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? For Bill Hansen regarding 3 vs 4 strut design

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jb8431
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? For Bill Hansen regarding 3 vs 4 strut design

Postby jb8431 » Wed Feb 08, 2012 5:03 pm

Bill,

I have vacillated a bit about my next kite purchase because of design variations among companies. Being a flyer and not a designer and so little quality info on design other than forums where opinion reigns without solid data.

My question is with more companies going to 3 and 4 strut kites. I am a little confused
About the design difference between center strut vs no center strut. Having flown a 5 strut delta hybrid for the last 3 years I flew two 4 strut delta hybrids and found them to be much less stable than my kite with the center strut. The demos with the 4 strut kites were in less than ideal wind, but I was able to fly my 5 strut kite back to back with one of them and got going no problem eventhough the wind was terrible up and down gusty while the 4 strut kite was struggling just stay in the air( not sure if the lack of center strut was the issue or not). Also there were 4 other people on the water with center strut kites that were kiting just fine. Perhaps my experience would have been better with more ideal wind, but other kites were flying very well inspite of the lousy wind.
Have you designed Any 4 strut kites with no center strut and if so what are the pros and cons from your experience with this design platform. The kites where I have had the issue without naming companies have a huge gap in the center between the 2 medial struts.
I have a 6 strut 9m kite with 2 struts just to the right and left of center and it is a great kite with none of these stability issues.

If your willing to comment on this I would really like to here some designer opinion on this topic.

Good winds!

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Re: ? For Bill Hansen regarding 3 vs 4 strut design

Postby Hansen Design » Wed Feb 08, 2012 7:41 pm

Hi jb:
Good question!
I have experimented with zero to 8 strut inflatable kites and you can check the archives here to see some of those experiments. I have also tested many kites by deflating various struts to monitor the effect and this is something you can easily do yourself. My conclusion is that a center strut stabilizes the canopy (and profile) when the kite is under load and subject to compression where it will tend to become more 'C' shaped. When this happens, the canopy is 'jammed' forward in the center of the kite and the profile in this critical area becomes distorted. The distortion is a function of load and creates a less stable and predictable flight response as the load and distortion changes. A center strut provides a compressive-resistant member which in unison with the wingtips and low stretch material along the trailing edge, creates a diamond-shaped structure which is less likely to distort in the middle.

My conclusion is a center strut and the wingtip struts are the most important struts in any kite. There are some perceived but mostly unsubstantiated advantages of even strut kites and a properly designed one with sufficient structure and bridle support should perform well, but IMHO (based on experience,) a similar kite with one less strut would likely be equal or better. While a 4 strut may be lighter (and cheaper to build) than a 5 strut, I have not found them to be superior to a 3 strut kite and the popularity of contemporary 3 strut kites (both 'c' shaped and flat) in today's market seems to bear this out.
My 2¢...
Cheers! :thumb:

jb8431 wrote:Bill,

I have vacillated a bit about my next kite purchase because of design variations among companies. Being a flyer and not a designer and so little quality info on design other than forums where opinion reigns without solid data.

My question is with more companies going to 3 and 4 strut kites. I am a little confused
About the design difference between center strut vs no center strut. Having flown a 5 strut delta hybrid for the last 3 years I flew two 4 strut delta hybrids and found them to be much less stable than my kite with the center strut. The demos with the 4 strut kites were in less than ideal wind, but I was able to fly my 5 strut kite back to back with one of them and got going no problem eventhough the wind was terrible up and down gusty while the 4 strut kite was struggling just stay in the air( not sure if the lack of center strut was the issue or not). Also there were 4 other people on the water with center strut kites that were kiting just fine. Perhaps my experience would have been better with more ideal wind, but other kites were flying very well inspite of the lousy wind.
Have you designed Any 4 strut kites with no center strut and if so what are the pros and cons from your experience with this design platform. The kites where I have had the issue without naming companies have a huge gap in the center between the 2 medial struts.
I have a 6 strut 9m kite with 2 struts just to the right and left of center and it is a great kite with none of these stability issues.

If your willing to comment on this I would really like to here some designer opinion on this topic.

Good winds!

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Re: ? For Bill Hansen regarding 3 vs 4 strut design

Postby Bille » Wed Feb 08, 2012 8:57 pm

Hansen Aerosports wrote:Hi jb:
Good question!
...
My conclusion is that
a center strut stabilizes the canopy (and profile)
... the canopy is 'jammed' forward in the center of the kite and the profile in this critical area becomes distorted.
The distortion is a function of load and creates a less stable and predictable flight response as the load and distortion changes. A center strut provides a compressive-resistant member
...


My conclusion is
a center strut and the wingtip struts are the most important struts in any kite.
...
While a 4 strut may be lighter (and cheaper to build) than a 5 strut, I have not found them to be superior to a 3 strut kite and the popularity of...
My 2¢...
Cheers! :thumb:
...

Thanks for your response ,I learned a bunch ; & making correlation(s)-- between a HG & a kite-board Kite
i see what your talking about when the airfoil gets jammed forward.

I've had battens Fall Out while flying because the device holding them in
was broken. When this happens there is a distinct deformation from the
high-point of the air-foil and it travels forward.

I "Think" this contributes more --parasitic drag--,(drag caused from distortions), than anything, causing a mild Yawing turn if the batten that's missing is towards the tip.

I "Think" what causes the main problem is now that the air-foil is shifted forward,
it also distorts the Trailing edge. This will add --induced drag--,(a change in
the way the air flows causing Lift).

If Ya place a Flap on an airfoil then put it down a bit, it will make Lots of
Lift "AND" Drag . A distorted Trailing Edge on a kite,will cause the air that flows off
the airfoil to do much the same.Only it's Random lift & drag because the distortion
never stays the same for more than a moment or two.

Replay the first 0:08 seconds, 3 or 4 times
http://www.youtube.com/watch?v=jAoh0Ppwbt0

On This one, go to 1:08 and watch how the turbulence comes off the
back of the airfoil as the Angle of Attack is increased.
Nearly the same things happen when Ya change the Trailing Edge,(TE)
of an airfoil ; Only the change is WAY more drastic because the actual
Lift of the foil is changed.
http://www.youtube.com/watch?v=6UlsArvbTeo

And Last, this as a visualization for what the air flowing Off the Trailing Edge
of a kite that has flutter, ((not supported well or flapping like a Flag)).
http://www.youtube.com/watch?v=woLm7dWs ... re=related

Bille

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Re: ? For Bill Hansen regarding 3 vs 4 strut design

Postby jb8431 » Wed Feb 08, 2012 10:20 pm

Bill,

Your a true Gentleman of the sport. I greatly appreciate your input and your answer, which is certainly consistant with good common sense, but none the less it is nice to here from one of the experts. Thanks for making yourself available on the forum.

My post was not placed to criticize four strut kites, just to understand them a little better. So those of you who love yours, have a blast! :thumb:

Best regards

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Re: ? For Bill Hansen regarding 3 vs 4 strut design

Postby kitepilot » Thu Feb 09, 2012 5:23 am

Bill,
Thanks for all of your post. As a professional pilot I'm always interested in aerodynamics and experience(which is actually more important than aerodynamics) because no matter what the facts say, if it works it works. And some things can't be explained away.
Aloha KP

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Re: ? For Bill Hansen regarding 3 vs 4 strut design

Postby Bille » Thu Feb 09, 2012 8:19 am

I'm starting to think that i May have "Over-stepped" a bit on my above post ??
Anyone ?

Should i be using the delete function ??


Bille

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Re: ? For Bill Hansen regarding 3 vs 4 strut design

Postby plummet » Thu Feb 09, 2012 9:56 am

Bille wrote:I'm starting to think that i May have "Over-stepped" a bit on my above post ??
Anyone ?

Should i be using the delete function ??


Bille



i wasn't offended! and since its all about ME... your safe!...hhehehe

ps i enjoyed the discussion

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Re: ? For Bill Hansen regarding 3 vs 4 strut design

Postby tomatkins » Thu Feb 09, 2012 8:57 pm

Bille wrote:I'm starting to think that i May have "Over-stepped" a bit on my above post ??
Anyone ?

Should i be using the delete function ??


Bille


Bille,

You haven't "over-stepped"...you probably have been "over-inspired"...Bill Hansen has that effect on the scientific half of our brains. He inspires us with his well thought-out and well-stated explainations, making difficult concepts seem simple and clear.

Thanks go out to both Bille, and Bill...you guys are the reason I come to this forum on a daily basis. :thumb:

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Re: ? For Bill Hansen regarding 3 vs 4 strut design

Postby eree » Fri Feb 10, 2012 8:06 pm

jb8431 wrote:......My post was not placed to criticize four strut kites, just to understand them a little better. So those of you who love yours, have a blast! :thumb: .....


well i'm not going to be so polite.
you don't have to be aerodynamics engineer to see what is good and what isn't. look at the nature, natural selection shows us: almost 100% of every advanced living beings have central rigid support structure to support its body. like spine for the mammals.

I have seen the most ugliest and horrible canopy flutter in the middle of the best kahoona's canopy close to the LE when it was slightly overpowered and sheeted out.

and look at the official photos of the genetrix origin from their website. can somebody call that LE aerodynamic?

origin2-1.jpg
origin2-2.jpg

do you need more proofs?

if i'm not mistaking first serious kite with even number of the struts was takoon years ago, then came the followers. takoon has quickly realized this concept won't work without proper support of the center part of the canopy, and now although they still have even number of the strut, distance between two struts closest to the middle is minimal. so, now they have is 4 struts for sales argument (for originality, i guess?) and enough support in the middle area of the canopy.
but then why have 4 struts with two struts close to each other in the center of the wing when you can have just 3 struts and weight save?
of course brands, that once followed popular idea now can not confess they were after cheap popularity. and some of them still continue with this nonsense.

jb8431
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Re: ? For Bill Hansen regarding 3 vs 4 strut design

Postby jb8431 » Sat Feb 11, 2012 4:43 am

Eree,

You are right honesty is better!

I demoed the Origin 2 and it was the worst kite I have ever flown. I told the rep and he kindly took the kite back. He explained to me that the very famous designer Marshal Camblong who designed the hydra did not want to do 4 strut kite because of stability flaws. But the reps convinced him on account of market trends. What a sad thing. I have the orinal origin kite 9m with 6 struts and it is one of the most Fun and powerful kites I have flown...bloody awesome kiteloops. This kite is more adequately described having 2 center struts.
http://t2.gstatic.com/images?q=tbn:ANd9 ... 9MEvYyDGQz


Notice the center strut placement in the picture above.

Now I encourage Genetrix to go back to that design as it was great!!!!!


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