GWTW Forum
December 17, 2017, 01:50 PM *
Welcome, Guest. Please login or register.
Did you miss your activation email?

Login with username, password and session length
News:
 
   Home   Help Forum Info Login Register Chat  
Welcome to the GWTW Forum.
Guests (non-registered users) can view the forum but are unable to post.  If you don't have anything to say then why would you bother to register?
One of the most popular sections of the GWTW Forum has long been the Swap Meet.  A great place to sell old, seldom flown kites or to get great deals on used (gently flown) kites.  Only registered users can see the Swap Meet section, let alone wheel and deal.  1000's (literally) of kites have changed hands thanks to the Swap Meet.
There are several more benefits to being a registered user, but you'll have to join our little community to find out all the "secrets".
Questions or concerns? Contact Steve ... just drop an email to: forum.gwtwkites@gmail.com

Pages: 1 2 [3]   Go Down
  Print  
Author Topic: Gliders  (Read 54266 times)
0 Members and 1 Guest are viewing this topic.
HK-guy
Trade Count: (0)
**
Offline Offline

Posts: 25

Location: Hong Kong

« Reply #30 on: January 23, 2017, 07:48 AM »

Thank you so much for the lesson Doug. It's so clear and easy understand.

About the Dihedral. How about the flex of the spars that create a kind of dynamic change on this angle, provide active stability by the wind or line pull?
The Dihedral seems never be a fix angle right?
Logged

Always Night-Flight, Mostly No-Wind, Sometimes Gusty, Never Smooth...... I'm still like flying.
Doug S
Trade Count: (0)
****
Offline Offline

Posts: 570


Location: Byram Township, New Jersey

« Reply #31 on: January 23, 2017, 11:35 AM »

HK-guy,

Great question!  The following provides my thoughts.

For my Bird of Prey glider kites, I measure the static dihedral angle with the glider kite held vertical by the nose, with the nose pointing up.  This removes the effect of gravity on the wings, which droop slightly at the wing tips when not in flight on a glide.  Consider this to be the minimum dihedral angle, which will increase under the conditions described below.

For a given dihedral angle, the sail area that you see looking straight down (projected sail area) is the area of the sail that is providing lift for flight.  Think of this area as the shadow it projects on the ground.  The sail area you see looking from the side, from the wing tip to the center spine, provides stability like the vertical surfaces on an airplane.  With too little dihedral, the glider kite will not want to track in a straight line, and may drop a tip and spin on its own without line commands.  With too much dihedral, the glider kite will just want to fly straight, and be hard to turn or spin under line commands.  I have found that 20 degrees overall or 10 degrees on each side works for me when measured in a static position, as described above.  Regarding sail loading, we use just the projected sail area to accurately calculate the area of the sail that is lifting the mass of the glider kite.

Regarding the flex of the wing spars in flight, the more the wings flex upward, the more stable the glider kite will be.  The increase flex makes it harder for a glider kite to climb under line tension.  As indicated above, the ability to turn will be reduced.  The more flex also reduces the amount of projected sail area providing lift, thus increasing the sail loading.  An increase in sail loading will cause the glide speed to increase.  It also will increase the minimum speed where the glider kite will stall.

As an example, my initial prototype for the Bird of Prey 36 had a CST DPP 0.039 in. OD carbon tube frame.  As indicated in my May 18, 2014 post on this forum, this initial prototype weighed only 5.7 grams and had a beautiful slow glide due to the very low sail loading.  The problem was that under load of the flying line for the climb, I couldn’t get this initial prototype to climb above 15 feet under no wind conditions, because the wing spars would flex too much, allowing a large portion of the sail area to washout.  The turns were slow because the wing tips would flex under load and introduce more stability.  I changed the frame to the next size up of the DPP carbon tubes (CST DPP 0.059 in. OD carbon tube), and this Bird of Prey became an entirely new glider kite with an incredible climb and responsive to line commands.  The average weight of the Bird of Prey 36 with this frame and the current run of Cuben fabric is about 8 grams.  With the stiffer and heavier frame, this glider kite became my go to kite for Indoor Single Line Ballet competition.  Indoors, I have flowing this glider kite over 40 feet above my head in the Wildwood Convention Center.

For carbon tubes with a diameter equal to or less than 0.157 in. OD, I use the CST DPP carbon tubes because of their extra strength and resilience, with a lighter unit weight than other materials available to us in the kiting community.  As a side note, I cut down the CST DPP 0039 in. OD carbon tube frame and used it in my Bird of Prey 24S, where the “S” stands for stiff.  The original Bird of Prey 24 with the solid 0.03 in. OD carbon rods is a forgiving little glider kite, but the frame was a little more flexible than I liked.  With the stiffer frame, the total weight stayed the same, but it now flys like a smaller version of the Bird of Prey 36.  For the standard version of the Bird of Prey 24, I switched to the CST 0.03 in. OD carbon rod, which provides a little more stiffness than this size rod that can be obtained from other sources.  For fun, I also have versions of the Bird of Prey 24 that I play with that have the CST DPP 0.028 and 0.033 in. OD carbon rods.  For my Bird of Prey 18, I use the CST DPP 0.028 in. OD carbon tube frame, which provides the right amount of stiffness and flexibility, with a total kite weight of only 1.3 grams.

For my Bird of Prey glider kites, I have a cross line that maintains the desired dihedral angle, which is connected to each wing spar at the center of pressure horizontal location for the sail, as measured from the center spine.  Between these two connection points, the wing spars and sail are relatively stiff.  Beyond the two connection points on the wing spars, the wings flex under load, as dictated by the strength of the selected wing spars.  This allows the wing tips to move and washout for turns under line commands.

Yours in kiting,

Doug
« Last Edit: January 23, 2017, 02:51 PM by Doug S » Logged

"We never really grow up, we only learn how to act in public."
HK-guy
Trade Count: (0)
**
Offline Offline

Posts: 25

Location: Hong Kong

« Reply #32 on: January 24, 2017, 11:20 AM »

Thanks once again for the detail talks Doug.
I just found your last post was 2 years ago and think that my reply may not get noted.

So, the spars flexibility is really a matter (not just the weight, balance is important).

I don't think I can get the exact materials to fit the strength in spec. But at least now I got the picture in mind what I have to look for.
If I prefer a glider have better climb ability then the stability on the same set of frame. Maybe I can play with the cross line, or spreader position to keep the Dihedral (at least can keep it at the nose part right?).
Logged

Always Night-Flight, Mostly No-Wind, Sometimes Gusty, Never Smooth...... I'm still like flying.
Doug S
Trade Count: (0)
****
Offline Offline

Posts: 570


Location: Byram Township, New Jersey

« Reply #33 on: January 25, 2017, 11:03 AM »

HK-guy,

For a better climb with an existing frame, move the bridle connection back towards the tail a slight amount.  With this moved location, the response from line commands for turning will be reduced slightly.  A stiffer frame will give you a better climb without changing the bridle connection point.  For my Bird of Prey glider kites, it would be my suggestion not to change the dihedral angle.

Yours in kiting,

Doug
Logged

"We never really grow up, we only learn how to act in public."
thief
Global Moderator
Trade Count: (+30)
*****
Offline Offline

Posts: 5220


Location: North Shore of Massa-WHO-setts

WWW
« Reply #34 on: January 25, 2017, 11:21 AM »

as Doug says:
tweak the bridle to climb more....
Personally i LOVE a kite that climbs more than a straight out glider for outside....i can fly it in a smaller arena and have more fun....the first gen Plutz gliders that ceewan made were phenomenal climbers but not as good at climbing...those had a sliding lead weight on them to move the center of gravity to work with as well.
a 61/49 from Ken McNeil is a great, much bigger, climber xUL kite (eXtra UltraLight wind)...not as much of a glider and can drop like a stone if you drop the line tension.
you might like to check out this blogspot where I have listed out many of the xUL kites out there and have flight notes about most of them.
http://windsweptkites.blogspot.com/2013/11/listing-out-xul-single-line-kites.html

Dihederal is most commonly referred to as the hard plastic bit that slides on a spreader and accepts the proximal ends of spreaders.   They are forced into their defined angle.....


But...a kite like Ramlal Tien's Oiseau does not have that fitting, but still has a slight angle back of the wings...in this case there is a couple of rods that are on the back of the kite that are forcing the wings back down...this is a more active setup and can be tweaked for wind speeds and kite activity levels as well.

Logged

Kites kayaks & corgis again!!!
HK-guy
Trade Count: (0)
**
Offline Offline

Posts: 25

Location: Hong Kong

« Reply #35 on: January 25, 2017, 01:39 PM »

Dihederal is most commonly referred to as the hard plastic bit that slides on a spreader and accepts the proximal ends of spreaders.   They are forced into their defined angle.....

But...a kite like Ramlal Tien's Oiseau does not have that fitting, but still has a slight angle back of the wings...in this case there is a couple of rods that are on the back of the kite that are forcing the wings back down...this is a more active setup and can be tweaked for wind speeds and kite activity levels as well.

There're always so much to learn.......
Thanks thief for your link. (but seems some of your pic not show correctly)
And Doug your kindness advise.
Logged

Always Night-Flight, Mostly No-Wind, Sometimes Gusty, Never Smooth...... I'm still like flying.
thief
Global Moderator
Trade Count: (+30)
*****
Offline Offline

Posts: 5220


Location: North Shore of Massa-WHO-setts

WWW
« Reply #36 on: January 25, 2017, 07:02 PM »

Ah thanks! Holdovers from pix growing out of Picasa...
Logged

Kites kayaks & corgis again!!!
Pages: 1 2 [3]   Go Up
  Print  
 
Jump to:  


Support the GWTW Forum

Kite Classifieds Ad
Kite Classifieds

A Wind Of Change
A Wind Of Change

FMKS
Fly Market

A Wind Of Change
skyshark

Blue Moon
Blue Moon Kites

Our forum is made possible by the good folks whose ads appear above and by the members of our community (PayPal donation button at top)
In case you missed it each ad is linked to the sponsors web site.  So please, take a moment and visit our sponsors sites as this forum wouldn't be possible with out them.
Interested in running an ad for your business or kiting event?  Contact Steve at advertise.gwtwkites@gmail.com for a quote.

Cal Custom

Powered by MySQL Powered by PHP Powered by SMF 1.1.8 | SMF © 2006-2008, Simple Machines LLC
SimplePortal 2.2.1 © 2008-2009
Valid XHTML 1.0! Valid CSS!