This video is in St Martin I think. Is there a similar effect in Sydney? I have seen photos of guys sailing pretty close to the runway.

Way cool!!!!!!!!!!!!!

I personally have not experienced the exhaust from a jet engine sailing giving me a boost at Kyeemagh. The jets are quite a lot higher than the waterline. You definitely hear them though and can smell the burned kerosene. Plus if you look closely passengers can be seen inside and some of them wave to us. Sailing at Kyeemagh in a strong NE is definitely something every windsurfer should experience.

Don't think the runway layout at Sydney aligns in a way for the jet exhaust to be useful for windsurfers. Years ago I sailed a few westerlies at Kurnell, under the flight path of landing aircraft. I got the feeling that the best gusts came through a minute or so after a landing plane passed overhead. The downwash of an aircraft introduces quite a bit of momentum to the atmosphere. Way more than the jet exhaust would. I figured the downwash might possibly bring the higher winds aloft down to the surface. Hard to quantify, and my imagination might have exaggerated the effect of course.

I used to sail behind the seaplane at Palm Beach for the same effect.

I've had a couple of jet blasts, as they rev their engines to turn on to the main runway after waiting on the taxiway. It was only about 5 knots stronger than the wind by the time it got down to the water and a bit warmer.

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shear tip said..
I've had a couple of jet blasts, as they rev their engines to turn on to the main runway after waiting on the taxiway. It was only about 5 knots stronger than the wind by the time it got down to the water and a bit warmer.

probably not the healthiest way of doing a sport

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stehsegler said..

shear tip said..
I've had a couple of jet blasts, as they rev their engines to turn on to the main runway after waiting on the taxiway. It was only about 5 knots stronger than the wind by the time it got down to the water and a bit warmer.

probably not the healthiest way of doing a sport

The smell of exhaust Jet A1...Mmmmmmmmmmm...Ah , the serenity.

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Cambodge said..

stehsegler said..

shear tip said..
I've had a couple of jet blasts, as they rev their engines to turn on to the main runway after waiting on the taxiway. It was only about 5 knots stronger than the wind by the time it got down to the water and a bit warmer.

probably not the healthiest way of doing a sport

The smell of exhaust Jet A1...Mmmmmmmmmmm...Ah , the serenity.

Yeh, sometimes the smell of jet fuel and exhaust is full on as you get close to the runway, especially when sailing up near "The Beach".

Generally the super-hot runway in Summer months affects the wind angle in close proximity (more East in it), but I can't say I've ever noticed any effect from the jet engines. However, on very still days, when the bay is glassy, I've seen the water get ruffled up as a big Boeing u-turns.

I think the jet fuel fumes have got to you Nigel..... When the wind goes over the land -which is a rough surface, it causes drag on the wind and turns the wind direction right (in the Southern hemisphere)( left in Northern Hemisphere). Resulting in less Coriolis effect on the wind. It can be 10-15 degrees different as it travels across the land. So when you are close to the runway the direction is right of the wind compared to further away from the runway, where it reverts back to the original wind direction.
Noticeable on the way back after a run, if you gybe and stay close to the runway you can lift up all the way to the Northern beach area. If you gybe and are further away from the runway you don't get the right shift effect of the wind and end up only making to the Kyeemah car park beach area.
We also experience some convergence of the wind near the runway if there is enough North in the breeze, giving an increase in wind strength.
Fez

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Fez said..
I think the jet fuel fumes have got to you Nigel..... When the wind goes over the land -which is a rough surface, it causes drag on the wind and turns the wind direction right (in the Southern hemisphere)( left in Northern Hemisphere). Resulting in less Coriolis effect on the wind. It can be 10-15 degrees different as it travels across the land. So when you are close to the runway the direction is right of the wind compared to further away from the runway, where it reverts back to the original wind direction.
Noticeable on the way back after a run, if you gybe and stay close to the runway you can lift up all the way to the Northern beach area. If you gybe and are further away from the runway you don't get the right shift effect of the wind and end up only making to the Kyeemah car park beach area.
We also experience some convergence of the wind near the runway if there is enough North in the breeze, giving an increase in wind strength.
Fez

Maybe I didn't explain very well.

The top arrow is NE, the arrow across the runway has more East in it, which you call right. I presume this is due to heat rising off the runway and causing a localised effect on the wind close to the runway. This makes it easier to head further North, beside the runway on a starboard tack, to "The Beach" (not Kyeemagh beach... "The Beach").


This is "The Beach"

Whatever it is the wind is heaps better south of the runway. Far less holes. I spent many hours one afternoon in a NE'r Sailing up and down from Le Sands to Brighton and back and it was consistently much better off the southern end of the runway.

I get that right next to the runway is a speed strip, but the wind is both stronger and more consistent, and the chop large enough to actually make blasting smooth, further south.

Also you don't have to carry gear down the path of death. And it smells nicer.

I cant imagine Australian air safety officers being comfortable with a runway that is a little bit to short as the one in the video seems to be. I imagine its that casual Caribbean attitude and a tiny GDP that is the cause.

Nigel.... your drawing is correct, but it is doesn't have anything to do with the heat from the runway. It is caused by the drag of the land effect on the wind. I lecture in this subject for a job for the last 35years, so it is best to understand the processes in place.
Reference reading for you is a book on"Wind Strategy" by Derek Haughton.

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Fez said..
Nigel.... your drawing is correct, but it is doesn't have anything to do with the heat from the runway. It is caused by the drag of the land effect on the wind. I lecture in this subject for a job for the last 35years, so it is best to understand the processes in place.
Reference reading for you is a book on"Wind Strategy" by Derek Haughton.

David, that's fascinating. At which university did you lecture on Coriolis effect the past 35 years? I thought you were a draftsman at Downer or have I confused you for someone else?

Fez is describing the Ekman spiral. I'd say that at the windsurfing scale a change in surface roughness will just swing the wind towards the roughness like dragging a paddle out one side of a canoe.


The Coriolis force is pretty small compared to the local topographic and thermal forces on the wind. I've just googled a paper which gives 30km as the distance scale below which anything due to Coriolis force is generally immeasurable. Basically the earth has to have enough time to rotate out of the way in the time the air takes to travel 30 km. ( Although the paper is investigating a combination of stratification where the Coriolis effect does come through on a scale less than 30km. But either way it'd be a special case. )

http://www.cpom.org/people/jcrh/QJRMS-130.pdf

Locally, when the Bellambi anemometer, on a bit of a bluff on a 10 metre tower,, reads SSW the sand on the nearby local beach is blowing slightly inland from the SSE. That's a swing in the opposite direction to the larger scale Ekman spiral as Fez describes.

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Ian K said..

Ian, I read the wiki on the Ekman Spiral, and it's exactly as Fez explained it, but on a macroscopic scale. However, what you are describing is different. I'm confused ?

en.wikipedia.org/wiki/Ekman_spiral

That's right The Ekman spiral is intertwined with the Coriolis force. The large macroscopic circulation systems are set up with the pressure gradient balancing the Coriolis force. The Coriolis force is proportional to the wind speed. The air lower down slows down due to surface friction but the atmospheric pressure from above permeates to lower altitudes. So down low the pressure gradient has more effect and hence bends the wind towards the centre of low pressure, or away from the high pressure. We're just arguing that the pressure gradient left over is pretty small, so the Ekman spiral takes quite a few kilometres to be modified by changing surface features. Way more than the mesoscale distances within Botany Bay.

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Ian K said..
The Coriolis force is proportional to the wind speed.

Is this effect similar to a gyroscope ?.. eg: the faster you change the orientation of a gyro the more force you need to change it ? (with the wind being the out rim of a gyro)

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Ian K said..
So down low the pressure gradient has more effect and hence bends the wind towards the centre of low pressure, or away from the high pressure.

Ok, Understood

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jn1 said..

Ian K said..
The Coriolis force is proportional to the wind speed.

Is this effect similar to a gyroscope ?.. eg: the faster you change the orientation of a gyro the more force you need to change it ? (with the wind being the out rim of a gyro)

It's due to the rotational component of the earths surface as it spins. The air wants to go in a straight line but the earth rotates beneath it. Coriolis force is not actually a real force it's an apparent force. But the maths works out as if it is a true force. Coriolis force varies with latitude. There's none at the equator and maximum at the poles. Everywhere else is somewhere in between. The often used analogy is to imagine shooting a billiard ball on a rotating table. To notice the effect the table has to either rotate quickly or be huge (bigger than Botany Bay at least).

It's an interesting point about the gyroscopic effect. The air circulating a low pressure system does have angular momentum so there will be something going on. I'm thinking the precession will just act to tip the circulation into the earth's surface, which is solid enough to hold things steady so precession doesn't need to be worried about.