A WARNING TO ALL BUILDERS
ABOUT THE USE OF FULL-SCALE DRAWINGS
The plans for most homebuilt aircraft with wood wings include a full-scale drawing of the wing rib. In addition, other items on the aircraft may have full-scale drawings available from the designer to be used as templates in the construction of the aircraft.
It is standard practice for homebuilders to have their original plans duplicated, creating a "working" set of drawings from the "master" set of drawings. These working drawings are the ones that the aircraft is actually constructed from while the master set is put away in a safe place.
WHEN HAVING FULL-SIZE DRAWINGS DUPLICATED, ALWAYS CHECK THEM FOR DIMENSIONAL ACCURACY AGAINST THE ORIGINALS. It is VERY common for the copy to have been slightly enlarged or reduced during the duplication process. Tell your duplicators that the drawings are full-size templates and that it is critical that they duplicate the drawings EXACTLY. If they cannot guarantee accuracy, go somewhere else. When you pick up your copies, place the duplicate over the original and hold both up to a light. If the drawings aren't exact, do not accept the duplicate for use.
BE ESPECIALLY CAREFUL WITH FULL-SIZE WING RIB DUPLICATES! If you've already made your jig out of a copy of the rib template, a quick check for accuracy is to measure the dimension between the fore and aft spar center lines. On the Hatz CB-1 it should be 25 inches. If this dimension on your template does NOT equal 25 inches, then the template is not usable.
-Doug MacBeth
American Hatz Association