North American XB-21

North American XB-21 Dragon
Type:	Medium long range bomber
Design country:	United States
Manufacturer:	North American Aviation
First flight:	December 22, 1936
Number of pieces:	1

The North American Aviation XB-21 Dragon (Model NA-21) was a bomber aircraft made by the US manufacturer North American Aviation, Inc in the 1930s, only one of which was manufactured.

history

On January 15, 1936, North American submitted the NA-21, a design for a twin-engine high-altitude bomber in response to the USAAC Circular Proposal 36-528 . The first flightthe subsequently commissioned prototype took place on December 22, 1936 with Tommy Tomlinson, who had extensive experience in high-altitude flight, at the wheel. At the beginning of the test, the front turret and the armament on the back of the fuselage had been replaced by panels. The maximum speed was determined to be 354 km / h, later the turbochargers were removed and the engines were fitted with new panels and exhaust ducts. On further flights, the propellers also received hub caps, but without any improvement in performance.

After factory testing at North American, the NA-21 was transferred to Wright Field in Ohio in March 1937 for further flight tests by the US Army Air Corps (USAAC). The other flights also went without incident, but the NA-21 (later referred to as NA-39) did not receive an order for series production from the USAAC. An order from USAAC to deliver five more aircraft (YB-21) for operational testing was canceled shortly afterwards. The aircraft returned to North American and was purchased as the XB-21 by the USAAC for $ 555,000 in early 1939. It was then given the serial number 38-485 and the name Dragon . Until it was retired, the XB-21 continued to be used for research flights, with North American being able to use the experience gained later in development. The name Dragon was given again for the Douglas B-23 .

The fact that the Douglas B-18 Bolo, developed at the same time, was produced in considerable numbers (351 units), despite the lower performance compared to the XB-21, is mainly due to the high price of the North American construction. The XB-21 cost 122,600 US dollars, while the B-18 was available for just 63,977 US dollars.

construction

The prototype was a middle-decker with aluminum-clad wings and fuselage. All control surfaces were covered with fabric. The very deep front fuselage had a step in the lower part of the fuselage, which made the connection to the slim rear part. In order to save weight and increase the tank volume, the wing center section was sealed with DuPrene, a sealant from DuPont that was new at the time. One saved 450 kg in weight, as there was no need to install individual separate tanks, and 9000 liters of fuel could be carried along. The wings had statically and aerodynamically balanced ailerons and spread flaps . The fuselage was designed in half-shell construction and had unusually large dimensions with a width of 2.1 m and a depth of 3.6 m. The ten-person crew was offered a certain level of comfort, as in addition to the greatest possible soundproofing and heating, two loungers for rest periods on long-haul operations and a Sperry autopilot were provided.

The drive consisted of two Pratt & Whitney R-2180-1 Hornet radial engines, which were equipped with F-10 turbochargers for use at high altitude and each delivered an output of 1200 PS (895 kW). The landing gear retracted hydraulically back into the engine nacelles, the lower part of which was braced against the fuselage. A maximum bomb load of 4500 kg could be carried.

Technical specifications

Parameter	Data
crew	10
length	18.80 m
span	28.90 m
height	4.50 m
Wing area	104 m²
Empty mass	8655 kg
Flight mass	12,362 kg
Marching speed	306 km / h
Top speed	354 km / h
Service ceiling	7620 m
Range	3,154 km
Engines	2 × Pratt & Whitney R-2180-1 Hornet radial engines with 1200 PS (895 kW) each
Max bomb load	4536 kg

See also

• List of aircraft types

literature

• Bradley Engbrecht: Solitary 'Dragon' - The North American XB-21 . In: AIR Enthusiast No. 92, March / April 2001, pp. 10-12

Web links

Commons : North American XB-21  - Collection of Images, Videos, and Audio Files

• NORTH AMERICAN XB-21. Archived from the original on April 5, 2015 ; accessed on May 27, 2016 . 
• youtube video with photos of the XB-21