There are several causes for this condition. Please see the table below.
Note.
Some yawing to the left, (port) on takeoff is a normal condition, and some use of right rudder is to be expected when the aircraft has enough ground speed to give rudder authority.
Root Causes for this inherent condition, are:
1. Prop. wash hitting the port side of the fin, yawing the aircraft to port.
2. Engine reaction torque putting more force on the port wheel thus creating a fulcrum out of it, leading to a swing to port.
Both of these root causes are normally addressed with engine right trust as this provides an equal and opposite balancing starboard yaw.
Link to related article > Tracks Right on Takeoff Run
| No. | Cause | Fix | Comment |
| 1 | Undercarriage alignment error. | Ensure the under carriage axle line is perpendicular to fuselage. | If the undercarriage has been knocked or bent, for example with a rough landing, then tracking will have been upset. Check by looking at the undercarriage from underneath the fuselage to ensure the axle line is perpendicular to the longitudinal axis of the fuselage. |
| 2 | Insufficient right thrust. | Increase engine right thrust. |
i.) Right thrust is incorporated in the main to counter the prop. wash and engine reaction torque effects. If right thrust is absent insufficient, a strong turn to port on the takeoff run will usually be seen. ii.) If right thrust is correct, aircraft will usually still swing to port on the initial part of the takeoff run. (contribution from Adrian Smith). The reason here, is that at very low air speed, when forward motion is just beginning, the fin/rudder combination has little aerodynamic effect. For this reason it is normal for pilots to expect to make rudder corrections during the takeoff run just as soon as the fin/rudder combination becomes aerodynamically effective. iii.) If right thrust is absent or insufficient however, then the ability of the fin to correct the takeoff run is marginalised and in the worst case the takeoff can prove impossible to correct. iv.) Should the pilot manage to get airborne with right thrust absent or insufficient, then he should see that the aircraft flies with significant left, (port) yaw. If the pilot manages to trim the aeroplane on aileron and elevator for hands off straight and level flight with such a right thrust error present, then the aircraft will be seen to fly in a continuous flat turn to port. For this reason optimised right thrust is essential. Fortunately it is easy to incorporate, with one to two degrees being usual. Further adjustments being made after flight tests.
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| 3 | Excessive friction on port main wheel. | Lubricate main wheels. | If the port wheel has high friction it will create drag. The wheel will become a fulcrum and the aeroplane will yaw to port. |
| 4 | Fin alignment error. | Correct the fin alignment. |
Check visually by sighting centrally down the fuselage from the front of the aeroplane. If the fin is offset, the offset will be visible. A quick temporary fix for this condition is rudder offset. Once the fault is correctly diagnosed, the pilot will typically make small adjustments until the ground tracking is correct. Note: Building errors like this should ideally be picked up before the maiden flight. Note a second possibility is the banded tailplane. Here the fix is to key the tailplane to the fuselage such that once banded on it cannot move.
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| 5. | Wing warp. | Correct the wing warp. |
If one wing is warped it will create extra drag and turn the aircraft. If an aircraft with this condition gets airborne it will be considerably out of trim and will require fast action by the pilot at the trims to get the aircraft flying. Note: Building errors like this should ideally be picked up before the maiden flight. |
Comments
20th. April 2016
Added points 4. and 5.
Article tidied and improved with added detail.
The idea for point 4., fin alignment, is contributed by Adrian Smith.
21st. April 2016.
Extensively modified point 2. in line with Adrian Smith's point that some yawing to port is normal on the takeoff run and corrected using rudder by the pilot.
Improved the header on Root Causes for the inherent port yaw on most aircraft.