Snake - 26-12-2012 at 04:45 PM
After some testing for my school project kite, I have concluded that measureing the pull and L/D of the kite is extremely difficult. Traction kites
are very unstable and don't like to stay still. Over a 30 second period I had the pull differ by 15-20 pounds. A small bridle adjustment made the kite
almost unflyable. Since I don't know much about non-traction kites and how they will preform and react to changes I have decided to pick a new project
for the science fair.
So now I have tons of fabric to make a kite and nothing to make. After seeing all the kites on http://2e5.com/ and finding this: http://www.laboratoridenvol.com/projects/singleskin/sk-nr.ht... , I became inspired to make a semi-single skin arc. Semi-single skin because the
leading edge will have cells to add rigidity and prevent leading edge collapse. Webbing will be running through channels sewn to the skin to take the
load off the skin and create a more efficient profile.
Here is a crude drawing of my design. The blue line is the skin of the kite, the black rectangles are webbing, and the red would be the opening for
air to enter the cells.
Proletariat - 19-1-2013 at 01:25 AM
Snake, you're obsessed with modding the arc. I love it! I was recently thinking of a Single skin with front "tubes" that would send air in channels
(from correct bridling) to help keep the kite rigid. The problem / benefit with your design is that it would have no inherent lift -- only that given
by AoA, wind speed and apparent wind. I think that's totally fine, I mean that's what my LEI does for the most part. But the arc becomes an arc
because of the lift created outward (radially) by the pressure gradient. So I think (and I'm just spitballin' here) that the arc is awesome because of
its stability. That stability comes from a) the twinskin + chord baffles (or whatever you call them). B) the solid sticks at the end and c) the fact
that the arc is constantly pushing itself out radially.
Any way, I love the idea of the semi-single skin kite. But I don't think arc is the answer (yet). The NPW5(and 9) that I've now seen in person have a
similar fold-over nose for rigidity and it works well (on an approximately square kite). I don't think it would work well on an arc.
What I would like to see on an arc is an air-filled baffle that provides rigid structure to an arc on both the leading edge and also along the chords.
If you could figure out a way to inflate struts front to back AND enforce a rigid Bernoulli foil shape of varying widths along the kite, that would
be one awesome (and really heavy) kite.
markite - 19-1-2013 at 06:46 AM
I think you may find all the variations of what you are thinking about are out there in one form or another. There are single skin totally soft kites
like the NPW, there are single skin with Battens like the ParaskiFlex and C Quad, there are open cells foils, closed cell foils and LEIs.
The LEI is somewhat similar in concept to the single skin with rigid battens except that is uses inflated tubes for the stiffness. With an LEI you do
not need a lower skin. The leading edge tube and the shaped skin give the virtual airfoil shape. If you added a pre inflated sealed leading edge tube
and battens to an arc then it's simply an LEI with a bottom skin which is un necessary (and as you mentioned heavy). If you add a tube and battens
that inflate with air movement you have to remember that air is essentially lazy and and needs to be driven into areas to inflate. Single line kites
and windsocks often have very large openings to get air flow as quickly as possible because they are somewhat stationary on a line and not not moving
forward. Older foils or simpler foils have a lot of openings along the leading edge to get air in. Faster foils reduce the leading edge intakes to a
smaller number and rely on a fast moving kite to get air in and cross vent to inflate but you'll see you have very light wingtip pressure if you over
steer a foil or fly in gusty winds how easy it easy to collapse a wing tip. So having a kite like an arc with self inflating struts would be difficult
to get them inflated from the start, it would take some flying and then to maintain pressure they would need to have the snorkle or one way intake
valves which need that pressure to keep them inflated. Having thin struts that were inflated by movement would not have much stiffness to them, they
would need to be a larger size. And right now the entire kite is a larger size and as it moves and inflates and seals closed with pressure the kite
outer skin shape is very stiff in flight. When you land an arc fully inflated it's tight (then gradually loses air as it sits on the ground). But the
maybe a more important question is why would you want to create the struts and stiffer leading edge on an arc - there would be benefits to a stiffer
design to gain low end performance as well as turning etc but then you negate the benefits by adding a lot of weight. Then in higher wind the flexing
of the arc shape is what helps absorb gusts etc - so a very stiff kite in higher gusty winds wouldn't be as forgiving.
I think it's great that you are considering different ideas and that could lead to a new design. I'm just hoping to give you some more things to
consider in your thought process. Keep the ideas flowing.
Bladerunner - 19-1-2013 at 11:26 AM
I wonder if you have looked into C quad Snake ?
They are a freakin' amazing kite ! I think it is the all too easily damaged spars were the downfall of this design. FAST and they fly very early. The
rigid frame makes them very responsive.
Simply finding a way to make the Cquad more indestructable would be amazing. Working with it's aspect ratio ALA Paraskiflex would be interesting as
well?
markite - 19-1-2013 at 04:27 PM
Sorry, tried to edit spelling on my earlier post and it's giving me a new response....now I have to think of something to say....
Snake - 19-1-2013 at 09:57 PM
I may have came up with a better design. Instead of an open front, I have the curved top skin like a NPW, but with a thin pieces of plastic to hold
the shape of the nose and prevent collapse. A stiff LE is needed to prevent collapse so the AoA can be lowered. The lower the AoA the bigger the wind
window. You also get a bigger depower range and a faster kite, all of which are needed if you want your design to be successful.
Bladerunner I have not tried anything with c-quad. Exploding spars put me off right away. Maybe adding several short spars with something flexible
inbetween would stop them from breaking when they hit the ground.
Proletariat - 19-1-2013 at 10:56 PM
Hey Mark, so I was wondering about the LEI design (I have a 13m), and maybe you can answer this question.
So the inflated leading edge acts as the front of a foil, but the bottom is obviously not flat, so air above / below the skin have to travel roughly
the same distance, thus negating the pressure gradient that generates lift. So in your previous post, you intimated that the lazy air underneath the
skin (and behind the leading edge bladder) is sort of stationary. So does this make sort of a "Bernoulli foil of air?"
Or does the proper "foil" part just not matter because the LEI uses mostly AOA lift to remain aloft?
Thanks in advance. I always wondered about this.
krumly - 20-1-2013 at 09:24 AM
Proletariat -
The idea of different transit distances for the air across the top surface of an airfoil as opposed to the bottom creating a pressure differential
that generates lift is a myth. Think about it like this: If you had a symmetrical airfoil, with no camber, and that theory were correct, a
symmetricall airfoil couldn't generate any lift. Inverted flight would also be impossible. But matter of fact, many aerobatic planes have symetrical
airfoils, and they do fly fine right way up of inverted.
For a pretty accesible explanation of how lift is actually generated by any foil, check out this link:
http://www.allstar.fiu.edu/aero/airflylvl3.htm
Bottom line, air has viscosity and air next to the wing wants to pull the air 'above it' along with it. An airfoil acts to divert a that mass of air
down off the trailing edge. This generates lift. The larger the mass of air, or the more that mass of air is accelerated downward, the higher the
reaction force (lift).
krumly