The technical aspect
- The kite (carrier)
- The lifting messenger
I propose you to build a Rokkaku. Let me tell you at first that the Rokkaku was
initialy design for kite fighting in japan. You can then imagine it is very effective and strong,
and will be quite reliable if used as a carrier. He is widely used for photography from
a messenger, too. This is the kite we need !
The size of the rokkaku depends on the wind you are used to face in your countryside,
and the weight of the glider you intend to tow. For light airplane (hlg, and glider up to 1 kg), I think that a 2m high
Rokkaku is to be used. The sail area is great enough to keep the line taut, and the kite is than
still easy to handle when drew up. He will fly even with quite strong winds, to tow heavier gliders.
A bigger kite would be usefull for wider sailplane, or light winds, but then the stuff around the kite
would be quite more unusual : strong line, big carbon spar....
You could also use a big "delta" kite, you may find plan for such kite on the web...
For a first attemp, a 2m rokkaku looks good. If you are interested, you can built a family of rokkau, with
as many size as many wind force.
You need to cut half the kite in a carton board, in order to have the shape (a "template" would be the accurate word ?)
and then be able to draw it on the fabric, and its symetric side. For this follow the small plan display on this page, with
L=40cm for a 2m high kite. Add 1cm of spi fabric all around the different patch, in order to make an hem on the edge.
All the spar will be made of 8mm carbon or hard wood. To allow the rokkaku to fly, it needs diedral to give it its stability.
For this you have to bend the horizontal spar as exposed on the drawing, by streching a string between its extremities.
Without this diedral, the kite would not be reliable.
And then the bridles : they are responsible of the flying skills of the kite.
You need to be quite precise in the lengh of each one. Lets have a look on the drawing !
You have to make triangles A,A',A" and B,B',B" with AA"=A'A"=BB"=B'B". The points A, A', B and B' are the middles of
each half span of the kite. Then a small bridle, whose lengh must be adjustable, links A" and B". The
kite line will bee hanged in A". You can then fly it !
And now, try the sewing machine !!
The lifting messenger
The messenger must be built with care to be reliable. The principle of all the different messengers is the same, but there are many
sort that exists : I propose you one that I have tried. It climb until it reaches a stop on the line, and then shut
down and go back down. Here is a precise drawing of the mechanism.
It is not me that draws this, but
Anthony Thyssen, whose web site is
really interesting for the messenger builder. I made the same as him, but with all lengh x1.5.
Take a look on his site !
Apart from the shuting down mechanism, the sails on the messenger are the same as on the kite.
This sail is only smaller, and the carbon spars are not so stiff : 6mm for the body, and 4mm for the sail.
Go on his site, and then tell me if you have unsolved problems about glider towing.
You need to know some things to use this device, that you would learn by using it, but by knowing it
before, you will save time...
- The kite itself needs to be trimmed according to the wind of the day. Here are the main principles.
In fact, it looks like quite a sailplane : adjusting the lenght of the A"B" string
causes the same effect as if you move the CG of your glider. Lenghten it is the equivalent of moving the CG aft, it becomes more stable and soft , while shorten it
is the same as moving it back, the quite is more franc and pull more on its line .
Indeed, you will also change the pulling on the kite
line by adjusting the string. It depends on the strengh and the regularty of the wind, you may need more or less pulling, and more or less stability, also...
Giving more diedral by strechting the string on the horizontal spar will create greater stability, but less pulling.
- The lifting messenger has to achieve 3 goals : climbing well on the line, shutting down properly, and coming back quickly on the earth.
So you need good gliding skills of the line, and reliability of the shutting system. You can use "shrouds" on the messenger sail, in order to
trim its angle with the wing according to the angle of the line with the ground.
And always keep in mind that a coming down messenger can hurt !
That's all, now you can try it !
Anyway, enjoy your flying with your kite !!!!