Influence of Changes in Engine Power
Chapter 4.7
Thrust Line
The force of the thrust line changes with the increase or decrease of the engine power. The direction of the torque on the pitch axis is determined by the engines location.
The THRUST LINE EFFECT depends on the power.
Thrust Line
For most basic training aircraft the power changes cause the following effects:
To be able to react in a predictable manner, you need to know the THRUST LINE EFFECTS of the aircraft used.
The Slip Stream Effect
The SLIP STREAM EFFECT is generated by the airflow around the wings, the airframe and the control surfaces by the propwash. The air flowing through the propeller creates a greater lift and more efficiency on the control surfaces.
For aircraft with a front engine, the SLIP STREAM EFFECT depends on the power and airspeed.
It must be corrected for each power setting and airspeed.
In cruise flight, it is normally compensated by the aircraft design.
The Slip Stream Effect
The SLIP STREAM EFFECT as a Disturbance Effect on Aircraft with a Front Engine
The SLIP STREAM EFFECT acts on powered aircraft with a front engine in a special way.
Lateral Axis:
During changes in engine power, due to the air current near the fuselage, some of the aircraft’s parts produce a particularly noticable moment on the lateral axis.
The SLIP STREAM EFFECT as a Disturbance Effect on Aircraft with a Front Engine
The SLIP STREAM EFFECT acts on powered aircraft with a front engine in a special way.
Vertical Axis:
The spiral airflow around the aircraft generates a performance-dependent lateral pressure on the airframe, wing, stabilizer and fin. This causes a SKIDDING. The direction of the disturbance depends on the rotating direction of the engine.
The SLIP STREAM EFFECT as a Disturbance Effect on Aircraft with a Front Engine
The SLIP STREAM EFFECT acts on powered aircraft with a front engine in a special way.
Indication:
The ball indicates when the longitudinal axis no longer agrees with the direction of flight, in other words when the aircraft is skidding.
The SLIP STREAM EFFECT as a Disturbance Effect on Aircraft with a Front Engine
The SLIP STREAM EFFECT acts on powered aircraft with a front engine in a special way.
Correction:
The correction is made first by pressing the rudder pedal on the side where the ball is located and then the rudder is trimmed.
The SLIP STREAM EFFECT as a Disturbance Effect on Aircraft with a Front Engine
The SLIP STREAM EFFECT acts on powered aircraft with a front engine in a special way.
The compensation of the SLIP STREAM EFFECTS (as a disturbance) is of great importance for maintaining direction during take-off roll (see chapter 12).
The P-FACTOR as a Disturbance Effect on Aircraft with a Front Engine
The P-FACTOR (propeller factor) disturbs propeller-driven airplanes when flying at high angles of attack and high RPM with a force around the vertical axis. The disturbing effect is caused by the asymmetrical airflow of the propeller.
The P-FACTOR as a Disturbance Effect on Aircraft with a Front Engine
Vertical Axis
As with the SLIP STREAM EFFECT, a clockwise rotating propeller is assumed here. If an aircraft experiences a positive angle of attack (see chapter 3.3.1), the downward rotating propeller blade has a higher angle of attack α compared to the upward rotating propeller blade. This results in a higher efficiency on the right side of the propeller and thus a force around the vertical axis (YAW) of the aircraft. This force depends on the angle of attack (AoA) of the aircraft and the propeller speed and causes the aircraft to turn to the left both in climb and in horizontal slow flight.
The P-FACTOR as a Disturbance Effect on Aircraft with a Front Engine
Indication
The ball in the inclinometer indicates when the longitudinal axis of the aircraft does not coincide with the direction of flight when the aircraft is slipping.
The P-FACTOR as a Disturbance Effect on Aircraft with a Front Engine
Correction
Correction is made by pushing the rudder on the side to which the ball is deflected (on the right side of the rudder pedal when the propeller is turning right). When flying with high angle of attack and high RPM (rotating during take-off, climb, horizontal slow flight and e.g. when flying a looping) the pressure on the rudder pedal depends on the angle of attack. The required pressure on the pedal can be quite high under certain circumstances.
The compensation of the P-FACTOR (as a disturbance) has a great importance for the directional stability in the take-off run after rotation (chapter 12). Also the P-FACTOR must be compensated in climb flight (chapter 7) and in slow flight (chapter 10).