Archive of the Yahoo! Groups mailing list for the Bug hand-launch glider 2002-2018

From: "Mark" <flyeround@...>
Date: Wednesday, March 7, 2012 10:30 AM
Subject: Wing Stringing - or Wing Spars, Turbulators and Aerodynamic Efficiency
Just a few thoughts from a traditional "stick and tissue" builders viewpoint. As far as I know what follows is common on both sides of the Atlantic. I'm in the UK. "Stringers" are the, usually, supplementary strips used to give shape to a fuselage in traditional building, say in a scale model, "Longerons" are the full length structural fuselage members. The full-span members of a wing are usually called "spars", and their use is structural BUT their use in increasing the aerodynamic efficiency of a wing has also been known in modelling for many, many years because of the effect they have of turbulating the flow of air over a wing. (July & October 1947 Aeromodeller articles talk about them being "well known" and the 1938/39 Zaic Yearbook talks about experiments by a Mr Jacobs) See also Wikipedia "Aifoil Turbulator" and elsewhere no doubt, for a fuller explanation but basically any spanwise disruption of the flow of air over a wing will induce turbulance in the boundary layer and the effect of this is to reduce drag. Even now in the days of very smooth,regular and even wing surfaces the world-class free flight guys will add "disruptors" or "turbulators" on their shiny smooth wings by adding one or more very narrow strips of tape along the wing near the leading edge to create this effect. The same effect can of course be built in by using wing spars which will alter the way the covering material covers the wing. Interestingly too, rough wing surfaces can act the same way – so what does this say about the shiny film in almost universal use? I know there are also theories about the sagging of covering material between ribs and how this may, or may not, reduce efficiency, and obviously wing spars would reduce this effect. I have it in mind though that, counter-intuitively, this has little effect on the efficiency of a wing – but I could be recalling the article I read wrongly, and I will do some more research if people are interested. Most of this knowledge is within the vintage areomodelling movement where these methods of building are commonplace. Very little is new in this world – it just has to be re-discovered! Keep the BUG flying!