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 Post subject: 10M kite in 30 knots converted to horsepowerPosted: Tue Jul 31, 2012 10:56 pm
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Joined: Wed May 27, 2009 2:50 pm
Posts: 196
Ok so I was wondering just for fun .. I was jumping 30 feet the other day and I was wondering just how much power my kite had to yank me 30 feet into the air in like 2 seconds. I was wondering if anybody had a guess as to just how much horsepower that kite must have to do that. I was guessing it could have about as much power as a 200 horsepower boat. how could you convert this if it is at all possible ??

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 Post subject: Re: 10M kite in 30 knots converted to horsepowerPosted: Wed Aug 01, 2012 5:04 am
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Joined: Sun Jan 06, 2002 1:00 am
Posts: 2552
Location: Mauritius, waterman since 1960
Thats what I always tell my students.
That thing has 200 horsepower, so you have to learn to handle these if you don't want to get hurt.
Power without control is f.... dangerous (spiderman)
Nico

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 Post subject: Re: 10M kite in 30 knots converted to horsepowerPosted: Wed Aug 01, 2012 7:17 am
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Joined: Wed Oct 12, 2011 6:52 am
Posts: 43
This reminds me of those examples in physics

d=3ft=9.1meters
F=75kg * 9.8meters/second = 735Newtons
t=2 seconds

W=F*d=6688.5 N-m
P=W/t=6688.5 / 2 = 3344.25 N-m / s

1 N-m / s = 1 Watts

1 horsepower = 745.7 W

3344.25 W = 4.48 horsepower

My guess is about 4.5 horsepower, I could be wrong though, I'm pretty rusty on physics and it wasn't fun

Here are some pages that came in handy:
http://www.convertunits.com/from/N-m/s/ ... ational%5D

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 Post subject: Re: 10M kite in 30 knots converted to horsepowerPosted: Wed Aug 01, 2012 8:56 am
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Joined: Wed Aug 03, 2005 6:25 pm
Posts: 764
Location: Vancouver
jteabird wrote:
I was wondering if anybody had a guess as to just how much horsepower that kite must have...

This addresses your question in some detail. I wrote it five years ago, about force, pressure, energy and power:
http://kiteboardbc.com/phpBB3/viewtopic.php?f=1&t=178

And here's an excerpt from it:

POWER

Power is the rate at which a device can convert energy from one form to another, and is usually measured in watts or horsepower. It can be a confusing term, because the relevant types of energy have to be defined. A 100 watt lightbulb converts electrical energy to light energy and heat energy at a rate of 100 watts, but if the lightbulb is only 20% efficient, that means it only converts electrical energy to light energy at a rate of 20 watts.

A bouncing rubber ball, and a jumping kiteboarder, both convert energy alternately between kinetic and potential forms, but because they aren't sustainable processes, power ratings aren't relevant in these examples.

In some circumstances, power can be quantified by multiplying a force by the speed at which that force is exerted. Here are some examples of power calculations based on specific examples:

1. Heavy(ish) kiteboarder on freestyle board going 25 mph with 30 lbs resistance (independent of wind speed and kite size): power = 2.0 hp

2. Light kiteboarder on high L/D ratio board (eg Spleene Session) going 18 mph with 20 lbs resistance: power = 0.96 hp

3. Same kite as in example (1.), attached to a Honda Civic with tires overinflated to reduce resistance, on a broad reach on an airport runway, with wind blowing like !@#\$%, chicken loop mechanically fastened to car (pilot couldn't possibly hold it), going 50 mph with 40 lbs resistance (rolling resistance only, apparent wind over the beam): power = 5.3 hp

A kite alone does not generate power. Power is generated when a traction kite and surface vehicle interact as a system, whether that vehicle is a kiteboard and rider, a buggy and rider, a car, an ice boat, or whatever.

The maximum achievable power is based largely on what the vehicle can handle. A given vehicle will have a maximum practical upper limit to power generation. If the vehicle is a particular kiteboard and rider, they may have an approximate upper end of 1.5 hp, regardless of whether they achieve it with a big kite in light wind or a small kite in high wind.

The heavier and stronger the rider, and the more efficient the board, the higher the maximum power will be. A 200 sq m monster kite wouldn't help a kiteboarder generate more power than with a normal kite, but a freighter or a heavyweight ice boat could generate huge power with the monster kite.

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 Post subject: Re: 10M kite in 30 knots converted to horsepowerPosted: Wed Aug 01, 2012 2:32 pm
 Very Frequent Poster

Joined: Fri Jul 16, 2010 6:27 am
Posts: 1396
Location: Ford Lake, Michigan
jteabird wrote:
Ok so I was wondering just for fun .. I was jumping 30 feet the other day and I was wondering just how much power my kite had to yank me 30 feet into the air in like 2 seconds. I was wondering if anybody had a guess as to just how much horsepower that kite must have to do that. I was guessing it could have about as much power as a 200 horsepower boat. how could you convert this if it is at all possible ??

we cruise at around 17 knots, so you are talking about going from 17 knots to wind speed, 30 knots in 2 seconds, 13 knots is 7mps, assume weight of 75 kilograms, 1/2mv^2 * 2 seconds = .5 * 75 * 7^2 * 2 is about 3500 watts, or

5 horsepower

woo hoo got the same answer as jolly

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 Post subject: Re: 10M kite in 30 knots converted to horsepowerPosted: Wed Aug 01, 2012 3:10 pm
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Joined: Sun Sep 04, 2011 5:37 pm
Posts: 975
JS wrote:
...

POWER

Power is the rate at which a device can convert energy from one form to another, and is usually measured in watts or horsepower.
...

The maximum achievable power is based largely on what the vehicle can handle. A given vehicle will have a maximum practical upper limit to power generation. If the vehicle is a particular kiteboard and rider, they may have an approximate upper end of 1.5 hp, regardless of whether they achieve it with a big kite in light wind or a small kite in high wind.

...

The moment i read that, i started wondering just how much power
it took to fly that Human powered bicycle ?

The one that crossed the English-channel only needed 0.4 horsepower (300 W),
In still air , to stay aloft.

http://en.wikipedia.org/wiki/Gossamer_Albatross

Imagine attaching 30M lines to That wing, then go boarding in maybe a 3kt wind?

Bille

 Attachments: 752px-Gossamer_Albatross_II.jpg [ 50.59 KIB | Viewed 712 times ]
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 Post subject: Re: 10M kite in 30 knots converted to horsepowerPosted: Wed Aug 01, 2012 3:25 pm
 Medium Poster

Joined: Mon Jul 20, 2009 5:16 pm
Posts: 101
Location: Jupiter, FL
The OP stated he was jumping 30' in the air, not accelerating from 17 kn to 30 kn.

I'm not going to try to redo the calcs, but there were some incorrect assumptions.

Chris

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 Post subject: Re: 10M kite in 30 knots converted to horsepowerPosted: Wed Aug 01, 2012 4:37 pm
 Very Frequent Poster

Joined: Fri Jul 16, 2010 6:27 am
Posts: 1396
Location: Ford Lake, Michigan
SO_FL_Kiter wrote:
The OP stated he was jumping 30' in the air, not accelerating from 17 kn to 30 kn.

I'm not going to try to redo the calcs, but there were some incorrect assumptions.

Chris

calculation of horsepower requires a time element, 30 feet in the air you can calculate the kinetic energy it's mgh, assume 75 kilogram kiter, gravity is 10 m/s^2, 30 feet is 10 meters, that's 75 * 10 * 10 = 7500 joules, but you can't convert joules into horsepower because it's not even the same units of measurement, joules * seconds = horsepower, trying to calculate horsepower from the height is like trying to measure miles per hour by telling you the distance is 100 miles. You can't figure out miles per hour from the distance without explaining how fast it took you to travel that 100 miles.

I like the answer 5 horsepower, both jolly and me got the same answer using entirely different methods and assumptions. Plus JS has it as his theoretical max horsepower kiting.

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 Post subject: Re: 10M kite in 30 knots converted to horsepowerPosted: Wed Aug 01, 2012 7:08 pm
 Medium Poster

Joined: Fri Apr 01, 2011 10:31 pm
Posts: 74

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 Post subject: Re: 10M kite in 30 knots converted to horsepowerPosted: Wed Aug 01, 2012 9:02 pm
 Very Frequent Poster

Joined: Wed Aug 03, 2005 6:25 pm
Posts: 764
Location: Vancouver
edt wrote:
...trying to calculate horsepower from the height is like trying to measure miles per hour by telling you the distance is 100 miles.

Exactly. Even if you know the time it takes to achieve a given height, it's still irrelevant to any power calculation because it's not a sustainable process...like a coasting skateboarder riding up a ramp.

edt wrote:
I like the answer 5 horsepower, both jolly and me got the same answer using entirely different methods and assumptions. Plus JS has it as his theoretical max horsepower kiting.

No, better read that again. My reference to 5.3hp was a theoretical example involving a kite-driven car on an airstrip.

Maximum power depends most significantly on the strength and technique of the rider, efficiency of the equipment, wind speed and point of sail. Here are theoretical maximum estimates for a strong 200lb rider...

1. maximizing upwind progress on a typical freestyle twin tip: 1hp
2. maximizing upwind progress on a race board: 2hp
3. on a beam reach on a typical freestyle twin tip: 2hp
4. on a fast broad reach (at the edge of control) on a twin tip or race board: 3hp
5. making a speed run in ideal conditions, on a speed board: 4hp

These figures would be about a third less for a 100lb rider, or about a fifth more for a 300lb rider.

Cheers,
James

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