Hey folks,

I'm working on my second NPW. The first I made was a 1.8m2 Teega; this time I decided to follow the NPW9b plans, and it is 3m2. I was going to use keels/ribs to reduce bridle lines, but I decided I need the bridling practice. I also used lawn trimmer line (per Randy/BigE123's suggestion) to add additional support to the nose. Here it is, done with sewing and awaiting bridling.




So, I'm sure I'll learn a bunch from actually flying the thing and comparing with the Teega, but I had some questions about the differences in design that you all could answer:

1) The Teega design suggests to curve the trailing edge and trim off the corners between the outer and middle panels. Why? Is it for looks, for smoothness? Do people not trim it off because it's barely simpler not to and it doesn't really matter? Is it better to leave it for just that little bit of extra sail area? I kind of wish I did it this time on my 9b, as my gut tells me that it would be a smoother wind profile.

2) The Teega design doesn't include side darts for the nose and employs vnose bridling. Why? Are the darts there better for nose shape? I've read people using vnose with the darts, so it's not a one-or-the-other thing. What do the side darts do for the nose shape that benefits the Teega but not the 9b? I did the side darts this time, and I'm planning on using vnose bridling -- is that crazy?

3) The Teega uses trailing edge leech lines, which I decided to keep for my 9b. It seems like these are handy to have regardless of design for sail tuning purposes, and I presume they're not in the 9b designs simply because the Teega came after it.

Thanks in advance!

-DL

Great project!

Dig that jackolope!

The 9b is masterwork of bridles, I always thought the first teega was the simplified cut down version. Some of makers are more qualified to answer ??? ....nice work .
I do recall my npw5 would handle reverse flight well maybe with cut TE I imagine it's does even better with faster spin around .

Nice work FIniteState! That kind of aplique is really difficult. (So difficult I can't even spell it.:D)

One thing to keep in mind in comparing designs is that kite design involves a lot of trial and error, and the designs out there now all started from the NASA wind tunnel reports, but various people tried different things. Some worked, others didn't, but the designs that evolved may or may not be the best possible. NASA, by the way, did try various things to improve the parawing performance, and aside from the general shape (i.e keel width, keel angle, etc) not much made a lot of difference. NASA was really trying to optimize a glider - not a kite so their goals weren't the same. But they did provide the starting point, and kite hobbyist have done the rest. Bear in mind also, that the people who worked hard to publish the plans also have some pride in authorship and tend to believe their variation is the best of the bunch.

As for the Teega v. 9b. I've not built a Teega, and I think that Kitemakte4 a few other are the only to have built it on this forum. I read a lot about it and the other NPWs and I can say this much: the curved trailing edge is pretty unique to the Teega. None of the other NPW's (5, 9, 21, single keel, and few if any of the NPW variations NASA tested in the wind tunnel) used a curved trailing edge. The plan designer is, however, a very respected expert who in fact developed the bridles used in Tom White's 9b plans. He developed the Teega after testing a lot of designs including the 9b.

NASA came up with the nose darts in their wind tunnel testing as a way of reducing nose collapse. In very first parawings there was just a straight nose. Adding the nose curve helped the L/D a lot. They even tried to use foam to shape the nose. They had 2 side darts as I recall, and I think kite makers eventually decided one was all that was needed. The Teega designer apparently felt like none is needed. The NPW 21 designs out there use the original 2 darts.

The leech line is used mainly for kites (such as the NPW 21) where adding line tension to the TE is helpful in eliminating flutter. (You will recognize it when you see it.) I had some flutter in NPW 21 I built, and eliminated it by simply putting in a dart. The 9b doesn't have that problem so a TE leach line is normally not added.

You don't need to even use any darts for the nose. Ian has mentioned (and I have tried) using a tension line in the nose seam and then just shortening it by the amount the nose darts would reduce the curvature of the nose. I've done L/D comparisons of some of the kites I've made, and cannot tell that the conventional nose actually improves performance relative to the conventional nose darts. It may or may not - but the differences are fairly insubstantial. It doesn't look as attractive as the conventional nose design though.

The nose is a very critical part of the NPW and key to its performance. My feeling is that Ian's strimmer line support is probably the best way to improve that without a lot of complexity and weight.

Check out 2e5.com, and download the NPW research reports. Those show the original development of the NPW's. You will find that many of the design out there now (esp. the 9b) have changed a lot from the NASA days.

Finally, Tom White mentioned to me in an email that the most important thing in how well the NPW kite performs is not so much the material the kite is made of, but rather the flying lines. He recommended spectra line because it is one of the lightest and strongest available.

Sorry I don't have any clue re your questions, but hey, the kite looks great!

Thank you, all! Indeed, Randy, the jackalope probably took as long to do as the rest of the kite. Also, thanks for all the info! I've been piecing it together from various bits here and there, and it's fascinating. I had recalled stumbling upon the actual NASA reports and had meant to read them but lost the link, so thanks for that!

Nice one FiniteState! Your right there, once you start doing designs, the design swamps the overall build time, BUT you now have a truly unique design :D

As Randy says the NASA reports show differences of curved TE, there is so much info in those reports, I've always stuck to a straight TE.
I'll need to dig my union jack 9b out see what nose bridle I did, vnose with darts seems to stick in my mind. The side darts are to create the overall nose shape and as Randy says you don't need to use them but I think it's neater.

The plans I initially got for the NPW21 had wing leech lines only, I went for more Teega like (I haven't built one but liked the idea) and did the centre panel as well. After flying it and tuning it I went back and put them on my 9b and yes they do make things better in terms of helping the nose. The nose supports do pretty much eliminate the need for the centre panel TE line, but again with it in gives that extra element of tunability.

With respect to the nose, not sure what size you built, I now split the centre panel in to three sections to give me an extra two seams to put the nylon lines into, you can see them on this one:

If you look at the TE you can also see the curve made by the tension line, I tend to find I have 1 - 2cm more than the Teega calculation on the wings and a bit more on the centre, a double stopper knot on my line reduces it by @1.5cm so I add a knot at a time behind the previous one, this then means if it's too much I remove the last knot. I also put a bead behind the knot to stop it pulling into the seam. Plastic beads like the one used for children's handicraft stuff, I got a pack of 100 for peanuts in different colours.

Thanks, BigE123. That's really helpful. My kite is 3m, which is about the largest area kite you can make with the height being from selvage to selvage on my 58" fabric -- that is, for single-piece panels.

By the way, the shadows in that picture confuse me. It looks like the camera view is on the leeward side of the sail (that is, the kite is being blown from behind), but the flying lines are on the front side as well. I simply can't shift my perspective to see it correctly.

Oh, another quick question... Do you bother to seal your applique in any way? I had used a glue stick for initial tack and then zigzagged it (with extra bartacks on the sharp corners), and I am thinking about seam sealing it, too.

:D No tricks it is just an illusion the kite is inflated from the line side.

I use something called hemline "wash 'n' wear" hem glue to hold the pieces in-place, it's supposed to dry clear, which it does but you can see it with light behind the material, so I try and cover the whole piece with a thin layer, put it in place and put a book on top, leave over night then zig-zig stitch it all round. The pirate and batman in my signature pic were a bit more tricky as I hot cut the shape out of the main panel then stitched the yellow / white in-place. Hence going for white on the big NASA I built, no hot cutting the main panel!

Went to han#@%$#! fabrics recently and they actually have good ripstop now. not that stretchy stuff that is used for rain coats. I think I will make one after I finish my kite trike project.

Thanks, BigE123! Good luck on your build, Shortlineflyer.

Wow, beautiful NPW there. Let's see it flying!

I've not had much time for NPW building lately, but I will note that I always dart my noses, use a leech line in 21s, and that Ian's strimmer line nose support is one of the best and simplest ideas to come along in the world of NPWs for quite awhile!

If you want to go bigger, we worked on a calculator that could do 2-piece center panels a year or two ago, which resulted in my 7m NPW21 out of similar width material with little wastage.

Sorry, I'm a little lost, is there a difference between NASA NPW9b to NPW21? Where do I find NPW21's plans?

There are different versions of the NPW design. They go back to the 1960's when NASA was trying to design a wing system to replace the parachutes used to recover space capsules. They tried many different designs and tested them in wind tunnels. They didn't have enough time to perfect the design, so they ended up just using the parachutes. Nothing much happened until decades later when hobbyists discovered these designs made good traction kites. The NPW-5 and and NPW 9 were the main ones used. These designs were tweaked a lot and the plans were published online. The NPW 21 was developed later on by a number people including one of the former members of this forum. He isn't active now, but if you are interested in his plans, send me a PM with your email address and I will send you his program.

I will also email you copies of the NASA wind tunnel test reports which are interesting as well.

I like the NPW-21 plan the best. It has very good performance and requires less bridles than some of the other versions. I also like the very easy to build single keel NPW.

Here are some videos of NPW's I've made. NPW 21 5.0 M

https://youtu.be/d8QJHBY4Fos


This video shows the single keel NPW.

https://youtu.be/N_QDlEUiBEU


Here is an NPW 5.

https://www.youtube.com/watch?v=SVojDSJlFCw

I also built a few NPW 9b, but like the other versions better.

Quote: Originally posted by Randy

Here are some videos of NPW's I've made. NPW 21 5.0 M https://youtu.be/d8QJHBY4Fos This video shows the single keel NPW. https://youtu.be/N_QDlEUiBEU Here is an NPW 5. https://www.youtube.com/watch?v=SVojDSJlFCw I also built a few NPW 9b, but like the other versions better.

I currently build a 3.9m NPW5 and am looking for the best model to build a 6m. I thought NPW9b was the same as NPW21