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Important Update regarding Open-EZ Rev 5 Templates


*** IMPORTANT ***

Inaccurate reference measurements have been identified in the Open-EZ Revision #5 Templates that can result in improper airfoils. In 3 of the 14 templates the X and/or Y reference dimensions are off by exactly 1 inch. This was a result of human error (mine) where I used the 1" mark on the tape measure as "zero" (for accuracy), but forgot to subtract 1" at the far distance.

Specifically, the following is the status of the Revision 5 templates:
  • A1: 23" x 16.5" is good
  • A2: [s]23" x 17"[/s] should be 23" x 16", building to incorrect dimensions will result in:
    • The GU canard core templates will be ~1/4" less thick than they should be.
    • The instrument panel bulkhead will be ~1/4" short (relative to the waterline).
    • Printing and not scaling to match the measurements would have been better in this case (assuming a ~1/8" typical "first try" inaccuracy of most large format printers).
  • A3: 23" x 17" is good
  • A4: 23" x 17" is good
  • A5: 23" x 16" is good
  • A6: 22" x 17" is good
  • A7: [s]23.5" x 18.125"[/s] should be 22.5" x 17.125", building to incorrect dimensions will result in:
    • Just a bigger reference drawing, since the aspect ratio is preserved 1:1.
    • Printing and not scaling to match the measurements would have been better in this case (assuming a ~1/8" typical "first try" inaccuracy of most large format printers).
    • Ary Glantz has an excellent write-up on his blog site how he discovered this issue and corrected it.
  • A8: 23" x 17" is good
  • A9: 23" x 16" is good
  • A10: [s]17" x 22"[/s] should be 17" x 21", building to incorrect dimensions will result in:
    • A longer main wing chord and overall skewed hotwire templates at butt-line 55 and 23.
  • A11: 23" x 17" is good
  • A12: 23" x 17" is good
  • A13: 23" x 16.5" is good
  • A14: 23" x 17" is good
These correct dimensions above are entirely accurate and verified. If you print templates, adjusting scale as necessary, using these corrected dimensions you will have perfect templates. If your reference checks are off at all, it means your prints are off; NOT the marks themselves.

What to do if you've already built something

Most of the templates are accurate, and there's no cause for alarm in those areas. However...

Canard (the 'GU' canard)

If you have already built your canard with the A2 templates you must destroy your canard and either find plans for the Roncz canard or wait for the next Open-EZ update. If you've gotten this far you should know you would prefer the Roncz canard versus the GU canard anyway (and hopefully never built the canard).

Main Wing

If you have already built your main wing with the A10 templates you may have seen butt-joint surfaces off ~1/8" along a straight-edge. This can be addressed as part of the standard wing glassing, filling, smoothing, and finishing operations. Regardless, I would wait for the updated Open-EZ templates to compare against before you consider flying.

Your responsibility as a distributor of 'Open-EZ Rev 5' template files

The Revision 5 templates have not been available from the Canard Zone since January 26, 2010, but several web sites and other sources have since made these templates available (even before then). If you manage one of these web sites or have downloaded the template files and shared with others, it is your responsibility to notify everyone who has or will have downloaded the template files of this information. If you know of one of these web sites or download locations please pass along and share a link to this post.

Next Steps

Plans and efforts are already underway for an update to the Open-EZ templates, with a much improved technique for ensuring accurate analog AND digital template versions. Understand that simply because someone may have templates or drawings that are "in CAD" does not necessarily make them more accurate than something hand-drawn on paper. The concern is twofold: 1) what source was used to serve as the CAD reference (was the source accurate?), and 2) how exactly were the templates (dimensions) translated from analog to digital? In the case of the Open-EZ templates, several original plans were utilized (at least 4 different complete original sets) to determine and set accurate reference dimensions and marks. The Open-EZ templates are precise to <1/64" relative to the templates that were inspected.

Please be careful. If in doubt, stop and get help, and by all means feel free to share your situation here.

Sincerely,
Jon


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