John Farley explains the
contemporary significance of the RAE/DERA/QinetiQ's work on their VAAC
Harrier TMk2 XW175 and the historical background to this success...
On the 16th of May 2005 Justin Paines, a QinetiQ civilian test pilot,
pressed the 'coffee bar button' and thereafter everything happened
exactly as intended and just like I had wanted it to for years. The
'coffee bar button' was in the rear cockpit of Harrier XW175 (the
second two-seater ever to fly, way back in 1969) and the result of
Justin pressing it was that 175 looked around, sniffed the air with its
satellite navigation system, decided where Justin's coffee bar was
located, took him to it and landed him safely, gently and of course
vertically, on board HMS Invincible.
UNIFIED
FLIGHT CONTROL ©
JF
Farley
This
first fully automatic recovery of a Harrier to a ship was the end of a
journey on which RAE scientists embarked in 1952. Yes, that is correct.
The journey started eight years before Bill Bedford broke his ankle and
the doctors decided the only thing he was then fit to 'fly' was the
first prototype P1127 tethered to the grid at Dunsfold. Just what were
RAE (later to become DERA and now QinetiQ) scientists up to all that
time ago that eventually led to the Invincible landing fifty three
years later? Also why was I so keen for such a capability to
be developed? I will try to explain.
By 1951 the senior management of RAE realised that the thrust of jet
engines was increasing all the time and that one day an aircraft with a
thrust greater than its weight would become possible. But how could the
attitude of such an aircraft be controlled in the hover?
In an attempt to answer this question Dennis Higton, a former
RAE apprentice who had joined the Aerodynamics Research Flight at
Farnborough at the end of his apprenticeship in 1942, devised
a rig to investigate the feasibility of controlling the attitude of a
hovering aeroplane by means of small jets mounted in the nose, tail and
wingtips. The layout he used is shown in RAE Tech Memo 286 of
April 1952 in which Higton reported his work.
These early experiments showed that a reaction control system was
indeed suitable and enabled Higton, working with colleague Roger Duddy,
to draw up the specification for a full size piloted rig to be used by
the RAE. This rig, which first hovered tethered under a safety gantry
at Rolls-Royce Hucknall in 1953,flew free for the first time in 1954
and was known as the Flying Bedstead. From those early days the
scientists of the Aerodynamics Research Flight at RAE - or simply Aero
Flight as they were known - worked continuously to develop and improve
the handling qualities of jet lift aircraft. After the Flying Bedstead
they commissioned the Short SC1 which they operated from the new RAE
research airfield at Thurleigh, near Bedford.
From the start the RAE approach to the control of jet VSTOL aircraft
was to use a high degree of autostabilisation to make the handling as
easy as possible for the pilot. Hawkers on the other hand favoured
simplicity as a means of reducing the control system failure cases.
Accordingly the initial Hawker P1127, Kestrel and Harrier aircraft
could be flown without artificial aids, relying on the pilot to
compensate for any inherent handling deficiencies.
With hindsight both teams were correct. The RAE approach was without
doubt the ideal way ahead for the pilot but - and it was a big but -
the electro-mechanical engineering reliability of automatics in those
days was far from assured given the technology then available. Because
of this, the Hawker approach of simplicity and reliance on the pilot to
compensate was absolutely correct during the 1960s and enabled the
Harrier to happen.
Once the Harrier went into service, there was a slow but continuous
trend to add devices to it that made control easier and safer for the
pilot at low speeds. Not surprisingly the RAE Aero Flight input into
the development and certification of these aids was considerable and
from 1964 onwards they were helped in this work by having their own
P1127. By 1964 six P1127 aircraft had been flown at Dunsfold
and naturally the later aircraft incorporated lessons learned from the
earlier ones. Because of this the standard of the original prototype,
XP831, was by then looking fairly unrepresentative so the ministry
allocated it to Aero Flight at Bedford. At that time I happened to be
serving there as an RAF Flight Lieutenant and was fortunate enough to
be given the job of collecting it from Dunsfold. Three years later,
following the retirement of Bill Bedford, my luck continued and I took
my uniform off and joined Dunsfold as their new junior test pilot.
Later in 1970 Dunsfold Chief Test Pilot, Hugh Merewether, asked me to
represent him at a meeting being held at RAE Farnborough. Hugh
explained that it appeared the RAE boffins had ideas for making life
easier for jet VSTOL pilots and so he needed somebody to go and keep
tabs on them. He pointed out that as a former RAE apprentice I was
obviously the bloke for the job and anyway he had better things to do
that afternoon. At that meeting it was clear to me that the eventual
aim of the scientists was to hand over control of the aircraft to a
computer leaving the pilot just to tell that computer what manoeuvre he
wanted it to fly. If this happened it would mean the Harrier pilot's
nozzle lever would no longer be needed because control of the nozzle
angle – as well as everything else that the pilot hitherto
controlled – would be left to the computer.
As I drove back to Dunsfold I was quite excited about what I had heard.
After using my left hand to operate the nozzle lever and throttle for
six years, it was clear to me that it was only a matter of time before
I made a mistake and moved the wrong one with potentially disastrous
results. Therefore I welcomed the boffins' ideas although I realised it
might take a few years to turn them into reality (it actually took
twenty nine!). Meanwhile the RAF had only two years experience with
their Harriers and the provision of this single nozzle lever was seen
as the simple masterpiece that had enabled VSTOL to happen. Rather
naturally at Kingston and Dunsfold, any talk of removing the nozzle
lever was as close to Harrier Heresy as you could get so care was
needed when broaching the subject. Anyhow they were all so busy coping
with the USMC decision to buy Harriers it was not reasonable to expect
them to give serious consideration to futuristic ideas.
Time passed and I became increasingly frustrated that the RAE approach
to specifying the modifica- tions of a Harrier to start flight trials
had turned out to be so conservative in that they were not intending to
split the control of the four engine nozzles. I remember talking to
Kingston aerodynamicist Robin Balmer about this in the mid seventies
and suggesting that if we let a computer put the nozzles down on one
side only, we could get rates of roll in low speed combat that would
make any opposition's eyes water. Equally by putting down the front or
rear pair we could pitch in a way nobody else could even dream about.
It seemed so obvious to me that the Pegasus offered a ready made way to
endow the aircraft with unmatchable manoeuvrability. However, such
ideas were viewed as too way out. Not surprisingly the Kingston design
office and spiritual home of "Keep it simple, stupid" (and that is
meant as a compliment not as a criticism) was not about to change
horses in mid stream and take the lead in the brave new world of
computer-based systems or fly-by-wire as they are called today.
My apologies - I digress. By 1982 the RAE programme, now called VAAC
for Vectored thrust Aircraft Advanced flight Control, had laid the
three key foundation stones needed for eventual success.
The first of these was the choice of a two-seat aircraft for the
programme. Had the team chosen to modify a single seat Harrier, they
would only have been able to test tomorrow's ideas on today's Harrier
pilots - hardly the best way to conduct open minded research. (NASA
went this route with a modified Harrier and I suspect lived to regret
their decision).
The second was installing something termed the Independent Monitor
(IM). The IM was essentially a special computer that was carried around
in the test aircraft for many sorties during which time it was taught
by the Harrier crew to recognise the safe limits of Harrier operation.
It was then sealed and became the basis for the subsequent
airworthiness certification of the aircraft as a research tool. When
the trials proper started, the IM was thus able to keep an unblinking
eye on what the (single channel) experimental equipment was attempting
to do with the various Harrier controls. If it detected anything that
looked like going outside what the human pilots had previously agreed
was a limit, it instantly disengaged the experimental kit and handed
the aircraft back to the safety pilot in the front seat. That way the
safety pilot would always be left with a recoverable situation.
The third foundation stone was that by then two Bedford men, scientist
Peter Nicholas and test pilot Flight Lieutenant Peter Bennett, had
conceived the notion of something called Unified. To cut a long story
short, this meant that if the pilot wanted the aircraft to go up then
the stick had to be pulled back and to go down the stick was pushed
forward. Sound familiar? Well yes, but Unified was conceived for use at
any speed. Helicopter pilots raise or lower a lever called
'the collective' to go up or down in the hover while Harrier pilots use
the engine throttle for the same thing. The aim of Unified was to allow
the pilot to fly using the stick at any speed. You may prefer to think
of it as eliminating the concept of a 'stalling speed'. When the pilot
asked to fly slower than the stalling speed, the computer merely put
the nozzles down and used the engine instead of the wings to support
the weight. This of course was what human (superhuman?) Harrier pilots
already did but only after special and expensive training. Unified
enabled any fixed wing pilot to handle a Harrier in the circuit without
extra training. Easy though Unified may appear, it was in actual fact
far from straightforward to optimise and approve all the necessary
software. After all, exactly how did various pilots want the aircraft
to react to their demands at different speeds and so on?
In 1983 I turned into a pumpkin and retired from Harrier test flying
but the VAAC team were kind enough to keep in touch with me and I was
invited back in 1993 and again in 1999 to fly the aircraft and comment
on how I thought they were getting on. In 1999 my safety pilot was one
Squadron Leader Justin Paines. When I got out after our couple of
sorties at Boscombe, I told him that I thought the team had cracked it
and that Unified was the way ahead. Shortly after that, following a
detailed and quantitative evaluation trial where the VAAC was flown by
many test pilots including several from the USA (some of whom had never
been in a Harrier before) the VAAC team was able to convince the US
Joint Strike Fighter Programme Office that their ideas were indeed the
way ahead.
Again there was much more to selling Unified to the US than my account
might suggest. Justin Paines, who led the final test pilot push, was in
no doubt that the opinion of Harrier squadron pilots on both sides of
the Atlantic was bitterly divided. While some saw the attraction of
Unified others were seriously opposed to it. The opposition even
included senior BAE test pilots. As I saw it the opponents all had many
years of successfully using the nozzle lever and arguably it was that
skill that made them better pilots than those who had no such
experience. It made them better in the circuit, better in the bar, and
probably better in bed. As for the mistakes Harrier pilots had made
over the years it was only lesser mortals, not people like them, who
moved the wrong lever. Expecting such senior operators to vote for
abolishing the nozzle lever was akin to expecting turkeys to vote for
Christmas.
In the end I am glad to say that the VAAC team's arguments in favour of
deskilling the process of flying jet VSTOL won the day, thus saving
costly training as well as reducing the likelihood of accidents. The
JSF will be in service for 50 years from now so many of its future
pilots have yet to be conceived. Thankfully the aircraft is to be built
with them in mind, not yesterday's nozzle lever men.
Finally what about my wish for a 'coffee bar button'? In many
of the conversations I had with Harrier pilots about the controversial
idea of Unified, I was at pains to point out that although I wanted to
get rid of their beloved nozzle lever I was not a boffin's nark and
against the operational pilot's point of view. In fact quite the
reverse. I believed that while operational pilots were over the target
(and being shot at on our behalf) their views about what they needed to
do their job were paramount. However, once they turned their back on
the target and their operational job was done, they should be able to
press a 'coffee bar' button whereupon the aeroplane would then take
them home safely, day or night, in any weather, regardless of whether
they were exhausted, injured or (heaven forbid) it was just their day
to make a mistake during their approach to land.