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Aviation History
1951
1951 - 2241.PDF
The Air 100, an advanced French design which impressed the Royal Air Force party very favourably. The Arsenal 4111, a French experimental all-metal sailplane equipped with oxygen, heating and heated pitot-head. SEEKING St. AUBAN'S STANDING WAVE . . . north and south. The outstanding features of the whole area are the Lure Mountain and the Penitents Slope. The Lure is a slightly concave ridge facing north-west on the west side of the valley, the top being approximately 3j6ooft above the valley floor. The Penitents Slope (it would rank as a mountain in England) also faces north-west, but is situated on the eastern side of the valley; the top is 1,300ft above the valley floor. The airfield is situated about in the centre of the valley, six miles from the Lure Mountain and ii from the Penitents. Except for the Durance River, most of tie valley is broken ground covered with scrub. From the gliding point of view an item of further interest is a large factory adjoining the airfield, which, apart from manufacturing chlorine, produces, also, very good if somewhat smelly thermals ! The airfield has a maximum length in the direction of the pre- vailing wind of 1,200 yd, and is all grass. There are three per- manent hangars, and domestic and administrative buildings, which, whilst far from luxurious, are adequate. Aircraft equipment consists of 35 gliders and sailplanes, mostly of high or medium performance, and all capable of extended soar- ing flights. All high-performance sailplanes are fitted with oxygen equipment, and two with special forms of cockpit healing. Tugs are three Fieseler Storch aircraft (Morane-Saulnier-built) and, in addition, there is an assortment of small powered aircraft used by the instructors and for communication purposes. M.T. consists of seven vehicles of various sizes, and two winches. Last year the Centre completed 5,100 hr of motorless flying with this equipment, having taken in 20 courses of 25 pupils each, and given each pupil between 10 and 12 hours' flying, including dual. By the time a pupil has completed the course he is likely to have done about 50 to 100 hours and, if necessary, would be capable of proceeding, with very little additional instruction, to advanced flying training on military aircraft. The outstanding point about St. Auban is that it is in the direct track of the Mistral, the strong, stable wind that blows down the Rhone Valley. It is most often associated with an anticyclone over the Atlantic and another over Russia, causing a northerly flow over France of cold, stable air, which is apparently funnelled by the Rhone and subsidiary valleys in to the east, most of which also run north and south. When the Mistral is from the north, good lift occurs on the Penitents Slope up to a height of 3,000ft— that is, up to three times the height of the slope, as is normal. We found that under northerly wind conditions the Lure Moun- tain produced practically no lift, because its concave ridge faces north-west. In the same circumstances, the valley itself produced a strange mixture of rapidly alternating lift and sink in such a way that experienced pilots could stay apparently indefinitely at 3,000ft over the middle of the valley, facing into wind. This was no doubt due to the fact that the valley suddenly narrows a few miles north of St. Auban. We found that the wave-producing Mistral has to blow from the north-west; that is to say, normal to the concave Lure ridge, and this happens comparatively rarely. For the Mistral to blow from •.his direction with any speed, there would normally have to be an anticyclone off Portugal, a depression over Norway and a secondary depression over the Gulf of Genoa. Under these conditions, the air is then triggered into a wave by the Lure Mountain and eddies from it produce a marked roller cloud immediately to leeward. When this occurs, the lift on the Penitents Slope, which is seven and a half miles away downwind, remains unaffected except at a great height. There have been many occasions when inexperi- enced glider pilots have used the slope lift to the best advantage and have reached sufficient height to penetrate the wave. One such case occurred whilst we were there, and an 18-year-old pilot reached more than 12,000ft on a day when there was thought to be no wave. We were told that on other occasions, when a strong north-west wind has been blowing, there has been no wave effect on the mountain but a complete wave covering the slope, so that pilots over that slope have found themselves in the wave without effort. However, the heights obtained in this way have in no way compared with those attained in the Lure Wave. The conditions of flying in the wave were identical with those experienced in Germany, and exactly the same as reported experi- ences of flying in the Helm Wind and the Long Mynd wave in this country. On approaching the wave, violent turbulence was experi- enced which stopped completely when the glider came fully under the influence of the wave and began to ascend. As long as one remained in the wave, the air was very smooth and produced the strange humming or singing noise which has been reported of all waves. The following account of a flight in the wave, by a U/T. pilot member of the expedition, with a French instructor, M. Lafargue, gives an excellent idea of conditions. (The member in question, not a qualified power pilot, had 1 hr 30 min dual gliding and 9i min solo in his logbook.) Personal Experience The met. experts (he writes) had predicted wave conditions for the forenoon, but no pilot had been fortunate enough to find any- thing except very rough air. Lenticular clouds were visible through- out the day, but gradually faded, and none existed at the time of take-off. Cu-nim clouds stretched across the sky westwards of the airfield, and my instructor, pointing to the heaviest concentration of them towards the north-west, prophesied a storm. Our aircraft was a C.800 two-seater, in which pupil and pilot sit in echelon, the former on the port side, about two feet forward of the instructor. The arrangement is admirable, since the instructor remains out of the pupil's vision unless the latter looks sharply right, while the former can observe and discuss everything with ease. In my case instruction was given in French, generally within the limits of my comprehension, though sometimes gesticu- lation supplied gaps. The flight started with an aero-tow given by one of the hard- worked Fieseler Storchs. It was my second aero-tow, and the first on which I took control from the beginning. We wobbled our way up in a strong, gusty wind, the sailplane generally anywhere but in the correct position to the tow. My instructor occasionally advised me—"More up, my friend," or "More down if you like"— until, fed up by being banged about for eleven minutes, he took over. The difference was not so marked as I had hoped, nor was he able, as was the case in a previous flight, to place the sail- plane at exactly the position he wished. It was, in fact, as he said, a very bad day for flying and, since conditions seemed to be worsen- ing he decided at 1,300 metres to cast off. In less than ten seconds later all turbulence ceased. We had reached a standing wave. I took over again in conditions of absolute calm; the aircraft was flying towards the north-west and we rose rapidly, then moved slightly backwards over the ground. Occasionally a vibration made (Extreme left) St. Auban's chief met. officer discusses die day's weather with M. Caudry (in beret), the C.F.I. A Morane of 1926 vintage, still fully serviceable and occasionally used for towing gliders. Standing smartly at attention is W/C. Ingle, one of the R.A.F. party.
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