In 1936, aircraft manufacturer Boulton-Paul was busy building the prototype of its P.82
– which would go on to become the Boulton-Paul Defiant. But before the prototype of the famous
turret fighter was completed, the British Air Ministry was already contemplating its
replacement. Their primary concern was gun calibre. The
P.82, and the other aircraft being developed towards the same specification, featured four
.303 calibre machine guns. With the rapid development of aircraft with all-metal structures
by the mid-1930s, especially those with stressed metal skin as well, it was feared that this
armament would not be enough to bring down enemy bombers quickly. Ideally, the Air Ministry
wanted a fighter that could do the job in just one or two attack passes at most, and
so their attention switch from machine guns to cannons.
In March 1936 they issued specification F.18/36. This called for a twin-engine, three seat
aircraft, which could be capable of 375mph at 15,000 feet, and it was to be armed with
a four-cannon turret. As with the previous specification, this aircraft was to intercept
formations of enemy bombers, ideally approaching from below, and blast them out of the sky
with the concentrated firepower of its turret. In a departure from their usual strict attitude,
the Air Ministry proved to be quite flexible with this specification. In discussions with
several manufacturers, ideas were put forward for numerous alterations that, on paper at
least, the Air Ministry was mostly happy to oblige.
Discussions were made on the benefits of 23mm cannons in place of the 20mm cannons, a suggestion
put forward by Hugh Dowding; others focused on concerns that placing all four guns in
a single turret was impractical, instead pushing for a dispersed layout, despite the fact that
this would increase crew requirements and reduce single point accuracy; and some discussions
strayed even further from common sense, with the suggestion that the interceptor should
instead drop specialised high-explosive bombs on enemy bomber formations instead. Thankfully,
sanity prevailed, and this particular suggestion was put aside rather quickly.
Unsurprisingly, Baulton-Paul was interested in submitting a design for this specification,
not least because they were worried their existing project could be cancelled because
of it. As a result of consulting with various manufacturers, the Air Ministry issued a revised
specification in 1937 -F.11/37, and it was to this that Boulton Paul put forward their
new design: the P.92. In March 1938, three prototype of the P.92
were ordered; one to be powered by Rolls-Royce Vultures, one with Napier Sabres, and a third
to be used specifically for turret and armament development. By May 1938, Boulton-Paul already
had a mockup ready for inspection. Part of the new specification required that
the turret must be able to fire through 360 degrees of azimuth, including being able to
fire straight ahead, and this is why the P.92 looked like it was wearing a giant hat. This
was in fact a boulton-paul type L turret that was housed in a streamlined, 13ft diameter
cupola. It would contain four drum-fed 20mm hispano cannons, which had 120 rounds for
each gun, and it was powered by the same electro-hydraulic systems that the company had developed for
its other turrets. Much of the turret was buried in the aircrafts
shoulder-mounted wing, which from necessity had a very thick centre section so that only
the upper part of the turret was exposed in the slipstream. This part of the wing was
also significantly reinforced to reduce flexing, something that was not ideal for a 13-foot
diameter ring filled with ball-bearings. The fuselage was to be built up in five sections:
front, centre, the rear in two halves, and then the tail. Because the turret was to be
built into the thickened wing, the fuselage could be given a very thin cross-section to
help reduce drag. Unfortunately this, in combination with a few other things, would make the aircraft
a nightmare from points of crew comfort, and indeed crew safety.
The P.92 was to have a crew of three: a pilot, a gunner, and a navigator. The navigator was
included due to the predicted range of 2,000 miles, and the fact that the gunner couldn’t
really see below the horizon. The Navigator and pilot were sat in tandem at the front
of the fuselage. The pilot’s cockpit was just ahead of the propeller arcs, giving excellent
forward visibility, and because of this proximity to the propeller special attention was given
to soundproofing for both the pilot and the navigator cabins.
There was, however, the question of bailing out. The pilot could jettison the canopy and
jump out the normal way, but the proximity of rapidly spinning metal blades meant that
an alternative solution was desired. Unfortunately, the alternative was equally unpleasant. Instead,
the pilot could tilt his seat back by 110 degrees and slid out of the bottom of the
aircraft, upside down, and backwards. This was not only a nauseating experience, and
not too dissimilar to a means of egress later found in the TV Show Thunderbirds, but in
testing it revealed a very high risk of head injury.
This risk was deemed acceptable, and to be fair there was little alternative in the age
before the ejection seat, and this interesting addition to the prototype was approved.
Before construction of the prototypes had properly begun, it was decided that such an
aerodynamically unique airframe required substantial wind tunnel testing. Boulton-Paul did not
have a suitably large wind tunnel for such a task, and so they built a 2:7th scale model
for the Royal Aircraft Establishment’s wind tunnel instead. These tests were carried out
between March and September of 1939, during which time tentative construction work had
begun on the first two prototypes. It was found that turning the guns outboard
when elevated above 45 degrees created substantial amounts of drag, but determining the exact
effects was difficult, and so to further explore this problem a ½ scale flying replica of
the aircraft was built. As Boulton-Paul were no longer equipped to build wooden aircraft,
and as a lot of their manpower was now wholly taken up with the P.82 Defiant, construction
of this test aircraft was given over to Heston. Known as the P.92/2, it was built with an
all-wood structure, with a ply monococque fuselage; it had a fixed undercarriage for
simplicity, it was powered by 130hp Gypsy Major engines; and the gun turret was represented
by a plywood hump, though no dummy guns were installed.
Unfortunately, building a 1/2 scale version of the aircraft presented a litany of problems
that delayed the whole enterprise, not the least was the problem of finding a ½ scale
pilot. Installing the required instruments, flight testing, and camera equipment meant
that various hole had to be cut into the monocoque…which wasn’t exactly good for its structural integrity;
modifying the engine nacelles presented both heating and maintenance difficulties; and
then there was the problem of safety. Though there were pilots of a small enough
stature to somewhat comfortably operate the aircraft, being able to do so safely was a
different matter entirely. The means of escape in the event of an emergency was even more
challenging than on the envisioned full-scale version. An emergency exit panel was installed
behind the pilot seat on the port side, and by operating a small handle the pilot could
collapse the seat, open the panel, and wriggle his way out…except that said handle could
not actually be reached from the pilot’s seat. To solve this issue a piece of string
was attached to the handle, which the pilot could then pull, but reportedly those pilots
who saw the aircraft preferred to take their chances by bailing out in the traditional
way, spinning propeller blades be damned.
In the end the specification and the project behind the P.92 was cancelled before this
½ scale model even made its first flight. Not only were the demands of the war putting
an emphasis on the production of more simple designs, but the early experiences of the
Baulton-Paul Defiant were convincing the Air Ministry that the drawbacks of turret fighters
were greater than their supposed benefits. Though the prototype P.92s were abandoned,
the ½ scale model was still completed and it made its first flight in the spring of
1941. It then went on to complete a series of test flight programs, first with Boulton-Paul
at Wolverhampton, and then at the Experimental Establishment at Boscombe Down.
Most of these tests were done to evaluate the aerodynamic effects of the turret system,
but for whatever reason the purpose of the design was not disclosed to the Establishment
and their team assumed it was supposed to house a new type of airborne radar. Nevertheless
the tests were carried out and the aircraft performed better than expected. It was found
to be pleasant to handle, with hardly any faults; the controls were responsive, and
it was both laterally and longitudinally stable. The main complaint, unsurprisingly, was a
complete and total lack of pilot comfort due to the cramped conditions and an unacceptable
level of safety from the point of bailing out. Additionally, though the aircraft was
quiet enough, it was thought that the proposed sound-proofing would have been totally inadequate
for the full-scale version. Plans had been put in motion to install a
powered dummy turret, complete with fake guns, for further aerodynamic testing, but as the
proposed timeline for all of this was predicted to be at least a year (6 months to build,
and then another 6 to iron out various problems) this final project was dropped, and at some
point in late 1941 the aircraft was broken up for scrap.
Had the P.92 actually gone into production, the tests at least showed it had the promise
to be a semi-decent night fighter – the horrific choice of the Vulture engines notwithstanding.
But was it was, the Boulton-Paul Defiant would be the company’s only major design to see
wartime service, and indeed they would not produce another until after the second world
war had ended. The only thing that came somewhat close to what the P.92 could have been was
the Northrop P-61 Black Widow, though it differed from the P.92 in a number of ways - but the
story of the P-61 is one for another day.
As always thank you all so much for watching, and a big thank you of course to the patrons.
Have you ever had one of those weeks where everything goes wrong? Well that was me this
week, so if I sound a bit tired today that is because I have mentally clocked out and
I am going to go and consume my body weight in snacks. A big thank you of course to our
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