BUILDING FROM SCRATCH PT 5: PROFILI...

Sticking with the Internet I would now like to give you an example of the digital revolution at its very best. Profili is an airfoil plotting programme produced by Italian Stefano Duranti, and has been around in its earlier versions as freeware, that is to say, you can download it and use it for free. The latest version, 2.1, has increased functionality, and to use its full range of features you need to register and pay a small fee, currently standing at around 10 Euros. It has been said, with some truth, that a magazine columnist is a Scotsman with all the generosity squeezed out of him, but even by my miserly standards that ain't a lot of dough.
So, what do get for your money?
Opening up the programme and looking in the profile library, you will find the sum total of 2,202 airfoils, and if you've ever seen the co-ordinates for just one airfoil, you'll know that an awful lot of work went in there. Having selected the required airfoil, you click on the 'Begin Printing' button and then fill in the necessary parameters, such as chord length, sheeting thickness etc. Clicking 'Rib components management' brings up a dialog box that allows you to input the positions and thickness of the spars, LE and TE. You can also specify whether or not you want the spars aligned vertically (good for spar webbing) or at right angles to the wing surface. Clicking on the 'OK' button brings up a pair of ribs on the screen which, for reasons I can't fathom, are offset from each other, meaning that at the larger sizes they are printed over two pages. A reference line allows you to line up the two parts to produce the final template.
If you want to produce a set of ribs for a tapered or elliptical wing, a dialog box allows you to input the root and tip chords (any pair from the thousands in the library) and to set up the spar parameters in a similar way to the single rib. When processed, the ribs appear to be set on individual sheets of paper (those that aren't large enough to spread over two), so don't get all excited unless you have plenty of paper in stock. For the type of models I design and build, the foregoing describes pretty much all I need to get the job done, but for those who are in love with the whole idea of airfoils, there's plenty more. Profili will allow you to draw many kinds of polars of all the airfoils in the database for different Reynolds numbers.
You can also filter airfoils by geometric parameters to call up similar airfoils to the one you are studying.
To any experienced PC (or Mac) user, an hour or two at the keyboard should allow you to successfully access this programme's features, and even a raw beginner should have sussed it in a few evenings. To any serious modeller this a must-have utility for three reasons:

1: It's ultra simple and easy to use...
2: It costs no more than a couple of pints of Old Peculiar...
3: Although without the more sophisticated features of a programme like Compufoil, Profili will accomplish all the basic tasks you need for designing a sailplane wing and allow you to instantly access all those airfoils.

Stefano has obviously put an enormous amount of work into his brainchild and it typifies much of the downloadable stuff on the Internet which many selfless individuals have provided the wider benefit of us all.