Helium bubbles used to show bird aerodynamics

https://youtu.be/2sh8_3-R90I

At 0:58 in the video the bird's wingtip vortices are described as "This helps provide lift". This statement caught my eye.

However, Wikipedia (https://en.wikipedia.org/wiki/Wingtip_device) mentions that "Wingtip devices increase the lift generated at the wingtip (by smoothing the airflow across the upper wing near the tip) and reduce the lift-induced drag caused by wingtip vortices, improving lift-to-drag ratio.

A contradiction?

- John non-aero-e DeRosa

These are journalists describing science. I think more accurate would be "these vortices are a consequence of the process of generating lift with that wing". They create drag, which we don't want, but they come with the lift which we want.

An analogy would be to say "the rubber you leave on the road from your tires creates all the thrust for your car". Tearing up the tires and heating the road from the slipping rubber rob some of the engine's energy, but you can't go forward without them.

On Mon, 24 Feb 2020 23:21:59 -0800, Bret Hess wrote:

These are journalists describing science. I think more accurate would be
"these vortices are a consequence of the process of generating lift with
that wing". They create drag, which we don't want, but they come with
the lift which we want.


Yes, that's fair. A wing can't generate lift without generating tip
vortices. The energy used in spinning them up adds to the aircraft's
sinking speed, but clever wing design, which may include winglets and/or
wingtip shaping as well as a carefully designed wing planform can reduce
the energy that goes into spinning up tip vortices and hence will reduce
the sinking speed of the aircraft.

For a very readable account, try "Affandi Darlington on winglets", which
first appeared on PPrune but may have vanished unless The Wayback Machine
has a copy. I have a local copy I can send if you can't find it anyplace
else.

Peter Masak's "Winglet Design for Sailplanes" and Wil Schuemann's "A new
wing planform with improved low-speed performance" are both worth
reading. A web search will find the Masak paper and Wil Schuemann's paper
is in the Soaring Symposium archive.

When I developed my 'Delta-G' series of F1A class competition free flight
gliders, I used a combination of Wil Schuemann's planform ideas, first
seen by glider pilots on the S-H Discus, combined with Hoerner wingtips,
also common on gliders from the first glass airframes until winglets took
over, and had decent competition results with this series of models.


--
Martin | martin at
Gregorie | gregorie dot org

Martin Gregorie wrote on 2/25/2020 2:10 AM:
When I developed my 'Delta-G' series of F1A class competition free flight
gliders, I used a combination of Wil Schuemann's planform ideas, first
seen by glider pilots on the S-H Discus, combined with Hoerner wingtips,
also common on gliders from the first glass airframes until winglets took
over, and had decent competition results with this series of models.

I flew hand launch gliders in early60's. My best glider had a planform identical
to the original Discus. It was called the "Sweepette". The cover on this article
shows the 1960 version:

https://indoornewsandviews.files.wor...0/inav-113.pdf

I wonder if Wil Schumann was inspired by the Sweepette, or some earlier version of
that planform?
--
Eric Greenwell - Washington State, USA (change ".netto" to ".us" to email me)
- "A Guide to Self-Launching Sailplane Operation"
https://sites.google.com/site/motorg...ad-the-guide-1

On Thu, 19 Mar 2020 08:28:33 -0700, Eric Greenwell wrote:

I flew hand launch gliders in early60's. My best glider had a planform
identical to the original Discus. It was called the "Sweepette". The
cover on this article shows the 1960 version:

https://indoornewsandviews.files.wor...0/inav-113.pdf

I know it well: Lee Hines has been a good friend ever since 1983, when I
was on the way back from the Australian WC and stopped over on my way
home to fly in some Californian comps. I did the MaxMen's comp at Taft
and the Sierra Cup at Sacramento, travelling with Lee.

I got 2nd in in the Sierra Cup that year - an epic event with 10 rounds
flown Saturday and Sunday morning. Flyoffs started at 1:30 PM on a hot,
thermally afternoon. We flew 4,5,6 and 7 minute flyoffs before those with
clockwork timers dropped out en mass. By the 10 minute round it was
cooling off and only Walt Ghio and I were left. We both blobbed it, but I
dropped more than he did.

Halcyon Days!

I wonder if Wil Schumann was inspired by the Sweepette, or some earlier
version of that planform?

Lee seems to have developed the Sweepette in the late 60s and got the
Model Of The Year award for it in 1970.

I have a copy of Wil's article on modifying an ASW-12 so he could fly it
in Standard Class, and that modification included his new planform, but
annoyingly, the article doesn't show a date. The ASW-12 was introduced in
1965, so its at least possible that Wil was first with that planform.
AFAIK Lee has never followed developments in fullsize gliding in any
detail. He was always more interested in Formula 1 GP racing, and spent a
season as a Goodyear gofer (and got into the partys) when Jimmy Clark,
Graham Hill, etc were to top drivers.

Do you know when Wil was flying that modified ASW-12?


--
Martin | martin at
Gregorie | gregorie dot org

"How do you determine the tail is lifting in gliding flight?"

Agree. Do we have wind tunnel testing to prove the theory that your fixed stab is always providing upwards forces on the aft end of the fuselage?

I used do some free flight modeling.
Mostly Dick Mathis designs.

On Monday, February 24, 2020 at 10:33:46 PM UTC-6, John DeRosa OHM Ω http://aviation.derosaweb.net wrote:
https://youtu.be/2sh8_3-R90I

At 0:58 in the video the bird's wingtip vortices are described as "This helps provide lift". This statement caught my eye.

However, Wikipedia (https://en.wikipedia.org/wiki/Wingtip_device) mentions that "Wingtip devices increase the lift generated at the wingtip (by smoothing the airflow across the upper wing near the tip) and reduce the lift-induced drag caused by wingtip vortices, improving lift-to-drag ratio.

A contradiction?

- John non-aero-e DeRosa

There are always wing tip vortices when a wing is generating lift, but they can be tight and concentrated, like a horizontal tornado, or broad and diffuse. The tight and concentrated carry more energy that the diffuse vortices, even though the vorticity (and the generated lift) is the same.

Rich L

On Wednesday, February 26, 2020 at 6:26:53 AM UTC-8, Richard Livingston wrote:
On Monday, February 24, 2020 at 10:33:46 PM UTC-6, John DeRosa OHM Ω http://aviation.derosaweb.net wrote:
https://youtu.be/2sh8_3-R90I

At 0:58 in the video the bird's wingtip vortices are described as "This helps provide lift". This statement caught my eye.

However, Wikipedia (https://en.wikipedia.org/wiki/Wingtip_device) mentions that "Wingtip devices increase the lift generated at the wingtip (by smoothing the airflow across the upper wing near the tip) and reduce the lift-induced drag caused by wingtip vortices, improving lift-to-drag ratio.

A contradiction?

- John non-aero-e DeRosa

There are always wing tip vortices when a wing is generating lift, but they can be tight and concentrated, like a horizontal tornado, or broad and diffuse. The tight and concentrated carry more energy that the diffuse vortices, even though the vorticity (and the generated lift) is the same.

Rich L

It is unclear here whether it was the journalist reaching the wrong conclusion or the scientists feeding her a bad conclusion. Obviously, vortices don't create lift for the bird (although flocks use the vortices of the leading bird for additional lift).

Tom

Also not correct is the statement that a glider with a lifting tail would be unstable.
Most earlier freeflight model gliders did have lifting tails, and no in flight controls.
R,
Chris

On Wed, 18 Mar 2020 22:44:42 -0700, Chris Behm wrote:

Also not correct is the statement that a glider with a lifting tail
would be unstable. Most earlier freeflight model gliders did have
lifting tails, and no in flight controls.

What do you mean by 'early'? :-)

A more correct statement would be 'all current competition free flight
models have lifting tails'.

I used to design my own F1A and F1J/1/2A models as well as building them,
and all had lifting tails.

My F1A towline gliders had their CG at 55% of mean wing chord. The
stabiliser operated at a positive lift coefficient of 0.05, which for the
sections I used (B8403, 7% Clark Y and Woebbeking), put the stabiliser
smack in the middle of its minimum drag bucket. Win-Win!

I used a 10 degree swept back LE on the wing's outer panels, straight TE
and raked Hoerner tips. This combination does two things. The sharp angle
where the tip, raked at 30 degrees with the TE longer than LE, meets the
TE tends to localise the tip vortex. The spanwise flow encouraged by the
swept outer LE and the upper tip surface rolling down to meet the lower
surface at a sharp edge tends. In theory these push the tip vortex
further outboard, so increasing effective aspect ratio, but who knows for
sure? However, the design was easy to fly and trim and won its share of
contests.

My F1J design (small stab, long moment, VIT and autorudder) flew best
with the CG at 65% of mean chord, so it used a similar trim setup to my
F1A gliders, while the 1/2A was a modified traditional model (George
French '1/2A Train'), so it had a shorter moment arm and large (35% of
wing) stab. It was also fitted with VIT and autorudder and liked having
its CG at 80% of mean wing chord.

All three designs were stable in wind and turbulent conditions, easy to
trim and fly, and had good contest records.


--
Martin | martin at
Gregorie | gregorie dot org