Today we’re taking a look at the Douglas XB-7, a curious looking gull-winged bomber
that was developed at the very beginning of the 1930s, though originally it had not been
designed with bombing in mind.
In the summer of 1929, the US War Department was looking to upgrade the ageing fleet of
observation planes that were currently in use with the Army Air corps.
At the time, Douglas was the main supplier of this type of aircraft, and they were of
course keen to remain so.
This led them to develop an all-metal monoplane with high-mounted gull wings, of which a contract
was soon awarded for two experimental aircraft to be dubbed the XO-31.
However, at the same time as this the War Department had also ordered two prototypes
of the experimental Fokker XO-27.
This was a design that made use of several innovative features, and as such it promised
to offer a substantial improvement in performance and operational flexibility over the other
observation aircraft currently operated by the Air Corps.
Naturally, this new development rather worried the directors at Douglas, who viewed the Fokker
as a potential threat to their position as the leading supplier for observation aircraft,
and thus they instructed their design team to work on something better.
This they did in rapid time, and in March of 1930 a design was submitted to the War
Department for a twin-engine, all-metal monoplane.
This was then approved in an equally quick time period, and a contract was offered for
the construction of the XO-35 and the XO-36.
Both of these aircraft were very similar in appearance, each having high-mounted braced
gull wings and each being clad in a skin of corrugated duraluminiun, and they bore a strong
family resemblance to the smaller, single engine, XO-31 which had been ordered earlier
that year.
Like the design by Fokker, the Gull-winged Douglas featured several modern and innovate
design concepts.
Chiefly, it featured a retractable landing gear, with the undercarriage units retracting
into the engine nacelles, though in the interest of reducing damage in a wheels-up landing,
the lower part of each wheel protruded from the nacelle to soften the blow of impact.
The fuselage was constructed as a semi-monocoque, and this house the aircrafts four crew members.
It was to have an observer gunner in an open cockpit in the nose, a pilot in an open cockpit
just forward of the wings, a gunner in an open cockpit in the rear fuselage, and a radio
operator – who had the esteemed luxury of being in an enclosed station amidships.
Unlike with some later designs, the open cockpit arrangement wasn’t as much of a problem,
as the Douglas prototypes were not expected to achieve face-ripping speeds above 200mph.
That being said, it was not expected to be a slouch either; this was partly thanks to
its aerodynamics, and partly due to its powerplant.
Both were powered by the 25 litre, liquid-cooled Curtiss Conqueror V12.
These were enclosed in nacelles attached to the underside of the wing and the fuselage
by a series of struts.
When first ordered, the two aircraft were only intended to differ in the model of engine
used, with the XO-35 having two geared versions of the Conqueror, and the XO-36 having two
direct drive models.
However, before the XO-36 was completed, the Air Corps, noticing that its predicted performance
eclipsed their Keystone aircraft, decided to have it completed as a light bomber.
At the same time as this they also ordered Fokker to complete their second prototype
as a light bomber as well, with the intention that the two designs would be evaluated against
each other.
And so, the Douglas was redesignated as the XB-7, and the Fokker as the XB-8.
The XO-35 was the first Douglas model to be completed, this flew for the first time in
the Spring of 1931 before going on to complete manufacturer trials, and tt the completion
of these trials it was then delivered to Wright Field in October for service testing.
The XB-7 was completed shortly after, and after a longer series of manufacturer trials
it would also go to wright field in July of 1932.
These trials were mostly longer due to the additional structural tests that were required,
as the aircraft had been slightly re-designed to carry 1,200 pounds of bombs on racks beneath
the fuselage.
While undergoing trials at Wright field the XO-35 was extensively damaged on the 11th
of July 1932.
Repaired and overhauled, it was then flown again at Wright Field, and along with a stint
of being flown in air mail operations in 1934, it would accrue 999 hours of flight time before
being too worn out to pass its annual inspection in 1938.
By the time both prototypes were first flying at Wright Field, the Air Corp’s interest
in the project had grown, and an order had already been placed for twelve service aircraft,
this order consisted of five Y1O-35s and seven Y1B-7s.
This order would be completed over the course of 1932, with deliveries taking place between
August and November.
The service test aircraft differed from the prototypes in a number of ways.
The engines were different, with the Y1B-7s receiving standardised geared variants of
the Conquerer, the two models selected either having 640 or 675hp, and the Y1O-35s were
also powered by two geared versions that either produced 650 or 675hp.
The fuselage, having been lengthened by 11 inches to improve the centre of gravity, also
had its corrugated duralumin skin replaced by smooth sheet metal.
Along with this, an adjustable tab was also added to the rudder to improve handling in
the event of engine failure, and the tailplane – which on the prototypes had been wire
braced – was now supported by metal struts.
Along with the external changes, the internal fuel capacity was increased by 116 US gallons,
or 439 litres.
And this was done to comply with a new directive that required all service aircraft to have
a minimum endurance of 2 hours plus another 2 on reserve, as, surprisingly, a short flight
endurance was unattractive in the air force of a country that was the size of a continent.
Aside from this, other changes included a modified fuel distribution system, improved
engine controls and oil cooling systems, and some general upgrades to the equipment for
both the pilot and radio operator.
Though they boasted improved performance figures, including a top speed of 182mph and a surface
ceiling of 20,400 feet, their appeal to the Air Corps was rapidly diminishing – courtesy
of the sleek new design that was being proposed by Glenn-Martin, the soon-to-be-realised B10
that we covered in a recent video.
As a result of this, no production orders would be placed for either of the Y1O-35 or
the Y1B-7, however this did not mark the end of their use.
In early 1934 the US civil aircraft industry was being rocked by the Air Mail Scandal.
In a nutshell, the was the result of a congress-led investigation of contracts awarded as part
of the 1930 Air Mail Act.
These contracts were the result of a meeting between the Postmaster General and the executives
of top airlines at the time, this closed-door affair of course prevented any smaller airlines
from competing for said contracts, and their subsequent complaints resulted in a senate
investigation.
The fallout of this resulted in President Roosevelt cancelling all air mail contracts
in February 1934, and he then requested the Air Corps to take over the air mail routes
while new contracts were being arranged.
This caught the Air Corps somewhat off guard, as very few of their aircraft were suited
to the task, but the newly re-designated Douglas O-35 and B-7 appeared better suited than most,
and so they were assigned to the mail routes in the so-called Western Zone- and area that
was particularly challenging.
This was the most difficult zone because of the mountainous terrain, and the pilots assigned
to it urgently needed to familiarise themselves with the routes they were about to fly.
Unfortunately, it would not take long for the terrain and the elements to claim their
first victim, as it was during one of these familiarisation flights that a B-7 crashed
in Idaho.
The Pilot, 2nd Lieutenant James Easthman was circling the aerodrome waiting for a break
in the weather, being caught in a snowstorm, when his plane stalled and he was killed in
the crash.
Four days later, and in the shadow of that tragedy, the Air Corps officially began its
mail carrying duties.
However it was not an easy endeavour.
From the outset they were plagued with severe winter weather, and that coupled with being
poorly prepared or equipped for night-time operations, lead to more crashes and the deaths
of 13 airmen.
By the time the regular mail service was restored, three more B-7s had been lost, with an overall
loss ratio of one aircraft per 353 hours of flight time.
After this, the B-7s saw limited use, as they were quickly becoming worn out and made obsolete
by newer aircraft designs.
They would eventually be withdrawn from use in 1938, with all of the models ending their
days in a scrapyard.
In terms of designs, the B-7 was a bit of a dead, and a lot of that can be attributed
to the rapid pace in which aircraft design evolved during this period.
In the span of a few years things went from biplanes to monoplanes, and many planes were
obsolete within months of leaving the hangar for the first time.
Some made it, some didn’t, and the B-7 was one of the latter.
Once again thank you all for watching, and an even bigger thank you to my newest patreons
– my goodness you lot were quick off the mark, and a special shoutout to Delliardo
and Kevin for their support as Wing Commander tier patreons.
Thank you all so much, and I’ll catch you all next time.