Jedelsky style for small wings

11 October 2022

Respect to Mr. Jedelsky who came up with his jedelsky construction:

• thick balsa leading edge sheet (sanded to front-upper curvature later, making the leading edge stronger to withstand wing dings)
• thin balsa sheet rear of leading edge sheet (forming to the rear-upper curvature)
• identical ribs to maintain the airfoil (simplified one rib template for almost any wing planform and did you know that these ribs are longer then the wing chord for stable construction and excess protrusions shall be trimmed off after the top sheets are in placed?)
• if trailing edge at wing tip is shorter than wing root, washout results; vice-versa for leading edge taper and trailing edge taper towards wing tips. (automatically creating washout without causing stress to the wood components)
• when the wing tip is shorter than the wing root, the depth/thickness of the wingtip goes progressively lesser because the bottom of the ribs is trimmed off (automatically creating a tapered thickness across the span of the wing)

However, it is relatively heavier then a framework style wing construction, so it may be too strong (read "heavy") for small and very light wings because too much balsa is used. 

So the solution is to change this sheet construction to frame construction, but this loses some of its simplicity and adjustments have to be made and compromises accepted.

The first order of conversion may be using a rectangular section of thin balsa sheet to frame the trailing edge, leaving large area of wing that is rear of leading-edge sheet empty and to be covered by tissue. The front edge of this strip will present a slight bump air flowing underside, but this bump should not affect the airflow much because it is going to be used for a slow flying model and my priority goes to air flow over the upperside (and looks).

The second adaptation is to the ribs.

The jedelsky rib has the front as a straight slope and the rear as a curved slope to accept the trailing sheet. However, there is only a trailing edge strip in placed for a jedelsky frame-work styled wing, so the rear need not be curved. At the trailing edge receiving the thin trailing rectangular strip, it could be a straight slope as well. The original jedelsky idea is to leave the in-between proud of the rear edge of the leading edge and front edge of the trailing rectangular strip and when the glue has set, trim away in-situ to form that bit of curve for supporting the tissue covering. But each rib will be different for anything other than a rectangular wing planform because the leading and trailing strips are not paper thin. So this is not going to work, as I cared more for looks upper surface.

The compromise to make identical ribs possible is to make each rib to comprise of a lower main rib which is largely triangular in view for the gluing of the leading-edge sheet and trailing edge strip, and then an upper rib to support the tissue covering. These upper ribs are not identical, they have to be customised to each distance between the rear of the leading-edge sheet and the front of the trailing edge strip. It is not a cap-strip of consistent thickness; it is a trapezoidal extension on top of the lower main rib that is measured and cut to the actual distance.

   

Now, some checks for consideration.

It is going to be used for small, light, slow flying models. I would probably use 1/32" balsa sheet for the trailing edge sheet. This means the bump is equally small and on the scale of things, what is that over a mere few inches of wing chords? Maybe simple triangular ribs will be enough. If we view the model from 2 metres away, I think the 'bent' airfoil would look ok.

The main strength of the wing is dependent on the leading-edge sheet. Since the intention is to use 1/32" trailing sheet, the leading sheet should be slightly thicker, maybe a minimum of 1/16" for super light and upto 1/8" for rough and tumble. 

For 1/8" leading sheet, I think it is neater if the rear end is shaved to 1/16" or thinner for minimal sanding and better looks. So a simplified 'blank' for the 1/8" leading sheet is to have the rear edge shaved/sanded down from the middle of the strip to the rear end at 1/16", 1/32" if I am daring.

All the above is just thinking about it. When doing up for real, I may realise something I overlooked and adapt accordingly.