Subject: Bomber series--Curtiss XNBS-4

From: [email-masked] (joseph.f.baugher)
Date: 24 May 94 01:17:35 GMT

In 1922, Curtiss received a contract to develop two examples of a night 
bomber intended to replace the Martin-designed NBS-1 biplane 
bomber that was at that time the only twin-engined bomber in Army 
service.  They were assigned the designation XNBS-4.  

Curtiss had built 50 Martin-designed NBS-1s for the US Army Air 
Service in 1921/22, and the XNBS-4 drew heavily on that experience.  
Like the NBS-1, the XNBS-4 was a conventional biplane powered by two 
Liberty 12 engines mounted inside nacelles attached to the lower wing.  
A crew of four could be carried.  However, the XNBS-4 differed from 
the NBS-1 in having a welded steel-tube fuselage instead of a wooden 
one.  A new and thicker Curtiss C-72 airfoil replaced the RAF 15 
airfoil of the NBS-1.  The bomb-aimer's position was built into an 
offset on the port side of the fuselage instead of under the nose 
gunner's position as was the usual position.  Unlike the NBS-1, the 
XNBS-4 had a boxlike biplane tail, which was somewhat of a retrograde 
step.  

The serial numbers of the two XNBS-4s were 68571 and 68572.  The first 
XNBS-4 was delivered in May of 1924.  

One of the XNBS-4s was modified by having each engine nacelle extended 
aft of the wing trailing edge so that it could accommodate a defensive 
gunner position in the rear.  It was hoped that this arrangement would 
offer a clearer field of fire for the gunners than the more 
conventional fuselage-situated positions.  This was not an entirely 
new and unique idea, having been tried out on British and German 
bombers during the War.  

The XNBS-4 offered no real advantage over the existing Martin-designed 
NBS-1, and was not ordered into production.  However, it did provide 
Curtiss with valuable design experience which culminated in the 
successful Condor bomber and transport series of 1927-29.  

Specification of the Curtiss XNBS-4: 

Two 435 hp Liberty 12A liquid-cooled engines.  Maximum speed 100 mph 
at sea level.  Cruising speed 82.9 mph.  Landing speed 53 mph.  
Service ceiling 11,100 feet, absolute ceiling 13,000 feet.  Initial 
climb rate 283 feet per minute.  An altitude of 5000 feet could be 
attained in 11.5 minutes.  Range was 500 miles with 2000 pounds of 
bombs.  Empty weight 7864 pounds, gross weight 13,795 pounds.  
Wingspan 90 feet 2 inches, length 46 feet 5 inches, height 15 feet 9 
inches, wing area 1524.4 square feet.  Armed with five 0.3-inch Lewis 
machine guns, two each in positions in the nose and aft cockpits, and 
a single Lewis firing downward from the bottom of the fuselage.  A 
bombload of 2100 pounds could be carried.  

Sources: 

  United States Military Aircraft Since 1909, Gordon Swanborough and 
  Peter M. Bowers, Smithsonian, 1989.  

  American Combat Planes, 3rd edition, Ray Wagner, Doubleday, 1982.  

  Curtiss Aircraft, 1907-1947, Peter M. Bowers, Naval Institute Press, 
  1979.  

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