Rokkaku's frame

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[Michel]

Hi all,

What do you recommand for a 200 cm x 160 cm Rokkaku for light winds ( ->  8/10 mph) ? :

-> Diameter : spine and cross spreaders

-> Carbon or fiber

-> One or two parts with ferrule

Thanks for your advices. 

[MtnFlyer]

According to the recommendations at KiteBuilder, use .414" FG for the spine and .350" FG for the spreaders. Carbon tubes could be sized smaller.

Fiberglass will bend more than the stiffer carbon and be good in higher winds, but carbon would be thinner and lighter and might provide better flight in light winds.

I've sparred in 1, 2 or 3 sections depending on finished spar length and rod lengths I have or can get, but just be sure that joints are placed symmetrically.

Good luck. Hope that helps.

[melnsct]

I just finished building two Roks.
I use Skyshark P400 for the spine and P200 for the spreaders.

[mikenchico]

Premier uses Skyshark P300's all the way around in their 6 foot Rok's. Besides saving about a pound over the fiberglass they do high winds well too. So if your truly looking for low wind performance you could get away with P200's but I might be thinking about a 7 point bridle at 10 mph if your setting the kite heavy for battles.

Of course your spine will end up 3 pieces like Premiers, glue the 14" short length to one of the full length rods if your worried about stray parts. Or you could get real fancy and use 7PT x 40"s with 3PT 32.5"s for the spreaders.

[Fore Check]

I just completed a Rok at just about that size, framed with a P400 spine and P300 spreaders.

It's first couple of flights were in gusty 15 mph wind and it flew like a champ.

Most recently was in 8-10 mph wind and it could certainly go in less (lighter) wind too.  I highly recommend the SkyShark framing. 

On a Rok of that size, I'd definitely go with P300 spreaders.  P200 will only shave about 10 total grams from the kite dropping to the 200, and the 300's are quite a bit stiffer.

Here's mine.

[Fore Check]

BTW - to address the other part of your question regarding lengths and ferruling:

If you use SkyShark tubes, they are 32.5" long each.  So, for the spine you will need 2 full length spars and a trimmed piece (about 13-15" in your case) to make the total length.  I did this too, and put the short piece in the center of the overall span.

For the spreaders, you will need two pieces per spreader.  I had to trim mine just a bit as I designed mine around an overall width of 58"  (147.5 cm) due to the width of the fabric I was working with.  I trimmed them so that the ferrule was in the center of the span so that I wouldn't have any left-to-right weight imbalance due to the 3" long solid carbon internal ferrule used.  Probably not necessary due to the overall size of the kite, the ability to trim the flight attitude with the standard 4 point bridle, and the relative weight of the ferrules, but hey - I'm a nerd.

Additional pics, including some construction details, can be found here.  It had been a while since I last flew a Rok when I took it out for the first time, so the first 2 sets of flight pics you will notice that I had a *lot* of bow set in the spreaders with the adjustment lines (after this was observed and pointed out to me by another poster, I flew it again with less bow and it looked and flew even better)

http://www.kitebuilder.com/forums/viewtopic.php?t=7888

[Michel]

Many thanks for your advices my friends.
 
I wish to use my Icarex Rokkaku in light winds (-> 10 mph) and thinks that a SkyShark frame would be a good choise.
 
But...

I just completed a Rok at just about that size, framed with a P400 spine and P300 spreaders.
 
It's first couple of flights were in gusty 15 mph wind and it flew like a champ.
 
On a Rok of that size, I'd definitely go with P300 spreaders.  P200 will only shave about 10 total grams from the kite dropping to the 200, and the 300's are quite a bit stiffer.
 
Most recently was in 8-10 mph wind and it could certainly go in less (lighter) wind too.  I highly recommend the SkyShark framing.

OK but would'nt be P200 SkyShark better for light winds (more flexible and lighter) ?   
 

BTW - to address the other part of your question regarding lengths and ferruling:
 
If you use SkyShark tubes, they are 32.5" long each.  So, for the spine you will need 2 full length spars and a trimmed piece (about 13-15" in your case) to make the total length.  I did this too, and put the short piece in the center of the overall span.

I have read that ferruled spars often broke and that is was better to frame the Rokkaku with full lenght : 200 cm for the spine and 2 x 160 cm for the cross spreaders. What do you think about this ?
 
And for the spine : 32.5" SkyShark in the middle + 2 x external little spars is not better ?
 
And what do you use please for the ferrule : internal SkyShark ferrule or external ?

Thanks again.

P.s. : nice Rok Fore Check ! 

[Fore Check]

Many thanks for your advices my friends.

........



OK but would'nt be P200 SkyShark better for light winds (more flexible and lighter) ?   

Sure - shaving weight will always extend the lower wind range.  However, the difference in advertised weight for full length (32.5") SS P200's and P300's is 2.5 grams.  You will use 4 spars for the spreaders (2 for each spreader) which means the maximum weight savings is 10 grams.  Cutting them down a whisker will mean that the weight savings will actually be a hair less.    If saving 10 grams is important to you for the extended lower end wind range, by all means - use the P200.  However, I prefer to use the P300 for the extension of the comparable upper wind range between the two because I think that 10 grams compared to the weight of the entire finished kite will be / is such a small percentage of the overall weight that the savings would be basically negligible. 

For an example of the wind range of mine (built with 0.75 oz Ripstop Nylon, by the way) - I just took it down after having it anchored out front for the last 4 hours.  When I launched it, there was just above a whisper of wind (about 5 mph).  I had loads of fun playing with it, watching it hang there with the bridles all but slack, and even had it thermal straight up a time or two.  Then I anchored it and went about working in the yard.

Fast forward to about a half an hour ago when I took it down.  The wind had picked up to 17 mph with gusts over 20.  Honestly.  It would climb and ride out "gusts" at the top of the wind window and seemed happy to be there.  Sure, the spreaders were swaying back under heavy wind load, but it sure handled the wind just fine. 

Great kite.   

I have read that ferruled spars often broke and that is was better to frame the Rokkaku with full lenght : 200 cm for the spine and 2 x 160 cm for the cross spreaders. What do you think about this ?
 
And for the spine : 32.5" SkyShark in the middle + 2 x external little spars is not better ?
 
And what do you use please for the ferrule : internal SkyShark ferrule or external ?

Thanks again.

P.s. : nice Rok Fore Check ! 

True - a ferruled connection is a stress point and often where a break will occur.  So, if you can use a full length spar without a ferrule this is a good practice.  But, see my remarks above.  Heavy load on the SkyShark spars with no problem at all ferruled in the center of the span.  A key tip is to use a bit longer of a ferrule than what you'd think the bare minimum is.  For instance, a "standard" SkyShark ferrule is a 3" length of solid carbon rod as an internal ferrule (1.5" of rod inside the end of each tube for the ferrule.)  You can use 4" or 5" for added stability of the ferruled connection.

Besides, on the spreaders, if you put the full length spar centered on the spine with two pieces on either end so that you don't have a ferrule in the middle, you will add more weight in ferrules than you will save going with P200's over P300's.   


Regarding the spine - if you can find a full length spar that is 200+ cm long in carbon or wrapped carbon, please, let us know!     You can probably find one in wood or perhaps fiberglass, but I prefer the lighter and stiffer carbon (like pultruded Avia) or wrapped carbon (like SkyShark.)

For the ferrule, as I mention above, SkyShark is ferruled internally with lengths of 0.2400" OD solid carbon rod.  3" is considered a standard length.  I buy full length (48") carbon rods and cut them for ferrules myself.

Thanks!

[Michel]

Many thanks again for your advices Fore Check. 

Regarding the spine - if you can find a full length spar that is 200+ cm long in carbon or wrapped carbon, please, let us know!     You can probably find one in wood or perhaps fiberglass, but I prefer the lighter and stiffer carbon (like pultruded Avia) or wrapped carbon (like SkyShark.)

No problem Fore Check. I have ø 8 mm Structil 200 cm for the spine and 165 cm Structil for the cross spreaders.

Is that a good choice ?

[Fore Check]

I don't have any experience with the Structil tubes; but I went to their website and found some 8mm tubes with a 6mm ID at that length.  Sounds beefy!

If their flexural modulus is similar to Avia pultruded carbon, then you'll certainly have spars that are plenty stiff.

[Michel]

Thanks all ! 

For instance, a "standard" SkyShark ferrule is a 3" length of solid carbon rod as an internal ferrule (1.5" of rod inside the end of each tube for the ferrule.)  You can use 4" or 5" for added stability of the ferruled connection.

And what about a hollow .240 Avia 10 cm ferrule ? The weight of a solid .240 Avia 10 cm ferrule is about 4,5 g ; the weight of a hollow one only 2,7. I could save about 7 g more...

For the spine, do you glue the 2 ferrules into the 35 cm center spar or a ferrule into each external standard 82,6 cm spar ? 

Thanks my friends.