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Author Topic: iFlite Question  (Read 1114 times)
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skyguy48
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« on: February 25, 2014, 02:32 AM »

I flew a friend's iFlite last year at the Air Force Museum in Dayton Ohio and fell in love. I had never tried indoor flight and had a blast!

My lovely wife bought one for me and it arrived yesterday,  Smiley
Worked out great, as I recently found a place where they are willing to let me have access a few evenings per month.  Smiley Smiley

The one I flew was vented, which is what I now have.
Newbie question:
Why would an indoor kite be vented? (Zero wind!) And what might be the difference in flight between a vented and standard version?

TIA

Bill

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thief
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« Reply #1 on: February 25, 2014, 04:50 AM »

the vented version of the iFlite(s) have a better glide than the standard version does....
The iFlite II only comes in vented version for that reason....

Another mind twister is the vented Ginga..it is a low wind outdoor active kite that is vented...the vented is just a sweeter flyer - it is not a high wind version!
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skyguy48
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« Reply #2 on: February 25, 2014, 06:23 AM »

Thanks Thief!
That's what I was hoping for,
So a vented kite glides better..... weird.
Just the opposite of what I would have thunk. Goes to show what I know.  Cheesy

Anxious to go play now.
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thief
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« Reply #3 on: February 25, 2014, 06:37 AM »

yep...the vented glides better...
same idea as the Willi Koch woven deltas have more lift than a standard delta because of the surface area being broken up..
plus they look cooler too.....Patrick did try a few iFlites and IIs with two smaller holes, one on each side of the spine and they did not work as well...
This "venting" is also on Horvath's models as well....

Go fly!

btw: I strongly advise you to have multiple iFlites in your quiver....they are one of the most "wanted to try" kites out there....and you can carry a bunch easily too Wink
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Allen Carter
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« Reply #4 on: February 25, 2014, 09:16 AM »

Venting disrupts the airflow over a surface, causing turbulence and slowing the kite. This helps a sport kite in high wind, but can also help a very efficient gliding kite to slow it's forward flight and make for a longer glide. The iFlight is so light and efficient that the loss of lift is less of a factor.
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thief
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« Reply #5 on: February 25, 2014, 09:26 AM »

the iFlite is very very light and some flyers swear that they can tell the difference between a vented and a standard one......

personally i like the look of the standard ones more Wink
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Doug S
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« Reply #6 on: February 25, 2014, 06:01 PM »

skyguy48,

I have been thinking about your question all day, and the following provides my thoughts.

We need a little background before we talk about the iFlite II.  Recent research has changed our thoughts on how airfoils work, as published by David Anderson and Scott Eberhardt of Boeing in 2001 and 2009.  The following link provides access to one of their recent articles on the subject.

https://drive.google.com/file/d/0B_TPx1W-lkmSclJkQ1FEZFNrRHM/edit?usp=sharing

Simply put, the angle of the sail to forward flight has more to do with generating lift then the actual shape of the airfoil.  This is why our little thin surface glider kites work so well at their very light sail loadings, defined as weight of the kite divided by its sail area.  The difference in air pressure at the trailing edge and the air flowing around from the upper surface to the lower surface causes the rear of the kite to want to push upward and pitch the nose downward around the neutral point.  In simple terms, the neutral point is just a point where 25% of the sail area is in front and 75% of the sail area is in back.  We use the neutral point as a point of reference for the center of pressure and to make measurements.  The actual center of pressure moves forward and backward, based on the angle of the sail to forward flight.  To compensate for the air trying to push our glider kite into the ground, we use a bowed or flexible center spine that induces a slight curve in the center of the sail, which provides the equivalent of a slight amount of up elevator in a flying wing.  With a flexible center spine, the bridle and the air pressure at the back of the sail cause the sail to curve upward.  Also, we locate the center of center of gravity at a close point behind the neutral point of the sail to assist in holding the tail from rotating at the gliding speed of the kite.  If a glider kite has no slight curve in the center spine during flight and/or the center of gravity was located at/or in front of the neutral point, our glider kites would just dive and not recover.

Now to your question regarding the iFlite II with the hole in the middle.  In the center span of the sail that is the width of the hole, the air flowing over the sail does not see a hole, but sees two different lifting surfaces in the limited width of the sail before and after the hole.  This gives the air the ability to flow around the sail at the beginning of the hole, where the air reacts like it's the trailing edge of the sail.  When the air flows over the sail at the rear of the hole, it's reacts like it's the leading edge of a new sail.  For this limited span, the air movement is acting the same as it would with a Canard glider kite.  Also, due to the slightly curved nature of the center spine, the angle of the front portion of the sail in front of the hole is angled upward more that the rear portion of the sail behind the hole, as is the case for a Canard glider kite.  A glider kite with many smaller holes of the same equivalent area would not perform as well, where the smaller holes would induce more turbulence to the flow of air, thus reducing the effective area of the sail that can create lift.  The glider kite with many holes would have the same effect as using spoilers on a sailplane, which are designed to destroy the lift over that portion of the wing.

The joy of our little glider kites is that our flying provides real time feedback about performance, and we can make minor trim changes to dial in each unique glider design.  In my case, I use documented theory and a few simple computer programs to help understand what is happening, so that our starting point and changes we make can be measured.  The actual performance of the glider kite is all that matters.

Just my thoughts,

Doug
« Last Edit: February 25, 2014, 06:18 PM by Doug S » Logged

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skyguy48
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« Reply #7 on: February 26, 2014, 12:58 AM »

Thank you gentlemen.
I flew a little bit in my living room and was most impressed with the ease of flight. Very nice kite.
I don't own any very light line, so I used some sewing thread. I was ok, but I'm curious what sort of line others might recommend.

Thanks again! Great group here!
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Doug S
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« Reply #8 on: February 26, 2014, 03:43 AM »

skyguy48,

I would recommend 10 to 20 lb. spectra line.  I personally use 10 lb. spectra in yellow so that I can see it, although I still step on it at times while flying.   The link where I purchased my flying line is provided below.

http://www.cabelas.com/product/PowerPro-Hi-Vis-Yellow-Line-150-150-Yards/739094.uts?Ntk=AllProducts&searchPath=%2Fcatalog%2Fsearch.cmd%3Fform_state%3DsearchForm%26N%3D0%26fsch%3Dtrue%26Ntk%3DAllProducts%26Ntt%3Dpower%2Bpro%2B10%2Blb.%2Bspectra%26WTz_l%3DHeader%253BSearch-All%2BProducts&Ntt=power+pro+10+lb.+spectra&WTz_l=Header%3BSearch-All+Products

When you obtain your line, you want to tie a 1/2 in. tail at the end of the loop that you use to connect your line to the kite, so you can pull on this tail to remove the larks head knot from the bridle connection knot on the kite.  The main loop should be about 2 in. from the 1st knot at the tail end to the 2nd knot, which provides enough of a loop to make a larks head knot.  I also use a small spool that allows the line to come off easily on one side, which is the type of spool used by fighter kite flyers.

Just my thoughts,

Doug
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thief
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« Reply #9 on: February 26, 2014, 04:12 AM »

i use 50# spectra....a weird line that came with a Guildworks Minergy Deca many years back.....i like having a thicker line that is easier to handle...
Damon Meheux's feathers come with line that is made for tying flies.....super thin...but quite strong.....

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stapp59
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« Reply #10 on: February 26, 2014, 06:26 AM »

I'ts great what can be done these days with aerodynamic engineering, computer modeling, and wind tunnel testing.  In the end prototypes are built, tested, and tweaked to make a solid working design. 

My skills limit me to building, testing, and tweaking with a basic understanding of the underlying principles. There is a wind tunnel on campus, do you think?  Oh never mind.  Roll Eyes

Carry on Doug, I like reading your posts.  Smiley

In my case, I use documented theory and a few simple computer programs to help understand what is happening, so that our starting point and changes we make can be measured.  The actual performance of the glider kite is all that matters.

Doug
« Last Edit: February 26, 2014, 09:00 AM by stapp59 » Logged

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Doug S
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« Reply #11 on: February 26, 2014, 04:17 PM »

stapp59,

Thank you for the reply and we come at design kites in a very similar manner.  Due to my engineering background, I just like to draft the shape of a potential new design in AutoCAD, and then input the final concept into another program to determine where the initial balance point should be.  It has been my preference to waste computer time and paper, than our expensive kite building materials.

I enjoyed your comment, but I don't think our glider kites could survive a traditional wind tunnel test. Cheesy

If you are interested in low Reynolds Number aerodynamics, Dr. Michael Selig is doing great things at the University of Illinois at Urbana-Champaign campus.  I have been following Michael's work since we both flew RC Sailplanes back in the 1980s.  The following provides the link to his Subsonic Aerodynamics Research Laboratory at the college:

http://aerospace.illinois.edu/m-selig/uiuc_lsat.html

skyguy48,

Sorry for hijacking your thread.

Later,

Doug
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stapp59
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« Reply #12 on: February 27, 2014, 03:06 AM »

Doug,

Thanks for the link to Dr Selig's work!  The traditional Aero classes I took did not address low RN situations except for a brief mention. 

A step up to Autocad would be useful.  I have a 2D CAD app I've been using for years though it has a limited toolset. 

+1 on the wind tunnel  Cheesy

Cheers,
Steve

Sorry Skyguy48. Those gliders look really good though...

I enjoyed your comment, but I don't think our glider kites could survive a traditional wind tunnel test. Cheesy

If you are interested in low Reynolds Number aerodynamics, Dr. Michael Selig is doing great things at the University of Illinois at Urbana-Champaign campus.  I have been following Michael's work since we both flew RC Sailplanes back in the 1980s.  The following provides the link to his Subsonic Aerodynamics Research Laboratory at the college:

http://aerospace.illinois.edu/m-selig/uiuc_lsat.html

Doug
« Last Edit: February 27, 2014, 06:13 AM by stapp59 » Logged

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skyguy48
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« Reply #13 on: February 27, 2014, 01:45 PM »

No hijack worries here guys.  Smiley  Tons of great information.

Found some hardly used 35# spectra in the bottom of a bag, so will be trying that out this weekend.

Thanks again for all the help.
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