Whilst I am in limbo waiting to sell my house and move to the new one with
the 3 car garage to start my tail kit project, which patiently sits in its
box, I feel its time to contribute a few titbits that have come across my
desk in the last fortnight. I'll call these the "Aussie Chat" and if you
like them, thats great, if you don't, simply trash them. If you don't want
them in this forum tell me and I'll practice my typing on something else. If
you do want them, let me know.
This first one is a summation of another British aircraft whose success I
can truly only wish for the Europa. I should know. I spent over 1000 hours
strapped into one! Here goes!
Quote:
"For those of you have flown, passengered in, or even looked in wonderment
at the Britten Norman Islander should enjoy this article.
"ACOUSTIC LIFT TECHNOLOGY"
Undaunted by aerodynamic reality, the design team at Pilatus/Britten-Norman
has announced plans for the BN2_XL (Extra Loud), promising more
noise,reduced payload, a lower cruise speed, and increased pilot workload.
We spoke to Mr Fred Gribble, former British Rail boilermaker and now Chief
Project Engineer. Fred was responsible for developing many original and
creative design flaws in the service of his former employer, and assures he
will be incorporating these in the new BN2-XL technology under a licensing
agreement.
Fred reassured BN-2 pilots however that all fundamental design flaws of the
original model had been retained. Further good news is that the XL version
is available as a retrofit.
Among the new measures is that of locking the ailerons in the central
position, following airborne and simulator tests which showed that whilst
pilots of average strength were able to achieve up to 30 degrees of control
wheel deflection, this produced no appreciable variation in the nett flight
path of the aircraft. Thus the removal of costly and unnecessary linkages
has been possible, and the rudder has been nominated as the primary
directional control. In keeping with this new philosophy, but to retain
commonality for crews transitioning to the XL, additional resistance to foot
pressure has been built into the rudder pedals to prevent overcontrolling in
gusty conditions ( defined as those in which wind velocity exceeds 3 knots).
An outstanding feature of Islander technology has always been the adaptation
of the 0-540 engine, which mounted in any other aircraft in the free would
(except the Trislander) is known for its low vibration levels, so as to
cause it to shake and batter the airframe, gradually crystallise the main
spar, desynchronise the accompanying engine, and simulate the sound of fifty
skeletons fornicating in an aluminium dustbin.
Britten-Norman will not disclose the technology they applied in enhancing
this effect in the XL, but Mr Gribble assures us it will be perpetuated in
later models and sees it as a strong selling point; "After all, the Concorde
makes a lot of noise," he said, " and look how fast it goes."
However, design documents clandestinely recovered from the Britten-Norman
shredder have solved a question that has puzzled aerodynamicists and pilots
for many years, disclosing that it is actually noise which causes the BN-2
to fly. The vibration set up by the engines and amplified by the airframe,
in turn causes the air molecules above the wing to oscillate at atomic
frequency, reducing their density and causing lift. This can be demonstrated
by sudden closure of the throttles, which causes the aircraft to fall from
the sky. As a result, lift is proportional to noise rather than speed,
explaining amongst other things the aircraft's remarkable takeoff performance.
In the driver's cab ( as Gribble describes it), ergonomic measures will
ensure that long-term PBN pilot's deafness does not cause inflight dozing.
Orthopaedic surgeons have designed a cockpit layout and seat to maximise
backache, enroute insomnia, chronic irritability, and terminal (post-flight)
lethargy. Redesigned 'bullworker' elastic aileron cables, now disconnected
---From the control surfaces, increases pilot workload and fitness.
Special noise retention cabin lining is an innovation on the XL, and it is
hoped in later models to develop cabin noise to a level which will enable
pilots to relate ear pain directly to engine power, eliminating the need for
engine instruments altogether.
We were offered an opportunity to fly the XL at Britten-Norman's
developmental facility, adjacent to the Britrail tea rooms at Little
Chortling. (The flight was originally to have been conducted at the Pilatus
plant, but aircraft of Britten-Norman design are now prohibited from
operating in Swiss airspace during the avalanche season).
For our mission profile, the XL was loaded with coal for a standerd 100 nm
with Britrail reserver, carrying one pilot and nine passengers to maximise
discomfort.
Passenger loading is unchanged, the normal under-wing protrusions inflicting
serious lacerations on 71% of boarding passengers, and there was the usual
entertaining confusion in selecting a door appropriate to the allocated
seat. The facility for the clothing of embarking passengers to remove oil
slicks from engine cowls during losding has also been thoughtfully retained.
Startup is standard, and taxying, as in the BN-2, is accomplished by brute
force. Takeoff calculations called for a 250 decibel power setting, and the
rotation force for the (neutral) C of G was calculated as 180 ft/lbs of back
pressure.
Initial warning of an engine failure during takeoff is provided by a
reduction in flight instrument panel vibration. Complete seizure of one
engine is indicated by the momentary illusion that the engines have suddenly
and inexplicably become synchronised. Otherwise, identification of the
failed engine is achieved by comparing the vibration levels of the windows
on either side of the cabin. (Relative passenger pallor has been found to be
an unrelliable guide on many BN-2 routes because of ethnic considerations).
Shortly after takeoff the XL's chief test pilot, Capt. "Muscles" Mulligan,
demonstrated the extent to which modern aeronautical design has left the
BN-2 untouched; he simulated pilot incapacitation by slumping forward onto
the control column, simultaneously applying full right rudder and bleeding
---From the ears. The XL, like its predecessor, demonstrated total control
rigidity and continued undisturbed.
Power was then reduced to 249 decibels for cruise, and we carried out some
comparisons of actual flight performance with graph predictions.
At 5000' and ISA, we achieved a vibration amplitude of 500 CPS and 240
decibels , for a fuel flow of 210 lb/hr, making the BN-2XL the most
ifficient converter of fuel to noise since the Titan rocket.
Exploring the constant noise-variable speed and constant speed-variable
noise concepts, we found that in a VNE dive, vibration reached its design
maximum at 1000 CPS, at which point the limiting factor is the
emulsification of human tissue. The catatonic condition of long term BN-2
pilots is attributed to this syndrome, which commences in the cerebral
cortex and spreads outwards.
We asked Capt. Mulligan what he considered the outstanding features of the
XL. He cupped his hand behind his ear and shouted "Whazzat?"
We returned to Britten-Norman field convinced that the XL model retains the
marque's most memorable features, while showing some significant and
worthwhile regressions.
Pilatus/Britten-Norman are however not resting on their laurels.Plans are
already advanced for the three-engined Trislander XL, and noise tunnel
testing has commenced. The basis of preliminary design and performance
specifications is that lift increases as the square of noise, and as the
principle of acoustic lift is further developed, a later five-engined
vertical takeoff model is another possibility.
Gidday for now.
Regards
Tony Renshaw
The Aussie Connection
Builder No. 236
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