dynamic soaring

[bagmaker]

Dont quite understand any of this, but it is interesting enough, with great graphics


http://translate.google.com/translate?hl=en&sl=de&u=http://www.lfm.mw.tum.de/lfm_sources/albatros.html&sa=X&oi=translate&resnum=7&ct=result&prev=/search%3Fq%3Dalbi2.mpg%26hl%3Den%26lr%3D%26client% 3Dfirefox-a%26rls%3Dorg.mozilla:en-US:official%26hs%3DtY8


Bagger

[jeplane]

In his 1978 book Streckensegelflug (lit. "distance sail flight".
Cross-Country or Long-Distance Soaring), Helmut Reichmann describes a
flight made by Ingo Renner in a Libelle sailplane over Tocumwal in
Australia on 24 October 1974.

On that day there was no wind at the surface, but above an inversion at
300 metres there was a strong wind of about 70 km/h (40 knots). Renner
took a tow up to about 350 m from where he dived steeply downwind until
he entered the still air; he then pulled a sharp 180-degree turn (with
very high g) and climbed steeply back up again. On passing though the
inversion he re-encountered the 70 km/h wind, this time as a head-wind.
The additional air-speed that this provided enabled him to recover his
original height.

By repeating this manoeuver he successfully maintained his height for
around 20 minutes without the existence of ascending air, although he
was drifting rapidly downwind. In later flights in a Pik 20 sailplane,
he refined the technique so that he was able to eliminate the downwind
drift and even make headway into the wind.

Just amazing and fascinating!

Richard
ASW19 Phoenix

[[email protected]]

amazing is right.

[[email protected]]

It is absolutely fascinating. The RC guys have reached 300+mph doing
this. I personally have clocked someone flying a 2M wingspan RC glider
doing 209mph. It is amazing how fast the energy builds up and how
quickly speed goes from 40 to 150+

It requires nerves of steel and amazing reflexes to dive to the ground
at 200+ and pull out only a couple of feet above ground though!


wrote:
> amazing is right.

[Frank Whiteley]

wrote:
> amazing is right.
A few threads on this over the years. Gary Osoba's talk at the SSA
Convention a few years ago was very interesting.

http://tinyurl.com/2tx953

Frank

[Ralph Jones]

On 18 Jan 2007 07:16:21 -0800, "Frank Whiteley"
> wrote:

>
wrote:
>> amazing is right.
>A few threads on this over the years. Gary Osoba's talk at the SSA
>Convention a few years ago was very interesting.
>
>http://tinyurl.com/2tx953
>
I read a mathematical analysis of this perhaps 25 years ago...the
basic principle is extracting energy from the curl of the air
velocity.

Curl is a vector-calculus term that can be visualized like this:
Imagine you cut out some little paper flowers, toss them into a
flowing stream and watch them float by. If the flowers rotate, the
flow has curl. The curl is a vector pointed along the axis of
rotation, and its magnitude will normally vary from zero at the center
to a maximum along the banks, with its direction upward in the left
half of the stream and downward on the right.

Shear is just a special case of curl; in pure sheared flow, the value
of the curl is large at points on the shear plane and zero everywhere
else. The usual explanations of dynamic soaring refer to pure sheared
flow, but that isn't necessary: it can be done wherever the curl value
is nonzero.

The most interesting conclusion is that if the curl is the only source
of energy (in other words, there is no vertical velocity component to
complicate the issue), the optimum strategy is amazingly simple. Most
of the variables fall right out of the calculation, and the result is:
Circle in a 55-degree bank. Go to the left if the curl direction is
upward, right if it's downward.

rj

[flying_monkey[_1_]]

> I read a mathematical analysis of this perhaps 25 years ago...the
> basic principle is extracting energy from the curl of the air
> velocity.

Curl? I hoped I'd never hear that term again. That is probably why I
couldn't
complete the Electrical Engineering curriculum in college. Maxwell's
equations
for Electricity & Magnetism - first equation, stated in english: Curl
beta = 0.
ED: What's curl?
Math Geek: Oh, that's just the divergence of the gradient.
ED: Ok, I kind of understand gradient, but what's divergence?
Math geek: Long-winded string of uncomprehensible words.

Ed flunks out.

> The most interesting conclusion is that if the curl is the only source
> of energy (in other words, there is no vertical velocity component to
> complicate the issue), the optimum strategy is amazingly simple. Most
> of the variables fall right out of the calculation, and the result is:
> Circle in a 55-degree bank. Go to the left if the curl direction is
> upward, right if it's downward.
Seems that if you have this really high wind velocity above a certain
level
and zero below that, then trying to circle is going to be difficult to
impossible.
If you have one wing stuck below the layer "anchored" in zero wind, and
the
other in the high velocity layer, you're going to get "rolled",
spanwise, across
the sky, and there's nowhere near enough aileron power to stop that.
And, how would you know if the curl is upward or downward? Seems like
if you guess wrong you get thrown at the ground, real hard.

Ed

[bumper]

> wrote in message
ps.com...
>
> It is absolutely fascinating. The RC guys have reached 300+mph doing
> this. I personally have clocked someone flying a 2M wingspan RC glider
> doing 209mph. It is amazing how fast the energy builds up and how
> quickly speed goes from 40 to 150+
>
> It requires nerves of steel and amazing reflexes to dive to the ground
> at 200+ and pull out only a couple of feet above ground though!


My understanding is that the average albatross possesses nerves of steel and
amazing reflexes!

Or maybe it has something to do with aptitude and talent (g).

When I was in the US Navy, I used to marvel at them. They'd follow in the
ship's wake for hours, turning and wheeling, sometimes with their wing tips
just inches from the water, though never flapping.

Wonder, if they caught a wing tip by mistake, would all hell break loose,
would they suffer a broken boom?

bumper

[Ian]

flying_monkey wrote:

> ED: What's curl?
> Math Geek: Oh, that's just the divergence of the gradient.

Get a better maths geek. Curl ain't div grad.

Another maths geek.

[Robert Ehrlich]

wrote:
> amazing is right.
>

Particularly the pilot at the end of the video.

[Robert Ehrlich]

Ralph Jones wrote:
> ...
> The most interesting conclusion is that if the curl is the only source
> of energy (in other words, there is no vertical velocity component to
> complicate the issue), the optimum strategy is amazingly simple. Most
> of the variables fall right out of the calculation, and the result is:
> Circle in a 55-degree bank. Go to the left if the curl direction is
> upward, right if it's downward.
> ...

But in the case of wind shear discussed here as mentionned on the
site quoted in the first post of this discussion, the curl direction
is horizontal, perpendicular to the direction of the wind.

[Ralph Jones]

On Fri, 19 Jan 2007 01:19:21 +0100, Robert Ehrlich
> wrote:

>Ralph Jones wrote:
>> ...
>> The most interesting conclusion is that if the curl is the only source
>> of energy (in other words, there is no vertical velocity component to
>> complicate the issue), the optimum strategy is amazingly simple. Most
>> of the variables fall right out of the calculation, and the result is:
>> Circle in a 55-degree bank. Go to the left if the curl direction is
>> upward, right if it's downward.
>> ...
>
>But in the case of wind shear discussed here as mentionned on the
>site quoted in the first post of this discussion, the curl direction
>is horizontal, perpendicular to the direction of the wind.

I haven't seen any analysis of that, but I'm betting that with
sufficient horizontal curl you could climb by making successive loops.
But a porpoising technique might make a bit more sense...;-)

rj

[Tinwings]

The one with nerves of steel is the one holding the radar gun with a
several pound RC "missile" coming at them at 200+ !

wrote:
> It is absolutely fascinating. The RC guys have reached 300+mph doing
> this. I personally have clocked someone flying a 2M wingspan RC glider
> doing 209mph. It is amazing how fast the energy builds up and how
> quickly speed goes from 40 to 150+
>
> It requires nerves of steel and amazing reflexes to dive to the ground
> at 200+ and pull out only a couple of feet above ground though!
>
>
> wrote:
> > amazing is right.

[JS]

In the last year, the USAF Test Pilot School has been conducting
dynamic soaring test flights with a Blanik L23 at low level (sometimes
down to 100' AGL) over the lake bed.
Jim

[Ralph Jones]

On 19 Jan 2007 05:18:50 -0800, "JS" > wrote:

>In the last year, the USAF Test Pilot School has been conducting
>dynamic soaring test flights with a Blanik L23 at low level (sometimes
>down to 100' AGL) over the lake bed.
>Jim

Hmmm, sounds like there's some kind of stealth UAV in the works...;-)

rj

[SAM 303a]

"Ian" > wrote in message
ps.com...
>
> flying_monkey wrote:
>
>> ED: What's curl?
>> Math Geek: Oh, that's just the divergence of the gradient.
>
> Get a better maths geek. Curl ain't div grad.
>
> Another maths geek.
>
You know they're hardcore when they say 'maths' instead of 'math'

I pretty much stand in awe of long division....