Winglets - myth or magic?
Paul Tyler
I have listened to a lot of club-house scarydynamics promoting their benefits
but would really appreciate at least a semi-mathematical means of evaluating
their worth.
Does anyone out there have an explanation of how, and under what
circumstances winglets do whatever it is they do? I will keep the chain
saw on the wall for the moment.
Paul Tyler
ESRL/ITD DSTO Australia
p...@itd.dsto.gov.au +61 8 259 6294
Charlie Kuehmann
Tyler) wrote:
> I am considering a suggestion that I fit winglets to my ASW-19B.
>
> I have listened to a lot of club-house scarydynamics promoting their benefits
> but would really appreciate at least a semi-mathematical means of evaluating
> their worth.
>
> Does anyone out there have an explanation of how, and under what
> circumstances winglets do whatever it is they do? I will keep the chain
> saw on the wall for the moment.
Winglets impact the aerodynamics of the wing by altering the spanwise flow
and the structure of the vortex system downstream of the wing which leads
to induced drag. Thus the winglet reduces the induced drag of the wing
and makes it act like a wing of higher aspect ratio. Without going into
much of the gory details, a number of points should be made. The addition
of a winglet will also add profile drag, to gain the most benefit this
must be kept low. Interference drag due to the joint between the wing and
the winglet must also be considered in any winglet design. By a rough
calculation the decrease in induced drag is proportional to the square of
the lift coefficient and is therefore is more pronounced on airplanes with
higher wing loading especially near the tips. The addition of winglets
will also modify the root bending moments of the wing and this must be
considered and the structure modified if needed. I hope this helps, you
might try a standard aerodynamics text for some more details,
"Aerodymnamics, Aeronautics, and Flight Mechanics" by B. W. McCormick is a
good one.
Cheers,
Charlie
--
If you want the views of my employer ask them. These are mine.
BIRL Industry Research Laboratory
kueh...@nwu.edu
Roy Bourgeois
>
I will keep the chain
>saw on the wall for the moment.
>
Use the chain saw. All they do is increase cost to build, time to assemble, and create
problems for you wing runner (nothing to hold on to).
Regards,
Roy B.
Peter Nyffeler
>Use the chain saw. All they do is increase cost to build, time to assemble, and create
>problems for you wing runner (nothing to hold on to).
>
>Regards,
>
>Roy B.
I gues Roy has never flown an ASW-24 with and without winglets!
The difference is, as you would fly two complete different gliders.
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Andy Wright
you need to refer to an article by Peter Masak in soaring magazine. I can't
remember which issue it was but I'll try and find out for you.
Regards
Andy Wright
Mark Bearden
and (2) winglets for your ASW-19. As to the first, I'll leave it to
others for specific results, but I think it's fair to say most everyone
who has tried a relatively recent winglet design with some sort of
Std./15M high-performance glider has been very satisfied - many are
downright ecstatic. Both performance and (especially) handling are
improved measurably.
The traditional knock on winglets was that they primarily helped
low-speed (i.e. climb) performance, with a net penalty at the high-end -
so they worked better in weaker conditions (flying slower/lighter). The
new designs have seemed to move the cross-over point to a higher airspeed
(better design, generally smaller) such that they seem to work better at
virtually all usable airspeeds. Most who have the option to fly with or
without them opt to always use them - especially when the non-winglet
handling might not be as nice as desired.
As to the '19, I'll plead guitly to a bias, as I'm sending mine off to
have winglets installed next week. Given the age of the design and the
fact that they are less-likely to be used for serious competition, little
work has been done with winglets with this ship. There was an OSTIV
paper published in the early '80's referencing some theoretical as well
as real-world testing done on a '19 in Germany. The results, as I
recall, showed about 1 1/2 points of L/D improvement at best glide, but
there was a marked drag increase at higher speed (not sure of the details
- I have a copy of the article if you're interested). But the design was
unlike the winglets in use today - especially in the length (I think it
was at least 1 meter, maybe 1.5 meters).
There are at least two '19's in New England and one '15 in the mid-west
(same wing planform) that I know of flying with newer winglets. I think
all three owners are very happy with the results - again, especially the
handling, but also a perceived improvement in both climb and glide. Keep
in mind you may or may not improve the resale value of your glider
(assuming you pay to have the work done as opposed to yourself). While
it should improve the ship in multiple ways, that may or may not be of
value to the next owner (who probably won't be shopping for a '19 because
it's the newest/best performing thing).
Albion H. Bowers
In a previous article, ro...@bdworc.iii.net (Roy Bourgeois) says:
>In article <pot.10....@itd.dsto.gov.au>, p...@itd.dsto.gov.au (Paul Tyler) says:
> I will keep the chain
>>saw on the wall for the moment.
>Use the chain saw. All they do is increase cost to build, time to assemble, and create
>problems for you wing runner (nothing to hold on to).
Winglets do provide measurable performance increases. however, more span
is a better compromise. Given span limitations, you have to pick a point
to design to, and careful selection of that point will improve performance.
Poor selection can make winglets work terribly compared to `clean' wings.
Al Bowers
--
Al Bowers DOD #900 NASA Dryden Flight Research Center
work: bow...@wilbur.dfrc.nasa.gov personal: ak...@yfn.ysu.edu
"...tactics always degrade strategy..." -Frank Bethwaite, HPS
G Lodge
If I am not mistaken, winglets (if designed properly) can either
help reduce wingtip vortices and thereby increase airspeed; or, they
can *create* wingtip vortices that rotate in a manner that actually
gives your glider a push. It accomplishes this by utilizing some
of the energy your glider loses as it descends (like a waterfall
electric generator). I am not familiar with the physical parameters
required, but I am familiar with this type of vortex generator as
they are used by trucking companies to increase fuel efficiency by
eliminating drag behind trailors (although the truck still pushes a
lot of air).
Other neat uses of winglets are rudder attachments that allow the
craft to fly sideways without yaw. An analogous elevator system
attached front and rear would allow change in elevation without pitch!!
I seriously doubt that these things would be used on unpowered aircraft
due to load restrictions but vortex generators in themselves are
merely a modification in the shape of the winglet. Since winglets
are a regular attachment on glides, I wouldn't be surprised in the
least if they are already in use.
Happy soaring.