straight or curved leading edge design
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kite_pilot:
hi guys,
just curious to know,some sport stunt kites have very straight leading edges and some have more curved leading edges!
whats the difference between the two r.e flight Characteristics please ?
which is the better shape r.e performance ?
its amazing how sport stunt kites fly when you think about it isnt it?
thanks
glen
tcope:
Over the years I've made the following observation on this. Disclaimer... I'm not an expert and I've never spoken to one about this (so I'm betting that smarter people know much more then I do, to the point it's probably obvious to most).

I feel that curved edges allow the kite to make smoother turns. Kites with straight edges seem to make more "stiff" turns. I always thing of it that the kite makes a turn just like it's leading edge. If it's curved then the turn is nice ans smooth. If it's straight then the kite turns and locks on when you stop turning. Such a kite would be good for precision flying such as a ladder move or square turns.
Hadge:
Can I recommend reading this

http://www.iannewham.com/kitedesign/design.html
cerfvoliste:
The "French Invasion" brought the straight leading edge to America with as much impact on Sport Kites as the "British Invasion" had on Rock and Roll. And in addition, with their use of tail weights and a high aspect ratio, pitch based tricks became popular and more accessible.
That may be an over simplification, and there is still a lot to be said for for the curved, low aspect ratio kites.
@

Remember, No Matter Where You Go, There  You Are.
Doug S:
Stunt kite design questions peak my interest, and I just had to throw in my 2 cents.  Since I am an old timer regarding Stunt Kites, I thought I would offer a little firsthand observations and experience on the history side of stunt kite development.  Please note I am an old precision guy, so a lot of my contributions to stunt kite designs were directed to achieve a very controllable stunt kite that would fly on rails and respond as requested in our old time precision events.

Now for a little history.  In the late 1980s, stunt kites were large and loud, with straight leading edges and shallow sails.  Eight foot wing spans were the norm for competitive stunt kites, and a lot of upper body strength was needed to hold onto and compete with these kites in moderate winds.  Please note were didn't have the building materials that are available to us today.  So we were using fiberglass tubes and heavy pultruded carbon frames with ripstop nylon sails.  These kites were heavy as tanks!

Light wind performance was a real problem.  About this time, I threw my hat in the stunt kite design arena to see if I could design a better mouse trap.  Since I primarily fly inland off of the coast, having a stunt kite for light winds was very important to me to refine my competition skills.  So we found a practical engineering solution to silence the sail, which reduced the drag and increase the lifting potential of the sail.  To do so, we added a leach line and gently curved the lower portion of the leading edge just enough to tension the sail and leach line.  This allowed us to use the available building materials to fly in lower wind speeds.  The attributes of this type of kite complimented the precision and ballet competition demands at that time.  Others made their sails more efficient by adding more of a curved leading edge to tension their sails, without the use of a tensioned leach line.

In aerodynamics, everything is a tradeoff and a balancing act.  You donít get something from nothing.  The goal is to try and keep the flying attributes you like, without adding ones you donít.  With the addition of the leach line, we stopped the sail from naturally curving back.  This removed the sailís natural ability to washout at the tips preventing tip stall problems.  So we created silent kites that would fly in lighter winds, but would tip stall as soon as you slowed the kite down.  They turned great, but kept on turning and turning and turningÖ  To cure this problem, we added additional standoffs at the end of the wing spars that provided a fixed amount of tip washout.  Others increased the sail depth for the single standoff location.  In higher winds these efficient sails make the kite fly much faster and pull even harder.  The second set of standoffs helped control the forward speed, and were made longer for flying in higher winds.  It became quite common to have many different line weights and lengths to control the forward speed of the kite.

With the more efficient sails, our kite didnít want to stop when asked to in flight.  You make a kite more efficient, and it wants to keep on going and going and goingÖ  To resolve this problem, we move the center of gravity location lower and lower, until it ended up just above the midpoint of the sail, which is the point where 50 percent of the projected sail area is above or below this point.  The lower center of gravity also provided us with a huge wind window.  Then we started making the sail depth deeper and deeper and deeper...

This evolution continued into the late 1990s, at which time slack line tricks became the driving force in stunt kite development.  Some of the things we did to make our kites more efficient, were detrimental to slack line tricks.  So as the type of fly requirements evolved, so did the designs to meet the flyers competitive needs.  Stunt kites got noisy again and used straight leading edges again.  They also became smaller.  These changes with much deeper sails also drastically reduced the size of the wind window.

So in a generalized summary after my long dissertation, stunt kite designers who want to achieve certain flight attributes will use a curved or straight leading edge, depending on what they are trying to achieve with their design.

What has always interested me is finding a method to quantify the flying attributes of a kite, so one can compare these numbers, with numbers of other designs to see what makes them tick.  In my review of some posts by stapp59, it appears he has the same curiosity.  In the 1990s, I developed a program, Geokite, which is in a spreadsheet that reduces the attributes of a kite to a couple key numbers, which I then could use to compare and evaluate a variety of changes in the shape of a kite.  It just took a ruler and the program to do this.  For our kiting community and on May 4, 2012, I posted a link to download my program under the Kite Building and Repair Section of this great Forum.  Geokite took me many many hours to develop and refine, but it does a great job of reducing a design to key attributes.

If you what to see what makes your kite tick, join a few of us on the dark side, download the program, measure your kites and compare your numbers.  Please use my engineering and programing efforts to take your current designs to the next level.

Ok, now I am done preaching.  Have fun and enjoy!

Doug
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