Carbon Tubing Comparison

[SegelFlieger]

After several Chat discussions with other Kite Life members I was encouraged to share the following information:

Carbon Tube Deflection and Weight Comparisons

I have created my own standard method for measuring stiffness-to-weight ratios for carbon tubing commonly used for sport kite construction for my own personal use as a kite builder and hopefully this information will be helpful to others who would like to build or mod their own frames. 

In this report you will see how my testing of a group of commercially available tubes compare against this standard.  Any frame material can potentially be compared using this test.

Test Definition:

A deflection test has been defined to measure the standard deflection of a 62“ length of carbon tubing suspended with a fulcrum at it’s center-point, 31”.  This length was chosen for convenience since it represents the length of two standard revolution 1.5/B-Pro spars.

A 1 pound weight is suspended against a 62” length of tubing.  A fulcrum is placed at the center of the length to suspend the tube vertically; a loose or permanent ferrule is used to connect multiple sections of tubing and is placed in the center for the measurement to create the 62” length.  The 1 pound weight is suspended with 37” of line on each end of the 62” length forming a triangle with 37” sides.  A second line is then attached to each end of the 62” length of the tube being measured to create a parallel line beneath the bow that is created by the weight.  The distance from the center of the tube to this line is then measured.  The weight of the tubing is calculated without ferrules.  This defines the nominal weight of the tube in g/in.

SU1:  Stiffness units (version 1 is where the 1 comes from in SU1) are defined by the amount of deflection at the centerline of the 62” bow and are in units of inches.

W: is the weight of the tubing sample used in g/in.  This is a measurement of the tube without a ferrule.  These results are the average of several tubes. 

SU1/W: represents a stiffness-to-weight ratio and can be used to compare other tube materials.  This becomes the standard for comparison in my chart and the chart is sorted from the highest value to the lowest value.  A high value means that the tube will weigh less but be less stiff (more deflection).  A low value means that a tube will perhaps weigh more but be more stiff (not deflect as easily).

For frame weight comparisons, nominal weights were calculated for a Rev 1.5/B-pro frame and a Rev B-2 frame. Nominal weight values do not include the weight of ferrules or adhesives.

Note: m2 stands for measurement of a second group of tubes.

					in case the picture can't be enlarged, here is the chart again in text format:
					Rod SU1     W g/in    SU1/W     Rev 1.5 Nom. Frame wt g Rev B2 Nom. Frame wt g Sky Shark P90 4.5000 0.3226 13.9492 50.0030 39.5185 Sky Shark P1X m2 3.7500 0.4021 9.3260 62.3255 49.2573 Sky Shark P1X 3.7500 0.4154 9.0274 64.3870 50.8865 Race Rods 31" silver 3.7500 0.4194 8.9413 65.0070 51.3765  Rev Race Rod silver B-2 3.7500 0.4286 8.7494 66.4330 52.5035 Sky Shark P1X m3 3.6250 0.4021 9.0152 62.3255 49.2573 Rev 2 Wrap silver 3.4375 0.4597 7.4777 71.2535 56.3133 Sky Shark P2X 3.1250 0.4516 6.9198 69.9980 55.3210 Sky Shark P2X m2 3.1250 0.4740 6.5928 73.4700 58.0650 Sky Shark P200 3.0000 0.4677 6.4144 72.4935 57.2933 Sky Shark P3X 2.8750 0.5323 5.4011 82.5065 65.2068 Sky Shark P3X m2 2.7500 0.5265 5.2232 81.6075 64.4963 Rev 3 Wrap silver 2.5000 0.5000 5.0000 77.5000 61.2500 Sky Shark P400 2.5000 0.7282 3.4331 112.8710 89.2045 Rev 3 Wrap w/ Green Stripes 2.3125 0.4194 5.5138 65.0070 51.3765

MODERATOR UPDATE:

On October 16, 2016 at 0:40 PM, riffclown said:

I kind of like the way it's arranged now..

But it's also pretty easy to import into Excel and manipulate the sorting as you see fit. Here's the latest chart in XLS format.

You can even filter out manufacturers as you see fit..

KiteRodComparison.xls

 

 

[Stuart McCullough]

Thanks for sharing this, good info!

 

[Exult]

Thanks for sharing result of general interest!!! ++Good!

I'm probably just "morning sleepy" or post vacation slow, but I didn't get the weight and 37 inch triangle part I must confess. This test seems elaborate and specific with much thought behind however. Is this from using knowledge from gliders (line of thought: Segelflugzeug or Segelflieger both means sailplane in German to my understanding)?

If the unit of stiffness as defined here is length (inches), the larger deflection you get the more "stiff" the spars are? Would it be more appropriate to call the stiffness something else like flexibility or deflection? If calling something stiffness I would inverse the unit so it would be one divided by the length of deflection.

Also when checking the stiffness numbers of your measurements they do not differ so much between the P200 and the P2X. This is a bit surprising and interesting considering the manufacturers (?) (or at least the Bilboquet kite and sport shop's) words for the Skyshark PX Series Straight Carbon Tubes: "The big difference is the tubes are made with a higher modules of carbon which makes them 15% to 20% stiffer that the old P series tubes". This is not at all a criticism of your measurements, more to honor your "messen ist wissen" approach.

[SegelFlieger]

Thanks for your comments Exult and Stuart!

I'm glad that you find this information useful. I intended for SegelFlieger to translate as "Sail Flyer".  Perhaps my translation to German wasn't proper.  I wanted to choose SegelMacher as a name but thought that this was more of a "flying" community so I thought I would adapt.  I have a lot of experience making kites; and I am always learning.  I have no experience with gliders though.

In reply to your comments Exult:

The 1 lb weight was chosen because I had one on hand.  I also had a 2 lb weight and was concerned about breaking the tubes at the ferrule when I saw how much they flexed.  1 lb seemed about right to give enough deflection to make a measurement; a smaller weight would not deflect the tubes enough to give accurate measurements.

The 37" lengths of line suspending the weight were chosen to be as long as possible without having the weight touch the ground for the least stiffest tubes.  I used a tripod to balance the tubes at their center while making a measurement.

I agree that the SU1 value is confusing since a larger number means less stiff.  It's confusing like the gauge naming of electrical wire (14 ga is larger in diameter than 22 ga).  Too late to change that now, it would only be more confusing :).

The PX series of Skyshark tubes replaced the P series as you probably already know.  A P2X is supposed to be very similar to a P200 performance-wise but in appearance the PX series has a checkered appearance and the P series has a solid color appearance.  You are right "measuring is knowing"... that's how they measured in my test.

Nice to meet you!

[Exult]

10 hours ago, SegelFlieger said:

I'm glad that you find this information useful. I intended for SegelFlieger to translate as "Sail Flyer".  .........  I have a lot of experience making kites; and I am always learning. ...... The PX series of Skyshark tubes replaced the P series as you probably already know.

Few enjoys shouting in an empty forest.
My deeds are those of a dual line kite flyer and the associated repair making. I'm a wannabe kite builder that have two kite building books (how is that for a start?), but find that the kite using aspects (along with rest of life) are too time consuming to initiate any form of from scratch kite building. I buy kites to experience and hopefully learn from the differences. However, I've more recently tried to get oriented in the jungle of spars.

10 hours ago, SegelFlieger said:

I intended for SegelFlieger to translate as "Sail Flyer".  Perhaps my translation to German wasn't proper.  I wanted to choose SegelMacher as a name but thought that this was more of a "flying" community so I thought I would adapt.

First, don't "adapt", your kite building abilities are a "feather in your cap" - everywhere. Secondly, I find it a good name no matter the language. If you think of it literally, it is almost poetic. I get images of either a framed quad or a horisontal yacht sail (somehow) hovering only a few meters away in light wind only a metre or so above the ground.

Another aspect of the stiffness, do you have any idea if it is rotationally symmetric? I.e. will the deflection remain the same if you rotate the the tube along its axis? The reasons for asking are two. First when doing reading up on spars I stumbled on a Youtube fishing rod making video (Finding The Spine Of A Blank: Rod Building 101, https://www.youtube.com/watch?v=FjtQWeFj4co ) where they looked for irregularities in the rod by rotating it. Second, I got an old broken 6mm pultruded carbon tube (from the last millenium - imagine, my wife thinks I'm "keeping stuff"). Looking at the crossection of the old tube, it does not look very symmetric.

 

[riffclown]

Thank you for sharing this. Nice work and very solid approach to a repeatable process..

[SegelFlieger]

12 hours ago, Exult said:

Another aspect of the stiffness, do you have any idea if it is rotationally symmetric? I.e. will the deflection remain the same if you rotate the the tube along its axis? The reasons for asking are two. First when doing reading up on spars I stumbled on a Youtube fishing rod making video (Finding The Spine Of A Blank: Rod Building 101, https://www.youtube.com/watch?v=FjtQWeFj4co ) where they looked for irregularities in the rod by rotating it. Second, I got an old broken 6mm pultruded carbon tube (from the last millenium - imagine, my wife thinks I'm "keeping stuff"). Looking at the crossection of the old tube, it does not look very symmetric.

 

This was a very interesting video.  I bet a spine does exist in all rods or tubes.  Since the sections of tubing used for kite making are quite short compared to a fishing pole and are very stiff, relatively speaking, I think that it would be hard to measure.  A spine would be really hard to keep track of when assembling a kite.

Regarding the pultruded carbon tube that you have (and what's worse than keeping stuff is throwing away stuff and later wishing you hadn't)... Carbon wrapped tubes are made using a more precise process than pultrusion.  I'm not an expert on the subject but I have spoken to the owner of SkyShark a few times.  Carbon tubes are made by wrapping a carbon cloth impregnated with resin around a mandrel and then cured.  After a tube is cured it is then precisely sanded into the desired outside diameter of the tubing.  The mandrels used for this specific purpose are expensive and SkyShark has invested a lot of money in the proper tooling.  I have been told that some manufacturers do not buy the specific tooling but use "drill bit" rod stock for mandrels (less expensive); you might be able to tell which manufacturers these are because the inside diameter of the tube is not the standard .244" .  A roll test is a good indicator if your tube is not uniform.  If you roll it on a flat surface there should be no wobble and it should roll freely.

Well, I am off to WSIKF tomorrow but I look forward to discussing or answering any questions when I return.

[Exult]

Regarding the possible presence of a spine in wrapped spars. I kind of thought that wrapped spars would have virtually no variations in thickness when rotated along the longitudinal axis. When inspecting the kite (ITW Hydra) during the recent "un-boxing event" I spotted an asymmetry in the cross-section of one Dynamic DT-15 lower spreader spar, when viewed from the thickest (inner) side where the centre-T normally would be. The walls of the spar closest to the centre-T was 0.65mm where thinnest and 0.95 to 1.0mm where thickest when measured with a caliper. How far this asymmetry reaches into the spar I have unfortunately no idea of.

(To make the best of this situation I transferred the LS connector rod (which wasn't properly glued from the start) from the good LS to the un-symmetric LS. The idea being that the glued connector rod should add to the strength.)

[makatakam]

All wrapped tubing will have a spine. How severe or prominent depends on the thickness of the cloth. The only exception would be a tape-style diagonal cross-wrap with the ends of the tube cut off after curing. Unfortunately, that makes the tube VERY expensive.

[riffclown]

The recent conversations about the spine in a wrapped rod was only started to try and explain some QC issues.. The spine conversation has taken on a life of its own. IMO, If we are down to conversations about the spine orientation to prevent breakage we've ignored the issue..

BUT!!!!!

Conversations about spine orientation to duplicate flex, stiffness and bounceback can be considered valid for those fliers advanced enough to detect those minute differences.. I'm personally not one of those.. But there are fliers especially in the extremely light wind categories that could perceive those minute differences in performance.

 

@SegelFlieger

I applaud the efforts to provide some true measurement and comparison from the Scientific approach.. Thank you

[John Barresi]

PS: On a Rev, the spine of a shaft will always orient itself to either side of the verticals, top or bottom of the leading edge due to flex... I've heard a "spine the wrong way" argument from a particular quad / spar company when folks were questioning recent spar quality, that's hogwash - the only thing we feel on the Rev style kites is flex, snap back, weight, etc, the spine was never a factor.

[John Barresi]

Quote

 

Rev Race Rod 3.7500 0.4286 8.7494 66.4330 52.5035
Rev 2 Wrap 3.4375 0.4597 7.4777 71.2535 56.3133
Rev 3 Wrap 2.5000 0.5000 5.0000 77.5000 61.2500

Curious, were these measurements made on Rev rods with or without the green band on either side of the label?

(not to be confused with "Green Race", the green label trim indicates an era of manufacturing, old vs new)

[SHBKF]

In the world of cost no object reinforced plastics a technique called filament winding is employed for complete control of the characteristics of the final product.  This might be done in an item like a radome for a the nose of an aircraft where consistency is important for imaging accuracy of the radar antenna it covers.  The radome is wound, cured, ground & then corrected on a radar range.  If we could make our own mandrels, source resins & fibers, we could fabricate our own custom tubes with a bit of experimentation & practice.  These would not have a spine.  It would be quite extreme to do so not to mention a bit expensive.

 Just out here in the sticks thinkin',  SHBKF

[SegelFlieger]

3 hours ago, John Barresi said:

Curious, were these measurements made on Rev rods with or without the green band on either side of the label?

(not to be confused with "Green Race", the green label trim indicates an era of manufacturing, old vs new)

These measurements were made with Rev rods with the silver labels and feather insignia.  No green band on either side of the label.

[John Barresi]

Good to know, thanks.

Would be interesting to see a similar comparison between the two variants of Rev rod (green stripe and none).

[SegelFlieger]

1 minute ago, John Barresi said:

Good to know, thanks.

Would be interesting to see a similar comparison between the two variants of Rev rod (green stripe and none).

I am also curious about the difference.  Given an opportunity I will test them and post the results.

I also agree about the spine orientation taking a natural position while the frame is under load.  However, friction in the leading edge pocket, ferrules and connectors can complicate the process of "natural spine orientation".  I suspect it doesn't really matter that much compared to the dynamic complexity of the sail as you fly.

[Wayne Dowler]

It will be nice to know if the new "GT" rods are different in both thickness and deflection. Been looking for the reason for them being "different" in feel and in breakage.

PS: Been flying since 1989 and NEVER thought about my rods having a spine! Threw them into place, whether as spreaders on a dualie. or rods in my Revs. Any breakages have been explainable so far - ie, rod not seated fully, stepped on, contact with street, etc. Everyone of them was explained by circumstances. Have seen a flex difference with my own eyes, but not a weight comparison. Or variances in wall thickness.  

Interesting!

 

[SegelFlieger]

I have added some new measurements to my carbon tube comparison chart.  First of all I would like to note that I have sorted the list by the SU1 (Stiffness Unit Version 1) column so that decisions to use a frame of each design would be based on frame stiffness.  Again, total nominal Frame weights are based on 5 ea x 31” spar length for Rev 1.5 or B-Pro , and 5 ea x 24.5” spar length for the B2.  Total frame weight does not include ferrule weight as you may choose your own ferrule when building your own frame.  The additions to the chart include the Sky Shark P400, additional measurements for a new batch of Sky Shark P1X, and also the addition of a Revolution 3 Wrap “green stripped” rod which is a apparently newer version from Revolution.

After measuring the Revolution 3 Wrap “green stripped rod” I have to say that I am very impressed with its characteristics.  A frame built with this rod will be the stiffest rod shown in my list but has the same frame weight as the “silver” race rods and the Sky Shark P1X.  The total frame weight difference is 12.5g or 16% less weight for the “Rev 3 Wrap green striped rod” compared to the original Silver 3 wraps rods.  Considering that “Frame Weight” is the largest contributor to your total kite weight (~40%) when flying an Icarex (PC31) constructed non-vented sail, this frame would allow a ”Light Wind Flyer” to have a stiffer response and a “High Wind Flyer” to have a stiff frame with a “light kite” response. 

Here is the updated chart:

					in case the picture can't be enlarged, here is the chart again in text format:
					Rod SU1     W g/in    SU1/W     Rev 1.5 Nom. Frame wt g Rev B2 Nom. Frame wt g Sky Shark P90 4.5000 0.3226 13.9492 50.0030 39.5185 Sky Shark P1X m2 3.7500 0.4021 9.3260 62.3255 49.2573 Sky Shark P1X 3.7500 0.4154 9.0274 64.3870 50.8865 Race Rods 31" silver 3.7500 0.4194 8.9413 65.0070 51.3765  Rev Race Rod silver B-2 3.7500 0.4286 8.7494 66.4330 52.5035 Sky Shark P1X m3 3.6250 0.4021 9.0152 62.3255 49.2573 Rev 2 Wrap silver 3.4375 0.4597 7.4777 71.2535 56.3133 Sky Shark P2X 3.1250 0.4516 6.9198 69.9980 55.3210 Sky Shark P2X m2 3.1250 0.4740 6.5928 73.4700 58.0650 Sky Shark P200 3.0000 0.4677 6.4144 72.4935 57.2933 Sky Shark P3X 2.8750 0.5323 5.4011 82.5065 65.2068 Sky Shark P3X m2 2.7500 0.5265 5.2232 81.6075 64.4963 Rev 3 Wrap silver 2.5000 0.5000 5.0000 77.5000 61.2500 Sky Shark P400 2.5000 0.7282 3.4331 112.8710 89.2045 Rev 3 Wrap w/ Green Stripes 2.3125 0.4194 5.5138 65.0070 51.3765

[Wayne Dowler]

I would suggest grouping according to manufacturer, ie SkyShark together, Rev rods together. That way you could look for a comparative rod in the chart, if you know your Rev rods as a sort of standard to be compared against. IMHO

As fliers, we don't always go by flex, as much as the reflex - the ability to return to straight after flexing. Weight in general, is an after thought! Too light and the kite becomes victim of the winds, hard to control. For those of us that throw our kites on shorter lines, you have to have some mass or the kite gets blown off course or doesn't have enough "ommph" to reach the end of the lines. YMMV

[riffclown]

I kind of like the way it's arranged now..

But it's also pretty easy to import into Excel and manipulate the sorting as you see fit. Here's the latest chart in XLS format.

You can even filter out manufacturers as you see fit..

KiteRodComparison.xls

[SegelFlieger]

To address the “flex” vs. “reflex” characteristics of carbon tubes I have created a carbon tube “dynamic response” test that quantifies 3 dynamic properties of each 31” tube that was measured:

1. 1^st Amplitude from a 5” perturbation (inches)
2. Frequency of vibration (Hz, cycles per second)
3. Settling time from a 5” perturbation (seconds)

There are currently 10 different tubes in my sample set.

Before I present the results of the test I would like to hear from some experienced fliers regarding what you prefer in the “reflex” of your kite frame under 4 wind conditions… the purpose being that I might be able to add a commentary to the test results that explains your experience. 

Here is a question:

Considering “reflex”, “snap-back”, “recoil” (all meant to be descriptions of the same thing), which frame do you prefer under the following wind conditions?

• Very Light Wind (0-2.5 mph):
• Light Wind(2.5-5 mph):
• Medium Wind(5-10 mph):
• High Wind(10-15+ mph):

 

 

A report of my testing will follow “your” responses (pardon the pun), perhaps explaining what you experience when you fly a certain frame and will be posted as a blog.

I look forward to hearing your responses.

S.F.

[Edmond Dragut]

 0-3 i use 2 wraps or diamond 

3-5 2 wraps

5-10 3 wraps

10-15 4 wraps or combination of 2+3 wraps

[SparkieRob]

In my "street kite" I use 2 wrap outlers with a black race centre FOR ALL WIND CONDITIONS.... Hard working kite that one.


Sent from my iPhone using KiteLife mobile app

[Wayne Dowler]

0 - 2.5: diamonds Probably push them up to about 5, but if the wind is freshening - time to switch!

2.5 - 5: Bl. Race

5 - 10: Bl. Race

10 - 15+: 3 wrap or Gr. Race    PS: Only exception is a 100% Shook - I use Bl.Race in it.

I also use a hybrid frame in my Zen (Rev 1 size) of 2 wrap center, Bl. Race wingtips, Zen verts with magic sticks

No SkyShark frames in possession at the moment.

[makatakam]

• Very Light Wind (0-2.5 mph):     Diamond, P90
• Light Wind(2.5-5 mph):               Diamond, 2-wrap, P100
• Medium Wind(5-10 mph):           Black Race, 2-wrap, p200
• High Wind(10-15 mph):               Black Race, Green Race, 3-wrap, P300
• Heavy Wind(15-25 mph):            Green Race, 4-wrap, P400
• Extreme Wind(25+ mph):            SLE, 4-wrap, 2+3-wrap, P400

These are what I will start with depending on the sail. If the kite does not respond as I wish, I will use a hybrid to achieve what I'm looking for. If the wind is gusting above the average I go heavier on the mid-section of the leading edge. If the wind is fading below the average, lighter. I usually match the uprights to the mid-section of the LE. I use the stock frames in the Zen and the II's, and the Speed Series kites. I do not use magic sticks, but would go one step lighter whenever possible if I did use them.

To be perfectly honest, I'm lazy, and most of the time I use the frame that is in the sail I choose to fly. I have my kites set up for specific wind conditions and just grab the one that most closely matches the conditions. I usually will switch kites if I don't like what is happening, and won't change the frame unless I find the wind to be truly annoying. In super-heavy, extreme winds, I will double up the LE or use the SLE leading edge.