Last month we discussed some of the things to look for in the environment that might give you an indication of where a thermal is. This month we will discuss how to recognize when your sailplane flies into what you are searching for, that area of lift. Since we are not in the saiIplane, unlike a pilot of a full-sized sailplane, we must rely on visual signals that the airplane relates. These signals require the pilot to watch his aircraft very closely for slight changes in attitude or small movements.
For these changes in the flight path of the aircraft to be visible it must be trimmed to fly in a steady state without the pilot having to continually make corrections. When I say properly trimmed, I'm refining to the airplane being able to fly straight and fat, without the nose bobbing up and down and no tendency to turn right or left. This requires that the center of gravity be at least near what the manufacturer has recommended and that the airframe is somewhat straight and true. Additionally, the control surfaces must be set so the sailplane will not be stalling or turning when the transmitter sticks are in the neutral position. I will assume that you have accomplished this already and your airplane can fly for a short period of time hands-off.
Probably the most obvious indication of lift occurs when you fly your sailplane into an extremely strong thermal causing it to rise quite visibly. These thermals are know as *Helen Keller* lift by some of our club members {ed. Graduates of the Ray Charles Soaring School!}. They usually are not very numerous in my experience and therefore it is necessary to look for other indications of lift being in the area of the aircraft. Also, beware when these areas of lift do occur there are generally areas of extremely strong sink nearby as well. When flying along in a steady straight flight path, sometimes your aircraft will suddenly roll violently in one direction or the other. What may have caused this to occur is that the wing that rises has touched the edge of a thermal. The rising air from the edge of the thermal has caused that wing panel to rise in relation to the other. In this instance you want to turn towards that high wing and possibly back down wind slightly, to account for your reaction time, to find the thermal
Sometimes when your sailplane is gliding along you may notice the tail rise as if the airplane was in a dive, but not speedup towards the ground. What probably caused the tail to rise was that the airplane flew into lift. When the airplane flew into the area of lift, that area was rising in relation to the air the airplane just left. Since the aircraft is naturally stable, the airplane is attempting to attain stable flight by pitching nose down, thus causing the tail to rise. The opposite of this effect also occurs when the sailplane flies into or is flying in an area of sink, the aircraft then appears to be flying tail down or dragging it's tail as some of us are prone to say {ed. actually it more like "dragging it's a*s"}.
One very subtle indication of lift that can occur is that the airplane will shake or wiggle slightly. This is probably caused by the airplane flying through the turbulence that is at the edge of the thermal. I have at times seen my airplane wiggle slightly, start circling and found the airplane in a thermal. Another very subtle indicator of lift occurs when your sailplane starts to yaw one direction or the other. If this appears to be persistent, then turn the sailplane towards the direction of the yaw. You may have to search around a little, but I've found many thermals this way and some have been quite large and strong. This effect requires that you can recognize when your sailplane has deviated from the flight path, on which you have directed it. Probably what causes this effect to occur is that the air around the thermal is being drawn into it, the vacuum cleaner analogy, therefore the sailplane is drawn towards the thermal as well.
The most subtle indication, of lift, that you may have heard some of your fellow fliers describe is when the air is said to be buoyant. This type of thermal is very difficult to recognize when your sailplane enters it. I can only describe it as though the sailplane just does not appear to be sinking as rapidly and seems to be lighter than a few seconds before. Sometimes these areas of lift are found very near to the ground and are quite often a thermal in its early stages of development. An area like this will sometimes grow into a very strong thermal. It may require patience and smooth flying to not fall out of such an area, but it is extremely exciting to climb out from a low altitude when you catch a thermal like this.
As you can see almost all of the indications of flying into lift require an aircraft that is properly trimmed. Also a pilot who is aware of the aircraft and how it reacts to the environment is essential in being able to recognize when the sailplane has stumbled onto that area of lift. Please note that not all sailplanes will indicate lift the same way, nor will they necessarily signal lift with all of the above mentioned behaviors. So, that is it for now until next month when I will discuss some of the techniques that I use when flying in a thermal, Good Luck hunting for thermals.
M.W.
