Don’t Anchor to a Speed!

A classic beginner mistake is to cruising too slowly between thermals. Many pilots feel that cruising “fast” is simply in the domain of competitive flying and doesn’t apply to them. However, I will demonstrate that flying faster is extremely important when dealing with sink. Yet disconcertingly, most beginners are only taught to fly at minimum sink and best-glide speed. However, it is often safer and more conservative to fly considerably faster than best-glide speed; you will often arrive at Point B at a higher altitude if you do so!

The reason that cruising at best-glide speed is often a bad idea is because the air is rarely still! The moment there is any sinking air, the pilot must fly much faster to compensate for the sink. Flying at best glide speed only makes sense if the air is rising or is smooth.

To illustrate why, suppose a glider sinks a little over 1 knot when it flies at 50 knots. This means that it will travel around 48 feet forward for every foot of altitude it loses. We call this the Lift/Drag Ratio and we observe that this sailplane is gliding at 48 to 1.

Now suppose that we fly into air that is sinking at a leisurely two knots down. By flying at 50 knots, the variometer will now read 3 knots down and the glider would only have a third of its original performance. Instead, it will only go 16 feet forward for every foot it loses, worse than a 1-26!

Now suppose that we put the nose down and fly at 80 knots. For most modern gliders, this would only minimally affects its performance. Sure, it will sink faster than at 50 knots, but only by one additional knot; its L/D would now be 40-1.

If we fly at 80 knots in the two knot down sink, our variometer would now read 4 knots down and our L/D would be 20-1. This is 20% more efficient than if we were flying at 50 knots in the same air! To put this in perspective, the pilot would arrive HIGHER at a desired point.

Naturally this matters most if the air is sinking between the thermals. However, conservation of energy dictates that the more air that goes up, the more air must come down to reach equilibrium. Disregarding the effect of atmospheric pressure systems, the very presence of thermals means that a glider has a higher probability of hitting sinking air in cruise.

How does this relate back to anchoring? Since pilots are trained to cruise at best glide speed, they tend to be hesitant to fly faster. It is painful to “put the nose down”. In a way, it feels like you are admitting defeat. In the short term, the glider is sinking faster and it feels like the “bad” situation unfolds more quickly. But as we learned, flying faster is often the right thing to do.

In summary, it is prudent to discard best-glide as the primary anchor for cruising speed. For most modern gliders, I would suggest anchoring around 70 knots instead. The pilot should automatically default to this speed and then adjust for the circumstances. If the new pilot spends most of their time flying at this speed instead of best glide, they will have more success staying up and going places.