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Pump my Kite, right!

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Toby
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Pump my Kite, right!

Postby Toby » Fri Jul 20, 2018 3:34 pm

Pump my Kite, right!

http://www.ralfgroeseldesign.com/blog/p ... kite-right

rgd 1.png

Having been a kite designer for many years, I’ve travelled the world and visited countless kite spots. Now, I feel that it’s time to talk about an essential topic that for some reason has always been deemed unimportant and never discussed in enough detail: The right inflation pressure.

It seems there is a lot of uncertainty amongst the kite community, as I often see more incorrectly pumped kites flying around than ones equipped with the right pressure. The most obvious are kites that haven't been inflated enough. This results in shaking and jellyfishing through the air, which can only mean that the kite is not providing the intended performance and handling characteristics.
In this blog post we will explore this topic and ensure that you leave with the knowledge of how to find the correct kite pressure for your next session.

THE AIR

‘Light as air’ is quite an irritating and confusing saying. Just because we cant see air, it still has a weight of 1.293 kg/m² per m³ (at 0°C/1013 mbar) and we can feel it’s force once the wind starts to power our kite. Its ability to be compressed relatively easily, gives us the chance to use this medium to inflate and stiffen up the Leading Edge and struts.
If you compare it to riding a bike or driving a car, you know that an incorrect tyre pressure will deliver differences in behaviour. As a passionate racing car driver, I’ve learned that even an imbalance of 0.05 bar pressure makes a huge impact on grip, brake performance, handling and feedback. So, what does this mean for our kites?

Pressure and Diameter

First of all, we have to understand that we are dealing with two variables, the Leading Edge diameter and inflation pressure, both of which are highly dependant on each other in terms of the overall structural kite stiffness. In terms of design, I always have to take these two variables into consideration and here is why: Imagine a 6 m² kite has the same LE diameter as a 14 m², for example 8%. Due to the fact that the 14 m² center profile is 2 m long, the effective LE diameter is 16 cm. On our 6m² kite sample, the center profile is 1.4 m long, resulting in a 11.2 cm LE diameter, drastically smaller than the 14 m² kite.

rgd 2.png

The load - weight of the rider- captured by the inflated frame is the same on both kite sizes. As we all know, a thinner tube is easier to bend than a thick one. This means, I have to find a way to increase the structural stiffness on a smaller kite in order to insure a compact and solid frame. This is achieved by increasing the LE diameter. As a general rule, the smaller the kite, the thicker the LE diameter becomes. Unfortunately, the diameter is only one of two variables, and the tube-pressure has a much higher influence on the general flight characteristics. The bending resistance of a LE pumped to 6 PSI is around 60 % higher than on a LE which has be inflated with 3 PSI.

rgd 3.png

On the water

What does this mean for you? All DUOTONE kites are developed with a LE pressure of 6 PSI. For testing, I use an electric pump which automatically switches off once the correct pressure has been set. This allows me to validate the different kite samples correctly.
If you pump your kite to 4 PSI only, the flight characteristics will change in a negative manner. Under load, the kite will certainly start to deform. You will experience a softer steering pressure, a wobbly bar feedback and you will lose jumping performance as the tips start to flare out. It will also be more difficult for you to ride upwind as the kite starts to oscillate, meaning it starts to vary its position within the wind-window frequently. The only positive side effect will be an improved water relaunch in light wind conditions with big kites, as the wing tip easily deforms and therefore catches air more easily.

Overinflation, a threat?

The reason for under-pumped kites seems to be the fear of bursting the LE if pumped harder.
Within my entire career, I’ve never once broken a single kite due to a well pumped LE. Yes, a kite can break, that's not even a question, but the times of kites exploding whilst sitting on the beach are well behind us. Professional kiteboarders such as Aaron Hadlow or Lasse Walker have to pump their kites to the absolute max, especially in competitions like the Red Bull King of the Air where they are totally overpowered. The kite has to withstand extreme stress and the inflated frame has to be pressurized as much as possible in order to perform as intended. The DUOTONE kite pump is equipped with a pressure gauge, indicating 8 PSI max. You can be sure that every professional kiteboarder is pumping their kites to at least 7 PSI, regardless of the application range.

The perfect pressure

Unfortunately, there is no perfect pressure I could recommend to you. Much like the tyre pressure on your car is adjusted to the load factor, you also have to understand that your kite needs to be adjusted sometimes. We have the following variables which have to be taken into consideration: Rider’s weight / kite size / application range (wave, freestyle, school etc.) wind conditions and conditions at the spot itself. What I can recommend is to try it out for yourself. Fly your kite with 4 PSI and then increase the pressure to 7 PSI. You will notice that the entire flight characteristics of your kite will change.

rgd 4.png

Conclusion

If you are looking for the perfect kite session, you have to take care about the right inflation pressure. If you are not a kite school looking for maximum relaunch abilities, you should always pump your kite at least to 6 PSI. Heavy riders and kiters looking for ultimate jumping and looping performance in strong, gusty winds, should consider inflating their kites up to 8 PSI.

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Re: Pump my Kite, right!

Postby All+the+gear=no-idea » Fri Jul 20, 2018 4:02 pm

Mate, can't you turn your calculations into an APP :) taking into account wind velocity + bladder size + weight of rider + intended style of session? Oh, and then can you come and pump up my kite to show me :) ;)

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Re: Pump my Kite, right!

Postby grigorib » Fri Jul 20, 2018 6:23 pm

15m used to get 8psi
11m and smaller 10psi

the bottom line - more strut diameter-> less pressure to pump. Like for any inflatable tire for last 130 years....

Looking at others' underinflated (often shapeless in water) kites makes is weird to watch.
There should be ads for "Men are shocked finding these simple tricks to solve limp strut problem!"

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Re: Pump my Kite, right!

Postby ciscokitesurfer » Fri Jul 20, 2018 7:30 pm

thank for the information - interesting topic

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Re: Pump my Kite, right!

Postby The Captain » Fri Jul 20, 2018 7:30 pm

How much will the pressure increase due to solar warming? A black leading edge in the sun will warm the internal air, increasing pressure.
I could figure it out, but I am too lazy...
P1T1=P2T2

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BillyGoatGruff
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Re: Pump my Kite, right!

Postby BillyGoatGruff » Fri Jul 20, 2018 7:45 pm

6 PSI on all Dutone kites... :o wow..seems very low. I ride all my Naish Torch's on 9 to 10 PSI and have never blown a kite. Dacron is super strong, the leading edge is double nylon stitched.
Last edited by BillyGoatGruff on Fri Jul 20, 2018 9:24 pm, edited 1 time in total.

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Re: Pump my Kite, right!

Postby dazarter » Fri Jul 20, 2018 8:22 pm

I pump up to 9 - 10 psi every time every kite - no problems what so ever and perfect handling. i start and land kite with what feels like 3-5 psi in them -way to low for the lite to perform proberly...

pump it ip!

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Re: Pump my Kite, right!

Postby alfredo68 » Fri Jul 20, 2018 8:44 pm

Pump like a rock (but try not to crash it) and then how important is it to lock the valves of each strut? i always forget though.....

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Re: Pump my Kite, right!

Postby PullStrings » Fri Jul 20, 2018 9:18 pm

New kite 17 sqm....6.5 PSI...but as the dacron casing of LE gets old and softer from UV rays..salt air...and a lot of usage ... pump it close to 8.5 PSI

Too much PSI can be dangerous to pop the stitching of the LE seam....use common sense...good to test different pumps with different gauges...they can differ by 1 or more PSI...get used to your kites as of how many pumps it takes.

Some like to count the downstrike pumps instead of relying on the gauges. Some do both.

Be consistent...get to know your pump

As far as clipping shut the struts every time I believe it is wise. On the water all kinds of things can happen.
A connecting hose could come off.
A cut in one connecting hose
A leaking strut
A leaking LE from valve or a LE wingtip burst..etc.

So the more air you have at your disposal in the kite the better if the kite starts deflating out on the water

Also after landing if you have clipped them all you have a chance to test if the LE has lost air pressure. Feel first by hand the struts to make they are all hard with same pressure.( gives you also a chance to see if a strut got softer )

Then unclip just one of them that feels hard ( generally i test with center strut since its near the inflate/deflate valve but if that strut got soft use an other one )

Unclip it and listen....if it stays quiet...all good
If you hear air from strut rush into LE then it has lost air

You will hear something even if real small leak of 0.5 PSI

If leak small don't bother fixing yet but do the same test next time after session. A 2hr session is usually best.

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Re: Pump my Kite, right!

Postby Kamikuza » Sat Jul 21, 2018 1:51 am

IMO if you've got a one-way valve, you're not able to get an accurate reading anyway, as the pressure you read is resistance at the valve as the air goes into the kite. Even trying the tricks in the recent Cabrinha video, you get wildly different readings depending on how fast you depress the plunger.

Ping and fold. If it can't handle that the kite is fubar.
BillyGoatGruff wrote:
Fri Jul 20, 2018 7:45 pm
6 PSI on all Dutone kites... :o wow..seems very low. I ride all my Naish Torch's on 9 to 10 PSI and have never blown a kite. Dacron is super strong, the leading edge is double nylon stitched.
This is jolly jape that such folks as the Australian Ozone distributer and his shop staff like to play ... the manufacturer recommends 6psi on the website and in the manual, then the dealers and distributors go online and recommend folks pump it up to 8psi to "get the best performance" but if you have any issues with the LE material or stitching, they default on the warranty because "you over-inflated it".

What fun!


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