Kite bladder volume

Nak · Thu Apr 05, 07 8:01 pm **Kite bladder volume**

Just for grins I pumped up a couple of kites with an air tank this morning so I could determine bladder volume. The results surprised the shit out of me!

'04 19m Fuel 86 gallons!!!

Now I know why I like using an electric pump with big kites!

The math: 26 gallon air tank. Starting psi: 150 psi, End psi: 90
19m Fuel Starting psi: 0 End psi 3

P1 * V1 = P2 * V2

Nak

Edited because I messed up the math. I think I have it right now. Anyone want to check this?

EdG · Since 19 Dec 2005 425 Posts Just a Kook that's Obsessed

there are some strange people on the forum Shocked

Nak · Thu Apr 05, 07 8:48 pm

jsj · Since 11 Sep 2006 83 Posts Hood River

umm. you need to re-read your thermo book and maybe do a little reality checking:

6" dia cylinder 30' long, vol = 10179in^3 or 44 gallons

P1V1=P2V2 works for "work done at the boundary of a simple compressiible system in a quasiequilibrium process"*

e.g. - a moving piston. Hint: the fact that your tank pressure does not equal your bladder pressure should make you wonder whether there is some problem......

The right way to do the calc miiiight be to determine mass lost in the tank then apply ideal gas law (conservation of mass).

Or you could simple estimate based on geometry.

Electric pumps are a for girlie men.

jsj

* Wylen and Sonntag, Fundamentals of Classical Thermodynamics 3rd Edition

Nak · Thu Apr 05, 07 9:52 pm

Hey jsj,

Yeah, thermo was 28 years ago... Obviously I need a refresher. Anyway that's why I edited the post. I think I have it right now at 86 gallons. What do you come up with? It seems about right just thinking about the volume.

Should have checked my math after first looking at it, but the opportunity to ride came up. Gotta have priorities! Very Happy

Still should have checked before posting. Embarassed

Electric pumps are for those who'd rather ride than spend time pumping. especially when time is limited! I'm pretty sure I've done enough in life to be assured of my non-girlieness without having to use a hand pump. Very Happy

Nak

Hein · Since 08 Mar 2005 1314 Posts Possessed

Might be better to determine the mean diameter and length
of the struts and LE and calculate the volume that way.

But if you are just wanting to figure the energy needed to
pump up a kite then the pressure drop and volume of your
air tank will tell you that. But that won't take into account the
frictional and heat losses it will take to pump the tank back
up.

Easy way:
Turn off everything in your house and use the compressor
to pump up the kite 10 or more times. Read your electric
meter before and after. KW-hours right there.

Reaper356 · Since 10 Dec 2006 781 Posts Salem / LC Oregon Opinionated

jsj · Since 11 Sep 2006 83 Posts Hood River

Nak, you've got got me there. My thermo was only 20yrs ago.

I hereby retract the bit about girlie-men.

cheers

jsj

Nak · Sun Oct 18, 09 6:25 pm

Hi Tim!

Hey, question for you. I bought one of your kite pumps here a few weeks back. I'm having problems getting it to work. When I first tried to pump up a 7m Cult, it wouldn't inflate it at all. All of the air went out the little venturi holes? The inflation valve on the kite was replaced with an Airtime valve, so it has a one way flapper valve. The Volo pump vented all of the air out the venturi; it wasn't applying enough pressure to overcome the flapper valve. Also, when I got home the little gizmo that presses on the CO2 tank valve fell out of the pump and rolled into oblivion. So anyways, I need a new one of those. Also, I'm wondering if something must be wrong with my pump?

Thanks for any help you can give me!

Nak

Blue · Since 03 Jul 2007 469 Posts I used to be Obsessed

pdxmonkeyboy · Mon Oct 19, 09 10:20 am

Anybody that is dismissive of electric pumps has never pumped up my 14m T2.

The electric pump is MONEY for that thing!!

bwd · Since 04 Aug 2007 385 Posts Obsessed

tuna · Since 20 Aug 2009 15 Posts Ocean Shores, WA

Hey there, this was the only reason I could think of for wanting to know the volume of your kite. I posted this bit on PSKite a little while back.

*******************

I'm not sure of the exact volume displaced by an inflated kite... so consider a kite with a 6" diameter leading edge that is 12' long. The volume of the kite is therefore 2.35 cubic feet. It will take 3.32 cf of "Air" to inflate the kite to 6psi.

Weight of 2.35 cf Air (Air displaced by your kite) = 0.176 lbs
Weight of 3.32 cf Air (Air in your kite) = 0.249 lbs
Weight of 3.32 cf Helium (Helium in your kite) = 0.037 lbs

0.249 lbs - 0.176 lbs = 0.073 lbs (weight added to your kite when you inflate it with "air" to 6psi)
0.037 lbs - 0.176 lbs = -0.139 lbs (Additional positive buoyancy gained by filling your kite with helium to 6psi)

if you fill to 9psi the weight savings becomes about 0.122 lbs. The benefit decreases as you inflate to a higher psi.