Editing Consolidated B-24 Liberator (section)

==Design and development==
[[File:XB-24 in Flight.jpg|thumb|XB-24 in flight]]

===Initial specifications===
The Liberator originated from a [[United States Army Air Corps]] (USAAC) request in 1938 for Consolidated to produce the B-17 under license. After company executives including President [[Reuben Fleet]] visited the [[Boeing]] factory in [[Seattle, Washington]], Consolidated decided to submit a more modern design of its own.<ref>Taylor 1969, p. 462.</ref>

The new Model 32 combined designer [[Davis wing|David R. Davis]]'s wing, a high-efficiency [[airfoil]] design created by unorthodox means,<ref>{{citation|jstor=3105326|title=The Davis Wing and the Problem of Airfoil Design: Uncertainty and Growth in Engineering Knowledge|journal=Technology and Culture|volume=27|issue=4|pages=717–758|last1=Vincenti|first1=Walter G.|year=1986|doi=10.2307/3105326|s2cid=112031158 }}</ref> with the [[twin tail]] design from the [[Consolidated Model 31]] [[flying boat]], together on a new fuselage. This new fuselage was intentionally designed around twin bomb bays, each one being the same size and capacity of the B-17 bomb bays.

In January 1939, the USAAC, under Specification C-212, formally invited Consolidated<ref name=":0">Baugher, Joe. [http://www.joebaugher.com/usaf_bombers/b24_1.html "The Consolidated XB-24."] ''USAAC/USAAF/USAF Bombers: The Consolidated B-24 Liberator'', 8 August 1999. Retrieved: 15 June 2010.</ref> to submit a design study for a bomber with longer range, higher speed and greater [[Ceiling (aeronautics)|ceiling]] than the B-17. The specification was written such that the Model 32 would automatically be the winning design. The program was run under the umbrella group, "Project A", an Air Corps requirement for an intercontinental bomber that had been conceived in the mid-1930s. Although the B-24 did not meet Project A goals, it was a step in that direction. Project A led to the development of the [[Boeing B-29 Superfortress|Boeing B-29]] and Consolidated's own [[Consolidated B-32 Dominator|B-32]] and [[Convair B-36 Peacemaker|B-36]].<ref>Craven and Cate 1949 {{page needed|date=May 2015}}</ref>

===Design===
The B-24 had a shoulder-mounted high aspect ratio Davis wing. This wing was highly efficient allowing a relatively high airspeed and long range. Compared to the B-17, it had a {{convert|6|ft}} larger wingspan but a lower wing area. This gave the B-24 a 35-percent higher [[wing loading]]. The relatively thick wing held the promise of increased tankage while delivering increased lift and speed, but it became unpleasant to fly when committed to heavier loadings as experienced at high altitude and in bad weather. The Davis wing was also more susceptible to ice formation than contemporary designs, causing distortions of the aerofoil section and resulting in the loss of lift, with unpleasant experiences drawing such comments as, "The Davis wing won't hold enough ice to chill your drink".<ref name=":1" /> The wing was also more susceptible to damage than the B-17's wing, making the aircraft less able to absorb battle damage.{{citation needed|date=August 2016}}

The wing carried four [[Supercharger|supercharged]] [[Pratt & Whitney R-1830-35 Twin Wasp]] engines mounted in cowlings borrowed from the [[Consolidated PBY Catalina|PBY Catalina]] (similar except for being oval in cross-section allowing for oil coolers mounted on each side of the engine) that turned 3-bladed [[Variable-pitch propeller (aeronautics)|variable-pitch propeller]]s.

The [[tailplane]] featured two large oval vertical stabilizers mounted at the ends of a rectangular horizontal stabilizer. As early as 1942, it was recognized that the Liberator's handling and stability could be improved by the use of a single vertical fin. The single fin was tested by Ford on a single B-24ST variant and an experimental XB-24K: it was found to improve handling. However, all Liberators were produced with twin oval fins, with the exception of eight preproduction B-24N aircraft. The B-24N was intended as a major production variant featuring a single tail. Over 5000 orders for this version were placed in 1945, but they were cancelled due to the end of the war. The single fin did appear in production on the [[Consolidated PB4Y-2 Privateer|PB4Y Privateer]] derivative.<ref>{{cite web|url=http://www.joebaugher.com/usaf_bombers/b24_19.html|title=Consolidated XB-24K Liberator}}</ref><ref name="aerofilesConsolidated"/><ref>{{cite book |last=Simons |first=G. |title=Liberator: The Consolidated B-24 |publisher=Pen & Sword Books Limited |isbn=978-1-78303-591-5|date=2012 }}</ref>

The B-24's spacious, slab-sided fuselage (which earned the aircraft the nickname "Flying [[Boxcar]]")<ref name="44th BG History">Allan, Chuck. [http://www.chuckallan.com/history/History_44th.html "A Brief History of the 44th Bomb Group."]''chuckallan.com''. Retrieved: 15 June 2010. {{Webarchive|url=https://web.archive.org/web/20070808083844/http://www.chuckallan.com/history/History_44th.html |date=8 August 2007 }}</ref> was built around two central bomb bays that could accommodate up to {{convert|8000|lb|kg}} of ordnance in each compartment (but rarely did, as this decreased range and altitude). The forward and aft bomb bay compartments were further split longitudinally with a centerline ventral catwalk just {{convert|9|in|cm|spell=in}} wide,<ref>Hillenbrand 2010 {{page needed|date=December 2011}}</ref> which also functioned as the fuselage's structural keel beam.

An unusual four-panel set of all-metal, tambour-panel "roller-type" bomb bay doors, which operated very much like the movable enclosure of a [[rolltop desk]], retracted into the fuselage. These types of doors created a minimum of aerodynamic drag to keep speed high over the target area; they also allowed the bomb bays to be opened while on the ground since the low ground clearance prevented the use of normal bomb bay doors.<ref>Green 1975, p. 84.</ref> The occasional need during a mission for crewmen to move from fore to aft within the B-24's fuselage over the narrow catwalk was a drawback shared with other bomber designs.

The Liberator carried a crew of up to ten. The pilot and co-pilot sat alongside each other in a well-glazed cockpit. The navigator and bombardier — who could also double as a nose or ''wiggly ear'' gunners (guns mounted in the sides of the aircraft nose) — sat in the nose, fronted on the pre-B-24H models with a well-framed "greenhouse" nose with some two dozen glazed panels and with two flexible ball-mounts built into it for forward defensive firepower using [[.30-06 Springfield|.30 caliber (7.62 mm)]] [[M1919 Browning machine gun|Browning M1919]] machine guns (later versions were fitted with a powered twin-.50 caliber (12.7&nbsp;mm) [[M2 Browning|M2 Browning machine gun]] nose [[Aircraft gun turret|turret]]). The radio/radar operator sat behind the pilots, facing sideways and sometimes doubled as a waist gunner. The flight engineer sat adjacent to the radio operator behind the pilots; he operated the upper gun turret (when fitted), located just behind the cockpit and in front of the wing.

Up to four crew members could be located in the waist, operating waist guns, a retractable lower [[ball turret]] gun, and a [[Tail gunner|tail gun turret]] matching the nose turret. The waist gun hatches were provided with doors. The ball turret was required to be retractable for ground clearance when preparing to land as well as for greater aerodynamic efficiency. The tail gunner's powered twin-gun turret was located at the end of the tail, behind the tailplane.

The B-24 featured a tricycle undercarriage, the first American bomber to do so,<ref name=":1" /> with the main gear extending out of the wing on long, single-oleo strut legs. It used differential braking and differential thrust for ground steering, which made taxiing difficult.<ref>Hillenbrand 2010, p. 64.</ref>

===Armament===
{{More citations needed section|date=December 2016}}
The defensive armament of the B-24 varied from transport variants, which were usually unarmed, to bombers armed with up to ten .50 caliber (12.7&nbsp;mm) M2 Browning machine guns located in turrets and waist gun positions.

Early model Liberators were fitted with a top-mounted turret, a tail turret and single machine guns located in the waist and in the glazed nose. The B-24D initially featured upper, belly and tail turrets, plus swiveling single guns in the waist and on either side of the nose. The belly turret was a periscopically sighted Bendix model. The turret proved unsatisfactory and was soon replaced by a tunnel gun, which was itself omitted. Later D models were fitted with the retractable Sperry ball turret.

The B-24H saw the replacement of the glazed 'green house' nose with a nose turret, which reduced the B-24s vulnerability to head-on attacks. The bombsight was located below the turret.

Long-range naval patrol versions often carried a light defensive armament. Being on long-distance patrols, they generally flew outside the range of enemy fighters. Also, the necessity of range increased the importance of weight and aerodynamic efficiency. Thus naval patrol often omitted top, belly and nose turrets. Some were fitted with a belly pack containing fixed, forward-facing cannon.

===Prototypes and service evaluation===
{{More citations needed section|date=December 2016}}
The U.S. Army Air Corps awarded a contract for the prototype XB-24 in March 1939, with the requirement that one example should be ready before the end of the year. Consolidated finished the prototype and had it ready for its first flight two days before the end of 1939. The design was simple in concept but, nevertheless, advanced for its time.
Consolidated incorporated innovative features such as a tricycle landing gear and Davis wing.

Compared to the B-17, the proposed Model 32 had a shorter fuselage and 25% less wing area, but had a {{convert|6|ft|m|abbr=on}} greater [[wingspan]] and a substantially larger carrying capacity, as well as a distinctive twin tail. Whereas the B-17 used 9-cylinder [[Wright R-1820]] Cyclone engines, the Consolidated design used twin-row, 14-cylinder [[Pratt & Whitney R-1830]] "Twin Wasp" radials of {{convert|1000|hp|kW|abbr=on}}. The maximum takeoff weight was one of the highest of the period.

The new design would be the first American heavy bomber in production to use tricycle landing gear – the [[North American B-25 Mitchell]] medium bomber's predecessor, the NA-40 introduced this feature in January 1939 – with the Consolidated Model 32 having long, thin wings with the efficient "Davis" high [[aspect ratio (wing)|aspect ratio]] design (also used on the projected Model 31 twin-engined commercial flying boat)<ref>Donald 1997, p. 266.</ref> promising to provide maximum [[fuel efficiency]]. Wind tunnel testing and experimental programs using an existing Consolidated Model 31 provided extensive data on the flight characteristics of the Davis airfoil.<ref>Birdsall 1968, p. 40.</ref>

Early orders, placed before the XB-24 had flown, included 36 for the USAAC, 120 for the [[French Air Force]] and 164 for the [[Royal Air Force]] (RAF). The name "Liberator" was originally given to it [[British military aircraft designation systems#Names|by the RAF]], and subsequently adopted by the [[United States Army Air Forces|USAAF]] as the official name for the Model 24.<ref name="Taylor 1968, p. 463">Taylor 1968, p. 463.</ref> When France fell in 1940, their aircraft were re-directed to the RAF. One outcome of the [[British Purchasing Commission|British and French purchasing commissions]] was a backlog of orders amounting to $680m, of which $400m was foreign orders, US official statistics indicating tooling, plant and expansion advanced the previously anticipated volume of US aircraft production by up to a year. A consequence of the British orders went beyond requests for specific modifications: as the RAF accepted some designs while rejecting others, American production was – to some extent – re-directed along specific lines that accorded with British doctrine, the B-24's capacious bomb bay and ability to carry 8,000&nbsp;lb ordnance a case in point.<ref name=":1" />

After initial testing, the '''XB-24''' was found to be deficient in several areas. One major failure of the prototype was that it failed to meet the top speed requirements specified in the contract. As built, the XB-24 top speed was only 273&nbsp;mph instead of the specified 311&nbsp;mph. As a result, the mechanically supercharged Pratt & Whitney R-1830-33s were replaced with the [[turbocharger|turbo-supercharged]] R-1830s. Additionally, the tail span was widened by {{convert|2|ft|m|abbr=on}} and the [[pitot-static system|pitot-static probes]] were relocated from the wings to the [[fuselage]]. The XB-24 was then re-designated XB-24B—these changes became standard on all B-24s built starting with the B-24C model.

[[File:YB-24.jpg|thumb|An early B-24D]]
In April 1939, the USAAC initially ordered seven '''YB-24''' under [[Consolidated Aircraft|CAC]] contract # 12464. The US policy at the time, despite neutrality, was that American requirements could be deferred while its Allies could immediately put US production into the war effort. The added advantage was the American types could be assessed in the European war zone earlier. Thus the first six YB-24 were released for direct purchase under CAC contract # F-677 on 9 November 1940. These aircraft were redesignated '''LB-30A'''. The seventh aircraft was used by Consolidated and the USAAC to test [[armor]] installations as well as [[self-sealing fuel tank]]s. Initially, these aircraft were to be given USAAC serials 39–681 to 39-687. Due to deferments of the US requirements, the US purchase was twice postponed, and the serial numbers were changed to 40–696 to 40-702. When the RAF purchased the first six YB-24 aircraft, the serial numbers were reassigned to an early batch of B-24D funded by the deferment.

=== Flying the B-24 ===
Lindell Hendrix, later a test pilot for [[Republic Aviation]], flew B-24s for the Eighth Air Force.<ref>Hendrix, Lindell ("Lin"), "Requiem for a Heavyweight", Wings, February 1978, A Sentry Magazine, page 20.</ref> Hendrix preferred the B-24 to the B-17. In Eighth Air Force combat configuration, the aircraft carried {{convert|8000|lb|kg}} of bombs. It could manage an altitude of no more than {{convert|25,000|ft|m|abbr=on}}, three or four thousand feet less than a B-17, but it flew {{convert|10|-|15|mph|km/h|abbr=on}} faster. Its lower altitude made it more vulnerable to flak. Hendrix figured that Germans understood it was easier to hit, and that it carried more bombs.

It was necessary when flying the B-24, to get "on step". This meant climbing to about {{convert|500|ft|m|abbr=on}} above cruise altitude, levelling off, achieving a cruise speed of {{convert|165|-|170|mph|km/h|abbr=on}}, then descending to assigned altitude. Failing to do this meant that the B-24 flew slightly nose high, and it used more fuel. The Davis wing made the B-24 sensitive to weight distribution. Hendrix claimed that a lightly loaded B-24 could out-turn a P-38 Lightning. A heavily loaded B-24 was difficult to fly at speeds of less than {{convert|160|mph|km/h|abbr=on}}. The B-24's controls were heavy, especially if the control rigging was not properly tensioned.

B-24s leaked fuel. Crews flew with the bomb bay doors slightly open to dissipate potentially explosive fumes. Hendrix did not permit smoking on his B-24, even though he was a smoker. Chain smoker [[Tex Thornton|"Tex" Thornton]], then in command of the US Army Air Corps' Statistical Control, flew across the Atlantic in a B-24, and was not permitted to smoke. Thornton's Statistical Control group demonstrated that Eighth Air Force B-24s were taking lower casualties than B-17s because they were being given shorter, safer missions. The B-17s actually delivered more bombs to the target than B-24s.<ref>Byrne, John A., The Whiz Kids: The Founding Fathers of American Business and the Legacy They Left Us, Currency Doubleday, Page 50</ref>