Fundamentally, airplanes carve just two shapes in the sky: straight lines and curves. The turn certainly is the most common form of curved flight, and all pilots can perform this highly versatile maneuver. But it seems few can adequately describe the mechanics of it. Unfortunately, an incomplete understanding of turning flight can lead to inappropriate control inputs during critical operations. Losing control of the airplane while turning is a causal factor cited in many accident reports. Therefore, knowing what controls our turns is an important, yet often overlooked, piece of information.
Steady, level, coordinated turns occur when the vertical component of lift offsets the weight of the airplane. Without using flaps, we can only change the magnitude of lift two ways: by altering airspeed and angle of attack. Both of these are controlled by pitch.
Total lift, composed of vertical and horizontal components when banked, still acts perpendicular to the relative wind and to the wingspan. And back pressure on the yoke then increases G-load and total lift. It's the growing horizontal component of lift that forces the airplane away from a straight flight path. As the flight path bends in the direction of this force, the tail assembly continually weathercocks the nose into the changing relative wind, resulting in a smooth, sweeping arc.
Aileron inputs merely characterize turns. They cannot, and do not, curve the path of flight. Ailerons do permit a wide range of possible curves by pointing the total lift force in different directions. Since pitch controls angle of attack and, hence, the magnitude of lift, it's how we manipulate the elevator control that actually determines the turn's shape and quality.
While it's convenient to think that back pressure holds our altitude in a turn, it does not (at least, not directly). Back pressure increases the angle of attack, which decreases airspeed. This decreases any additional power required to maintain steady flight as long as decreased airspeed is acceptable. In essence, we trade airspeed energy to hold altitude when pulling in a turn. If both airspeed and altitude are to remain constant, more power will be required.
The elevator truly is our turn control. We can summarize its control function with a simple formula: Airspeed + G-Load = Curved Flight. We mix roll, yaw, and power with pitch to flavor our turns. Combining different proportions of these ingredients gives each turn its own distinct character. Let's review the general recipes for some turns, keeping in mind that the exact amounts of roll, yaw, pitch, and power needed will vary from airplane to airplane. Also, not all of the recipes discussed yield safe, healthy turns!
Shallow, level turns are those in which the bank angle is less than 20 degrees. They are characterized by almost imperceptible increases in G-load, and the natural stability of many airplanes tends to roll the wings back to level.
Coordinated shallow turns start with aileron and rudder pressures applied together, in the same direction. Once the desired bank is attained, the aileron input must be relaxed to stop the roll; however, a small amount of residual aileron pressure may be required in the direction of the turn simply to keep the bank constant. The rudder must be readjusted as well to maintain coordinated, yaw-canceled flight. Slight (in some cases, imperceptible) back elevator pressure pulls the airplane around to a new heading.
We generally compensate for minor altitude excursions during shallow turns by adjusting our elevator inputs, rather than adjusting bank angle or power settings. Keep in mind that elevator inputs directly affect our airspeed, which affects the power required for steady, level flight. We're trading off a surplus of one parameter (airspeed or altitude) for a deficiency in the other. Small changes in elevator inputs during shallow turns have a minimal effect on the G-load experienced.
Medium, level turns are those in which the bank angle is between 20 and 45 degrees. They are characterized by slightly higher, yet relatively small G-loads. The inherent stability of many airplanes holds the bank constant. We start these turns just like shallow turns: aileron and rudder pressures together, back pressure on the yoke to curve the flight path.
In a properly rigged airplane, once a specific medium bank angle is established, the aileron input must be neutralized. The rudder is adjusted accordingly, since most adverse yaw disappears when the aileron input is removed. A look out at the wings should reveal no aileron deflection at all. If you can trim off the back pressure, you should be able to release the control wheel while the airplane remains in a nice, medium banked turn.
Steep turns are those in which the bank angle is greater than 45 degrees. They are characterized by noticeable G-loads, which grow rapidly with increasingly steeper bank angles. Many airplanes tend to over bank in the direction of steep turns because the outside wing travels faster than the inside wing, thus generating slightly greater lift (and greater induced drag, which requires corrective "rudder action").
Once the bank is established, aileron pressure opposite to the direction of turn may be required to maintain a constant bank. Significant back pressure on the yoke is needed to sustain steady flight. Altitude excursions now are corrected more effectively by modifying the bank angle.
Steep turns provide vivid examples where the belief that pitch controls altitude serves merely to aggravate turn characteristics. Where the elevator presents the illusion of altitude control during shallow turns (by trading airspeed for altitude), it only tightens the steep turn and could cause dramatic increases in G-load, airspeed, and angle of attack as the altimeter unwinds.
If you are having difficulty maintaining a constant altitude in a steep turn, while maintaining back pressure, reduce the angle of bank in a coordinated manner and then increase back pressure. Once the lost altitude is regained, the bank angle can be reestablished. If you attempt to regain lost altitude in a steep turn by applying back pressure before reducing the angle of bank, you'll likely end up in a tight descending spiral. This is probably contrary to your desires, and it also tends to over stress the aircraft, which is never a good thing.
The underlying characteristic of all skidded turns is excess yaw in the direction of the turn. They are uncoordinated maneuvers. Typically, the unnecessary yaw is pilot-induced, with too much rudder applied in the direction of turn. Both the deflected rudder and the inside wing point toward the ground when skidding.
Excess yaw generates a secondary roll in the direction of the turn, thereby increasing the turn's angle of bank. Yaw slices the nose earthward through the horizon, too. These actions alter the character of the turn and can negatively influence the pilot's perception.
Reacting incorrectly to a skidded turn by using opposite aileron to stop the increasing bank, followed by additional back pressure to hold the nose "up," pave the way for the classic unintentional spin (see "Cross-Control Stalls" in the Flight Training Handbook, AC 61-21A, page 152). Unless we intend to enter a spin, at high altitude, in an airplane approved for spinning, after a lot of dual instruction, skidded turns serve absolutely no useful purpose. They are a sure recipe for disaster, so don't skid your turns.
The underlying characteristic of all slipping turns is excess yaw opposite to the direction of turn. Like skidded turns, slipping turns are uncoordinated. During a slipping turn, the inside wing points toward the ground. The deflected rudder, however, points skyward, opposite to the direction of turn.
Aileron pressure must be held in the direction of a slipping turn to maintain a constant bank angle. This pressure offsets the roll induced by the opposite rudder. Yaw and roll, therefore, are not necessarily coupled, as in the dangerous skidded turn. In fact, yaw and roll act in different directions, making a slipping turn somewhat spin resistant. Transitioning into and out of slipping turns requires precise control over our control inputs. Otherwise, it's possible to transition into a spin-prone skid.
Slipping turns are performed by adding a little more bank, or reducing some opposite rudder pressure, or a combination of the two, along with an increase in elevator back pressure to pull the airplane to a new heading. Looking along the inside wing should reveal an upward-deflected aileron, while the slip/skid indicator shows the ball resting toward the inside of the turn.
Since skidding and slipping turns are uncoordinated maneuvers, turn rates in a slip will be slower in comparison to coordinated turns, but faster in a skidding turn. Slipping turns allow us to lose altitude quickly, particularly during a high landing approach. They are vital for coping with such in-flight control failures as split flaps, jammed ailerons, or a deflected rudder. They are also an effective maneuver for crosswind landings.
Left to their own devices, most airplanes display a natural tendency to bank and turn by themselves. This tendency is called spiral instability. Spirals will self-propagate and become tighter unless the pilot reacts appropriately to stop them. Attempting to arrest the descent and hold the nose "up" with additional elevator back pressure only aggravates the spiral. It also generates increased load factors on the airplane and pilot. Once the airspeed exceeds maneuvering speed, "pulling up" can induce structural failure.
Since unintentional spirals can descend rapidly, reduce the power to idle. This slows the rate of altitude loss and prevents over-speeding of fixed-pitch propellers. Release the elevator back pressure. This action lowers the angle of attack, reduces the G-load on the airplane, and loosens up the spiral. Next, roll the wings level using coordinated aileron and rudder inputs. Once the wings are level, recover the pitch attitude - gingerly if the airspeed is high (see "Steep Turns" and "Unusual Attitudes and Recoveries" in the Instrument Flying Handbook, AC 61-27C, pages 86-91).
Turning flight commands striking a balance between angle of bank, airspeed, and G-load. These elements must complement one another. We must continually juggle roll, yaw, pitch, and power variables while executing turning maneuvers. When practicing turns, keep these points in mind:
Avoid leaning away from the turn just to keep your head perpendicular to the horizon. Leaning with your turns instead will give you a better feel for the G-loads being imposed, a clearer picture of your elevator inputs, and a better "seat of the pants" feel in the turn. Pitch movements are easier to see when your head and feet form a line perpendicular to the airplane's lateral axis.
Expect adverse yaw to be greater when rolling out of a turn due to decreased airspeed and higher angles of attack compared to level flight. Rolling to wings level after completing a turn generally requires more rudder pressure (in the same direction as roll) compared to that used to roll into the turn. Use coordinated aileron and rudder pressures whenever changing your bank angle.
Above all, any time you botch a turn, don't "pull" more. Instead, pull less. Then reduce the angle of bank, which will immediately reduce the airplane's stall speed, increase the power available, and decrease the power required for steady flight. All of these attributes give us increased control over the airplane. Analyze your difficulty, then try it again!