Cross-Coordinated Dangers, If Any, Lie

stic K and rudder to fully understand where the true Cross-Coordinated dangers, if any, lie. Let’s first look at two common pattern maneuvers Cross-controlling is often necessary to maintain and how crossing the controls actu- coordinated flight, but it can be dangerous. It’s not ally results in coordinated flight. whether you cross the controls, but how and when. Initial ClimB A safe and efficient normal takeoff and initial climb require some BY DAVID St. GEORGE aileron input to counter the pilot’s right rudder pressure, which is ap- here is a growing “terror” in the fallacy seems to reside in some plied to keep the wings level and flight training of any cross- fast-track flight schools that never the ball centered. This is cross- Tcontrolled flight condition. venture far from the maneuvering controlled flight! Many CFIs caution students to envelope’s center and teach only the During the initial high-power, “never cross-control,” with little minimum maneuvers required on low-speed climb, most singles or no explanation, as if require right rudder it were unquestionably pressure to center the “In a normal takeoff and climb, some aileron pres- and inherently evil. This ball. This induces a right admonition is especially sure against the right rudder is necessary to keep the rolling moment. Left stressed when flying at wings level and the ball centered. This is cross-con- aileron input against the any airspeed lower than right rudder is subtle but cruise. But the emphasis trolled flight!” necessary to keep the on avoiding cross-con- wings level as the ball is trolled flight is a disservice to the FAA tests. centered. Once the plane is “subtly primary students and displays a There certainly are dangers cross-controlled” in this manner, it fundamental misconception of encountered with some aspects of will climb much better because drag aerodyanimcs and basic airman- cross-controlled flight at low speeds. is minimized. In fact, I often can ship. The most extreme form of this The greatest true danger, fueled by achieve an additional 150 fpm in a fallacy intones, “Never slip to land; fear, is failure to understand and Cessna 152. This debunks the myth you’ll be low, slow and cross-con- teach the flight-control pressures that a 152 only climbs in the sum- trolled, will stall, spin and die.” necessary for coordinated flight mer because the earth curves! The root causes of these cautions while low and slow. To get com- Crossing the controls in this in- is obscure fortable and proficient in stance results in coordinated flight, but this area of flight, you and coordination should be the true need to spend some goal in climb to achieve safe and ef- time there. Instead, ficient performance. The important most pilots—and fact is the plane is finally coordinat- their inexperienced ed, streamlined and performing bet- CFIs—demonstrate ter. You will start to feel centered in increased muscle ten- the seat, too, with no leaning right sion just when fluidity, and left, as in a slip or skid. This Slipping Turn Skidding Turn grace and correct control can be strange stuff to those believ- usage are most necessary. ing cross-controlled flight is an evil Since the first step in effective bogeyman. Here we are, slow and in risk management involves clearly a high angle of attack and cross-con- identifying the hazards, we need to trolled, but finally coordinated. carefully analyze this flight condition and the source of these rumors crosswind Turn Upon reaching the turn to the Sometimes, keeping the ball centered means crosswind pattern leg, most train- Coordinated Turn crossing the controls. ing airplanes are still in a climb. 1 www.aviationsafetymagazine.com A viation S afet Y April 2006 stic K and rudder As the pilot rolls into a left crosswind turn, left rudder and aileron Bank Vs. Rate Of Turn are obviously required during the roll. But once a stable turn The basic difference between a slip and a skid is the rate of turn. Both configuration is established to the involve cross-controlled flight—or uncoordinated flight, if you will—but left, right (top) rudder—or at least the fundamental difference is whether the airplane’s heading is chang- relaxed left rudder pressure—is ing relative to the bank angle. Here are the basics: required to stay coordinated. The SLIP (Of course, this presumes a left- In a slip or a slipping turn, hand pattern. If you are turning to the airplane is not turning at Slipping Turn Vertical fly a right-hand traffic pattern, the the rate appropriate to the Lift rudder and aileron together yield a bank being used, since the Lift coordinated roll in that direction. airplane is yawed toward But once the right turn is estab- the outside of the turning lished, some right rudder pressure flightpath. Put another way, Centrifugal the airplane is banked too Force must be maintained and left aileron Horizontal much for the rate of turn, so Lift pressure—or at least relaxed right the horizontal lift component aileron—introduced to stay coordi- is greater than the centrifugal nated and maintain the appropriate force. bank angle.) Equilibrium between the Weight Load There are some important points horizontal lift component and to make about coordinating your centrifugal force is reestab- turns at this position in the pattern. lished either by decreasing the bank, increasing the rate of turn, or a combination of the two changes. Just A Moment The SKid First, pilots must distinguish the Remember that the funda- stabilized turn requiring subtle mental definition of either a Skidding Turn cross-controlled flight at high slip or a skid is that the rate Lift Vertical angles of attack from the airplane’s of turn is inappropriate to the Lift rolling moment in the climb con- bank angle. In contrast to a figuration, which requires rudder slip or slipping turn, a skid or Centrifugal and aileron together. Remember skidding turn results from an Force also: In the stabilized-turn con- excess of centrifugal force Horizontal Lift figuration, the rudder pressure you over the horizontal lift component, pulling the airplane to- need is always to the right—due ward the outside of the turn. to torque and “P Factor”—and is Put another way, the rate of not symmetrical. In other words, turn in a skid is too great for the rudder required to turn right the angle of bank. Weight Load is more than needed to turn left. Correcting a skidding turn This, of course, presumes a single- thus involves a reduction in the rate of turn, an increase in bank, or a engine airplane with a propeller combination of both. turning clockwise when viewed from the cockpit. ball and the VSI to verify perfor- higher wing with the rudder. This If any of this is new information, mance. Before you discovered this is rudder force away from the turn, I would recommend finding a good rudder pressure, all turns to the reducing the rate, and always re- CFI who knows how to use his or left in the pattern were actually sults in a slip. Ironically, when this her feet and practicing climbing skidding turns: the rate of turn was maneuver is first introduced to a spirals at a safe altitude in both excessive for the bank angle. student they hate the “feel” of a slip directions. The objective will be In a coordinated descending turn because it is so alien. The sensation to “tune” the aircraft with rudder you feel straight up in the seat and is of your butt falling to the inside pressure, based on your “seat-of-the- the ball is centered. If you are in a of the turn or lower wing. Unfortu- pants” feel first, then to check the turn and want to slip, step on the nately, most students seem to love April 2006 A viation S afet Y www.aviationsafetymagazine.com 1 stic K and rudder thus creating a balanced situation. Quick Tip: Coordinating The Roll Before you pick up a pen to write me a nasty letter, let me say that this maneuver is quite different in When initiating a turn, look straight out over the nose. If it a climbing turn with the slipstream pivots on a point, you are coordinated. If the nose swings generated by full power energizing in the direction of the bank, you’re adding too much the rudder. A slip in this configu- rudder in the direction of the bank. If it swings opposite ration is not at all benign, and the the bank, you haven’t added enough. Don’t focus on the airplane can spin quickly “over ball; it only depicts what already went wrong! the top.” For this reason I always Practicing the classic “Dutch roll” exercise—banking left advocate the slip to land as the tool and right on a point—is a good way to achieve a feel for of last resort to create the neces- this elusive balance. sary descent. First add drag, then reduce more power; finally, slip if you must. the “feel” of a skid probably since with power at idle. Amazingly, that is what you feel in a car going while maintaining a full slipping The FATAL SKid Scenario around a turn. Clearly, a lot of train- stall, nothing exciting happens. The evil twin of cross-controlled ing is necessary here to overcome This surprises every student and flight that started all the rumors (again) the “automotive paradigm” that is why this demonstration of death and destruction is actu- (see the sidebar on the opposite is so powerful.

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