From: pat@cs.strath.ac.uk (Pat Prosser)
Newsgroups: rec.kites
Subject: FlowForm
Date: 11 Nov 92 13:58:39 GMT
Organization: Comp. Sci. Dept., Strathclyde Univ., Glasgow, Scotland.
Originator: pat@kelvin-02


                         FLOW FORM (Enlargement)


>>I've had a close look at the big flowforms Art Ross from Vancouver
>>builds.  He has built a few in the 500-1500 square foot range, along
>>with smaller sizes.

>1500 feet^2?  That's a BIG kite.

Yes .... I suppose it is. On Sunday (8th) I was flying in Gourock.
I put my FlowForm up at 12.00 and ATTEMPTED to bring it down at
17.00 It took two of us to walk it down on 400' of line. My FlowForm is from
Rawlings book and is 2m by 1.5m (approx). So its not big,
but in a strong wind it pulls like a horse. In a medium wind I fly 
it on 600lb line.

However, 500 to 1500 sq feet is not unusual. Look at the festival 
kites, and in particular Martin Lester's MegaLegs. They are about 50' long.

>>The main change is to make the airfoil thinner and move the high point
>>forward.  There's not a lot of science necessary; flowforms are
>>relatively forgiving about cross-section.  Guessing from only having
>>seen his kites, the body proportion is roughly 3-4 units span to 5 units
>>chord.  He also uses longer "legs" than the book plans show, partly for
>>stability and partly for effect.

>By legs I suppose you mean the keels?

No, he means legs. The FlowForm has a "sort of" U shaped trailing edge.
The centre of the "U" is open, and the two ends are (generally) closed.
In Lester's legs (and Natelie's legs) these sections are extended, and
the "heel" on each foot is open.

>5:4 sounds like most of the flowforms I've seen; mostly but not quite square.
>(sort of like a TV screen)

Mines approx 4:3, so it is relatively high aspect ratio. It is also
"flat" rigged (as apposed to "crown" rigged).

>>Cell width (the spacing between ribs) doesn't scale linearly for either
>>flowforms or parafoils.  For 30 square feet it shouldn't be a problem,
>>but for larger foils you need to put the ribs proportionally closer
>>together to get the cross-section to keep its shape.

I don't agree on this. The FlowForm (lets call it an FF) scales up without any
problems. Again, refering back to the MegaLegs there are only 3 keels and 5 risers.
There appears to be no attempt to increase the number of risers to improve the section.
In my FF I have 5 keels and 9 risers. I feel confident that I could scale this
up to probably 2 or 4 times the dimensions (4m x 3m or 8m x 6m) without having to alter the
the shape, or increase the number of keels or risers. However, I rekon that the 4mx3m would
require at least 4 people to land it in a strong wind. I have thought about building a 
4mx3m, but it might be too much of a problem to manage on the site ... but I'll probably do
it anyway ... in black!

I strongly recommend the FF in Jim Rowlands book on soft kites. I think that his FF 
is the best flying soft kite that I have. Of all the soft kites that I have
(1 FlowForm, 3 parafoils that I have built, 1 TakoTako, 1 MantaRay, 1 small foil) the FF flies 
in the least wind, is the most stable, and flies in the highest wind (I have not
yet found an upper limit). Next year I expect that the FF will become my regular 
"travelling" kite with 500lb dyneema (at present it is the small 1.5m x 1m foil with 300lb
spectra).

>Got any suggestions (Pat, are you out there?  This means you!) for dealing
>with, laying out, cutting, etc., the large pieces of fabric for the
>top and bottom of the kite?  I mean this in terms of laying it out, marking,
>cutting, etc.  I'm not really used to huge pieces of fabric, but I have
>no interest in a little flow form...;-)

My 1st suggestion would be to buy Jim Rowland's book. His FF looks something
like the plan below.

                           Leading Edge

          -------------------------------------------------
         |           |            |            |           |
         |           |            |            |           |
         |           |            |            |           |
         |           |            |            |           |
         |           |            |            |           |
         |           |            |            |           |
         |           |            |            |           |
         |           |            |            |           |
         |           |            |            |           |
         |           |            |            |           |
         |           |            |            |           |
         |           |            |            |           |
         |           |            |            |           |
         |           |            |            |           |
         |           |-------------------------|           |
         |           |                         |           |
         |           |                         |           |
         |           |                         |           |
         -------------                         -------------

In his plan he has three pieces for the back, and 3 pieces on the front. 
I use 4 pieces. That is, where JR uses 1 piece for the centre section I divide this in 2.
This makes it more manageable, easier to scale up, and improves the build quality (because
it is neater to join the risers to the top and bottom surfaces when you are also 
joining together two pieces of cloth anyway). 

I also work from left to right. That is, I do not do the top (sewing the top sections together,
with their risers) and then do the bottom (join top to bottom with keels), neither do I do the left
half then the right half then join them (I used to do this but there is a neater way). What I now
do is start from the left, all the way to the right, and when I get to the last seam (lets say top
left to last risers) I turn the kite in on itself, so that I make that last seam inside out. When I
do this the whole FF is contained within a single cell. I then turn that inside-out, and close off
the trailing edge. So, when it is finished there are no outward facing seams, and the kite looks 
excellent (and everyone wonders how the hell you built it, as it appears to defy solid geometry).
I have now used this technique twice, one on the 100sqft foil, and on the FF. The result is
fantastic. 

Building a parafoil is a huge pain in the ass, and building a FF is a pain in the ass.
The reason the FF is less of a pain is because there are less parts (only 5 keels above, only
9 risers, in the parafoils I have 13 risers and 21 keels). It is largely a repetitive task, so
make templates for: the risers, the keels. When you make the keels make sure that you get the weft
and weave in the correct orientation. That is


        \                / 
         \              /
          \            /
           \          /
            \        /
             \      /
              \    /

Assume that the / is the trailing edge of a keel. Cut the cloth such that the natural length of the
cloth lines up with /. You should then cut a strip of ripstop (again lengthwise) and hem the
leading edge \ of the keel with that strip. That way you will have a keel that will not distort
under load, and will be durable (and you will have a nice kite for a long time :-).
So, this is obviously expensive. You dont do a "best fit" to maximise usage when cutting cloth.
You do a "best fit" that maximises the orientation/strength of the finished product. In my FF 
which is 2m by 1.5m (approx 3m square) I need 12m of ripstop. If I double the size I expect I would
need about 20m (and that still corresponds to great value as far as I am concerned).

You need to cut holes into the back and front surfaces. I hot cut with a soldering iron. To get
circles of the correct diameter I measured all the cups, glasses, saucers, soup plates, dinner
plates, my pizza plate, pots, pans and medicine bottles in the house, until I identified the closest
matches. I then used these objects as templates. 

If you work left to right, and think things out well in advance, YOU SHOULD NEVER HAVE MORE THAN 2
CELLS TO THE RIGHT OF THE NEEDLE AT ANY TIME. Therefore, it is not really the width of the FF (or
parafoil) that is a problem, but the length. And length really isnt a problem (is it Boys :-).
To accomodate the width I sometimes put a chair to my left to rest the material on, or I roll it up
and weigh it down with some large object (and that is my Phd thesis, I knew it would come in
handy).

The bridle is a dawdle, but expensive. I think I used in excessive of 120' of line for the FF,
and more than 250' on a parafoil.

In summary ..... do a bit of reading, do a bit of thinking, make you templates, cut your cloth,
hem all the parts, and then assemble. Give yourself lots of time (templates one day, 
cloth cutting some other day, hemming on a Sunday (good therapy), assembly on Saturday, rig and fly
on Sunday). You might feel like giving up after cutting the cloth (I certainly felt that way on
each of the parafoils I built). When you start hemming everything you definately swear that you
will NEVER do this again. Assembly is great fun. You see a parafoil/FF appearing before your very
eyes. It is as if it grows out of the sewing machine, getting bigger, and bigger, and .....
and the room is full of material. I love it! And then you finish it, fly it, and say 
NEVER again. And then someone asks how did you do it, and you tell them, and then you think "I bet
I could make it AT LEAST twice as big, and in black".


Get me out of here. Look what you've done to me.