Marc Arnold

Mountainous terrain is welcomed by a soaring pilot in search of lift. Valleys heat unevenly as the sun hits different sides of canyons throughout the day. Gentle breezes over complex topography dislodge heated bubbles of air to kick off thermals. Stronger wind flows up the face of inclined terrain generating ridge lift. And the smooth flow of wave lift can be found high over mountains where air resembles the laminar flow of water over a boulder in a stream.

The sport of cross country soaring instills a valuable discipline of thinking about alternatives. In spite of all the positive indicators, I was sinking through 10,000 foot MSL as I approached the 9,000 foot high terrain ahead. If lift was not found, I would fall back on Plan B: Gliding back to Big Piney. At 50:1, the Stemme can glide more than 7.5 NM per 1,000 feet in still air. Given my proximity to Big Piney, there was still enough altitude to make it back. And, of course, starting the Stemme's Limbach engine was the third alternative. Fortunately, Plan A worked.

A band of violent lift flexed the wings upward as my flight path passed just 300 feet above and south of the vertical face of a 1000 foot high cliff. The shaft of lift coming off the face was narrow. Each circle was marked by violent transitions between light and very strong lift. The HUDIS computer indicated an average lift of 7.8 knots (780 feet per minute), but the instantaneous readouts varied from 3 to over 15 knots. Passing in and out of the strongest lift was like riding a bucking bronco. Before long, the digital head up display read 16,000 feet and Jackson Valley spread out before me.

The cliff proved to be a good omen. The strong lift over the hills bordering the east side of the valley were perfect for "dolphin flight". By pulling up to go slow in the areas of lift and pushing the nose down to go fast in areas of sink, high speed can be accomplished in a straight line. Based on the strength and prevalence of lift in the area, I entered a high MacCready number into the glide computer. Thirty miles zipped by in half as many minutes as I followed the aggressive nose down commands displayed by the glide computer.

Straight dolphin flight offers a good opportunity to take care of housekeeping chores. First, I contacted Jackson Hole to provide a position report and check on the weather along the route. Next came a timely use of the urinal. Then a snack of food followed by a deep draught of water. Rehydrated and refreshed, it felt like the start of a new flight.

The cumulus clouds gave way to blue sky and smooth air over Yellowstone National Park. With lift or signs of lift for twenty miles ahead, I turned the MacCready number to zero and followed the slower speed commands to optimize the glide for distance (at the expense of speed). It was now more important to conserve my altitude and arrive at the next area of lift with the most altitude possible.

For many pilots, much of the joy offered by flying stems from the opportunity to exercise their judgment in varying circumstances. For the VFR pilot, accurate flight planning and execution offers its rewards. For the IFR pilot, a sense of accomplishment comes from shooting a precision approach to minimums in actual conditions. For a sailplane pilot, each mile of a two hundred mile flight is a triumph!

Barring mechanical failure or unforecast weather deterioration, the pilot of a powered plane progresses from Point A to B with little call on his judgment. Cross country soaring, on the other hand, is a continuous challenge to the pilot's judgment: Is that wisp of a cloud 5 miles straight ahead likely to develop into lift by the time I get there, or should I divert to the cloud off course to the right which clearly marks lift now, but which is past its prime and may only have sink by the time I get there? Should I take the time to pick my way around the perimeter of the blue "hole" ahead where there isn't likely to be lift, or do I have enough altitude to go straight across and find lift on the other side?

How the soaring pilot answers the myriad judgment questions determines the outcome of the flight. To put this in perspective, a world class sailplane pilot racing during a typical four hour flight makes a decision critical to his success every ten seconds.

Now approaching Yellowstone Lake, I was now confronted by a typical judgment question. The minor bumps on the south side of the lake showed little evidence of lift and my altitude was down to 2,000 AGL. There wouldn't be any lift over the cool surface of the lake ahead, yet an area of promising CU's lay on the far side of the lake. Is it wiser to use the altitude to glide across the lake, or use the altitude to search for lift on this side of the lake, then cross with ample reserve? I decided to exploit what lift could be found on this side before crossing the water.

Turning into the first thermal, it soon became apparent that it only offered enough lift to achieve zero sink. I searched for and found another, then another. But finding and centering each weak thermal cost altitude. After ten minutes, I'd lost 1,000 feet and was now trying to work a weak thermal over an open meadow. This is the pattern that leads to an "outlanding" in an unpowered sailplane. As altitude is lost, the search area is further constrained more and more by the necessity to stay in the proximity of a suitable landing site. A few more minutes, and the outcome became clear. I boxed in and wouldn't be soaring away from this field today.

Rather than just start the engine and fly away, I went through the process of setting up for an outlanding. This practice keeps me current in off-field landing technique and ensures a viable alternative in the unlikely event the engine fails to start. A close observation of the field revealed no hazards such as boulders or fences or power lines. The surface of the lake revealed the wind direction and velocity. Set up on final and ready to go through with the landing, I deployed the propeller and started the engine in five seconds.

Only six minutes of climbing under power northwest and I was back in a solid 4 KT thermal climbing in sight of Old Faithful. Back up to 12,000 feet, I turned northeast and dashed into the mountains of Yellowstone. Flying around the summit of a peak, I traded waves with a Park Ranger staffing a lookout station. There was good lift over the peak so he had the pleasure of watching me circle many times as I gained a thousand feet and set off to the next peak.

For the remaining 30 NM to Bozeman, the lift was widespread. The eagles were up in numbers and they marked the better thermals for me. I hopped from one gaggle of eagles to the next, marveling at their superior skill in finding the strongest core of the thermal. Sharing thermals with eagles is surely the best way to view Yellowstone National Park, a vantage point rarely seen.

Five and a half hours after leaving Rock Springs, I was cleared to land at Bozeman, Montana after an arriving Challenger. We both taxied to Sunbird aviation where a sociable Bar-B-Q was in progress. Newly found soaring friends graciously opened their home to me where I spent the night.

7/16/94 Bozeman, MT

After ridge soaring with my new friends in the morning, my bags were packed once again and I was aloft once again in a northwesterly direction, this time to my northernmost destination, Kalispell, Montana. I shut the motor down about 10 minutes into the flight, just east of Three Forks. The early morning thermals were very weak and it was difficult to hold my altitude. Once again, my search area had narrowed to a small area within gliding distance to an open field. It looked like a repeat of my experience the previous day and I began to think an engine restart would be necessary.

It was south facing ridge line with green pastures forming a patchwork quilt below. My shadow passed a farmer pulling a hay wagon. He pulled his tractor over to the side of the road and waved. Only a few hundred feet away it was easy to see him and I waved back. He climbed up onto the hay, took out what seemed to be a lunch, and sat watching me circle low over the field. Evidently, he was interested in my search for lift. My broad looping circles took me over each of the objects which might "trigger" a thermal -- a small shed, the bare rock at the summit of a small hill, the paved road -- Anything which might radiate more heat than the surrounding terrain.

Visualize the triggering of thermals by imagining droplets of water hanging from the ceiling of a damp basement. If you reach up and touch one droplet, not only does it run down your finger, but many nearby droplets run to the point of your finger and follow the first droplet. Now turn that image upside-down and picture a layer of air a few hundred feet thick heated by warm ground. The warmer air is ready to break loose and rise in many places, but it takes one particular spot to trigger the start. Experienced glider pilots in search of a low "save" pass over potential trigger points. Once the bubble breaks loose, other warm air flows in and up the same path, just like the droplets of water down your arm.

Then, I felt a significant bump and focused my full attention on centering this little thermal. It would be my last chance before starting the motor. Where did this particular thermal come from? I couldn't be sure which of the likely candidates was responsible. Nonetheless, I doggedly stayed with it and found it grew stronger as my altitude increased. Having attached myself to this bubble of air, we drifted together along the ridge line. Constantly turning, the bank angle of 30° and airspeed of 45 Kias remained nearly constant. Each revolution, however, wasn't symmetrical. Small adjustments of bank angle during each rotation moved the center of the circle small but critical amounts. These minute adjustments exploit the thermal and extract the most kinetic energy possessed by the bubble of air. At 12,000 feet, I made one last turn and saw the farmer's tiny vehicle where he'd pulled over. It's nice having an audience.

Negative 10° flaps and 110 kts across the next valley. Cumulus clouds were forming ahead over higher terrain. There was strong lift under the clouds. Climbing at 1,000 fpm, it only took a few turns before I approached cloud base, then headed on course.

The strong lift of my previous thermals and the nearby large runways at Helena International gave me confidence. I passed several good thermals and continued abeam the airport getting lower over the mountains south of airport. My thinking was that the northerly winds would flow against the hills and kick up thermals, but I was wrong. There was only sink.

Only ten minutes earlier I optimistically passed useable lift. Now I was scratching for any lift I could find, no matter how weak. Ultimately, I started the motor and headed north in search of lift. After four minutes, I pulled up and centered a very weak thermal at less than 1,000 feet. Once established in a climb, I shut down the motor.

[continued]