A story about out-of-the-ordinary and dangerous flying conditions

Local pilots called it the hill going laminar. The event does not happen very often. When it did happen, a crowning plus was added to the list of pros and cons that sets hill site clubs slightly aside from the mainstream of gliding.

I suppose this club was much the same as the rest of the very few hill clubs in existence. Probably, from a piloting point of view, the environment could be more exacting in certain conditions. For a flat site pilot - it would be alien in any conditions.

The small airfield was perched 800' (267 m) above the valley floor, on the inside corner of an L shape where west and south facing ridges met. Prevailing winds against these slopes forced air upwards, enabling gliders to soar for as long as the wind blew. The view was spectacular, but often the place was cold and draughty.

When the soaring winds blew, landing approaches were made directly through the curl-over. Final turns of over 700' (213 m) above site became the order of the day over the down wind boundary, and often required 1000' (304 m) - about the length (or less) of the available landing area. Approach speed calculations frequently stopped at maximum rough air speed, and pilots hoped that would be speed enough. Flying in the hills is demanding, requiring knowledge and skills seldom found elsewhere.

Pupils do not soon fly solo at sites such as this. Even when solo, it may be many months before a pilot was checked out in certain wind directions and strengths. This reflected on the summer commercial course season.

There was a deliberate trade-off between the natural beauty of the place and flight difficulties. The holiday courses were more of a stimulating and different holiday than any planned progression of flying skills towards an objective.

Six months of passenger flying would be just tedium for a full time instructor and, I believe, the resident instructor each year did teach the course members to fly. Even if, as in my own case, there was a pressing and private self-justification.

When the hill went laminar again for me it was upon a Friday at the end of an unsatisfactory week. Most of the flying had been in and out of 400' (120 m) cloudbases, loitering over short stretches of ridge a couple of miles away, waiting for rain showers to clear the airfield so that a quick change of pupil could be made - then do it again - but always with the out-landing field sitting there on the valley floor so far below, as a lifeboat.

Certainly the course members had exclaimed "Ooh" and "Ahh" and "Isn't it great" but the views had not been spectacular at all - certainly not for a holidaymaker anyway.

This Friday was different. The sky had been clearing to blue during the day, while a steady 25 knot (46 km/hr) westerly wind blew. The ridge had been steadily working to 1300' (396 m) above site and visibility was 20 miles (32 km) or more.

I was getting some catching up done for people who were accustomed to looking at concrete and glass squares. Today, most of them sat in stunned awe, hovering above a wild grandeur they had only previously seen in pictures.

The final flight of the final course member began at around 4:30 p.m. The total endeavors of the winch driver and myself produced a 350' (106 m) launch. This was of no consequence. The glider only had to be flown forward to enter the band of ridge lift. The student did this and turned north, climbing. Meantime, I made my routine scan of the windsock below me, and then positively stared at it. The windsock was now drooping to an angle indicating that the ridge should no longer be producing lift. But the glider was continuing to climb.

An eerie feeling set in that gravity was being defied by means other than natural. This is a disquieting feeling the first time it is encountered, and is also a certain sign that the hill had 'gone laminar'.

The phenomenon always happened in a westerly, late in the day, and was usually accompanied by a reduction in surface wind speed at site level. Despite this, forecasting when the event may happen was never possible. One minute you might be gnawing bones in turbulent hill lift and fighting to stay up. A couple of minutes later Mother Nature would be taking you out for a free lunch. Like most unexpected free lunches the treat did not happen often. More such treats were always eagerly awaited.

Even though the air was smoothing around the glider, I double checked conditions by requesting the student to turn away from the ridge and fly out over the valley. The glider continued to ascend.

Passing 1800' (548 m) above site, a mile in front of the ridge face, I contemplated that this was the nearest man would come to anti-gravity. In real terms, the 'hill going laminar' meant that a light wave system was present, probably reinforced by gentle anabatic effects as the day went through the diurnal process. This produced a situation where the valley was now full of weak lift extending upwards, usually to 2500' (762 m) or so.

The glider would now climb until the rising air equaled the glider's sinking speed and then the machine would stay aloft. The glider could therefore be flown over a large distance, within reason, wherever the pilot chose.

Of such conditions are made the finest training conditions possible in a glider. So my attention rested upon my student in front of me. Long flows of light brown hair cascade over neck and shoulder straps, then disappear behind my instrument panel. On the other side of that head I know are wide grey eyes that on several evenings this week have sparkled into my own as their owner chatted.

At times, she has projected a curious mixture of images - the grace of a young gazelle combined with the exuberance of a child on an outing, and a seriousness of intent about flying. Alongside this, she had spoken of her impending marriage to the quiet, friendly guy who had dropped her off at the club last Sunday. She talked of their plans for an early family and the struggle to buy a country cottage.

I look beyond her now and think that there will be little money for gliding for some time. Perhaps this will be her last flight.

Thoughts of incipient spins and rudder co-ordination in steep turns fade from my mind. Instead, I tell her that the glider is hers for half an hour, take it where she will and look at anything which pleases her. As she coos with delight and begins to take us towards a greystone village a couple of miles away, I relax back in my seat and simply absorb the view of shadows deepening in steep hillside clefts, as the sun sinks further.

There are no pressures on a pilot when the hill goes laminar. Those routine, almost subconscious tasks of angles, distance from the airfield, potential outlanding paddocks and all the rest of it fade, leaving in their place a vacuum which allows only for total enjoyment of flight. An enjoyment which even a passenger with no responsibility cannot fully share for they lack the unifying fact of control between the machine and the environment that bridges reality to the senses and hence to the emotions.

Hands on or not, an instructor is always 'flying' the aircraft. So, when the first tremor comes, I should know its origin, but I do not.

The tremour is sub-sensory. There is no sound, not tangible vibration, but it is there and then fades. The second tremor is more apparent, probably magnified by the smoothness of the air..

Instruments provide no information that is not already known. The glider is flying at 37 knots (68 km/hr), topped out in zero sink 2300' (700 m) above airfield. We are heading north east and are half way to an interesting rock formation jutting from the top of a hill. A rapid scan of the sky, plus ground smoke sources, gives no indication of any airmass change. There are no clouds at all.

After fifteen minutes floating around in whipped cream air conditions and no apparent outside influences, my thoughts turn to the airframe. At this time there is no alarm, just aroused interest.

In this type of glider, the instructor sits well back in the fuselage, below the wings. For normal operations, this causes an irritating restriction of vision as large parts of the airframe block out the view. Now this becomes an advantage because it is the airframe that I want to look at and I can see a great deal of it from where I sit.

The undersurface of the wings and ailerons are studied, and are intact - not doing anything strange, and appear normal. I rest finger tips upon the aileron balance cable passing through the cockpit above my head - no sign of internal vibration.. The four wing attachment bolts and pins are in clear view and are as they should be. The lift struts and aileron drive cables that are routed up them also appear normal.

I take off my shoulder harness and loosen my seat belt, twisting around to look aft. We definitely still have a tail which appears functional! To cross-check again I lightly grasp the rudder cables passing down the side of the cockpit walls. This proves only that someone was over-eager with the grease on the last service - I wipe my hands on my overalls.

With a little contortion, it is possible to obtain a peripheral view down the inside of the fabric covered, steel tube framed, rear fuselage. There is no unusual amount of light down there to indicate a loose fabric patch or open inspection panel disturbed by the airflow.

The shaking is now noticeable enough for my young gazelle in the front cockpit to be taking less notice of the view and more of the aircraft. My interest turns to unease and I take control back from her with a casual comment intended to calm her.

Having direct control of the glider gives me no further information. We are placidly flying along in totally smooth air, but the glider is shaking and I cannot see any cause.

The upper surfaces of the wing cannot be seen, so I partially open the spoilers to establish any difference. No change. I open the spoilers fully, the glider descends and the shaking fades away. After 500' (152 m) of descent and a couple of turn reversals, I am satisfied that there is nothing wrong with the airframe. I close the spoilers, hand back control to the student and request her to complete her half hour. As I re-buckle my shoulder harness I dwell on Airforce stories of gremlins and feel annoyed.

Three minutes later, the shaking comes back and increases rapidly. I take control instantly. This time, I am alarmed and fear makes the first caressing stroke with its filthy fingers. The direct vision panels are chattering in their slides on the canopy walls, and my student has developed a distinct edge to her voice as she asks what is happening.

I do not know what is happening. The shaking changes into a hard vibration similar to driving a car rapidly over a cobblestoned street.

All at once, I have had enough. My student's future plans involve her arrival at a church to be for a wedding - not something else. I open the spoilers and turn the nose for home.

That unconscious workload has returned. I study angles and distance, but my concern is with time. I peer down at known out-landing paddocks to see if there are any sheep in them today - just in case time does become pressing.

The vibration has abruptly gone again and all is smooth. Remembrance, realisation and relief arrive simultaneously - Cobblestones! Just Cobblestones!

The brain is a fascinating device, Whilst it is humming along content that its owner is a highly responsible, efficient, experienced, and steely eyed ace of some alleged kind - it has also been leaning against a flying club bar a few years ago, listening to a conversation about boundary layers in wave.

I choose my next words carefully. 'That was interesting, was it not?'

'Was it?' Answered a small voice from the front seat.

'Certainly! Look - what happens when a breeze passes over a still area of water?'

'You get ripples.' An overtone in her voice indicates that she might be thinking that I have gone mad.

'OK! Now you see that smoke down there? That shows the direction of movement of the airmass we are flying in. But, today, there is a another layer of air above us going in a different direction, and probably at a different speed. Where the two layers meet you get ripples, just like the wind blowing over a pond. For reasons you now know, they call it Cobblestones. Let's go back up and feel that again.'

The beauty of the hill going laminar is you can do exactly that in a glider, more or less anywhere. You simply close the lift spoilers.

After a couple more contacts with the boundary layer my student is cooing again and wanting a go for herself. Over the next ten minutes I have time for some quiet thought, even though my teeth fillings are being vibrated loose at one minute intervals.

I ponder that when Mother Nature hands out a free lunch there may be a catch to remind one not to take it for granted. Experience always costs something, and today the coin I paid in was fear. But the currency was ignorance. A little knowledge is all that may stand between enjoyment and misery.

After we land, my pupil is scooped up by a quiet, friendly young guy who has turned up while we were flying. As they walk towards the club buildings I hear her chattering excitedly, waving one hand in slow undulations through the air while the other describes sharp little zig-zags. He just smiles and I do not think he cares much what she is describing. Having her there is sufficient for him.

Meanwhile, I have become the centre of a small crowd scene. Half a dozen club members have turned up early for the weekend. They are kindly offering to take care of the glider for me and put it away, while making it obvious that I will then owe them a favour. Their kindness does not match the ruthlessness with which they decide amongst themselves who will be having the first evening ride on the laminar hill.

They have fended off my opening remarks about current conditions. As their resident instructor for the season, I am of their kind, but I am not one of them - it is their club and I can tell them nothing. I note they are all experienced and keep my peace. I wonder if they have met Cobblestones before!

The Club Secretary walks up with the usual weekly course summary form for me to complete. 'How do you like the hill going laminar?' He enquires.

"As the Bard probably did not write - 'Tis a thing of beauty and wonderment,' I replied, 'But sometimes it can just be a Load of Cobblers!'

He looks puzzled as I take the form from him.

I turn for the clubhouse. I wish to say goodbye to some people who are getting ready to leave.

- Helix