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Aviation History
1976
1976 - 0224.PDF
302 Private MB" cumuli similar to those seen in Europe, the air rising up the higher sun-heated mountain faces seems to be warm enough to continue rising in spite of heat losses due to expansion as the pressure reduces. The explora tion of these anabatic currents promises to be one of the most in teresting features of the expedition. What goes up must however even tually come down, and the comple mentary currents, the very strong To soar the Himalayas ... A preview of Dr Brennig James's Himalayan gliding expedition by David Kent. To soar along the South Face of Annapurna and climb to its 26,490ft summit in the air rising from sun-heated rock—these are among the compelling objectives which have led Dr Brennig James to plan this month's gliding expedition to the Himalayas. An attempt in 1960 failed before it began when the sponsoring publica tion went out of business. This time Dr James will be independent of out side financing. He will in his own words "go for broke for two years" unless, as seems likely, some return can be obtained from sponsorship and a television film. The expedition's glider, a Motor Cirrus (see Flight, July 31, 1975), and a comprehensive assortment of tools and maintenance materials were de livered by road to Nepal at a cost of some £300 in petrol. The aircraft will be given a thorough check by David Kent, the expedition's second pilot and engineer. First flights will take place in the triangle between the base at Pokhara and the east-west Annapurna ridge lying 35 miles to the north. It is expected that the flight pattern will not change much during the early stages. After take-off from Pokhara airstrip, elevation 2,900ft, the aircraft will be motored to the height at which late-morning thermals can be en countered. Then, once the Motor Cir rus is established in lift, its engine will be switched off and retracted. The glider will then be soared up to inver sion level—usually found at about 12,000ft—and thermal-hopped north wards until it reaches the steeper south-facing rock slopes of the Anna purna complex. Unusual soaring conditions During a non-flying reconnaissance visit in 1974 Dr James discovered fierce winds blowing anabatically up the sun-heated cliffs. These apparently continue upwards through the inver sion level, located about halfway up the higher mountains, to form what he terms "anomalous cumuli" several hundred feet above their peaks. Thus, while the main free thermals con dense out at inversion level to form winds which blow down the valleys, are well known to Himalayan moun taineers. The very size of the mountains and valleys poses interesting problems for the glider pilot, with strong winds blowing from different directions at different levels in the same valley. Height can be lost unexpectedly in such conditions but the downward velocity components of these air- streams inevitably decrease near the ground, which slopes down towards Pokhara at an average gradient of almost 1 in 10. With a gliding angle of around 35:1, the aircraft will hope fully be able to take itself out of trouble even if there are problems in starting the engine. This is an impor tant consideration as there is hardly any level ground suitable for landings away from home, and even the steeper earth-clad slopes are terraced with paddy fields, some of them as little as 2ft wide. Few maps available Very few detailed maps of Nepal are available, but with the aid of photographs taken by the Herzog and Bonington climbing expeditions (which tackled Annapurna from the north and south respectively) a useful picture of the ridge can be built up. It is believed that the prevailing wind blows from the west at about lOkt (but possibly varying from calm to lOOkt), not very conducive to ridge or wave soaring off the main east-west ridge. Fortunately there are three spurs running southwards and enclos ing two glacial cols, and the orographic lift produced by these features, to gether with thermal lift on the near- vertical faces of the ridge, should pro vide a satisfactory climb. The un- climbed 22,900ft peak of Machha- puchare on the centre spur also makes a fine soaring objective. Conditions are expected to vary con siderably. On calm, cool days it is often necessary to fly with a wingtip only 30ft from the cliff face in order to climb in the thin layer of air mov ing up the mountain. With a strong wind blowing on to the ridge, by con trast, it is possible to climb by simply circling in a col. FLIGHT International, 7 February 1976 There may be an even more dramatic source of lift. The high- altitude Jetstream blows relatively close to the Himalayan peaks. Some meteorologists have suggested that it blows directly along the Annapurna ridge, first passing over the huge 26,800ft bulk of Dhaulagiri, then across the deepest valley in the world, the 12,000ft cleft between Dhaulagiri and Annapurna. Given the right lapse- rate conditions, this wind could generate a system of standing waves which would carry a glider well above 40,000ft. The severe turbulence asso ciated with the rotor of a similar wave system in the American Sierra Nevada has been known to cause structural failure, however, and it will be necessary to tread cautiously in such conditions (see Flight, Feb ruary 2, 1975). Both of the expedition pilots have previously flown among mountains, but even the writer's thermal climb in front of the Matterhorn is small beer in comparison with the oppor tunities presented by the Himalayas. There will be much to learn among the 25,000ft peaks. One dangerous characteristic of the area which emerged from the mountaineers' photographs is the formation of com plete cloud cover south of the Anna- Dr Brennig James at Wycombe Air Park in the Motor Cirrus on the eye of its departure by road for Nepal. The aircraft and its re tractable Hirth two-stroke engine were des cribed in "Flight" for July 31, 1975 purna ridge at the 12,000-14,000ft inversion level. A glider pilot soaring high on the mountain could easily find himself cut off above this cloud and having no alternative but to glide by dead reckoning to a point above the Pokhara valley, where, after a radio call to the airstrip tower to check cloudbase, he could let down on instruments. Nepal is a benign monarchy in which permission is required for travel between administrative areas. Permission is being obtained initially for the expedition to operate between Pokhara and the Annapurna ridge. If the weather is favourable and the early flying in this area successful, it may be possible to move the area of operations westwards towards Everest.
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