How to specify straightness or profile of surface, of extruded airfoil with GD&T?

[potrero]

I'm struggling with how to provide specifications on a drawing of a 2D-extruded airfoil. At any section, we can easily spec the airfoil's cross-sectional shape using Profile of a Line. But, since this foil is very long (high aspect ratio), we are concerned with indicating how much "bow" and "twist" is acceptable.

Datums: we can define "A" to be essentially the chord line, and "B" to be perpendicular to chord, and tangent to the foil leading edge. "C" is one of the ends.

We've determined that the tolerance for bow in the direction generally perpendicular to the chordline is different from the tolerance for bow in the direction parallel to the chord line. Additionally, the bow perpendicular to chord is allowed to exist in only one direction (toward the concave side).

We could allow something like 0.5 degrees of twist from end to end.

Can anyone help with some advice on how to specify the "bow" and "twist" tolerances? I think some sort of compound tolerance of both Profile and Line may work, but I'm not sure how to set it up.

Thanks in advance.

 

[tbuelna]

potrero,

My older copy of ASME Y14.5M-1994 in section 6.5.5 discusses combined profile control using profile control points, parallelism control of edges, and datums.

 

[drawoh]

potrero,

This is a good question for forum1103.

A GD&T profile tolerance allows you to specify allowable variance.

Read up on the fixturing of flexible components.

Read up on datum targets.

--
JHG