Newsletter 24
Summer 2009
Updated on 20May2009
Published by the Hawker Association
for the Members.
Contents Hawker Association

Cygnet News
F-35B Lightning II News
Folland Spirit Of Hamble
Harrier News
Hawk News
Hawkers In The 1950s
Hawkers in The Late 1930s
Hurricane News
R&D Department
Tempest News
Testing V/STOL Projects
World War 2 Experiences
    On 11 February Dr Michael Pryce 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.
    By 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.
    For his 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 work.
Testing V/STOL Projects

    In his work with Kingston and Warton people he determined that the 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 proved by 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 current 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.
    In sub-scale model testing the understanding of scaling is critical to the development of  'fudge factors' relating model results to real world 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.
    A test 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 tunnel 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 propulsion concepts.
    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.