so when attempting to break land speed records with kites... it seems that its always high wind and small kite... as in the case of NABX and the current record... IIRC it was a 2.7m vapor and some high wind (not sure on the wind)

Why then, cant you break records, or attain speeds like this with larger kites, in slower wind?

Ive heard of a 10.8 reactor pulling bugs 20mph in 5ish mph wind... so would the 10.8m reactor smash records if you took it out in the mid 30s? (120mph WOOOOOO )

My best guess is that the larger sail provides more drag than the smaller, and this drag keeps the wing from moving forward in the window, and keeps it back, providing more lateral pull, and not forward pull.

Am i right? Thoughts?

You have to be able to resist the pull of the kite to generate speed with it. There is a theoretical limit of reaching X times the speed of the wind. You can't circumvent that rule by going with a larger kite. In fact, the multiple goes down as the wind speed goes up and kite size goes down. Aries record was barely over 2 times the wind speed. I've been into the mid 20's with the big RII having not more than 8-9 mph winds. With only 5 mph, you would cruise in the mid to upper teens. After the wind gets above 9-10 with that kite, the side pull becomes too great to maintain a straight line.

It's all about efficiency.

A larger kite weighs more, so it loses some energy supporting itself in addition to providing drive.

Large kites, also have more total bridle area producing more drag.

A smaller kite requires less air to maintain internal cell pressure. More cell pressure means a stiffer "air-frame" that is capable of cutting through the air more efficiently. To exploit this, the Vapor 2.7 has 33 cells. :o :o

More cells for a given size (within reason) result in smaller cells running at higher internal pressure -> stiffer air frame -> increased flight efficiency.

Wider aspect ratio/lower profile kites give up some stability, but trade that off for creating a knife's edge that rips through the air wicked fast.

ATB,
Sam

curiosity gets the best of me sometimes... and i think about stuff way too much

i really like the details... this is right up there with my A/R question, lol
if point A is true, and point B is true, does A=B

lol, the answer of course is rarely, if ever... but the details, and the greater undestanding gained, is what im after... these discussions are really what keep me here! Helping newbies, and kite pr0n are fun... but the indepth knowledge found around here is awesome!

Thanks for the input

mass , power, drag...the limit is the "useful" power and balance of all elements to yield speed.

a large powerful kite might require a turning plow to hold the system together and not yield much forward speed.

a small kite matched with resistance allows the system to maintain a line and produce speed

I have found with my 10.8 Reactor that the limiting factor is how much power I can hold.

On a low resistance like snow I can get going in about 4mph . The kite feeds on my speed and gains more and more power as it sees more apparent wind. At a point I can no longer hold a line and must slow down or start getting sent downwind. I would guess I am going only about 15mph when this happens. That is more than 3 times the wind speed.

I can get to much higher speeds with even my 15m arcs but need a higher bottom end . Again I can go about 3+ times the wind

Clearly there are a few factors in play here. I find my top end 1 of 2 ways. Either the kite won't go any faster in a given wind in a given direction or it builds up so much speed I can't keep a line.

Drew google "downwind faster than the wind" , it will have your head spinning for a while.

Angus has a bit on his site that wraps this up pretty succinctly. If that doesn't nail it down for you, Peter Lynn discusses the the concepts involved with the detail and precision of the venerated engineer he is.

You are trying to compare a ratio with a fixed value and that dog won't hunt.

The Red Nek version is a kite hits the lift to drag ratio "wall" at a fixed speed, not a ratio of actual to apparent wind speed. The "wall" is the physical limitation of drag based primarily on bridle lines and then on the profile and aspect ratio. At that speed, it's a zero sum game, it can't fly any faster, that's the top end of the kite. In gross terms, more bridle lines equals more drag, "thicker" profiles that present more "Face" to the wind equal more drag, low aspect ratio (longer path the air has to follow) equals more drag.

If the "wall" of a 10m kite is 20 mph, when the apparent wind hits 20 mph, that's all you're gonna get out of it. Equilibrium ! If you can figure out how to get it up to that speed on the least wind possible, you can achieve a pretty reasonable ratio of actual wind speed to ground speed but that doesn't change the fact that your kite is maxed out.

I think the physical limits are 2.8 times the wind speed and I have friends that log some incredible speeds on snow when its 20 to 30 mph on lei's

What if you weren't restricted to a narrow beach, say you had vast open spaces to roam.
What if you could bomb downwind for miles and miles with big winds, big kites and big balls, would a smaller kite propel a buggy to a higher top speed vs a bigger kite ?

Quote:

Originally posted by RedSky What if you weren't restricted to a narrow beach, say you had vast open spaces to roam. What if you could bomb downwind for miles and miles with big winds, big kites and big balls, would a smaller kite propel a buggy to a higher top speed vs a bigger kite ?

Yup, assuming it were the "same" kite, (same profile, aspect ratio, planform, etc.) if nothing else, the smaller wing would generate less bridle drag and that alone would let it run fast than the larger one.

In the vast snowfields of the Rockies where you can let it go to the limit, big, light lei's,long boards and long ski's and huge balls rule. If you were to take the most efficient foil you can find and go head to head with the big lite tubes it would be no contest.

Quote:

Originally posted by g-force junkie I think the physical limits are 2.8 times the wind speed and I have friends that log some incredible speeds on snow when its 20 to 30 mph on lei's

No, that number depends on the L/D (lift/ drag ratio) of the kite. The higher the L/D, the closer the kite gets to the edge of the window, the higher multiple you can achieve.

I routinely do 3X on the beach with buggy speed documented by the GPS and the wind range during the run documented by a commercial weather station on the beach that reports every 20 min.

I've heard 4x bragged, but not documented.

It is my 10.8 Reactor that I am pretty sure I am pushing the 2.8 with ?

I don't have fact numbers but feel like I am not stretching the truth when I say I have been going in 4 ( maybe 5 ) mph. I am pretty certain a am getting very close to 15mph when I can't hold a line even though it seems the kite could go faster ???????

I guess I'm ?

Quote:

Originally posted by Bladerunner It is my 10.8 Reactor that I am pretty sure I am pushing the 2.8 with ? I don't have fact numbers but feel like I am not stretching the truth when I say I have been going in 4 ( maybe 5 ) mph. I am pretty certain a am getting very close to 15mph when I can't hold a line even though it seems the kite could go faster ??????? I guess I'm ?

Nope, not crazy. That may very well be the "wall" where you can't get the kite to fly any further ahead of the wind, it sits back in the power window and generates lateral force rather than leading force. It's a tremendous amount of force, no doubt but that's the point where the drag of the kite defeats the lift of the kite. Equilibrium at a fixed air speed !

Bottom line, it's about apparent wind at the kite. Basic equations that applies to lift on a wing or thrust from a propeller (same thing, different orientation):

Force = Air Density/2 x Area x Velocity ^2 x Lift Coefficient
Power = Air Density/2 x Area x Velocity ^3 x Lift Coefficient

Projected area affects linearly. Double area and you double lift force or pull/tension on lines.
Lift Coefficient is dependent on airfoil section, aspect ratio of wing, and angle of attack. Has a linear affect on force and power.
Apparent wind speed affects force as square of wind speed; power as cube of wind speed.


Tell me which factor matters most if you have a need for speed...

krumly

Quote:

Originally posted by krumly Bottom line, it's about apparent wind at the kite. Basic equations that applies to lift on a wing or thrust from a propeller (same thing, different orientation): Force = Air Density/2 x Area x Velocity ^2 x Lift Coefficient Power = Air Density/2 x Area x Velocity ^3 x Lift Coefficient Projected area affects linearly. Double area and you double lift force or pull/tension on lines. Lift Coefficient is dependent on airfoil section, aspect ratio of wing, and angle of attack. Has a linear affect on force and power. Apparent wind speed affects force as square of wind speed; power as cube of wind speed. Tell me which factor matters most if you have a need for speed... krumly

The one you didn't mention... drag.

A wing can generate all sorts of power but if that power is transmitted through lines that are at a bad angle to the direction of travel, you're out of luck. That's exactly what happens when you max out a kite. The force moves further and further back in the window until it becomes unusable and actually a determent by decreasing stability of the platform anchoring it.

Just like any other form of speed sport, decreased drag equals increased speed. If ya wanna go fast, you and your gear have to be as smooth and efficient as possible.

greasehopper -

I purposely omitted any discussion of drag and the relevance of lift-to-drag ratio as a measure of efficiency. Just wanted to make the point that BY FAR the biggest factor in lift production and power generation is the 'apparent wind' seen by the kite, which correlates to the 'true' wind speed.

No matter the size or efficiency of a kite, higher wind velocities equal more pull and more potential power. But as you've pointed out, how well the kite makes use of the wind and how your setup translates power from the kite into your speed across the ground or water is a more nuanced and complex subject.

krumly

Opps, sorry. Point well taken... and entirely valid on it's own merits.

:o

Wow! I always learn so much when these threads take off!

Thanks for all the input!!

my head hurts lol. jking but wow you guys take your kiting seriously.

I don't know that I take kiting seriously so much as we all come from some pretty diverse and sometimes technical backgrounds. That just means many in the community have had reason to study some of the finer points of physics at length. Newton's law apply to jumbo jets, flying squirrels and kites alike, all the same forces and limitations are at work.

That's one of the great things about THIS forum, the knowledge base always seems to be greater than the sum of the parts.

That's one of the great things about THIS forum, the knowledge base always seems to be greater than the sum of the parts.

LOL. awesome greasehopper.

All theoretics and technical details aside I think it comes down to the pilot on the ground, enviromental conditions, room to run and equipment. As well as luck in the form of being in the right place at the right time.

My best speeds have been on medium size kites in lighter winds than what the buggy guys have been using on the playa. Very much counter to the general conscensus.

In regards to a speed limit on a given wing I'm not convinced that they have set speed limits, at least not that I'm at risk of reaching. I've found that some wings do seem to max out eventually only to find later that with a change in conditions they will go faster. But with a lot more effort than is really reasonable to make it worth pursuing. I find it highly unlikely that many wings would be prone to V-Max type failures.

I'm better off not knowing the details and theorectical design limits. To quote General Yeager "that one thing you don't do, you don't believe anything anybody tells you about an airplane." Unless the designer themselves is telling me what the kite can or cannot handle I take it all with a grain of salt. People's opinions on kites is all very subjective at best. A kite will do things for me that it won't for others and vice versa.

Even with the designer's input I'm better off in going out and finding out for myself what the limits of my kites are. The big factor that has been keeping my speeds down has been room to run. Last season we scouted out and found some good spots. I'll be in better shape this year to make use of that space.

We'll see what this season brings.:wee:

Re Feyd's 'I find it highly unlikely that many wings would be prone to V-Max type failures,' I totally agree.

If I'm overpowered and can't hold an edge, I'm probably being yarded downwind. Certainly lowers the stresses on the kite and rigging, even as it kicS-P-A-M-L-I-N-K-s my butt!

krumly

AWSOME point Feyd

Very true each pilot, buggy, tire, and kite combo is different. To say that the max is 2.8x the wind isn't exactly truthful in that case instead of using a 2.7 vapor to set 82. mphs wouldn't they have gone almost 120 with a larger kite in the winds. I heard but am not for sure that the wind was like 45 mph that day.

Don't forget that the speed of X times the wind diminishes as the wind speed goes up and kite size goes down. It isn't a global limit either, its just the limits of that rider, kite and conditions at the time.

As was said above by Phreerider, you only benefit from "useful" power and I"m sure that since Arie ended up in the bushes beside the playa after breaking the record that he couldn't have made use of more power from a larger kite that day. Maybe a .1 or .2m larger kite, but certainly not the next size up IMHO.

Bushes = Brake.

This too much paper talk. Just get out and do it.

Also tune kites helps too, play around with your bridles.

Manufacture data is just a reference point.

2nd Pryo's comment regarding the knowledge base in this forum. I may be a "seat of the pants" flier but it is always nice to know that when I have a question about the numbers there are people in here that have that stuff dialed.

Bridles?, what the hecks a bridle?;-)

We don't have bushes we have trees and rocks. If I'm in the trees then I'm in real trouble.

Feyd, you point out one other thing that plays a HUGE role in developing speed. On the race track as well as the windpower sport arena, Side Bite is King. Holding an edge/line is key to developing power and speed. Skis and snow boards will win that battle nearly every time against a buggy on dirt as the slip angle of a tire's contact patch is nothing compared to a board edged up hard. Maybe a buggy on asphalt with the right tire and chassis geometry in the right conditions could come close, maybe. The bad part about that scenario is when the buggy finally unhooks... things are gonna get really exciting in a big hurry. I don't see it ending well even with a bit of brush = brakes.