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Stac Performance Virtual Wind Tunnel front page article
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Thoughts on this front page article? http://www.slowtwitch.com/...ind_Tunnel_6443.html

Here's some questions and thoughts from a swim partner/professor whose work is in verification and validation in scientific computing

"Depends a lot on what models they are using. I don't believe 1-2% agreement w/ wind tunnel data, especially if they are putting the rider in the open air, whereas the wind tunnel has tunnel wall effects. I'd be more likely to believe delta values (rather than absolute drag values), but still not to within 2%.


Would like to know what CFD models they are using for turbulence. Looks like a large eddy simulation (LES)."

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milesthedog on strava
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Re: Stac Performance Virtual Wind Tunnel front page article [milesthedog] [ In reply to ]
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first, before someone writes something both i and they may regret, we have no relationship, that is, i have no relationship, with this company. no money changing hands. no contemplation of money changing hands. i've never spoken to these folks. did not know they existed until the article popped up in our queue.

perhaps cody beals may want to chime in and speak to your question. i grilled tony on the tech until i was satisfied the article was slowtwitch-worthy. cody's participation in the project played no small part in my decision to publish on the product.


Dan Empfield
aka Slowman
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Re: Stac Performance Virtual Wind Tunnel front page article [milesthedog] [ In reply to ]
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I'm curious to try it out and compare the results to my A2 data and field testing data.

WTB: TriRig Omega SV (not x). PM me if you have one :)
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Re: Stac Performance Virtual Wind Tunnel front page article [GreenPlease] [ In reply to ]
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GreenPlease wrote:
I'm curious to try it out and compare the results to my A2 data and field testing data.

great idea; and get Kiley to do the same and there could be an some interesting discussion. If answers come in, I'll shoot them over to the professor friend and relay his feedback. Very cool stuff, though and good article.

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milesthedog on strava
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Re: Stac Performance Virtual Wind Tunnel front page article [milesthedog] [ In reply to ]
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Very cool! I'm sure Cody will chime in, I'd also love to try this out.
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Re: Stac Performance Virtual Wind Tunnel front page article [milesthedog] [ In reply to ]
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Very interesting, and I've played with similar things myself using lidar point clouds (which are probably much more accurate and denser than their multi-baseline stereo-type pointclouds).

But I think this may ultimately lose out to the newer real-world testing products coming out (with integrated air velocity sensors ,etc).
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Re: Stac Performance Virtual Wind Tunnel front page article [milesthedog] [ In reply to ]
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Looks cool and if they could help people with helmet selection than that would probably be one of the key take-always that most people get from a tunnel session.

I would be interested in seeing how well their point cloud models a cyclist. The body scans on the NoPinz site look they are pretty high resolution. You could get a pretty good idea of frontal are with a decent scan.
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Re: Stac Performance Virtual Wind Tunnel front page article [milesthedog] [ In reply to ]
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I think people might be missing the point here.

The inputs, via an iPad video and scanner, to generate a 3D model, will always be less accurate than testing in a tunnel. However, IF they are accurate enough to parallel wind tunnel testing results, that's sweet. If it's accurate enough to differentiate between helmets say, (again, matching wind tunnel testing), and it can do that for only a couple of hundred bucks, then that's gotta be good news?

As I see it, it's not perfect and it's not as good as a wind tunnel test, but it's faster and cheaper with reasonably accurate results, so surely that's good enough?

It's like taking happy holiday snaps on your phone, instead of having a professional photographer with a truckload of gear, on holiday with you. We all take phone pics, because they are good enough for the purpose, given the price.

I hope they do well and when I decide to get a bike fit next, I'm thinking this would be a good thing to do at the same time.

TriDork

"Happiness is a myth. All you can hope for is to get laid once in a while, drunk once in a while and to eat chocolate every day"
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Re: Stac Performance Virtual Wind Tunnel front page article [trail] [ In reply to ]
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trail wrote:
Very interesting, and I've played with similar things myself using lidar point clouds (which are probably much more accurate and denser than their multi-baseline stereo-type pointclouds).

But I think this may ultimately lose out to the newer real-world testing products coming out (with integrated air velocity sensors ,etc).

I tend to agree (Zipp's Aerostick... which is what a rep called it... comes to mind).

WTB: TriRig Omega SV (not x). PM me if you have one :)
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Re: Stac Performance Virtual Wind Tunnel front page article [tridork] [ In reply to ]
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tridork wrote:
I
The inputs, via an iPad video and scanner, to generate a 3D model, will always be less accurate than testing in a tunnel..

...but it's faster and cheaper with reasonably accurate results, so surely that's good enough?

One of the problems with less precise analysis techniques is they require the user to be more particular about inputs and to have a expertise on when tests will be useful and when circumstances will lose accuracy. GIGO

The problem with Stac, then, may be that it is inherently harder to get accurate results but also lowers the barrier to entry for testing.
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Re: Stac Performance Virtual Wind Tunnel front page article [Karl.n] [ In reply to ]
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Karl.n wrote:
tridork wrote:
I
The inputs, via an iPad video and scanner, to generate a 3D model, will always be less accurate than testing in a tunnel..

...but it's faster and cheaper with reasonably accurate results, so surely that's good enough?


One of the problems with less precise analysis techniques is they require the user to be more particular about inputs and to have a expertise on when tests will be useful and when circumstances will lose accuracy. GIGO

The problem with Stac, then, may be that it is inherently harder to get accurate results but also lowers the barrier to entry for testing.


On the assumption that their results are as accurate as they say, then I'm keen, even though I know it's not going to be perfect. To me, it seems like a great way to decide which helmet to buy. Or maybe, which bike/frame, or which aero bars (straight vs ski bend) or any number of other things.

It's way more accurate than reading a manufacturers brochure, or listening to the guy at your LBS (he'll just recommend what he has in stock). And that's worth at least a hundred to me. If they really want to sell to us trigeeks, they have to work "carbon" into their sales pitch somehow. (that last bit, pink?)

TriDork

"Happiness is a myth. All you can hope for is to get laid once in a while, drunk once in a while and to eat chocolate every day"
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Re: Stac Performance Virtual Wind Tunnel front page article [milesthedog] [ In reply to ]
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I had missed this article and the tech until yesterday when it popped up on Mat Steinmetz's facebook feed. I talked to one of the engineers for a bit on the phone today, and I'm actually pretty excited to try this out. They (Andrew) were very upfront regarding the capabilities and limitations. One thing that really grabbed me was realizing for subsequent models, they are always starting with exactly the same baseline. Once the scan is done they can drop an aerohead or a Rudy on there, pull the bottles off the back, model in an XLAB bta set up, etc. One of the primary error inducers in tunnels is failure to replicate baseline positions.

Anyway, I think it is promising enough to warrant a closer look, and I see it as a step up in many ways over simple frontal area modeling.

Going nowhere in the pool? We can help.



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Re: Stac Performance Virtual Wind Tunnel front page article [FindinFreestyle] [ In reply to ]
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I didn't realize that they were able to substitute helmets or move parts of the 3-d models around. I think a problem with this is getting the virtual helmet to sit on your virtual head the same way you would actually wear the thing would be impossible, but that is the same as running helmets you aren't really familiar with in the tunnel. It usually takes me a while to get the adjustment system set up so that the tail sits close to my back. That would make this a way more appealing application.

Can they raise or lower hand position?
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Re: Stac Performance Virtual Wind Tunnel front page article [milesthedog] [ In reply to ]
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"I had the opportunity to visit the FASTER wind tunnel twice with Ventum, my bike sponsor,” Beals continued. "STAC has used that data to validate the VWT and demonstrate its impressive accuracy.”

Aaaaaaand you lost me.
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Re: Stac Performance Virtual Wind Tunnel front page article [FindinFreestyle] [ In reply to ]
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FindinFreestyle wrote:
I see it as a step up in many ways over simple frontal area modeling.

frontal area is only half the equation (CdA), and arguably the lesser half of it at that.

Cd is king in my mind... take a sphere shape in the wind and reduce it by half, you reduce CdA by a factor of one. Take that same sphere and keep the area but make it an airfoil and you reduce CdA by a factor of 10. Streamlining bluff bodies is where it's at in bike fitting.

Eric Reid
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Ask me: Scody Optimized Speed Suits | CeramicSpeed Oversized Pulley Systems | HUUB Skinsuits and Wetsuits | Ventum Bicycles and Frames
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