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Author Topic: Reza 10' Rok rebuild  (Read 3510 times)
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wseaton
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« on: July 03, 2018, 12:25 PM »

Bought this massive kite a few years ago on clearance from somebody online (I forget) and have finally got around to rebuilding it so it flies decently. Unfortunately Premier designed this expensive beast to be pulled by 10yr kids on mountain bikes through the woods. Not even sure how other flyers were able to keep it up in the air to make youtube vids.

First problem is the tent poles used for framing. At least half inch on the horizontals and even bigger on the middle spine. Now big Roks like a strong, stiff middle spine, but the horizontals were ridiculous. How exactly are you supposed to bend 1/2" carbon fiber into a nice bow that Rok's like, especially with the sail sewn tension pulls that was intended? Well, you don't. You try to grunt and pull those horizontals into a bow, get the kite somewhat stable, fly it, then the tension on the sail trying to keep those carbon fiber rods bent stretches the sail, pulls them slowly straight, and turns the Rok into a spinning fighter kite. Fun for kids to watch, but when you've spent >$300 on a kite it's painful to watch. Normally I used a string to pull the horizontals on a Rok and not try to do it with the sail, but the thick carbon fiber wasn't having it.

So, first thing I did was replace the horizontals with .24 carbon fiber which drastically cut the weight. Next I removed all the flimsy side pockets and replaced them with heavy duty nylon webbing and velcro. Still not done with this part yet, but it works for now. While many roks like some bow in both the top and bottom horizontals this kite preferred none or a tiny bow in the top and lots of bow in the bottom. Even if not tensioned 7' of .24 carbon fiber will bend in the wind on it's own, so that was solved for the upper by just leaving it alone.

Bottom spreader was a bit more ingenious. Rather than deal with trying to bend carbon fiber to make a stable rok I used a cochrane dihedral and cut the spreader in half. The dihedryl connector creates a fixed 30degree'ish angle, and aerodynamically it functions the same as a bow. Theoretical of course, but it worked perfectly. I now have 10.5' Rok that flies great and bolts onto the sky like it should, but with no bow tensioners.

After all my fixes I retuned the bridle and now have a kite that will fly in 4-12mph winds opposed to the previous wind range of 13-14mph. Had it out yesterday, and with inland winds 4-8mph I had the big kite locked in with a 75-80 degree AoA almost right over head with 500' of 100lb black poly. One of the most remarkable kite flites I've had.

Just in case somebody is wondering this is not a good kite for KAP. This kite does not have nearly the lift you would think a big rok has, and my 7' Gomberg Zenith Delta has a lot more vertical pull in less wind. The Zenith doesn't make cars pull over though :-)

I'll try to get a youtube vid posted of that 500' flight.

https://www.youtube.com/watch?v=UdUM4LgWC4A&feature=youtu.be

« Last Edit: July 03, 2018, 12:35 PM by wseaton » Logged
Lee S
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« Reply #1 on: July 03, 2018, 04:36 PM »

I've never flown or seen a Rok that doesn't have back bow lines for tension. I have a 10 ft Rok that sounds very similarly framed, it was built by a SF bay area flyer/builder for Berkeley winds, which can be very strong. As a result, this kite will either not quite fly, or rip your arms out Cheesy Super fun!
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wseaton
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« Reply #2 on: July 03, 2018, 06:56 PM »

Technically there is plenty of 'bow' in the kite....I just did it without tensioners.

The  dihedryl connector creates a 'V' shaped in the lower horizontal of about 30 degrees. Aerodynamically a bow accomplishes the same thing, but the 'V' connector is oh so much easier and doesn't stress the rods.

The upper horizontal has just a bit of bow in it created by wind pressure. Smaller roks I've  had prefer about the same bow top and bottom, but this kite prefers the former set up.

Just want to warn people this kite will likely not perform well out of the package. I always wanted a big rok....just had to fix problems with this one. I'm building my own 8' later on, and going to try and design it so it can handle a stronger wind range. This kite does not like winds over 12mph and just sits low and unhappy in the wind envelope.
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Lee S
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« Reply #3 on: July 03, 2018, 09:30 PM »

Sounds like you're having fun. I once asked David Gomberg (kite seller and a guru at the Rokkaku) if the correct setup for a Rok was flatter at the leading cross spar, or flatter at the rear spar, and his answer was "yes".  Kind of just gotta play with it. 
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Oldgoat
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« Reply #4 on: July 04, 2018, 08:29 AM »

Locked in at 500' with a 75 - 80 degree flight angle, nice. Smiley
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thief
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« Reply #5 on: July 04, 2018, 12:24 PM »

Of course the dihedral stresses the rods......probably much more than using bow lines by my guess. The bow lines will create a smooth curve across the spreaders while a dihedral because it only holds the rods a small amount puts pressure where the rod comes out of the fitting.

I find dihedrals to be better for flatter kites and bow lines much better for kites that need variation in their said shape.

Personally I have found that kite companies that do reproductions of kites have put a lot of work in the kite and have come to a point where the kite files and looks great. Of course you can spend a butt load of money to reframe but why bother
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Hal
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« Reply #6 on: July 04, 2018, 12:25 PM »

Have had the same kite for 13 years, lots of flight time on it as Reza designed it in winds from 6-20 mph.  To each his own.
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Hal
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Allen Carter
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« Reply #7 on: July 04, 2018, 04:57 PM »

Reframing and all is fine, do what you want, YMMV.

But putting a great looking kite like that so high up is a crime.  Cheesy
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Allen, AKA kitehead
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« Reply #8 on: July 05, 2018, 04:42 PM »

Yup, no question that the dihedral is stressing the spars more than bowing would. You've created a stress point on each spreader at the point where it meets the dihedral, as well as on the spine where the dihedral sits. Not saying that what you've done won't work, but that's just the physics of it.

But really what you've done is eliminate any adjustment for wind speed. A rok should be tuneable for the conditions, and whether you want stability (basic beach flying) or instability (a rok battle). You've removed that option.

That said... it's your kite. Do what you wanna do.
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KaoS
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« Reply #9 on: July 05, 2018, 06:10 PM »

Yup, no question that the dihedral is stressing the spars more than bowing would. You've created a stress point on each spreader at the point where it meets the dihedral, as well as on the spine where the dihedral sits. Not saying that what you've done won't work, but that's just the physics of it.

Not entirely true.  It very much depends on where the bridle lines support the frame.

If you bridle any flat or dihedralled kite only on the spine, wind pressure on the wingtips will induce a high stress point on the spreaders at the centre of the kite.

If you were to (theoretically) bridle the same kite only at the wingtips, wind pressure on the centre of the sail would also induce a high stress point on the spreaders at the centre of the kite BUT in the OPPOSITE direction to the first example.

If you bridle the same kite part way along the spreaders (exactly where varies, depending on distribution of sail area), you eliminate the stresses almost completely.

THAT'S the physics of it  Wink
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Kevin Sanders

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« Reply #10 on: July 05, 2018, 06:41 PM »

I do so enjoy when Kaos and I agree on disagreeing. He's right, of course, but.... unless the spar is floating inside that dihedral, there's a wear point where the edge of the dihedral hits the spar. No matter where it's bridled, any flexing of the spar will cause pressure at that point, and eventual breakage.

Kevin, you bring the dihedral to Knysna, I'll bring a spar, and we can experiment.
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Steve Hall
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« Reply #11 on: July 05, 2018, 07:35 PM »

Reza's Eagle of Paradox ... beautiful kite.
I'm with Allen ... way to high.
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Steve ...
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Oldgoat
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« Reply #12 on: July 06, 2018, 09:44 AM »

Ok guys, now discuss what happens with one long spar vs having a ferrule in the center.
This should be fun Wink
 Smiley
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thief
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« Reply #13 on: July 06, 2018, 10:15 AM »

longer rod would be better...fibers would be longer and you would be able to get smoother bow ...but more prohibitive to purchase and to carry......
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wseaton
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« Reply #14 on: July 06, 2018, 01:26 PM »


Personally I have found that kite companies that do reproductions of kites have put a lot of work in the kite and have come to a point where the kite files and looks great. Of course you can spend a butt load of money to reframe but why bother

Sounds like a lot of you lost your AARP cards and the neighbor kids won't get off your lawn.

I've owned many kites by Premier including their giant Deltas and they are built the same way; for 10yr old kids to pull them by their mountain bikes through the woods in 25mph winds while dragging upside down. The kite, when purchased didn't indicate it was built by Premier or I would have avoided it. Last, kite makers move production to whatever factory in china gives them the best labor and cheaper costs. I dare say this kite bought when it first hit the market is likely quite a bit different over it's production run. Premier builds kites / toys, not Jet fighters.

Next, the original kite out of the bag was unflyable. I'll state that again, and I don't really care if you believe me. The main reason was the over sized rods for the horizontals used the sail as a tensioner, which anybody with an IQ over 50 knows doesn't work with a Rok. Eventually the sail stretches and changes the bow making it unstable.  The cloth tensioners on the kite were also horribly delicate and tore badly on the first flight.

So, those of us with Rok experience and a brain use strings to affix tension. I took it one step further and used a fixed part to accomplish the same aerodynamic affect, which it does. This is a big kite that is a PITA in the field to assemble, and eliminating frakking around with bow tension and other junk has drastically reduced the time it takes to assemble and get it in the air.

Next, the pockets and most of the sail attachments had to be replaced because they were severely undersized and used flimsy material that wore out on the first flight. The horizontal rods also would slip out of their pockets because the velcro straps were also under sized.  I had to replace and repair all of that with much heavier duty nylon webbing. For a > $300 kite this is absurd, so defend premier all you want. Speaking of David Gomberg, I've met him at kite festivals, own several of his kites, and we've had a good laugh about Premier and their Q/C.

Rather than screw around with Bow angle to adjust for wind I use a smarter trick and use a length of elastic cord on the lower bridle for bigger kites and delta. Roks don' need more than a center bridle attachment on the lowers. This allows the kite to fly more efficiently because the elastic allows AoA to change with wind gusts and not pulse up and down inland winds. I use a similiar trick on my large traction kites.

What YouTube videos I see of this kite show it at low AoA, and wobbling like a drunk because they are using the sail tensioners and don't know how to adjust a bridle. Mine is up 500', flying at a nearly impossible AoA for a large rok, and bolted in the sky like a Rok should because of my improvements. If you can do better with this kite by all means buy one stock and show me what I'm doing wrong. Have fun pulling your $375 out of a tree.

As for the height, I'm in a parking lot, not a beach festival, and showing the stability of my improvements with inland wind (in a parking lot).  If I flew it lower you would likely be complaining about something else.

Last night I put up a custom made 5' rok using ultra thin carbon fiber and a mylar sail in winds so slight they coulnd't be felt. That thing was etheral, and I'm using some design points to build a large tissue lame day flyer that will stop traffic. I won't bother posting in this forum further.
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