wrote:
On Jan 1, 10:36 am, "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

To further emphasize Udo's point, for the Antares:

The boundary layer remains laminar up to 95% of the wing chord on the
lower surface of the wing, at which point turbulent flow is triggered
using turbulator tape in order to avoid laminar separation bubbles.
Research performed for Lange Flugzeugbau have shown that there is no
discernable difference in performance between a well designed
turbulator tape and triggering the boundary layer through blowing. On
the on the upper surface, the boundary layer remains laminar up to 75%
of the wing chord. This is the highest value currently available.

How much savings could be obtained in this case, and what would be its
impact on the glider performance ? Perhaps someone more expert than I
could calculate this. We could ask Loek Boermans perhaps...

Best Regards, Dave

To elaborate further,
Since the airfoil of the Antares is an evolution of the ASW27 airfoil
it will have similar characteristics.
The values that Dave ascribes to the airfoil are correct.
One must remember the 95% laminar flow on the bottom only happens
in cruise and the 75% laminar flow on top takes place in climb.
Due to flap deflection in climb the bottom transition take place well
ahead of the hinge line, at least one chord flap, most likely more.
In that case, "if" the deturbulator installation does not interfere
with
the attainability of the 95% laminar flow, it could improve climb.

I have my doubts so, as the interference of the flap deflection
dominated the turbulent flow in front of the hinge line.

On the top surface we have the opposite, the laminar flow is now
extended in climb to 75% due to the flap defection and A of A
setting to operate at optimum CL

In cruise it will move forward but by how much I do not know exactly,
my guess is about 8 to 10% chord.
That would mean the transition would be at 65% chord and a small
improvement could be had with the Deturbulator in cruise,
again, provided it does not interfere with the laminar flow that is
achieved in normal climb. At first blush it looks like the application
of this device is more suitable for none flapped wings, as extended
laminar flow on the top surface is more difficult to attained.
I hope that is not the case.

Udo