$\zeta$ $\eta$ day

If the lag angle in a helicopter( $\zeta$ ) is given to be 30, and Krish applied a force parallel to an inclined friction less plane where the inclination is just because of $\zeta$ with the horizontal, then $\eta$ of the helicopter's blade due to the Krish's force is?

Details : Angle measured in degrees. Use your mind what can be $\eta$ is?