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Post your polar and VMG

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davesails7
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Re: Post your polar and VMG

Postby davesails7 » Tue Apr 25, 2017 2:41 am

Gave it a try. Pretty cool. Not sure it turned out exactly right because I was riding in a small area, so didn't have a lot of straight line runs. Also wind may have been shifting a bit.

Wind: 8-12 Knots
Water: Pretty Much Flat
Foil: Spotz2
Kite: 15m Sonic2 on 17m lines

A little underpowered. Started out around 12 kts of wind, so went for 15m instead of 18m kite, but then it started dying out pretty quickly and I wished I had taken the 18m.

Will try again and do longer upwind and downwind runs with more power.
Attachments
Polar1.png

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Peter_Frank
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Re: Post your polar and VMG

Postby Peter_Frank » Tue Apr 25, 2017 8:40 am

Be careful comparing and deducting too much from polars :wink:

In my experience, they might give you an "idea" how the performance has been, but they will also have a huge error margin.
Must say I dont like em myself, eventhough they are pretty ha haa :D

Because, you never have stable wind exactly the same direction, and even quite small windshifts, will make the polar way to good than it really is in terms of angles and speed - you seem to be able to go crazy upwind and downwind at huge speed, which in real life is not the case and blurred by an unknown factor of windshifts.

Even IF you have consistent wind, it will often change direction slightly, when you ride closer to shore, compared to a bit more out, so here is also an error.

One has to look closely at the exact tacks and measure the average VMG on these (both tacks right after each other), in order to get any really useful information.

Also, take Gunnars examples with the racefoil and Go foil - it looks like the Go foil can not go fast nor upwind at all :roll:
And this is not true - to some extent of course yes this difference exists, but in the first scenario it is powered maybe with a racekite and heeling upwind pushing hard, in the second scenario it is extremely lightly powered with a tube kite, and not cranking upwind but having fun in the waves.
If you turned the kites and goals around, you would see a very different picture :naughty:

8) PF

evan
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Re: Post your polar and VMG

Postby evan » Tue Apr 25, 2017 11:01 am

That is why I prefer the best 500m average VMG over the polar. GPS action replay gives you the option to display the average speed, angle and VMG over the last xxx-meters (standard set to 500m), downside is that you nee to scroll through your entire session to get the best values and you need to include a tack or gybe to filter out the windshifts. Comparing straight-line angles and VMG with this method is impossible because you can not know the true wind angle at your exact time and location on the water and even when you include a tack/gybe and have an equal length before and after the tack/gybe your average can be affected by a short windshift.

Here are some examples of me on a 11m Aero, need to dig trhough my gps-logs and find maybe better values:
Attachments
2017-04-05-4 downwind.JPG
2017-04-05-4 downwind.JPG (50.03 KiB) Viewed 1030 times
2017-04-05-2 upwind.JPG
2017-04-05-2 upwind.JPG (34.52 KiB) Viewed 1030 times

gwicke
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Re: Post your polar and VMG

Postby gwicke » Thu Jun 22, 2017 3:02 am

A polar plot from the windrace app, using doppler speeds.
Gear: Sword 1 & Diablo 11m (IIRC)
Spot: Coyote Point, SF Bay area
Attachments
polar.jpg

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Horst Sergio
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Re: Post your polar and VMG

Postby Horst Sergio » Tue Aug 08, 2017 7:04 pm

Peter_Frank wrote:
Tue Apr 25, 2017 8:40 am
Be careful comparing and deducting too much from polars :wink:

In my experience, they might give you an "idea" how the performance has been, but they will also have a huge error margin.
Must say I dont like em myself, eventhough they are pretty ha haa :D
My words and as I haven't got such a polar-Rorschachtest-maker :D I just can present another way to measure at least my downwind vmg:

overtaking-Ballon.jpg
The wind in the picture comes from the right side as the masthead fly showes. In the moment of the picture I (on the right corner) was around 600 m directly upwind of the ballon which was always around 40 m above ground (20 m diameter).
Medium wind was metered by movement of the ballon at its height to be around 14 knts, 15 m² Chrono V1, 16 m lines, Bionic back wing.

It tooks me 3 km to overtake the ballon :D

So my downwind VMG was around 18 knts. If the factor of being faster than the wind was 1,25 is not that clear as the wind is a katabatic one with sometimes pretty high gradient, anyway for sure I was a bit faster than the wind and had a nice private race and demonstration. :)

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alexrider
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Re: Post your polar and VMG

Postby alexrider » Thu Aug 17, 2017 5:43 am

Horst Sergio wrote:
Tue Aug 08, 2017 7:04 pm
...
The wind in the picture comes from the right side as the masthead fly showes. In the moment of the picture I (on the right corner) was around 600 m directly upwind of the ballon which was always around 40 m above ground (20 m diameter).
Medium wind was metered by movement of the ballon at its height to be around 14 knts, 15 m² Chrono V1, 16 m lines, Bionic back wing.

It tooks me 3 km to overtake the ballon :D

So my downwind VMG was around 18 knts. If the factor of being faster than the wind was 1,25 is not that clear as the wind is a katabatic one with sometimes pretty high gradient, anyway for sure I was a bit faster than the wind and had a nice private race and demonstration. :)
:thumb:
QED to the sceptics of "Downwind Faster Than The Wind - update" thread.
viewtopic.php?f=1&t=2361300

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alexrider
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Re: Post your polar and VMG

Postby alexrider » Thu Aug 17, 2017 6:25 am

Difference between the Airush Ultra 17 (black) and Sonic FR 18 (red) with the Cab Double Agent 2017 with 60 cm mast I was kindly lent that day. Although there was somewhat less wind during the Sonic run (I reckon 8 knots, 10 knots max), the VMG approached 10 knots. Manoeuvres (gibes) were unquestionably easier with the Ultra however, except board-dragging (but that's not a manoeuvre) upwind with the kite low. Delta LEI with their forward CoG tend to fall when kept low in light winds.
2017-08-11_065834.jpg

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Peter_Frank
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Re: Post your polar and VMG

Postby Peter_Frank » Thu Aug 17, 2017 11:42 am

Impressive to see such a huge difference in upwind ability between a LEI and a foil kite alexrider :thumb:

The foil kite has about 30 % better upwind VMG than the LEI, even when a tad less wind, so most likely more than 30 % in same wind.

Also evident that the speed on tight reaches or halfwind is about the same, as expected.

On a higher AR racewing I think the difference will be even higher particularly in VMG.

Good to see it tested, and not just something we all know but dont have in numbers or graphical presentation.

I still prefer the LEI as soon as its 7 knots and up, as I dont race, but use the foil kites in 5 to max 7 knots.

8) PF

Mossy 757
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Re: Post your polar and VMG

Postby Mossy 757 » Thu Aug 17, 2017 4:55 pm

10 knots downwind with an 18m race foil kite?! Remind me to NEVER buy a Cabrinha hydrofoil... :rollgrin:

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alexrider
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Re: Post your polar and VMG

Postby alexrider » Thu Aug 17, 2017 5:52 pm

Mossy 757 wrote:
Thu Aug 17, 2017 4:55 pm
10 knots downwind with an 18m race foil kite?! Remind me to NEVER buy a Cabrinha hydrofoil... :rollgrin:
I admit Sonic-Cab Double Agent is a strange combo, Mossy. A few thoughts however:
- should I have refused the offer to try the combo that day?
- the idea was to get up foiling early, never to go fast
- I'm scared of speed on a hydrofoil anyway
- and the Cab is such a fun board (I've "upgraded" to Zeeko, but still love the Cab)
- slow IS fun
- by all means, don't buy a Cab DA, but you could at least try
- I'm the kind that thinks barnstorming and touch-and-gos on Piper Cub is more fun than zipping along the country with a fast craft
- what do you call downwind? Straight downwind? Anything past 90 is downwind, and the polar indicate 15 knots @120 degrees
- can you read the polar? :naughty:
- race foil kites excel upwind; downwind, their high aspect ratio is of little help
- is Greg the Alien, the kite role model to many riders, doing a lot more more than 10 knots under any point of sail?
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