On 11 February Dr
once again addressed the Association, this time on the importance of
testing, particularly in the context of pioneering jet V/STOL aircraft
and contemporary ASTOVL aircraft including the F-35B.
Mike is now working for the Centre for Research in the Management of
Projects at Manchester Business School undertaking research on NECTISE
(Network Enabled Capability Through Innovative Systems Engineering) (!)
looking at organisational aspects of TLSM (Through Life Systems
Management), a project 60% funded by BAE Systems.
understanding the current work of the Harrier and Typhoon engineering
teams and working with BAE Systems he expects to deliver advice on
improving the efficiency of these operations.
DPhil Mike explored the technical, managerial and political issues
around the acquisition of ASTOVL combat aircraft, looking particularly
at the design and testing work undertaken at Kingston and Warton from
the 1960s to the 1980s. The contents of this talk originated in that
In his work with Kingston and Warton people he determined
two organisations had quite different philosophies. In simple terms,
Warton tested a large number of possible configurations then selected
the best for design and build, whereas Kingston used the experience and
expertise of its engineers to conceive a design which they believed
would be successful and then tested and refined it before build.
The classical testing process starts at the concept which is
model tests, followed by design, rig tests of systems and components,
build and flight test. V/STOL aircraft testing has to deal with unique
issues requiring special test facilities and specialist knowledge, the
work often being highly empirical. The chaotic nature of the gas flows
beneath V/STOL aircraft makes it essential, but difficult, to relate
model test results to the full scale, real world regime. It is possible
to predict reasonably well nozzle flows until they hit the ground but
thereafter the flows, fountains, recirculations and lift losses are so
dependent on small changes that only testing can provide the answers.
n the case of the P.1127 the first (hovering) flight was, in
academic parlance, a 'TRL7' (Technology Readiness Level 7) event,
meaning that Hawkers really knew very little about what went on
underneath the aeroplane and what the consequences would be. However,
at the time it was the only way to go.
There had been some V/STOL model
testing at NASA and some transition testing in Hatfield and ARA wind
tunnels. The techniques developed from these pioneering efforts are in
use today on the F-35B programme, including the Kingston hot gas rig
now at Warton.
Although the X-35B
demonstrator successfully completed
its programme some years ago, Lockheed Martin are not proposing to
hover the F-35B until some months after first flight, this cautious
approach being deemed necessary because of small, but possibly
important, configuration changes - no TRL7 events here. Also, an
'accident' is unthinkable because of the political fall-out.
sub-scale model testing the understanding of scaling is critical to the
development of 'fudge factors' relating model results to real
conditions. Lessons from Harrier experience were that accurate nozzle
models were vital and trends were what should be looked for. PCB
(Plenum Chamber Burning) Harrier testing is a good example.
Harrier constructed from units from crashed and redundant aircraft plus
an intake plug made cheaply by Kingston apprentices, and fitted with a
PCB Pegasus, was suspended beneath a gantry at Shoeburyness range. The
effects on hot gas ingestion of nozzle toe-in, strakes and cross dams
were measured then compared with sub-scale model test by Rolls-Royce
Bristol and Kingston. All the results were different, mainly due to
nozzle and toe-in differences, but the trends were clear.
Project design testing using sub-scale models include wind
tests on hot gas ingestion and transition, VIFF with PCB and the
effects of noise and heat on structures. Special test rigs and
techniques are required and the results of all the tests must be
integrated. Here Kingston, with its small, closely knit
teams, was at
an advantage. Systems and specimen testing also plays a part. Reaction
controls, flying controls, hydraulics, structures, avionics, cockpits
etc etc must be rig tested to support development, certification and
production quality control.
Turning to flight testing Mike
pointed out that the P.1127 and Kestrel flight tests proved the
concept, not just the vehicle. Dunsfold was where V/STOL became an
everyday event. There things could be regularly seen that other
organisations had been trying for years to achieve. Another very
important flight test programme had been the VAAC Harrier. To overcome
the Harrier problem of having three pilot's hand operated flight
controls (stick, throttle and nozzle lever) which gave different
results in V/STOL and conventional flight, and only two pilot's hands,
which inevitably led to occasional confusion and accidents, the RAE
pushed for a simpler arrangement applicable to more complex ASTOVL
DB Harrier T2 XW175
was fitted with an adjustable
digital flight control system in the front cockpit with the
conventional system retained in the rear for a safety pilot. Over 23
years of flight testing, simulating numerous control concepts, the
inceptor strategy was defined. Here there are but two pilot's hand
controls or inceptors; stick and throttle. No matter which flight
regime you are in, pulling the stick back makes you go up, pushing it
forward, down. This British system is in the F-35B and will allow any
current military pilot to fly the aircraft easily. In fact, a PPL
holder has flown the VAAC Harrier from VTO to VL with no practice. This
system ensured UK participation in the F-35 programme and will bring
£100 bn of business to this country.
Some lessons from
studying V/STOL testing are clear: the experience gained is sometimes
worth more than the results and this experience resides in the people;
empirical testing is essential for V/STOL because of the chaotic flows
which cannot be modelled accurately on a computer. The importance of
testing is often not understood outside the industry; 'design' may be
glamorous but testing is vital.