Soaring in the Atmosphere
In keeping with the idea of my blogs remaining more neutral in tone, I have excerpted parts of a Term Paper from 1992 in Meteorology 302 San Francisco State University.
The topic was how soaring pilots use atmospheric conditions to get high and stay high. Courses are laid out on maps for contests, and the fastest around the turn points wins.
Records are also set for the highest altitude gains, and long distance flights.
The space shuttle had a glide ratio of 4-1. That is, for every four feet of travel forward there will be a drop of one foot.
Some high performance sailplanes have a glide ratio of 45-1 or better. I have not kept up with any improvements in sailplane technology, but all flights now are plotted with GPS instruments.
Since the object of soaring pilots is to get as high as possible the thermals are used to obtain seven hours of flying on a hot desert summer’s day.
Here are some examples of lift that are found in the Southern California desert where I did the majority of my real soaring.
Thermals are simply bubbles of rising air that are warmer than the surrounding air. Since the nature of the soil, presence of trees, and water courses and existence of large parking lots can all determine the uneven heating rate of the ground, good pilots develop an inventory of most likely thermal locations.
A soaring contest is held so that all planes are launched during the midafternoon when there is an optimum chance of encountering developing thermals. When there is only one nearby, all the pilots congregate there, flying in the same direction. This is known as a gaggle.
In the Antelope Valley in past decades thermals have been known to “top out” routinely at 16,000 to 18,000 feet which is the legal operating limit for motorless flight, or aircraft without transponders.
The recent development of the cities of Victorville, Palmdale and Lancaster has produced a lot of air pollution that old timers blame on the repression of boomer thermals. There is a noticeable inversion of brown air over these towns until the four o’clock west wind scours the basin.
When the cooler marine air flows through the mountain gap at El Cajon Pass there is a convergence, producing lift that is quite well marked by the moisture and smog from Los Angeles.
Smoke from the boron mine and cement factory near Quartz Hill can also be used as a wind indicator by pilots who are too high to see airport windsocks.
Another convergence favored by pilots is located in Elsinore, and was used extensively by both hang glider pilots and soaring pilots in the 1970’s. The flying activities have been moved out now due to population growth.
On the coast line near the University of California San Diego it has been traditional to use sea breeze ridge lift at Torrey Pines. This is localized lift, so the flight pattern of hang gliders and remote control model airplanes is simply to fly back and forth parallel to the beach, always careful to make turns away from the ridge.
For real big time sustained lift pilots depend on the winter wave showing up during February or March in the Antelope Valley. This is where everyone from student pilots to old pros can get a chance to earn badges.
When a large stable air mass moves over the mountain ranges the air is deflected upwards. This upward flow is smooth and steady, but the trick is to balance the speed and sink rate of the plane against the speed of the upward deflection. There are optimum points and danger zones. If the pilot miscalculates and cannot find the best rate of lift- usually in the front of the mountain crest, and gets into the rotor zone, he can sustain a bit of damage or worse. The sink is correspondingly strong, and can pose a problem if the airport is any distance away.
I personally flew a Cessna 150 through a rotor zone before edging out of it to safety.
When Bob Harris made his record breaking wave flight to 49,000 feet over Inyokern, he had to fly against the wind with full spoilers to get down. His angle of descent was practically vertical. Luckily the airport was underneath him at that location; otherwise it would have been an out-landing in the desert scrub.
My connection to this flight was in the capacity of “line boy” hooking up the tow line and clearing for traffic. I think my finger prints were frozen into the underside of the wing tip at 49,000 feet where the outside temperature was surely a minus 30 degrees F.
This flight was the new absolute altitude record for sailplanes and has been entered in the Guinness Book of Records, published in 1992.
End of Part One.