Is there a chart or good article relating kite size and wind speed to Hp generated . just wondering what’s actually going on up there w/ these engines. I understand the other variables involved. Just looking for an idea or ballpark #......i tend to relate to Hp.

Not sure if there are any charts handy but....

Source: http://en.wikipedia.org/wiki/Horse_power#Definitions_of_term

1. Imperial horsepower = exactly 550 foot-pounds per second is approximately equivalent to 745.7 watts.
   
2. Metric horsepower = 75 kgf-m per second is approximately equivalent to 735.499 watts.

Source: http://www.guardian.co.uk/environment/2008/aug/03/renewablee...
Scientists from Delft University of Technology in the Netherlands harnessed energy from the wind by flying a 10-sq metre kite tethered to a generator, producing 10 kilowatts of power.

I expect there is a difference in the amount of power generated under static and "in motion" (apparent wind) conditions.

After that...break out the sliderule and abacus.

I really need to find a job that pays based on Google-fu.

ATB,
Sam

Perhaps this would also help

Sail load calculator

There are just too many variables to quantify this. I can change a kites power by adjusting my angle upwind or downwind just a few degrees. And it's continuously variable too. Ease downwind and power lessens while speed increases if well powered. Upwind and power increases while speed decreases. If not fully powered, these can reverse.

My understanding, too, is that that are too many dynamic variables to allow for calculating a static watt production in airborne kites.

The board drag, surface friction, wind gradient, sail material porosity, line stretch, rider weight, slope inclination....There are WAY too many variables that must be put into control. The only way that I can think of a reasonable experiment is in a controlled wind tunnel with the kite affixed to a non-moving point.

Of course.... an experiment like this won't take into account apparent wind factors (which could drastically alter a kite's performance attributes.)

Easier to just say.... "Big kite? Lots of power. Small kite? Maybe lots of power, too."

This should make it easier to decide, eh?

-joedy

i would just like 1 solid Hp example.... i know this could be discussed endlessly w/out an answer and i am looking to keep it simple. So lets say Brian’s speed record run..... can a hp # generated by the kite be calculated???.. on the runs avg,,,, or at any pt. of that flight?? i get that the # would be changing at all times. im sorry im not asking anyone to do my math for me... if someone knew that there kite was capable of producing __hp@__mph in __wind my itch would be scratched...thank you for the links i find all this info interesting

I can't even imagine all the variables that would have to be considered in figuring this out. Take for example Brian's run which was in a heavy buggy, with a 2.5 m +/- fixed bridle kite over a fair amount of distance. My runs are much shorter and often on a 12m (roughly 7m projected) kite with nothing attached but my fat butt.

As joedy pointed out, just the variables involved with the drag on the surface (brian on a buggy, me on skis) have a huge effect on what the kites can or can't do.

Believe me I understand your frustration at not being able to find a defined answer. I gave up a long time ago and pretty much just go out and ride until I'm in the right place at the right time with the right kite on the right ski on the right surface and hope to catch the right gust. If you could divise a way to calculate hp from known variables after the fact. Like if you had a given rider on a given kite taking into acct. drag and surface friction on the vehicle, windspeed, forward speed, acceleration and g-forces produced you might be able to extrapolate how much hp was generated at a certain moment. Line stretch would probably play a factor as well.

My 2 cents

Drawbar horsepower. This is used to determine hp of a train.
This can be done with a dynamometer connected between the kite and harness on the power lines. It maintains a record of drawbar (pull) and speed. Could possibly very accurate if you were able to adapt one to kiting.

I think the drawbar example is very close to what you would need. The train is a little simpler because the force on the draw bar is conveniently aligned with direction of travel.

The complexity in the kite problem is that the you need the vector product of the force applied by the kite and the velosity of the kite. Recall that velocity is the speed and direction of the buggy. I think you would need to collect buggy speed and direction with with a GPS. At the same time you would need to measure load on the lines and the angle between the flying lines at the pilot and the buggy.

You could set it up like this: Use a depower kite as the buggy engine. Install a strain gauge with a digital output inline with the trim line below the bar--like between the trim line and the chicken loop. Feed the strain gauge data to a data collector that has its clock synched with the GPS clock. I'm not sure how to collect the angular data for the flying lines--perhaps optically with a video camera mounted above the trim looking at the flier?

To get good kite load data, the pilot would need to trim the kite so the bar can ride on the stopper and transfer all load through the strain gauge. I think you could safely let the pilot two-finger steer on a long bar--the effect will be negligible.

If you combine these three data points: buggy speed, kite load applied to CL, and the angle between the kite lines and the buggy's direction of travel you can calculate the effective power applied to the pilot. What's more, you can see this value over time.

There is one big weakness in this calculation: if the buggy slides you don't know the angle between the direction of travel and the flying lines. The GPS would record accurate speed data, and the load data would be fine if the pilot does not correct at the kite, but the angle would be wrong.

Does anyone have any great ideas about how to correct for that? You could do it with an inertial navigation system but this I am hoping for a simpler solution. Are their GPS the incorporate gyros? I need a device that can reconcile the device's orientation with the direction of travel. Heck, if such a device existed you could install one on the buggy and one on the kite lines to get the angular difference.

Anyone? Help me out here.

Philip

Feyd is actually correct. What he says (without specifically saying) is that experience is really the only gauge that you can use when it comes to kite engines. Once you are attuned to your flying location and conditions, experience will give you a general sense on how much power a kite will produce.

One thing that I have found to be a better guide than trying to come up with raw power is to consider the kite as an aeronautical wing. Once you start seeing kites this way, you start to consider aspect ratios, chord length, wing thickness and profile changes (like the Speed 3 de-power, for example.)

While these won't give you raw HP numbers, they will place the kites in certain categories that are easily to quantify. We call some kites "gruntier" and this generally means that they have lower aspect ratios, longer wing chords and tend to sit deeper in the wind window. These characteristics are indicative of the type of session that you're likely to have, but not necessarily the amount of HP that it will end up generating.

A smaller kite on a windier day will generate just as much HP as a larger kite on a lighter wind day. HP alone, won't really tell you what to expect, but having an idea of how the wing geometry will conduct itself in the air will give you an idea what you're in for.

I do agree, though, that there is a LOT of room for kite research and a lot of design ideas that can revolutionize the sport even now.

-joedy

i agree on all the above..and i am not looking to create a theory thread cause we could do this forever, particularly w/ all the variables..but.....it is an engine that is producing power so i guess that means, we are producing hp.... i'd be shocked if at this point nobody has placed a range on what we do know.... an upper level or what is possible?? or a simple,,, hey ukno your throwing around 100hp up there in this kinda wind w/ that kite... yea, it changes all the time and its way more important to know your foil than know the #'s......but hp is something most get...and i simply was wondering??

That wondering had created innovations that improved our way of life including the fun factor.
As far as throwing a 100 hp kite into the wind is not for me. Maybe 1-2 hp on a pain free day.
1 hp @ 33000 ft lbs/min. seems quite a bit to consider, I ride atb. Possibly 4-5 for a buggy. Think go-cart.

Horsepower? ATB? I just had to...
http://www.youtube.com/watch?v=Vm3Ttjbe1Rc

Well, in crude numbers, one horsepower is about 750 watts.

One horsepower will lift 100 pounds 33 feet in about 6 seconds or so.

Simply doubling the numbers gives something akin to 2 horsepower lifting 100 pounds 66 feet in 3 seconds.

I think that it's conservative to presume that kites that are generating about 4-5 horsepower can lift a 200 pound flyer in about a second or two.

Of course, this is the For Dummies version. A safer (and smarter) solution is to heed the manufacturer provided wind chart ranges and your own little voice in the back of your mind that whispers, "Maybe taking the 15m Speed III out in 30 knots may not be your best idea today."

-joedy

33 ft in 6 seconds is about a 22 mph lift. :shocked2:
Now cruising the beach... Awesome

Quote:

Originally posted by joedy Simply doubling the numbers gives something akin to 2 horsepower lifting 100 pounds 66 feet in 3 seconds.

What? You don't double all of the numbers!!! If you have double the power you can do one of:
Double the mass
Double the distance
Halve the time

Not all three, you need eight times the power to do that.

Yeah, that makes sense now that you mention it.

I have a sneaking suspicion that the 4-6'ish HP range is probably not too far from the real-world value.

-joedy

I think we have deviated from what horsepower really is. It isn't the power used to cruise along. HP by definition is about acceleration. This would be easy to calculate with known mass and a GPS track showing speed attained in a known distance. Feyd is probably able to accelerate faster than any of us but he is missing the mass of the buggy. This might actually be interesting to come up with some numbers. Ice and dry lake surface would give better numbers due to rolling resistance being least significant there.

Bob I think in our application power is used to cruise. Horsepower = foot-pound force per minute (ft-lbf/min).
This would be the power it takes to move mass along the direction of travel.
In the auto industry horsepower is related to speed and being the fastest. Bragging rights.
Velocity is the rate of change of the position of an object, speed.
In the end of all things said, Joedy reminded us of the safety side of this sport.

Hmm. Maybe we have deviated from what you want to talk about but power is exactly what keeps you moving at speed. You can decompose the units of power into force x speed. That the vector product of the force applied and the speed of travel and you will get power, watts, hp, call it what you will. It's the thing a physicist or an engineer calls power.

Are you more concerned with kiters call grunt? I'm not sure what physical concept that would be. I'll think about it but for the moment I'm stuck.

By the way, I figured out an omission my in my how-to-calculate-power-at-the-CL post. The angle of the kite above horizontal--assuming the buggy is traveling on level ground--also figures into the vector product of velocity and the kite's force vector. The data collection isn't easy, but it is doable.

I think it might be a lot more practicable to approximate the power input to the pilot and buggy by collecting typical loads, angles and speeds during steady state riding.

Philip

Since part of the calculation for horsepower is time, I would contend that horsepower is what affects a 0-60 time in a car. Torque is what allows you to maintain speed up a hill or against resistance like wind on your frontal area. If you change the term to " power", then that is just the ability to do work, a much less constrained term.

Thanks for not calling me fat, Bob.

Oh wait, that's not what you meant by "missing the weight of the buggy". I get it.

Not sure if I follow that. My books tell me hp is the power to move and torque gets you there faster,(acceleration). Hp will maintain velocity after torque is maxed. At the track torque is what rules for 0-60 runs.
Having a few extra ponies under the hood always helps though. Again bragging rights. My money is on the torque
curve.
This does deviate from the original question. Pbc is thinking in the right direction. Above my skillset.
I am still relatively new to kiting and had thought how much power is produced by a kite at the top
of its wind range.
Abkayak should receive a gold star for the question of the month.

When I am trying to answer outsiders questions about our sport I point out the our kites replace a motor boat to a wake boarder.

Using this logic and knowing you can't pull somebody with less than about 20hp I am guessing we produce at least that much to get up and going + boost ? I know I used to ride 2 skis behind a 7m outboard when I was young so ... ? :dunno:

Yeah, but that outboard motor has to displace the drag of the skiers as well as the drag of the boat itself, so it's a close comparison, but not an exact one (insofar as horsepower ratings are concerned.)

With our engines, the resistance is much less and varies considerably depending on land, water and vehicle conditions.

I have to think that somebody in the history of mankind has already calculated the force of a cubic meter of air (at a specific density) traveling at a specific speed. If nothing else, a simplified projected area calculation should provide a theoretical starting point for determining a kite's energy potential.

In a way, manufacturers already do this by posting the kite sizes, but as we've been discussing, there are just too many dynamic variables which would prove challenging to convert to controlled conditions. Kite sizes get us in the ballpark, but end up being just one of the many variables that determine if a kite will be a good choice on a specific day.

I'm not into sailing, but does anyone know how the sailboat racing crowd determines (or limits) sail sizes in certain classes? Is it purely based on surface area or limited by mast height? I would think that sailboat racing tries to equal all of the variables for the competitors so that skill alone is mostly the determining factor.

-joedy

Quote:

Originally posted by Streetrider56 Bob I think in our application power is used to cruise. Horsepower = foot-pound force per minute (ft-lbf/min). This would be the power it takes to move mass along the direction of travel. In the auto industry horsepower is related to speed and being the fastest. Bragging rights. Velocity is the rate of change of the position of an object, speed. In the end of all things said, Joedy reminded us of the safety side of this sport.

Bob is correct. Power is more applicable to acceleration than speed.

You need a lot of power to go fast because you are trying to overcome drag. At high speed aerodynamic drag is the major factor preventing acceleration. To go faster you need to accelerate, and to do so the power output of your engine needs to be greater than all sources of drag and the losses within the system.

Increasing the power output of a car will increase the top speed, but you could also increase the top speed by reducing the drag (by improving the aerodynamic profile, using fairing, etc...).

At lower speeds there is less aerodynamic drag, so power output has a greater affect on acceleration. There is still drag from the surface and any moving parts in the system, plus any losses in converting power into propulsion, but you can get a rough estimate of the power of your propulsion source using the acceleration and mass from standing or slow speed, and assuming that drag and losses are small.

This would work best in an environment where the drag actually is small, like skis on ice, or a buggy on a hard flat surface.

Torque is not really relevant for a kite like it would be in an engine. Torque is just a rotational force. If you combine torque with angular velocity (i.e. a spinning shaft) you have power. So yes, you need torque to accelerate using an engine, but increasing the torque also increases the power.

Horsepower is just a measurement of power.

Quote:

Originally posted by pbc Hmm. Maybe we have deviated from what you want to talk about but power is exactly what keeps you moving at speed.

Power is required to keep an object moving a speed if there is drag to overcome. If there is no drag, then the object will retain the same speed without any power required.

Quote:

You can decompose the units of power into force x speed. That the vector product of the force applied and the speed of travel and you will get power, watts, hp, call it what you will. It's the thing a physicist or an engineer calls power.

True, but what is the force? In this case it is the force required to overcome drag. If you can calculate drag, then you can calculate power, but calculating drag is very difficult. This also assumes that the speed is constant over the period that you measure. You could measure the forward force applied by the kite through the lines, but this is also very complicated.

Quote:

Are you more concerned with kiters call grunt? I'm not sure what physical concept that would be. I'll think about it but for the moment I'm stuck.

What does grunt do? It causes you to accelerate. This is power, the difference is that is really only applies at low speed. A gust at high speed also causes you to accelerate, but it would be harder to quantify a gust.

Quote:

I think it might be a lot more practicable to approximate the power input to the pilot and buggy by collecting typical loads, angles and speeds during steady state riding. Philip

There are two ways you could do it. Take measurements while in steady state (at speed), or measure acceleration.

Measuring acceleration from a standing start is far easier than trying to work out the forward component of force from the kite. Of course this would only give you a power output from the kite at slow speed, whereas race kites increase in power output the faster they go.

If I have lost anyone, note that the acceleration is a component of force, i.e. Force = mass x acceleration

A constant acceleration can be calculated if the starting velocity, time, and distance travelled are known. You can use this acceleration and the mass to work out the force. Since you already have distance you can use this force to determine the work, and since you have time you can convert the work into power.


Now I am going to really lose everyone

If a kite buggy under zero drag conditions accelerates at a constant rate I can use the initial velocity, mass, distance travelled, time taken, and the following equations

P = W/t
W = F.d
F = m.a.
a = (Vf - Vi)/t
Vave = d/t
and assuming a constant acceleration Vave = (Vi + Vf)/2

to work out the power of the kite.


a = 2d/(t^2) - 2Vi/t
note that if Vi = 0, then this is just a = 2d/(t^2)

P = (2m(d^2))/(t^3) - (2Vi.m.d)/(t^2)
note that if Vi = 0, then this is just P = (2m(d^2))/(t^3)

P = power
W = work
t = time
F = force
d= distance
m = mass
a = acceleration
Vi = initial velocity
Vf = final velocity
Vave = average velocity

Hope you all followed that :singing:

And we wonder why there are no girls on this forum.....


But just to add to the cornfusion, wha about friction or coefficient of friction? How does one quantify that and how can it be applied to your equation? Again using the ski/buggy example the buggy must sluff off some energy in the form of lateral friction loss. Even if the appearance is that it is heading in a straight line I'm sure there is some minor level of drift. A ski in the otherhand, on an ice surface with the right tune and right skier will not suffer from lateral drift and will act as if it is literally on rails.

Never mind the energy loss involved with buggy frame flex, tire deflection or even variations of tire pressure or the effects that temperature has on that variable.

And speaking of temp. Cold dense air vs. warm air as well a humidity probably have some role here as well?

Quote:

Originally posted by DemBones ... Hope you all followed that :singing:

Sounds good. I like this.

Now describe the gear that will allow that measurement. I think you'll need a pretty high sampling rate.

Philip