Perfect Rev Spar

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RevJB
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Perfect Rev Spar

Postby RevJB » Fri, Nov 06 2009, 06:21 PM

I'm curious, what would make a perfect Rev spar? Is it different for the leading edge versus the verticals?

As an example,the race rods are stiffer than a 2 wrap and lighter than a three wrap. Could that be carried to the extreme?

Would it be ok for a spar to have no flex? For the verticals?
Can a spar be too light weight so the kite wouldn't have any momentum?

If you aren't doing tricks, is the LE or vertical under more stress?

Is there a shape for the kite that flies best in all winds. Should the flex be independent of wind speed , if that was possible.

Ok, too much thinking and not enough flying :wink:
Last edited by RevJB on Fri, Nov 06 2009, 11:21 PM, edited 1 time in total.
John
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Mike
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Re: Perfect Spar

Postby Mike » Fri, Nov 06 2009, 07:29 PM

I assume we're talking about Rev spars.

I've seen both vertical and LE spars break, so if the spars weren't damaged, that means that the stress can higher on either component under different conditions.

When we swap in stiffer spars in higher wind, some of that is to adjust the shape of the kite, so that lends some credence to the theory that there is one good shape.

Do we need spars to create momentum? Kite boarders use kites with an inflatable leading edge. So maybe you don't.

In the end, I expect no one really knows without doing some sort of controlled wind tunnel test.

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Re: Perfect Spar

Postby Jeepster » Fri, Nov 06 2009, 10:35 PM

Most fliers hate the the SLE leading edge (7/16" ID) because it's too stiff. The 3-wrap (yes there is a 4-wrap SLE rod) has less than half the deflection of a 4-wrap rod ... and it weights about 50% more than a 4-wrap rod. Thus, based on the comments of most fliers, it would seem that too much mass and stiffness is unacceptable.

The only exception to the too stiff rule might when the winds are extremely low ... the Virgina guys swear by the quad sticks they use.

No one flies with P090 SkyShark rods, so likewise, it would seem that an extremely light-weight, weak rod is unacceptable.

Within those two extremes is plenty of room for discussion based on personal preference.

I favor the theory that, in normal winds, there is an optimum shape that gives the best control ... that's why we have the various rod strengths! Either that or it's a conspiracy to simply sell more rods!!

Cheers,
Tom

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RevJB
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Re: Perfect Rev Spar

Postby RevJB » Fri, Nov 06 2009, 11:48 PM

Mike is right, I was speaking of Rev spars. I've edited my initial post. I forgot there's something else besides Rev's. :-)

Mike's comment about inflatable edges is interesting. It does seem that for a given deflection, lighter is always better. I have a crazy idea for a test. Fill the LE rods with just enough helium to offset the weight and create neutral buoyancy and see how they fly. Not sure there is enough volume of air inside the tube to do this. Still might be fun to try. It would be easier if you put only one ferrule in two spars on the LE.

Does anyone know of someone putting helium in an inflatable leading edge?

If a standard shape is good, wouldn't it be easier to tension the ends of the spars with lines to the appropriate shape, like a Rok, and then use one spar for all winds?

Although I don't have access to a wind tunnel, I could take pictures of kites with different spars in the same wind conditions and see what shape fliers like best. I'm guessing there may be a strong dose of personal preference.
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Mike
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Re: Perfect Rev Spar

Postby Mike » Sat, Nov 07 2009, 06:33 AM

Helium: I have a tank of helium in my basement, and I can tell you that the tubes don't have near enough volume. You know those long skinny balloons for making animals? They won't float if you fill them with helium, so the volume/weight ratio for the spars wont work. Fun idea though, I like outside of the box thinking.

Tensioning the spars: That is done in part by sewing the leading edge in a curved shape. The current trend in Rev LEs seems to be leading toward more curve. Supposedly, the ends drop down about 2" lower than the center. Revs sails vary quite a bit, so I've never confirmed it. If someone has a recent Bazzer Pro in which he did the entire kite, including the LE, we might be able to check that.

Personal preference: that's why it's hard to judge. In order to feel the small differences, you have to be a very good flier. But the really good fliers can fly anything. I've seen John Barressi fly home-made kites that were very difficult to fly and do 1/8 perfect clockwork turns, etc. The "bad" kite and the "good" kite fly pretty much the same in his hands.

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Re: Perfect Rev Spar

Postby Jeepster » Sun, Nov 08 2009, 10:19 AM

Opps, I stand corrected ... someone is flying with SkyShark P090 rods ... and even lighter 2PTs for the wings. I found this on the Rev forum while surfing for the answer to another question.

Also to digress a bit..I flew a local flyer's slightly modded 1.5 SUL over the weekend. Its a stock 1.5SUL sail and bridle but the leading edges were SkyShark P90s and the tips were 2PTs. Nary a breeze out there when I was struggling to put my B-Series with race rods in the air and his SUL is flying without any problem. Feels almost like flying an indoor kite outdoors. Weight savings from his setup compared to all race rods is typically about another 20grams.

Cheers,
Tom

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RevJB
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Re: Perfect Rev Spar

Postby RevJB » Sun, Nov 08 2009, 11:18 AM

I found the most scientific explanation of Rev flying I've ever seen. There is also a Rev simulator.

http://buchholz.hs-bremen.de/revsim/revsim.htm

http://buchholz.hs-bremen.de/revsim/mkreal/paper.htm

Scroll down to the section called Stability and Autopilot for a discussion on why inverted flying takes more work.

Image

Connect two matches by two strings (Fig. 14 upper left). The left match could now symbolize one of the handles and the right match could stand for the corresponding vertical spreader spar of the kite. If the kite rises (Fig. 14 upper right) matches and strings still form a parallelogram. The angle of attack is therefore not dependent on the altitude of the kite.

If, as shown in Fig. 14 middle left, the kite has rolled on its back () and the handles did not roll (), according to Eq. (12) a stability angle between kite and handles builds up (). If now the kite rises (Fig. 14 middle right) the angle of attack is decreased, thus the lift is increased and therefore the kite rises even more. No stable equilibrium is possible. The pilot persistently has to actively control the kite to stabilize it at a certain altitude. This aerodynamical instability is one of the main reasons, why it is much more difficult to fly a REVOLUTION® on its back than in its normal flying position.

If the kite has rolled one (or more) full turn(s) (), the stability angle becomes a multiple of too (Fig. 14 lower left) leading to a stable configuration. Even though the lines are crossed the kite rises parallel to the handles with a constant angle of attack (Fig. 14 lower right). Neglecting the friction of the lines the handling qualities are identical to the unrolled case.


[/hr]



I did find the answer to the weight question buried in a discussion of parameters for the simulator

Mass
The mass (weight) heavily influences all the reactions of the kite. A heavier
kite does not accelerate as fast (because of its greater inertia), it does
not rise as high (because of the greater gravity force) and usually it does
not turn as fast (because of its greater moment of inertia).


Based on above, it seems for a given deflection curve, less weight is always better.
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Mike
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Re: Perfect Rev Spar

Postby Mike » Sun, Nov 08 2009, 04:58 PM

The matchstick handles may be misleading. The handles are considerably shorter than the vertical spars, not like it's shown in the diagram. That would make much less difference in the upside down diagram. Also, you angle your wrist with respect to the kite. And there's the stretch of 120' of line.
I don't how much difference all that makes 'cause it would take more brain power than I got right now...

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Babbman
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Re: Perfect Rev Spar

Postby Babbman » Mon, Nov 09 2009, 11:34 PM

the perfect spar is the one that let's me just fly...

Chris (aka Babbman)

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Jeepster
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Re: Perfect Rev Spar

Postby Jeepster » Tue, Nov 10 2009, 01:27 PM

Babbman wrote:the perfect spar is the one that let's me just fly...


Chris,

Your inclusion of the word "just" in the above posting is curious. Please elaborate.

Cheers,
Tom

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Babbman
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Re: Perfect Rev Spar

Postby Babbman » Tue, Nov 10 2009, 03:37 PM

Jeepster wrote:
Babbman wrote:the perfect spar is the one that let's me just fly...


Chris,

Your inclusion of the word "just" in the above posting is curious. Please elaborate.

Cheers,
Tom


Babb don't mince words...lol

I've gone the entire route with kiting over the last few years. I started out buying a kite for every possible wind condition. Then I started matching spars to wind conditions. Then I started matching line and line length to wind conditions.

And after I got done doing all that and getting it right, either the wind changed or it was time to pack up and go home or back to work.

and I have a whole bunch of expensive kites and accessories that's just sitting doing nothing...lol

So I took it down to it's most basic elements. 2 Rev kites (standard & vented), 1 spar set (race rods), 1 set of lines (120's).

And I figured a couple of things out...

1) wind conditions here suck and are never steady. duh..lol
2) I don't have enough time to switch everything around trying to keep up with the suck (see #1 above) and still fly
3) With few exceptions, we either have wind or we don't. I don't even keep a set of 4 wraps in my bag any more and I won't carry an SLE under any circumstances.
4) Weights of rods just don't matter to me, I just settled on Race rods cause they are light, strong and I've never snapped one. I hate changing rods and I haven't found a need to since I started using them. I know there are variations in the weight of each rod but since I don't live where the wind is steady and smooth as glass, a gram here or there isn't going to matter. My muscles and hand positions will just take care of the differences, as they do with 'the suck' (see #1 above) or when the lines stretch, etc...

I learned long ago in everything I do that it is never the arrow, it is the Indian, so I just go with it. I know when to switch to a vented, I know when to just quit flying. Above all, with the methods I use for setup and tear down, I get to utilize whatever time I have....

"to let me just fly"

Oh yeah. I use 2 P90's as downspars on the 1 SUL that I carry. Why? Cause I had a 2 wrap bust during a dive stop and Dave gave them to me as temporary replacements. They are light and I've had no issues with them at all so until they break, they'll stay in... I also carry a 40' line set for when I HAVE to fly in variably light winds... (i.e. no winds)

That's about it!

Down to 1 bag, 2 kites and lines and I'm good to go for almost any situation I care to fly in... :up:


Chris (aka Babbman)



They that can give up essential liberty to obtain a little temporary safety deserve neither liberty nor safety...
Benjamin Franklin, Historical Review of Pennsylvania, 1759


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Mike
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Re: Perfect Rev Spar

Postby Mike » Tue, Nov 10 2009, 04:16 PM

Jeepster wrote:
Babbman wrote:the perfect spar is the one that let's me just fly...


Chris,

Your inclusion of the word "just" in the above posting is curious. Please elaborate.

Cheers,
Tom


I think he means he wants spars that allow him to just fly vs. spars that offer both flying & X-ray vision.

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Re: Perfect Rev Spar

Postby Babbman » Tue, Nov 10 2009, 08:54 PM

Mike wrote:
I think he means he wants spars that allow him to just fly vs. spars that offer both flying & X-ray vision.


Um, I'd rather they stop a speeding bullet... specially here in Aurora...

lol


Chris (aka Babbman)



They that can give up essential liberty to obtain a little temporary safety deserve neither liberty nor safety...
Benjamin Franklin, Historical Review of Pennsylvania, 1759


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Re: Perfect Rev Spar

Postby Jeepster » Tue, Nov 10 2009, 10:24 PM

Chris,

Thanks for the complete answer. I think many fliers, after an initial learning period, follow your idea of flying what you have installed.

Many will claim that the verticals take the most load, so it's interesting that you've been flying with P090 rods in that position with no problems.

Cheers,
Tom

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Re: Perfect Rev Spar

Postby Babbman » Tue, Nov 10 2009, 10:48 PM

Jeepster wrote:Chris,

Thanks for the complete answer. I think many fliers, after an initial learning period, follow your idea of flying what you have installed.

Many will claim that the verticals take the most load, so it's interesting that you've been flying with P090 rods in that position with no problems.

Cheers,
Tom


My SUL is rarely flown and only when winds are really light and on 40' lines.. not much pressure at all on the sail... but it held up through a few gusts


Chris (aka Babbman)



They that can give up essential liberty to obtain a little temporary safety deserve neither liberty nor safety...
Benjamin Franklin, Historical Review of Pennsylvania, 1759


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Mike
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Re: Perfect Rev Spar

Postby Mike » Tue, Nov 17 2009, 01:05 PM

There were some words spent on discussing Rev spars over on the Rev forum here.

My comments over at Rev lately seem to be on the negative/skeptical side, so I thought I'd pose the questions I have over here. Any engineers got ideas?

I don't think the comparisons are valid. Paper airplanes and balsa airplanes need weight in the nose because you throw them and then let go. There's no further control and the weight helps to keep the plane have the right attitude. Also, airplanes fly horizontal, into the wind, while kite fly closer to vertical with the wind. Commercial airlines don't seem to have extra weight in the nose either. (donut eating pilots excepted)

The comparison between heavy and light balls seems off too. Movement of the kite is caused by wind blowing against the sail (whether its generated by mother nature or your feet). The more wind you feel, the better. A *light* ball will feel the wind, a bowling ball will not. Sure it's easier to throw a tennis ball, but that's because the heavier ball negates the air resistance better. Not what we want with kites. Or at least it's much more complicated than throwing a ball.

The Zen may very well fly much better, but I just think their analogies over at Rev aren't good ones.
For starters, they experimented with different spars to vary the weight. That also changes the flex which changes the shape of the sail. That's really important. They should have thrown weights in the leading edge instead.

Anyway, if there's anyone here who's an engineer or knows one, I'd like to hear what they have to say.

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Re: Perfect Rev Spar

Postby Jeff » Tue, Nov 17 2009, 04:29 PM

I agree Mike. Nose weight in gliders is all about maintaining direction, not lift. A plane that is not producing thrust is going to want to move through the air in the way the passing wind will allow...the heaviest part forward.

Now, do they have a point about a heavier spar handling turns better? Maybe. The momentum in the leading edge will be affected by its mass. How it turns is probably somewhat affected by its momentum. How much, I have no idea.

The overall weight of the kite...I don't know. I guess it will have an effect, but I'm not sure how much difference very small changes would make. We know that a Rev 2 is faster than a 1.5 which is faster than a Rev 1. I believe that's a function of the wind being able to impart a certain amount of energy to the sail to move the mass of the kite, and the more mass it has to move, the more energy is required. Now, the smaller kite has a smaller surface area, so it would appear that the weight of the kite is a larger factor in the equation than the area.

I don't doubt that various designs of the Zen have given different results and flight characteristics, but it's something that is being understood and tuned through trial and error, not scientific understanding of aerodynamics. Hell, the calculus alone is way beyond me...
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Re: Perfect Rev Spar

Postby BillLamm » Tue, Nov 17 2009, 07:16 PM

I don't know for sure but.... :wink:

I think the string in our hand and how it is bridled to the kite is the proverbial weight on the front of the glider... A gliders flight is a carefully balanced game of falling to build wind speed that creates lift...

The speed of the kite is (A) wind speed and (2) surface area of the sail... and I suspect at the end of the day the stiffness of the frame will have more to say about speed and control in turns than the momentum from difference of a few grams.

the more I fly with arrow shafts or a set of 3 wraps on a tyvek/duct tape or a rip stop nylon with no vent sails the more I think Babbman is right.... (I just want to know if he is having a spare kite sale any time soon)

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Re: Perfect Rev Spar

Postby Babbman » Tue, Nov 17 2009, 07:36 PM

I get rally anal about this subject..lol... cause none of it really matters until you accomplish the most basic part of anything which is learning. And you learn by practice. Not by weighing spars or changing them out when the wind changes a few mph or buying a kite that claims to fly in no wind...

The one word I saw over on the Rev thread that Mike pointed out more than any other WAS?... TA DA!

PRACTICE!!!!!

I've watched some of the best rev fliers fly. I've seen them flying and having as much control in low winds as I seem to have in higher winds. In low winds, they are flying while I am on the ground. They have the same kite I have. Sometimes even a heavier spar than mine. But they fly.

WHY

Because they have perfected the proper technique for it by flying which is actually (shhhh) <practice>.

It's not all about grams of weight, type of sail, bridle or all of the engineering aspects of it. OF COURSE the engineering has an effect but the engineering (for the most part) has been done and the result is in our hands. What happens after that is up to us.

Really... think about watching someone who has never flown a Rev and while you are out there flying nice and pretty in a 7mph wind, they can't even get it up off the ground. Why?

Because you practiced enough to be able to fly. Now, you just need a lot more practice to learn to fly in low winds. Really...

AND, it's why I've settled into just 2 kites for 99% of my flying.

And why I WILL be selling a bunch of kites...lol...

So I can afford a Zen.... :up:

But it won't stop me from practicing...lol


Chris (aka Babbman)



They that can give up essential liberty to obtain a little temporary safety deserve neither liberty nor safety...
Benjamin Franklin, Historical Review of Pennsylvania, 1759


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RevJB
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Re: Perfect Rev Spar

Postby RevJB » Tue, Nov 17 2009, 08:39 PM

First, I totally agree with Babbman about practice. My son can fly in less wind than me because he is a better flyer. I can now fly in lower winds than before because I've practiced.
(I'm certainly willing to practice some more with used kites. Say the word Chris when you are ready to sell some. :up: )

Having said that, I guess I have an engineer hiding in me because I like understanding how things work, including Rev kites. Unlike my son, my flying isn't instinctual. I do better when my brain gets how things work.

I agree with Jeff that the more mass, the more energy is required.

Jeff wrote:... We know that a Rev 2 is faster than a 1.5 which is faster than a Rev 1. I believe that's a function of the wind being able to impart a certain amount of energy to the sail to move the mass of the kite, and the more mass it has to move, the more energy is required. Now, the smaller kite has a smaller surface area, so it would appear that the weight of the kite is a larger factor in the equation than the area...


Based on what appears to be the mathematical model, less mass is always better for a given design and weight is not needed in the same manner as a paper airplane. I agree with Mike that the airplane weight is to keep wind from the sides from overly impacting the flight.

RevJB wrote:I did find the answer to the weight question buried in a discussion of parameters for the simulator
Mass
The mass (weight) heavily influences all the reactions of the kite. A heavier
kite does not accelerate as fast (because of its greater inertia), it does
not rise as high (because of the greater gravity force) and usually it does
not turn as fast (because of its greater moment of inertia).


Based on above, it seems for a given deflection curve, less weight is always better.


I'll save the practice for the field and the engineering for the downtimes and have the best of both worlds. The more I learn the easier it is for me to practice.
John

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