On the Condor forums, the user Vertigo believes that
- Increasing inversion height allows more and denser CUs.
- Lowering inversion height below cloud base results in blue thermals and no CUs
- The lower the inversion height the better the wave if there is enough wind
- The higher the cloud base, the few the CUs but thermals will be stronger
TimKuijpers observes that, in real life thermals diminish toward the end of the afternoon. In Condor, there is less fall off at the end of the day so start time is not as critical as in real life.
Here are some comments from Glider Flying Handbook, an FAA publication for glider pilots, on the subject of blue thermals:
- Convective Condensation Level ( CCL )
- On some days, when only a few thermals are reaching the CCL, the initial wisps may be the only cloud markers around. The trick is to get to the wisp when it first forms, in order to catch the thermal underneath. (Glider Flying Handbook, 10-2)
- Lack of Cu does not necessarily mean lack of thermals. If the air aloft is cool enough and the surface temperature warms sufficiently, thermals will form whether or not enough moisture exists for cumulus formation. These blue or dry thermals, as they are called, can be just as strong as their Cu-topped counterparts. Glider pilots can find blue thermals, without Cu markers, by gliding along until stumbling upon a thermal. With any luck, other blue thermal indicators exist, making the search less random. (Glider Flying Handbook, 10-2)
- When a thermal rises to an inversion it disturbs the stable air above it and spreads out horizontally, thus depositing some of the aerosols at that level. Depending on the sun angle and the pilot’s sunglasses, haze domes can indicate dry thermals. If the air contains enough moisture, haze domes often form just before the first wisp of Cu.
- Usually upon entering a thermal, the glider is in lift for part of the circle and sink for the other part. It is rare to roll into a thermal and immediately be perfectly centered. The goal of centering the thermal is to determine where the best lift is and move the glider into it for the most consistent climb. One centering technique is known as the “270° correction.” [Figure 10-8] In this case, the pilot rolls into a thermal and almost immediately encounters sink, an indication of turning the wrong way. Complete a 270° turn, straighten out for a few seconds, and if lift is encountered again, turn back into it in the same direction. Avoid reversing the direction of turn. The distance flown while reversing turns is more than seems possible and can lead away from the lift completely. [Figure 10-9]
- Often stronger lift exists on one side of the thermal than on the other, or perhaps the thermal is small enough that lift exists on one side and sink on the other, thereby preventing a climb. There are several techniques and variations to centering. One method involves paying close attention to where the thermal is strongest, for instance, toward the northeast or toward some feature on the ground. To help judge this, note what is under the high wing when in the best lift. On the next turn, adjust the circle by either straightening or shallowing the turn toward the stronger lift. Anticipate things a bit and begin rolling out about 30° before actually heading towards the strongest part. This allows rolling back toward the strongest part of the thermal rather than flying through the strongest lift and again turning away from the thermal center. Gusts within the thermal can cause airspeed indicator variations; therefore, avoid “chasing the ASI.” Paying attention to the nose attitude helps pilots keep their focus outside the cockpit. How long a glider remains shallow or straight depends on the size of the thermal. [Figure 10-10] Other variations include the following. [Figure 10-11]
- 1. Shallow the turn slightly (by maybe 5° or 10°) when encountering the weaker lift, then as stronger lift is encountered again (feel the positive g, variometer swings up, audio variometer starts to beep) resume the original bank angle. If shallowing the turn too much, it is possible to fly completely away from the lift.