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

"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

On Feb 20, 11:56*pm, Jock Proudfoot wrote:
Anyone know in round numbers, what % increase in L/D garden-variety
winglets give?

It will always be a bit less than adding the same length in (equally
well designed) wingtip extensions instead.

You only go upwards if some external influence (class rules in gliders
and Americas Cup yachts, airport gate spacing in the 747-400) prevents
you from going sideways.

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."

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

Kevin,
I won't name the kit supplier for obvious reasons, but we did spend some
considerable time getting the locating pins back to true and parallel,
before we could even start the fitting.

It was indeed a memorable moment when we sawed the first old tip off and
it fell with a klunk onto the floor.

From memory we only gave only 1 or 2 deg toe-in. There is a 'flat-ish'
surface on the outside winglet face to establish toe-in. It is a very
complex mod. because there are so many variables, I remember 6 of them:
~ rotational pitch
~ toe-in/out
~ splay (dihedral)
~ total span in and out
~ vertical position
~ fore/aft position

For the best match of the airfoil profile between winglet and wing, we
simply chose the 'least worse' position. Wing tape helped the final
match and covered some sins. Poland did a proper job later.

The main reference point established was the top rear tip (projected out
with layers of tape), which was used for all checks. On a non-flying day,
it might be worth running these checks on your assembled glider, I would
also use a point at the front of the wing/fuse join. It's amazing how
span can vary between left and right wings.

Also I believe we made a mistake with the tear-drop shaped eurathane
stick-on tip skid by sticking it on in the direction of flight. Next time
that gets replaced I will try and align it with the best l/d airflow.

Of course the real expert on all of this is Afandi Darlington, compared
with his expertise, one is reminded of the great philosopher Homer
Simpson's all-embracing observation:
"Doh- I wish I knew Stuff".

bwBB


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