Hi guys and girls,

Im getting a bit more tech , full stres analysis of a PTW style buggy frame AND i have somthing to measure the force on the kite lines and even a tow rope.

Help me out here, i need loads for the pilot, a load from the hard wire on the upwind side of the buggy frame rail and a load for the tyre grip to put into the software. What is the best way to test this with the tension guage (measures kg force) , obviously the static load is easy, but how do i predict the dynamic/rolling load ?

Also beach racer tyres are possibly just off the boat and a carbon leading link is on the horizion with a lot of help from those who know what they are doing with those materials, im just the mold maker but im learning .

carbon sock 100mm circ , does it like to be crushed into a smaller shape ? can it streatch out a little to go over a larger shape ??

A carbon sock compresses to fit over a larger object and stretches to conform to a smaller one... why are you using a dreadful complication like a carbon socks? Bad enough to get over a boom or a mast unless in a dry layup VARI or VART - definitely not fun when sticky. :?

No idea... I know you have to factor in your vector of pull for the kite(ie. angle off the deck and angle forwards) to workout how much of the weight is relieved... ie. how much pull is sideways(and up) and how much is forward if you want to break it up into components to 'grade' individual parts that way.

This is quite a wide range unless you factor in race conditions only with the kite far back in the window and say 45 - 60 degrees off the deck.

From there you can start working with an average 85kg pilot. CoE is pretty much the pubic bone for a comfortable seated position.

i think an awful lot will become apparent when we get to the beach. an start testing
...i have one theory about lines and sideslip/downwind drag and how to simulate it with the van/loadcell.....we need a set line for the buggy to try an follow,
an A to B set out by flags exactly 90degrees to the wind..
we then go for a hard out run with the kite and we try to measure either A at what angle the buggy is pionted upwind sliding to achive a point to point with the flags....OR...we dont slide the buggy and measure howmuch we have traveld downwind and missed flag B by.
problems...in test A its all very well to steer the buggy upwind to combat downwind pull from the kite and go in a straight line because the buggy DOES bully the kite into a straight line but it wont bully the van.
and in test B if we allow the kite to pull us where it wants all we get is the angle for the van to drive at to follow the kites pull path.
i tink we have to mix the 2 tests togeather somehow to get what we want but im not sure how to do it yet.
we definently need a device to measure buggy angle upwind vs our a/b test track 90degrees to the wind (gps/compass/waypoints?)
and something to measure the angle of the kite in the wndow relitive to the buggy AND the wind.
like i say, all this will be a lot easier to explane on the beach...i think :?

not to be too "the glass is half empty" but i think your gona find out a whole lot of nothing with your load cell. but don't let that stop you!

i've also discovered speed makes a big difference to traction. the faster you go the less traction you have.

Well Mr Plummet. since you ask: in order to get the 45-60 degree tow angle you'd need a ski-pole(think ski boat) mounted on the towing ute(unless the tow-rope is too short to be safe) I though even you'd like the idea of testing some ATB dynamics behind the ski-ute! I can think of at least one good way to practise flat three handle passes... :twisted:

Figures will give you a range to simulate at best. What bugs my mind is how dynamic that range is in this application and how trying to fix it or put a handle on only limits the buggy's design parameters. I can tell you for instance that a buggies coefficient of rolling resistance is in a range of 0.02 - 0.03 for hard sand but how do you allow for the variance in vehicle weight when a sine'ng kite varies the weight. Albeit a couple of kilograms which also changes the rolling load and then going faster relieves the weight even more.

myglass is half full on this one, i am expecting relative loads to be usable, as long as our test is consistent then we should be able to use the load cell as a control to work out which tyre set is better at 30kmph , 50 kmph etc . I have also noted the grooves begin to plane at higher speeds and become less effective, you can see it in the trailing sand pattern. We have a grooving tool though and i expect less rubber and wider grooves could work or zero grooves could be the best option for ultra high speeds to increase the contact patch. Currently we dont know how much load the kite puts the farame under for designing buggies and we cant use a variable kite and wind speed to predict the best tyres for side force unless we test for months and at least two buggies with identical weights and idemntical kites, i have never found identical kites, one is always faster than the other.

the load cell should give a repeatable control to use , when its going from grass tread to grooves even i can say its going to be better, but when you get down to a 10% improvment its almost impossible to tell , but really worth having. Granted the load cell will not answer all our questions though.