Discus Winglets

[Peter F]

Hi Folks,

Two questions

1) Anyone out there know how to check the alignment
of winglets that have been retrofitted to a Discus
(CS if it makes any difference)?
I believe this is fairly critical & if it's wrong then
I'm better off flying with the 'normal' tips

2) Anyone out there have access to a study done in
the early nineties, by David Colling I think, on turbulator
tapes for Discus Winglets?

Thanks

PF

[Wayne Paul]

Peter,

Peter Masak wrote an article for Free Flight based on David's research.
http://www.wgc.mb.ca/sac/freeflight/92_02.pdf
(I would like to thank the SAC for making their publications available
online.)

An html version of this article can be found at:
http://www.soaridaho.com/Schreder/Technical/Winglets/Masak.htm

David Masak has the tooling to produce this version of the Masak winglet for
Schreder RS-15, HP-16 and HP-18 sailplanes.

Wayne
http://www.soaridaho.com/Schreder

"Peter F" <REMOVE_TO_R...@yahoo.co.uk> wrote in message
news:3v8o4lF...@individual.net...

[Wayne Paul]

Error Correction! It is David Colling that has the tooling to produce
winglets for Schreder designs!!

Wayne
http://www.soaridaho.com/Schreder

"Wayne Paul" <wa...@soaridaho.com> wrote in message
news:11oudk1...@corp.supernews.com...

[hc_ph...@yahoo.com]

PF,
Since you are asking the question I assume you suspect there is some
sort of a problem caused by your winglets. It probably is not your
imagination. I had a type of glider a few years ago that had a
reputation for being unstable at low airspeeds, but could be much
improved with winglets. It came with Masak winglets so for about the
first 100 hours I never flew with the factory tips because as poor as
the handling was I thought it would be worse without the winglets. And
the glider still felt unstable. Finally as an experiment I flew with
the factory tips and discovered it had MUCH better handling
characteristics. I never flew with the winglets again. Upon closer
inspection I noted that one winglet was visibly mis-aligned with the
wing leading edge.
Not sure what it would have cost to fix it since I sold the glider, but
the moral to the story is that the low cost answer may simply be to fly
with the factory tips. The Schempp Hirth engineers probably knew what
they were doing when they designed the factory tips for your Discus.
Respectfully,

[uncl...@ix.netcom.com]

CS is provided with tip ribs installed for winglet mounting so this
should be quite accurate.Rib angles out 2mm over about 250mm chord at
cut point. This is shown in TN 360-13 describling installation.
As to angle of the flying surface measurement,place winglet root rib on
suitable surface and measure distance of leading edge and trailing edge
from ref surface at known spanwise point. With this information, you
can determine if they are the same and what the angle is.
Early winglets produce by Peter Masak has the angle out(toe) at a much
larger degree than more recent designs to try to avoid stalling at high
angles of attack. This results in poorer performance at high speeds.
More recent designs use improved airfoils and reduced toe to load the
winglet more helping low speed while improving the high speed cross
over point.
Maughmer designed winglets provided by M&H are an example of this
approach and work very well.
Hope this is of some help.
UH

[Kevin Neave]

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

[Udo Rumpf]

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

[Peter F]

Many thanks for the info so far.

There appears to be 3 sets of winglets in existence...
Masak,
Schempp,
Maughmer.

How do the Schempp Factory winglets relate to Masak
winglets from the early '90s, are the figures of 55%
& 20% from David Collings work likely to apply to the
Schempp winglets?

M&H sell Maughmer winglets, but they're also the agents
for Schempp Hirth. Are their winglets for the original
Discus from the Schempp factory (Fat & Draggy) or are
they Maughmer design (Newer, thinner etc. etc)? This
second question is purely academic as I've already
got a set of factory winglets & am not in the market
for more, but if anyone here knows the answer I'd still
be interested

Thanks

[g l i d e r s t u d]

M&H make and sell the Maughmer winglets. Yes they are the S-H agent,
but the factory winglets are different. Give them a call on Monday,
tell them you dont like the factory winglets you think they are ugly
and not rigged correct, you want to buy a pair of Maughmer winglets for
you cs.

The Maughmer winglets are taller, thinner, sexier, better handeling,
more effecient, and they look a lot better.

Garret
Discus 2ax (with Maughmer winglets) driver