Discus Winglets

Hi,

I went through the same mill a couple of years ago.

If you do a couple of searches on Google Groups for
Colling Discus Turbulator
and
Masak 'New Winglet Design'

You'll find a couple of postings by Peter Masak which
suggest that the laminar flow on his design for the
Discus Winglet extended to about 55% chord on the outer
surface and about 20% on the inner.

I don't know what the relationship between Masak's
winglets and the Schempp factory winglets are.
M&H Soaring sell winglets designed by Mark Maughmer,
but they're also the agents in the US for Schempp Hirth.


Does anyone know the relationship, if any, between
the three sets of winglets (Masak, Maughmer & Schempp
Hirth) for the original Discus?

Regards

Kevin

All three winglets are evolutions of the previous winglet.
The Maughmer winglets are more or less integrated.
they are designed to take the flow of the complete wing
into account. The winglets generally have much thinner
airfoils 8%- 9%. The lower the Reynolds number the
thinner the airfoil has to be but still work well enough to
allow for the occasional exceeding of higher angles of
attack, as in, when not flying to string in the centre.
The CL in max climb is around .5, that is what the winglet
sees. If the toe angles are right. That would mean max
Cl of .8 to .9 are tolerable. After that they become draglets.
On the high speed side Cl of .25 is desirable. The winglet
at that point has very little wrap around flow. Her the toe
angle should be such that it still allowing attached flow on
the upper surface (inboard). The cross over point is
normally 90 kt in 15 meter class glider if you fly often
faster than that you should carry water.

The last time Peter and Mark collaborated, a much thicker
airfoil was use, the PSU 12.5%. This airfoil work fine but
was unnecessary thick.

I do not know what Peter used in the first winglet iteration.

In the case of the Discus, which has very efficient plan
form to start with, it is very easy to make things worse and
the small winglet do not make it easier. I suspect it to have
to large toe out (trailing edge outboard).

The smaller the wingtip chord the smaller the toe out.
This would indicate the winglet stalls right from the start
which effects the outer portion of the wing. The effect is not
just localized to the winglet. Only when the wing carries the
full weight of the glider is there enough wrap around flow to
stop the stall. but any slight misalignment to the direction of
flow will alternately stall and unstall the winglet in normal flight.
The same would apply if the winglet had negative two out but
the effect maybe less noticeable.

I would check the following. Set up the glider with the tail
horizontal, measure the distance from the centre line of the
fuselage to the wingtip without winglet. Set up two stakes.
With that measurement from the nose and from the tail.
Now you have a parallel line This will show if the cut on the
tip of the wing is square and at the same time you can
measure the angle at which the winglet panel is set.

If it the winglet has a PSU 12.5% airfoil I would look for a
setting of about 2 deg. but no more then 2.5 deg.
I would not be surprise if 1.5 deg in case of the Discuss
would be best.

On my Super HP 18 with a 18" wingtip chord I use a 9%
airfoil and a 3.5 toe angle. I will use on my new project a
wingtip chord of 14" and I will reduce that angle by 1 deg.
I hope that will give you a bit of inside This is all the wisdom
I have on this subject which I have painstakingly
accumulated over the last 12 years.
Regards
Udo


Masak 'New Winglet Design'

You'll find a couple of postings by Peter Masak which
suggest that the laminar flow on his design for the
Discus Winglet extended to about 55% chord on the outer
surface and about 20% on the inner.

I don't know what the relationship between Masak's
winglets and the Schempp factory winglets are.
M&H Soaring sell winglets designed by Mark Maughmer,
but they're also the agents in the US for Schempp Hirth.


Does anyone know the relationship, if any, between
the three sets of winglets (Masak, Maughmer & Schempp
Hirth) for the original Discus?