The helix is given by $x = \cos t$, $y = \sin t$, $z = t$, for $0 \le t \le 4\pi$.
Then $\vec{r}(t) = \cos t \vec{i} + \sin t \vec{j} + t\vec{k}$.
$d\vec{r} = (-\sin t \vec{i} + \cos t \vec{j} + \vec{k})dt$.
$\vec{F}(\vec{r}(t)) = 4\sin t \vec{i} - \cos t \vec{j}
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