*Purpose of Fuselage*. The fuselage of a monoplane or tractor biplane is
the backbone of the machine. It forms a means of connecting the tail
surfaces to the main wing surfaces, carries the motor, fuel and pilot,
and transmits the weight of these items to the wings and chassis. With
the exception of the wing structure, the fuselage is the most important
single item in the construction of the aeroplane. Fig. 1 shows a typical
arrangement of a two-place biplane fuselage equipped with a water-cooled
motor. The motor E, propeller Y, and radiator R are placed in the front
of the fuselage, and considerably in advance of the wings W and D.
Immediately behind the motor is the passenger’s seat A and the fuel tank
F. The pilot’s seat B is placed behind the trailing edge of the wings
and is behind the passenger’s seat. The cockpit openings G and H are cut
in the fuselage top for the passenger and pilot respectively. The rear
extension of the fuselage carries the control surfaces, L being the
vertical fin, M the rudder, O the fixed tail or stabilizer, and P the
elevator.
*Resistance*. To reduce the resistance in flight, the fuselage is of as
perfect streamline form as possible, the fuselage being deepest at a
point about one-third from the front. From this point it tapers out
gradually to the rear. With the motors now in use it is only possible to
approximate the ideal streamline form owing to the front area of the
radiator and to the size of the motor. Again, the projection of the
pilot’s head above the fuselage adds considerably to the resistance. The
wind shields I disturb the flow of air. The connections to the tail
surfaces and to the chassis members K also add to the total resistance.
An arched "turtle deck" J is generally provided, of such a shape that
the pilot’s head is effectively "streamlined," the taper of this deck
allowing the disturbed air to close in gradually at the rear. The flat
area presented by the radiator R is probably the greatest single source
of resistance, and for this reason the radiator is sometimes placed at
the side of the fuselage, or in some other position that will allow of a
better front end outline. An example of this construction is shown by
Fig. 2 in which the radiator R is placed behind and above the motor E.
The front fuselage end Z can now be made of a more suitable streamline
form.
[Illustration: Figs. 1-2-3. Fuselage and Motor Arrangement of
Tractor Biplanes.]
Fig. 3 is a view of the front end of a typical fuselage in which an
air-cooled rotary type of motor is installed. Since the diameter of this
type of motor is seldom much less than three feet, it is necessary to
have a very great diameter in the extreme front. The motor housing or
"cowl" marked E has a diameter "d" which should smoothly blend into the
outline of the fuselage at "b." In the older types of construction there
was often a very considerable break in the outline at this point,
especially in cases where the circular cowl was abruptly connected to a
square fuselage. A break of this sort greatly increases the head
resistance. A "spinner" or propeller cap marked Z in Fig. 3 is an aid in
reducing the resistance offered by the motor cowl and also reduces the
resistance of the inner, and ineffective, portion of the propeller
blades. The cap in any case is smaller than the cowl opening in order
that cooling air be admitted to the enclosed cylinders.
*Distribution of Loads*. Returning to Fig. 1, we note that the weight of
the fuselage, pilot, passenger, fuel, control surfaces and motor are
carried to the upper wing W by the "cabane" strut members C-C and stays,
the lower wing being connected directly into the sides of the fuselage.
Continuations of the cabane members on the interior of the fuselage
inter-connect the upper and lower wings (shown in dotted lines). The
interplane stays in connection with the cabane members bind the wings
and fuselage into a unit. A vertical line "CP" passes through the center
of pressure of both wings, and approximately through the center of
gravity of the machine. In other Words, the machine is nearly balanced
on the center of pressure line. The turning moments of weights behind
the CP must approximately balance the opposite turning moments of the
masses located in front of the CP. The exact relation between the center
of pressure and the center of gravity will be taken up later.
Variable loads such as the passenger, gasoline and oil, are placed as
nearly as possible on the center of pressure line, so that variation in
the weight will not affect the balance. In the figure, the passenger’s
seat A, and the fuel tank F are on the CP line, or nearly so. Thus, a
reduction in the weight of the fuel will not affect the "trim" of the
machine, nor will a wide variation in the weight of the passenger
produce any such effect. As shown, the passenger’s seat is placed
directly on the top of the fuel tank, an arrangement widely used by
European constructors. In the majority of American machines the fuel
tank is placed at the top of the fuselage instead of in the position
illustrated. As the pilot is considered as a constant weight, his
location does not affect the balance.
When at rest on the ground, the weight of the rear end of the fuselage
is supported by the tail skid N. The length of this skid must be such
that the tail surfaces are kept well clear of the ground. The center of
the chassis wheel Q is placed in front of the center of gravity so that
the weight of the machine will cause the tail skid to bear on the ground
when the machine is at rest. If the wheel were behind the center of
gravity, the machine would "stand on its nose" when making a landing.
The wheels must be located so that the tendency to "nose over" is as
small as possible, and yet must not be set so far forward that they will
cause an excessive load on the tail skid. With too much load on the
skid, the tail will not come up, except after fast and prolonged
running, and heavy stresses will be set up in the framework due to the
tail bumping over the ground at high speed. The skids should not be
dragged further than absolutely necessary, especially on rough ground.
With proper weight and wheel adjustment, the tail should come up in a
short run. The wheel adjustment will be taken up under the head of
"Chassis."
*Position in Flight*. In normal horizontal flight, the center line of
thrust CT is horizontal or nearly so. This line of thrust passes through
the center of the motor crankshaft and propeller. In an upward climb,
the CT is inclined at the angle of climb, and since the CT indicates the
line of flight, the streamline curves of the body should be laid out so
that the axis of least body resistance will coincide with the line of
thrust. When flying horizontally at the normal speed, the body must
present the minimum of resistance and the wings must be at the most
efficient angle of incidence. In climbing, or flying at a very low
speed, the tail must necessarily be depressed to gain a large angle of
wing incidence, and hence the body resistance will be comparatively high
owing to the angle of the body with the flight line. It is best to have
the least resistance of the fuselage coincide with the normal horizontal
flight speed. This condition at once establishes the angle of the wings
in regard to the fuselage center line.
*Center Line of Resistance*. The center line of thrust should pass
through the center of total head resistance as nearly as possible. The
total resistance referred to is composed of the wing drag, body and
chassis resistances. In an ordinary military type of aeroplane this line
is located approximately at one-third of the gap from the bottom wing.
Owing to variations in the drag of the Wings at different angles, this
point varies under different flying conditions, and again, it is
affected by the form and size of the fuselage and chassis. The exact
location of the center of resistance involves the computation of all of
the resistance producing items.
In addition to passing through the center of resistance, the center line
of thrust should pass slightly below the center of gravity of the
machine. In this position the pull of the motor tends to hold the head
up, but in-case of motor failure the machine immediately tends to
head-dive and thus to increase its speed. The tendency to dive with a
dead motor automatically overcomes the tendency to "stall" or to lose
headway. With the centerline of thrust determined, and with given motor
dimensions, the fuselage position can be located at once in regard to
the wings. This is good enough for a preliminary layout, but must be
modified in the final design. As before explained, the centerline of
thrust is located at a point between the two wings, approximately
one-third of the gap from the lower wing.
In machines having a span of 35 feet and over, it is a trifle less than
one-third the gap, while in small speed scouts it is generally a trifle
over one-third. This rule checks very closely with the data obtained
from 22 standard machines. Thus, in a machine having a 6-foot gap, the
propeller centerline will be located about 2 feet above the lower wing.
The top of the fuselage (measured under the stabilizer surface) is from
5 to 8 inches above the center line of thrust. At the motor end, the
height of the fuselage above the CT is controlled by a number of
factors, either by the type of motor, or by the arrangements made for
access to the motor parts. In a number of European machines, the motor
sits well above the top of the fuselage, this always being the case when
a six-cylinder, vertical water-cooled motor is used. With an air-cooled
type, the top is governed by the cowl diameter.
*Motor Compartment*. The space occupied by the motor and its accessories
is known as the "motor compartment," and in monoplane and tractor
biplane fuselage it is located in the extreme front of the body. The
interior arrangement varies with different types of motors and makes of
machines. With rotary cylinder motors, the "compartment" is often
nothing but a metal cowl, while with large water-cooled motors it
occupies a considerable portion of the body. Water-cooled motors are
generally covered with automobile type hoods, these usually being
provided with "gilled" openings for ventilation. Owing to the heat
generated in the motor, some sort of ventilation is imperative at this
point. Whatever the type, the compartment is always cut off from the
rest of the fuselage by a fireproof metal partition to guard against
fire reaching the passenger or fuel tanks. The fuel and oil should
always be separated from the motor by substantial partitions since a
single carbureter "pop" may cause serious trouble.
[Illustration: Fig. 4. Mounting and Cowls for Rotary Cylinder
Motors. Courtesy "_Flight_."]
Accessibility is a most important feature in the design of the motor
end, and hence the hood should be of the hinged automobile type so that
it can be easily raised for inspection or repairs. In the Curtis JN4-B
Military Training Tractor, the cylinder heads and valve mechanism
project slightly above the top of the hood so that these parts are amply
cooled and are entirely accessible. Access to the carbureter can be had
through a small hand-hole in the side of the hood. The radiator in this
Curtiss model is located in the extreme front end of the
fuselage—automobile fashion. The propeller shaft passes through a
central opening in the radiator. In Fig. 6 the vertical motor E is set
down low in the frame, the upper part of the fuselage F ending at H. The
engine bearer B, which carries the motor, forms the top part of the
fuselage at this point. The engine is thus in the clear and access can
easily be had to every part of the motor. The radiator is in front of
the motor at R. When in flight the motor is covered by a sheet metal
hood similar to the folding hood used on automobiles. This type is used
in the Martin, Sturtevant, and several European machines.
[Illustration: Fig. 5. Motor Compartment of a Curtiss Tractor
Biplane Using a Front Type Radiator. Note the Two Exhaust Pipes
Which Carry the Gases Over the Top of the Wings.]
Fig. 7 is a very common front end arrangement used with side radiators.
The top fuselage member F is brought down in a very low curve, leaving
the greater part of the motor projecting above the fuselage. At the
extreme front, the upper fuselage member F joins the engine bearer B,
the connection being made with a pressed steel plate. The radiator R is
shown at the side of the fuselage. The cylinders are not usually covered
when in flight. In the front view it will be noted that the radiators
are arranged on either side of the fuselage. A side view of the H. and
M. Farman Fighter is shown by Fig. 10. This is a very efficient French
machine which has seen much active service in the war. The front end is
much like that shown in Fig. 7 except that a spinner cap is fitted to
the propeller boss. A "V" type motor allows of the radiator being
mounted between the two rows of cylinders, and in a position where it
will cause the least possible head resistance.
[Illustration: Figs. 6-7. Various Motor Arrangements, and
Radiator Locations.]
[Illustration: Fig. 10. A Type of H. and M. Farman Tractor
Fighting Biplane. This Machine Uses a "V". Type Motor, with the
Radiator in the Valve Alley. The Gunner and the Machine Gun Are
Mounted in the Rear Cock-pit. It Will Be Noted That the Body Is
Raised Well Above the Lower Wing So that the Gun Field Is
Increased. The Pilot Is Well Ahead of the Entering Edge of the
Lower Wing. Courtesy of "_Aerial Age_."]
The fuselage is of excellent streamline form and shows careful study in
regard to the arrangement of the power plant. Unlike the majority of
machines, the fuselage is raised well above the bottom wing, this being
done evidently to increase the range of the gun in the rear cockpit. The
increased height allows the gun to shoot over the top plane at a fairly
small angle, and the height above the ground permits the use of a very
large and efficient propeller without having an excessively high
chassis. At the rear the fuselage tapers down to a very thin knife edge
and therefore produces little disturbance.
[Illustration: Fig. 11. Radiator Mounted at Leading Edge of
Upper Wing. This Type Is Used with the Sturtevant and Lawson
Aeroplanes and Is Very Effective Because of the Improved
Circulation.]
Fig. 11 shows a Sturtevant Training Biplane in which the radiator is
mounted at the front edge of the upper plane. This arrangement was
originally introduced by the Sturtevant Company in their steel biplanes
and has proved a very efficient type for cooling, although the radiator
must affect the lift of the top plane to a very considerable extent.
*Pilot and Passenger Compartments*. These compartments contain the
seats, controls, and instruments, and in the military types contain the
gun mounts and ammunition. In some battle-planes, the passenger or
"observer" occupies the rear seat, as this position gives a wider range
of fire against rear or side attacks. This arrangement is true of the H.
and M. Farman machine just illustrated and described. In the large
German "Gotha" the gunner occupies the rear position and fires through,
or above, a tunnel built through the rear end of the fuselage. In some
forms of training machines, the pilot and passenger sit side by side
instead of in tandem, as this arrangement allows better communication
between the pilot and student, and permits the former to keep better
watch over the movements of the student. A notable example of this type
is the Burgess Primary Trainer. A side-by-side machine must have a very
wide fuselage and therefore presents more head resistance than one with
the seats arranged in tandem, but with proper attention to the
streamline form this can be reduced so that the loss is not as serious
as would be imagined from a view of the layout.
The seats may be of several types, (a) the aluminum "bucket" type
similar to, but lighter than, the bucket seats used in racing
automobiles; (b) the woven wicker seat used in many types of German
machines, or (c) the modified chair form with wooden side rails and
tightly stretched leather back and bottom. Whatever the type, they
should be made as comfortable as possible, since the operation of a
heavy machine is trying enough without adding additional discomfort in
the form of flimsy hard seats. In the older machines the seats were
nothing more than perches on which the pilot balanced himself
precariously and in intense discomfort. A few pounds added in the form
of a comfortable seat is material well spent since it is a great factor
in the efficient operation of the machine. Wicker seats are light,
yielding and comfortable, and can be made as strong or stronger than the
other types. It seems strange that they have not been more widely
adopted in this country.
All seats should be slightly tilted back so that the pilot can lean back
in a comfortable position, with a certain portion of his weight against
the back of the seat. Sitting in a rigid vertical position is very
tiring, and is especially so when flying in rough weather, or on long
reconnaissance trips. The backs of the seats should be high and head
rests should be provided so that the pilot’s head can be comfortably
supported against the pressure of the wind. If these head rests are
"streamlined" by a long, tapering, projecting cone running back along
the top of the fuselage, the resistance can be considerably reduced.
This arrangement was first introduced in the Gordon-Bennett Deperdussin
and has been followed in many modern machines. In the Deperdussin, the
pilot’s head was exposed directly to the full blast of the propeller
slipstream and a head support was certainly needed. Small, transparent
wind shields are now fastened to the front edge of the cockpit openings
which to a certain extent shield the pilot from the terrific wind
pressure. These are quite low and present little resistance at high
speeds.
[Illustration: Fig. 12. Hall-Scott Motor and Side Type Radiator
Mounting on a Typical Tractor.]
A heavy leather covered pad, or roll, should be run entirely around the
edge of the cockpit opening as a protection to the pilot in case of an
accident or hard landing. The roll should be at least 3 1/2" in diameter
and should be filled with horse hair. All sharp edges in the cockpit
should be similarly guarded so that in the event of the pilot being
thrown out of his seat, he will not be cut or bruised. Each seat should
be provided with an improved safety strap that will securely hold the
pilot in his seat, and yet must be arranged so that it can be quickly
and easily released in an emergency. In flight the occupants must be
securely strapped in place to prevent being thrown out during rapid
maneuvers or in rough weather. Buckles should be substantial and well
sewed and riveted to the fabric so that there will be no danger of their
being torn out. The straps must be arranged so that they will not
interfere with the free movement of the pilot, and so that they will not
become entangled with the controls. It is best to copy the sets approved
by the government as these are the result of long continued experiment
and use.
[Illustration: Fig. 13. Deperdussin Monoplane with Monocoque
Body. Note the Streamline Form of the Body and the Spinner Cap
at the Root of the Propeller.]
Care must be taken to have the seats located at the correct height from
the floor so that the legs will not become cramped. In the majority of
machines, the vertical rudder is operated by the feet. Unless the seat
is at the proper height, the pilot will be in a strained position as he
cannot shift around nor take his feet from the rudder bar. Either the
rudder bar or the seat should be adjustable for different lengths of
legs. Usually the adjustment is made in the rudder bar since it is not
usually advisable to shift the seats owing to the necessity of having
the pilot’s weight in a fixed position. In some old types of monoplanes,
the pilot sat on a small pad placed on the floor of the fuselage.
Needless to say, this was a horribly uncomfortable position to be in,
but as the flights of that time were of short duration it did not matter
much. If the feet could be removed occasionally from the rudder bar the
matter of seat position would not be of so much importance, but to sit
flat on the floor, with the legs straight out, for a couple of hours is
a terrible strain and has undoubtedly caused many accidents through
cramps.
As both the passenger and the fuel are varying weights, the fuel tank
seat idea is good. This allows both of these items to be placed at the
center of gravity of the machine where weight variation will have no
effect on the balance of the plane. In this position, however, the fuel
must be pumped up to a higher auxiliary tank since the main tank would
be too far below the carbureter for gravity feed.
The flooring of the cockpits can be either of veneer, or can be built up
of small spruce slats about 1/2" x 1/2", the slats being spaced about
1/2" apart. The latter floor is specified by the government for seaplane
use, and is very light and desirable. The floor is placed only at points
where it will be stepped on. Observation holes are cut in the floor on a
line with the edge of the seats so that the occupants can view the
ground without looking over the edge of the fuselage. The observation
port holes are about 9 inches in diameter. Glass should never be used in
the cockpits except for the instrument covers, unless it is of the
non-splintering "triplex" laminated type of glass. The use of
inflammable celluloid should also be avoided as being even more
dangerous than the glass. The triplex glass is built up of two or more
layers of glass, which are cemented together with a celluloid film
applied under heavy pressure. This form of construction is very strong,
and while it can be broken, it will not fly apart in the form of
splinters.
All instruments should be placed directly in front of the pilot so that
he can take observations without turning his head. Usually all of the
instruments, with the exception of the compass, are mounted on a single
"instrument board" placed in front of the pilot and directly under the
forward edge of the cockpit opening. The compass can be placed on the
floor as in American machines, or inserted in the upper wing as in some
European machines. The motor control apparatus is placed where it can be
reached conveniently from the seat. Oil gages, gasoline gages, and
revolution counters are generally placed on the instrument board where
they can be easily observed. If a wireless set is carried, the switches
are placed on, or near, the instrument board. Owing to the uses to which
the different machines are put it is impossible to give a list of
instruments that would be suitable for every machine. The simplest
machine should have the following instruments:
*Altimeter*
for measuring altitude.
*Clock*
of special aeroplane type.
*Incidence indicator.*
*Air speed indicators*
for measuring the speed of the machine relative to the air.
*Gasoline, oil and pressure gages*
for determining amount of fuel.
Instruments for Navy and Army machines are of course more complete. In
the specifications for Army Hydroaeroplanes (twin motor type 1916) the
following instruments are specified:
*Aneroid Barometer*.
Graduated in feet, and reading from sea-level to 12,000 feet.
*Compasses*.
One in each cockpit. To be of the Sperry Gyroscopic type with an
elastic suspension and properly damped. Shall be attached to, and
synchronized with, the ground drift indicator.
*Ground Drift Indicator*.
Located in observer’s cockpit. For noting drift due to side
winds. See illustration on page 244.
*Clock*.
Special aeroplane type, built to resist vibration.
Located in pilot’s cockpit.
[Illustration: Fig. 14. Aeroplane Compass of the McCreagh-Osborn
Type. (Sperry)]
*Gasoline Supply Gage*.
To indicate the amount of fuel in gravity service tank at all
attitudes of flight, and shall be visible from pilot’s seat. A
gage in the main tank will also be desirable that will register
the approaching exhaustion of fuel. This indicator should
register when 75% of the fuel in the main tank is exhausted, and
then record the remainder continuously.
*Air Speed Indicator*.
One in pilot’s cockpit.
*Angle of Incidence Indicator*.
Sperry type. To be located in pilot’s cockpit.
*Inclinometer*.
For measuring angle of inclination of longitudinal axis of
machine. In pilot’s cockpit, and placed on instrument board in
the vicinity of tachometers.
*Bank Indicator*.
For indicating the proper amount of bank on turns. In pilot’s
cockpit.
*Map Board*.
One revolving map board placed in pilot’s cockpit.
*Map Desk*.
One folding map desk in observer’s cockpit.
[Illustration: Fig. 15. Sperry Ground Drift Indicator.]
*Tachometers*.
For measuring speed of motors in revolutions per minute. Pilot’s
cockpit.
*Self-Starter Switch*.
For operating self-starter. On instrument board in pilot’s
cockpit.
Among the other accessories specified in the cockpit for the above
machines are a Pyrene fire extinguisher; a 2-gallon water breaker; a
speaking tube for communication between the pilot and observer (1" to 1
1/8"); a flashlight signal for speaking tube; and a tool kit. The weight
of the tool kit shall not exceed 11 lbs.
[Illustration: Fig. 16. Cock-pit of a "London and Provincial"
Biplane. Control Lever in Foreground and Instrument Board Under
Cowl. Courtesy of "_Flight_."]
*General Proportions of the Fuselage*. The total length of the fuselage
depends upon the type of power plant, upon the span or chord of the
wings, and upon the arrangement of the tail surfaces. The rear end of
the fuselage should be far enough away from the wings to insure that the
rear surfaces are not unduly affected by the "down-wash" or the
"wake-stream" of the wings. A very short fuselage gives a short lever
arm to the control surfaces, hence these surfaces must be very large
with a short body. With the stabilizer surface close to the wings, the
"damping" effect is slight, that is, the surface does not effectively
kill or "damp down" oscillations. Large tail surfaces are heavy,
difficult to brace, and cause a very considerable amount of head
resistance. The extra weight of a long fuselage is generally offset by
the increased weight caused by the large tail area of the short body
type.
When machines are crated and shipped at frequent intervals, a very long
fuselage is objectionable unless it is built in two sections. It also
requires much storage space and a very long hangar. Machines for private
use must often be sacrificed from the efficiency standpoint in order to
keep the dimensions within reasonable limits. An aeroplane requiring an
enormous hangar has certainly no attraction for the average man. Every
effort must be made to condense the overall dimensions or to arrange the
extremities so that they can be easily dismounted. Exhibition flyers
require specially portable machines since they ship them nearly every
day, and the expense of handling a long awkward fuselage may alone
determine the choice of a plane. It is usually best to divide the body
at a point just to the rear of the pilot’s seat, although many flyers
look upon a two-part body with disfavor unless they can be shown that
the joint connections are as strong as the rest of the fuselage.
[Illustration: Fig. 19. Fuselage Dimension Chart for Two Place
Aeroplane Fuselage. Upper Diagram Is the Water Cooled Type and
the Lower Figure Applies to a Machine with a Rotating Air Cooled
Motor. See Table of Dimensions on Page 248.]
As a guide in the choice of fuselage proportions, a set of diagrams and
a table are attached which gives the general overall dimensions of
several prominent makes of machines. The letters in the diagram refer to
the letters heading the columns in the tables so that the general
dimensions of any part can be readily determined. I do not claim that
these dimensions should be followed religiously in every case, but they
show what has been done in the past and will at least suggest the limits
within which a new machine can be built.
[Illustration: Fig. 20. Fuselage Dimension Diagrams Giving the
Principal Dimensions of Speed Scout Machines. Upper Figure Shows
Typical Scout with Water Cooled Motor (Curtiss), While Lower
Diagram Shows an Arrangement Common with Rotary Air Cooled
Motors (Nieuport)]
Fig. 19 gives the outline and dimension letters for two-place machines
of what is known as the "Reconnaissance Type." Both water-cooled and
air-cooled motor equipments are shown, the top machine being of the
water-cooled type while the lower figure shows a typical two-place
machine with a rotary air-cooled motor. Underneath this side elevation
is a front view of the fuselage, and a section taken through the point
of greatest depth. As shown, the fuselage is of square cross-section,
but the dimension B applies equally to the diameter of a circular
cross-section. Dimension C gives the height of the curved upper deck, or
"turtle deck" of the fuselage. Dimension D shows the extreme length
extending in front of the leading edge of the lower wing, and T shows
the length of the rear portion back of the leading edge of the lower
wing, the leading edge being taken as a base of measurement. The
location of the deepest section, measured from the extreme front of the
fuselage, is given by E, the depth at this point being indicated by B.
The extreme width is shown by I. In the machine shown, side radiators
are used, the blunt front end dimensioned by G and K being the dimension
of the front engine plate. When front radiators are used, the dimensions
G and K also apply to the size of the radiator. The amount of advance,
or the distance of the chassis wheel center from the leading edge is
given by S, and the distance of the wheel center below the leading edge
is given by R. V is the length of the engine projecting above the
fuselage top. The passenger or observer is indicated by 1 and the pilot
by 2. The top plane is 3 and the bottom plane 4. The engine is located
by 5, and the top fuselage-rail, or "longeron," by 7. Turtle deck is 6.
[Illustration: * Round monocoque body, dimensions (B) and (F)
measured from outer diameter or top of circle]
Fig. 20 gives the diagrams of speed scout machines, both of the
air-cooled and water-cooled types. These are the small, fast, single
seat machines so much used in the European war for repelling air attacks
and for guarding the larger and slower bombing and observation machines.
The upper drawing shows a Curtiss Speed Scout equipped with a "V" type
water-cooled motor and a circular front radiator. While the front of the
body is circular, it gradually fades out into a square cross-section at
the rear. The lower machine is a Nieuport speed scout equipped with a
rotating cylinder air-cooled motor. In this scout, the diameter of the
motor cowl is given by dimension K. Body is of square cross-section. It
will also be noted that the chord of the lower plane is less than that
of the upper plane and that the deep body almost entirely fills the gap
between the two wings.
[Illustration: Fig. 21. Curtiss J N 4-B Fuselage Boxed for
Shipment.]
With some of the later speed scouts, the body entirely fills the gap
between the wings and the top plane is fastened directly to the top
members of the fuselage. This makes windows necessary in the sides of
the fuselage. When vertical water-cooled motors are used on speed
scouts, the front view is entirely cut off, for these are very large
motors and project above the fuselage for a considerable distance. This
obstruction is avoided in the Curtiss speed scout shown, by the use of a
"V" type motor. It will be noted that these two scouts, especially the
Nieuport, are of excellent stream line form, a very important item with
such high speed machines. The propeller of later Nieuports is provided
with a conical spinner cap which evidently reduces the head resistance
to a considerable extent. The different portions of the machine are
indicated by the same figures as in the case of the reconnaissance
machine.