Hey guys, Today i was out practicing flying my 11m waroo. Very light wind so its an effort to keep it in the air! Although its good for practice! Anyhoo I pumped up the LE pritty darn hard. Like my pump felt like it was going to break.

( I dont think its the oringal best pump just says double action hand pump on the side)

I done the drum flick as well as the LE bend. Theres 5 struts on the waroo and i tried to bend it around the 2nd strut from the center. I could bend it, but its was quite firm. I was flying the kite for about 15 min and the wind dropped and it fell into the water (small waves) As soon as the kite hit the water it kinda folded on its self. The wind picked up and draged it back to the sand where i was JUST able to re-launch it when the wind was heavy enough.

I think the colder water took the pressure down in the LE, and the factor of very low wind wouldnt have helped either. I have a feeling my pump may not be strong enough??? But then i think i am pumping it up fairly hard.

Thanks for input!

Based on the ideal gas laws then yes the cold water can have an effect on the pressure inside a kite.

Assume that the leading edge takes 50 pumps of a 2 litre volume pump to fill (not pressurise but fill) this gives an approx volume of 100 litres or 0.1metres cubic

pumping to 7 psi ish is equivalent to 0.5 bar (half an atmosphere) so that gives a pressure of 50,000 Pascal or N/m^2

Temperature is assumed 25 deg C which is 298.15 Kelvin

Hence ideal gas law Pressure x Volume / temperature = constant

so 50,000 x 0.1 / 298.15 = 16.77

hence the constant =16.77 in this example

In this case Volume is Constant as it is restricted by the dacron

so reducing the temp by 10 degrees c assuming the water is 15 deg c or 283.15 K

p = 16.77 x Temp (283.15 K) / Volume (0.1) = 47484.5 Pa or approx 5% of the pressure

This is assuming that the sea temperature instantly cools the air in the bladder and the effect of the sun on the canopy has not increased the air pressure by adding heat.
Air is actually crap at conducting heat so I really doubt that the cool down would happen that quickly even though the surface of the bladder will cool quickly due to contact with the water.

Your kite probably bent due to being full of water behind the leading edge and you pulling to hard to try and relauch it before the water has had a chance to drain off the canopy

Try kiting in more wind and letting the kite drift to the edge of the window before yanking on the steering line to relaunch the kite.

i think you will find its more like 10% change in pressure with those figures

regardless, do you really think a reading of around 1/2 a psi on your pump gauge makes much difference to how inflated the kite is? or that ur pump gauge is at all accurate? or that the temperature difference is really that much?

:)

check for leaks.

YE OLD PHYSICS.

P1V1/T1=P2V2/T2

Where P1 is the initial Pressure
V1 is the initial Volume
T1 is the initial Temperature
P2 is the Pressure after it has been exposed to the cold air/water
V2 is the Volume after it has been exposed to the cold air/water
T2 is the Temperature after it has been exposed to the cold air/water

As we can see, Presure is DIRECTLY PROPORTIONAL to Temperature (ie, as Temperature goes down (due to the cold) the Pressure also goes down (hence the folded kite))

andyy said...

YE OLD PHYSICS.

P1V1/T1=P2V2/T2

Where P1 is the initial Pressure
V1 is the initial Volume
T1 is the initial Temperature
P2 is the Pressure after it has been exposed to the cold air/water
V2 is the Volume after it has been exposed to the cold air/water
T2 is the Temperature after it has been exposed to the cold air/water

As we can see, Presure is DIRECTLY PROPORTIONAL to Temperature (ie, as Temperature goes down (due to the cold) the Pressure also goes down (hence the folded kite))

You passed physics Yatesy but I bet you failed spelling! he he

andyy said...

colinwill78 said...

if it's a leak the kite will stay deflated.
if it is temperature then the kite will self inflate when it warms up........ never heard of that happening....yet.

dude are you saying this with any knowledge of phyiscs at all?? douche

He is correct. Of course the air in the kite will not heat up immediately but if flown for long enough, the pressure will increase.

Extreme example, have you ever left your bike tyre, fully inflated in a car, in the sun, without air con? If you have, you know they burst too bloody easily. Anyway, as previously explained, pressure is DIRECTLY PROPORTIONAL to temperature. As temp goes up, so does pressure.

Are you mob really interested in a physics lesson? Seems so, with the wind thread and this one.

Thats not dyslexia, its just bad speling....

I had a mate called Kelvin.....he wasn't very smart.

only when the pressure was on!


and that, my friends, is how you change a semi-intellectual thread with some useful scientific answers into an inane non-serious bunch of crap!!!


next!

sunseeker said...

andyy said...

YE OLD PHYSICS.

P1V1/T1=P2V2/T2

Where P1 is the initial Pressure
V1 is the initial Volume
T1 is the initial Temperature
P2 is the Pressure after it has been exposed to the cold air/water
V2 is the Volume after it has been exposed to the cold air/water
T2 is the Temperature after it has been exposed to the cold air/water

As we can see, Presure is DIRECTLY PROPORTIONAL to Temperature (ie, as Temperature goes down (due to the cold) the Pressure also goes down (hence the folded kite))

Don't forget though that the temp needs to be in Kelvin so even if the temperature of the air dropped by 10 degrees (which is extremely unlikely), the pressure would only drop from 10psi to 9.6psi. Or if you started at 8psi it would only drop to 7.7psi. (Assuming starting temperature is around 25 degrees C). This is not a major drop in pressure at all and would not cause the kite to fold.

Spot on Nick - good to see the Engineers are setting things straight. Both calcs (yours and Karve's) show a 5% or less pressure effect if you actually managed to lower the air in the LE 10deg (doubtful if not in water for long). It is not a temperature thing. I kite in PNG and the water temp is often not much different to the air temp and I have experienced the apparent lowering of pressure after some time on the water, even though there appears no leaks.

I reckon it could be any of a number of things, but most likely a combo of a few. Like you not actually pumping as hard as you think (grease your pump, it makes a big difference!); Kite is wet - heavier and folds on itself more easily; pull from the lines tends to fold a kite more as well if the wind is light and not pushing it out to it's flying profile.

If no leaks - check your pump and pressure to make sure you are pumping enough. That is the likely cause/solution. There is only one thing that you have to worry about cold water deflating......

Or just don't drop the kite