I don't have the time to get the Maths and physics out however I think alot has todo with Humidity. Hot and Humid (think Darwin Cairns Bali) 25kts and I'm on my 12m verses Cold and Dry (Think Perth and most seabreezes) 25kts and I'm flying on my 9m. I don't care what the science says I know that my kite feels a difference

Intheozone said...

I don't have the time to get the Maths and physics out however I think alot has todo with Humidity. Hot and Humid (think Darwin Cairns Bali) 25kts and I'm on my 12m verses Cold and Dry (Think Perth and most seabreezes) 25kts and I'm flying on my 9m. I don't care what the science says I know that my kite feels a difference

The force on the kite is directly proportional to 0.5*rho*Velocity^2. This is undisputable scientific fact and if we don't believe this, then planes will start to fall out of the sky :)

Plummet has shown that rho (air density) will vary by (at the extreme) 10-15%.

However a wind gust can typically be around 40% stronger than the steady breeze. When you take a steady velocity of 18 knots, this is a gust of 25 knots. So using the Velocity^2, you will see a force change of 92%!!!!

To get a 15% increase in force, you only need a gust of 19.5 knots above the steady 18 knots. (19.5^2/18^2=1.17).

Small changes in velocity will greatly outweigh the effect of density changes. A warm tropical breeze may be more steady at 18 knots, whilst a winter breeze or seabreeze will be more turbulent and gusty at 18 to 25. This is because the winter front(high gradient) or sea breeze (thermal) are shorter in duration (~8 hours) whereas a tropical (low gradient) breeze may be a longer duration (24 hours).

Intheozone said...

Kitepower Australia said...

beefarmer said...

yet somehow, when you stand on the beach in bali, and you feel a good 25 kt wind in your face, and you look out and see the white caps a good 25 kt wind would produce, you rig up and go out and its not 25 kts, it's 18.

Or at least that's how it seemed to me.

Reckon thats more to do with local issues like depth of water, sun angles, and you being less familiar with wind in Bali - meaning you just under estimated the wind.
16 degrees of temp difference of the air can only make around 1 knot of difference (if that), not 7/8 knots like you are thinking.
Its got to be just underestimating.

Have you even been to far north queensland or Perth to kite??? Compare FNQ with Sydney Wind. what size kites are you riding and what wind speed in each??

Yep been kiting all over Oz, and even just recently in say Port Douglas it blew approx 24-28 knots, I used a 9M C4 and was well powered up, my friend who is at least 10-15kg heavier than me used a 10.5 Core.
If I was in Perth in similar strength winds, I would be using the same kite, and have used the same size kite in 25 knots at Safety Bay last summer.

I made all the calculations a couple of years ago. I don't remember the exact details any more, but the difference between a typical winter day (10 deg C, wet, frontal weather) and a typical summer day (30-35 deg C, dry, seabrezee) worked out to be around 5%.

The effect of the cold air in winter is PARTIALLY CANCELLED OUT by lower pressure and higher humidity.

Now regarding tropics like Bali etc. - it is true the wind is considerably weaker, because unlike in the South all the factors reinforce each other ie:
- reasonably high temp (say minus 5% density)
- low pressure (say another minus 5% density or more)
- high humidity (say another minus 2% density)

Well maths aside. My practical experience between winter and summer is this. My temps are lower than you perth guys. We might see maybe 30 as push. but could be down to 5-10 deg c in winter.

Summer seabreases are definately cleaner smoother more predictable. it makes them easier to ride. the winter frontal wind is definately more variable. an 18 knot day is more likely to be a 16-22 knot day.

i ride the same size kites from summer to winter. i don't ride a bigger size for the same wind speed in summer. But i do notice more power in winter on my biggest size kite. that would be the 15m speed 3. i find i have a couple of knots extra low end in the wind which makes the difference between the walk of shame and staying upwind. at the upper end 30+ knots i can't notice any difference. a storm is a storm winter or summer.

^lol I figured you would have a certain knowlage of this subject puetz.
Could skinny winds be caused by non linear wind