This can be manipulated into V$_{S}$  times the square root of the  load factor (which equals weight × G loading). For example, if a glider stall speed is 34 knots, consider the  following formula (34 × √1.2 (load factor) = 34 × 1.10 = 37  at 30° ) for thermalling: •  In a 30° banked turn, load factor is 1.2 Gs. The  approximate square root of 1.2 is 1.1. Now multiply  34 knots times 1.1 yields a 37-knot stall speed. Since  the minimum sink speed is 40 which is still above  the stall speed but by only approximately 3 knots, the  margin of safety is decreasing and the pilot should  consider increasing the minimum airspeed by a factor  proportionate to the stall speed increase, in this case  44 knots (40 × √1.2 (load factor) = 40 × 1.10 = 44 at  30°).  •  In a 45° banked turn, load factor is 1.18 (34 × √1.4  = 34 × 1.18 = 40.12 knots at 45°). Now multiply 34  knots times 1.18 which yields a 41-knot stall speed.  The minimum sink speed of 40 knots is now below  the stall speed. The pilot should increase the minimum  airspeed proportionately to the stall airspeed, and the  new speed would be 48 knots (40 × √1.4 (load factor)  = 41 × 1.18 = 48 at 45°), a 7-knot safety factor. •  In a 60° banked turn, load factor is 2.0 Gs. The  approximate square root of 2.0 is 1.4 (34 × √2.0 = 34  × 1.41 = 48 knots at 60°). Now multiply 34 knots times  1.4 which yields a 48-knot stall speed. The minimum  sink speed of 40 knots is now below the stall speed.  The pilot should increase the minimum airspeed  proportionately to 57 knots, yielding an 9-knot safety  (40 × √2.0 (load factor) = 40 × 1.41 = 56.4 at 60°). •  Improper determination of minimum sink speed. •  Failure to maintain proper pitch attitude and airspeed  control. Minimum sink airspeed is always lower than best L/D  airspeed at any given operating weight. If the operating weight  of the glider is noticeably less than maximum gross weight,  then the actual minimum sink airspeed at that operating  weight is lower than that published by the manufacturer.  Common errors regarding minimum sink airspeed include: Best glide (L/D) airspeed is defined as the airspeed that results  in the least amount of altitude loss over a given distance. This  allows the glider to glide the greatest distance in still air. This  performance is expressed as glide ratio. The manufacturer  publishes the best glide airspeed for specified weights and  the resulting glide ratio. For example, a glide ratio of 36:1  Best Glide Airspeed Speed to Fly means that the glider loses 1 foot of altitude for every 36  feet of forward movement in still air at this airspeed. The  glide ratio decreases at airspeeds above or below best glide  airspeed. The best glide speed can be found from the glider  polars in Chapter 5, Performance Limitations. Common errors regarding best glide airspeed include: Much is said about the importance of maintaining the  best gliding speed, but what is important is to maintain  an optimum glide speed, a penetration speed that takes  atmospheric conditions into account (e.g., sinking air or  a headwind). The gliding community refers to this as the  speed to fly. The normal recommendation for countering  a headwind is to add one-third to one-half of the estimated  wind speed to V$_{BG}$ , which increases the rate of sink but also  increases the ground speed. For a tailwind, deduct one-third  to one-half the estimated wind speed from V$_{BG}$, which  reduces both the rate of sink and the groundspeed. Bear in  mind that, for safety, it is better to err towards higher rather  than lower airspeeds. To illustrate this, the polar curve in  Figure 7-35  indicates  the optimum glide speed when adjusted for headwind,  tailwind or sinking air. For a tailwind (A), the starting point  on the horizontal scale has been moved a distance to the left  corresponding to the tailwind velocity. Consequently, the  black tangential line contacts the curve at an optimal glide  speed that is lower than the best L/D no-wind glide (B), with a  slightly lower rate of sink. This is the opposite for a headwind  (C), shown by the purple line, and sinking air (D), shown  Figure 7-35.  Polar curve for optimum glide speed adjusted for  headwind, tailwind, and sinking air. Airspeed Headwind Tailwind Sinking air Glide Rate of sink Minimum sink A B C D 7-37 •  Improper determination of best airspeed to fly and not  factoring in lift and headwinds. •  Failure to maintain proper pitch attitude and airspeed  control.