so there's margin for roll correction in either direction. The yaw string in that moment, due to turbulence or normal awkwardness, will DANIEL L.JOHNSON wobble back and forth between a slip and a skid, "centered" on the average. But the wing does not care about its average air- flow; it cares about each moment's flow. How to Spin "The middle of the air" (metaphori- cally) is the safe place to be, but the centered yaw string, in a steep turn, is at the border between a skid and a slip, Unintentionally so a (literally) centered yaw string is (metaphorically) "on the edge of the air" vector pointing straight down? (centered Try to stay in the middle of the air. in a slow turn. Humorously, an actually- Do not yo near the edges of it. ball) o o J middle yaw string is metaphorically at • Does it mean drag is balanced be- The edges of the air can be recognized the brink of the cliff. by the appearance of ground, tween the wings? Thus, we should prefer the yaw string buildings, sea, trees, • Does it mean that each wing is to flop between center and our high side, and interstellar space. about equally far from stalling? not crossing the center to the low side. It is much more difficult to fly there. These things are easy to synchronize "Attention," as we explained last - unknown wit when nearly level (up to a 30-degree month, acts through 'built-in brain net- bank). But as the turn becomes steeper, works that can be improved with training hesis: Most gliding fatal accidents it becomes impossible to meet all four of and practice. Instructors use words like occur due to stalls (Rich Carlson, these conditions simultaneously. Most T "protocol" and "discipline" to describe the SSF). Most of these occur close to the important, a centered yaw string no result of successfully training the atten- ground, usually in the turn from base to longer means that each wing is about tion networks. final, but they also occur, surprisingly, equally far from a stall. We must train attention toward the during free flight. In a steep turn, the yaw string and the most important things while turning, What are these pilots paying attention ball become less relevant to safety. The especially while landing. Training done to? What might have been done to avoid position and responsiveness of the con- well teaches the pilot to shift attention this? More to the point, what are pilots trols is more important. If the stick is doing who never stall inadvertently? against the high-side stop (due to over- among various key items during the The principle is simple: don't skid slow banking from differential lift), you have changes of flight, landing, and takeoff, turns, and; he who skiddeth a slow turn no control in the roll axis. This causes and teaches disciplined rigor to this at- stalleth, spinneth, and (quite possibly) anxiety when turning steeply, slowly, in tention protocol. dieth. Note carefully: Unless any turn a narrow, turbulent thermal. To teach, "keep the yaw string cen- is perfectly coordinated, we either are All you need to do is add enough top tered," is a good thing as a general skidding somewhat or slipping some- rudder to balance the drag (reduce the principle, but religious obedience to what. The skid — bottom rudder - tends down-wingtip angle of attack) - this this pedantry is not a good thing, if by to create a spin. The slip - top rudder - restores roll control very nicely, and this we come to believe that it defines "improves" the sink rate, safely. you'll be able to comfortably make con- piloting virtue, or believe that a centered Caveat 1: this and all other discussions tinual steep turns in any glider or air- yaw string always indicates coordinated of aircraft control assume smooth air. In plane. When you do this in an airplane, flight, or that it's most important to keep turbulence, whether in the pattern or in you may be a half-ball off center, and in it centered. a thermal, small turbulent vortices may a glider, the yaw string may drift 10 or 15 This would be inexact. betray your best intentions - a reason to degrees to the top side. • The yaw string indicates the direc- then carry extra speed. Therefore the safe pilot is maintain- tion of airflow in which it lives. Coor- Caveat 2: A discussion of the relation- ing balanced controls, "coordinated" dinated flight centers the yaw string in ship of the yaw string to coordinated or slipping but never skidding. The straight and level flight. In turns, this .flight becomes, frankly, somewhat com- pilot is in danger who is, while turning isn't always precisely true. plicated in a slow, steep turn in turbu- slowly and steeply, cluelessly loyal to • Coordinated flight, in a steep turn, lence, especially with long wings. In the instruction, "always center the yaw is not the safest condition - it's the most fact, what people mean by "coordinated string." It's not, just then, important to elegant condition. If the goal is to stay flight" becomes rather vague: center the yaw string. It's important to "in the middle of the air," midway be- • Does it mean straight flow of air maintain control responsiveness (with tween dangers, a centered yaw string over the canopy? (straight yaw string) speed) and to maintain "coordination" does not keep you there in a steep turn. • Does it mean the net "gravitational" that keeps the stick near the center, • Keeping our attention on centering May 2014 the yaw string distracts us from paying Here's how the perceptual bits work to attention to other much more important take us out of "the middle of the air." details like airspeed, aim point, angle of attack, apparent flight track, other traffic, The rising horizon and obstructions on the runway. This is not as serious an issue in the flat- SOARING Perceptions are crucial. There are three lands, where the effect is pretty subtle. But perceptual features that may delude a when there are hills or mountains nearby, SUPERSTORE landing pilot into flying too slowly or it is serious. While we're above every- skidding a slow turn: thing, we see the real horizon. As soon as • the horizon, we descend below any hump of earth, its • vection, or the sense of speed, and ridge line becomes a false horizon. • the movement of the down wingtip To understand that the ridge is a false across the ground. horizon is easy; to keep track of where Our surround changes during descent the real horizon is located takes actual GOODYEAR - MICHELIN - SPECIALTY in the pattern, creating three mispercep- attention. Look down the valley. Find tions that trick landing pilots: the true horizon. Swivel your head back • The horizon begins to rise. If we and image that horizon line onto the keep the nose at the same point on the mountain. Do this several times while horizon as we did when high, we will you descend - if you don't, you will tend steadily slow down. (Fail!) to raise the nose. OXYGEN SYSTEMS • The ground moves faster and faster. If you don't keep track of the actual We may slow down to make this feel horizon, for example by "transferring" it AEROX - MOUNTAIN HIGH right. (Fail!) to the mountain, your subconscious per- • The down wingtip moves forwards ceptions may cause you to feel as though across the ground. This may cause us to a strong hand is pulling the stick back feel that: while the airspeed decays mysteriously, • We are failing to turn with the over and over again, (which a pilot at the intended small radius. This may inspire Reno convention asked me to explain). AVIO us to step on the inside rudder (Fail!) But why are you paying attention to the • We are moving too fast. This may horizon, anyway? It's airspeed we want, TRIG - BECKER cause us to induce back pressure to slow and we put the nose at -whatever attitude down. (Fail!) keeps the airspeed where it's meant to How is this relevant to the yaw string? be: 1.3 VSO + % the gust velocity (more, Simply this: There's no one thing that if it's really gusty). If you're trying to fly we can fixate our attention to, and remain attitude in the pattern instead o/~manag- safe. The loyal yaw string, the wingtip, ing airspeed, it's time to do some seri- the horizon, the sense of motion: none ous practice to revise unhelpful habits of these is enough. We should also pay of attention. (Correct practice leads to NATIONAL - STRONG attention to the wind noise, the control correct decisions.) responsiveness, and - most important — where we're headed, the apparent and the Vection intended touchdown points (these are Vection is apparent movement, in dis- different). We need to scan these, we need tinction to actual movement. The clas- to integrate the information they provide sical vection illusion is you sitting in a INSTRUMENTS with our knowledge and experience. stopped train, and beginning to move WINTER -UMA If we are watching only the horizon, or smoothly backwards - until you realize the ground under us, or our wingtip, we from the lack of vibration that it's the train on the other track moving forward. I SSSS58 may cause the yaw string to point down FREE toward hell, or cause the airflow to lose There's a similar vection illusion when its affection for our wing, which may take we are up high — it seems as though CATALOG! us there.