Fractured Axel

jimothy · Fri Apr 02, 2004 1:18 pm

Just a few quick notes to let people know what I've done and the results.

Basically, I'm reframing a std Impact to make a UL

I've used Avia G-force skinny ULs for the leading edges, and Avia G-Force superskinny SULs for the lower spreaders.

At the moment, the spine and upper spreader have remained un-changed (though I may change them in future to save yet more weight.

I've also replaced the LE connectors with tAPAs (tiny APAs) which weigh about a quarter as much as standard. Altogether, replacing the LEs and connectors has saved me 50g and the change of spreaders about 10g.

The kite now weighs in at about 215g, although I could easily lose another 20 by downsizing some other bits and peices.

Anyway, after reframing as detailed above, I took it out for a test fly - unfortunately, the winds were shocking - about 8mph up high, so I tucked myself in behind some trees to try to keep out of the wind, but of course I was now subjected to extremely dirty, gusty air, and the wind kept changing direction on me - not fun!

Anyway, I flew every time the wind dropped and got in a few little sessions. The kite seemed quite nicely balanced, sitting nicely in both fade and turtle positions, and pitched well, doing nice little JL launches from a flapjack-style start. Also wrapped up very easily (Note to self - add some yoyo-stopppers!) which is refreshing as by other low wind kite (the Amazing) doesn't like to pitch.

More when the wind settles.....

SteveR · Fri Apr 02, 2004 1:26 pm

JIm you out this afternoon?

jimothy · Fri Apr 02, 2004 1:32 pm

Sorry mate, can't make it later - the missus needs a lift to get her car back from MOT, plus have to sort out E111 and other stuff.

Fri Apr 02, 2004 2:00 pm

ok, ok enough of this HUL stuff, cos I don't want to take the blame when things go wrong !
Anyways sound like you've pretty much achieved what you wanted, and thats the main thing.

jimothy · Fri Apr 02, 2004 2:02 pm

ok craig - consider it changed

jimothy · Sat Apr 10, 2004 6:34 pm

Today I replaced the standoffs, some more fittings, and the upper spreader with lower-weight versions and the kite now weighs 199g. Last time I took it out, it was sitting deeper in the turtle position than the standard and was rolling up easier in the same winds. Hopefully losing a bit more weight won't affect this too much, but if it does then I can always add a bit to compensate. I'm still using the basic spine, and changing this to something a bit lighter should give me more room to redistribute weight if needed.

Sat Apr 10, 2004 7:00 pm

You had UL weather today? Lucky you - I was fighting the Evo Vent and Std Nirvana all afternoon in 12 - 16mph.

The deeper turtle: I'm guessing that you've got less weight in the tail than you have on the standard? That could be the main reason for this, my N. UL conversion is similar and after discussion with Juha I'm reducing the tail weight in my standard.

Replaced standoffs: You just used something lighter? (What?) Or have you changed the lengths?

I find my conversion a good deal floatier than the standard, does the Impact mod act the same way?

SteveR · Sat Apr 10, 2004 7:56 pm

Following extrat from ABW's site: thinking if there is any way we can measure the C o G of both the kites for comparison...

"Creating an ultralight version of an existing kite is not a simple matter of putting some lighter spars in it. Doing so may reduce the overall weight of the kite, but it also changes the weight distribution and shifts the centre of gravity. It is particularly important for an ultralight kite designed for flying in light wind that the kite is balanced correctly."

What will be interesting is the comparison to the factory UL, assuming that if the C o G os in a different position, and that the sail profile is the same, therefore the C o P is the same, it will fly differently.

Shame you aint about tomorrow as winds might be ideal to try it out. Next time..!

Sat Apr 10, 2004 7:59 pm

I think the CoG could be measured in much the same way as anything else... Hang it from each corner and project a vertical line from the fulcrum (imaginary line in this case). One wingtip and the nose should be sufficient as the kite has a line of symmetry in the spine.

jimothy · Sat Apr 10, 2004 8:01 pm

Wind was about 6-8mph today - didn't need the UL, but flew it anyway to compare the two.

re. deeper turtle - I realise that weight distribution is probably the cause - not that I'm concerned - it wasn't too deep to exit smoothly, and allowed for some very nice rising turtles. As this afternoon's changes took about 5g off the upper spreader, and about 10g off the lower spreader, this may change the balance, but I an always add a little weight to get it right.

Standoffs were changed from 3mm to 2mm carbon, same lengths, but switched the slighlty longer ones to the centre positions, as this is how both my other Impacts are set.

I'll give more details on flight characteristics (like float) in the next couple of days, winds permitting.

Sat Apr 10, 2004 8:14 pm

I will add that changing the CoG need not be the end of the world... we change the center of gravity fairly drastically by adding 15-20g to the tail of a kite, that's about 5% of the weight of a standard.

Of course it *might* make an adverse difference, but it needn't be something to lose sleep over.

Juha · Sat Apr 10, 2004 8:21 pm

Andy wrote:
The deeper turtle: I'm guessing that you've got less weight in the tail than you have on the standard? That could be the main reason for this, my N. UL conversion is similar

UL versions always seem to sit a bit deeper in the turtle, even with kites where extra tail weights are not used in any version. This subject was (briefly) discussed at GWTW at some point, I'll see if I can find the thread...

Juha

Sat Apr 10, 2004 8:46 pm

Juha wrote:
UL versions always seem to sit a bit deeper in the turtle, even with kites where extra tail weights are not used in any version.

Strange - even without weights in the equation I'd expect a simple UL conversion to be proportionally heavier in the tail than their standard counterparts, simply because of the larger amount of material across the bottom of the kite.

jimothy · Sat Apr 10, 2004 8:55 pm

Andy wrote:
Strange - even without weights in the equation I'd expect a simple UL conversion to be proportionally heavier in the tail than their standard counterparts, simply because of the larger amount of material across the bottom of the kite.

I'm not so sure about this - in a turtle postion the pivot point is shifted to the point where the lines cross the lower spreaders - this surely means that the majority of the kite is "above" (nearer the nose than) the pivot point, rather than "below" it - I'd guess this might explain a deeper turtle.

Eddie Green · Sat Apr 10, 2004 9:09 pm

The DS 3 used to be heavier in the tail than the DS 2, which made backspins harder.

Fractured Axel

Impact UL reframe project

Impact UL reframe project