Today we’re returning to the curious topic where, in the 1920s, the British Air Ministry
went through a phase of trying to mount 37mm automatic cannons onto various aircraft.
Last time we looked at the Vickers type 161, and today – in a slight departure - we will
be looking at two aircraft: the Bristol Bagshot and the Westland Westbury.
The reason for this is that one of the planes covered today has a very brief history, and
when making a separate video for it the time barely made it to four minutes, and so I decided
to combine them.
Both of these aircraft were born out of Air Ministry specification 4/24, which called
for a multi-seat twin-engine fighter capable of carrying two automatic shell-firing guns.
The potential of heavy guns had been recognised in the First World War, and attempts had been
made to adapt several types, including the 37mm Coventry Ordnance Works Gun, also known
as the COW, for use on various aircraft.
It was a pair of these guns which were ultimately required to be used in fighters designed to
this specification, although this was not initially disclosed in the specification details.
Aside from familiarity, this choice of armament was made for a variety of others reasons as
well, chief among them being the trends of French bomber design by companies such as
Farman, Amiot and Potez, which included research in using 20mm cannons.
Both Bristol and Westland submitted designs to meet this specification by the end of 1924,
however both designs were fundamentally different in concept.
Bristol’s design team, led by Frank Barnwell, favoured a monoplane configuration with an
all-metal wing and fuselage, whereas Westland’s team, led by Arthur Davenport, went with a
far more conservative arrangement.
As it was the first one to fly, lets start by covering the Westbury.
Originally, the design featured a two-bay biplane configuration, but after wind-tunnel
testing this was revised to a three-bay design with high aspect ratio.
In June 1925, Westland received an order for two prototypes.
The first would be built in the more traditional style of having an all-wooden wing structure,
and the second would have wings built from a mix of duralimunium spars and wooden ribs.
The fuselage was built in three separate sections that were bolted together at the longerons.
The forward unit, which was all wood and covered in ply, contained the front gun turret which
held the first of the two COW guns.
This was installed on a special mounting that allowed the weapon to be trained through 360
degrees in azimuth.
The movement of the gun was controlled by a brake pad that allowed a spring mechanism
to engage or disengage the weapon from its current position.
Training the gun itself was done by a hand cranked pinion gear that was engaged to a
base-ring.
The whole mounting was provided with a rotary platform for the gunner, and a fixed cylindrical
shield was carried by the ring.
Eventually, the mounting would prove to be useful and innovative enough for Vickers to
purchase its productions rights for later use.
The second unit formed the central portion of the fuselage, this started just in front
of the pilot’s cockpit and extended back to the rear gunner’s position.
Unlike the forward section, this central piece was built from steel tubing covered in ply.
This section housed the station for the other COW gun, but unlike the on in the nose, this
one was on a simple trunnion mounting.
It was designed to be fired in a fixed position, aiming upwards into a formation of aircraft,
though it did also have a limited arc of fire.
The third fuselage unit comprised the rear section of the plane and was of mixed construction,
with steel-tube longerons and spruce girder frames.
This section could be easily removed as the fairings were attached to the longerons by
a series of clips, which made transportation and maintenance easier as the tail section
could simply come away.
As the Westbury had a deep fuselage, the three crew positions were connected by an access
passageway, which when needed could allow just one gunner to operate both COW guns when
required.
The pilot could enter his cockpit either by climbing up the fuselage aft of the wing,
or they could enter via the rear-gunner position and climb through the internal passage.
The first prototype was powered by a pair of 450hp Bristol Jupiter 6s, each driving
a wooden two-blad propeller.
These were housed in nacelles on the inboard section of the lower wings.
The fuel and oil tanks, starting magnetos and priming pumps were all contained in these
nacelles, and the whole arrangement could fit into a standard railway truck for easy
transport.
This first prototype flew for the first time in September 1926 and immediately went into
initial flight trials and wind tunnel evaluations.
As a result of this, modifications were made to the second prototype which was still under
construction.
These included a more rounded nose, the addition of a small ventral fin between the V struts
of the tailplane, and the lengthening of the engine nacelles to allow the installation
of Jupiter 8 engines.
The first flight of the second prototype took place at Yoevil in 1927, after which it went
to Martlesham Heath.
During the trials at Martlesham both COW guns were tested, and upon the firing of the rear
gun the fabric and ribs of the upper wing were damaged by the concussive blast.
Thankfully the plane landed without incident, and some further modifications were made so
that it wouldn’t shoot itself to pieces in the future.
Chiefly, this involved the fitting of a rubber-sprung protective shield over the upper wing to deflect
the offending muzzle blast away.
The nose gun was also test fired in a number of positions, including directly into the
line of flight despite it providing over 2000 lbs of recoil force with each discharge.
Despite attempts at rapid disassembly, and the possibility of stalling out due to gun
recoil, both Westbury prototypes performed well.
They even handled easily with one engine stopped, or even turning against the running engine,
but by this time Air Ministry interest in such heavy aircraft was waning and the specification
for the aircraft was abandoned.
Despite this, Westland gained valuable experience with installing and operating the COW gun,
something that would serve them later in the specification that led to the Vickers 161
and Westland COW fighters.
The Bristol Bagshot was less fortunate than the Westbury.
As mentioned earlier, it was a more modern design, being built in a monoplane configuration,
having an all-metal shoulder-mounted cantilever wing and a steel-tube fuselage.
The wing was built from two main steel spars and had duraluminium ribs, with the whole
arrangement, like the fuselage, being clad in fabric.
The wide-track landing gear was a curious arrangement, featuring aerofoil-section axel
fairings that were meant to contribute to the overall lift.
How effective this actually was…was sadly never recorded.
Initially, like the Westbury, the Bagshot had not been designed specifically with the
37mm COW gun in mind, this change came after work on the prototype had begun.
On receiving the updated specification, and confirming the required equipment changes,
it was realised that the Bagshot would be overweight and unable to land at a speed slower
than 57mph – with the specification itself calling for a landing speed of just 50 mph.
Frank Barnwell, who was leading the design team, suggested making an experimental rolled-strip
fuselage – which would be interchangeable with the existing one – that would save
weight providing the tests were successful.
The alternative was to abandon the project altogether as he believed it would be a waste
of time and resources to pursue other options.
Unfortunately for Barnwell, the Air Ministry declined to cancel the contract, and he was
ordered to complete the Bagshot, if only to compare it with the competing Westland in
a Biplane versus Monoplane style evaluation.
Powered by a pair of Bristol Jupiter 6s, the Bagshot was flown for the first time on the
15th of July 1927.
The first flights on that day went without incident, but subsequent flights were almost
disastrous.
This was because at higher speeds the lateral control was ineffective due to wing torsional
flexibility, which caused aileron reversal – something that was of course only discovered
when the aircraft was in the air.
Luckily Cyril Uwins, the test pilot, managed to land the Bagshot safely, and the aircraft
was brought back into the factory for an exhaustive structural testing program.
At the conclusion of said tests, Barnwell realised that the only hope was to redesign
the Bagshot as a biplane, which virtually meant starting again from scratch.
No further attempts were made to fly the Bagshot until the full test results had been examined
by the Air Ministry, who eventually retained the aircraft to conduct more research on the
tortional stiffness of cantilever wings.
The Bagshot was scrapped by late 1931, and the Westland Westbury’s didn’t last much
longer, though the latter did prove useful as a testbed for various automatic cannons.
The most important takeaway from these designs was the need for structural reinforcement,
for even with muzzle deflecting shields installed, the Westland planes continued to suffer from
the recoil forces of firing such heavy armaments.
Fixing large guns onto relatively fragile airframes would continue to prove a challenge
over the coming years, but it would certainly lead to some interesting and even successful
designs.
But that’s a story for another day.
As always, thank you all so much for watching and I’ll catch you all next time.