Winglet performance

Anyone know in round numbers, what % increase in L/D garden-variety
winglets give?

At 10:56 20 February 2011, Jock Proudfoot wrote:
Anyone know in round numbers, what % increase in L/D garden-
variety
winglets give?



Some relevant articles he

http://www.mandhsoaring.com/Winglets.html

As with all things soaring - it depends.

In an attempt to summarise / save some reading. My understanding is as
follows:

You can take it that a correctly set up winglet affects performance
equivalent to adding approximately 50%-70% of the winglet span to the
wingspan. Resulting in higher aspect ratio and lower induced drag.

Problem is that as speed increases the form drag becomes dominant over
induced drag. So - only for a specific speed and AoA range do winglets
reduce drag (sometimes significantly). Get your design wrong and the
performance is actually easily impaired rather than improved.

Either way you get what you paid for. Some are set up for better
cruise,some are set up to improve climb performance, some are set up to
tame poor handling at low reynolds numbers, some are just tacked on
without any clear idea...

Theoretically the winglet can be set up to generate lift with a forward
component to the vector extracting waste energy from the tip vortex -
improving glide efficiency. Doing this well involves some complex
geometry and arcane design which I don't claim to understand.

On many gliders adding a winglet improves the handling, and so
indirectly improves achieved performance.

Bruce
--
Bruce Greeff
T59D #1771 & Std Cirrus #57

In article ,
BruceGreeff wrote:

As with all things soaring - it depends.



When asked what airfoil he used on his HP winglets, Dick Schreder
replied "I use the ROF-POB airfoil. Questioned further he elaborated
"Round on front-pointy on back".

H301 "WB" "Why yes dear, I'd much rather go with you to pick out
countertops than fly my glider."

"Berry" wrote in message ...
In article ,
BruceGreeff wrote:

When asked what airfoil he used on his HP winglets, Dick Schreder
replied "I use the ROF-POB airfoil. Questioned further he elaborated
"Round on front-pointy on back".


I am aware of a lot of Schreder sailplanes with winglets; however, I haven't come across any with Dick's plywood slabs described above bolted to the wingtip rib. Almost all the HP/RS-15 winglets are based on (copies of) the winglets described in the Free Flight page 6 article by Peter Masak.(http://www.wgc.mb.ca/sac/freeflight/92_02.pdf)

HP pilots note that winglets definitely improve aileron effectiveness resulting in higher roll rates.

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

Just to throw my voice into the mix - my DG-300 was retrofitted with
(factory-supplied) winglets...

The difference in L/D is so small with most winglets, that even if its
working correctly it would be hard to notice... Like others have said
- its "almost as good as" an equal improvement in span. What's the L/
D difference between a good 15-meter ship and a good 16-meter ship?
Very little.

However, I do notice an improvement in slow-speed handling with my
winglets on. This is where I believe a lot of people derive benefit
from them: Improved airflow over the wing at slow speeds and while
turning can directly translate into better thermalling performance,
both in reduced drag and in improved aileron control/authority.

--Noel

"Jock Proudfoot" wrote in message ...
Anyone know in round numbers, what % increase in L/D garden-variety
winglets give?


Back in 1997, when winglets were entering the soaring scene, an article was published in the Free Flight magazine's April edition entitled "Do Winglets Work?" It can be found on page 16 of the following link. (http://www.wgc.mb.ca/sac/freeflight/97_04.pdf)

As for percentage of improvement, US racing handicaps are adjusted from as little as 0.002 to 0.010 in the case of the Discus 2b.

Wayne
HP-14 "6F"

My Discus CS had factory fitted winglets.

However the "Cut line" between wing & winglet wasn't as per the details
in the Schempp modification. (I assume the factory use a jig)

This lead me to have doubts as to the correct AoA of the winglet, so I
stopped using them (After about 5 years!)

In general use I found there to be no difference with or without, so I
continued to fly without them and didn't take the hit on the increased
handicap.

I never found an effective way of measuring what the toe in/out of the
winglet was, or figures for what it should be.

In summary, correctly fitted winglets may make an improvement but it's
easier to make things worse than to make things better

PF

Having fitted winglets to my Mosquito some years ago I can say
there is (i) a small increase in climb rate (ii) possibly better l/d
and (iii) a definite improvement in handling.
For example, the left wing would drop at stall before, now it
stalls evenly. Also the handling at higher flap settings is vastly
improved.

On BGA handicapping, this amounts to a 1% performance
increase overall.

However...
- we spent 11 whole days getting them on straight and true

- the original kit was jigged incorrectly and would have resulted
in misalignment (food for thought when done professionally)

- the foil profile did not match the wing at the join. This was
corrected with re-fairing when the glider was refinished in Poland

Was it worth doing? Absobloodylutely!

bwBB




My Discus CS had factory fitted winglets.

However the "Cut line" between wing & winglet wasn't as per
the details
in the Schempp modification. (I assume the factory use a jig)

This lead me to have doubts as to the correct AoA of the
winglet, so I
stopped using them (After about 5 years!)

In general use I found there to be no difference with or
without, so I
continued to fly without them and didn't take the hit on the
increased
handicap.

I never found an effective way of measuring what the toe
in/out of the
winglet was, or figures for what it should be.

In summary, correctly fitted winglets may make an
improvement but it's
easier to make things worse than to make things better

PF

At 06:58 22 February 2011, Bill Bullimore wrote:

However...
- we spent 11 whole days getting them on straight and true

- the original kit was jigged incorrectly and would have resulted
in misalignment (food for thought when done professionally)

- the foil profile did not match the wing at the join. This was
corrected with re-fairing when the glider was refinished in Poland


Whose winglet kit did you fit to your Mosquito, how did you know the
correct toe in/out angles (i.e "Straight & True) & how did you measure
the the toe angle when fitted.

I'm dubious about the factory fitted winglets on my Discus B - again the
cut angle on the winglet doesn't match the Schempp tech note. But the
performance doesn't seem to be any worse with them than without and they
stop the tip dolly falling off (When manoeuvring on the ground, before we
get ay sarky comments!) so I continue using them.

Kevin