Just a theory from a "non engineer":
DS (Dynamic Soaring) what is that ? Lately I have been using some
brains on why and how this is happening. My latest "lightbulb" in my
head came after looking at a trick on the tv. Moving air has less
pressure and will actually be able to create a lift that can move
pretty big objects and offcourse air upwards. I have made a movie
for you - too understand how and why I think we can fly under
the "share layer" as we call it.
<http://www.grini.no/dshow.wmv>

What do you say guys ? Should I go to the slope and start blowing ?-)

Regards Jojo
www.grini.no / jo(at)grini.no

--- In F3F@yahoogroups.com, Pierre Rondel <pierre.rondel@f...> wrote:
>
>
> Yes you are right, this is a small slope, but with a very good
lift and
> probability to fly.
> You can see an aerial picture at the following URL:
> <http://pierre.rondel.free.fr/brie.htm>
>
> Regards,
>
> Pierre.
>
>
>
> Selon jaffee@e...:
>
> >
> >
> >
> >
> > That's pretty cool.  You can actually see what I would assume
would be the
> >
> > sweet spot, where the seperation layer seems to be "notched" a
short
> >
> > distance behind where it seperates from the top of the hill. 
Anyway,
> >
> > that's where I'd want to be flying through. :)
> >
> >
> >
> > I'm a bit suprised that there is not a more prominant rotor, but
perhaps
> >
> > the hill is too small for that?
> >
> >
> >
> > At 12:55 PM 2/26/04 +0100, marcel guwang wrote:
> >
> > >Hello all,
> >
> > >
> >
> > >Julien Giraud did an interesting work on 2D airflow simulation
around the
> >
> > best french DS slope near gernoble...
> >
> > >               
> >
> > >http://jugiraud1.free.fr
> >
> > >
> >
> > >It's worth a look...
> >
> > >
> >
> > >Marcel

you are right Jo, on one of our DS slopes I always land behind the rotor, and some times I can stay up for a few passes in the back side of the slope, not DSing...

Marcel

Since moving air has lower pressure (the air above share layer) this
creates the moving air below share layer. The speed of a DS plane is
created below share layer because there the air is rising.

Regards Jojo

I am getting all sorts of strange emails from guys. So I will again
say: I am not an engineer. I was only hoping that there were someone
out there that might calculate a bit..
BUT I am trying to get ideas out there and trying to find the answer.
Richard (below) says that research will surprice me ????
That statement does not give me anything :-(

I will rest my case..

Hilsen (Regards) Jo Grini
www.grini.no - email: jo@g...

----- Original Message -----
From: "Richard Frawley" <rfrawley@jma....>
To: "Jo" <post@vfkm....>
Sent: Monday, March 01, 2004 10:31 AM
Subject: Re: [F3F] Re: DS airflow


> no, I suggest you re-think your assumptions as they are not in
accordance
> with current molecular flow modeling theory.
>
> I have also seen DS where the air below is not in fact rising at
all, it is
> either neutrally buoyant or falling slightly.
>
> With research, what you find will surprise you.

Like I said Jo. Just accept the fact that it works and go out and enjoy it.
No point in beating yourself about the head getting into 'analyses
paralysis'.
(Unless of course you are paid to find out why/how DS works).

Just relax and let it all wash over you. It will all be over with soon!
:-)

Andy E
(An Engineer!)

Sadly I am not paid to do this (maybe good since i would not keep
the job for long ;-)
But I cant let it go since I am thinking model sailplanes 50% of my
time not asleep. And the weather makes it hard and cold to get up
the slopes with planes and everything. But since you say "it will be
over with soon" I guess someone will explain soon then ? Because the
sharelayer theory about flying over and under is not good enough for
my mind to rest on.
Maybe it is too complex to show here in txt (but I doubt) but hey we
have websites available all over the net.

Regards Jojo, www.grini.no
(an electrician/electronics that fly a lot)

I like your theory Jo ! why always think inside the square ? OK, my
2c here. When it is foggy on our slopes, we can clearly see the fog
running up hill on the dark side and after probing the air with our
toys, we are very sure that the air flow is unable to produce normal
lift.

Is the airflow simply the curl-back part of the rotor or generated by
the phenomenon demonstrated in Jo's wine-glass experiment ? I have
no idea but it will really be interesting to know whether the air
flow helps to push our moldies screaming across the sky.

Does the site mentioned by Marcel have an English version ? I cannot
read French.

Y C Lui

Hey Jo,

We all know about Bernoulli (faster moving air = lower pressure), but it isn't
clear this is what is happening in your experiment. I would like to see an
addition to the experiment with your two glasses. I would like to see you blow
a stream of smoke across the glasses while you film the experiment. Note that
it is important you choose the correct kind of smoke, preferably of the cannabis
variety!

Bottom line is it isn't clear which way your experimental "wind" is blowing.
Maybe you are blowing down INTO the first glass which creates a swirling
action. The pressure of your breath follows the contour of the glass, creating
a swirling action and blowing directly on the cork (?) which in turn follows the
swirling air mass and is pushed along the contour of the glass achieving some
velocity with associated momentum. The momentum of the cork carries it along
the inner contour of the glass and eventually it exits with some velocity above
the glass. At this point, the cork enters your air stream is is further pushed
out over and into the other glass. There you go, maybe Bernoulli has nothing to
do with it.

Here is another DS explanation. I don't fully agree with this description, but
it is more fodder for the pondering:

http://www.billpattersonart.com/dszone.swf

This requires Macromedia player - hit the plane icon in the lower left for the
DS explanation. This site also has the video footage for some of the top DS
speeds the SoCal boys set (the other plane icons).

Even more fodder: here is a page on the DS devised and practiced by the
Albatross:

http://www.wfu.edu/albatross/atwork/dynamic_soaring.htm

This may not quite satisfy you since it is different than the circuits we fly.
But if you think of it this way: "fly against the wind with increasing wind
gradient; fly with the wind with decreasing wind gradient" then they are both
the same thing. The gradient in the case of the Albatross is a more gradual
thing while our gradient is a rather abrupt shear. But the principle is the
same: the aircraft is piloted to undergo an increase in airspeed when flying
upwind and also when flying downwind. On average airspeed = ground speed so the
increased airspeed turns into increased ground speed.

The "on average" part is a bit of hand waving. My theory on this point is that
the airspeed is converted to ground speed during the turn. Essentially, you use
the increased airspeed to "bang" the plane during the turn. The "bang" is the
burst of acceleration imparted to the plane as it is generating lift through the
turn. Of course there is a limit because some of the imparted energy is
dissipated by the drag (ever increasing with velocity), but this captures the
process.

What d'ya think?

-- James
 

At 09:34 PM 3/2/04 -0800, James Osborn wrote:

>This may not quite satisfy you since it is different than the circuits we
fly.
>But if you think of it this way: "fly against the wind with increasing wind
>gradient; fly with the wind with decreasing wind gradient" then they are both
>the same thing. The gradient in the case of the Albatross is a more gradual
>thing while our gradient is a rather abrupt shear.

IMO, I think this may be what Jo is experiencing at his flying site. The
shear layer might be large and ill-defined enough that there is no obvious
"whump" on the top turn. But, there's still a gradient that can be used to
get energy.

Hearing the "whump" is always nice, but you don't always hear it, even when
it's obvious the plane is going through the layer.
____________________________________________________________________________
Brett Jaffee: jaffee@e...

Sorry cannabis is illegal here in Norway and I am not doing drugs :-)
But normal smoke is ok (though expensive due to taxes)
So this time I was blowing from under the glass and with smoke (and
smoke from cold/warm air since the temperature was -10 celcius
today). Sadly the smoke is not strong enough to be seen really good
and my camera only holds 15 frames a second.
The video is edited: <http://www.grini.no/dshow.wmv>

It might be that the "rotor" inside the glass liftes my kinder egg.
But thats cool. It is still being lifted. This time by a rotor or
pretty high energy down in the glass. Maybe its both the rotor and
low pressure that does the job.

Your theory about getting speed from the turns does not compute for
me (and the same for the albatross). Why ? Well I have always found
that the groundspeed gets lower abobe shearlayer and that the turn
below sharelayer is the place I get acceleration. So then it is your
turn to get out experimenting. Use your radarguns and find the speed
going down and up after each turn. I would think the speed is higher
on the way up (just after the turn) than down (just after the turn
again). Though this is still theory and theory can be written in
many ways with many solutions.

Happy flying (I am going out to fly on the ice again. Sadly no DS
possible)
Regards Jojo, www.grini.no