You gotta zoom in to see the plunge marks. There is a circle with a half line the diameter of your selected router bit. And you can copy/paste them. But they are very small. Until you zoom in you probably would not see them.

I have built some ribbed wings but I covered them with 1mm Depron sheeting. I like the way you are doing yours.

It will interesting to see how it fares when you apply the film covering and heat.

 

hmmmm, it looks like whoever modified my original plunge code broke it. I'm not sure who changed it, but I did see in the comments that they had made changes to the plunge code.

 

Hi rjarois,

I won't say it won't work, but think the spar can be built alot stronger. Haven't design a wing before, but I have built balsa models and familiar with the theory. So my 2 cents worth:

The bending stress is actually zero at the middle of the spar and maximum at the edge. So what you want is a carbon on the top and bottom surface of the spar. The material placed in the center is less important, except to hold the structural parts together. If you ever built any balsa model, that's how the spar is made with spruce top and bottom; and vertical grain balsa in between. Basically, you want to build something more like a large tube than a thin rod.

-Kwok

 

I am using a single carbon tube in my foam wings and it works just fine. However, I have a foam sheet covering my wing. That could be quite different than if you are covering with a film covering.

Check my tribute 4D posts.

 

Have you seen this design? I remember him, because he had some of the best videos and his plane looked like a really good design:
http://www.rcgroups.com/forums/showthread.php?t=827488

-Kwok

 

It's just two carbon tubes instead of 1 in the middle. Here is a quick cross section.

Attached files

 

Randy, to add to Kwok's explanation, the portion of a wing that ALWAYS fails first is the Upper Skin, in compression. Don't believe me? Take 2 straws from a broom and hold them together, parallel, from the ends, one directly above the other. What you are simulating is the upper and lower beams on one wing, from the root to the tip.
Now bend them as if the wing were flexing upward at the tip, keeping them taut.
What happened? Did the lower straw break because of the added tension? (nope)
Did the upper straw bend in the middle and collapse in compression? (absolutely)
Even steel or concrete beams fail on the compression side of the beam, in bending. Ask your college Dynamics Professor if you still don't believe me.
My point is this: The most important surface or spar to stiffen with carbon is the upper one, as close to the upper, outer surface as practical. :geek:

 

Hi, I don't want to give the mistaken impression that it's got to be done a certain way. Design is all about compromise. If you think it strong enough, then certainly you can do something because it has other benefits, like cheaper or simpler. I mean, flat foamies, break all the rule and generally need to be strengthened with carbon. But I have seen, built up foam wings, that use no carbon. In the end, you make you choices and you take you chances.

Here is one I am looking at , the regal. It just has single spruce spar and a KF wing, which would be very similar to your single carbon tube. So go for it!
http://www.rcgroups.com/forums/showthread.php?t=712006

-Kwok