Martin XB-48
| Martin XB-48 | |
|---|---|
 Martin XB-48 in flight |
|
| Type: | Prototype of a tactical bomber |
| Design country: | |
| Manufacturer: | |
| First flight: |
June 22, 1947 |
| Commissioning: |
Flight tests ended in 1948 |
| Production time: |
Was never mass-produced |
| Number of pieces: |
2 |
The Martin XB-48 was a six - engined medium - weight bomber that was developed for the US Air Force in the mid-1940s but never went into series production.
Development history
origin
In June 1943, the Army Air Force (AAF) asked American aircraft manufacturers for design proposals for medium to heavy jet bombers . The background was advances in the development of jet engines, which now provided sufficient power to be used for the first time in larger bombers. In order to meet the high demand as quickly as possible, the Air Force planned to procure several different models. The request turned into an official competition on November 17, 1944, in which four companies entered with their designs: North American Aviation with the XB-45 , Consolidated Vultee Aircraft Corporation with the XB-46 , Boeing with the XB-47 and just Martin with the XB-48. Of these, ultimately only the B-45 and the B-47 came beyond the experimental stage and were produced in series.
development
In December 1944, Martin presented the Luftwaffe with a first draft (Model 223) and was then commissioned to build a model by May 1, 1945. Although the development status of the XB-48 was behind that of the competition in mid-1945, the Air Force agreed the continuation of the project. In mid-1946, the US Air Force pushed for a production decision and evaluated the four competing designs. Since the work on the XB-45 and XB-46 had progressed further, she initially decided in favor of the B-45 and waited until they had flown before accepting the XB-47 or XB-48.
On December 13, 1946, Martin undertook to deliver two prototypes at a fixed price of 10.9 million US dollars , the first of which had to have flown by the end of September 1947 and the second by the end of June 1948.
construction
The XB-48 was equipped with six Turbojet engines from General Electric , three of which were mounted in housings directly under the unearthed wings, with ventilation shafts for cooling in between. Since the relatively thin wings were set high on the fuselage, the main landing gear could only be attached under the fuselage in tandem, as was the case with the B-47 and later with the B-52 . The two pilots sat behind one another under a glass dome, the navigator / bombardier in the glass nose.
First flight and tests
Development was delayed due to problems with the new types of engines, but initially stayed within the agreed time frame. On June 22, 1947, the XB-48 took off in Baltimore , Maryland , on its 38-minute maiden flight . Problems arose with the controls: When landing at the Patuxent River naval airfield , the aircraft came off the runway, and the brakes also failed. The second prototype did not start until October 16, 1948, almost three months later than contractually agreed.
The first copy completed 52 flights with a total of 41 hours at Martin, followed by the Air Force another 50 flights with 64 flight hours. The second XB-48 had 15 flights and 14 hours and 25 flights at 49 hours. During flight tests it turned out that the bomber was around 6.3 tons heavier than the manufacturer had intended; the opened bomb bay caused turbulence and the hydraulic system of the first machine did not work properly.
End of program
Although the XB-48 was completed half a year earlier than the XB-47, the US Air Force decided to purchase the Boeing B-47 immediately after its maiden flight on December 17, 1947 . The final evaluation of the two designs took place in the spring of 1948 after the flight tests. The decisive factor was the more modern design (swept wings, engines in nacelles) and the assumed higher power reserves (speed, bomb load) of the B-47. When Boeing received the first order for its bomber in September 1948, the competition was decided. Although the Martin Company tried to get a move on by providing four propeller turbines in modified housings for their design (Model 247-1), the Luftwaffe rejected this proposal on March 31, 1949 and the B-48- The project was officially over.
Martin dismantled the first prototype in autumn 1949 in order to obtain spare parts for the second copy. The US Air Force initially used the second and last XB-48 as a test platform for de-icing systems, before finally being subjected to structural tests in September 1951 until it was destroyed.
Technical specifications
| Parameter | Data (estimated) |
|---|---|
| length | 26.2 m |
| span | 33.0 m |
| height | 8.1 m |
| Wing area | 124 m² |
| Empty weight | 26.5 t |
| Maximum takeoff weight | 46.5 t |
| Maximum bomb load | 10.0 t |
| Top speed | 841 km / h |
| Maximum altitude | 13,100 m |
| Range | > 2,900 km |
| drive | Six General Electric J35 -GE-9 (TG-180-C1) with 17 kN thrust each |
| crew | Three (pilot, copilot, navigator / bombardier) |
See also: experimental aircraft , list of aircraft types
literature
- Marcelle Size Knaack: Encyclopedia of US Air Force Aircraft and Missile Systems. Volume II, Post-World War II Bombers 1945–1973 . Washington, DC 1988. pp. 528-535, ISBN 0-912799-59-5
