[126] frequently
referred to by such unflattering names as "widow maker" and "the
flying prostitute" (i.e., no visible means Of Support). The
zero-lift drag coefficient of the B-26 was 0.0314, which was
considerably lower than the 0.0406 of the B-24 and about the same
as the value of 0.0302 for the B-17. Other characteristics of the
B-26 included a maximum speed of 274 miles per hour at 15 000 feet
and the ability to carry a 4000-pound bomb load for a distance of
1100 miles. Armament consisted of 11 .50-caliber machine guns
capable of being fired in various directions; several fixed,
forward-firing guns were provided for ground attack use.
The Martin B-26 was ordered into
production directly from the drawing board in September 1940, and
a total of 5157 were built. The aircraft was used in both the
European and Pacific theaters of operation but was little used in
the peacetime Air Force following the cessation of hostilities in
1945. The North American B-25, counterpart of the B-26, was
produced in greater numbers than the B-26 and is perhaps better
known today because it was the aircraft used by James H. Doolittle
in the famous Tokyo raid of April 1942. About 9800 models of the
B-25 were constructed, and they served with the Air Force
following World War II in a variety of training and support roles.
In other countries, they remained as a primary bomber aircraft
until comparatively recent years.
Multiengine bombers, such as those just
discussed, usually dropped their bombs from a level flight
attitude or, in the case of medium bombers in the ground attack
mode, from a shallow dive. In contrast, an entirely different
technique known as dive bombing was pioneered by the U.S. Navy
during the decade preceding World War II. In this method of
operation, the aircraft was put into a vertical or near-vertical
dive at an altitude 15 000 to 20 000 feet and aimed directly at
the target. Bomb release usually took place at about 3000 feet,
after which the aircraft made a high-g dive recovery to a level
flight attitude. Dive bombing was found to be especially suited
for use against small, slow-moving targets such as tanks and ships
and was employed with devastating effectiveness against Japanese
naval forces during World War II.
Dive bombers were usually single-engine
aircraft with a crew of two: a pilot and a rear-facing gunner
situated behind the pilot. The most widely used U.S. Navy dive
bomber during World War II was the Curtiss SB2C Helldiver series
of which an SB2C-1 is illustrated in figure 5.10. The name
"Helldiver" traced its origin to an earlier Curtiss dive bomber of
biplane configuration that appeared in the 1930's.
[127]
With a wing span of nearly 50 feet and a normal gross weight of 14
730 pounds, the SB2C-1 was a large single-engine aircraft.
Equipped with a 1750-horsepower twin-row radial engine, the
aircraft had a maximum speed of 281 miles per hour at 12 400 feet;
a stalling speed of 79 miles per hour facilitated operation of the
SB2C-1 from the short deck of an aircraft carrier. Internal
storage was provided in the fuselage for a 1000-pound bomb.
Typically, the aircraft could carry this bomb load for a distance
of 1100 miles. Armament varied with different models of the
aircraft. In one arrangement, four .50-caliber machine guns were
fitted in the wings and the observer had two .30-caliber
guns.
Figure 5.10 shows the configuration of the
SB2C-1 to have been entirely conventional for its time. A feature
of the aircraft not evident in the photograph was the dive brakes
used for limiting the speed of the aircraft while in its steep
dive to the target. Trailing-edge split flaps that opened in a
symmetrical configuration from the top and bottom surfaces of the
wing were employed for this purpose; the symmetrical arrangement
minimized the effect of flap deployment on longitudinal stability
and trim. To reduce tail buffeting, the flaps were perforated with
a large number of holes in the order of 3 inches in diameter (the
exact size is not known). For landing, only the lower surface
flaps were deflected. The need for dive brakes can be explained as
follows: First, the normal acceleration, or g-load experienced by
an aircraft during dive recovery, varies inversely as the radius
of the pullout maneuver and directly as the square of the
velocity; second, the accuracy with which the bomb can be dropped
increases as the altitude of bomb release is reduced. Since 9 g's
is about the maximum normal acceleration that a person can
withstand and remain effective, the structural design...
Figure 5. 10 - Curtiss SB2C-1
carrier-based scout bomber.
(NASA]
[128]...of the
Helldiver was based on this loading. Hence, the dive speed had to
be limited to stay within design load limits and, at the same
time, permit bomb release at the desired altitude. Most modern jet
fighters, of course, employ some form of speed brake, but the use
of such devices was not common practice on World War II aircraft
except for aircraft designed for dive bombing.
First flight of the Helldiver took place
in December 1940, and it first entered combat in November 1943.
Including Canadian production, a total of over 7000 Helldivers
were manufactured. The type was withdrawn from service in the U.S.
Navy in 1949 after a long and useful career.
Fighter Aircraft
Each of the major Allied and Axis powers
developed a series of effective fighter aircraft. The British
Hawker Hurricane and Supermarine Spitfire will long be remembered,
particularly as being responsible for the air victory in the
critical Battle of Britain in 1940. The famous German
Messerschmitt 109 was the principal antagonist of the Spitfire and
Hurricane during the Battle of Britain, and together with the
Focke-Wulf 190, formed the mainstay of the Luftwaffe fighter
forces until the end of World War II. The Japanese Mitsubishi Zero
probably is the best-remembered Japanese fighter in this country
because of the role it played in the attack on Pearl Harbor in
December 1941. The North American P-51 Mustang, the Republic P-47
Thunderbolt, and the Lockheed P-38 Lightning are the best known of
the U.S. Army Air Force fighters employed in World War II; the
Grumman F6F Hellcat and the Vought F4U Corsair are equally well
remembered for the outstanding role they played as Navy fighters
during the fierce conflicts in the Pacific area. A brief
description of the North American P-51 and the Grumman F617
follows. These aircraft are considered typical of World War II
land- and carrier-based fighter aircraft as employed by the United
States armed forces. Because of its unusual configuration and
interesting technical features, the Lockheed P-38 Lightning is
also discussed.
The North American P-51 Mustang is
considered by many to represent the highest level of technical
refinement ever achieved in a propeller-driven fighter aircraft.
The P-51 was originally designed to a British specification for
use by the Royal Air Force (RAF) and was later adopted by the U.S.
Army Air Forces. The aircraft was ordered by a British purchasing
commission during the hectic days of April 1940, [129] with the
understanding that the prototype was to be completed within 120
days. The prototype was completed on schedule; however, first
flight was delayed until October 1940. The aircraft first saw
combat service with the RAF in July 1942. At first, the aircraft
was equipped with a 12-cylinder Allison in-line engine of about
1200 horsepower. With this engine, the aircraft was intended as a
low-attitude fighter and ground-attack machine. Later, the North
American airframe was mated with the British Rolls-Royce Merlin
engine, and this combination resulted in one of the outstanding
fighter aircraft of World War II The Merlin was a liquid-cooled
engine that employed 12 cylinders arranged in a V-configuration
and was equipped with a two-speed two-stage gear-driven
supercharger. The engine developed 1490 horsepower at takeoff and
was capable of producing 1505 horsepower under war emergency
conditions at the critical altitude of 19 300 feet. The Merlin
engine was produced under license in the United States by the
Packard Motor Car Company.
The P-51 Mustang was produced in many
variants, of which the most numerous and best known was the P-51D
illustrated in figure 5.11. Specifications for the aircraft are
given in table
III. Figure 5.11 shows the aircraft
was equipped with a low wing, which was a highly...
Figure 5.11 - North American
P-51D fighter. [Peter C.
Boisseau]
[130] ...favored wing
position for fighter aircraft during World War II. The use of the
in-line engine of low frontal area resulted in a fuselage of
relatively low total wetted area and gave the aircraft a lean,
streamlined appearance. The low frontal area of the in-line engine
was one of the chief advantages cited for this type of power
plant; the disadvantage was the vulnerability of the cooling
system to enemy fire. The aft location of the cooling radiator and
its associated inlet and internal flow system is of interest. The
system was designed with the objective of obtaining a net thrust
from the cooling air as a result of heat addition from the engine
coolant. This feature no doubt contributed to the very low drag
coefficient of the aircraft. The P-51 was also the first aircraft
to utilize the NACA laminar-flow airfoil sections, discussed
earlier. Although it is doubtful that any significant laminar flow
was achieved on production versions of the Mustang, the low-drag
airfoils did provide improved characteristics at high subsonic
Mach numbers.
A typical value of maximum gross weight
for the P-51D was 10 100 pounds, although this value varied to
some extent depending upon the external armament and fuel load.
The wing loading corresponding to the 10 100-pound gross weight
was 43 pounds per square foot, and the power loading was 6.8
pounds per horsepower. A typical maximum speed was 437 miles per
hour at 25 000 feet, and the stalling speed was 100 miles per
hour. The zero-lift drag coefficient of 0.0163 was the lowest of
any of the aircraft analyzed herein, and the corresponding value
of the maximum lift-drag ratio was 14.6. The Mustang was therefore
an extremely clean airplane. The aerodynamic cleanness of the
aircraft was due, in large measure, to careful attention to
detailed design and continued refinement of the aircraft during
its production lifetime.
The Mustang was utilized in various types
of fighter operations, including high-altitude air-to-air combat
as well as ground-support and interdiction missions. It had a
service ceiling of 40 900 feet and could climb to 20 000 feet in
7.3 minutes. Armament varied but usually consisted of six
.50-caliber machine guns, three in each wing, and it could carry
two 1000-pound bombs or six 5-inch rockets. Equipped with drop
tanks, the P-51D had a range of 1650 miles at a speed of 358 miles
per hour and an altitude of 25 000 feet. In contrast to the short
range of contemporary British and German fighters, the range
capability of the Mustang, as well as the P-47 and P-38, allowed
it to be used with great effectiveness in escorting formations of
B-17 and B-24 bombers on long-range missions. The P-51 was the
only fighter to fly over three enemy capitals - Berlin, Rome, and
Tokyo.
[131] A total of 14
490 aircraft of the P-51 series were constructed. The aircraft was
used in all theaters of operation during World War II, was called
into use by the U.S. Air Force again during the Korean War, and
was used by a number of foreign air forces for many-years. Many
P-51 aircraft are flying in the United States today as unlimited
racing aircraft and even for executive transport use. A turboprop
version of the Mustang has recently been proposed as a cheap,
close-air-support aircraft for use by small, undeveloped countries
in various parts of the world. An interesting history of the P-51
aircraft is given in reference 66.
Entirely different in configuration from
the conventional single-engine fighter of World War II, the
twin-engine Lockheed P-38 Lightning is depicted in early form in
figure 5.12. In this unusual but highly practical arrangement, the
pilot and armament were housed in the center pod, and the
liquid-cooled engines together with cooling-air intakes,
radiators, and turbosuperchargers were located in the twin booms
that also supported the tall. The P-38 was the first fighter
designed in the United States to be equipped with a tricycle
landing gear: the nose gear retracted into the center pod; and the
main gear, into the booms. It was also the first United States
aircraft of any type to employ external surfaces composed of
butt-joined metal skins with flush rivets. Other innovations
employed in later versions of the aircraft included hydraulically
boosted ailerons and provisions for use of partial....
Figure 5.12 - Lockheed YP-38
twin-engine fighter. [Rudy Arnold
via ukn]
[132] ...deflection
(8°) of the trailing-edge Fowler flaps. Both of these
modifications were intended to enhance maneuverability in combat.
Powered controls and, to a lesser extent, maneuvering flaps are
used on most modern jet fighters.
The P-38, intended as an interceptor with
the mission of destroying enemy bombers at high altitude, was
designed according to specifications issued in 1937 that called
for speeds of 360 to 400 miles per hour (sources differ on the
exact value) at 20 000 feet and the capability of reaching that
altitude in 6 minutes. The specification also contained demanding
requirements for range, endurance, and landing and takeoff field
length. A single-engine aircraft could not meet the mission
requirements with any engine available at that time. Hence, the
P-38 employed two engines. First flight of the prototype XP-38 was
in January 1939, and the aircraft was first deployed in Europe by
the United States Army Air Force (USAAF) in the fall of
1942.
At a normal gross weight of 17 500 pounds
and with a wing span of 52 feet, the P-38L, for which data are
given in table
III, was for its day a large
fighter. All versions of the aircraft were equipped with Allison
V-12 liquid-cooled engines; those on the P-38L developed 1470
horsepower each. Maximum speed was 414 miles per hour at 25 000
feet; stalling speed was 105 miles per hour. The P-38 could climb
to 20 000 feet in 7 minutes and had a service ceiling of 44 000
feet. With internal fuel only, the aircraft had a range of 475
miles at 339 miles per hour, or 1175 miles at 195 miles per hour;
with drop tanks, the range was 2260 miles.
Indeed, the P-38 was a high-performance
aircraft. Even the prototype exceeded 400 miles per hour in 1939.
Although its high speed was one of the great virtues of the P-38,
this desirable characteristic was responsible for a serious
problem encountered in the development of the aircraft. Little was
known at that time about the problems associated with penetrating
the Mach number regime characterized by large effects of
compressibility (see discussion of fig. 5.6), and even less was
known of means for alleviating such problems. A combination of the
high speed reached in steep dives, together with a less than
optimum high Mach number airfoil section, caused the P-38 to
suffer severe compressibility problems. These problems manifested
themselves in the form of buffeting, loss of control, difficulty
in recovering from dives, and-in some cases-complete destruction
of the aircraft. Many different modifications were tried before a
successful solution to the problem was found. In the spring of
1942, NACA in conjunction with Lockheed devised a simple fix that
came to be known as the dive-recovery [133] flap (not to be
confused with the dive brake used on the SB2C. A short-span flap
was located at the 30-percent-chord position behind the leading
edge of the lower surface of the wing, just outboard of the booms.
Deflection of these flaps in a high-speed dive increased the lift
on the wings so that successful dive recovery was possible. Such
flaps appeared on production aircraft beginning with the P-38J
version. Among other aircraft employing this very effective device
were the P47 Thunderbolt and the P-59 and P-80 jet fighters. (See
chapter
11.)
Although never designed as a fighter for
air-to-air combat with other fighter aircraft, the Lightning was
widely used and highly effective in this role, particularly in the
Pacific theater of operations. More Japanese aircraft were
destroyed by the P-38 than by any other aircraft, and the two
highest scoring American aces of World War II, Majors Richard I.
Bong and Thomas B . McGuire, Jr., both flew the Lightning. It was
used in all theaters in which the USAAF operated. As a fighter,
several different combinations of armament were employed. Most
aircraft had four .50-caliber machine guns and a 20-mm cannon
located in the nose ahead of the pilot. Also, it could carry bombs
weighing up to as much as 3200 pounds or 10 5-inch rockets. In
addition to duties as a fighter, a photoreconnaissance version of
the aircraft, designated F-5, saw extensive service. Many other
types of military duty such as bombing and ground attack were
performed by the P-38.
Nearly 10 000 P-38's, including all
models, were produced. Several of these are still flying today in
the hands of dedicated antique aircraft collectors, and they were
used for many years after World War II in aerial survey work.
German pilots in North Africa paid the P-38 a tribute of sorts
when they dubbed it "Der gabelschwanz teufel" (the fork-tailed
devil).
Navy fighter aircraft are intended
primarily for operations from the short decks of aircraft
carriers. Operation from an aircraft carrier poses certain
constraints during the design of the aircraft. For example, the
relatively short length of the flight deck (about 700 feet for the
larger carriers employed during World War II) imposed restrictions
on the stalling speed of the aircraft and thus required that Navy
fighters have somewhat lower wing loadings than their counterparts
in the USAAF. A tail hook must be provided to give rapid
deceleration of the aircraft on touchdown, and this in turn
required special strengthening of the rear portion of the
fuselage. Furthermore, a carrier-based aircraft must be designed
for higher landing sink rates than normally encountered in
land-based aircraft; this higher sink rate requires a heavier
landing gear and attachment structure. Since storage space both on
the flight and [134] hanger decks is at a premium on an aircraft
carrier, provision must also be made for folding the wings so that
the required parking space is reduced. A number of aircraft
companies specialized in the design and production of fighters for
use on aircraft carriers. The Grumman Aircraft Engineering Company
was one of the leading producers of Navy fighter aircraft during
the 1930's (as it still is today), and the Navy entered World War
II with the Grumman F4F Wildcat as its first-line fighter.
Early in 1941, Grumman began the design of
a new fighter as a replacement for the Wildcat. Much combat
experience had been obtained in the European conflict and was
utilized in the design of the new aircraft. Following entry of the
United States in World War II in December 1941, the Wildcat saw
extensive service in combat against the Japanese. Although the
Wildcat was a good aircraft, it was not really competitive with
the Japanese Zero shipboard fighter. The lessons learned in action
with the Zero were also incorporated in the design of the new
Grumman fighter. The prototype of this aircraft, known as the F6F
Hellcat, first flew in June 1942, and deliveries of combat
aircraft were made to the Navy in early 1943. The first
operational use of the Hellcat was in the attack on Marcus Island
from the carrier USS Yorktown
in August 1943. It is indeed
remarkable that the aircraft could be developed from a prototype
to combat status in little more than a year.
The Hellcat is illustrated in figure 5.13,
and some of its characteristics are listed in table III. The aircraft was a rather bulky looking low-wing
monoplane equipped with an 18-cylinder Pratt & Whitney
twin-row radial engine of 2000 horsepower. The engine was equipped
with a geared supercharger and gave 1970 horsepower at 16 900
feet. Although the USAAF deployed highly successful fighters with
both air-cooled radial and liquid-cooled in-line engines, the U.S.
Navy had employed air-cooled radial engines exclusively since the
mid-1920's. Apparently, the Navy felt that the advantages of
simplicity and reduced vulnerability to gunfire offered by the
radial engine more than offset the disadvantages of increased
frontal area. Although not evident in figure 5.13, the landing
gear of the F6F retracted rearward and was enclosed within the
wing root stubs. Outboard of the landing gear the wing could be
rotated and folded aft so as to lie essentially flush along the
sides of the fuselage to minimize the deck area required for the
aircraft's storage.
The Grumman F6F was, for its day, a
relatively large aircraft with a fully loaded weight of 12 441
pounds. The wing loading, however, was only...
[135] Figure 5.13 - Grumman F6F-3 carrier-based
fighter. [Peter C. Boisseau]
...37.3 pounds per square foot, which gave
a relatively modest stalling speed of 84 miles per hour. The
aircraft had a maximum speed of 375 miles per hour at 17 300 feet.
In spite of its bulky appearance, the Hellcat was a clean aircraft
having a zero-lift drag coefficient of only 0.0211. Range of the
Hellcat was 1090 miles on internal fuel only, and with drop tanks
it was 1590 miles. It had a service ceiling of 38 400 feet and an
initial rate of climb of 3500 feet per minute. Its armament
consisted of six .50-caliber machine guns, three in each wing, and
two 1000-pound bombs or six 5-inch rockets.
The Grumman F6F Hellcat, of which 12 274
were produced, is considered by many to be the outstanding
shipboard fighter of World War II. It was the standard
carrier-based fighter employed by the U.S. Navy from mid-1943
until the end of World War II and accounted for the destruction of
nearly 5000 enemy aircraft in air-to-air combat. The British Royal
Navy took delivery of over 1100 Hellcats, which were used in
operations from their carriers. The Hellcat was unusual, as
compared with other combat aircraft employed in World War II, in
that very few modifications were made to the aircraft during its
service life. The F6F served for several years in the U.S. Navy
following the close of the war.
Afterword
[136] The
propeller-driven combat aircraft powered with reciprocating
engines played a decisive role in World War II and reached a high
level of perfection during that conflict. The revolutionary jet
engine shaped the course of development of high-performance
military aircraft in the post-World War II period. The propeller
continued, of course, to be employed on various types of utility,
transport, and patrol aircraft; but the development of the jet
engine spelled the end for the high-performance propeller-driven
fighter, bomber, and attack aircraft. The postwar development of
propeller-driven aircraft has been primarily concerned with
commercial and general aviation operations and is considered in
the next chapter.
