What conventions are used to determine the orientation of principal axes?

[paddles069]

Hi, having trouble determining the convention for determining the orientation of the principal axes.

(Please refer to the attached file for a diagram of my question)

So in Q1, theta = -19 degrees and the principal axes is rotated one of the following the conventions (from what I can tell):
1 - clockwise is negative or,
2 - angle starting from positive z axis going towards positive y-axis is negative

In Q2 however, theta = -12.15 degrees but the principal axes is rotated following one of the following conventions:
1 - counterclockwise is negative
2 - angle starting from positive z axis going towards positive y-axis is negative

Am I missing a convention here? Why do the two problems follow opposite conventions?

 

[SteamKing]

What's the width of the flange in the Z section in Q2?

 

[paddles069]

The width is not important in answering my question.

 

[nvn]

paddles069: Counterclockwise is positive. Therefore, there appears to be a typographic mistake in Q2. I think the -12.15 deg in Q2 should instead be 12.15 deg.

 

[SteamKing]

If you want to check the orientation of the principal axis of the Z section without knowing the width of the flange, good luck!