PANS OPS: “ A straight departure is one in which the initial departure track is within 15 degrees of the alignment of the runway centerline. “
Also: “ The minimum obstacle clearance equals zero at the departure end of the runway (DER). From that point, it increases by 0.8 per cent of the horizontal distance in the direction of flight assuming a maximum turn of 15 degrees”
Just don’t turn 16 degrees.....