Do Winglets reduce ground effect

[Jonathan St. Cloud]

Not being an aerodynamicist, I was wondering if winglets decreased ground effect. So would an ASW-20 (without winglets) be able to glide further in ground effect than an ASW-20 (with winglets), all else being equal?

[Dan Daly[_2_]]

On Thursday, December 15, 2016 at 10:12:12 PM UTC-5, Jonathan St. Cloud wrote:
> Not being an aerodynamicist, I was wondering if winglets decreased ground effect. So would an ASW-20 (without winglets) be able to glide further in ground effect than an ASW-20 (with winglets), all else being equal?

I googled it and this website answers the question https://www.quora.com/Do-aircrafts-with-winglets-experience-lesser-ground-effect . Not about the ASW-20 specifically.

It is on the internet, and therefore, must be true.

[Michael Opitz]

At 03:23 16 December 2016, Dan Daly wrote:
>On Thursday, December 15, 2016 at 10:12:12 PM UTC-5,
Jonathan St. Cloud
>wrote:
>> Not being an aerodynamicist, I was wondering if winglets
decreased ground
>effect. So would an ASW-20 (without winglets) be able to glide
further in
>ground effect than an ASW-20 (with winglets), all else being
equal?
>
>I googled it and this website answers the question
>https://www.quora.com/Do-aircrafts-with-winglets-experience-
lesser-ground-effect
>. Not about the ASW-20 specifically.
>
>It is on the internet, and therefore, must be true.
>
Winglets are a way to get most of the benefits of increasing the
span without actually increasing the footprint. The big advantage
for existing aircraft being retrofitted is that winglets don't produce
lift per se, so there is not much change to the bending moments,
therefore the spars don't have to be beefed up as they would for a
straight wing extension. (See the 15-18 m discussion on RAS.) For
airliners with a limited footprint available at gates, winglets allow an
increase in performance with retention of useage of the same gates.
Most general aviation winglets are specifically optimized for that
particular aircraft's cruise speed.

For gliders that have a span limit in their class, winglets are a
(relatively) cheap and easy way to increase performance. The
early glider winglets were generally good at increasing climb
performance, but hindered at the high speed end. The newer
generation of Maughmer type winglets are optimized to perform
much better over a broader speed range in gliders.

So, an ASW-20 with winglets is really like a ~16 meter ASW-20 at
altitude. The winglets probably reduce the ground effect
somewhat, but do they reduce it to a level less than a regular 15m
ASW-20? My guess is that the effects are probably too small for a
pilot to really notice a difference. It might be an interesting
Master's degree project for some grad student who has access to
the wind tunnel time to test the theory out....

There is a whole category of aircraft designed to operate in ground
effect in order to boost their range/payload. They are called WIG
(Wing In Ground effect) aircraft. Some have winglets which are
also pontoons going down, and others have winglets that go up at a
~45 degree angle. I guess the aerodynamic winglet/ground effect
reductiuon question is not settled with these aircraft either. See:
https://www.google.com/search?
q=WIG+aircraft&rlz=1C1CHWA_enUS602US603&espv=2&biw=128
0&bih=918&tbm=isch&tbo=u&source=univ&sa=X&ved=0ahUKEwj
Z0auP7vfQAhVBKGMKHbCTCvsQsAQIMQ#imgrc=_

RO

[Steve Leonard[_2_]]

On Thursday, December 15, 2016 at 9:23:56 PM UTC-6, Dan Daly wrote:
> On Thursday, December 15, 2016 at 10:12:12 PM UTC-5, Jonathan St. Cloud wrote:
> > Not being an aerodynamicist, I was wondering if winglets decreased ground effect. So would an ASW-20 (without winglets) be able to glide further in ground effect than an ASW-20 (with winglets), all else being equal?
>
> I googled it and this website answers the question https://www.quora.com/Do-aircrafts-with-winglets-experience-lesser-ground-effect . Not about the ASW-20 specifically.
>
> It is on the internet, and therefore, must be true.

There may be lesser benefit from winglets, but you started with more performance, so the end result is likely that you will still have more performance with your winglets in ground effect than without your winglets in ground effect. Assuming your winglets actually boosted your performance. Personally, I don't believe it is entirely proportional to tip vortex strength, but has a lot more to do with downwash field strength. Short spans with big chords get a larger benefit from ground effect than long spans with narrow chords. Just my opinion.


Steve Leonard

[Jonathan St. Cloud]

The reason I asked in the Russell Holtz book, he states that "The closer the wings are to the ground, the more the ground interferes with the development of the wing tip vortices..."

On Thursday, December 15, 2016 at 8:45:06 PM UTC-8, Michael Opitz wrote:
> At 03:23 16 December 2016, Dan Daly wrote:
> >On Thursday, December 15, 2016 at 10:12:12 PM UTC-5,
> Jonathan St. Cloud
> >wrote:
> >> Not being an aerodynamicist, I was wondering if winglets
> decreased ground
> >effect. So would an ASW-20 (without winglets) be able to glide
> further in
> >ground effect than an ASW-20 (with winglets), all else being
> equal?
> >
> >I googled it and this website answers the question
> >https://www.quora.com/Do-aircrafts-with-winglets-experience-
> lesser-ground-effect
> >. Not about the ASW-20 specifically.
> >
> >It is on the internet, and therefore, must be true.
> >
> Winglets are a way to get most of the benefits of increasing the
> span without actually increasing the footprint. The big advantage
> for existing aircraft being retrofitted is that winglets don't produce
> lift per se, so there is not much change to the bending moments,
> therefore the spars don't have to be beefed up as they would for a
> straight wing extension. (See the 15-18 m discussion on RAS.) For
> airliners with a limited footprint available at gates, winglets allow an
> increase in performance with retention of useage of the same gates.
> Most general aviation winglets are specifically optimized for that
> particular aircraft's cruise speed.
>
> For gliders that have a span limit in their class, winglets are a
> (relatively) cheap and easy way to increase performance. The
> early glider winglets were generally good at increasing climb
> performance, but hindered at the high speed end. The newer
> generation of Maughmer type winglets are optimized to perform
> much better over a broader speed range in gliders.
>
> So, an ASW-20 with winglets is really like a ~16 meter ASW-20 at
> altitude. The winglets probably reduce the ground effect
> somewhat, but do they reduce it to a level less than a regular 15m
> ASW-20? My guess is that the effects are probably too small for a
> pilot to really notice a difference. It might be an interesting
> Master's degree project for some grad student who has access to
> the wind tunnel time to test the theory out....
>
> There is a whole category of aircraft designed to operate in ground
> effect in order to boost their range/payload. They are called WIG
> (Wing In Ground effect) aircraft. Some have winglets which are
> also pontoons going down, and others have winglets that go up at a
> ~45 degree angle. I guess the aerodynamic winglet/ground effect
> reductiuon question is not settled with these aircraft either. See:
> https://www.google.com/search?
> q=WIG+aircraft&rlz=1C1CHWA_enUS602US603&espv=2&biw=128
> 0&bih=918&tbm=isch&tbo=u&source=univ&sa=X&ved=0ahUKEwj
> Z0auP7vfQAhVBKGMKHbCTCvsQsAQIMQ#imgrc=_
>
> RO

[[email protected]]

On Friday, December 16, 2016 at 1:53:05 PM UTC-5, Jonathan St. Cloud wrote:
> The reason I asked in the Russell Holtz book, he states that "The closer the wings are to the ground, the more the ground interferes with the development of the wing tip vortices..."
>
True. That said, how far the wing is from the ground would have a bigger affect on drag than whether the wing has winglets.
FWIW
UH

[[email protected]]

The ground can have a reducing effect on winglets, I'm looking at you Voyager.

[Michael Opitz]

At 18:53 16 December 2016, Jonathan St. Cloud wrote:
>The reason I asked in the Russell Holtz book, he states that "The
closer
>the wings are to the ground, the more the ground interferes with the
>development of the wing tip vortices..."
>
That is because the flow becomes more and more 2 dimensional. The
ground effect goes up exponentially, the closer you get to the ground.
You can measure it in a wind tunnel, but it would be very hard to
measure in an actual glider because a difference of 6" or a foot in
height above the ground would have more of an effect than the
winglets probably do on their own. (presuming that one is already
flying really, really low) At least in a wind tunnel, you can set the
parameters and then make measurements. I don't have my references
handy, but I believe that the ground effect starts to become noticeable
when one is about 1/2 wingspan AGL. It then rapidly increases the
closer one gets to the ground. That is why I think that one won't be
able to see much of a difference with or without winglets. You are in
the area of 3'-4' off the ground, and in that area of the ground effect
curve, being off a foot in height (one way or the other) will make a
much bigger difference on that exponential curve than winglets (or
no winglets) ever will. In real life you just can't fly it that close
unless
you have a real sensitive radio (type) altimeter to measure exactly how
low you are.

RO

[Jonathan St. Cloud]

It is rainy in Southern California today so continuing on with ground effect. My first and only real experience at needing and losing ground effect was flying a helicopter out of Bishop Airport one hot summer day. Lifting off full of fuel and trying to keep turbine temps in the green, or only brief forays into the yellow, I was just a few feet off the ground building speed after departing helicopter pad, I was doing fine, until I moved off the pavement and was over taller grass. I immediately needed more power as the ground effect suddenly had disappeared.

[Charlie M. (UH & 002 owner/pilot)]

I would sorta guess you had "thermic help" when over the pavement while you may have had sink over the grass.

[Jonathan St. Cloud]

I do not think I had "thermic help" over the hot concrete/pavement. I think the tall grass negated the ground effect.

On Friday, December 16, 2016 at 1:51:22 PM UTC-8, Charlie M. (UH & 002 owner/pilot) wrote:
> I would sorta guess you had "thermic help" when over the pavement while you may have had sink over the grass.

[Michael Opitz]

At 22:09 16 December 2016, Jonathan St. Cloud wrote:
>I do not think I had "thermic help" over the hot
concrete/pavement. I
>think the tall grass negated the ground effect.
>
>On Friday, December 16, 2016 at 1:51:22 PM UTC-8, Charlie M.
(UH & 002
>owner/pilot) wrote:
>> I would sorta guess you had "thermic help" when over the
pavement while
>you may have had sink over the grass.
>
I would hazard to say that rotorcraft ground effect is not the same
as fixed wing ground effect. That is a whole other ball of wax...
When they took Bin Laden out, they had practiced in a mocked up
area with chain linked fences surrounding the "compound". The
reality was 8' concrete walls which deflected the blast upwards to
create a vortex. As I recall, the temperature inside the compound
was also ~15°F hotter than forecast (or reported by agents in the
field). That pilot did a great job in a controlled crash, as the
conditions inside the compound (vortex, temps, altitude) would not
let him hover at that weight. Rotorcraft (V-22 included) downwash
and vortices are a whole other animal unto themselves. Comparing
them to glider ground effect is "apples to oranges"...

While I do live in "helicopter central" (Close to the main Sikorsky
plant), I only have a cursory understanding of that arena through
education and friends / family in that business. I would leave the
technical answer to your rotorcraft question to a rotary aircraft
specialist. Sikorsky's "Skunk Works" is in Elmira, and I assume
there are some of those employees who are also glider pilots that
can answer your helicopter related question. I know that one of our
old glider club members transferred there to work at the
"Hawkworks" when it first opened.

RO

[[email protected]]

Hovering in ground effect takes less energy over hard surfaces than over water or grass. Well known. No idea if it matters for fixed wing ground effects, my guess is not, or not significantly.