Joa, I think there is enough data to say that VG's operate essentially as
you and your competitors claim - especially when used on the relatively poor
airfoils found on GA aircraft. i.e. they do reduce stalling speeds.

But, would that benefit a glider tug? I notice no claims that the climb
speed at a typical towing speed of 70 knots is improved in any way. I would
expect little improvement from VG's in the climb rate @ 70 knots.

Just for your edification, a tow plane has some special requirements. For
example, there is the need to get a heavily ballasted glider up to aileron
control speed as quickly as possible. ( An open class glider may have more
than 600 pounds of water in its wing tanks.) The 0-60 acceleration time is
very important. VG's don't help here.

Perhaps you are unaware that a fully ballasted glider will have a stalling
speed significantly higher than a Pawnee's. A nightmare scenario is a tug
that lifts off and starts to climb away at a speed near the stalling speed
of the glider it's towing. VG's might make this situation much worse.

I expect that a Pawnee would land slower if equipped with VG's but they land
pretty slow as it is. Perhaps a slightly shorter landing roll might shorten
the turn around time between tows but even here the landing roll is usually
determined more by the need to clear the airport boundary fence with a 250
foot rope dragging behind. Perhaps there would be a small increase in the
service life of tailwheels and main tires with lower touchdown speeds but
again, few tuggies like to hang in the air waiting for the airspeed to
dissipate and the weight to be transferred to the wheels on gusty
afternoons.

Now, the Pawnee isn't by any means a perfect tow plane. It probably
consumes 80% of its horsepower pulling itself through the air leaving only
20% to tow the glider. However, I doubt VG's would help with that either.

Now, if we were talking about a candidate tug whose only shortcoming was a
high stall speed, adding VG's might make sense. PA-28 - 235's maybe?

Bill Daniels

"Land Shorter!" wrote in message
m...
Actually Dave, vortex generators are WELL proven. They have been
since the 50s. That's why nearly every airliner and military aircraft
in the US uses them.

In the past VGs were considered a "band aid" and many aircraft
designers were too proud to use them ("...*my* wing doesn't need
them..."). This is starting to change as more and more aircraft
companies are realizing the benefits of VGs.

The other big reason VGs haven't taken off quicker has been the price.
Most STCed versions run up to and over the $1000 mark and that's just
too much for most folks to spend.

They aren't for every aircraft. In fact most modern/clean sailplanes
won't benefit from using them on your laminar wings (though zig-zag
and dimple tape, a version of VGs, often works very well). But for
non-laminar airfoils, especially for STOL aircraft that need to
operate safely when low and slow (like your tugs), my vortex
generators are just the ticket.

In fact don't take my word for it... visit my site and check out the
links to other companies making VGs. I've listed them in the "info"
section. I think you'll find that VGs, as well as those of us that
market them, are far from "flim flam".

If you're still not convinced then go read a good aero design book
(Hoerner's books, etc) or read the numerous NACA and NASA reports, or
look at any of the wind tunnel studies done on VGs by major
universities (Ohio State, etc). All of them say that VGs will do
exactly what I say they will.

Joa
www.landshorter.com





(David Bingham) wrote in message
. com...
Be real careful about unsubstantuated claims for much better
performance. Show me an unbiased independent appraisal of the
performance of an aircraft with and without these vortex generators
that shows a measurable improvement. I bet you can't. There are so
many flimflam products on the market that promise the world but
deliver nothing. If there really is an improvement why
haven't the manufacturers of aircraft ALL been using them? What's one
of the timeless truths concerning life? Buyer beware! There is always
a sheep to be sheared.
Dave