Subject: Bomber Series--Douglas B-7

From: [email-masked] (joseph.f.baugher)
Date: 18 Jun 94 19:50:30 GMT

In early 1930, the Douglas aircraft company submitted a proposal to the 
Army for a twin-engined observation plane.  It was designed to compete 
with the Fokker XO-27, two examples of which had been ordered in June 
of 1929.  

The Douglas proposal was for a monoplane with high-mounted braced gull 
wings and metal construction with corrugated duralumin covering on the 
fuselage and tail surfaces.  It was to be powered by a pair of Curtiss 
Conqueror twelve-cylinder liquid-cooled Vee engines that were housed 
in nacelles attached underneath the wing by a series of struts.  The 
main undercarriage members retracted backwards into the engine 
nacelles, but the lower portion of the wheels remained exposed in 
order to reduce the amount of damage in the event of a wheels-up 
landing.  Four crew members were to be carried--an observer/gunner in 
an open cockpit in the nose firing a single 0.30-inch machine gun, a 
pilot in an open cockpit just ahead of the wing, a gunner in an open 
dorsal cockpit in the rear fuselage firing a single 0.30-inch machine 
gun, and a radio operator in an enclosed cabin admidships.  

On March 26, 1930, the Army ordered two example of the Douglas 
proposal.  One was designated XO-35 (30-227) and the other XO-36 
(30-228).  The two planes were to be almost identical to each other, 
with the primary difference being that the XO-35 had two geared 600 hp 
Curtiss GIV-1570C (military designation V-1570-29) Conquerors driving 
three-bladed propellers and the XO-36 had two direct-drive 600 hp 
Curtiss V-1570C (military designation V-1570-23) Conquerors driving 
two-bladed propellers.  Since the propellers of the XO-36 were of 
smaller diameter than those of the XO-35, the engine nacelles of the 
XO-36 were to be mounted 8 inches closer to the aircraft centerline.  

The performance of the XO-35/36 promised to greatly exceed that of the 
lumbering Keystone biplanes that were at that time the standard USAAC 
light bombers.  Consequently, the Army decided to have the XO-36 
completed as a light bomber rather than as an observation plane.  It 
was assigned the designation XB-7, and was to have been equipped with 
racks for 1200 pounds of bombs underneath the fuselage.  At the same 
time, the Army ordered that the second Fokker XO-27 be completed as a 
light bomber under the designation XB-8.  

The XO-35 flew for the first time in the spring of 1931.  It was 
delivered to Wright Field on October 24, 1931.  The XB-7 was delivered 
to Wright Field in July of 1932.  The XB-7 had racks for 1200 pounds 
of bombs underneath the fuselage.  Both planes had corrugated metal 
fuselage and tail coverings.  The tailplane was supported by wire 
bracing.  

On August 22, 1931, the USAAC ordered seven Y1B-7 bombers and five 
Y1O-35s.  Serials were 32-308/314 and 32-315/319 respectively.  These 
were delivered between August and November of 1932.  Both the bomber 
and observation models standardized on geared versions of the 
Conqueror engine.  The Y1B-7 was powered by a pair of 640 hp V-1570-33 
or 675 hp V-1570-52 engines, whereas the Y1O-35 was powered by a pair 
of 650 hp V-1570-39 or 675 hp V-1570-53 engines.  

The service-test aircraft differed from the prototypes in having 
smooth rather than corrugated metal covering on their fuselages and in 
having fabric covering for their movable tail surfaces.  The length 
was increased from 45 feet to 45 feet 11 inches, and an adjustable tab 
was added to the rudder.  The tailplane was now supported by metal 
struts rather than by wires.  Fuel capacity was increased by 116 US 
gallons.  The fuel distribution system was modified and the engine 
controls and the oil cooler were improved.  

Shortly afterward, the Army lost interest in twin-engined observation 
aircraft and no production examples of the Y1O-35 were ordered.  The 
Y1B-7 was rapidly made obsolete by advances in bomber technology (such 
as the Martin B-10), and no production was ordered for this version 
either.  

The seven Y1B-7s were assigned to the 11th and 31st Bombardment 
Squadrons at March Field in California, becoming the Army's first 
monoplane bomber to enter service.  They were later redesignated B-7.  
One was lost in a crash during its first year of operation.  The five 
Y1O-35s (later redesignated O-35) entered service with Observation 
Squadrons at Crissy and Mitchel Fields.  

On February 9, 1934, President Franklin Roosevelt cancelled all air 
mail contracts with civilian carriers and ordered the Army Air Corps 
to take over the flying of the air mail.  The Army had few aircraft 
that ware suitable for this mission, but a motley collection of 
bombers, transports, observation planes, and even fighters were 
assembled.  Among the planes assigned to air mail duty were the XO-35, 
the five O-35s, and the six surviving B-7s.  These planes were assigned 
the mission of carrying the air mail from Cheyenne, Wyoming to the 
Pacific coast, a particular dangerous route since it involved flying 
over a lot of mountains.  By June 1, 1934, when the Army Air Corps 
finally stopped flying the air mail, four B-7s had been lost in 
accidents.  However, the XO-35 prototype and all five of the O-35s 
survived the air mail duty.  

Following the completion of the air mail duty, the O-35/B-7s which had 
survived returned to more conventional military roles, and they 
remained flying until nearly the end of the 1930s, despite their 
obsolescence.  The XO-35 was surveyed on October 28, 1938, with the 
XB-7 being surveyed six months later.  The last of the O-35s was 
surveyed in February of 1939.  The two B-7s which had survived the air 
mail ordeal were surveyed in 1938/39.  No O-35/B-7 bombers survive 
today.  

Douglas XO-35		30-227
Douglas XO-36 --> XB-7	30-228
Douglas Y1B-7		32-308/314
Douglas Y1O-35		32-315/319

Specification of the Douglas Y1B-7 

Two 640 hp Curtiss V-1570-33 or 675 hp V-1570-52 Conqueror 
twelve-cylinder liquid-cooled Vee engines.  Maximum speed: 182 mph at 
sea level, 177 mph at 5000 feet.  Cruising speed: 155 mph.  Landing 
speed 78 mph.  Climb to 5000 feet in 3.7 minutes.  Climb to 10,000 
feet in 8.7 minutes.  Service ceiling 20,400 feet, absolute ceiling 
21,800 feet.  Normal range 411 miles, maximum range 632 miles.  
Weights: 5519 pounds empty, 9953 pounds loaded, 11,177 pounds maximum 
Dimensions: wingspan 65 feet, length 45 feet 11 inches, height 11 feet 
7 inches, wing area 621.2 square feet.  Armed with two 0.30-inch 
machine guns, one in a flexible nose position and the other in a 
flexible dorsal position.  1200 pounds of bombs could be carried on 
racks underneath the fuselage.  

Sources:

  McDonnell Douglas Aircraft Since 1920: Volume 1, Rene J.
  Francillon, Naval Institute Press, 1988

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

  American Combat Planes, Ray Wagner, Third Edition, Doubleday, 1982.

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