as already posted, (viewtopic.php?f=197&t=2391006&start=190
) I´m an engineering student, sailmaker and started last year making my own designs on foilkites and made 3 smaller sizes (1.5m², 2.3m², 4m²) for kite buggy mainly. The 4m² is now depowerable and closed cell. Now after I´m feeling a little more confident in what I´m doing- at least confident enough to invest in materials for bigger kites on a students budget I did some more thorough research on aerodynamics and kite design as I was doing in previous designs. The first three kites were more to learn the manufacturing process and see how all the parameters work together.
What was working really well in those last 3 kites: manufacturing process, sewing accuracy, inflation, skin tension (without using D-Ribs and straps for simplicity), sewing and designing the bridle.
What I want to improve: I think i used a very shitty profile: (NACA2415 to 19%thickn. in foilmaker). As I analysed this profile in XFLR5 i also knew why in hindsight
(Pitching moment etc.)
Then I analysed some 10 more profiles used in popular freeride and race kites and those DIY profiles that were discussed at this forum. I quickly could understand the impacts especially of the shape of the camberline on stability. When doing stability analysis I mainly watched out for the location and strength of the resultant lift force on the profile, and watched out to choose an airfoil where it is not behind 30% of chord for as many AoA and relevant Re Numbers as possible as I wanted a stable kite. I then designed an airfoil using the spline function which would fit my demands and interpolated it with Airfoil sections used in modern depowerable kites to see if it was getting better or worse on a stability point of view. I came out with an airfoil which was oriented on some modern race kite profiles but a bit thicker, a bit less camber especially in the back 50% of chord and more reflex also. I got tolerable losses in L/D while gaining a lot of stability at least if XFLR doesn´t lie and I tested based on realistic values and numerical stability.
For the tips i went thinner and with even more reflex. My design ambition is not to make the best race kite ever nor to reinvent the wheel but just to get an ok kite that I can have fun with on the beach, snow and water all day and hopefully can understand more of what modern kite designers are doing and why they do certain parameters.
So in theory I´m quite confident with this profile now but before I will put it all together on my 11.5m² AR 5.3 Kite (Blue/Green) which I will do in late March/April, I will test the profile I´m using at first in a very simplistic kite which is in rectangular shape (like those old quadrifoils). I will build this kite in the following weeks and thought I´d share the process with you.
Why such an oldschool design? Because its fast for manufacturing! It will only have 4 different Panels (Same Rib shape, same top skin, same bottom skin same D-Ribs all over the kite-being rectangular and constant canopy curve)
Some Specs on this kite:
Closed cell, Depowerable
Proj. Area in %: 81%
Structure: Dribs full cell, primary bridle every third cell, spanwise straps.
Material: Ribs, Dribs, straps: Porcher Skytex 41g
Lower skin: Porcher Skytex 27g-32g ish from an old reserve parachute (never used)
Upper skin: Porcher Skytex 41g
Bridle: Liros DSL
When designing this kite I realized following benefits which are useful for fast manufacturing/research of design parameters:
-due to rectangular shape and constant canopy curve I can make the whole kite from 4 wooden cutting patterns. I put 8-10 layers of ripstop material on a glass plate. Then I put the wooden pattern on top and secure it with some clamps. I now can use the hot knife cutting for example 8 cells in one batch. This makes for very fast and precise manufacturing. Due to small holes in the pattern I can also cut some marks for bridle locations, D-Ribs and vents as well as alignment holes into all pieces of fabric really efficient.
Due to this method I could cut out all 32 Ribs in under an hour today!! (for a normal bi-elliptic 30 cell kite this took me up to 8h incl.paper-pattern printing, gluing and cutting)
It´s maybe even faster than using a pen plotter.
Pictures, D-Ribs, Upper and lower skin will follow Saturday.
-Spanwise internal straps can be made out of one long strap going through the whole span of the kite. I can therefore just mark this strap at a constant rate for a homogeneous strap tension.
-Because I´m using the center profile in all the kite for simplicity, I probably have to tune it towards the tips when flight testing. The bridle layout lets me do this really easy because I can already adjust the AoA and reflex of the tips in the secondary bridle at a constant value without touching the mixer or affecting the centre profiles. To avoid tip tucking this will do. When having a non constant chord at the tips a smooth AoA or reflex alternation by hand on the beach is really hard to do because each bridled cell would have to be fixed at a time, at least if it should be a clean transition. At best this will be done before hand in the bridle design on the computer, but not for me as being inexperienced with this new profile and using this quick simplistic kite as a practical study.
I was quite stunned how far I came today now being 4h into the manufacturing phase today. I still would have been into cutting paper patterns with a more complex design whereas today I spliced and sewed two dyneema mixers at different purchase rates, cut out all wooden patterns and already cut out all 32 ribs.
It could well be that I start to sew on my next free day, saturday.
I forgot to take pictures today they will follow.
sewing @Schietwedderunlimited Boatcovers