I don't know of anyone that has described slats or Vortex Generators (VGs) as a spin prevention device. They may contribute in a small way by delaying aerodynamic stall. However, if the plane can stall, it can also spin.
Vortex Generators: There is a lot of debate an a lot of wild claims in the STOL circles about the virtues of VGs on an aircraft. Many claim significantly slower stall speeds, but in almost every case, actual testing typically shows little to no difference in the actual stall speed. However, what VGs do very well is to energize the airflow over the wing to delay the detachment of the air flow. What that means to you as a pilot is that by proper placement of VGs on the wing of your plane, the boundary layer has more energy, and the ailerons will be much more effective through out the slow flight regime right down to stall. Depending on the aircraft, there may be a small reduction in stall speed. Nothing comes free, so there is a penalty in drag that you will pay for installing VGs on your wing. I installed VGs on my extended wing SuperCub clone. On a plane as draggy as the Cub, the drag penalty is unnoticeable, and I did indeed find that the ailerons are much more effective in extreme slow flight and high angles of attack. If they made any difference in stall speed, it wasn't really measurable as my SuperCub Clone simply will not break into a clean stall from slow flight. Slats: There's not much question that slats will delay aerodynamic stall at high angles of attack. They capture a lot of air and direct it over the top of the wing, creating an energetic air flow that will keep the flow attached down to a lower speed. But there is a huge drag penalty to pay for this STOL performance. The Zenith CH-750 is a good example of a plane with a fixed slat. It will fly at extreme angles of attack, and incredibly slow. However, cruise is also incredibly slow. Many of the Zenith owners are removing the slats from their 750s as they are finding the plane is much better mannered without the slats, cruises significantly faster, and looses so little in slow flight/stall speed that they find the trade off to be better without the flaps. Aerodynamic Slats: Aerodynamic slats are becoming all the rage with the STOL crowd. Many of the Valdez competitors are now sporting aerodynamic slats. The Cub style has a slat that pivots on the mounting standoffs, so they close off relatively cleanly for cruise, and pop open at high angles of attack. There is both a weight and drag penalty to be paid by adding these to your wing, but they are an easy retrofit to install. The Pegazair style has a slat that rolls straight out of the leading edge. I have flown with this style and found them to be highly effective and clean for cruise flight, but this type has to be designed into the wing before construction and also comes with a weight penalty and some complexity added to the wing build. I wouldn't think VGs would be a good solution for a KR. They will not prevent the wing from stalling, and are unlikely to noticeably lower the stall speed. They will not prevent a spin. However, they will make the ailerons more effective down into the stall. That's not something I have really found a need to have, and I would not be willing to pay the drag penalty on a clean plane like my KR. Regarding spins in a KR. I have spun my KR. It's been a number of years ago, and I did not allow the plane to go past a single rotation, so didn't allow the spin to fully develop. However, I did find my KR recovered the same as the numerous other planes I have spun. An additional note about spinning a KR. KRs are notoriously tail heavy. Mine was nose heavy enough at the time that I spun it that it required a miniumu of a 110# pilot to get it into the forward end of the CG, so I would expect it to recover quite easily. Over the years, with the addition of equipment, weight gain by the pilot and the replacement of heavy engine accessories with light accessories, the CG has moved aft quite a bit. I would not intentionally spin my KR today. However, I am still confident that if I did, it would still recover from an undeveloped spin. If spins are something that concerns you, I would recommend getting some spin training to the point where you become comfortable with spins. In the process, you will also become confident that you can avoid the stall/spin scenarios. -Jeff Scott Los Alamos, NM ---------------------------------------------- Found the link: http://www.stolspeed.com/slats-v-s-vgs Henni, South Africa -----Original Message----- Hi again all, After reading about the incident where a KR2 pilot was killed when he deliberately put it into a spin, I searched everything on the web that I could find about spin prevention. http://www.flyingmag.com/technique/accidents/aftermath-his-last-selfie[http://www.flyingmag.com/technique/accidents/aftermath-his-last-selfie] Must say, every single article lists vortex generators on the wings as a very good method of preventing spins to some degree. This have been something that I have always wanted to implement. I once read an article that the vortex generators worked so well on a certain light aircraft that the manufacturer stopped producing it with slats in the leading edge of the wing. The VGs achieved the exact same results without the slats. I now from a lot of reading that one will only loose around 3mph due the vortex generators. On the other hand, they will also reduce the stall speed by same. Plus, they are so easy to install - just glue them on using double sided adhesive strips This is something that I am definitely going to implement on my project. There is no weight penalty at all, we're talking ounces only. Anyways, something to consider. Henni, South Africa _______________________________________________ Search the KRnet Archives at https://www.mail-archive.com/krnet@list.krnet.org/. Please see LIST RULES and KRnet info at http://www.krnet.org/info.html. see http://list.krnet.org/mailman/listinfo/krnet_list.krnet.org to change options. To UNsubscribe from KRnet, send a message to krnet-le...@list.krnet.org
