Thermalling the Hollinghaus Way

Thermalling in a Slight Slip

Dick Johnson wrote a great article titled "Circling the Holighaus way" Click here and log-in on the SSA website.

At Sky Sailing we teach spins with each student pre-solo. One of the entries we do with students is circling slow, then getting the SGS 2-32 into a slight slip, then a more aggressive one. Then we transition into a skidding turn and watch the horizon rotate around as it enters the spin.

According to the article, the sailplane is more efficient in a slight slip while thermalling. In a slip, you accelerate the lower wing therefore requiring less opposite aileron. The lower deflected aileron creates more lift and more drag. The more aileron you are using the more drag you are creating. Instead, you can use a little rudder and the slip will utilize the dihedral effect (imagine straight and level and you push the rudder over, it will yaw then roll in that direction) and will help maintain the bank angle from over banking.

One consideration is where the yaw string is located in relation to the CG of the glider. Because the yaw string can be upwards of 2 meters away from the CG and the airflow around the canopy the yaw string indication can be exaggerated. Many times seeing a 10-degree slip is not unusual. Dick Johnson would see up to 20 degrees in his 16.6m Ventus.

This was most pronounced to me when flying my Nimbus 3. There was a large wingtip speed difference between the two wingtips as you circled and a lot of over-banking tendency going on. As I stayed in a slight slip I would greatly reduce the amount of opposite aileron required to maintain the bank angle. This was important because many times it would require full opposite aileron to maintain the bank angle. I would try not to give it too much thought on how I would roll out on course at that point in the flight.

Another consideration is that thermals are turbulent most of the time. So staying perfectly coordinated is very difficult. To avoid skidding the turn if you stay in a slight slip, the string will dance between coordinated and slightly too much of a slip and avoid skidding the turn.

Static buildup and an ugly piece of white tape is not the way to treat the most important instrument. Thanks to one Soaring pilot's obsession the MK IV yaw string is available.

 Garret Willat holds a flight instructor rating with over 8000 hours in sailplanes. His parents have owned Sky Sailing Inc. since 1979. He started instructing the day after his 18th birthday. Since then, Garret has represented the US Junior team in 2003 and 2005. He graduated from Embry-Riddle with a bachelor's degree in Professional Aeronautics. Garret represented the US Open Class team in 2008 and 2010 and the Club Class team in 2014. Garret has won 3 US National Championships.