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Author Topic: SkyShark P450 rods vs 8P  (Read 2490 times)
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« on: August 05, 2011, 11:08 PM »

Hi all,

Are the new SkyShark P450 rods stiffer than the 8P ?

Thanks in advance for your help.  Wink

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« Reply #1 on: August 06, 2011, 12:33 AM »

There's never been any published data on the P450 other then Jon's statement that they were stiffer then the P300. I don't think it's a new rod, I had the impression it was a special Jon picked up and doesn't seem to be available any longer direct from Skyshark.

Simon (Fore Check) has done some mathematics on carbon spars and found an equation that he feels is pretty reliable. If you have the diameter and wall thickness of both spars he may be able to figure out pretty close comparison. He published it over on Kitebuilder if you're up to equations yourself.

But Simon's equation doesn't allow for differences in the carbon matrix used. Problem is Skyshark appears to use a different carbon in the P400 then they use on the P90 - P300's, and Jon never said whether the P450 used the carbon from the P400 or the P300's or a different carbon all together. The published data shows the P400 is more flexible then the P300 although it has a thicker wall. The P300 has a standard deflection of .287" the P400 has a standard deflection of .302", the 8P has a standard deflection of .142" or nearly twice as stiff as the P300, it is also 12 grams heavier then the P300, the P450 falls somewhere between. In fact the 8P is the stiffest wrapped rod available according to the data I have, only the G-Force standard approaches it at .210" deflection.

« Last Edit: August 06, 2011, 01:49 AM by mikenchico » Logged

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« Reply #2 on: August 06, 2011, 12:56 AM »

Thanks for your answer Mikenchico.

. If you have the diameter and wall thickness of both spars he may be able to figure out pretty close comparison. He published it over on Kitebuilder if you're up to equations yourself.

                               I.D.     O.D.     Wt./gm     
            8P  32.5     .244     .319       28.0     
        P450   32.5"     .244"     .306"       23.0

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« Reply #3 on: August 06, 2011, 12:29 PM »


Mike is correct in that I'd feel a lot better about doing an actual deflection test because of the composite layup in order to do any mathematical predictive stuff with these.  From an engineering/materials testing standpoint, the equations work very well to predict deflection values for different geometries (i.e. sizes and shapes) of materials that are basically isotropic (carbon, fiberglass, metals, even wood if you understand or accept that the standard deviation on wood will be much higher than on composites or metals.) 

That said, Sky Shark tubes are composite tubes, made up of both carbon and a wrap of fiberglass.  Or even pultruded carbon wrapped with a woven carbon fabric for increased hoop strength in lieu of fiberglass (which appears to be the case for the P2X and P3X tubes.)  Anyways, because you have differing amounts of each part of the composite layup between tube numbers, it makes predicting the deflection of a "new" composite tube very difficult, and empirical bench test data is best.  Actual data is always best anyway, but I've found that the predictive data for known common materials (carbon and fiberglass) is very good and almost dead on, so I feel comfortable using it to "expand" the chart where certain sizes were omitted or were not tested originally (the 0.2810" OD pultruded carbon tube is a good example.)

HOWEVER - if the question is simply "which one is stiffer" in the 8P vs P450 in a simple, relative sense - I've asked John T. about these and the 8P is stiffer.  A set of deflection test data would nail down the how much stiffer and scale factors.

It is interesting to note that there is some debate on the accuracy of the P400 "standard deflection" that was in the original data set on the original chart (before I got my hands on it LOL)  I've read (elsewhere, can't find it at the moment) that the P400's tested and measured at 0.302" deflection were of a lighter modulus of carbon.

Anyways - when I was measuring a couple of tubes that I wanted to know more about that weren't on the chart, I set up a little deflection bench test for those and while I was at it I tested a handful of the P400's that I had on hand.  They were very consistent (as expected) and their average deflection in "standard" values was 0.227" with a range of 0.224 - 0.230.  These measured values are more consistent with the reality that P400's are in fact stiffer than P300's (flex a couple and you'll see that, relatively speaking, P400s are stiffer.)

I'll pick up a couple of P450's here in a couple of weeks and test 'em out and see where they land; I *think* they'll be a little stiffer than P400's, but the 8P will still be the "Big Kahuna" for the Sky Shark straight tubes.

For what it's worth....

« Last Edit: August 06, 2011, 12:44 PM by Fore Check » Logged
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« Reply #4 on: August 06, 2011, 12:39 PM »

Very nice answer, many thanks Simon !  Wink
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