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Kites! Kites! Kites! => Kite Building and Repair => Topic started by: RonG on April 25, 2012, 04:36 PM



Title: Doug Stout's stunt kite design tool
Post by: RonG on April 25, 2012, 04:36 PM
Anyone remember Doug Stout, and his mathematical approach to kite design?  Doug gave me a copy of the article he wrote about it circa 1995, and if memory serves there was a spreadsheet to go along with it as well.

He produced some interesting kites and was an active competitor on the US circuit back in the day.


Title: Re: Doug Stout's stunt kite design tool
Post by: Doug S on April 25, 2012, 07:50 PM
Ron,

Thank you for remembering me.  A few years ago I got back into kiting for the fun of it and built an updated 7-foot version of my Raptor (1995), called the Bird of Prey (2009).  I am very thankful to Jon at Sky Burners for helping me select the framing materials from his great SkyShark tubes for the two versions of the kite (Standard and Light Wind).  This past winter I started updating my old Geokite Program in the current version of Excel, which was originally written in Lotus 1-2-3.  The updated version will hopefully be able to capture and model the effects of the tail weight and active bridles in the current breed of stunt kites.  The update is currently on hold, since I have been expanded my kite enthusiasm into the world of no wind delta and canard soaring kites, where I also use Geokite to assist in the design process.

For those who have not seen my old article, the Geokite programís main focus was to calculate aerodynamic centers of our unique flying platforms (i.e. geometry), while also calculating the center of mass for each component and mass balance of the design, so that you can estimate the final weight of the kite prototype and have it balance at the desired center of gravity and static margin.  The program also calculates a three point bridle as an excellent starting point for each design.  Since kite materials can be quite costly, the program saved me quite a bit of construction time and materials.  I only needed one prototype for each of my subsequent stunt kite designs that were sold under my boutique kite company, Falcon Aero Designs:  Falcon-SL (1992), Talon (1993), Talon-2M (1994), Raptor (1995).  In the fall of 1990 to the spring of 1991, it did take numerous modeled stunt kite designs for each prototype and 10 actual prototypes to calibrate and refine the program.  During this time, I experimented with using a leach line that was used in the 6th prototype, which also had a high aspect ratio.  The results of this initial work allowed me to develop my first contest ready stunt kite design (10th prototype) called the Falcon (1991), which I introduced to the stunt kite community while competing at the 1991 Wildwood, New Jersey Event.  With the Falcon, I also introduced the concept of a totally silent kite by using of a leach line, and all of my subsequent stunt kite designs used a leach line.

In closing, I wish to thank Ron for introducing me to this forum, which continues to be a great location for me to understand how our kiting community keeps pushing the envelope of designs with the incredible materials that we have to work with.  While working with Jon, I also acquired one his excellent Solus Stunt Kites.  Ron also introduced me to Will Sturdy and I have acquired one of Will's excellent Sabre II Stunt Kites.  This year I am hoping I can teach these old hands some new tricks.  Thank you again.

Sincerely,

Doug Stout


Title: Re: Doug Stout's stunt kite design tool
Post by: Cydonia on April 26, 2012, 10:22 AM
Is it possible to have a look to this article & the program????


Title: Re: Doug Stout's stunt kite design tool
Post by: Doug S on April 26, 2012, 05:00 PM
This excellent forum does not let one post a PDF file, which is the format my article is in.


Title: Re: Doug Stout's stunt kite design tool
Post by: zippy8 on April 26, 2012, 05:11 PM
This excellent forum does not let one post a PDF file, which is the format my article is in.
Verily thou canst post a link unto a PDF.

Mike.


Title: Re: Doug Stout's stunt kite design tool
Post by: inewham on April 27, 2012, 12:32 AM
I too would be very interested to see the article and Geokite, if you need somewhere to put it let me know. I can host it and put links on here.


Title: Re: Doug Stout's stunt kite design tool
Post by: mikenchico on April 27, 2012, 07:56 AM
What Ian said, your post and previous posts have gotten my attention too and I would be very grateful to view any of your research you would share. Google Drive, MS Live/Skydrive, Dropbox or Ian's offer, dozens of free ways to share files now. I'd really look forward to seeing your research Doug.



Title: Re: Doug Stout's stunt kite design tool
Post by: Doug S on April 27, 2012, 08:14 PM
I sent Mike an E-Mail with a copy of my technical article so he can provide a link for others to download.

As to my current kiting distractions, the attached picture shows three canard kites I have recently built.  The top one is my version of Leong Ceewan's great Plutz kite design.  The one on the lower left is a larger version (4-foot wing span) with my preferences for sail shape and a front sail (black in color), which can be removed.  And as they say on the old Monty Python show "Time for something completely different," the one on the lower right is my sweep forward canard I call the Arrow.  All three glide great.  The sweep forward canard kite is a work in progress regarding framing stiffness on the canard wing, which I hope to have resolved when the wind becomes more reasonable.

Doug

(http://drive.google.com/uc?export=view&id=0B_TPx1W-lkmST041X3FwQXlmd2c)


Title: Re: Doug Stout's stunt kite design tool
Post by: st3307 on April 27, 2012, 08:21 PM
I  am not   much  into  Glider  Doug   but   dang  them  look   nice        some  times  I  wish  I  did  not  have  a  phobiea   of  sewing


Title: Re: Doug Stout's stunt kite design tool
Post by: mikenchico on April 27, 2012, 08:52 PM
Here's Doug's Article he forwarded to me - I haven't gotten to look it over yet myself, I wanted to get it accessible for those interested. View it or right click and 'save target as' on Windows if you prefer.

Technical Article - Stunt Kite Aerodynamics by Doug Stout.pdf (http://www.sysmatrix.net/~mikenchico/Technical_Article_Stunt_Kite_Aerodynamics_by_Doug_Stout.pdf)

*Cydonia - Sorry were are sort of polluting your thread, we get sidetracked sometimes and don't mean you any disrespect or intention to detract from your work either, I hope you find Doug's work usefull too - Mike



Title: Re: Doug Stout's stunt kite design tool
Post by: Cydonia on April 27, 2012, 10:04 PM
there's no problem for me. it is very interesting to compare with doug's work.
I could probably complete my file with this article.


Title: Re: Doug Stout's stunt kite design tool
Post by: mikenchico on May 04, 2012, 01:13 AM
Doug has also shared his Excel sheet that he mentions above

Geometric Stunt Kite Comparison by Doug Stout - May 2 2012.xls (http://www.sysmatrix.net/~mikenchico/Geometric_Stunt_Kite_Comparison_by_Doug_Stout-May_2_2012.xls)

And his original article again to keep them in one spot
Technical Article - Stunt Kite Aerodynamics by Doug Stout.pdf (http://www.sysmatrix.net/~mikenchico/Technical_Article_Stunt_Kite_Aerodynamics_by_Doug_Stout.pdf)

Many thanks again Doug for sharing all this info

Here's Dougs email

Mike,

I have been getting some questions on my stunt kite design article.  To assist our stunt kite design friends, I have attached my current version of Geokite 8 in Excel.  I have reformatted the input sheet.  I need to reformat the output and graphic equation sheets, and add other interesting things in the future.

As a treat to everyone and show them how the program works with real data, the file includes my old school Bird of Prey design, which shows how I use a model (equations within many of the cells) to automatically adjust the shape of the kite by only changing a few values.  Please post the link to allow our stunt kite design friends have fun with it, and take my years of work to the next level.  Have fun with it and thank you.

Sincerely,

Doug Stout




Title: Re: Doug Stout's stunt kite design tool
Post by: Doug S on May 04, 2012, 06:58 AM
Mike,

Thank you for posting for me, but Geokite was not included as one of the links.  To assist and as suggested by you, I setup a Google Drive for the files.  The following provides the links to my Technical Article, Geokite 8, and a comparison of my modeling efforts back in the 1990s.

      :)  Technical Article - Stunt Kite Aerodynamics by Doug Stout.pdf - https://docs.google.com/open?id=0B_TPx1W-lkmSRnZuQWJVbzFYRVk

      :)  Geokite 8 with Bird of Prey Stunt Kite Design - Program and Stunt Kite Design by Doug Stout - May 2 2012.xlsx - https://docs.google.com/open?id=0B_TPx1W-lkmSQ3dRQVdwaFBiZ0U

      :)  Geometric Stunt Kite Comparison by Doug Stout - May 2 2012.xls - https://docs.google.com/open?id=0B_TPx1W-lkmSOVFHZUM5dUdQTms

If anyone has any problems downloading the files, please let me know.  Please note that as a disclaimer, Geokite was designed by me for my sole use in modeling and designing kites many many years ago, but not in a place far far way.  I am not offering the program to be critiqued, but as a learning tool for others who wish to use modeling techniques to design kites.

To allow you see how Geokite 8 works with a real stunt kite, the file includes my modeling efforts for my Bird of Prey, which was modeled in 1999, updated in 2003, but not constructed with current materials and construction techniques until 2009.  My picture to the left is of my Bird of Prey.  Please note that I did not update the input values for the mass balance section, which is why the estimated and actual weight, CG and SM do not match.  When you have been modeling kites for a long as I have, a specific shape will provide a CG where desired.  Poor excuse, but I got lazy and I adjusted the CG with the Center Spine, as indicated in a sheet in the third link. 

Geokite uses 10 panels per side to allow for a curved LE and TE, and placement of the standoffs where I desire.  You will note that in many of the input cells there are equations the reference other cells on this sheet.  Using a spreadsheet allows me to build a mathematical model of the kite within the program, where you can change a few key parameters and the entire shape of the kite changes automatically.  Most of the equations in the input cells are in the Sail Shape Section and Material Center of Mass Location Section of the Input Sheet.  If you wish to measure one of your own kites or design from scratch, just enter your own data and input 0 in the unused cells.

With regard to my experience, it is my preference to have the end of the upper spreader (Upper Bridle Connection Point) and the inner standoffs align with the PAC, when using only two standoffs or four standoffs with the outer standoffs being near the lower spreader/wing spar connection point.  This preference normalizes the pressure of the air under different wind speed conditions (i.e. the rate of turn and control of the kite stays the same over different wind speeds).  You will note that a good starting point for a three point bridle is with the connection point over the PAC, which can be viewed in the Graphics Ė Top View.  This will provide a neutral moment arm when compared to the PAC.  I use an adjustable lower/outer bridle line to shorten this line and move the bridle line connection point outward to obtain the desired control.  In the Graphics Ė Top View, you will see that another preference is to have a 90 degree angle between the two lower bridle lines.

Regarding the depth of the sail, since many current trick stunt kites have much deeper sails than back in the late 1990s, the included model of my kite allows you to change the length of the inner standoff (Input Sheet:  Panel 4, Cell E29) or the outer standoff (Input Sheet:  Panel 6, Cell G29) and see how the depth of the sail automatically changes it shape when viewed in Graphics Ė Top View.  With the current breed of trick stunt kites using close together standoffs, I would have to update the model so that outer standoffs would be at Panel 5, and one could vary the span of this panel to adjust the standoff spacing.  Also, it may be prudent to align the PAC to be centered between the inner and outer standoffs when they are close together.  Just my thoughts and enjoy my old work.

Sincerely,

Doug Stout


Title: Re: Doug Stout's stunt kite design tool
Post by: mikenchico on May 04, 2012, 07:27 AM
Sorry Doug guess I missed there were two different attachments in the last two mails. It was late last night  :( 

Glad it got you to get into one of the free hosting arrangements available now. Hopefully you'll find it usefull in sharing your generosity in the future. Thanks again


Title: Re: Doug Stout's stunt kite design tool
Post by: inewham on May 04, 2012, 11:33 AM
I hope you guys don't mind I've taken the liberty of splitting this thread and stickying both. Theyre both great pieces of work so its a good idea to keep them at the top where people can find them easily.

Thanks Cydonia and Doug  8)


Title: Re: Doug Stout's stunt kite design tool
Post by: Cydonia on May 10, 2012, 10:36 AM
Hi Doug,

I read your article which is very interesting but I have some questions.

when you calculate subpanel aerodynamic center, you the project sail area or the total sail area?
In other words, what is the stand off influence in the subpanel aerodynamic center.

the second question is about the trailing edge.

in your calculation the trailing edge of each subset is linear. Is there any changes on equations if I use a curve trailing edge?

last question.

How did you "cut" the sail in subpanel. I suppose that it's depend on the position in the trailing edge

thanks a lot for your work

Cydonia


Title: Re: Doug Stout's stunt kite design tool
Post by: Doug S on May 10, 2012, 02:11 PM
Cydonia,

Thank you for the questions.  The center of pressure (CP) for each panel is calculated for the projected area.  In my Geokite Program, I also calculate the CPs for when you view the assembled kite from the top and side, since it has been my experience that these values help us determine the effect of the three dimensional aspects of the sail.  My old college physics class teaches us to look at the forces apply to an object in 3 planes for flying platforms, which Geokite does for us.  If you download the Geokite Program and the Evaluation File, you will see what I mean.  If you vary the length of the standoffs in Geokite, you will see the side and top CPs move in the charts for the Front View of the kite shape.

The current version of Geokite discussed in the article allows up to 10 panels per side to represent the shape of the kite.  After modeling a kite, I load the modeled kite shape into AutoCAD and draft the kite in 3D, and then flatten the design to make the patterns for the sail material.  While in AutoCAD, I use polylines and a fit curve function to provide the curve to the leading and trailing edges.  I have found that 10 panels per side allowed me to break the design into enough smaller sections to provide the desired sail shape.

With my provided model for the Bird of Prey, you can see the values for the rate of curve for the trailing edge, between the center spine and the 1st standoff and between the 1st standoff and the tip.  The rate of curve for the trailing edge outside of the 1st standoff is the minimal amount of curve that allows my leach line to keep the sail silent.  Please note with careful work, the rates of curve for panel of the indicated locations are the same, to allow for a pleasant looking curved edge.  A rate of curve can be observed for the leading edge, from the upper spreader to the tip, which allows the wing spars to provide just enough tension to assist the leach line in keeping the sail silent, if one so desires.

To input an existing kite into Geokite, just divide the kite up into easy to measure locations, such as distances from the center spine to each standoff, upper spreader, lower spreader, etc.  In the modeled of my Bird of Prey, I add extra panels between these easy to measure points to allow the sail to reflect a curved leading and trailing edge.  Please remember that Geokite is in a spreadsheet for a reason, which allows me to develop equations for the shape of the kite, I call the model.

Play with Geokite and have some fun with my Bird of Prey model before you input your own kites.  Draw a real simple kite with two standoffs and play with the length of the standoffs to see how the top and side CPs move.  I hope the above answers your questions.

Doug


Title: Re: Doug Stout's stunt kite design tool
Post by: Cydonia on May 22, 2012, 01:48 PM
Hi Doug,

I have another question:

when you calculate aerodynamic center on top position why don't you use vertical subpanel aerodynamic center equation?

Thanks in advance for your response

cydonia


Title: Re: Doug Stout's stunt kite design tool
Post by: Doug S on May 23, 2012, 06:15 AM
Cydonia

Thank you for your question.  The Top and Side Panel Aerodynamic Center (PAC) calculations are my own derivation to calculate numeric values to represent the depth of the sail and washout.  In simple terms, we are calculating the area and the PAC of each panel that we can see when observed from the 3-axis plane view of the kite:  Front (X,Y), Top (X,Z) and Side (Y,Z).  The calculation of the Front PAC uses the X and Y values for each panel.  For the Top PAC, the Y values are replaced with the Z values representing the depth of the sail for that panel, with the X values being the same as the Front View.  In the Side View, the X values are replaced with the Z values representing the depth of the sail for that panel, with the Y values being the same from the Front View.  In Geokite 8, the Output Sheet provides the results of these calculations for each of these three views (Front, Top, and Side), which results are used to plot the locations in the Front and Top Charts.

Please note that the PACs for the 3-axis views provide numerical values that one can relate to the characteristics/personality of a specific stunt kite, which will allow one to objectively compare the values from stunt kites with different characteristics/personalities.  Charting the PACs allows one to observe how stunt kites with similar or different characteristics/personalities relate to one another, providing one with a performance window of PACs that represent what you like as the desired characteristics/personality in a stunt kite.  This evaluation technique allowed me in the 1990s to explore refinements in my numerous stunt kite prototypes and develop the window of PACs for the characteristics/personality I was looking for, which was a very easy to fly and predictable precision stunt kite that could perform all of the precision and trick maneuvers know at that time.  Since the tricks have evolved, one must develop the window of PACs that will provide a stunt kite with the desired characteristics/personality to perform these tricks in an easy and predictable manner.

I hope this answers your question.

Doug


Title: Re: Doug Stout's stunt kite design tool
Post by: n893 on June 15, 2012, 07:12 PM
Thanks for sharing all of this article... it's really open up my way of thinking of how complicated a stunt kite design process... :) :) :)


Title: Contemplating Designing and Building a Speed Kite
Post by: Doug S on August 13, 2013, 05:32 AM
Based on some research, I have revised this post.  I was humbled by the speeds that are currently being achieved.  I have flown control line combat model airplanes at those speeds, but it was many years ago.  It appears that a finely tuned speed kite is going to be challenging to fly.  Thus, it is a young manís sport.  Based on this, I donít think I could offer a design that would be faster than what is being currently flown.  I provided ae with some suggests on how to make what he is flying go faster, which he may have already taken into consideration.

I am in the process of updating Geokite because I have the itch to design something new in the dual line family.

Later,

Doug


Title: Re: Doug Stout's stunt kite design tool
Post by: ae on August 13, 2013, 08:08 AM
Ohh Speedkite,

I'm definitely interested in what you come up with.


Title: Updating Geokite for Something New
Post by: Doug S on August 30, 2013, 01:28 PM
I haven't posted for a while because I have been busy updating Geokite and retrofitting one of my old prototype kites.  The output section of Geokite is reformatted and less pages to print.  I will add the simple equation to calculate the moment force for tail weight in trick related kites.

I have the itch to build a new stunt kite, which may be a pure precision machine or a pure speed machine.  Maybe one of each (ae will be happy about the speed kite).  I havenít decided on the size of the precision kite, but would like to keep the effective sail area around 900 square inches, if it is to be flown in normal moderate wind conditions.

Updated the fittings on one of my Falcon prototypes (January 1991), which has a 9 to 1 aspect ratio.  It was my first design that used a leach line.  Also added new standoff pockets and a second set of standoffs at the wing spar/lower spreader connection points.  Now it should axel without catching the lines.  Will be using this kite to evaluate the benefits of higher aspect ratio kites for the two potential builds.  I have other prototypes with different aspect ratios to be used in the comparison, which also have additional outer standoffs that were added after the initial construction.  All of the original 9 prototypes were large with 100 inch wing spans.  The January 1991 prototype was very efficient, but had a tip stall problem due to the leach line, with a sail with much less draft than what is being used today.  The new outer standoffs should remove the tip stall problem.

I modeled some of the speed kites and was amazed that the aspect ratios are not that much different than the run of the mill stunt kites.  The difference is the speed kites have a more uniformly tapered sail shape, less leading edge sweep, and very little draft.  If you want speed, I have been told that you donít washout the tips for stability or have a leach line.  They must have some entertaining tip stall issues.  No wonder they are hard to take off until they reach flying speed.  This will be one of the engineering challenges I will try to overcome.

Later,

Doug