Understanding Propeller Torque and P-Factor: Difference between revisions

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(added propwash, which is actually the most important factor)
(→‎Propeller Torque Effect: change to conventional "clockwise from the cockpit")
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Torque effect is the influence of engine torque on aircraft movement and control. It is generally exhibited as a left turning tendency in piston single engine propeller driven aircraft.
Torque effect is the influence of engine torque on aircraft movement and control. It is generally exhibited as a left turning tendency in piston single engine propeller driven aircraft.


According to Newton's law, "for every action there is an equal and opposite reaction," such that the propeller, if turning counterclockwise (when viewed from the front), imparts a tendency for the aircraft to rotate clockwise. Since most single engine aircraft have propellers rotating counterclockwise, they rotate to the left, pushing the left wing down.
According to Newton's law, "for every action there is an equal and opposite reaction," such that the propeller, if turning clockwise (when viewed from the cockpit), imparts a tendency for the aircraft to rotate counterclockwise. Since most single engine aircraft have propellers rotating clockwise, they rotate to the left, pushing the left wing down.


Typically, the pilot is expected to counter this force through the control inputs. To counter the aircraft roll left, the pilot applies right aileron.
Typically, the pilot is expected to counter this force through the control inputs. To counter the aircraft roll left, the pilot applies right aileron.
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This correction induces adverse yaw, which is corrected by moving or trimming the rudder (right rudder).
This correction induces adverse yaw, which is corrected by moving or trimming the rudder (right rudder).


Aircraft with contrarotating propellers (propellers that rotate in opposite directions) counteract the torque effect, so that no compensation is needed.
On aircraft with contrarotating propellers (propellers that rotate in opposite directions) the torque from the two propellers cancel each other out, so that no compensation is needed.





Revision as of 07:41, 21 June 2006

This is an attempt to answer the frequent question "Why is my aircraft turning left all the time?"

This occurs only in aircraft with propellers at the front of the aircraft. Three distinct phenomena cause the effect, all causing the aircraft to turn in the same direction. They are:

Prop wash

A propeller pushes air not just horizontally to the back, but more in a twisting helix around the fuselage (clockwise as seen from the cockpit). As the air whirls around the fuselage it pushes against the left side of the vertical tail, causing the plane to yaw to the left. The prop wash effect is at its greatest when the airflow is flowing more around the fuselage than along it, i.e., at high power and low airspeed, which is the situation when starting the takeoff run.

Propeller Torque Effect

Torque effect is the influence of engine torque on aircraft movement and control. It is generally exhibited as a left turning tendency in piston single engine propeller driven aircraft.

According to Newton's law, "for every action there is an equal and opposite reaction," such that the propeller, if turning clockwise (when viewed from the cockpit), imparts a tendency for the aircraft to rotate counterclockwise. Since most single engine aircraft have propellers rotating clockwise, they rotate to the left, pushing the left wing down.

Typically, the pilot is expected to counter this force through the control inputs. To counter the aircraft roll left, the pilot applies right aileron.

It is important to understand that torque is a movement about the roll axis. Aileron controls roll. Prop torque is not countered by moving the rudder or by setting rudder trim. It is countered by moving or trimming the aileron.

This correction induces adverse yaw, which is corrected by moving or trimming the rudder (right rudder).

On aircraft with contrarotating propellers (propellers that rotate in opposite directions) the torque from the two propellers cancel each other out, so that no compensation is needed.


Further Reading: Propeller Torque Factor

P-Factor

P-factor is the term for asymmetric propeller loading, causes the airplane to yaw to the left when at high angles of attack.

The descending right side of the propeller (as seen from the rear) has a higher angle of attack (than the upward-moving blade on the left side) and provides more thrust.

According to What You Need to Know About Aerodyanics... by Franklin Gutierrez.


Gyroscopic Precession

This is the tedency of a spinning object to precess or move about its axis when disturbed by a force. The engine and propeller act as a big gyroscope. However, gyroscopic precession is likely to be minimal in a typical aircraft.

Gyroscopic precession is frequenly confused with p-factor.

One author maintains p-factor is caused by a combination of factors unrelated to gyroscopic precession http://home.earthlink.net/~x-plane/FAQ-Theory-PFactor.html