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Kites! Kites! Kites! => Single Line Kites => Topic started by: Josiah on January 17, 2011, 02:12 PM



Title: Some Rok questions (Tuning, launching, and framing)
Post by: Josiah on January 17, 2011, 02:12 PM
My parents bought me a "Gom-kaku" for Christmas this year.  For those unfamiliar, it is a 6' tall rokkaku made by Gomberg.  I finally had a chance to try and fly it this weekend, with spectacularly poor results...  So bad in fact that I decided to turn to all of you for a little help.

Tuning: First off, the bridle was missing any marks to indicate "neutral" or "starting position" tuning so I just tried flying it how it came configured right out of the box. Now, there wasn't much wind, maybe 5-7mph, but when I had a friend release the kite, it made absolutely no upwards movement.  It just caught the wind and pulled straight down-wind, not up into the sky.  I slid tow point "up" towards the upper spreader an inch and tried again.  Basically the same result.  I then moved the tow-point another two inches up (!) and tried launching.  This time it it just barely pulled up into the sky, even with me running backwards.  It wasn't anywhere near enough lift to keep the kite aloft though.  Since I had already moved the tow point so far up, I started wondering if it was a problem with the bridle, or my general launching technique.  So, does anyone know the bridle measurements for a Gom-kaku?  Any general comments on tuning a Rok?

Launching:  With the kite unable to fly, I started wondering if the problem had more to do with launching than with the bridle.  Since they fly at such a steep angle, do Roks have to be launched differently than say a delta?  Should the flat surface of the Rok be more parallel to the ground when launching since that is more like its actual flying condition?  How do you launch a Rok if you are by yourself?

Framing: Finally, the spine of the kite is sort of a strange assemblage of wrapped-carbon spars.  There are two full length spars furruled together (interior) and then another 4 inches ferruled onto each end of the full length spars.  When you go yo assemble it all, you can feel how much stress is put on the ferrule sections, with those occasional, tiny, crackling sounds.  I would feel much better replacing it with fiberglass or even pultruded rods with only a single ferrule.  Is there any compelling reason to keep the spine stock?  If it ends up a bit heavier, all it should require is a bit more wind, right? (As compared to having to change the bridle or something...)

Thanks, as always for the help!

 


Title: Re: Some Rok questions (Tuning, launching, and framing)
Post by: thief on January 17, 2011, 02:18 PM
did you send gomberg an email? i am certain he will respond quickly with all of your answers...


Title: Re: Some Rok questions (Tuning, launching, and framing)
Post by: Josiah on January 17, 2011, 02:37 PM
Yeah,  I sent him an email asking for verification of the bridle measurements...  I would still like to hear what others have to say about launching and tuning in general though, as he often refers me back here when I ask these general sort of questions.



Title: Re: Some Rok questions (Tuning, launching, and framing)
Post by: Allen Carter on January 17, 2011, 02:49 PM
I don't have tons of Rok experience, but all the ones I've flown launch right out of hand in strong wind and with 20 feet or so of line reeled out in lighter conditions. They fly easy. Every year at the Berkeley kite festival they have multiple Rok battles that always include some first time flyers.

I'd say considering the source, there is likely a very good reason for the design of the spine. With PXXX rods at 32.5", you'd need at least three sections to make 6'.


Title: Re: Some Rok questions (Tuning, launching, and framing)
Post by: Gamelord on January 17, 2011, 03:04 PM
I have to start with the basics...just cuz... :)

Did you tension the rear lines on the kite so that the Rok has the proper amount of bow in it?  If not, there should be two lines run across the back side of the Rok, one on the top spreader and one on the bottom spreader.  These two lines should be tensioned in a way that the kite will bow backwards away from you as you look at it from the front.  If you do not have any bow in the lines, the kite will fly very poorly or not at all.  Because of the above description of the way it flew (or tried to) I would assume that the tension on the lines is the problem.

You can tension the top and bottom spreaders differently to get different results.  Tightening the top line more than the bottom will make the kite more unstable which may be desired for fighting or single line controls.  Not tight enough and it could give the kite too much drag and make it fly poorly.

I am going from memory on the above, if someone else knows more then please correct me. :)

Hope this helps.


Title: Re: Some Rok questions (Tuning, launching, and framing)
Post by: Josiah on January 17, 2011, 03:10 PM
Allen: Whoa, no way this kite is flying straight out of hand as-is... Makes me lean more towards there being a problem with the bridle...

Gamelord: I had both rear lines tensioned, although properly, I don't know. ;)  With the kite resting on the ground, I had maybe 2-4" of bow in the top spreader, and maybe 4-6" of bow in the lower spreader.  I knew the kite needed to be bowed for stability, but maybe it needed way more than what I gave it?


Title: Re: Some Rok questions (Tuning, launching, and framing)
Post by: st3307 on January 17, 2011, 03:15 PM
 not  trying  to  be  a   smart   ass   but    did  you have  the  kite  pointed  the   right   way  there  is  a  top and  a  bottom  to  a   Rok ?


Title: Re: Some Rok questions (Tuning, launching, and framing)
Post by: ezme6 on January 17, 2011, 03:30 PM
I always bow my rocs 8-12 ", flatter for low wind, more bow for highter winds. I got a feeling yours has the bridle "upside down" The bottom legs attached to the top. A screw up at the factory maybe. Try flying it upside down the check.

Nice parents you have... :) A kite as a gift is really cool


Title: Re: Some Rok questions (Tuning, launching, and framing)
Post by: thief on January 17, 2011, 03:51 PM
The cracking sound MIGHT have been (I have not had a gom-kaku in my hands) the fact that there was not enough glue in the external ferrule to attach it to the rod....and what little glue is there is breaking...
this was a very common experience with the Premier Roks when they first came out....

launching....i bow the top and bottom the same ~3-4" on my kites....and then with the line attached i plop the kite on its tail and lean it back away from me -like getting a sport kite ready to launch.....then take a few steps back and give a tug....and then a quick release of line until it almost hits the ground then pump the kite up that way...

i do also launch them by unrolling ~50' of line and tying it off to an anchor and doing a self-supported long line launch....works quite well...

bridles....
i am not a fan of the bridles that are two pieces of line (each one goes from top to bottom) with a larkshead....
i MUCH prefer a bridle that has a loop going from one top hole to the other top hole and the same on the bottom and then one single leg between the top and bottom loop..

picture the letter H turned 90 degrees....

I like that because then you make your left/right adjustments separate from the sliding the attachment point up/down....this is a very easy change to make if you are interested in doing so.....

when flying the rok i find that i do not adjust the bow lines much...just moving the attachment point up /down....but around an inch or less is enough for my roks....

good winds


Title: Re: Some Rok questions (Tuning, launching, and framing)
Post by: tcope on January 17, 2011, 04:17 PM
The Gomberg Roc should have the trademark bird face on it... so I doubt it was upside down. Basically the Roc should be at a slight angle to give it life, with the upper part being slightly closer to the kite flier. I'm guessing your Roc started out the opposite way and as you moved the line up, it was leaning slightly forward. Move it further and see if it gets better.

Bowing is a matter of preference. In lower wind you want and can get away with less bow. This gives more lift. But as the wind picks up or if there is not enough bow the kite will sway back and forth. The upper part of the kite gives lift and the lower end keeps it stable... so more bow in the lower end ("more bow in the butt").

The spars are usually done as you mentioned so that the kite can be broken down into a standard length. The spars need to all be equal otherwise the kite will be unbalanced. You can't add the weight of an odd ferrel someplace. I think this is why it's like it is.

The spine does not need to be super tight... just enough to keep the sail tight before it's bowed. It will probably have some type of adjustment on it.

No big secret on he launch. In good wind it will take right off. In lower winds it might need a _slight_ push up to get it started.


Title: Re: Some Rok questions (Tuning, launching, and framing)
Post by: chilese on January 17, 2011, 05:55 PM
Here is a photo of Mr. Gomberg (left) checking a Rok before battle. The large amount of bow is due to the high winds at Berkeley Kite Festival.
(http://lh6.ggpht.com/_3waCPW86CRA/S2CqBnq_d5I/AAAAAAAAD6A/pQMx-tf-Ngg/s800/2369849620049870108LkqgjX_fs.jpg)
 (http://picasaweb.google.com/chilesej/2006Kites#5431528095414712210)


Title: Re: Some Rok questions (Tuning, launching, and framing)
Post by: KaoS on January 17, 2011, 06:03 PM
GKPI has a Rok tuning guide on their website

http://www.gombergkites.com/FAQ-R.PDF (http://www.gombergkites.com/FAQ-R.PDF)

I'd be inclined to call or email them if you are having difficulties


Title: Re: Some Rok questions (Tuning, launching, and framing)
Post by: Josiah on January 17, 2011, 07:09 PM
First off, big thanks to everyone for their comments. 

I took the time to measure the existing bridle (something I should have done to begin with). 

(http://lh4.ggpht.com/_HaYr42wQrDA/TTT-C9eYc0I/AAAAAAAAK1Q/5EjBe8DPFyY/s800/Gom-kaku.JPG)
Top loop: Green
Central leg: Blue
Bottom loop: Red


The bridle is made in essentially the H-format thief, and this guide (PDF) (http://asaha.com/ebook/wMzE1MzU-/Rokkaku-Bridle-and-Bow-Line-Building-Guide.pdf) recommend.  However, instead of using a prussic to attach the central leg to the top and bottom loop, there is an overhand knot loop tied into the top top and bottom sections.  The central leg then gets tied to the bottom and top loops.  The total length of the central leg is 18", and as you can see from the diagram, both the top and bottom loop are the same length. 

After reading the guide that I linked to, I'm wondering if the bridle should have a longer bottom loop?  But maybe you could get enough angle just from adjusting the tow point on the central leg? Would 18" be long enough for that?  Having no experience with Roks, I'm not sure. The kite came shipped with the tow point basically in the middle of the central leg, so no wonder it didn't fly.  In hindsight I should have kept moving the tow point up until it (maybe) worked...

I'll wait until I hear back from Mr Gomberg, but I'm tempted to remake the bridle the way it is done in the guide I linked to.  Any thoughts?


Title: Re: Some Rok questions (Tuning, launching, and framing)
Post by: nckiter on January 17, 2011, 07:16 PM
By all means check out the tuning tips at GKPI. The Gom Kaku I have flys fine in the wind range you describe. I have noticed on this kite though that the middle bridle leg is a bit short for my preference and if yours is the same, moving it 2" may have put you on the other side of the sweet spot. OK, I just saw your last post, the middle bridlle is shorter than I would like, the top and bottom are fine. You may want to just change out the middle, try a section about twice as long as the stock. I would also attach the middle to the top and bottom with a prussic and the pigtail to the middle with another prussic. It should fly from you hand, next time out try just holding the middle bridle between your thumb and forefinger, sliding up and down until you hit the spot where it wants to take off, then move your connection pigtail to that point and fly.


Title: Re: Some Rok questions (Tuning, launching, and framing)
Post by: tcope on January 17, 2011, 08:07 PM
What I _can_ guarantee you is that you will get _the_ best advise from David.... hand down. Feel free to ask him _any_ questions about tuning, possible modifications, adjusting for different winds. He will be a wealth of information.


Title: Re: Some Rok questions (Tuning, launching, and framing)
Post by: DGomberg on January 17, 2011, 08:56 PM
Hi Everyone!

I usually check GWTW every morning so didn't see this thread until lots of advice had been offered. Thanks everyone for your comments.

First, Josiah, I don't have an email from you. When did you write about the rok? It is unusual for me to not answer emails within 24 hours no matter where I am. So if you write and don't hear back, something has gone missing.

The last batch of Gomb-kakus came in with slightly shorted center legs on the bridle. I've asked they be lengthened on the next run. (Welcome to mass production!!) For optimal performance, slide the "tow point" high on this section so the kite leans forward 15-20 degrees. We don't usually mark a main setting.

If you prefer, you can easily replace this bridle section, or I'll be happy to do it for you.

Please let me know if you have any questions or problems. Will you be at Kite party? (I know you are in Southern Cal.)  I'm thinking of dropping in and would be happy to check things over on the beach.

Hope that helps!

David


Title: Re: Some Rok questions (Tuning, launching, and framing)
Post by: DGomberg on January 18, 2011, 06:39 AM
Found Josiah's email - sent yesterday afternoon - in my spam filter and sent him a PM. Happy to answer any other questions.

David


Title: Re: Some Rok questions (Tuning, launching, and framing)
Post by: Gardner on January 18, 2011, 09:39 AM
First, Talk to Dave Gomberg, he wrote the book on Rocs for US flyers and is a top ROC fighter.  Second, this is a kite designed and built for his company so he knows it.

I have one of his GomKocs and it flew great right out of the bag.

Gardner


Title: Re: Some Rok questions (Tuning, launching, and framing)
Post by: Josiah on January 18, 2011, 09:55 AM
Thanks again for all the replies, especially nckiter and David.

In summary, the bridle was assembled correctly, it was just way out of tune when it arrived.  I should have been braver/smarter and kept sliding the tow point up and up until the kite flew.  Still, I think lengthening the central leg will make tuning it easier, so I plan to make that change myself.  The kite is really nice, and it is amazing that you can get such a large, fully appliquéd kite for such a fantastic price.  I'm sure this will join my other GKites as one of my favorites!

For the record, I have always asked David any questions I have related to his products first, and posted the same questions to the forum later.  While he always gets back with great, friendly advice, it's nice to get another perspective and this way the question also gets "documented" here at GWTW.