Out of all the weird giant aircraft built in the 1920s and 1930s, the Beardmore Inflexible
is perhaps one of the most obscure – at least in terms of readily available source
material. The Beardmore Inflexible, also known as the
Rohrbach VI, can trace its origins back to the end of WW1. Adolf Karl Rohrbach had worked
for Zeppelin during the war, though famous for their giant airships, the company was
already looking at diversifying their aircraft portfolio as early as 1913 and were expanding
into the design of heavier-than-air aircraft. During the war, Rohrbach had been involved
with the design work of the massive R-Plane bombers, and following WW1 he designed the
Zeppelin-Staaken E.4/20 – which was an all-metal four engine airliner. Unfortunately, this
aircraft was to be scrapped in 1922 as it violated the terms of the treaty of Versailles.
Following this, Rohrbach founded the Rohrbach Metal Aircraft company, and began designing
even more aircraft, carefully evading the treaty of Versailles by having the aircraft
designed in Germany, but built in Copenhagen. Around the same time as this, the British
Air Ministry was beginning to recognise the importance of all-metal aircraft, especially
for larger designs. They issued a specification that called for the design of a large all-metal,
experimental transport aircraft. A contract was soon awarded to William Beardmore & Company,
which was based in in Scotland. Beardmore had built aircraft under licence during WW1,
but they were primarily involved with shipbuilding, locomotives and engine construction. As they
lacked aircraft design expertise themselves, Beardmore was tasked to work with Rohrbach
on the design on this new experimental aircraft. Beardmore would outline and dictate the aircrafts
specifications based on the air ministry’s specification, and Rohrbach would then work
on the main design. Once this design was completed, it was licenced to Beardmore in 1924 and construction
of the aircraft began. In what was rapidly becoming practice, especially
with large aircraft design, the aircraft’s design was tested in the Royal Aircraft Establishment’s
wind tunnel at Farnborough. The tests proved very promising, and this was down to the fact
that despite its large size, the Inflexible was of a fairly simple and conventional design.
Construction of the Inflexible was not exactly a rapid affair. Hampered by material shortages
and registration delays, the aircraft was not completed until mid-1927, and then it
had to be packed down and transported for testing. This presented its own issue due
to its vast size. The aircraft was disassembled and transported by sea from Glasgow to Ipswich,
however once it got there further transport was delayed as it was found that they would
need to build a specialised vehicle with steerable axels to get the aircraft from Ipswich to
Martlesham Heath Airfield. One it finally arrived, another problem arose as it was realised
that the Inflexibles wingspan was larger than any hangar opening that they had available.
Eventually a series of wheeled trolleys where built that allowed the aircraft to be stored
in the hangar sideways. In its final assembled state the Inflexible
made for an impressive sight. It was a shoulder-wing, tri-motor monoplane of all-metal construction,
a very futuristic design for 1927. It had a length of just over 23 meters, a wingspan
of 48 meters -greater than that of a B-29 super fortress-, and a maximum height of 6
and a half meters.
Like many early monoplanes, the Inflexible’s wings were rather box-like. The centre wing
section was formed by a wing box that was bolted onto the fuselage. Attached to each
outer section of the central wing were the outer wing sections, which were supported
by wing spars. A cable was used to keep the huge wings in tension during flight, this
cable ran from the rear wing spar to the lower fuselage. The curious wingtips look like somebody
put the final section of the wing through a photocopier set to 25%, but in fact they
are balance horns that were used to reduce control surface flutter. A suitable precaution
as the Inflexible’s ailerons spanned the outer half of each wings trailing edge. Due
to their immense size, the wings were also designed to carry the entirety of the aircrafts
fuel load, 2482 litres of fuel, split between four large wing tanks.
The wings were clad in the same metal that was used to make the rest of the aircraft:
which was Duralumin, a strong lightweight alloy of aluminium that is increased in strength
by the incorporation of copper, manganese, and magnesium. The fuselage was rectangular
in shape and consisted of two sections that were bolted together that made for easy maintenance,
disassembly, and transport. At the rear of this fuselage were the large vertical and
horizontal stabilisers. To help control its movement, a servo tab trailed behind the rudder,
and the aircrafts elevator spanned the entire width of the horizontal stabiliser.
Powering the Inflexible were a trio of 35 litre, 12-cylinder, Rolls Royce Condor II
engines, which had an output of 670hp each. Like everything else about the Inflexible
thus far, these engines were big, weighing 628kg, and they drove a large two-blade fixed-pitch
propeller. The radiator for the nose engine was located below the fuselage, and the other
two engines had their radiators mounted between the engine nacelle and the fuselage.
The Inflexible was a heavy beast. It had an empty weight of 11.3 tonnes and a maximum
weight of 16.7 tonnes. This heavy load was supported by two huge main wheels and a steerable
tail wheel. The wheels themselves were a bit of an innovation, specially developed by Dunlop
and with a diameter of 2.2 meters they were some of the largest wheels fitted to an aircraft
at the time. Originally, they had been designed as the more traditional wire-frame wheels
that were common on many aircraft at the time, but the Inflexible’s heavy weight buckled
them and a new, sturdier pair were made from aluminium and steel. Each wheel was supported
by a large shock-absorbing strut that extended from the rear of the engine nacelle, with
the wheel itself being supported by an A-frame mounted to the lower fuselage. Next to the
wheels was another innovation necessitated by the sheer size of the aircraft: a hydraulic
braking system, designed by a young and relatively unknown engineer by the name of Kurt Tank
– who would go on to produce such aircraft as the Fw-190.
Ground testing of the Inflexible began at the beginning of 1928, but before its first
flight it was decided to extend the length of the existing Martlesham Heath airfield
by another 400 yards as there were doubts that such a large and heavy aircraft could
take off on the current airstrip. It would be an unnecessary precaution however, as the
aircraft took to the skies for the first time on 5th March 1928 within the limits of the
original airfield length. The aircraft was flown by test pilot Jack Noakes, and he flew
the Inflexible for around 15 minutes, taking it up to an altitude of 1,014ft. He reported
that the aircraft had been stable and easy to control, although it felt sluggish. Follow
up testing confirmed that the aircraft was indeed underpowered, only reaching a maximum
speed of 175 km/h, and prompted the discussion for a replacement of its engines, though this
was never to happen. The low power also meant that the Inflexible handled poorly at slow
speeds on in less than idea weather, something that hurt the RAFs interest in the project.
During the course of 1928 the Inflexible made a few different public appearances and flights,
though the pilot was strictly advised to not attempt any kind of aerobatics. Despite capturing
public interest with its all-metal frame and innovative features, the aircraft failed to
secure any production contracts, and by 1929 its flying days were over.
Beardmore was already having financial struggles after WW1, and the failure of the Inflexible
to secure contracts along with various other misfortunes led to them closing their aircraft
development branch by the end of 1929. The inflexible has proven the feasibility of all-metal
designed aircraft, but the Wall Street crash and subsequent great depression put a stop
over all thoughts of modernising British aircraft until the mid-1930s.
The Inflexible was used for static testing in Martlesham Heath in 1930. The engines were
removed and placed into storage, and after the static tests the wings fuselage and various
components were used for corrosion testing. Which basically gave the people in charge
a fun excuse to let the airframe sit outside in the British drizzle and slowly rot away.
The remains of the aircraft were scrapped in 1931, with the only surviving item of the
Inflexible being one of its giant landing wheels which can be found on display in the
Science Museum in London. I mentioned at the start of the video that
there was a small amount of source material for this aircraft, my two primary references
for this were a book called Beardmore Aviation 19-13-1930 by Charles Mac Kay, and British
Prototype aircraft by Ray Sturtivant. I was able to borrow a copy of the former and I
own a copy of the latter.