory up to the present time. An engine of this type was used by
Mr. P. C. McCutchen of Philadelphia, Pennsylvania, in his 8 foot Voisin
Type Biplane Model, for which he claims a number of satisfactory
flights.
The engine is made from the best iron, steel, aluminum and bronze and
the complete weight including a special carburetor, spark plug and
spark coil is 2¹⁄₂ lbs. From the top of the cylinder head to the bottom
of the crank case the engine measures 7″. It is possible to obtain from
this engine various speeds from 400 to 2700 r.p.m., at which speed it
develops ¹⁄₂ h.p. The propeller used in connection with this engine
measures 18″ in diameter and has a 13″ pitch.
[Illustration: The Midget ¹⁄₂ H. P. gasoline engine]
It might be of interest to know that one of the parties responsible
for the development of this engine is Mr. H. W. Aitken, a former model
maker and who is now connected with one of the largest aëro engine
manufacturing companies in America.
STEAM POWER PLANTS