DS theory

This webpage just had to be an archive of my DS theories.
It was triggered by a few thougts I made thru my Diary

Jo Grini, jo(at)grini.no - www.jojoen.no

1st thought | My 2nd | My 3rd | My 4th  | My 5th 
Gliderking forum | F3F-list at Yahoo | Email Herrig | Site Jean-Luc
Ferdinand Hendriks | Matthieu Scherrer | Video 1,4mb | Video frame by frame pictures | DS videos | F3F DS simulator
Links

From a 1946 model book..

DAY .. 27.September 2008 - DS Up in the mountains for DS. Cool weather with some storm coming in. I think it was the "Ike" that rumbled US a week or so ago. The clouds came in but first the winds and man did I work them! It was violent and turbulent like nothing else before it smoothened out and the speeds were cool for half an hour and died out (no good readings on the radar above 130mph sadly). Ended the day with some nice aerobatic flying and a rudder that stopped working (blew the gears on the rudder servo after I forgot to tape the rudder. I usually does that when flying real heavy DS). It also gave me an opportunity to try a very cheap trick I read about on RcGroups and found on a stand at the Masters. A 23$ gyro was installed on one aileron of the Kobra and the gain set almost all the way down. It actually seemed to work. In medium to low speeds I do get twisted around a bit on this slope but now the model seemed to be on rails. I could see it worked at times as the gain was a bit high and since the gyro was only on one aileron you could see it did not correct the most violent turbulence correctly (differential not correct). Here is a video of some flying with the gyro ( 34mb .wmv )

YES Jojo goes 229mph with his Kobra DS
From Jojo's diary
DAY .. 8.June 2008 - 229MPH with Pike Kobra DS and Video
YES upped my personal best with 9mph and got a 229Mph (368km/h). Nice to see that the Kobra DS is rock steady and that if I had enough memory in the camera I am sure I was faster during the session (but not on video this time). Conditions were changing a bit with 6-10m/s winds on the front and lots of huge thermals coming thru. After the DS session (Petter flying his Wizard when not operating the camera...) we went down to the road and mounted the camera on the Pike Perfect SL electro to check out the nearby huge ridge. We wanted to see if there were some landing zone here but does not look more than a huge ridge with rocks sadly. View the DS and scouting video HERE (66mb)

NEW 24/6-07
RC-Soaring Digest is an old well known international magazine that has gone online.
In the June 07 issue there is an DS article

From Jojo's diary
DAY .. 12.June 2007 - Crossfire DS - 220MPH
On the third day Jojo made DS... or something ;) What a day! After a long period with hot weather the temperature came down a bit and the wind picked up. Me and my son went for the DS slope and the conditions were so promising that I took out my well used and heavily repaired Crossfire X-tail. It has a been repaired well I think because it held up for today's conditions. It started out with a very smooth DS zone. Rarely have I experienced a so calm DS zone. Speed was equal all around though not very fast. My son had fun with the radar gun and gave me the speed for each lap. They were stable around 80-110mph. Then it calmed a bit more so I landed and charged waiting for heavier conditions. I had said to him that I would be very happy with 150mph today and super happy with 200mph. A few biscuits and a soft drink later the wind picked up and when you were standing at the top the wind came from behind along your feet. Threw the model out (double carbon Crossfire with DS joiner) with 600g of ballast. 3 laps and it rumbled already. I had to fly pretty big circles and not to perfect. Otherwise I was sure it would blow up. But the conditions were still smooth and those who know me know that I just "have to". It was difficult to get good high readings but I found if my son just held it steady I could fly the same pattern each time and "present" the model. After plenty 120-150mph laps I had to narrow it down a bit and fly lower. This made the readings really bad. Maybe because of a close mountain in the background? The speed was now sometimes so high that I often had to bail out after just a few circles. Vertical after bail out was probably around 4-500m... I decided to use up the model and gave it my best shot. Did 2-3 goes at it and adjusted the flying path until my son had good signals. 5-6 circles later and my son screamed "220"!!!! My heart now pumped all it could but I wanted a backup reading of that. He screamed "193" and I bailed out! I was 100% sure the model would blow up but since the conditions were smooth it was mostly just a high rumbling and not so much "smack" each time I went thru the boundary layer. I also could fly mostly below the boundary layer but the the readings were not so consistent then. So I can now finally (after so many years) say that I have reached 220mph (354km/h) and a backup reading of 193mph. It was the greatest feeling I have had for a long time ;) I want to conclude one thing after so many days on the slope waiting for conditions... Wait until the temperature drops and you will have thicker air and more wind probably... You might have a rain shower but it might be worth it! My radargun is maybe not the best but I did get what I wanted and can atleast say that YES I can also go fast ;)
I cant wait to get a stronger secret weapon (yes it is produced but have not arrived. wait and read ;)

Left: My son Fredrik (10). Right: Jojo waiting for charging. Yes I charge with a 3 cell lipo and a small Jeti charger.

Left: DS slope senn from the highest point. Right: A VERY happy Jojo

News 4/12-06: More airfoils from Dirk Flug with comments:
These 2 foils are for smaller ds planes (2m or 80") and a Reynoldnumber of 500.000-1.000.000. You can use the thicker one at the wing root and the thinner one at the wing tip, or from the middle of the wing up to the tip.
(right click and "save as" or open in notepad)
- .dat files saved in .zip file
- .txt files: DP 1,72-8,32 DS - DP 1,79-8,37 DS

News 3/12-06: New DS record
The DS record is now confirmed at 302mph (486km/h) by Kyle Paulson with his Extreme 100". Lacking video of the actual 302 but HERE is 282mph. Here is a video of the earlier 301mph

News 25/11-06: New airfoils from Dirk Flug with comments:
The DP-airfoils are made for extreme top speed DS-sessions (Re = 1.000.000 - 2.000.000) . They are thick and dam fast.
If you will use them for a normal F3B or F3F soarer you will be disappointed. The design has a much longer laminar flow than
the DS-19 which is used by Brian McLean's Extreme. This should lead to a remarkable higher top DS-speed. The airfoils can be used by every private person. A commercial use is restricted by the designers copyright. If a commercial use is desired or someone needs a different design for a different task please contact dirk.pflug (@) bluetrust.de If you have built a soarer with one of these airfoils please contact me to tell me your flying impressions. If you are interested in a substantial support for a complete DS-soarer by my person or if you have any remarks to the airfoils please contact me.
(right click and "save as" or open in notepad)
- .dat files saved in .zip file
- .txt files: DP 1,68-8,37 DS - DP 1,72-8,16 DS - DP 1,77-8,23 DS - DP 1,82-8,21 DS - DP 1,87-9,07 DS
              - DP 2,00-8,55 DS - DP 2,05-8,65 DS - DP 2,06-8,67 DS - DP 2,47-9,48 DS

News from diary 8.july 2006
Videos from the weekend in Haugesund are ready. The camera went out of battery so the really good DS was not captured. But still some of the passes show pretty fast flying. I divided it into two videos. Chapter 1 is DS on "Ørpetveit" and Chapter 2 is F3F slope with 5-7m/s teaching Arild how to thermal and making dinner on the slope. Yes we had a good time ;-)
Chapter 1 (24,5mb) and Chapter 2 (42mb) - backup if server is slow: Chapter 1 and Chapter 2

News 28/11-05: Cool video with onboard DS HERE. Look at their website HERE
Very interresting to listen to the sound of the whole circuit!

News 9/11-05: Matthieu Scherrer have a new idea that is good according to my theory of vertical rotors on the backside.
Read the theory HERE . Backup HERE

  DAY .. 15. March - 2004 DS Theory
Lots of appreciated comments from you out there and lots of thinking beetween my flying. There two bigger comments that needs to be mentioned (and they need to be read thorughly before I can give you more ideas):
- First out is email from Andreas Herrig in Germany. I have pasted his email further down on this site. He also provided a lot more webpage-adresses that I need to read.. (look at link section on DS-site)
- Second is email from Jean-luc Foucher that has made a webpage with calculations with new theories. Pretty impressive. Look at http://perso.wanadoo.fr/dsjlf/ . A I can see it these theories can be used at both vertical and horizontal rotors back in our loved DS-zone. I have actually seen some of these calculations before when Jean-Luc visited me here in Norway (see diary 2.may.2003 and 11-12.october.2003).

One of the first things I take from these emails is that Andreas thinks that (on the lifting egg theory):
"What actually happens is, that a vortex forms inside the glass, because the (at first) resting air is driven by the air moving along the opening. This is an effect of friction. Now the egg is lying in moving air. Because it has a lot of drag, it will be blown away in circumferencial direction. Seen in the detail it might also be lifted from the glass surface because of the pressure gradient towards the vortex center."
So maybe friction makes vortex, rotors, windshears or whatever we will like to call the moving air in the DS-zone. And offcourse we do not need a frontside slope to make DS (we fly DS behind trees and on a opposite seaslope). Anyhow this moving air makes energy that we can use. Thats a fact (according to my practical flying atleast). My point is that I am looking too why the rotors form in the DS-zone. Offcourse there is no way we can know just how they will form.

But we know that the wind will not follow the terrain above a certain windspeed and drop in height. And since I have seen these "vortex'es" behind my slope I am curious to use them.
According to the theory of windshears we need to get quick in and out of the different layers of air to accelarate. And I like the sentence from Jean Luc: "You have to turn around, so that you create a lift force which generates the forward force.". And I know we can fly DS F3F on the backside but we only accelarate when we turn up again (again according to my practical testing). So we are back to maybe that the wind is accelerating the plane as long as the plane makes a certain lift force AND is moving thru a windshear down there in the DS-zone (vortex, rotors, windshears, etc). If we take the windshear theory we need to just hit the outside of the rotor (sweet spot ?) and not fly around it. But we can fly in differrent wind speeds and accelarate just by that.
So: Any big differences in wind can be used to take out energy. And terrain will make those differences.

  DAY .. 19. March - 2004 DS Theory
Webcamera and weatherstation on Storefjell were looking good but when I arrived the wind came too much from the side. I was hoping for some frontside action and DS in the back. But the meteogram showed that it should change in a few hours. So I killed some time by setting up a camera behind a big pile of snow. I used some tapestreamers to see what the wind was doing on on top and in the back. It was interresting when the wind was above 7-8m/s because then the light snow were turned around hard on the back. The wind died after a few hours. So I never got my flying done. But I have put togheter a funny video of what I could see on my tapestreamers and snow. Download it HERE (7mb .wmv)

News from diary 8.july 2006
Videos from the weekend in Haugesund are ready. The camera went out of battery so the really good DS was not captured. But still some of the passes show pretty fast flying. I divided it into two videos. Chapter 1 is DS on "Ørpetveit" and Chapter 2 is F3F slope with 5-7m/s teaching Arild how to thermal and making dinner on the slope. Yes we had a good time ;-)
Chapter 1 (24,5mb) and Chapter 2 (42mb) - backup if server is slow: Chapter 1 and Chapter 2

Video experiment:

Here you have the video and the frame by frame pictures

Then on the F3F-list at Yahoo or my backup HERE
 

Email from Andreas Herrig:

Hello Jo,

lately I looked at your website again and I realized, that there is a big lack
of understanding how DS works at you (and many other people).
And it really hurts my heart of an aerodynamicist, seeing some explanations
that are given for the DS effect. Please, don't feel set right with the
following words. Just quit reading here, if you think 'Hey, what does he want
to tell me'.
Probably many things have already been said by others. But I just want to
express my opinion and emphasize the right explanations.

Let's start with your glass experiment and the reduction of pressure with
increased speed. To be exact, it's the static pressure which drops. And this
means it is just a scalar quantity of the fluid. The static pressure has no
direction to pull into. Forces on bodies will only arise from pressure
differences.
It will be clear to you, that there is no force, when there is the same
pressure around the whole body (i.e. the egg). If you blow over the glass, of
course the static pressure drops inside, but there will be no reason for the
egg to move.
What actually happens is, that a vortex forms inside the glass, because the (at
first) resting air is driven by the air moving along the opening. This is an
effect of friction. Now the egg is lying in moving air. Because it has a lot of
drag, it will be blown away in circumferencial direction. Seen in the detail it
might also be lifted from the glass surface because of the pressure gradient
towards the vortex center.
Ok, I think this was clear to you before.

Now to the next misunderstanding: DS is made possible by the upward component
of the wind on the backside of an obstacle, compensating the permanent loss of
height due to drag. No!! No obstacle is needed for DS. And please, some simple
calculations will immediately tell you, that the lift can't be the speed
producing factor in DS.
Take an average plane with a lift to drag ratio of 10 (at the high speeds we
are away from the maximum L/D ratio). That is, in lift of 2 m/s (quite much)
you will reach 20 m/s (quite little) flying horizontally on the average (in
equilibrium). This can't be it.
And at the latest if you DS behind trees on flat land or taking full size
glider DS in different layers of the atmosphere (where there is no upward
component) this explanation will fail. Of course, the positive effect of rising
air is also welcome when DS'ing, because it reduces the energy loss to stay at
one altitude.

Some historical remarks: The roots definitely go back to manned gliders. In the
beginning of sailplane construction and flying it was common believe, that
birds (especially bussards) could climb because they exploited vortices of the
wind in the right way.
In these times, all flying was done on slopes because of starting. But it was
not completely clear, that it was the upward component of slope wind, which
made longer flights possible. Rather the idea of dynamic soaring existed
already in 1910 (and probably the suitable theory, remember Einstein derived
the general theory of relativity in 1916...). Several planes (Erich Offermann,
Friedrich Harth) were built with rotating wings to better exploit wind shears -
which was nonsens.
It's funny, that classical thermal soaring was invented later with
the 'rediscovery' of variometers (in the 1930's). The first flights of some
kilometers were believed to be made possible by wind shears (although it was
just upwind). Funny too, that Ludwig Prandtl (*the* aerodynamicist) was
sceptical to albatross flight being driven by wind shear. Rather, he ment they
used the lift over the waves.

Ok, now how and why does DS work? As the name implies, dynamic soaring is
different from normal 'static' soaring with more or less constant speed. The
basic principle is illustrated by a gust hitting a plane from below:

        plane moving to the right ---->

              previous direction of incoming wind
               <----
               ^\
               | \
 vertical gust |  \ resulting effective wind speed
               |   \

You see, the vector of effective wind speed is rotated downwards. As the lift
of the plane is always directed orthogonal to the free stream wind, a force
component results, which accelaretes the plane (not drawn). Or, the other
possibility is to use the gust for climbing with the effective velocity
remaining horizontal. In either way you gain energy, and that is the crucial
point. Whether it is in form of speed (kinetic) or heigth (potential) makes
only a small difference.

Now, what if you could *repeatedly* make gusts coming from below the airplane?
If there is a homogeneous wind field no way. What is necessary is a spatial
gradient of wind speed and/or direction and the suitable flight path to extract
a sufficient amount of energy. (Proper temporary changes of the wind vector are
*very* unlikely). The typical 'Parker Mtn. ridge shear' is the most easy to
realize and understand, but many other scenarios are thinkable. One just has to
open ones eyes.
To quantitatively explain DS, a deeper intrusion into mathematics and flight
dynamics is necessary. In the end you probably won't know much more than
before. Infinitely sharp wind shears are no requirement, rather it is the
gradient which drives the hole thing. But with shear layers of vanishing
thickness some simple calculations can be done which quickly get you the gist
(compare publications of M. Drela, J. Wurts and M. Guwang).

Attached I'm sending you some links (don't know if they still work, was for a
seminar in 2002) and pictures (from QFI and Mark Drela). You may also want to
download a video about Albatross flight from Munich University:
"http://www.lfm.mw.tum.de/lfm_sources/albatros.html".

You mention a slope, which makes it possible to DS below the shear layer. How
do you know, where the latter is located? I think it is also a significant
difference in wind speed or more probable direction, which is the driving
factor here. By the way, you could provide a small sketch?

Maybe I completely misunderstood you. Also, I didn't read all the posts in all
the forums. So forgive me in case of that for wasting your time.

Best regards,

Andreas Herrig

+ ------------------------------------------------------------ +
+  Andreas Herrig                                              +
+  Institut fuer Aero- und Gasdynamik                          +
+  Universitaet Stuttgart                                      +
+  Pfaffenwaldring 21                                          +
+  D-70550 Stuttgart                                           +
+  ----------------------------------------------------------- +
+  phone:    +49 711 - 685-3424                                +
+  fax:      +49 711 - 685-3470                                +
+  email:    herrig@iag.uni-stuttgart.de                       +
+  internet: http://www.iag.uni-stuttgart.de/laminarwindkanal/ +
+  ----------------------------------------------------------- +

Some attached pictures:

Email from Ferdinand Hendriks:

Attached presentation of DS by Ferdinand Hendriks (1mb) Download HERE

F3F / DS simulator

The Crrcsim is great fro practicing F3F in the french version.
But with wind from south instead of North you can fly DS at the same slope :-)
I think it is great for practicing DS. Not exactly as in real life but actually pretty close.
When the wind is set to south it quits showing the F3F times but in the same directory there will be a txt file that can be read.
DS F3F is pretty cool :-) Be sure to press +/- on your keyboard to get a better wiev in the start. And "R" is restart...
The sim is seated on Yahoo groups HERE
In the files section there is also a french F3F version that works great (with right click menus)
My edited copy for DS is right HERE (2,9mb). Sorry I can not help you to get it to work on your computer, your tx, etc....
But be sure to read the instructions.txt and howto.txt beause there might be some drivers that needs to be installed
There is no point in using this if you dont have your radio attached to the pc.
I use a USB interface that emulates a joystick signal from my older MPX Combi 80.

• Jojo's mainpage - www.grini.no
• Jojo's DS web (this page) - www.grini.no/ds
• Jojo's diary - www.grini.no/dagbok
   
• www.rcspeeds.com
• http://www.rcgroups.com/dynamic-soaring-126/
• Cyrille Cuénot - Nice videos of treelineflying and nice photos
• Site Jean-luc Foucher  -  http://perso.wanadoo.fr/dsjlf/
• 2D computer simulation by Julien Giraud
  Translator: http://babelfish.altavista.com
  insert the http://jugiraud1.free.fr and choose language
  About the slope by Pierre Rondel - http://pierre.rondel.free.fr/brie.htm
• Gliderking - Gliderking.com
• Gliderking  forum
• F3F groups at Yahoo
• Albatross theory - http://www.wfu.edu/albatross/atwork/dynamic_soaring.htm
• Bill Patterson DSzone - http://www.billpattersonart.com/dszone.swf
• Brett Jafee's Slope and power DS-page - http://home.earthlink.net/~jaffee/ds.html
• NorCal slopepage - http://www.thehelix.com/soaring/
• German DS-site by Artur Blömker - http://www.dynamic-soaring.de
• Nathan woods at ASRO with fastest speeds - http://www.sloperacing.com/results/ds-speeds.htm
• Adrian Law with DS in the UK - http://www.dynamic-soaring.co.uk/
• RC-groups DS - forum
• http://www.charlesriverrc.org/articles/flying/markdrela_ds.htm
• http://perso.wanadoo.fr/scherrer/matthieu/english/modelie.html
• http://www.wfu.edu/albatross/atwork/dynamic_soaring.htm
• http://members.tripod.com/douglasturner/id27.htm
• http://icarusengineering.com/Dynamic-Soaring-and-SE.htm
• http://www.charlesriverrc.org/articles/flying/dynamicsoaring.htm
• http://www.liftzone.com/articles/2002/oct/darkside/ds.shtml
• http://home.clara.net/barcs/archive/dynamicsoar.htm
   
• The DS record is right now at 262mph (421km/h) by Kyle Paulson late 2004. There are some threads on RCgroups with videos (Thread 1, Thread 2). Direct link to video
• OLD: The old DS record (18.june 2004) was 240mph (386km/h) by Kyle Paulson. Read at Gliderking.
  The DS record (2003) was at 232mph first made by Gary Legerton with a Opus sailplane.
  Small video HERE.
  The DS record were then tied by Kyle Paulson flying a Extreme sailplane.
  Video HERE
  BTW There are no "world record" only a cool figure on the internet :-)
   
• More links about DS ? Send ME email