From: pat@cs.strath.ac.uk (Pat Prosser)
Newsgroups: rec.kites
Subject: Re: Engineering involved in Kite Making?
Date: 9 Sep 92 11:44:56 GMT
Organization: Comp. Sci. Dept., Strathclyde Univ., Glasgow, Scotland.

In article <1992Sep9.004133.42857@kuhub.cc.ukans.edu> spaceman@kuhub.cc.ukans.edu writes:
>I have a question for those people who design and construct their own kites-
>
>How much of the process involved in your kite making involves calculations
>(estimations) of aerodynamic/structural properties, i.e. location of center of
>pressure, the amount of camber, and the frame members spec's to get 
>specific pull (light flight or power- considering the strength-to-weight
>ratio)?
>

I build single line kites (rigid and soft), and the occasional stunt kite
(usually big or brutal). I know absolutely bugger all about aerodynamics,
other than schoolboy physics (I'm a computer scientist). So, when I design/build
a kite I do not generally consider centre of pressures etc.

What I do consider are some of the following:

(1) How hard is it going to pull? That is, if I build it that big will 
it be possible to fly it without the assistance of a football team. 
Will I be able to get line that will take that loading, within a given cost budget?
Once I've launched it, how will I land it?

(2) How much material will it take, and can I afford it this month?

(3) I consider the production problems. That is, how do I join this to that?
Am I attempting to produce a shape that cannot exist within 3 dimensions?
Am I designing something that will take up the desired shape in the wind.

(4) If it is wrong, can I modify it? For example, if it has a bridle I can then adjust it, but if
it only has a keel (as in a "simple" delta) then if I get it wrong then it's wrong.
So I might design a delta with a keel that I can adjust :>)

(5) Will I be able to assemble it on the flying site? This is no joke.
You might be able to assemble the kite in your front room/workshop but not be able to do it in
blustery conditions in a muddy field.

(6) If I break anything will I be able to replace it (or will I have to get on the phone to Helmut
Georgi in Vienna to get a new one)?

So basically, my considerations are those of a production engineer "can I do it,
and how much will it cost". When it comes to choosing spars, bridle lines etc (ie the basic 
elements that take stress/strain) my decisions are based on exerience. I look at a spar and say
"That looks about right" (the TLAR school of engineering). However, I generally make two 
sets of spars for my single line kites. A heavy set, and a light set. With experience I then 
learn which set is unneccessary.

>!I know that there is an "artwork" aspect to it (who wants an ugly kite?),
> but how much 'engineering' goes into it?

I might classify the kites I build into 2 catagories: (a) those that I have built for the 1st time
and (b) those that I've built before. In class (a) you can put prototypes/inventions. There aren't
many of those. Also in (a) put kites that you've seen in books or in the air, but you aren't quite
sure of how exactly to build them (an example would be my first sled, my first Rokakku, my first parafoil,
flowform, tetrahedral kite, delta, swsk, etc). The kites in class (a) are rarely works of art.
The kites in class (b) I might then consider as works of art. That is, I might decide to build yet
another parafoil, but applique it in a certain way (such as get inspiration from the work of some
artist, Joan Miro perhaps). Nevertheless, every kite I build I learn something. I think I am
improving.

>
>A curious aerospace engineering student-
>paul

Well Paul .... here's a question for an aerospace engineer. For me the big challenge is production
(making joints, fitting things together, etc). However, I consider most of my kite FLYING as an
empirical study. I say "I wonder what would happen if I changed the shape of that keel, 
cut that trailing edge into this shape, adjusted the bridle as follows, attached a drouge
of this size there?"  Once I've answered that question I tend to move on. Empirical is the key
word here. I do not believe that there is a WORKING theory of aerodynamics that can be applied to
kite design. I do not believe that we have aerodynamic theories that accurately PREDICT behaviour
(I do believe that we have aerodynamic principles that can EXPLAIN behaviour we observe). If there was 
such a theory then why do we have wind tunnels? I believe that reality is too complex,
and that we are reduced to "suck it and see" (the SIAS school of empirical science).


Patrick
Newsgroups: rec.kites