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Design and Development of Stolspeed Vortex Generators
I originally became interested in vortex generators (VGs) in an effort to improve STOL performance on my homebuilt aircraft. See STOL Action video.The vortex generators improved STOL action very well as you can see, but from all that STOL flying I realized how valuable they are as safety devices on any aircraft. The safety benefits alone are so important that all aircraft should use them even if you’re not interested in STOL!
I’ve tried three brands of production vortex generators (CCI, Landshorter, and Pacific Northwest Aero), as well as homemade ones, in an effort to find the best vortex generator design. I placed a different brand on each wing and flew every test to the extreme limit, then swapped brands wing-to-wing to eliminate any bias in the aircraft itself, and did it all over and over again. Many, many hours of flight testing at first light when the air was still and steady. Any differences in performance should show up readily in this wing-against-wing balance test. Despite the very different shapes of each of these vortex generators, and claims of wind tunnel testing, etc., etc., I could detect no real difference in performance of any of the production brands of vortex generators – they all worked equally well!
All of the vortex generators that I tested worked well enough, but it seemed that all the designs of VGs could be considerably improved in regards both user-friendliness and appearance. All of them have sharp points on them, which once drew blood when a full jerrycan of fuel pinned my hand against one. The extruded aluminum ones have a long flat base that doesn’t fit the wing contour at all. The homemade ones do work but look pretty crude. All of them have angular lines and square corners, which doesn’t suit the sweeping, curved lines of a aerofoil wing, so they look like stuck-on after-thoughts.
Homemade
Pacific NW aero
Landshorter
C.C.I.
Stolspeed Smoky (discontinued)
Stolspeed Clear
Being a practical designer and tinkerer, always looking for better ways of doing things, I decided we need better vortex generators . So I designed my own vortex generators with fully rounded and flowing lines, and flight tested them against the production models – same performance again.
I decided to go with polycarbonate because it’s the ideal material for such a part. It’s very tough, flexible and resilient, and because it can be injection moulded, it can be made to any shape at all. This allows the base to be curved to suit the curvature of the wing surface. The other advantage of polycarbonate over aluminum is the flexibility that can be designed into the fin, so that it can ‘give’ and absorb impact rather than pass the impact to the wing skin.
I’ve seen an impact on an aluminum VG put a permanent dent in a tin wing – if it’s a fabric wing it’s likely to cause a tear. Stolspeed vortex generators have a very slim rounded fin to give them good flexibility, and a rounded, tapered base that ‘flows’ into the wing surface. They really do look like they’re meant to be a part of the wing rather than a ‘stick-on band-aid’. In clear material they’re almost invisible.
There are many different grades of polycarbonate, from food grade to bullet proof. I selected the material that’s used here in Australia for skylites and roof panels. Australia has a powerful lot of sunshine all year round, and some of the highest UV levels anywhere. This polycarbonate material, Makrolon® manufactured by Bayer®, has proven itself on many roofs for many years through sun and hail, then I take it to another specialist processor who melts in even more UV stabilizer. It’s increased the cost of the material, but we do want the very best, eh!
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