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Aerolab: Work in Progress

Fri, 01/29/2010 - 8:50pm by Andy Shen

 2/17 update A lot of things have happened in the three weeks since the original posting. It appears that Aerolab will make it into Golden Cheetah 1.4, where it will be a complete alternate view instead of a tab. The extra real estate will fit Greg Steele's interface, which has a tab for calculating air density (including an option that pulls data from a weather service), as well as tabs for creating and overlaying laps. 


The abilty to overlay tabs is especially interesting as barometrically derived altitude is far from perfect, so the option of comparing a slow virtual elevation lap with a fast virtual elevation lap should be even more revealing.

I got the idea to incorporate the iBike's wind data into Aerolab's calculations (the original version assumes that air speed matches ground speed). Froncioni got me a patch in 24 hours, and the result was stunning.


Here's a short interval I did analyzed by the original version of Aerolab. There was nothing I could do to make the plots fit. I was starting to wonder if I had grabbed the wrong interval, one where I sat up instead of staying in the aerobars.


Here's the same file with the iBike adjusted plot in red. There was a headwind that slowed me down, which Aerolab interpreted as an increase in pitch. With the headwind accounted for, the plots line up almost perfectly. This, to me, is a real testament to the iBike, and I'm more convinced that anyone who wants to play around with the Chung Method should do so with iBike paired with an ANT+ power meter.

Of course, none of this accounts for the effect of crosswinds. So could there be Aerolab hardware in the future?


Aerolab is Andy Froncioni's brainchild, a virtual wind tunnel freeware tool that utilizes the Chung Method. A basic explanation of the Chung Method is here, but for now suffice it to say it's a mathematical tool that lets you measure your aero drag with nothing but a power meter. Froncioni is still refining Aerolab, and hopes that it will be integrated as a tab within Golden Cheetah version 1.4 (1.3 is to be released soon).

Aerolab does a few cool things. First of all, it simplifies the Chung Method. Instead of manually extracting your power data and pasting it into an Excel spreadsheet, you can simply upload your data from your computer head into Golden Cheetah, or import an existing ride file. Aerolab creates the virtual elevation plot automatically, and you can tweak the plot with sliders for Cda, Crr, air density, and rider + bike weight.

Aerolab also adds another layer of data to the Chung Method. Whereas original Chung Method users had to do loops or out-and-back courses and level repeated landmarks on the course, Aerolab superimposes the course profile generated by your computer head over the virtual course profile, so you can compare the plots along the entire course. While the elevation plot generated by the altimeter in your computer head isn't necessarily 100% accurate, it does provide more detail with which to analyze your ride.

The blue line is virtual elevation generated by Aerolab, the green line is actual elevation from my iBike's altimeter. Tweaking the sliders will make the two lines match better.

Here's the same file, with better Cda/Crr estimates. Note how the VE plot is steeper on the last climb. I sat up at that point of the race, and the extra drag slowed me down. Since the Chung Method assumes consistent positioning, this slowing down is interpreted as a steeper gradient.

Aerolab is still in its infancy, and Froncioni is adding new features at a rapid rate. In cooperation with the eponymous Robert Chung, plans are currently in the works to include special views for superimposing loops and out-and-backs, as well as other course features. Provisions are also underway for tagging course segments with special attributes such as wind, road roughness, or a CdA multiplier. All this extra data will significantly help in finding the unique pair of parameters (Crr,CdA) that make the elevation profile 'work'.

Further features include additional sliders for elevation offset and drivetrain efficiency, as well as a table of wheels that will allow you to correct for the extra momentum you get from the rotational inertia of your wheels. An auto solve feature will generate Crr and CdA values mathematically instead of graphically.

Here's the next build of Aerolab, with sliders for drivetrain efficiency and elevation offset.

So why does Robert Chung think Aerolab is a 'game changer'? Aerolab brings the Chung Method out of the realm of engineers and aero geeks and into the hands of anyone who can download a power meter file. Once Aerolab is complete you'll be able to go out for a training ride, do an interval in one position, do another in a second position, and go home and find out which is faster. Want immediate feedback? Bring your laptop and analyze each run as you complete it. Breakaway artists can easily see if it's faster to ride in the drops or with their elbows on the tops. Considering a new wheelset? Borrow a friend's and see if it's as fast as the manufacturer claims. And best of all, this will all be measured in real world situations while you pedal at race intensity, as you're getting your training done.

You can download a PC version of Aerolab here and try it out for yourself. Just dig up an old TT file and import it (use files with little or no braking and no changes in position), and leave suggestions in Froncioni's comments section. Once Golden Cheetah 1.3 is released, Froncioni will have Mac and Linux versions available for testing as well. Check back here or at his blog for updates.

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Aero relevance?
By: Bent Overmi
Tue, 02/23/2010 - 2:33pm

"At what point does aero become relavent? is it when the rider is going above 16 miles an hour? 17 miles an hour?"

Its always relevant, but it becomes more and more so as speed increases. Not just speed, but additional environmental wind has to factor into any calculus.

The effect of drag is logarithmic. By the time you reach 30 mph of wind the drag accounts for approx 80% of the energy required to move forward. Keep in mind you could be going 17 mph into a 10 mph headwind and the effective drag would be the same as going 27mph with no wind.

You sometimes hear that a specific wheel is better above 25 mph (HED makes this claim about some of their disc wheels for instance) This is because as forward speed increases, it tends to mitigate the effect of wind from the sides. (put your hand out the window of a car at 60 mph and even if there are strong cross winds you wont feel them.) So if you are going to build a wheel for faster riders who are averaging above 25 mph you would optimize the wheel for less yaw. Whereas if you are targeting a design for say a triathlon rider with average speeds in the low 20s, you would optimize the wheel for a greater spread of yaw values.

Steve Hed often talks about this and it seems to make a lot of sense.

You can check out their online YAW calculator here for the combined effects of head and cross winds on effective YAW:

actually, rawbiht, i am a
By: the othah bob
Tue, 02/23/2010 - 2:28pm

actually, rawbiht, i am a suhly new englindah. but feel free to take youah chuhlishness elsewheyah just the same.

The Man
By: Warre Helmet
Tue, 02/23/2010 - 2:16pm

soooo...your stickin it to yourself???

Other Bob
By: Robert
Tue, 02/23/2010 - 2:16pm

Whoops. Sorry. Didn't realize you NY guys were so sensitive. I apologize for hurting your delicate little feelings. I'll go now. Ciao.

robert fail
By: the other bob
Tue, 02/23/2010 - 12:33pm

oh stop it, you know exactly what the original question was about and you chose to be a dick, so you get dickishness in return.

By: Robert
Tue, 02/23/2010 - 11:32am

So, I get that you think that was wrong. What I can't figure out is which of the following two you think is right:

  1. It becomes relevant whenever you don't want to go faster for the same power or go the the same speed with less power
  2. It doesn't become relevant whenever you want to go faster for the same power or go the the same speed with less power

Please clarify so it'll be easier to make fun of you.

By: Robert
Tue, 02/23/2010 - 11:24am

Thanks. It works on so many levels.

Free finger bang with
By: Nolan Flange
Mon, 02/22/2010 - 7:04pm

Free finger bang with purchase.

nice one..
By: Sam Lorica
Mon, 02/22/2010 - 6:58pm

funny. only 17K...

For sale: time trial bike,
By: Shivvy Metimber
Mon, 02/22/2010 - 6:36pm

For sale: time trial bike, used very little.

By: tubbs
Mon, 02/22/2010 - 2:33pm

Wow...that was insightful.

I am convinced...
By: West Coast Reader
Sun, 02/21/2010 - 9:02pm

I am convinced, clicking Order...

By: consumer reports
Sun, 02/21/2010 - 6:52pm

this is funny. lance doesn't use powercranks but "he pedals as if he did" (not only that, but hey, check out this ed coyle study that proves it!)... so the logical conclusion is not that you don't actually need a 1200 dollar crankset (that effectively renders an entire bicycle awkward useless) in order to improve pedal technique, but that you REALLY need it.

silly robert
By: physicist
Sun, 02/21/2010 - 6:47pm

go climb a hill in the aerobars and report back to us with less dismissive smugness.

Re: Aero
By: Robert
Sun, 02/21/2010 - 3:26pm

It becomes relevant whenever you want to go faster for the same power or go the the same speed with less power.

By: tubbs
Fri, 02/19/2010 - 3:43pm

At what point does aero become relavent? is it when the rider is going above 16 miles an hour? 17 miles an hour?

when i fart i'll typically
By: Elias Sealant
Wed, 02/17/2010 - 1:29pm

when i fart i'll typically have a 5 degree change in yaw, but any potential decrease in drag is offset by higher inertia.

Follow up
By: DC
Wed, 02/17/2010 - 1:25pm

This is great stuff, Andy and Andy! It would be great if one could get a step by step, maybe once GC 1.4 is out, on how one could do a few runs and compare CdA if you _do not_ have Ibike (say using data from Google Earth and doing the loop around Grant's tomb or a short loop in Central Park). Probably seems really simple to you all, but could be helpful for some of us.



Andy F is right about the
By: Andy Shen
Tue, 02/09/2010 - 10:37am

Andy F is right about the laps. Another approach is to get the elevation of your start and end points from Google earth and make the plot have the same elevation change. Having the barometric elevation helps, but barometric elevation isn't perfect either.

The CdA is mine, but that's on a windless day. CdA's you hear about are typically measured at 15 degree yaw, and will be higher as a result.

Re: Further Question
By: Andy Froncioni
Tue, 02/09/2010 - 10:10am

Well if you're doing loops, for example, you know that the net elevation always returns to zero.

If you do several loops at different speeds, then only one set of Crr-CdA combinations will level the ride data. The one thing you need to do is work with a very well-calibrated power meter.

Thanks for your question, and by the way -- the CdA numbers are not mine. Obviously some people have gotten pretty good at lowering their CdAs.



if i improve my flexibility
By: Piero Steerer
Tue, 02/09/2010 - 8:58am

if i improve my flexibility enough such that i can stick my head up my ass, will my cda improve?

Further question
By: Amine Setscrew
Tue, 02/09/2010 - 8:52am

Thanks, Andy, for keeping on this thread. I'm not clear on how one can calculate Cda using Aerolab without actual elevation. With actual elevation, you can tweak the Cda slider to match Aerolab's virtual elevation with the actual reading, thus getting an actual Cda. But without (as I have it), I just have one plot. I can move the plot up and down with the slider, but have no way of knowing what is more accurate. Or maybe there's something I'm overlooking? Hence the post.

Also, your Cda on the examples is low! I guess all the testing and adjustments you've been doing has paid off. No surprise.


i smoke 2 laps before i smoke
By: Doffo Stiff
Mon, 02/08/2010 - 3:00pm

i smoke 2 laps before i smoke 2 laps, and then i smoke 2 more.

Nope, the actual elevation
By: Andy Shen
Sun, 02/07/2010 - 1:08pm

Nope, the actual elevation helps, but isn't necessary. The real killer functionality is coming, the ability to take laps and overlay them. Comparing virtual elevation against itself will be very cool. You could do one lap slow and one lap fast, and then make the two plots match. Since Crr and CdA respond to speed differently, that would make very accurate results.

Equipment requirements
By: Amine Setscrew
Sun, 02/07/2010 - 12:00pm

Perhaps too late to ask, but looks as if you need something measuring actual elevation data during the ride for this to work. Is that correct?


does this mean i can wang
By: Raphael Fork
Tue, 02/02/2010 - 8:15am

does this mean i can wang chung tonight?

Re: This sounds really
By: Andy Froncioni
Mon, 02/01/2010 - 4:23pm

This stuff is quite amazing, but we're just simply making Robert Chung's invention more visual.

And yes, Ruben Cable, Aerolab will help you kill it in your time-trials. Don't be afraid to drop by and ask us questions, ok?



This sounds really
By: Ruben Cable
Mon, 02/01/2010 - 9:31am

This sounds really impressive. I have absolutely no clue what it means but sounds like a bunch of smart guys are behind it. Once I figure it out, park racing watch out, I'm going to be killing it.

Please Report Bug
Mon, 02/01/2010 - 9:15am


If you download this, try it, and have problems or feature requests, we are an Open Source project. Which means we deal directly with the user and we try hard to make sure all bugs get fixed and that you get a working copy.

But, to do so, you have to report the bug !

Please sign up to the Golden Cheetah mailing list and report your bugs/features:

Oh and we accept patches too. ;-)



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  • schmalz's log 2010 part 5 -

    On cannot ride on water and mightiness alone, and as I age, I find that I have to pay more attention to my nutritional needs, lest I become an empty husk of veiny gristle.

  • The Shen Method? -

    I've been playing around with the Chung Method for a while, and I've found a way to use it to pry apart Crr and CdA from a ride file.

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