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3 Answers

Is it true that left turning tendencies increase in ground effect?

Asked by: 3378 views Aerodynamics

In the flare, oftentimes I will end up using additional right rudder to maintain centerline. Is this due to an increase in left turning tendencies in ground effect? If so, why? I don't see any reason why left turning tendencies would be increased.

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3 Answers



  1. Kris Kortokrax on Sep 20, 2015

    Just take a minute to analyze the situation.

    Torque – the throttle is (or should be) at idle. No appreciable left turning tendency here.

    Slipstream – again power at idle. No increase in left turning tendency.

    Asymmetric disc loading – power at idle, no increase in left turning tendency.

    Gyroscopic precession – By flaring the airplane, you change the attitude to a tail low attitude. This would result in a right turning tendency during the flare.

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  2. Brian on Sep 22, 2015

    Though I’ve not read anything that addresses this topic explicitly I can tell you that ground effect alters the local flow around an airfoil. It does so in such a way that it shallows the steepness of both the upwash and downwash. To understand this picture a string being used, in 2d, to represent waves. If you tug on either end of the string the peaks and lulls of the waves would decrease; this is conceivably what ground effect is doing to the airflow.

    That being said the only tendency that would be effected is p-factor, and its effects would decrease as the relative wind angle would decrease. I would find it skeptical to argue that their effects increase. However, as Kris pointed out you are typically in ground in a situation where most of these occurrences would be negligible anyway. Perhaps that is why I’ve never found an analysis of the alteration of their characteristics in ground effect.

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  3. gilbert on Jun 12, 2016

    i totally agree with Kris,
    what i noticed through the years at a home base with prevailing slightly left cross wind is that more then often the pilots, once in the flare, fail to get rid of enough of the crab they used to maintain centreline during approach.
    2. there might also be some weathervaning during the flare.
    since the aircraft is at slow speed, it is easier for a left crosswind to slightly weathervane the aircraft by pushing on the vertical stabiliser and rudder, causing it to yaw to the left .

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