On Tuesday, November 6, 2018 at 5:29:49 PM UTC-6, Dirk_PW wrote:
I question why you would want to fly so slow, and to the point where you think you need to use vortex generators to increase safety margins. You're asking for trouble if you want to leave the ground that close to stall - especially towing a glider. Keep yourself safely above stall before leaving the ground please, then you won't need those silly VGs.


Huh? Isn't reducing stall speed a valid way to "keep yourself safely above stall"? Seems that VG's add to safety margins. What's silly about that?

"Safely above stall" is dependent on conditions. An unexpected bit of shear or encountering a sharp, strong thermal can stall you at a "safe" speed. So, unless you can just increase your tow speed as high as you like, you will always be at some risk of a stall. But we can't just arbitrarily pick our tow speed can we? Towing older, slower ships like 2-33's, Ka-7's, etc at 70 mph into strong thermal conditions will put a hell of a load on the structure. This is especially true these days since we are often flying very near max gross in our old trainers. Tow a little fast and you are flirting with structural damage. Towing at 60 or 65 is still a bit fast for some of the old birds, but does not provide much margin for the tug driver in an unmodified tug when encountering the shear and gust present on any soaring day. STOL kits and VG's give the tug driver a bit of margin when conditions are not ideal. And, unless you can see the air, you won't know when you are about to tow into those NOT ideal conditions.