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SNAPS "perpendicular adjustment question
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Art Smith  
#1 Posted : Saturday, May 27, 2017 9:20:12 AM(UTC)
Art Smith

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while attempting to establish a perpendicular with SNAPS from the vertices of a spline curve, some perpendiculars are shown and most are not.............. how do I adjust the SNAPS perpendicular settings to get perpendiculars from all of the spline's vertices ?? see attached image

Art Smith
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Art Smith  
#2 Posted : Tuesday, June 6, 2017 2:29:08 PM(UTC)
Art Smith

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in the absence of Aeropack source code, I'm guessing the "create airfoil" tool uses the selected leading edge and trailing edge to deduce the required chord, then uses a set of equations similar to those found at Airfoil Tools (http://airfoiltools.com/airfoil/naca4digit) to calculate a set of points for the upper and lower surface, and then connects each set of points with a spline. clearly then the spline doesn't pass through each of the points creating a challenge for the "perpendicular snap". if the points along the upper and lower surface defining airfoil spline were equally spaced, the problem could be simply overcome by distributing equally space points along the spline curves and using them in lieu of the calculated points. the points however are NOT equally spaced, they're cosine spaced to pack more points into the front of the airfoil where there's more curvature !!!

hence the question on how to "help" the perpendicular snap tool.................

Art Smith
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Tim Olson  
#3 Posted : Tuesday, June 6, 2017 4:08:00 PM(UTC)
Tim Olson

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>> clearly then the spline doesn't pass through each of the points

Hi Art

The equations for the airfoils came from Theory of Wing Sections. The points that are calculated from the resulting equations are then fit using a B-Spline. They are fit to within 0.0005 inches.

The difference you may see on the screen may be due to the display list. The display list is the visual representation of the equation to the screen.

To get the best displayed curve try using Edit : Resolution : Super Fine: Precise.

This is an option for equal point spacing along the curve (not wrt chord) to complement the cosine distribution. The cosine distribution typically does a better job at the leading edge.


Tim

Edited by user Wednesday, June 7, 2017 4:28:49 PM(UTC)  | Reason: Not specified

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Tim Olson
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Tim Olson  
#4 Posted : Tuesday, June 6, 2017 4:18:55 PM(UTC)
Tim Olson

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>>how do I adjust the SNAPS perpendicular settings to get perpendiculars from all of the spline's vertices ??

LogiCursor perpendiculars are calculated from the current cursor location back to the curve. I'll add in a Perp from location into PowerPack for you, something I have been meaning to do.


Tim


Tim Olson
IMSI Design/Encore
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Art Smith  
#5 Posted : Tuesday, June 6, 2017 5:38:45 PM(UTC)
Art Smith

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Tim-

thanks!! I've used the "equal" spacing option when only a cartoon/graphic is needed; it's cosine spacing whenever parts will be machined to the solid model.

"Theory of Wing Sections" is a great deal more readable than the original NACA reports which will never be mistaken for Tom Clancy or Raymond Chandler.....!!

Art Smith
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Art Smith  
#6 Posted : Monday, June 12, 2017 4:02:27 PM(UTC)
Art Smith

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a "Shout Out" to Tim and the team for the recent changes that fixed my normals problem!! the improved capability/new tools are a HUGE step forward !!!

Art Smith
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Tim Olson  
#7 Posted : Wednesday, June 14, 2017 11:42:57 AM(UTC)
Tim Olson

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Awesome!

Video showing the minor tweaks in SharkCAD Pro 1341 for AeroPack: NACA airfoils and new PowerPack: Line Perp.

http://www.csi-concepts.com/Demo/videos/NACA.mp4

Tim
Tim Olson
IMSI Design/Encore
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