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Author Topic: SUL kites for really low winds?  (Read 11064 times)
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damp_weather
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« Reply #45 on: October 06, 2012, 02:55 PM »

Mikenchico and Allen,

Yes you are right: 
Here are lengths of the standoffs (measured from sail to standoff tip):

QPro Standard inner: 285mm
QPro Standard outer: 274mm
QPro SUL inner: 272mm
QPro SUL outer: 260mm

a 12-13mm differnce is in English 1/2 inch.

I measured the lower spreaders' distortion by fully assembling the kites and placing them belly down on the floor, and then measuring between the lower leading edges and the floor at the lower spreader elbows.  The distances were:

QPro Standard: 56 and 59mm
QPro SUL: 59 and 74mm

..Visually it looked as if the standard's lower spreaders were more distorted because their distortion is more concentrated at their thin ends.

Jim,
I have been comparing two kites made by Mei, the SUL in November 07 and the standard in May 08.  - In view of an email from my local Prism agent on delivery times, stating that Prism are expecting a delivery of QPros in 3 to 4 weeks, I am wondering of QPros are still made by the Prism team in Seattle.  And are they made exactly the same way nowadays??

Anyway I compared the standard and SUL sails by assembling the leading edges and then laying the sails over each other, both flat on the floor, and in the air with the sails stretched between spine and wingtip.  The SUL's nose protection is slightly shorter, and there is extra protection at the standard's sail grabbers.  Also the leading edge sleeves are built from lighter material in the SUL.  The only significant difference in sail shape or size that I can find is that the tail of the standard sail extends 15mm beyond that of the SUL. -i.e. it extends further beyond the spine.  I am unsure about where the deviation in trailing edge that gives this difference starts - probably around the standoffs.
This difference that cumulates in 15mm difference at the sail tail tip was quite hard to spot.  - I had originally discounted it as a difference in how the sail was sewn past the spine fixings when I had first put the two sails next to each other.  The distances between sail grabbers and from inner sail grabbers to spines are the same for the standard and the SUL.
Associated with this 15mm difference is a difference in the length of the black reinforcement that runs from the tail tip up the spine.  In the SUL it is 247mm overall, but in the standard it is 265mm overall.
« Last Edit: October 06, 2012, 03:07 PM by damp_weather » Logged
Kantaxel
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« Reply #46 on: October 06, 2012, 04:26 PM »

I'm pretty sure Seattle is still building the Pros.................I believe Mei has retired.  Confirmation could be best ascertained by inquiring of Steve H.  I know that Team Cutting Edge used the Std. stand-offs on their SULs for the reason I can't remember, at this time..........chalk that up to Senility, I think? I know it was Jerry or Jim that told me that, but can't (again) bring back total recall.  I just remember hearing the story about Mark tweaking and tweaking the SUL at Ocean Shores all the while suffering from either post or pre-surgery of one of his knees....Uh,.......... the years are growing ever shorter and the blanks are becoming longer and more frequent.

Jim 
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ae
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« Reply #47 on: October 06, 2012, 07:18 PM »

Well one reason why the QPro sul has slightly shorter standoffs might be that flatter sails are more effective in actually "catching" the wind, thus make more out of the little winds a sul operates in.
And on the flip side, it makes the frame more strained, tricks are effected or not possible anymore etc.
Its a matter of finding the balance in the design between low wind ability, fly ability and what the kite should be able to do. Also flatter sails in general tend to be faster flying, something which might not be desired in a given design.

Example, i have a speedkite design that is able to be flown in 1km/h winds, it is pretty much flat. Standoffs are like 2 inches at most, at over 7feet wingspan.
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damp_weather
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« Reply #48 on: October 07, 2012, 03:56 AM »

I know that Team Cutting Edge used the Std. stand-offs on their SULs for the reason I can't remember, at this time.....
I recall that also.  - Thought they explained it gave a wider wind range for very little increase at the bottom end.  But wonder if they used exact Std. stand-offs, or Std. stand-offs cut down to SUL lengths?
Quote
.....chalk that up to Senility, I think? I know it was Jerry or Jim that told me that, but can't (again) bring back total recall.  I just remember hearing the story about Mark tweaking and tweaking the SUL at Ocean Shores all the while suffering from either post or pre-surgery of one of his knees....Uh,.......... the years are growing ever shorter and the blanks are becoming longer and more frequent.

Jim 
Yes.  Me too. - Keeping notes is very useful for coping with this, which is why often I jot down what I think might be useful in the future.  Keeping them in computer files makes it easier to search for them later on.  And they take up less space around the house.  Wonder if this is how Terry Pratchett (famous author) copes as he has had dementia for few years now.  He is still publishing stories fairly elaborate plots.


Back to QPro standard verses SUL, I had overlooked the most obvious difference - the length of the black reinforcement runs from the nose down the spine.  - The piece with "QUANTUM PRO" in silver letters.  Measured from the tip of the nose to the tip of the reinforcement, on the standard this is 543mm long, and on the SUL it is 495mm long.  - And the SUL also includes the "SUPER ULTRALIGHT" text.
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Kantaxel
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« Reply #49 on: October 09, 2012, 08:56 PM »

AS I recall they just changed over to the Standard's stand-offs.  We must remember they were completely set up with all kinds of spares...........Wouldn't it be nice?   Cool
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damp_weather
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« Reply #50 on: October 17, 2012, 01:28 PM »

...
Back on the search for different SUL for under QPro SUL flying speeds, I have been looking at the ratio of a kite’s weight verses its “effective” sail area, where “effective” approximates to the area that is calculated from the width and height of the assembled kite, rather than the area of the sail fabric when the sail is laid flat on a table.  The idea is that this figure will give a rough idea of the relative effort (= flyers speed running around) to fly the kite.  Early figures don’t contain any surprises other than suggesting that the Ocius SUL should be much more floaty than I have experienced.  When scales have been accurately calibrated I’ll post some details of the results.
- Well I have calibrated my scales and measured the ratio of kites' weights to "effective" sail areas, and the results don't show very clear trends. But as as I said I'd post the details, the story is below:

I was thinking of a figure of merit for kites that would be approximately proportional to the weight to lift ratio. 
My original idea was to estimate the effective area of the kite - that is the amount of air it catches, by: kite height x kite width/2. - This was approximating the kite sail as two triangles each of base: kite width/2 and height: kite height.  Of course this is much more than the actual kite sail as it assumes the kite sail extends right across between the wing tips.   A better approximation would be to use: spine length * kite width/2.  Because the sail is usually cut in at the standoff, this is still an over-estimate, but is not as bad as kite height x kite width/2.

There are problems with calculating the above from weight and sail dimensions quoted by manufacturers.  It is quite rare to find the spine length quoted (that is the length of the sail at the spine, rather than the length of the spine rod).  Also when the width is quoted, it is unclear as to whether this refers to the width of the kite between wingtips when assembled, or to the width across the sail when laid flat. Or it could be the width of the kite between the ends of the sail when assembled. - At least, these possibilities are how I explain the considerable differences between some quoted figures and the dimensions I measure on my own kites.

So the table below uses just measured figures from some of my own lighter wind kites.  I have ordered them roughly in order of low wind flying capability, best first.

                                                    dimensions (mm)                       figures of merit (grams/metre squared)

Kite                              Weight       Width   Height  spine Length      2*weight/            2*weight/ 
                                   (grams)                                                     (width x height)  (width x spine length)
------------------------
Benson Inner Space         140              2060    1100     865              124                       157       
Prism Ozone                    165              1980    1080     755              154                       220
Prism QPro SUL                229              2370    1000     860              193                       225
Skyburner Ocius SUL        138              2120     940      860              138                       150
Siebert ITrix                      83              1505     680      660              162                       167
Prism 3D 2003 version       72              1390     780       570              132                       181
Prism QPro std                 322              2405    1000      877              268                       305
Robertshaw Fury UL AS     239              2114     960      886              235                       255       


(In the list above I put the ITrix below the Ocius as I have found it difficult to fly outdoors as it is affected by slight
eddies in the air flow.  For its ability to catch gentle air flow, it probably deserves to go higher up.)

I was fascinated to see that the figures of merit for the Inner Space and Ocius SUL came out so close to each other, and yet the Ocius SUL wasn't yet flying so low for me.  So I put the kites next to each other for a more detailed comparison.  The amount their sails are cut in along the trailing edge is about the same in both kites.  In fact the shapes of the sails are very similar - the main difference being that the sail of the Inner Space is swept back (i.e. if the nose is "front", then the wingtips are swept "back") more than the Ocius SUL.  The main difference between the two kites seems to be the numbers and lengths of the standoffs (while the Inner Space has one standoff on each side the Ocius has two per side and they are longer).  If the sweeping back of the wings is ignored, one could make shape of the Ocius SUL's sail very similar to that of the Inner Space by disconnecting the inner standoffs. 
This reminds me of that in the early days of flying our QPro SULs, we disconnected the outer standoffs for lighter wind performance.  - I think that when the weather improves and there is some very low wind flying time, there are many hours of experimenting to be had in trying the Ocius SUL with inner or outer standoffs disconnnected. 
- All in all, this may bear out what Mike (zippy8) has posted about flattening sails.
« Last Edit: October 17, 2012, 02:06 PM by damp_weather » Logged
ae
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« Reply #51 on: October 17, 2012, 08:21 PM »

Hrmm, if i understood your table right, this would be the values for the Spectre XUL


Spectre XUL 80g 2490 950 950 67 67
Spectre XULcf 66g 2490 950 56 56

Yes, it is designed to have all 3 points sit on the ground when standing. wingtips and keel.
The cf version is my personal one with custom made framing, hence cf Smiley
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tpatter
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« Reply #52 on: October 17, 2012, 09:39 PM »

I'm a little surprised by some of these, so perhaps I am not understanding.

You are saying that your QPro SUL flys lower than your Ocius SUL?  Have you checked the bridle settings on the Ocius?

I do agree with the general data that suggests weight has little correlation with low wind flight to a reasonable degree.  Or sail area area. 

It seems to me that sail area and a coefficient of drag (not sure if this actually exists, but it seems logical) are some important variables.  I mean, in the end, the wind at a given low speed is going to pass over a sail of a given shape and area.  This 'friction' will create a 'lift' governed by the Bernoulli principle which will result in flight.  Am I wrong?


Tom
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ae
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« Reply #53 on: October 17, 2012, 10:09 PM »

Yes, sail and wing design has a greater influence then weight. Of course low weight helps a lot Smiley
And if you manage to combine both together you great an outstanding performing kite.
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zippy8
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« Reply #54 on: October 17, 2012, 11:46 PM »

If I may.....

                                                    dimensions (mm)             figures of merit
                                                                                          (gr/m squared)

Kite                    Mass            Width   Height  spine Length      2*mass/           2*mass/
                        (grams)                                            (w x h)      (w x spine)
------------------------
Benson Inner Space        140              2060    1100     865           124                    157
Prism Ozone               165              1980    1080     755           154                    220
Prism QPro SUL            229              2370    1000     860           193                    225
Skyburner Ocius SUL       138              2120     940     860           138                    150
Siebert ITrix              83              1505     680     660           162                    167
Prism 3D 2003 version      72              1390     780     570           132                    181
Prism QPro std            322              2405    1000     877           268                    305
Robertshaw Fury UL AS     239              2114     960     886           235                    255
Spectre XUL                80              2490     950     950            67                     67
Spectre XULcf              66              2490     950     950            56                     56
 

Megamind: Oh, you're a villain all right, just not a SUPER one!
Titan: Oh yeah? What's the difference?
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supervillain.
« Last Edit: October 17, 2012, 11:54 PM by zippy8 » Logged

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Allen Carter
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« Reply #55 on: October 18, 2012, 09:45 AM »

Mike, you lose presentation points on iOS. Your table is a mess.

Only a regular villain. I'm so disappointed in you!


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« Reply #56 on: October 18, 2012, 09:46 AM »

Prism Vapor 153g 2030 1220 -- 124 --

Didn't found how long the spine of the Vapor is, so i -- those values.
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« Reply #57 on: October 20, 2012, 11:18 AM »

Andre - Thank you for the additional figures.
Mike - Thank you for the table formatting.  I will try to remember how you did that for the next time.

I'm a little surprised by some of these, so perhaps I am not understanding.

You are saying that your QPro SUL flys lower than your Ocius SUL?  Have you checked the bridle settings on the Ocius?
Tom, 
I think that at the start of this thread I wrote that I found that my new Ocius SUL flew as low and no lower than my few years old QPro SUL.  This was based on a long quiet evening in June flying them back to back on the same 50lb x 75ft lines. - Frequently changing between kites.  I did try altering the Ocius bridle settings regarding nose tilt.  Currently I have it on the second knot from the top.  In common with another Skyburner kite: the Widow Maker, I didn't find that bringing the nose lower by using the very top knot helped.
As for the general setup of the bridle, I have nothing to compare it with, but trust it was OK as it was fresh new from Skyburner.
Comparing the sail with the Inner Space was very interesting, as they are so similar, except for the way the wing on the Inner Space is swept back, and for the standoffs.   Like the Inner Space the Ocius SUL even has some slack in the sail behind the leading edge, which should enable it to adopt an aerodynamic shape in flight (better than a flat sail).

The standoffs brought back to mind our early experiences with the Ozone and the QPro SUL.  The trick with the Ozone to getting it to fly so low was moving the spar grabbers of the outer standoffs inwards to release tension on the sail, but not so much that the kite became unsteerable, and if I remember correctly, putting the inner standoffs on the second sail holes from the middle - again the kite lost too much control with the first sail holes.  When we first got QPro SULs, we had an epidemic of sail grabber caps coming off, releasing the standoffs.  So it was very easy to try them without the outer standoffs, which helped the low wind flying by 1mph or more.  Nowadys I don't bother with this, which is probably down to the sail softening with use.

For the Ocius SUL, Jon Trennepohl has secured the standoffs very well.  I would have to cut off the plastic fittings to remove them.  So instead I intend to try flying with at most a pair of standoffs disconnnected at the lower spreader end, and be careful about catching the loose standoffs on the ground.  Or perhaps I'll just move the spar grabbers along to reduce sail tension.  We'll see how low the kite can fly, and I guess in the longer term, as the sail matures, this won't be necessary so much.

The other thing I can try, is that as the Ocius is a smaller kite than the QPro SUL, perhaps it would do better on shorter lines.

These are all ideas for time when the weather improves and I have some time off.
« Last Edit: October 21, 2012, 02:45 AM by damp_weather » Logged
Wayner
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« Reply #58 on: October 20, 2012, 11:42 AM »


The other thing I can try, is that as the Ocius is a smaller kite than the QPro SUL, perhaps it would do better on shorter lines.


+1
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« Reply #59 on: October 20, 2012, 01:24 PM »

A little from today:

https://vimeo.com/51823129

Wind was an abysmal zero to 1mph from varying directions, at different heights.... but sometimes even constant Smiley
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