Flight Principles: Effects of Controls and Aircraft Attitude and Power and Trim Management

Fundamental Flight Controls and the Airplane Attitude

• Flight instructors demonstrate controls used to alter aircraft speed, height, and direction, as well as the behavior of trimmers and flaps.

• The primary method of controlling an aircraft involves adjusting the attitude, which is the relative position of the aircraft's nose and the natural horizon as seen through the windscreen. This is often referred to as "the picture seen through the windscreen."

• Three control surfaces are used almost constantly during flight: the elevator, the ailerons, and the rudder.

• Regardless of aircraft orientation, including if the aircraft is inverted, a control movement always moves the aircraft in the same direction relative to the pilot in the cockpit.

Primary Effects of Controls

• Elevator: Located on the rear of the tailplane, the elevator moves up and down in response to the control column (stick).

  • Moving the stick forward causes the elevator to move down, creating more lift at the tail. This results in the nose moving down, a motion known as pitching.

  • Moving the stick back causes the elevator to move up, creating a downward force on the tail. This results in the nose pitching up.

• Ailerons: These are controlled by moving the stick from side to side (lateral movement).

  • Moving the stick to the left raises the left-wing aileron (reducing lift) and lowers the right-wing aileron (increasing lift). The resultant motion is rolling to the left.

  • Moving the stick to the right causes the aircraft to roll to the right.

  • The rolling motion persists until the control stick is returned to the central position.

• Rudder: Located at the rear of the vertical fin, the rudder moves left or right via rudder pedals.

  • In the cockpit, pushing one pedal forward causes the other to move back.

  • Pushing the left rudder pedal moves the rudder to the left, altering the airflow around the fin to produce a horizontal force that moves the tail. This causes the nose to move left, a motion called yaw.

  • Yaw occurs in the same direction as the pedal being pushed.

  • The rudder is essential for maintaining balanced flight, especially when changing power or speed settings.

Core Rules for Control Application

• Smoothness: Control inputs must be smooth.

• Perspective: The effects observed by the pilot are direct representations of control inputs.

• Neutralization: A control input's effect continues until the control is centralized, which neutralizes the input.

• Distance: The magnitude of the observed effect is dependent on the distance the control is moved.

Secondary and Further Effects of Controls

• Primary effects represent the immediate result of control movement, while secondary and further effects occur due to the aerodynamic design of the aircraft.

• Elevator Dynamics:

  • Primary Effect: Pitch.

  • Secondary Effect: Changes in airspeed.

  • Further Effect: None.

  • The airspeed change is not instantaneous; there is a short delay due to inertia (reluctance to change) before a steady speed is achieved.

• Aileron Dynamics:

  • Primary Effect: Roll (applying bank).

  • Secondary Effect: Yaw. Once banked, the aircraft sideslips toward the lower wing. Airflow over the fin and rudder creates a sideways force, causing the aircraft to yaw into the bank.

  • Further Effect: Spiral descent. Yawing causes the outer wing to move faster, generating more lift, which further increases the bank. The cycle repeats until the aircraft enters a spiral descent.

• Rudder Dynamics:

  • Primary Effect: Yaw.

  • Secondary Effect: Roll. As the aircraft yaws, the outer wing moves faster than the inner wing, producing more lift and causing a roll followed by a sideslip.

  • Further Effect: Spiral descent. Similar to the further effect of ailerons, the rolling and yawing lead to a spiral descent.

The Relationship Between Airspeed and Control Effectiveness

• All flight controls function by producing lift. According to the lift formula:     $L = C_L \frac{1}{2} \rho v^2 S$

• High Speed: Because lift increases with speed ($v^2$), controls are highly effective. Small movements produce high rates of roll, pitch, or yaw. The controls feel firm and require more physical effort to move.

• Low Speed: Controls are less effective. Large control movements are required to achieve the same result as at high speeds. The controls feel light and are easier to move.

• High Speed Summary: Controls are firm and very effective.

• Low Speed Summary: Controls are light but do not work as well.

Slipstream and Power Effects

• Slipstream is the air pushed backward by the propeller. High power settings create a fast slipstream, simulating the effect of increased airspeed over specific surfaces.

• Affected Controls: Only the elevator and rudder are affected by slipstream because they are positioned behind the propeller.

• Unaffected Controls: Ailerons are not affected by power changes because they are mounted at the wingtips, outside the slipstream path.

• High power makes the elevator and rudder more effective; low power makes them less effective.

Trim Systems and Management

• As a control surface is deflected more, the airflow creates greater resistance, resulting in "Stick Force."

• Trimming is the process of reducing this stick pressure so the pilot does not have to manually hold the attitude, preventing fatigue.

• Controls:

  • The elevator trim wheel is located on the cockpit floor between the front seats and moves forward/back.

  • The rudder trim wheel (if equipped) is located between the front seats. Note that the DA40 aircraft does not have a rudder trimmer; the pilot must maintain balance manually.

• Operation: Trimming is performed in the natural sense. If backward pressure is required on the stick to maintain an attitude, the trim wheel should be moved backward until the pressure is zero.

• Guidelines:

  1. Use controls to select an attitude.

  2. Wait $15$ to $20$ seconds after significant power or attitude changes for the aircraft to settle.

  3. Use trims only to remove control loads, never for maneuvering.

  4. Verify trim by momentarily releasing the control; if the attitude changes, re-select and re-trim.

  5. An aircraft is only in trim for a specific combination of speed and power; changes to either require re-trimming.

Aerodynamic Effects of Power and Airspeed Changes

• Power Increases:

  • Primary results: Pitch UP and Yaw LEFT.

  • Correction: Apply RIGHT RUDDER and FORWARD PRESSURE on the elevator.

• Power Reductions:

  • Primary results: Pitch DOWN and Yaw RIGHT.

  • Correction: Apply LEFT RUDDER and BACK PRESSURE on the elevator.

• Airspeed Increases:

  • Result: Nose pitches UP and RIGHT.

• Airspeed Decreases:

  • Result: Nose pitches DOWN and LEFT.

• The specific yawing behavior during power changes is caused by changes in the slipstream effectiveness and its helical (spiral) nature.

Flap Mechanics and Procedures

• Flaps increase both lift and drag at a given speed.

  • Increased lift allows for slower, safer flight and shorter landing runs.

  • Increased drag allows for steeper approach paths.

• Settings: The flap switch is located below the Multi-Function Display (MFD) screen and has three positions. Controls move downward to lower and upward to raise.

• Airspeed Limits ($V_{FE}$):

  • Take-off Flaps: $108\,KIAS$

  • Landing Flaps: $91\,KIAS$

  • General check: Always ensure speed is below $103\,knots$ before selection as a matter of good airmanship.

• Operational Stages:

  • Take-off position: Greater increase in lift than drag.

  • Landing position: Further increase in lift, but a much greater increase in drag.

• Pitch Behavior: Lowering flaps causes an initial strong pitch up (due to lift), followed quickly by a pitch down as drag reduces speed. Raising flaps produces the opposite effect.

• Technique (Limitation - Operation - Indication):

  1. Limitation: Confirm airspeed is within the operating limit for the setting.

  2. Operation: Move the switch or lever.

  3. Indication: Confirm the surface is moving and reaches the correct position.

Threat and Error Management (TEM)

• Clear communication regarding control of the aircraft is vital.

• Handover Procedure:

  • Giving control: Instructor says ‘YOU HAVE CONTROL’. Student places hands on stick and throttle and feet on pedals, then says ‘I HAVE CONTROL’.

  • Taking control: Instructor says ‘I HAVE CONTROL’. Student removes hands and feet from controls and says ‘YOU HAVE CONTROL’.

• Follow Me Through: The student places hands and feet lightly on controls to feel the instructor’s movements (speed and distance) without interfering.

Lookout and Scanning Techniques

• Effective lookout is mandatory for safety. Pilots must notify the instructor of any other aircraft seen.

• Scanning Method:

  1. Start the scan behind one wingtip.

  2. Scan along and below the horizon to the other wingtip.

  3. Scan above the horizon back to the original wingtip.

  4. Scanning must be done in blocks/steps; eyes must be momentarily still to register moving objects.

Throttle Handling

• The throttle must be moved smoothly.

• When increasing power, pilots must monitor engine instruments to ensure the engine does not exceed its operating limits.