View source for Martin XB-51

{{Short description|American bomber/attack aircraft prototype}}
<!-- This article is a part of [[Wikipedia:WikiProject Aircraft]]. Please see [[Wikipedia:WikiProject Aircraft/page content]] for recommended layout. -->
{{Infobox aircraft
  |name = XB-51
  |image = File:Martin XB-51 46-585 in flight.jpg
  |caption = First prototype, ''46-685'' during testing
  |type = [[Bomber]]
  |manufacturer =[[Glenn L. Martin Company]]
  |designer =
  |first_flight = 28 October 1949
  |introduction =
  |retired = 25 March 1956
  |status = Canceled in 1952
  |primary_user = [[United States Air Force]]
  |more_users =
  |produced =
  |number_built =2
  |unit cost =US$12.6 million for the program<ref name="knaack">Knaack, Marcelle Size. ''Post-World War II bombers, 1945-1973''. Washington, DC: Office of Air Force History, 1988. {{ISBN|0-16-002260-6}}.</ref>
  |variants =
}}

The '''Martin XB-51''' was an American [[trijet]] [[ground-attack aircraft]]. It was designed in 1945 and made its maiden flight in 1949. It was originally designed as a bomber for the [[United States Army Air Forces]] under specification V-8237-1 and was designated '''XA-45'''. The "A" ground-attack classification was eliminated the next year, and the XB-51 designation was assigned instead. The requirement was for low-level bombing and close support. The XB-51 lost out in evaluation to the [[English Electric Canberra]] which — built by Martin — entered service as the [[Martin B-57 Canberra]].

==Design and development==
[[File:Twin XB-51.jpg|thumb|left|Martin's two XB-51 prototypes, seen low over the runway on a high-speed pass]]

This unorthodox design, first flying on 28 October 1949, was fitted with three [[General Electric J47]] engines - an unusual number for a combat aircraft - two underneath the forward fuselage in pods, and one at the extreme tail with the intake at the base of the tailfin.<ref name= "Winchester p. 144"/> The innovative, [[Variable-incidence wing|variable incidence]] wings, swept at 35° and with 6° [[Dihedral (aircraft)#Anhedral|anhedral]], were equipped with leading edge slats and full-width flaps. Spoilers gave most of the roll control and undersized ailerons provided feel for the pilot.<ref>The Martin XB-51, Air Force Legends Number 201, Scott Libis, published by Steve Ginter 1998, {{ISBN|0-942612-00-0}}, p.5</ref> The combination of variable incidence and slotted flaps gave a shorter takeoff run.<ref name= "Winchester p. 145"/> Four 954&nbsp;lb (4.24&nbsp;kN) thrust [[JATO|Rocket-Assisted Take Off]] (RATO) bottles with a 14-second burn duration could be fitted to the rear fuselage to improve takeoff performance. Spectacular launches were a feature of later test flights.<ref name= "Winchester p. 144">Winchester 2005, p. 144.</ref>

[[File:Martin XB-51 rocket-assisted take off 061026-F-1234S-013.jpg|thumb|Testing RATO]]
The main landing gear consisted of dual wheel sets in tandem in the fuselage, similar to the [[Boeing B-47 Stratojet]], with outrigger wheels at the wingtips (originally proved on a modified [[Martin B-26 Marauder]] named "Middle River Stump Jumper"<ref name= "Winchester p. 144">Winchester 2005, p. 144.</ref>). The XB-51 was a large but aerodynamically "clean" design which incorporated nearly all major systems internally.<ref name= "Winchester p. 145"/>   The aircraft was fitted with a rotating [[bomb bay]], a Martin trademark; bombs could also be carried externally up to a maximum load of {{cvt|10,400|lb|0}}, although the specified basic mission required only a {{cvt|4,000|lb|0}} bombload.<ref>[https://books.google.com/books?id=Nt8DAAAAMBAJ&dq=1954+Popular+Mechanics&pg=PA126 "Pivoting Bomb-bay Door Permits Accurate Drops at High-Speeds."] ''Popular Mechanics'', February 1954, p. 126.</ref> Eight 20&nbsp;mm cannon mounted in the nose would have been installed in production aircraft.<ref name= "Winchester p. 145"/>

Crew was a pilot under a "fighter"-type bubble canopy and a [[SHORAN|Short-Range Navigation]] (SHORAN) navigation and bombing system operator/navigator in a compartment located lower than and to the rear of the cockpit; only a small observation window was provided.<ref name= "Winchester p. 145">Winchester 2005, p. 145.</ref> Both crew members were provided with a pressurized, air conditioned environment, equipped with upward-firing ejection seats.<ref name= "Winchester p. 145">Winchester 2005, p. 145.</ref> The XB-51 was the first Martin aircraft equipped with ejection seats, these being of their own design.<ref name="Tuttle">Tuttle, Jim. ''Eject! The Complete History of U.S. Aircraft Escape Systems''. St. Paul, Minnesota: MBI Publishing Company, 2002. {{ISBN|0-7603-1185-4}}.</ref>

==Operational history==
[[File:XB-51.jpg|thumb|46-685 on approach]]

In 1950, the [[United States Air Force]] issued a new requirement based on early [[Korean War]] experience for a night intruder/bomber to replace the [[Douglas A-26 Invader]]. The XB-51 was entered, as well as the [[Avro Canada CF-100 Canuck|Avro Canada CF-100]] and [[English Electric Canberra]]; the XB-51 and Canberra emerged from these as the favorites.

Test flights showed the XB-51 to be highly maneuverable at low altitudes and substantially faster than the Canberra and faster than most fighter aircraft of the era.<ref name= "Winchester p. 145"/> However, the XB-51's endurance was significantly lower than that of the Canberra and this factor was decisive in its cancellation. In addition, a [[Limit load (aeronautics)|load limiting factor]] of only 3.67&nbsp;[[g-force|''g'']] (36&nbsp;m/s<sup>2</sup>) meant that the general strength of the airframe was relatively low and would prevent tight turns while fully loaded. Additionally, the tandem main gear plus outriggers of the XB-51 were thought unsuitable for the requirement to fly from emergency [[forward airfield]]s.

While the XB-51 was not selected for procurement, it was decided that Martin would build 250 Canberras under license, under the designation [[Martin B-57 Canberra|B-57]]. Furthermore, Martin's rotating bomb bay would be incorporated into production variants of the B-57. A "Super Canberra", incorporating other XB-51 features, such as swept wings and tail-planes, was also proposed. This aircraft – although it promised much better speed and performance than the B-57 – never reached the prototype stage, mainly because the many changes would have taken too long to implement and test, before it could be put into production.<ref name= "Winchester p. 144"/>

Flights by the XB-51 prototype, ''46-685'', continued, for general research purposes, following the project's official cancellation by the USAF. A second prototype, ''46-686'', which first flew in 1950, crashed during low-level aerobatics on 9 May 1952, killing pilot Major Neil H. Lathrop. ''46-685'' continued to fly, including an appearance in the film ''[[Toward the Unknown]]'' as the "Gilbert XF-120" fighter.<ref group=note>A few seconds of test flight footage of an XB-51 also appeared in the 1951 ''[[Tales of Tomorrow]]'' episode "Plague From Space". Note: Although the XB-51 did not receive an official name, "Panther" had been suggested by the company.</ref> The surviving prototype was en route to Eglin AFB to shoot additional footage when it crashed during takeoff, following a refueling stop in El Paso, Texas, on 25 March 1956.<ref name= "Winchester p. 145"/>

==Specifications (XB-51)==
[[File:Martin XB-51 3-view line drawing.png|thumb|3-view line drawing of the Martin XB-51]]
{{Aircraft specs
|ref=''U.S.Standard Aircraft Characteristics''<ref>{{cite web|url=http://www.alternatewars.com/SAC/XB-51_SAC_-_11_July_1952.pdf|title=Standard Aircraft Characteristics: XB-51|publisher=US Air Force|date=11 July 1952|access-date=8 June 2017|archive-date=13 March 2016|archive-url=https://web.archive.org/web/20160313132924/http://www.alternatewars.com/SAC/XB-51_SAC_-_11_July_1952.pdf|url-status=dead}}</ref>
|prime units?=imp
<!--
        General characteristics
-->
|crew=2
|length ft=85
|length in=1
|length note=
|span ft=53
|span in=1
|span note=
|height ft=17
|height in=4
|height note=
|wing area sqft=548
|wing area note=
|aspect ratio=<!-- sailplanes -->
|airfoil=[[NACA airfoil|NACA 63A010]]<ref name="Selig">{{cite web |last1=Lednicer |first1=David |title=The Incomplete Guide to Airfoil Usage |url=https://m-selig.ae.illinois.edu/ads/aircraft.html |website=m-selig.ae.illinois.edu |access-date=16 April 2019}}</ref>
|empty weight lb=30906
|empty weight note=
|gross weight lb=57874
|gross weight note=
|max takeoff weight lb=62452
|max takeoff weight note=
|fuel capacity=
|more general=
<!--
        Powerplant
-->
|eng1 number=3
|eng1 name=[[General Electric J47-GE-13]]
|eng1 type=[[turbojet]] engines
|eng1 lbf=5200
|eng1 note=
<!--
        Performance
-->
|max speed mph=644
|max speed note=
|max speed mach=<!-- supersonic aircraft -->
|cruise speed mph=
|cruise speed note=
|stall speed mph=
|stall speed note=
|never exceed speed mph=
|never exceed speed note=
|minimum control speed mph=
|minimum control speed note=
|range miles=1075
|range note=
|combat range miles=
|combat range note=
|ferry range miles=1444
|ferry range note=
|endurance=<!-- if range unknown -->
|ceiling ft=41750
|ceiling note=
|g limits=<!-- aerobatic -->
|roll rate=<!-- aerobatic -->
|climb rate ftmin=6600
|climb rate note=
|time to altitude=
|wing loading lb/sqft=105.6
|wing loading note=
|fuel consumption lb/mi=
|thrust/weight=0.27

|more performance=
<!--
        Armament
-->
|guns=8 × [[20 mm caliber|20 mm]] [[Hispano-Suiza HS.404#United States|M24 cannon]] (0.79 in) [[autocannon|cannon]] with 1,280 rounds
|rockets=8 × High Velocity Aerial Rockets (HVAR) ''or''
|bombs= Up to 10,400 lb (4,720 kg) carried internally

|avionics=
}}

==See also==
{{Aircontent
<!-- From which older designs was this plane developed, and what planes did it lead to? -->
|related=
|similar aircraft=
<!-- aircraft with similar role, era, and capability -->
* [[Douglas A3D Skywarrior]]
* [[Douglas B-66 Destroyer]]
* [[English Electric Canberra]]
* [[Sud Aviation Vautour]]
* [[Ilyushin Il-28]]
* [[Yakovlev Yak-25]]
* [[Yakovlev Yak-28]]
|lists=
<!-- lists of similar aircraft (aircraft from the same nation, with the same mission profile, etc.) -->
* [[List of attack aircraft]]
* [[List of bomber aircraft]]
* [[List of military aircraft of the United States]]
|see also=
}}

==References==
===Notes===
{{Reflist|group=note}}

=== Citations ===
{{Reflist}}

===Bibliography===
{{Refbegin}}
* Andrade, John M. ''U.S. Military Aircraft Designations and Serials since 1909''. Earl Shilton, Leicester, UK: Midland Counties Publications, 1979. {{ISBN|0-904597-22-9}}.
* Boyne, Walter. "Attack, The Story of the XB-51, Martin's Phantom Strike Ship!" ''Airpower'', Volume 8, No. 4, July 1978.
* Jones, Lloyd S. ''U.S. Bombers, B-1 1928 to B-1 1980s''. Fallbrook, California: Aero Publishers, 1962, second edition 1974. {{ISBN|0-8168-9126-5}}.
* Mikesh, Robert C. '''B-57 Canberra At War 1964-1972''. London: Ian Allan, 1980. {{ISBN|0-7110-1004-8}}.
* Winchester, Jim. "Martin XB-51." ''Concept Aircraft: Prototypes, X-Planes and Experimental Aircraft''. Kent, UK: Grange Books plc., 2005. {{ISBN|978-1-84013-809-2}}.
{{Refend}}

==External links==
{{Commons category|Martin XB-51}}
* [https://web.archive.org/web/20121016143638/http://www.nationalmuseum.af.mil/factsheets/factsheet.asp?fsID=2663 USAF Museum: XB-51]
* [https://1000aircraftphotos.com/Contributions/PippinBill/6302.htm Several photographs of the Martin 234 XB-51 ''46-685'']
* {{IMDb title|qid=Q766600|title=Toward The Unknown}}

{{Martin aircraft}}
{{USAF attack aircraft}}
{{USAF bomber aircraft}}
{{Authority control}}

[[Category:Martin aircraft|B-51]]
[[Category:Trijets]]
[[Category:1950s United States bomber aircraft|B-51, Martin]]
[[Category:Variable-incidence-wing aircraft]]
[[Category:T-tail aircraft]]
[[Category:Aircraft first flown in 1949]]
[[Category:Mid-wing aircraft]]
[[Category:Aircraft with retractable bicycle landing gear]]