Quite a few people who watched my video on the P-26 peashooter wanted to know what the
large aircraft was in this photo, so let’s take a look at that now.
In 1930, the bomber squadrons operated by the US Army Air Crops mostly consisted of
slow biplanes.
Designs like the Keystone B-6, LB12, and the Curtiss B-2 were considered the norm, but
these designs were rapidly becoming obsolete.
That being said, change was on the wind and several manufacturers were pursuing the development
of new monoplane designs.
and one of them was Boeing.
Boeing wanted to take the lessons learned from designing their Model 200 Monomail transport
and apply them to a twin engine bomber.
The Monomail was their first successful attempt at an all-metal cantilever wing, and it also
featured a semi-monocoque fuselage which further improved streamlining.
If these same design principals could be applied to a bomber, it could radically improve its
performance and thus allow it to evade any potential fighter interception more easily.
Todays video technically covers three different Boeing designs, the Models 214, 215, and 246.
However, they are all closely related.
The first two were developed together, and then the 246 was developed after – and benefited
from lessons learned in the development of the previous models.
The first two of these aircraft were developed privately by Boeing at their own expense,
and the only thing that differed between the two was the type of engine they carried.
Like the Monomail, and indeed like many new aircraft at the time, these two aircraft introduced
some modern structural and aerodynamic concepts, but at the same time they also clung to some
traditional concepts.
The Model 214 and 215 would be some of the first big American aircraft to benefit from
the use of wind-tunnel testing.
These tests, conducted by NACA in 1927, had led to the development of a new streamlined
cowling for radial engines and the design concept of mounting engines in the front of
a single wing in a streamlined nacelle – further proving you can make bricks fly better if
you stick enough curvy bits on them.
Boeing’s new aircraft would also feature a type of retractable landing gear; though
it was not completely retractable, with part of the gear still exposed under the airframe,
it still resulted in a dramatic reduction of drag.
The design specifications for these aircraft are relatively similar, with the exception
of the different engines which also resulted in some weight differences.
So, to keep things simple, I shall quote the dimensions and specifications from the model
214.
It had a length of 56 ft, a wingspan of 76ft and an approximate height of 12 feet.
It had an empty weight of approximately 8500lbs and a gross weight of 13,600lbs.
In its original design specification, the 214 was powered by two 12-cylinder liquid-cooled
Curtiss Conqueror engines – specifically the GIV-1510C.
These drove a pair of two blade propellers and gave the 214 a top speed just over 173
mph, a cruising speed of 147mph, and a range of 1250 miles.
The aircraft would have a crew of five.
The bombardier -who also acted as nose gunner- occupied a cockpit in the noise, which was
equipped with a bomb sight and aiming window at the bottom and a mount for a flexible machine
gun around the top.
Because of the narrowness of the fuselage, the pilot and co-pilot occupied tandem cockpits
immediately behind the bombardier instead of sitting side-by-side in a single wide cockpit.
A radio station was located ahead of and below them in the fuselage, and a fourth cockpit
for a rear gunner was located on top of the fuselage behind the wing.
For its size the aircraft had a light defensive armament, just two 30 calibre machine guns.
That meant just one for each gunner position, which was one gun less than what you would
expect on contemporary biplane bombers.
The bombload was also relatively light, with 2200lbs worth of bombs being suspended under
the wings – again several contemporary biplane bombers could carry a bit more than that.
Along with this small-ish firepower, the was the total absence of consideration for the
physical endurance of the crew.
For in spite of the great advance in speed over contemporary bombers, all cockpits on
the Models 214 and 215 were open cockpits, which would have made for quite the blustery
experience.
The higher speeds would result in one innovation, however.
The new airspeed increased the loads on the control surfaces, as a result of this rudder
servo tabs were installed to assist pilots in operating the controls, this was the first
instance of this occurring on a completed American aircraft.
On the model 214, the tab was a small auxillary surface projecting aft of the rudder trailing
edge.
On the model 215 it was a tall narrow surface running the full height of the rudder trailing
edge.
The model 215 would be the first aircraft built to completion.
It was completed in civil colour and markings and flew for the first time on April the 13th
1931, achieving a top speed of 163mph.
It was tested by the Army as Boeing property on a Bailment contract under the designation
XB-901.
Results from the tests were favourable and the 215, along with the 214 were purchased,
with a further order of five aircraft for service testing.
The basic aircraft design was given the standard Army bomber designation of B-9 when purchased
later in the year, and the prefix Y was added to indicate service test status.
And so, the aircraft could be known as the Boeing model 215, the XB-901, or the YB-9.
The model 214, originally powered by the Curtis Conqueror engine, was completed as a military
aircraft following the favourable testing of the model 215.
As the 215 had already been designated as the YB-9, the 214 was given the designation
Y1B-9, and it made its first flight on the 5th of November 1931.
Though faster than the model 215 when it first flew, it was decided to change the 214 over
to radial engines when testing was completed.
The model 215 had recently been refitted with the more powerful supercharged version of
Pratt & Whitney’s Hornet B engine, and the performance gap had narrowed.
But the main concern was reliability.
The air-cooled radial engines were lighter and more reliable than liquid-cooled engines,
and they were less prone to the effects of damage from enemy fire.
The five aircraft ordered by the army for testing would arrive as the Boeing Model 246,
which would then be designated as the Y1B-9A.
The first aircraft flew on July 14th 1932, and the last was delivered to the army on
March 20th 1933.
As originally delivered, they were outwardly identical to the previous aircraft, with a
few minor exceptions.
They had the rudder tabs that were used on the model 214, their control surfaces had
metal instead of fabric covering, they used three-blade propellers, and incorporated many
internal structural and equipment changes.
Later the rudders were changed back to a fabric-covered type, using the same servo tab that would
be used on the model 247 transport.
These aircraft had an even higher top speed of 186 mph, making them all but impossible
to intercept during military exercises in 1932.
Despite the increased speeds, they still featured fully open cockpits and gunner positions;
enclosed canopies had been designed at the time of their construction, but for reasons
unknown they were never installed.
While these aircraft are one of a group that revolutionised bomber design, they were not
the first monoplane bombers developed for the US Army.
They were preceded by the Douglas B-7 series and the Fokker XB-8.
While both of these designs featured retractable undercarriages, their design concept was older
than the B-9, both aerodynamically and structurally.
Initial army enthusiasm following the appearance of the Boeing Model 215 brought unofficial
assurance of sizeable production orders, and Boeing believed they had a profitable future
with their new aircraft.
However, the risks involved in pioneering in a highly competitive industry soon became
apparent, when Glen L Martin company brought out their own private design.
This aircraft was slightly newer in design than the Boeing and had better performance,
the army was impressed, and they awarded large production orders under the designation of
B-10 and B-12, this would make the Martin B-10 America’s first mass-produced bomber.
This signalled the end of the Boeing YB-9.
Of the five aircraft that were in service with the Army Air Corps, two would be destroyed
in crashes in 1933, and the remaining aircraft were phased out of service shortly after,
the last being withdrawn in April of 1935.