What charateristics improve a kite's turn?
Clint Frysinger
I am interested in any information about what causes a stunt kite to turn.
In particular, what design features make one kite turn tighter than
another? Does the bridle position (both up/down and side to side) affect
this or does the wing shape? How about standoff location? Any info is
greatly appreciated.
Clint
Andy Wardley
Although nothing is guaranteed on any kite, the general rules are as
follows:
*) High bridle = tracks well, flies forwards well, turns slowly
Low bridle = tracks poorly, flies slower, turns fast
(the dynamic bridle effectivelt combines the best elements of
each - see http://www.peritas.com/~abw/kite/bridle.html)
*) Inboard bridle = difficult to turn, therefore tracks well
Outboard bridle = easy and fast to turn, may oversteer, track badly
*) Inboard stand-off = kite is stable (because more air is pushing against
the outer panels)
Outboar stand-off = kite is less stable and more inclined to turn
*) Long stand-off = deep sail, stable and solid in the air.
Short stand-off = shallow sail, less stable
*) Slack sail = noisy, innefficent, flies slowly and sturdily
Tight sail = quite, smooth and slick but may be sensitive
*) Straight leading edge = tracks well, better at precision
Curved leading edge = turns and tricks well.
As you can see, there is a trade-off between the two extremes of any
feature. If you want a radical trick kite, you might have a tight sail,
curved leading edge, outboard and low set bridle and outboard stand-offs
(like the Stranger, for example) but you loose precision. At the other
extreme, a straight L/E kite with slacker sail, inboard bridle and stand-
offs (say the Nothshore Radical) tracks like it's on rails, has excellent
speed tolerance and great precision, but it doesn't trick well.
The colour of the kite is also important. Red light has a shorter
wavelength than blue light and thus causes less optical resistance,
allowing it to fly faster. This is why kites like the Phantom Elite
have a "fade" pattern, putting the lighter, more resistive colours in
the center and the darker colours on the outside, thus reducing optical
drag at the wingtips.
A
(looks like I'm 3 days too late with that last paragraph, eh?)
--
Andy Wardley <a...@peritas.com> **NEW** http://www.peritas.com/~abw
A responsible and professional individual who has no need for silly
comments, inane banter or bizarre "in-jokes" in his signature file.
Ian Newham
In article <5i2uar$9...@aoxomoxoa.peritas.com>, Andy Wardley
<a...@peritas.com> writes
>Clint Frysinger <frysi...@osu.edu> wrote:
>>I am interested in any information about what causes a stunt kite to turn.
>>In particular, what design features make one kite turn tighter than
>*) Inboard stand-off = kite is stable (because more air is pushing against
> the outer panels)
> Outboar stand-off = kite is less stable and more inclined to turn
Though taking them a long way out to give a high washout angle (usually
with multiple standoffs) with a deep sail can give good tracking but
narrows the window.
Some other factors I've come across in my newbie attempts at kite design
(and I stress I am a newbie at design - some of the following may be
complete tosh, but it seems to work for me)
* Distribution of sail area across the sail. In loose terms If you have
a comparatively small amount of sail toward the tips and plenty of area
near the spine the kite will tend to turn tighter. Doug Stout described
this some time ago in terms of the 'areodynamic centre of a half sail'.
The closer this got to the spine the tighter the turn. Have a look on
deja news for the article.
* Trailing edge shape can have an effect on the location of the
aerodynamic centre, see above.
* 'Stallability' of the wing tip. AFAIK, kites turn due to a combination
of two effects. In a turn the tip stalls (so slows down, the rest of the
kite will try to pass it, hence turn) and more of the centre panel is
presented to the wind (so tries to accelerate around the rest of the
kite and turn). In my experience kite with easily stalled tips tend to
turn quickly. ISTR someone saying that oversteer is actually just the
tips stalling.
That can be manipulated in a couple of ways, pointy tips on a trick kite
give a handy bit of tip stall/oversteer, while some team kites have
winglets which straighten out the trailing edge at the tip and
discourage tip stall drag - my last homemade has these and gives me a
decent turn without oversteer (theres many other factors re winglets,
have a look at Dave Lord's homepage)
PS for tweaking standoff posn, I use a couple of crocodile clips with a
bit of 3mm brass tube soldered onto them and some rubber tube over the
jaws. With them I can move the standoffs around without the need to make
extra holes in the sail.
Ian Newham email: i...@helen.demon.co.uk
http://www.helen.demon.co.uk
Peter de Jong
On 4 Apr 1997 12:16:31 GMT, "Clint Frysinger" <frysi...@osu.edu>
wrote:
>I am interested in any information about what causes a stunt kite to turn.
>In particular, what design features make one kite turn tighter than
>another? Does the bridle position (both up/down and side to side) affect
>this or does the wing shape? How about standoff location? Any info is
>greatly appreciated.
>
>Clint
Hi
Beside all the good answers you got already there is another factor
that no one counts in when designing kites. I'll try to explain.
first there are these aerodynamic facts:
A tight sail flies faster than a billowed sail
If you put a load on a wing it wants to go faster.
Suppose you suddenly want to make a right turn. You tug the right side
of the kite, causing the wingload of the right wing to increase. Now
the right wing wants to go faster, causing the kite to want to go
LEFT. This effect slows down the desired right turn.
If you look at a hangglider you can see the solution for this: they
got a little keel between the spine and the sail. This allows the sail
to shift left and right a bit. If the right wing gets more load than
the left it will shift to the right, billow out more and the left wing
will tighten. This compensates the undesired effect.
In some of my kites with no stand-offs I just don't put the spine in
a tunnel. this is enough to allow the sail to slide a bit.
There are more ways to allow the sail to shift in turns, like using a
little mast at the back with a elastic line running over it to pull
the sail back like a standoff does, but I guess that would interfere
when doing tricks.
Maybe a small keel and flexible standoffs (thin glassfibre in a curve,
about 1.5 times the length of the straight one) would do the trick..
Regards, Peter
Greetings from Holland
Peter de Jong <p...@xs4all.nl>
A&F Custom Kites Werkhoven NL <http://www.xs4all.nl/~pdj>
Ian Jones
On Tue, 08 Apr 1997 15:03:54 +0100, Richard Bettis
<rbe...@fats.demon.co.uk> wrote:
>
>Actually, red light has a longer wavelength than blue, therefore has a higher
>resistance. White is a mixture of all wavelengths, while black, of course, is
>no light at all. Black is thus the "slippiest" colour, and hence the
>true(r) reason for the effect of the fade.
>
Thought I'd test this so I made a black kite and flew it in the middle
of the night without lights to see if it was faster.
But I still don't know because I could't see a thing.
Campbell, James E
In article <3347967...@news.xs4all.nl>, p...@xs4all.nl (Peter de Jong)
wrote:
> On 4 Apr 1997 12:16:31 GMT, "Clint Frysinger" <frysi...@osu.edu>
> wrote:
>
> >I am interested in any information about what causes a stunt kite to turn.
> >In particular, what design features make one kite turn tighter than
> >another? Does the bridle position (both up/down and side to side) affect
> >this or does the wing shape? How about standoff location? Any info is
> >greatly appreciated.
> >
> >Clint
>
I'd recommend that you look at the most recent edition of American Kite
Magazine for Andy Preston's explanation of the physics involved. Although
he doesn't get into the issue of vector mechanics, his explanation is
right on target from the intuitive point of view. It's good reading and
it will help you get started on the right track.
--
James E. Campbell (jcamp...@msmail3.hac.com)
Hughes Aircraft Company Leading Edge Kites
Richard Bettis
In article: <5i2uar$9...@aoxomoxoa.peritas.com> a...@peritas.com (Andy Wardley)
writes:
> The colour of the kite is also important. Red light has a shorter
> wavelength than blue light and thus causes less optical resistance,
> allowing it to fly faster. This is why kites like the Phantom Elite
> have a "fade" pattern, putting the lighter, more resistive colours in
> the center and the darker colours on the outside, thus reducing optical
> drag at the wingtips.
>
Actually, red light has a longer wavelength than blue, therefore has a higher
resistance. White is a mixture of all wavelengths, while black, of course, is
no light at all. Black is thus the "slippiest" colour, and hence the
true(r) reason for the effect of the fade.
This is actually quite a pronounced effect. A little extra drag at the wingtips
can significantly improve the way a kite stalls. This is (presumably) why the
Tramontana has those little red wingtips.
:)
(my sig has never been more correct....)
--
+=============================================================================+
| Richard Bettis | "I make no warranty with respect to this |
| <rbe...@fats.demon.co.uk> | statement and disclaim any implied/explicit |
| | suggestions of usefulness for any purpose" |
+=============================================================================+
Dave Lord
"Clint Frysinger" <frysi...@osu.edu> wrote:
>I am interested in any information about what causes a stunt kite to turn.
>In particular, what design features make one kite turn tighter than
>another? Does the bridle position (both up/down and side to side) affect
>this or does the wing shape? How about standoff location? Any info is
>greatly appreciated.
>Clint
It is my opinion that when the tips stall on a stunt kite it virtually
quits turning. When the angle of attack of the kite is decreased for
flying in light air the tips tend to stall in a turn and the kite
refuses to finish the turn. Washout at the tips keeps the tips from
stalling and you can get good turns with a lower angle of attack
(higher bridle setting). You can try this yourself, take a kite with a
tight skin and short or no standoffs and fly it in high winds. You
will be able to set the bridle low enough for the kite to fly and make
turns. Try it again in low winds with the bridle adjusted so it can
fly in the light winds. The kite will be reluctant to turn and may
flutter to the ground. Add a short standoff well outboard to provide
washout and notice the dramatic improvement. I don,t believe anyone
really understands what happens aerodynamically over the full range of
conditions but only know what works under the limited range of
conditions a particular kite flies in. I have talked to Peter Lynn
about this and he said that he agrees. He said that in an effort to
make a more efficient traction kite he experimented with variable
bridle systems that after launch reduced the angle of attack for less
drag. He said that as you came into the range of angles of attack that
airplane wings fly at steering by pulling on either line was not very
effective and in some cases reversed. He said he did not understand
what was happening nor had he talked to anyone who did.
Dave Lord
O1withwind
Clint,
The spring issue of American Kite has a comprehensive article on this
subject guided by Andy Preston the creator of the Stranger and Psyco by
cobra kites. Check it out!
PEACE&WIND
o1wit...@aol.com