Airfoil Sections

[Bootneck]

I have a problem in that I wish, through the use of an Excel Speadsheet, to produce a number of data points that will then be joined together using a spline to create a profile for an airfoil section. Although I have created the Excel spreadsheet with the relevant data (x and y co-ordinates), I don't seem to be able to assign the said data to points on a sketch before joining them together. Is there a way that I can achive what I'm proposing?

All and any help will be greatly recived

 

[SBaugh]

Have you not tried using "curve through free points" as it's called in SW03. In SW04 it's called "Curve through XYZ points". There you can browse for a *.sldcrv or a *.txt file. In Excel you can save your file is a text file.

If you make a file using this command and save it as a file the extension would be *.sldcrv.

Regards,

Scott Baugh, CSWP
3DVision Technologies

http://www.3dvisiontech.com

http://www.scottjbaugh.com

faq731-376

 

[TheTick]

With mathematically critical sections like airfoils, yoou need to pay special attention to curvature and curvature continity. SW splines have bad problems in this area.

Double-check the curvature comb of your splines. Newly drawn splines force themselves to zero curvature (instantaneously straight) at their ends unless specially modified.

If the ladies don't find you handsome, they should at least find you handy.

 

[gsmithengr]

I have a similar problem, I have XYZ coordinates for the end points of tubes in a space frame and want to take them from Excel and display a wireframe looking model of the frame. Since these points were entered by hand there's a good possibility of errors which I wanted to check for by examining the joints to see if they match up. I have written a program in "C" t calculate the tube lengths and angles needed to cut notches in the tube ends and wanted a way to check the wireframe data.

 

[Spinnerman]

I deal with airfoil shapes almost daily. I import an .xp file into excel, extract the points I need to a txt file then open that in the "curve though free points" command. Even though I have 250 to 400 points in each curve the shape is not smooth enough to use in manufacturing (cam) and requires further work in unigraphics. As TheTick said the spline function is not the best.

 

[TheTick]

Sounds like you could use some sort of best-fit least-squares processing of your points, i.e. best fit parabola or x-degree curve through the point cloud.

If the ladies don't find you handsome, they should at least find you handy.

 

[TheTick]

Just what equations/laws govern the shape of an airfoil?

If the ladies don't find you handsome, they should at least find you handy.

 

[sirmick]

I am no air foil expert, but my thinking is that for the top surface you want the profile to be a longer path than the the bottom surface. In order to reduce drag you would want the area normal to the path of flight minimized.

 

[TheTick]

I know with fluid flow, non-C2 (curvature) continuous surfaces can be disruptive. Tangency isn't quite good enough. This could be a big problem.

I did some tinkering. Looks like "Curve through free points" and "Curve through XYZ points" have the same curvature problems.

 

[sirmick]

You know Tick I had thought that C2 might be nicer than C1 or C0 for that matter. But looking at photos of the Stealth Fighter the wings look, at least from a large scale to be near C0 surfaces. Additionally, I remember reading, though I can't recall the source, about a wing treatment that was deliberately rough on the top surface in order to cause turbulence and a larger pressure drop over the wing.

I think what's important is that the fluid flowing over the top surface joins the the fluid flowing over the bottom surface nearing the trailing edge. IM(very)HO

 

[TheTick]

Interesting points, sirmick.

Achieving lift with C2 and C1 discontinuities is not impossible, it's just ineffecient. Also, it can cause stability issues. Ask the test pilot who coined the nickname "Wobblin' Goblin" for the F-117.

As far as roughness goes, I am familiar with that concept (from a college design project involving mortar projectiles). It is the same reason that golf balls have dimples and tennis balls are fuzzy. The principle (as I recall) is to create a thin layer of turbulence to offset the effects that minor imperfections would have on what can never be an ideal shape. This layer actually acts as part of the airfoil, smoothing out the path of the airstream. However, this microturbulence is on a much smaller scale than the overall width of an airfoil.

If the ladies don't find you handsome, they should at least find you handy.

 

[Arlin]

I have heard of a study where a special 'rough' surface actually reduces drag. IIRC, the surface pattern was like raised diamonds (like tread plate), BUT the pattern had to be completely RANDOM.