Since you're stuck in the orchard... (Just think,you have to put up with NO Internet Explorer related viruses.)..
To do the intermediate ribs, take the root rib coordinates and the tip rib coordinates...
Determine the difference at each x-ordinate for each y-ordinate between the two.
Determine how many ribs you want.
Divide the differences you've found by the number of ribs for each intermediate location.
For each intermediate rib then, add/subtract the ratio'd difference for each y-ordinate at the corresponding x-ordinate.
Plot the result.
I wrote a program many years ago to do this, and ouput the results in Autocad script file format, and Generic CADD batch file format.
It's very easy to do with BASIC, but the program I've written that does this runs only on a DOS machine. Sob!
If the spirit moved me I'd move the program to a Windoze thing, but Profili does it so much better..