This story is about my Diamond Distance flight from Sunspot near Alamogordo, NM to Alamosa, CO in a Nimbus 2C sailplane. Perhaps this narrative will give the reader a sense of the techniques and decision-making that goes into a cross country glider flight. There's nothing special about this flight - many pilots have gone farther and faster in lower performance gliders. The photo shows a plot of the flight log on a Sectional Chart. Cool colors mean the glider was losing altitude and warm colors mean it was gaining altitude.
Glider pilots can achieve recognition through the FAI badge program. The FAI Diamond Badge involves 3 required elements: Diamond Altitude is a 5,000-meter (16,404-foot) altitude gain above an in-flight low point, Diamond Goal is a 300-km (186.42-mile) cross country flight using a pre-declared Out and Return or Triangle course, and Diamond Distance is a 500-km (310.7-mile) cross country flight.
The last day of the White Sands Soaring Fiesta looked like it would provide good soaring weather for a straight out distance flight with a landing somewhere to the north. My crew, John Held and I had to drive back to Colorado, so we decided I would fly as far north as possible before landing. John would pick me up and we'd trailer the glider the rest of the way. We would stay in touch by radio. There would be scores of gliders over New Mexico, so we could ask them to relay messages if needed.
With the Nimbus 2C loaded with water ballast, the tow plane struggled off the runway at ALG. I released over the Sacramento Mountains near Sunspot, NM, solar telescope tower in a 500fpm thermal which took me to nearly 12,500 feet. My 1:40pm start was very late for a long cross country flight. Wary of the cloudless conditions, I glided north to Cloudcroft, NM at the best L/D airspeed of 65 kts. keeping both White Sands Regional and Carizozo Municipal within easy glide range. The conditions were marginal for starting cross country but I pressed on, making slow progress in the 2-300 fpm thermals.
Slowly and carefully working weak thermals took me north past Sierra Blanca Peak and the old ghost town of White Oaks made famous by Billy the Kid’s exploits. By 3:15pm, I was 85 nautical miles out, still under blue skies near the dirt strip at Lincoln Station, NM. There a 500 fpm thermal boosted me to 14,600 and high based Cu’s began appearing to the northwest. A wind shift announced that I had crossed an invisible airmass boundary between weak conditions in the Tularosa Basin to the south and the much stronger conditions over the high plains of central New Mexico. Up to this point, John had no trouble keeping up with me on the highway below.
All glider pilots flying cross country have some method for calculating the best airspeed to fly between thermals using a formula developed by Dr. Paul MacCready. The pilot must estimate the strength of future thermals and enter this into the glide computer as the "M" number. The higher the M number, the faster you glide. Changing the "M" setting in response to changing weather conditions is called "shifting gears". Since this is a SWAG at best, conservative pilots tend to set their glide computers for about half the expected thermal strength.
Setting my glide computer to expect 300 fpm thermals, I sped NW for the clouds. The thermal under the first cloud was 1200fpm so I up-shifted to M = 600. I reached 17,800 feet south of Estancia, NM and the flight hit full stride. My main concern now was that a strong thermal would bump me above 18,000 feet and ruin the flight with an airspace violation. I left 1000fpm thermals at 17,000 to provide a vertical cushion. Even so, my glide radius included most of central New Mexico.
For the next 2 hours the cycle of climb and glide hit a rhythm with the average ground speed near 115 kts helped by a 12 kt SW wind. The glides between thermals averaged 45nm, some as fast as 153Kts at a glide ratio of 148:1. The flight took me east of Albuquerque and to the Sangre de Christo mountain range east of Santa Fe. I was flying as fast as possible to make up time lost getting out of the Tularosa Basin. John fell far behind until we lost radio contact.
Reaching Taos, NM at 5:22, I could see an E-W line of rain showers between Taos and Questa, NM that marked a second airmass boundary. Sunlight was on the ground north of the showers so I cautiously pressed on as conditions were weaker.
Mosca Pass in Colorado proved to be the furthest northern progress I could make. Farther north in the the San Luis Valley condi looked grim with lightning and dust rings on the ground from microbursts. The Wet Mountain Valley east of Mosca Pass didn't look inviting either. Emergency landing options were sparse for the next 50 miles. At 6:28pm sunset was near and it was time to pick a landing spot.
Several airports including PUB (Pueblo, CO) were within reach but the rules allowed a loss of only 1000 meters between release and landing altitudes so landing at a low elevation airport could mean a distance penalty. I radioed a glider pilot near Taos asking him to relay a message to John to expect a landing 32 miles to my SW at Alamosa, Elev. 7539'. Within a minute, the pilot radioed that John was making his way through Taos and knew where I would land. Ten minutes out, I opened the ballast dump valves to get the glider down to its landing weight. Commuter and corporate turbine traffic were arriving and departing ALS so, not wishing to get in the way, I orbited for 15 minutes waiting for the CTAF to go quiet. After landing and pushing the Nimbus off the runway, a GPS check told the story - 318 miles was good for the Diamond distance. The flight had lasted five and a half hours.
A pair of commuter pilots weren't quite ready to believe my story until John drove onto the ramp at 8:15 to confirm it. We put glider in the trailer, grabbed dinner at a local restaurant and resumed the trek north by road. What a great way to spend a 4th of July weekend.
Next time, more about sailplane avionics.