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First taxi, can't straighten after starting a turn.

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  • #16
    Originally posted by Battson View Post

    This is true for any tailwheel with the king bolt at the correct angle.

    As you add weight into the plane, the king bolt angle will start approaching vertical, and reducing the forces required to re-centre. It's a self-correcting system.

    Are you guys using strong enough tailwheel steering springs??
    You need a spring with a barrel about 1" diameter, and the spring steel needs to be at least 3mm in diameter. 2.6mm spring steel will not be strong enough to command the tailwheel without using brakes / power to help.

    Bearhawk tailwheels can shimmy on hard surfaces, if you put a lot of weight on the tail while moving too fast. On grass, shimmy is never a problem in my experience.
    I have a T3 suspension with Jim Pekola's Tundra lite lockable tailwheel, which is full castering with no steering springs.

    Making progress on fixing this issue. Put my tail wheel on a dolly to eliminate the tail wheel / T3.

    Screenshot_20200610-094339.jpg


    With this, I was able to steer easily to both sides using the brakes.

    Next, I changed the tail wheel to the original leaf spring and Bob wheel. That helped and I am now able to steer to the right using the rudder, and straighten after a sharp left turn, though with a lot of throttle.

    Like before left steering is a non issue, but right turning takes too much effort. Talked to Jared and he confirmed that there should not be too much difference between the two sides. Being a zero time pilot I have no prior experience to compare with, so please bear with me.

    Started looking into the landing gear / main wheel alignment. It seems the problem lies here. Here is what I found:

    Wheel to wheel distance is 72.5" on empty weight.

    Left Toe-in: 1°47'
    Right Toe-in: 2°30'

    Here is how calculated this:

    Screenshot_20200628-203920.jpg

    Not sure why my two wheels are not equidistant from the center. To make sure my fuselage was aligned correctly with the engine crankshaft center I measured the rear landing gear attach point and that seems to well aligned. Could this be due to unequal shock strut lengths? Will measure this tomorrow.

    Screenshot_20200628-204727.jpg

    Found this explanation of the effect of toe-in and toe-out which seems to make sense with what I am experiencing:

    When the wheel on one side of the car encounters a disturbance, that wheel is pulled rearward about its steering axis. This action also pulls the other wheel in the same steering direction. If it's a minor disturbance, the disturbed wheel will steer only a small amount, perhaps so that it's rolling straight ahead instead of toed-in slightly. But note that with this slight steering input, the rolling paths of the wheels still don't describe a turn. The wheels have absorbed the irregularity without significantly changing the direction of the vehicle. In this way, toe-in enhances straight-line stability.

    If the car is set up with toe-out, however, the front wheels are aligned so that slight disturbances cause the wheel pair to assume rolling directions that do describe a turn. Any minute steering angle beyond the perfectly centered position will cause the inner wheel to steer in a tighter turn radius than the outer wheel. Thus, the car will always be trying to enter a turn, rather than maintaining a straight line of travel. So it's clear that toe-out encourages the initiation of a turn, while toe-in discourages it.

























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    Last edited by haribole; 06-28-2020, 07:54 PM.

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