Udo wrote:
The point is well taken that the Cirrus has a rather thick "first generation
glass" profile. It does produce both top and bottom separation bubbles, and
these tend to move, making the exercise of removing them more difficult. This is
why you will seldom see a std Cirrus with deturbulator tape - it does not appear
to work very well except at specific speeds. I agree it may be harder to show
large improvements on better behaved airfoils, but I suspect the old Wortman is
a good place to find out if it works in difficult conditions. I presume Dr Sinha
had a reason for choosing it beyond availability.


In fact it does not have a separation bubble, but will have a
transition bubble (If it had a separation bubble no one would want to
fly it) The Laminar transition is relative stable and moves only about
3% to 5% chord, top and bottom at all normal operating speeds.

There are two thing that can help improve "that airfoil" reduce the
size of the transition bubble and reduce the thickness of the turbulent
boundary layer. That this may be the case can be seen by the rather
large improvement in lower speeds and less so at a higher speeds.

I doubt a modern airfoil can be improved much in this way. How can a
90% laminar flow surface be improved, compared to the 40% on the Cirrus
wing. There is still the top surface of a modern wing airfoil, but even
there 66% can easily be obtained. I could see an application right
there for a 1% improvement. Since a lot of competitor will spent $1500
plus on winglets to get a 1% point improvement, I would not be
surprised to see this enhancement appearing on newer gliders some time
in the future on the competition scene, if it works, the price is right
and is easily maintained.

Udo

Sorry for bad terminology Udo.

My lack of aerodynamics taxonomy. Laminar to turbulent transition - I used the
separation word where I meant transition bubble. Can refer you to the discussion
on http://www.standardcirrus.org/ in the Issues Turbulators section.

The authors (Jim Hendrix et al.) refer to separation bubbles there, but only for
refference - I used it indiscriminately.

All I know is the nice laminar flow falls apart and this moves. I have only
inspected 8 different aircraft, so can't claim tobe a world expert on the
Cirrus, but so far none that I have seen have turbulators. I draw the (Possibly
incorrect) conclusion that they are not worth it on the airfoil...