| Nugget90 |
15th Apr 2018 16:02 |
BLEU in the 1970s
My last flying tour in the RAF, having been on Hastings, Hercules and VC10s beforehand, was to be with the BLEU Flight at RAE Bedford where between 1975 and 77 our main trials workhorses were HS748 XW 750 and BAC 1-11 XX 105.
Whilst 'Fog Flying' with the HS748 was the activity most commonly associated with BLEU, in fact there were several other activities connected with approach and landing performance that kept us occupied. As Fog Flying required extremely low Runway Visual Ranges to meet the requirements of the boffins on clear days we used an in-house developed 'Fog Blind' that, located in the left hand windscreen area, obscured the forward vision of the pilot in that seat (P1). Stabilised in pitch and roll, it 'opened up' a visual segment as programmed by the on-board BLEU scientists who then recorded how the pilot and the aircraft responded as the external visual cues became progressively evident. However, when very low visibilities existed we would get airborne and make a succession of autopilot approaches with P1 deciding whether or not to land, whilst P2 remained head down throughout monitoring deviations from the ILS. The pilots changed over after three approaches as P1 would have started to become familiar with the cues visible over the threshold. We didn't stop between approaches but carried out 'touch and goes': in thick fog all you can see is the 'streaming' of white lights as they pass under the nose. With P1 making sure that the aircraft stayed on the centreline P2 carried out all the internal changes of configuration and all on board trusting that the aircraft would get airborne again before we ran out of runway!. I should add that the on-board scientists might (or might not) cause P1's ILS localiser indicator to be off-set left or right of the true course so that as P1 saw the external cues he had to decide whether or not he might safely make an 'S' turn to align the aircraft with the runway centreline. P2 saw only the correct, unbiased localiser and glide slope indications. All manoeuvres were recorded on board as well as by the Bedford team of ladies who operated the highly accurate ground-based kinetheodolites, helping to develop standards for ground and aircraft equipment. It was all quite exciting, really.
Together with the BAC 1-11 we conducted Two Segment and Steep Approaches trialling autopilot laws that would deliver a smooth initiation of the upper glide slope, transition to 'normal' ILS guidance, and flares together with developing optimal external guidance to assist the pilot handling to execute a smooth roundout and touchdown and associated noise footprints. One of the aids we used was a set of four boxes, each of which emitted red and white beams divided precisely - the forerunner of what became PAPIs, Precision Approach Path Indicators, that ICAO were later to agree could be chosen as an alternative to VASIs. The aviation Press were shown PAPIs when we demonstrated the capabilities of a Mk 1 Ground Proximity Warning System at Bedford: whilst the 'level flight towards rising terrain' mode was carried out over the Malvern Hills, the remaining modes were demonstrated at our airfield where the PAPIs (that our man on the ground set to different slide path angles as needed) provided helpful positional and steep approach slope guidance. The Press were in fact more interested in PAPIs than in GPWS! It was whilst subsequently when I was serving in MoD that I learnt that funds targeted for the introduction of Tornados would not be spent before the end of that particular financial year and persuaded my bosses to sponsor industry to produce some sets for use at two RAF airfields where stabilised approaches would be of benefit. The success of this experiment encouraged the manufacturer to continue building PAPIs and now, of course, they may be encountered at many if not most aerodromes in the world that serve international air traffic. Much of the credit goes to those scientists at Bedford who saw the potential for this research aid to benefit both civil and military operations.
Much more went on at BLEU whilst I was there with the two aeroplanes I have mentioned, plus a Wessex 2 (for Microwave Digital Guidance Equipment trials) and the ex Radar Research Establishment Varsity WF 379 that we used for communications flying. And of course we helped our colleagues in Aero Flight when they needed a second pilot to sit in any of the miscellaneous aircraft they rejoiced in flying such as VC10, Puma, HS125, etc.
One last comment. Alongside the main runway at Bedford there was a device for measuring RVR by the conventional means of having a beam of energy directed at a sensor that would detect any loss due to intervening moisture etc. Strangely, there were occasions when in the morning when the Met staff went to retrieve the recorded data they would find that the readings had dropped suddenly to zero visibility whilst there was no other evidence that fog had occurred. One night they kept the device under close observation and saw, to their surprise, that a little owl had landed on the transmitting element and snuggled himself in - to keep warm!
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