Power Kite Forum

Nasa Star

Prussik - 2-10-2013 at 07:54 AM

I’ve had a pretty low opinion about Nasas in the past and the only reason Nasa Star caught my attention was because the depower idea reminded me of our similar R&D work in Wind Propulsion Institute some 10-12 years ago.

My impressions from the past, sporadic encounters with these kites were that they are bridled for power rather than the window width and forward pull. The same seems to be true is true of Nasa Star. This indicates to me the likelihood of a too steep AOA and/or too much braking. So the first thing I did was to release the brake pull a little. This immediately widened the window, significantly reduced the tendency to back-fly or tail-crash when underpowered. This alleviated somewhat my original scepticism about these kites and convinced me that it may be worthwhile to give them a more serious consideration. So the next thing I did was to correct things I didn’t like about Nasa Star starting with Z-bridles. They are made of thick nylon cord, which makes for big, snag prone knots and require larger than necessary line gobblers for adjusting the lengths. I replaced them with Spectra line. At the same time I changed the other thing I didn’t like –the brake function. Brakes were connected to A9-A12. They work better, in my opinion, when connected to A11,A12,B5,B6 . And finally –while replacing Z-bridles – I divided power connections into 2 parts: (A1-A6,B1,B2) and (A7-A10,B3,B4). Thus, after installing line gobblers, I can adjust the amount of brake pull as well as the AOA.

When I received the kites I didn’t have a spare, long line sets handy so I made short 5-line sets – 3-5 m. I never expected these things to work as well as they do. What I find particularly surprising how well they go upwind even when depowered. I can trim the 5-line on the go with the free hand and short gusts can be handled with the additional pull with the free hand. So instead of selecting a “small”, conventional FB on 45-50 m lines and taking advantage of flying to generate pull in the lulls, I can go with a “big” Nasa on short lines, park and go and use the 5-th line when overpowered. This gives a surprisingly wide wind range. Obviously, the range would be even greater on long lines but I am impressed enough to leave them on short lines for now.

Reducing the AOA and brake pull can be expected to decrease the power somewhat. This I consider to be a non-issue since one can select a kite size right for the conditions – the window width is more important. With the wider window, the direction of a reduced pull is closer to the beam reach of travel so the loss of the overall power doesn’t translate to an equivalent loss of the usable pull. I’ve revised my opinion about these kites.

bigkid - 2-10-2013 at 02:28 PM

Not bad, wondered when someone would tinker with the kite and post about it.
That about what I found. I decided to leave the kites as is. They are great kites the way they are to introduce newbies to the ragflappers. The Susan specials are the ones I have been tinkering with, going in a different direction thow.
Bite the bullet and get those kites on looooooong lines and post your findings, I would like to see if its what I found.
For every 100 feet of lines you need to extend the brakes another 10 to 12 inches.

John Holgate - 2-10-2013 at 04:28 PM

I have wondered about reducing the angle of attack slightly also - figuring it may do as you said. Any chance of a pic of how you've adjusted the AOA?

Edit: How do you think it would go if I rigged the bridles like this? The AoA adjuster should be pretty easy to make. I'll keep it as a two line with third depower line so my bar setup is the same. I think if I could give it just slightly less angle of attack, it would be perfect for me...


bigE123 - 3-10-2013 at 10:54 AM

Good work prussik, it confirms pretty much what I have found with my NASAs.
1: Z-bridle holds tension on the brakes and therefore does not allow fully releasing the brake lines when right at the edge of the window holding the kite back slightly.
2: changing the AoA on my bigger NASA kites resulted in a faster kite and a wider window.

One question on the NASA stars did you change the AoA right across the kite centre and wings? I found the NASAs were much more stable when just the centre panel AoA is changed leaving the wings "static".

Prussik - 3-10-2013 at 11:45 AM

John, my only concern with this (conventional) method of AOA adjustment is that doubling the trailing edge response may be too much – only experimentation can determine that. It may be necessary to group bridles differently giving more uniform distribution between the leading and trailing edge – again looks like good material for R&D. I would divide them into 3 equal parts and see what happens. This would eliminate brakes as such but with a bar you don’t need them. You may also find that you need finer adjustments and less range. If the surface drag is low then lower AOA can be beneficial.

My preference is for independent adjustment of 3 groups. I like to have brakes as well as depower. With line gobblers I adjust each of the 2 power leads and leave the brake lead alone. This way I can control AOA and brake load independently in small increments.

John Holgate - 3-10-2013 at 03:06 PM

I'm heading down the beach tomorrow, so I'll rig up the 4m and let you know how it goes.

Edit: This is how I ended up rigging it - I'm relying on a larks head knot for adjustment - if it slips too much, I'll figure out a plan B!

PS: What are 'Line Gobblers' ?


Prussik - 4-10-2013 at 08:37 AM


Quote:


One question on the NASA stars did you change the AoA right across the kite centre and wings? I found the NASAs were much more stable when just the centre panel AoA is changed leaving the wings "static".



If you look up John’s pictures above you’ll notice that the whole span (i.e. A’s and B’s) is affected and I don’t see any reason to do it any other way. In a handful of my encounters with Nasas over the last 15 years (most likely all NPW5’s) I have never came across “stability” issues – there were those other things I didn’t like. So not knowing the specifics and not having the experience of the many long lime Nasers, I am not in position to pass judgment on the subject other than to say that splitting the AOA would be the last thing on my mind as a solution to a problem. And the first thing would be the bridle lengths.

Demoknight - 4-10-2013 at 09:05 AM

Quote: Originally posted by John Holgate  

PS: What are 'Line Gobblers' ?


Line sheathes, I think.

bigE123 - 5-10-2013 at 01:29 AM

Quote:
If you look up John’s pictures above you’ll notice that the whole span (i.e. A’s and B’s) is affected and I don’t see any reason to do it any other way. In a handful of my encounters with Nasas over the last 15 years (most likely all NPW5’s) I have never came across “stability” issues – there were those other things I didn’t like. So not knowing the specifics and not having the experience of the many long lime Nasers, I am not in position to pass judgment on the subject other than to say that splitting the AOA would be the last thing on my mind as a solution to a problem. And the first thing would be the bridle lengths.

The reason I added de-power to my NASAs was not to fix a stability problem, as the kites were very stable to start with, it was to give me a wider wind range with the bigger kites.
I found that when on a low AoA the kite would sit at the apex and the wings would start to flap a bit. I therefore fixed the wing bridles and only varied the AoA on the centre panel, this resulted in a de-power set-up that allowed me to launch and fly on low power, giving a faster kite and still very stable kite, dive and bring the power in and the NASA is on full power :-)
Not sure if the NASA star bridle are the same as the "classic" NASAs with bridles grouped from LE to TE as opposed to foils grouped effectively from side to side making de-power a lot easier to do via the three groups A/B/C. Looking at the pictures they look like the AoA adjusters found on the blades.

John Holgate - 6-10-2013 at 12:10 AM

Test No. 1 with the lines rigged as in the photo was unsatisfactory - general characteristics of the kite didn't change a heck of a lot but I got 'floppy edges' !! And that was with about an extra mm or 2 on the middle/brake bridle adjustments. I'll try next with all the B's grouped with the first few A's and split the rest and see how that goes. The other trade off I thought of - if I gain a slightly faster kite/wider window, I may lose the ability to relaunch the kite from a nose down position - which is occasionally very handy. Particularly when parked at the side of the window - not something I'd sacrifice for a little more speed. I'll try plan 'B' over the next few days.

bigE123 - 6-10-2013 at 01:41 AM

John, when adding de-power to my NASAs I had to go further than a three group, on a NPW there are 10 bridle points plus two brake lines, I ended up splitting in to 5 groups. Even on a low AoA reverse take offs have not been an issue.

John Holgate - 6-10-2013 at 05:15 AM


Quote:

I ended up splitting in to 5 groups. Even on a low AoA reverse take offs have not been an issue.



Thanks - that's good to know. The NS2's have 12 A's grouped in pairs and 6 B's on the side, also grouped in pairs so I can theoretically split it into 6 A's without having to alter the original kite. Really, the stock setup is fine - it's just occasionally I think....if I could just tweak this bit..... :)

riffclown - 6-10-2013 at 05:32 AM

Quote: Originally posted by John Holgate  
I have wondered about reducing the angle of attack slightly also - figuring it may do as you said. Any chance of a pic of how you've adjusted the AOA?

Edit: How do you think it would go if I rigged the bridles like this? The AoA adjuster should be pretty easy to make. I'll keep it as a two line with third depower line so my bar setup is the same. I think if I could give it just slightly less angle of attack, it would be perfect for me...




Here's where I made a set.
http://www.powerkiteforum.com/viewthread.php?tid=26777

You're right, they aren't that difficult to make. They do take a bit of effort to get tuned since 1/8" of knot placement difference can have drastic effect on your kite (especially if both sides aren't exactly equal. I used pins to place mine and guide the knot placement and it still took a bit if work to get them to line up as I wished,

bigE123 - 7-10-2013 at 03:47 AM

Quote:
Thanks - that's good to know. The NS2's have 12 A's grouped in pairs and 6 B's on the side, also grouped in pairs so I can theoretically split it into 6 A's without having to alter the original kite. Really, the stock setup is fine - it's just occasionally I think....if I could just tweak this bit..... :)

That's why we don't all live in caves any more it's that "what if" that pushes things that bit further ;-) I thought single skin kites would be quite simplistic.... how wrong I was!!
I found that maintaining the profile is critical, with a foil you can get away with an element of compromise. I initially went for a change of AoA across the centre (A) and wings (B/C), but found that just changing the centre panel / middle wing bridles (C on a NPW) and leaving the wing edges on the original bridles gave a very stable kite (no wing flutter on low AoA), allowing the centre of the kite to move it's AoA to give the speed / power combination.
I've just got my big NPW rigged on to a four line de-power bar, so just need a test flight to see how that goes. Not sure whether it'll need a turbo bar because of the pulley system on the bar which gives a brake / power line combination for turning as opposed to a brake input only turn.

bigE123 - 7-10-2013 at 08:40 AM

Just a quick update.... turbo bar works a treat, using the slingshot bar just could not get it to turn properly. I need to put a couple of extensions on the brake lines as I had to pull the brake line adjusters right in so I'm left with no adjustment.

Prussik - 8-10-2013 at 08:04 AM

In principle, splitting the canopy into more adjustable segments would provide the opportunity to maintain the most correct airfoil assuming that all individual trimmings are spot on. As I described in the first posting, I divide mine into 2. So do those FB’s made with adjustable AOA. And they all work very well. I may change my mind about that but at this point I don’t see much, if anything, to be gained with more segments considering how small the range of adjustment is that is viable for proper operation. I never needed to split AOA control spanwise ( as in controlling the centre panel only ) but I can see this need to arise when there is too much AOA deviation from the optimal setting. If I didn’t use brakes, I would probably try 3 equal segments but at this point I appreciate the simplicity, precision and quickness of 2 segment adjustment.

AOA adjustments won’t do much good if the excessive pull on the trailing edge holds the kite back in the window as I believe is the case of NS2 in the original setting. As I indicated, this was the first thing I felt needed to be changed.

bigE123 - 9-10-2013 at 12:48 AM

Quote:
AOA adjustments won’t do much good if the excessive pull on the trailing edge holds the kite back in the window as I believe is the case of NS2 in the original setting. As I indicated, this was the first thing I felt needed to be changed.

Agreed on that one, minimum / no TE tension on the brake lines means it'll park right above your head, one little trick I've used is a leech line in the TE, you can add a little tension to it and it helps keeps the nose up without brake line tension.