Vortilons are small tabs which extend forward from the leading edge of the wings. The word actually comes from two words: Vortex and Pylon. Here’s some aerodynamic science for you:

Vortilons officially first appeared when Douglas was developing the DC-9.  As is typically the case, rather than re-invent the wheel, previous technology and parts are used to speed up development.  In the case of the DC-9, Douglas engineers, decided to use the same wing design as the DC-8. The difference between the two is that the DC-8 had four engines under the wing (on pylons) where the DC-9 had them on the tail.

When they started testing, the engineers discovered that the wing had significantly less lift at low speeds (landing and takeoff) than the DC-8 wing. Since the only difference in the wing design (other than the engine location) were the pylons, they installed just the engine pylons under the wing.  And the lift returned! So the engineers made the pylons shorter and shorter until the lift diminished.

The result became what is now known as a vortilon.

What happens is with swept wing designs (although similar behavior can also occur on non-swept wings), as the angle of attach increases, the flow of air begins to move span-wise (toward the side) as opposed to chord-wise (front to rear).  One of the solutions is to install a fence.

Mig-17 with stall fences.

This prevents the air from moving towards the wingtip. The down-side to stall fences is that while they are only needed during high angles of attach (landing and takeoff), they incur a permanent drag penalty.  Anything sticking out creates drag.  And drag reduces speed.

Vortilons create a rotating spiral of air (vortex) that acts as a stall fence. But they are only doing this at high angles of attack. During low angles of attack, the vortilons aren’t doing much of anything.  Think of vortilons as stall fences that mostly retract when not in use.

Here’s a Starship (because, you know, they’re cool) where you can see four vortilons on the lower, leading edge of the wing.

The vortilons which come with the kit are rough fiberglass and about the same size. Because this is a highly visible, finish type part, I deferred it to the guru of all things finish (Malcolm).

Here is a picture of a set of vortilons (from Jorge Bujanda’s site) after being trimmed down.  The size goes from large to small as they go inboard to outboard.

Then they have to be filled, primed, sanded, filled, primed and painted.

Now they do stick out a ways, so it would be real easy while working on the plane to run into one and break it off. So I’m not going to install them until I’m ready to fly. But the positioning is rather important. The location is easy to measure. Just measure out from the wingroot 18″, then 36″ more and then another 36″.  Getting them aligned is another story. For that Malcolm has a template he created.

First a mark is made on the leading edge. To get it perfectly on the leading edge, I kinda made a tool.

Then I placed the pencil against the leading edge with a level. While keeping the level/pencil perfectly plumb, I moved everything across the leading edge of the wing. The result is a perfectly straight line which is exactly on the leading edge of the wing.  Now I probably didn’t have to be that precise, but it wasn’t that hard.

Next the template is aligned with the mark on the leading edge and rolled under the wing.  Then simply mark the wing on that line.

Now when it’s time to install the vortilons, I just have to line them up with the mark.