Andy,

What's the status on your "Chung-on-a-Stick" project? Just curious.

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Joe

Andy, thanks for bringing this thread back up. I've meant to ask this some moons ago but kept forgetting it: what about track/velodrome runs?

We're considering booking a closed, 200m track in the upcoming weeks. For testing purposes, I thought of simulating a half-pipe by riding mostly in the lower ("flat") part of the track, and every lap, in one of the curves, go all the way up, touching the maximum at some specific marking (to give me a controllable point every 200m). The track is not so steeply banked, but we should still have 2-3 meters elevation. Would this suffice?

Would there be anything one should pay special attention to in this type of testing venue?

Thanks indeed,

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Ricardo Wickert | Team Magnesium Pur - Germany | My sporadically updated blog: The Thin Grad Line | My team-issued TT bike: Trek Speed Concept 9

2015 Sponsors & Partners: Magnesium Pur | Ullmax | B&W Bike Cases | Ristorante La Dolce Vita | Trek Bikes via Bici-Sport Binder

Ah, good question!

We have considerable track modelling experience. In some ways, it's the most difficult VE problem around. There are numerous challenges.

The issues are that the VE equations track the CG height, that the speed sensor measures *wheel* speed (not CG speed), that the tires are not always at 90 degrees to the bank, leading to slightly small wheel circumference, and that velodromes each have their own tailwind "microclimate", generated by the combined movement of the whole day's activity around the track.

All those things conspire to degrade VE accuracy.

If you ignore all that and get a pretty good handle on tire Crr, then you can still use Aerolab to do A vs B relative CdA testing. It works well, and produces results that are good enough. You don't need to do anything but ride the black line, or some other constant-height line.

Hope this helps...

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AndyF
bike geek

No need. Ride the black line.

Vary your speed, perhaps monotonically. Even a straw can stir a bath tub so you'll be building up a tailwind.

Robert, Andy -
I thought it was important to vary elevation to decouple Crr and CdA. We have a ball-park estimate for the tires, but it's the first time we'll be riding on a wood surface, so I'm not sure if we'll have it pegged down with the necessary precision.

On the other hand, the whole point of the velodrome trip is to perform "A vs B"-type comparisons (different hand/head positions and choice of aero helmets, mostly). So given that all runs should be done with the same wheels (= same Crr), maybe it shouldn't matter much anyway.

Thanks for all your input!

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Ricardo Wickert | Team Magnesium Pur - Germany | My sporadically updated blog: The Thin Grad Line | My team-issued TT bike: Trek Speed Concept 9

2015 Sponsors & Partners: Magnesium Pur | Ullmax | B&W Bike Cases | Ristorante La Dolce Vita | Trek Bikes via Bici-Sport Binder

Wait a couple of minutes between runs to let the tailwind die down a bit. It'll help a lot. Oh, and always make sure to double-check your results by running things in reverse order.

Example: A-B-B-A

That's just to make sure any slow changes in environmental conditions (rho or tailwind) don't lead to erroneous conclusions.

Also, get one of these (get the Bluetooth version, if you can):
http://www.kestrelmeters.com/...cing-weather-tracker

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AndyF
bike geek

Thanks for reminding me of the "editor" tab...that comes in handy dealing with the occasional Garmin speed drops :-/

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http://bikeblather.blogspot.com/

Still in development, but active.

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AndyF
bike geek

No...you just need a known elevation profile to decouple Crr and CdA...and what's a better known elevation profile than "0" all the way around? ;-)

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http://bikeblather.blogspot.com/

Just providing some background for Tom and Robert's replies, here...

No, to decouple Crr and CdA, you need to ride the same points on the course with different speeds. That way, only one combo of (Crr,CdA) satisfies:
F_observed_1 = CdA*0.5*rho*v1^2 + Crr*m*g
F_observed_2 = CdA*0.5*rho*v2^2 + Crr*m*g

Riding at the same speed all the time makes the 0.5*rho*v^2 term look constant in velocity.

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AndyF
bike geek

Got lucky and got some good conditions for doing a little more testing. The aerolab results look pretty good. See:

http://josephabank.blogspot.com/...ting-is-dz-nutz.html

Update: Aerolab Tips n' Tricks

I've been using Golden Cheetah 2.1 lately and just wanted to tell you about some new features that make Aerolab testing even more interesting.

1. Aerolab uses "Headwind" field, if it exists.
2. The Editor tab allows you to add a blank "Headwind" column.
3. The Editor tab allows you to copy-paste into and out of it, using an external spreadsheet.
4. The Editor tab allows you to delete the Altitude column.
5. Hovering over a curve lets you see a data bubble of exact values.

This is very useful because you can use it to do some amazing out-and-back protocol tricks. Here goes:

Out-and-Back Workflow

If you go into the Editor tab in Golden Cheetah you can add a "Headwind" field by right-clicking on the top bar of the table. Headwind is the total wind that hits the front of your bike, so it's the sum of wheel speed and wind speed.

This can be especially useful for out-and-back protocols. You can "inject" a column of headwind data by copy-pasting the wheel speed data into a separate spreadsheet. It should work with MS Excel, OpenOffice, or LibreOffice. Next, just create a formula in the spreadsheet to add +ive wind out and -ive wind back. Don't forget to sum this to the wheel speed data.

Copy-paste the new headwind column back into the GC Editor column. Now go to Aerolab and notice that headwind has been accounted for. Do the results look symmetric w.r.t. the turn-around point? If not, try a different wind value in the external spreadsheet model and try again.

When you're done, the VE curve should look completely symmetric about the turn-around point. Hover over mirror points on the curve to make sure they are at the same height. Or sight them using the grid by moving the whole curve up or down using the elevation offset.

Remember, if you have any questions, the Platypus Thread is the place!

Cheers!

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AndyF
bike geek

I want to add one more thing as well. The new Garmin 500 firmware (3.0) seems to cause way more data dropouts than before. In the raw data the dropouts are simply missed data points (missing seconds), but in Golden Cheetah it shows up as zero speed and either the same lat/long as the previous data point or zero lat/long as well. These data points will have a pretty big effect on Aerolab, so you have to fix them before doing any Aerolab analyses. The best way to fix them is to go into the Edit tab and average the speed and lat/long from the data points before and after the dropout.

I actually would turn off the GPS altogether. It's never ever been helpful for me.

Use a proper wheel speed sensor (Garmin GSC-10), if at all possible.

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AndyF
bike geek

That's fine, but that's basically irrelevant to the data dropout issue isn't it? It seems as if sometimes the Garmin unit just is busy doing other things and completely fails to record a data point (or two or three). This wouldn't be a problem if Golden Cheetah were to handle the dropout well, but what it does right now is it inserts a data point in where the Garmin left it out and then interpolates some fields (e.g. power) but at least in my experience (and this seems to depend a bit on the version of GC you use) it does not interpolate the speed -- it just puts a zero there. Not surprisingly the zero speed data point messes with Aerolab. In some versions of GC you can see the data drops as spikes in the Aerolab graph so you know to fix them, but in other versions of GC you can't see them on the graph and would have no idea that they are there.

Maybe not. Let me do some testing and see. I think the GPS unit is a big drain on the Edge 500 I have. My suspicion is that it gets in the way of proper ANT+ logging.

But let me check and see. Thanks for your input!

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AndyF
bike geek

Is that standard? I've always thought of that as "airspeed" and headwind (or tailwind) as just the wind component.

No, it's just the name "headwind' was ... ummm... an artefact of the development process I took for the iBike version of Aerolab. Awww, heck... it was late at night and I was tired, ok? :-)

So headwind = airspeed in Aerolab. Everywhere else, headwind is the ... ummm... head wind.

Cheers!

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AndyF
bike geek

You won't need to do this. Stay on the black line. Your CG height will go down in the turns and up on the straights. Level the curve over 10 or 12 laps and you should be ok. Make sure you run at pretty constant speed and level the same portion of the lap (the top of the VE curve on each straight).

This will be good enough for A vs B comparison.

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AndyF
bike geek

OK, so since we're making admissions, what's the standard for positive and negative yaw? If you're on a bike and you've got a pure headwind, that's zero yaw. If you then turn slightly to the left so the wind is now slightly on your right, is that positive yaw or negative yaw? Is it the same if you're in an airplane (i.e., if you yaw to the right, is that positive yaw or negative yaw)?

Let's use this as a convention, at least in the Platypus thread:
http://en.wikipedia.org/...ollpitchyawplain.png

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AndyF
bike geek

It was all clear to me until I looked at that picture!

Looks like bike convention follows airplane convention (IIRC), i.e. wind hitting the NDS of the bike corresponds to +ive yaw...

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http://bikeblather.blogspot.com/

Here's a quote from the Cervelo S5 White paper: "The figure above is a yaw-drag chart, a typical way of comparing the aerodynamic drag forces of different bicycles with a rider. Less drag (lower on the chart) is better. The vertical axis shows the drag force in grams, measured along the axis of the bike (not wind axes). This is the opposing axial force the rider feels due to the wind. The horizontal axis shows the yaw angle, or crosswind angle, in degrees. This is the angle the net wind makes with the rider, including both the wind created by the rider’s motion along the riding direction, plus any atmospheric wind (cross wind). Positive yaw (right side of the horizontal axis) is with the oncoming wind on the rider’s right side; negative yaw (left side of the axis) is with the oncoming wind on the rider’s left side." Is that consistent with the airplane convention?

I've only been a pilot for 26 years and I've never heard yaw expressed as positive or negative, just left or right.