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Aeronautics: Aerodynamic Wing Rib Design

In this section I'm showing the basics of how to design and draw an airplane wing rib.  I developed and tested this particular wing rib for a rocket-launched glider.  It needed to be balanced for both "high speed - low drag", and "low speed - high lift".  That's really an oxymoron in term and application, so a reasonable compromise must be found.  I tested this design on a small model that launched to about 350 feet in 1.5 second.  This wing rib was the first thing that I designed at the very beginning of the project, and it held true throughout.  It took another year and a half of trial and error to develop the glider, rocket body, and glider release/parachute mechanism.  It was launched, and flown without error or damage 72 times.  

The first aspect of the wing rib to decide upon; is the percent of the Cord Height (thickest part - line C) of the wing rib, to the length; from Leading edge to Trailing edge.  Note that line "A" is 36% of line "B".  36% is a very median amount.  Many higher speed, but subsonic aircraft measure 40 or even 42 percent, while a performance glider might measure closer to 25 percent.

The next aspect is, Cord Height to Rib Length Ratio.  In this ratio, you must consider, not only the effect on drag and lift, but strength of the rib and wing, also.  The ratio here, is 8:1. 

This is a suitable way of forming the curves in the leading edge.  You'll notice the I adjusted the size of the oval to create a curve between the leading edge and highest point of the cord.  There are a variety of ways to do this, but shown, is about the quickest and easiest.  Notice the small size of the oval used for the leading edge.  This is not typical for a low or moderate speed.  I specially decided on a sharper leading edge for the speed attained during the "rocket" launch.

Now you can see, I've flipped the oval in order to draw the back side of the curve.

The center line of the oval used for the curve, at the bottom of the leading edge must NOT extend to the cord, but to the base line.

Now you've got the basic shape, and it's reading for modifying for the leading and trailing edges, spars and stingers.  I found that "boxing" the top (only) of the leading edge added extreme strength without much weight.

You'll notice (below) that even though apparently setting flat, that the angle of attack is about 4.5 degrees.

I built this image very fast and it's a bit rough, but with some time and care they can be completed with fine detail and smoothness.  It's just a matter of how much time you put into the accuracy.

I've been meaning to work on this image to show it can be done with more quality.  This better, but I still didn't really spend much time on it. The bigger you make it, even if then you need to shrink it for your model, the better the quality of detail you can arrive at. - Ed

Most any drawing software that has reasonably accurate (0.01) scaling and grid options may be used for this application.



All material is the property of E. Alan Swearingen , and plagiarizing, downloading or hot linking images is expressly forbidden.



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