[14]...and propeller
were simply mounted behind the pilot, which allowed an
unobstructed forward field of fire. Several pusher-type aircraft
were developed. Typical of this design concept was the DeHavilland
DH-2 shown in figure 2.3, designed by Geoffery DeHavilland for the
Aircraft Manufacturing Company (AIRCO). The photograph depicts a
strut-and-wire-braced, double-bay biplane employing thin,
untapered wings. (A brief description of biplane terminology is
contained in appendix D.) A small nacelle situated on the bottom wing
contained the pilot's cockpit and gun in the forward portion and
the 100-horsepower Gnome Monosoupape rotary engine in the pusher
position in the rear. The horizontal and vertical tail surfaces
were mounted behind the engine on an arrangement of four
strut-and-wire-braced outriggers, or booms, which extended
rearward from the wings. Cutouts in the trailing edges of the
upper and lower wings provided clearance for the rotating
propeller, which had four blades to minimize the extent of the
cutouts and reduce the required spacing of the outriggers. The
smaller diameter four-blade propeller, as compared with a
two-blade propeller capable of absorbing the same power, also
reduced the length of the landing gear.
Figure 2.3 - British
DeHavilland DH-2 fighter; 1916.
[National Archives via Martin Copp]
[15] The pusher
configuration arrangement of the DH-2 offered excellent visibility
forward, upward, and downward to both sides, but a somewhat
restricted view to the rear. Armament first consisted of a
flexible, forward-firing gun or guns, but this was later replaced
by a single fixed gun.
The biplane configuration employed on the
DH-2, with detail design variations, was the most frequently used
wing arrangements on World War I aircraft designs. The biplane
design formula offered the best compromise between structural
strength, light weight, and aerodynamic efficiency consistent with
the state of the art. The British, as a matter of policy, were not
interested in monoplanes because they had a reputation, perhaps
undeserved, for structural weakness.
The DH-2 was of wooden frame construction
covered with fabric, except for the top and forward parts of the
nacelle, which were covered with plywood. Lateral control was
provided by ailerons located on both the upper and lower wings,
and the tail surfaces had both fixed and movable elements.
According to reference 82, the aircraft was sensitive on the controls with a
tendency to spin easily. Once they mastered it, however, pilots
found the aircraft to be strong, maneuverable, and easy to
fly.
A comparison of the data given in
table
I shows that the DH-2 was somewhat
faster than the Fokker, was of greater aerodynamic efficiency, and
had a significantly lower wing loading. The climbing capability of
a fighter aircraft is a very important performance parameter, not
shown by the data in table I. Curves showing the time required to climb to
various altitudes, based on data given in reference 82, are presented in figure 2.18 for all the fighter
aircraft discussed. The climb curves also give the DH-2 an edge
over the Fokker. These advantages of the DH-2, together with
control characteristics that were no doubt far superior to those
of the Fokker, were responsible for the success of the "little
pusher."
Major Leone G. Hawker, one of the early
British aces, commanded the first Royal Flying Corps squadron
equipped with the DH-2. While flying one of these aircraft, he was
shot down by the German ace Baron von Richthofen flying an
Albatros fighter. The DH-2 was a great success when introduced in
the spring of 1916 but was outclassed by far superior German
fighters by the time of Hawker's death in the late fall of 1916.
The aircraft was belatedly withdrawn from combat in the summer of
1917. About 400 DH-2's were built.
[16] One of the
truly great fighter aircraft of the early war years was introduced
to combat by the French in March 1916. The Nieuport 17,
illustrated in Figure 2.4,.was a development of earlier Nieuport
Fighters and was extensively used not only by the French but by
the British, Belgians, Italians, and Russians. After entering the
war, the United States also employed the aircraft as a trainer.
Many well-known Allied aces flew the Nieuport 17: Albert Ball and
William Avery Bishop of the British Royal Flying Corps and
René Fonck and Charles Nungesser of France exemplify aces
who earned at least part of their reputation while flying the
Nieuport 17. At the time the aircraft was introduced into combat,
a satisfactory gun synchronizing gear was not available, but the
deficiency was overcome by mounting a machine gun, which fired
over the propeller arc, on the top of the upper wing. This
arrangement is employed on the Nieuport 17 replica shown in figure
2.5. Subsequent versions of the aircraft employed the overwing gun
in combination with a single synchronized gun firing between the
propeller blades, or by a single synchronized gun alone. This
later configuration is employed on the aircraft shown in figure
2.4.
Figure 2.4 - French Nieuport
17fighter; 1916. [National Archives
via Martin Copp]
[17] The Nieuport 17
was a very neat, clean-looking, strut-and-wire-braced biplane
powered by the 110-horsepower LeRhone 9J rotary engine. More
properly, the configuration of the aircraft should be described as
a sesquiplane since the lower wing is of much smaller chord than
the upper one. The single-spar lower wing was connected to the
upper wing of this single-bay biplane by V-type interplane struts.
The small chord of the lower wing provided the pilot with
excellent downward visibility, which is the most probable reason
for the sesquiplane layout. In earlier Nieuport fighters, the
small, single-spar lower wing had shown a tendency toward
structural weakness; this deficiency was apparently corrected in
the model 17. Lateral control was provided by ailerons on the
upper wing only. The tail assembly consisted of an all-moving
vertical surface, together with a fixed horizontal stabilizer
equipped with a movable elevator. Construction was conventional
wood framework covered with fabric, except for the tail which had
a steel tube frame.
The data in table I indicate the Nieuport 17 to have been a light
aircraft with a good weight-power ratio, low drag area, and
high...
Figure 2.5 - French Nieuport 17
with wing-mounted gun; 1916. [Peter
C. Boisseau]
[18] ... maximum
lift-drag ratio. The maximum speed was 107 miles per hour
at 6500 feet. Comparing these characteristics, as well as the
climb curves in figure 2.18, with those of the Fokker E-III and
the DeHavilland DH-2 leaves little doubt of the superior qualities
of the Nieuport 17. According to reference 23, this fighter was so well liked by the Allies that
317 of them were still in front-line service in August 1917-a long
operational life for a combat aircraft in an era in which new
aircraft were being developed in a matter of months.
The Two-Gun Fighter
High on the list of great fighter aircraft
of the first world war is the name Albatros. Beginning with the
introduction to combat of the model D-I in August 1916, Albatros
fighters served in the German Air Force until the armistice in
November 1918. Introduced in January 1917, the D-III and its
refined variants the D-V and the D-Va were the best of the
Albatros fighters and were produced in the greatest numbers. In
November 1917, 446 D-III's and 556 D-V's and D-Va's were in
service in combat squadrons with the German Air Force. Air
superiority was again in Germany's hands from the late fall of
1916 until midsummer of 1917. So great was the carnage inflicted
on Allied aircraft by German pilots flying Albatros fighters that
April 1917 is still referred to by aviation historians as "Bloody
April." Among the famous German aces who flew Albatros fighters
were Manfred von Richthofen, Ernst Udet, Bruno Loerzer, and Werner
Voss. Although the name of Richthofen is usually associated with
the Fokker triplane, he scored most of his 80 victories flying
Albatros fighters (ref. 96).
Two views of the Albatros D-III are shown
in figures 2.6 and 2.7, and the characteristics of this version of
the Albatros are given in table I. The D-III was a streamlined strut-and-wire-braced
biplane that had V-type interplane struts connecting the
small-chord lower wing to the upper wing. According to some
sources, this arrangement was copied, at the insistence of the
German Air Force, from the very successful Nieuport 17. Power was
provided by a water-cooled, six-cylinder Mercedes engine of 160
horsepower. Not evident in the photographs is the airfoil-shaped
cooling radiator located in the upper wing. Water feed and return
pipes connecting the engine to the radiator can, however, be seen.
Also not visible in the photographs are the two fixed,
forward-facing machine guns synchronized to fire between the
revolving blades of the propeller. The Albatros fighters were
among the first biplanes to be armed in this way and may be
thought of as setting a trend in fighter design which was to last
for the next two decades. For example,...
[19] Figure 2.6 - German Albatros D-III fighter;
1917. [ukn via Martin Copp]
Figure 2.7 - Side view of
prototype Albatros D-III fighter.
[Peter M. Bowers via AAHS]
[20] ... the U.S. Navy
purchased its last biplane fighter with two forward-firing,
synchronized guns in 1938.
The Albatros had several structural
features worthy of mention. Of particular interest is the
fuselage, which was of semimonocoque construction. The term
"monocoque" comes from France and means single shell. Thus, the
true monocoque fuselage consists of an outside shell, usually
formed of plywood, which is held in shape by a number of
transverse bulkheads contained within the shell. Louis Bechereau,
a French designer, first employed plywood monocoque construction
in the fuselage of the 1911 Deperdussion racing monoplane. A
semimonocoque fuselage has, in addition to the transverse
bulkheads, several longitudinal members to enhance the stability,
stiffness, and strength of the structure. This type of
construction was strong, rigid, fairly light in weight, and
provided a smooth, streamlined shape. In addition, for a given
outside diameter, a large usable internal fuselage diameter was
available. The smooth, rounded shape of the fuselage of the
D-III can be seen in figures 2.6 and 2.7. Interesting
details of the semimonocoque type of construction, including many
photographs, are given in reference 91. A number of other German aircraft manufacturers
utilized this type of fuselage construction during the war years,
and it will appear again on some of the racing aircraft of the
1920's (chapter
3) and on the high-performance
Lockheed aircraft of the late twenties and early thirties
(chapter
4).
The wings of the Albatros D-III were of
conventional wood-frame construction covered with fabric. As in
the Nieuport 17, the lower wing had only a single spar to which
the V-type interplane struts were attached. The struts themselves
were streamlined steel tubes. Throughout the life of the D-III,
D-V, and D-Va designs, despite several modifications, the
single-spar lower wing showed an inherent structural weakness that
somewhat limited the performance of the aircraft. An examination
of drawings of the lower wing (given in reference 91) shows that the single spar was located well behind
the quarter-chord point (the approximate location of the
aerodynamic center in the chordwise direction). This spar location
suggests that the tendency of the wing to fail in high-speed dives
was probably the result of aeroelastic divergence, a phenomenon
apparently not understood at the time the Albatros fighters were
developed. An increase in torsional stiffness or a relocation of
the wing elastic axis, or a combination of both, is the usual cure
for divergence. A brief description of aeroelastic divergence is
given in the discussion of swept wings in chapter 10.
[21] Control of the
Albatros D-III was provided by ailerons on the upper wings and by
an aerodynamically balanced rudder and elevator on the tail
surfaces. The fixed portion of the vertical tail was covered with
plywood and had elements above and below the fuselage. The tail
skid formed an extension of the lower, or ventral, part of the
fin. The fixed portion of the horizontal tail, like most aircraft
of the period, was not adjustable and thus could not be used to
trim the aircraft longitudinally while in flight. Accordingly, a
constant push or pull on the control stick was necessary to
maintain level flight at a constant speed and altitude. A
rudimentary form of longitudinal "trim" system, consisting of a
sliding collar on the control stick connected by a hinged link to
the cockpit floor, was provided on the Albatros. A thumb-actuated
set screw in the collar could be tightened, and the stick was then
held in a fixed position; for brief periods, the pilot was then
free to use both hands for other activities such as attempting to
clear a jammed machine gun. The system is described and
illustrated in reference 91. Information on the handling characteristics of the
Albatros is limited, but what has been found indicates that it was
easy to fly, with no dangerous characteristics.
A comparison of the data given in
table
I for the Albatros D-III and the
Nieuport 17 leads to some interesting speculation. Although the
D-III was heavier and had more wing area and a more powerful
engine than the Nieuport, the values of the wing loading and the
power loading for the two aircraft are not greatly different.
Furthermore, the values of the zero-lift drag coefficient and the
maximum liftdrag ratio are about the same. These two aircraft can
therefore be considered to have about equal aerodynamic efficiency
and, accordingly, to exhibit about the same performance
characteristics. In fact, the maximum speeds given in table I are
about the same although the altitudes at which the speeds were
measured are somewhat different. Since, for small altitude
variations, the decrease in drag that accompanies the reduction in
air density is about offset by the reduction in power with
altitude, the speed comparison of the two aircraft in the table is
valid. Values of the time required to climb to various altitudes
are also about the same for the two aircraft at the lower
altitudes, as shown by the data in figure 2.18; however, the
climbing capability of the Albatros is clearly superior to that of
the Nieuport above 10 000 feet. This plus the heavier armament of
the Albatros are no doubt responsible for the generally accepted
opinion that it was a more effective fighter than the Nieuport
17.
[22] The Triplane Phenomenon
Mention of World War I aviation evokes in
the minds of many a vision of a brightly painted red triplane
handled with consummate skill by the "Red Baron" as he closes for
the kill of another Allied airplane. The triplane was, of course,
the Fokker model Dr.-1, and the pilot was the great German ace
Rittmeister Manfred Freiher von Richthofen. The Fokker Dr.-1 was a
manifestation of a design phenomenon that swept the aircraft
industry in the period 1917-18. During that time, no less than 34
triplane prototypes were constructed and test-flown in Germany
(ref. 69). Other triplane prototypes were designed and
tested by countries of the Allied Powers.
In today's terminology, all this triplane
activity may be classified as an overreaction to the introduction
in early 1917 of the British Sopwith triplane. This aircraft, in
the hands of a few excellent pilots of the British Royal Naval Air
Service, quickly made an enviable reputation as a formidable
fighter. Raymond Collishaw was perhaps the best-known British
pilot to fly the Sopwith triplane. Less than 75 of these aircraft
were employed in combat operations; but so favorable were the
reports of German pilots who had fought against the aircraft, as
well as those of a few pilots including von Richthofen who had
flown captured examples of the triplane, that the German
government issued an invitation to industry for the submission of
triplane prototypes for evaluation and indicated that production
contracts would be forthcoming for deserving designs. Hence, the
great triplane fad in Germany. Out of all this activity, the
Fokker model Dr.-1 triplane was the only type produced in
quantity; approximately 320 were ordered in the summer of 1917.
The type was used in combat operations for about 1 year but was
employed by a relatively few, elite squadrons of the German Air
Force.
A Fokker triplane replica is pictured in,
figure 2.8. The two wheels visible beneath the tail skid are not
part of the aircraft but are attached to a dolly used for towing
the aircraft on the ground. The Dr.-1 was a small, light machine
equipped with a I 10-horsepower rotary engine and, as indicated by
the data in table
I, had a gross weight of only 1290
pounds and a small upper wing of 23.7-foot span.
Although inspired by the Sopwith triplane,
the Fokker Dr.-1 bore it no resemblance except for the three
wings. The Sopwith employed a conventional strut-and-wire-braced
wing arrangement, whereas the Fokker had no wire bracing between
the wings and only a single strut connecting the lifting surfaces
near the tips. These struts were intended to reduce wing vibration
and flexing at high speed and did not materially contribute to the
static strength of the structure. Interestingly,...
[23] Figure 2.8 - German Fokker Dr.-1 triplane fighter;
1917. [author's collection]
...the first Fokker triplane flew without
any interplane struts at all. The wings themselves were
cantilever; that is, they obtained their strength entirely from
internal bracing.
The radical departure of the Fokker Dr.-1
structure from contemporary aircraft design concepts was made
possible by the use of wing airfoil sections much thicker than
usual at the time. The mistaken notion that low wing drag could
only be obtained with thin airfoil sections has been mentioned
previously. The Fokker triplane and subsequent Fokker designs
proved the incorrectness of the thin wing concept. The Gottingen
298 airfoil section of 13-percent thickness ratio, employed on the
Dr.-1, is shown in figure 2.9 in comparison with three thin
airfoils of the World War I period. These sections were of 4- to
5-percent thickness ratio.
The wing structure of the Fokker Dr.-1
consisted of two closely spaced box spars connected at the top and
bottom with plywood sheets; the resulting torque box provided
great strength and stiffness. The ribs were made of plywood with
lightening holes and shear braces, and the leading edges were
partially covered with plywood back to the front spar. The entire
wing, including the plywood leading edge, was covered with fabric.
In common with many World War I aircraft, the trailing edge of the
wing was formed from wire and usually assumed a ...
[24] Figure 2.9 - Four examples of airfoil sections
employed in wings of World War I airplanes.
... scalloped appearance after the fabric
had been tightened with dope. Following standard Fokker practice,
the fuselage, tail surfaces, and ailerons were constructed of
welded steel tubing. Illustrative drawings of the structural
details of the Dr.-1 are given in reference 69.
Large horn-balanced ailerons were employed
only on the upper wing of the Fokker Dr.-1. The planform of this
wing, including the ailerons is shown in figure 2.10 in comparison
with upper-wing planform shapes of several of the other aircraft
discussed here. The horn balance on the Dr.-1 wing is that portion
of the aileron that extends outboard of the wing tip and forward
of the aileron hinge line. The purpose of the balances, sometimes
informally referred to as "elephant ears," was to reduce the
aileron hinge moments, and thus the force that the pilot had to
exert on the control stick to roll the aircraft. According to
reference 72, the "raked" tips of the other planforms shown in
the figure might be expected to have a small beneficial effect on
the drag associated with the production of lift.
The horizontal tail of the Fokker Dr.-I
consisted of a fixed stabilizer with large horn-balanced
elevators. The vertical tail was an all-moving unit, without a
fixed fin, and was similar in design to that of the Fokker E-III.
Other features to note in figure 2.8 are the skids....
[25] Figure 2. 10 -
Wing-planform shapes of four World War I fighter
airplanes.
....under the tips of the lower wings and
the small winglike fairing that enclosed the axle between the
wheels of the landing gear. This fairing became something of a
trademark on many later Fokker aircraft.
The zero-lift drag coefficient of 0.0323
given in table
I for the Fokker Dr.-I was among
the lowest of any of the World War I fighter aircraft analyzed, as
was the drag area of 6.69 square feet. The maximum lift-drag ratio
was a correspondingly high 8.0. The low zero-lift drag coefficient
of the Fokker triplane was no doubt due in part to the relatively
small surface area of the fuselage in relation to that of the
wings. Another important ingredient contributing to the low drag
of the aircraft was the absence of the multitude of bracing wires
found between the wings on most other aircraft of that period.
These wires, or cables, were often of round cross-sectional shape.
On the basis of the drag coefficients given in reference
72, the drag in pounds of a [26] smooth,
0.25-inch-diameter wire at the speeds of World War I aircraft is
the same as that of a strut of the same length having a 25-inch
chord and an airfoil section of 10- or 12-percent thickness ratio.
The wires, intended to take only loads in tension, were, of
course, lighter than struts designed for the same purpose. The
gain in efficiency associated with a design from which the wires
are eliminated is obvious. A good description of the interplane
bracing cables employed on the Albatros D-Va is given in reference
91.
The speed of 103 miles per hour at 13 120
feet was not particularly high (table I); most discussions of the Fokker Dr-1 in the
literature indicate that the aircraft was slow but was highly
maneuverable and had an outstandingly high rate of climb. The
time-to-climb curves in figure 2.18 indicate a climb performance
for the Dr.-I that was far superior to that of the Albatros
D-III and the Nieuport 17; in fact, it had a better rate
of climb (indicated by the slope of the curve) than any of the
other aircraft up to an altitude of between 8000 and 10 000 feet.
Unfortunately, these data, taken from reference 82, cannot be considered conclusive since data from
other sources, for example reference 119, show much higher times to climb than indicated in
figure 2.18. Two sets of climb data are given in reference
69; one set is in essential agreement with the data of
figure 2.18, whereas the other is similar to that in reference
119. In an attempt to resolve this discrepancy, the
sea-level rates of climb for the Dr.-1 were estimated for several
different weights with the use of the methods given in chapter 6
of reference 90. The calculations showed that the climb data in
figure 2.18 might have been achievable with a light fuel load, but
not with full fuel tanks. The aircraft weight for which the climb
data of reference 82 apply is not known for any of the aircraft. The
superior climbing capability of the Dr.-1 must be attributed to
the thick airfoil sections that allowed operation at the high lift
coefficients required for optimum climbing performance, not to the
use of three wings instead of two.
The triplane fighter of World War I must
be considered as something of an aberration in the course of
aeronautical development. The design trade-offs and reasoning
underlying the concept of such an aircraft are nowhere adequately
explained in any of the reference documents. However, one might
speculate along the following lines: For a given wing span and
area, the effective aspect ratio (related to the drag associated
with the production of lift) of a triplane is higher than that of
a biplane or monoplane (ref. 103). Or, for a given aspect ratio, the span of a
triplane can be less than that of a biplane or monoplane of the
same wing area. Thus, the rolling inertia of the triplane can be
less [27] than that of a biplane or monoplane. Greater
maneuverability might, therefore, be obtainable with a triplane
configuration. Further, the triplane allows the wing area to be
divided among three relatively narrow-chord wings, which may be
arranged relative to the aircraft center of gravity in such a way
as to provide the pilot with better visibility than could be
achieved with a comparable biplane. Finally, for a given level of
longitudinal stability, the physical distance between the wings
and the tail may be reduced on a triplane as compared with a
biplane.
The quantitative theoretical relationships
between the drag-due-to-lift of monoplanes, biplanes, and
triplanes were not available in 1916; however, as indicated by
references 27 and 79, empirical design data together with qualitative
theoretical ideas were available in the literature. The possible
and perhaps nebulous advantages of the triplane, however, could
not prevail against the increased complication and cost of
constructing three wings instead of two and later, when monoplanes
were better understood, one.
In any event, the Fokker triplane will
remain an integral part of World War I aviation lore and will be
discussed as long as that era is of interest. And inextricably
interwoven with the Fokker triplane story is the name of the
highest scoring ace of World War I - the legendary Baron von
Richthofen.
Fighters in 1918
Discussed next are four fighter aircraft
that served with distinction in front-line combat operations until
the termination of hostilities in November 1918. Three of these
aircraft, the French SPAD XIII and the British Sopwith Camel and
Dolphin, were strut-and-wire-braced
bi-planes that had a conventional
wood-frame structure covered with fabric. The fourth, the German
Fokker D-VII biplane, had internally braced cantilever wings like
the Fokker triplane, together with a typical Fokker welded steel
tube fuselage.
Sopwith Camel
The Sopwith Camel evolved from the earlier
Sopwith Pup and, as can be seen in figure 2.11, was an
awkward-looking single-bay biplane powered with a rotary engine.
It was the first British fighter with two forward-firing,
synchronized machine guns. A small metal fairing...
[28] Figure 2.11 - British Sopwith F. I Camel fighter;
1917. [William T. Larkins via
AAHS]
...covered a portion of the guns, which
gave the fuselage a humped appearance when viewed from the side.
This hump coupled with the large dihedral angle of the lower wing
and the flat upper wing are allegedly responsible for the name
"Camel." The aircraft first began combat operations in July 1917
and was a front-line combat aircraft until the armistice in
November 1918. Camels accounted for the destruction of more enemy
aircraft than any other Allied fighter of the war - a total of
1294. Production of the Camel amounted to 5490 aircraft.
The flat upper wing of the Camel was
dictated by a desire for production simplicity. The original
intention was to construct the wing in one piece, although in
production it was made in three pieces. The dihedral of the lower
wing was accordingly made sufficiently large to compensate for the
flat upper wing. The Camel utilized a relatively new innovation in
wing-bracing wires. From a study of references 100 and 110 and an examination of detailed drawings of the
Sopwith Dolphin, streamline wires were used for bracing on both
the Camel and the Dolphin. (Streamline wires have a
cross-sectional shape much like a symmetrical airfoil section.)
Such wires were developed by the Royal Aircraft [29] Factory at
Farnborough, England and were first flown experimentally on the
SE-4 in 1914 (ref. 39). The Sopwith Pup and triplane, both of which
entered service in 1916, also had streamline bracing wires. The
advantage in drag reduction of using this type of wire rather than
the usual round wire is great; there is a factor of about 10
between the drag coefficients of the two types of wire. Yet, no
significant use was made of this improved type of wire during the
war except by British aircraft manufacturers. Because streamline
wire was first developed at Farnborough, it was known as
Rafwire.
The Camel was produced with a number of
different power plants of varying horsepower; the greatest number
of aircraft, however, had the Clerget 9B nine-cylinder rotary
engine of 130 horsepower. Characteristics of the Sopwith F.1 Camel
equipped with this engine are given in table I.
The Camel was a small, relatively light
aircraft with a gross weight of only 1482 pounds. Its maximum
speed of 105 miles per hour at 10 000 feet was not particularly
fast, and its zero-lift drag coefficient and maximum lift-drag
ratio do not suggest a very outstanding aircraft. The climb data
given in figure 2.18 show that the Camel performed better than the
Albatros D-III, but not so well as some of the other aircraft for
which data are shown.
All the reference literature, however,
credit the Camel with having superb maneuverability. Some of the
agility displayed by the Camel is usually attributed to the
Sopwith practice of locating the concentrated weights in the
aircraft-pilot, engine, guns, and fuel-in close proximity to each
other. Thus in the Camel the pilot's feet were beneath the rear
components of the engine, the guns were over his legs, and the
fuel tank was immediately behind his back in the fuselage. Some
idea of the bunching together of these elements around the pilot
is suggested by figure 2.12, where a present-day pilot is shown
-sitting in the cockpit of a Sopwith Camel replica. Certainly, the
pilot was not seated in a very favorable position to withstand the
effects of a serious crash.
In the hands of a skillful pilot, the
Camel was a formidable weapon. Unfortunately, the flying careers
of many mediocre or student pilots were ended abruptly and fatally
as a result of the bizarre handling characteristics of the
aircraft. In combination with the aerodynamic characteristics of
the aircraft itself, the torque and gyroscopic moments associated
with the heavy rotating engine gave an incredibly fast turning
capability but, at the same time, were responsible for the
peculiar handling characteristics of the aircraft. The confusing
way in which the controls had to be manipulated in left- and
right-hand turns...
[30] Figure 2.12-Pilot in cockpit of a replica Sopwith
Camel. [Flt. Intl.]
....provides an example of these
characteristics. Based on the information contained in appendix II
of reference 100 for the later Sopwith Snipe, the gyroscopic action
of the engine caused a nose-up moment in a left turn and a
nose-down moment in a right turn. Accordingly, left stick, a large
amount of left rudder, and moderate back stick were required in a
steep left turn; too much back stick caused the aircraft to stall
and spin. Right stick, a moderate amount of left rudder, and
full back stick were required in a steep right turn. There seems
little doubt that these odd control techniques could cause
confusion and indecision on the part of an inexperienced
pilot.
The Sopwith Camel has been called the most
loved and the most hated aircraft of World War I loved by those
who mastered it and exploited its peculiarities and hated by those
who did not. The outstanding dogfighting capability of the Camel
together with the record number of German aircraft it destroyed
give it an honored place in the World War I aircraft hall of fame.
If this were not enough, one version of' von Richthofen's last
fight has a relatively obscure Canadian ace, Captain A. Roy Brown,
shooting down the famous baron while flying . . . a Sopwith
Camel.
[31] SPAD
XIII
SPAD was the acronym of the French
aircraft company Societé pour Aviation et les Derieves,
headed by famed aviation pioneer Louis Bleriot, which produced a
line of highly successful fighter aircraft in World War I. The
SPAD model XIII C. 1 is the subject of the following
discussion.
The SPAD XIII descended from the earlier
model VII which first entered combat in the fall of 1916. In
contrast to the earlier aircraft, the model XIII was somewhat
larger, had a more powerful engine, and was equipped with two
synchronized machine guns rather than one. It entered combat in
the fall of 1917 and served with the air forces of most of the
Allied Nations, including the United States. Many famous aces flew
the SPAD, but to Americans the best known was Captain Edward V.
Rickenbacker, the top scoring U.S. ace of the First World War. A
SPAD XIII in the markings of the 94th Pursuit Squadron of the
American Expeditionary Force is shown in figure 2.13; the officer
shown is Captain Rickenbacker.
Figure 2.13 - French SPAD XIII C. 1 fighter; 1917. Captain Edward
V. Rickenbacker is in front of the airplane. [USAF]
[32] Figure 2.13
depicts a stubby but graceful-looking biplane with wings of equal
chord and span, configured with no stagger and relatively small
gap. The small gap in combination with the center cutout of the
upper wing gave the pilot excellent visibility over the top of the
wing. The design appears to be that of a double-bay biplane;
however, the inner struts served only to stabilize the rather long
wing-bracing wires and prevent their flapping and chaffing (ref.
22). The wires themselves consisted of round cables.
The cockpit was close behind the engine with the pilot's feet and
part of his legs located in aluminum tunnels beneath the engine
(ref. 110). The landing gear was positioned well forward,
ahead of the center of gravity, to minimize the risk of a
nose-over on landing. Ailerons were on the upper wing only, and,
as with the other aircraft described, no means of longitudinal
trim was provided.
The SPAD XIII was powered with the
Hispano-Suiza 8BA engine of 220 horsepower. The engine had eight
water-cooled cylinders in two banks of four arranged in a V-type
configuration, much like that of many modern automobile engines.
The distinctive round radiator, equipped with manually operated
(from the cockpit) shutters for controlling the cooling airflow,
may be seen in figure 2.13. Long exhaust pipes ran on either side
of the fuselage and terminated behind the pilot's cockpit. This
arrangement resulted in a relatively quiet environment for the
pilot (ref. 110). In an interesting survey of aircraft piston
engine development, Taylor (ref. 111) credits the Hispano-Suiza with being one of the
best and most advanced engines of World War I, as well as one that
served as a sort of progenitor for a long line of Curtiss and
Rolls-Royce liquid-cooled engines that culminated in the
Rolls-Royce Merlin of World War II.
The data in table I indicate that the SPAD XIII had the most favorable
power loading of any of the aircraft considered and a high (for
its day) wing loading. These characteristics coupled with a
relatively low zero-lift drag coefficient and low drag area gave
the SPAD the highest speed of any of the aircraft listed in the
table. As shown by the data in figure 2.18, the climb
characteristics of the SPAD were bettered only by three of the
Fokker aircraft.
The reference literature suggests that the
SPAD XIII was not as maneuverable as some of the other fighters,
but its high performance, great strength, and multigun armament
made it a highly effective weapon. Its ability to dive steeply for
prolonged periods of time without fear of structural failure is
emphasized in all the reference material. [33] Piloting the
aircraft required care, particularly at low speeds, and the use of
moderate amounts of power was recommended in landing.
Although the SPAD XIII incorporated no new
technical innovations, it synergistically combined an airframe of
relatively high aerodynamic efficiency and great structural
strength with an excellent engine to produce an outstanding
aircraft. It may be regarded as representative of the top of the
state of the art of a 1918 fighter aircraft equipped with thin,
strut-and-wire-braced wings. The SPAD was so highly regarded that
a number of countries maintained the aircraft as part of their
active air force inventory for several years following the war. A
total of 8472 SPAD XIII
aircraft were manufactured.
Fokker D-VII
In the early 1970's, the U.S. Air Force
announced with much fanfare a flyoff competition between
prototypes of a new lightweight fighter aircraft. The resulting
competition involved several years of research, engineering, and
detailed flight evaluation before a winner was announced, the
General Dynamics F-16. There was no novelty about the Air Force's
prototype competition; it is a time-honored method of selecting
military aircraft. The date of the first such competition is
unknown, but one of the most renowned of German World War I
fighters, the Fokker D-VII, was selected for full-scale production
after being chosen the winner from about 30 competing prototypes.
The time was late January 1918, and the place was Aldershof
Airfield near Berlin.
As an indication of the speed with which
prototype fighter aircraft could be developed at that time, Fokker
alone entered no less than nine different types. Each of the
competing aircraft was demonstrated by the manufacturer and then
evaluated by well-known front-line pilots. The Fokker D-VII was
the unanimous winner of the competition and first entered combat
in April 1918 - an indication of the rapidity with which the
unsophisticated aircraft of that era could be developed from
prototype to combat readiness. Over 800 model D-VII aircraft were
in front-line operations by mid-August 1918.
The Fokker D-VII is illustrated in figure
2.14 and, as can be seen, was a squarish-looking biplane equipped
with an in-line engine and an automobile-type radiator located in
the nose. The most advanced feature of the aircraft was the use of
internally braced cantilever wings that had thick airfoil sections
and a wooden structure similar to that previously described for
the Fokker triplane. The thick wings were...
[34] Figure 2.14 -
German Fokker D-VII fighter; 1918.
[Merle Omstead via Martin Copp]
....responsible for many of the fine
characteristics of the aircraft. The ailerons, located on the
upper wing only, as well as the elevator and rudder had horn
balances to reduce control forces. The winglike fairing between
the wheels is also evident in figure 2.14; one experimental
version of the D-VII had a fuel tank located in this fairing to
reduce the fire hazard. The production aircraft was powered with
either a Mercedes 160-horsepower engine or a BMW 185-horsepower
engine. Both engines were six-cylinder, in-line, water-cooled
types. The BMW- was the preferred engine, however, as the aircraft
proved to be somewhat underpowered when equipped with the Mercedes
(ref.