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Re: Aero sensors for dummies thread [marcag] [ In reply to ]
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Thanks, I found it. I expected crr to go down as the temp goes up, but this goes the other way.


https://docs.google.com/spreadsheets/d/1vTm2AQYKeDuabP8Qiv5_AjatJVNYSY_DRBOeFmO3-_8/edit#gid=2047093726


I use GC aerolab for AB testing. I generally dont compare day to day. I just do fastest previous position vs a different position. I have also used plenty of secondary options. I tried the aeropod and I was never able to get a good calibration in with it. I've also tried aerotune, which was mentioned earlier. I had good luck using it for the most part. Calibration and testing was very straightforward. A tests would be close to A and so on.
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Re: Aero sensors for dummies thread [RChung] [ In reply to ]
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RChung wrote:
pyf wrote:

Here is a pic of a double setup (530 in the center for Aerotune, 130 on the side for Notio). https://hostux.pics/image/uFG

Pierre,

Have you noticed whether you get different airspeed readings if the Notio is mounted elsewhere (like, at the end of the base bar vs. under one of the aerobar extensions)?

Robert,

I think Marc probably gives a much more informed answer to the one I'll give you... but here is what I can tell you :
- haven't tried moving the sensor around on same day with similar conditions to see if wind speed would come back different relative to sensor position... I'm always trying to measure differences between setups so the CdA reported is what it is and I'm not expecting an absolute value, as long as the differences are measured properly.
- one thing I've never understood with Notio and have told the Notio team is this "Once the calibration factor has been found, there is no need to change it unless the Notio or cockpit configuration changes (i.e. stack, angle, etc.).", most people are going to want to try to move their cockpit during an aero testing session, so if you need to change your calibration factor (3km out + 3km back with no car is a pain in the ass of a calibration if you ask me...) when you change your cockpit setup it becomes absolutely impossible to test changes in that area with the Notio IMHO.
- so by placing it on side of basebar I think you can do pretty much anything in the middle without having to worry about the calibration factor needing to be changed.
- BUT, having the sensor on the side gives very suspicious low calibration factor that makes the CdA wrong if you apply the calibration factor it gives you. Factory calibration factor on a Notio is 1.39 , when I have the sensor in the middle I'm always very close to factory calibration factor (between 1.38 and 1.395) to the point that I live it at 1.39 since the repeatability at different values is not good enough that it justifies changing it. With the Notio on the left of base bar, I'm getting calibration factor between 1.32 and 1.35 (which is a WIDE range) but also very low, you would think since it is a different position it would make sense to trust that a change in calibration factor is needed BUT this change will actually give me a very CdA (increase of around 0.02), so it seems the Notio to the side ask you for a lower calibration factor that you should NOT apply...

Don't know if this is all clear... and in case you could not feel it from my tone, I'm not the biggest fan of the Notio (actually for that reason but also a couple of other even more important ones). It's always exciting to install such a tool on the bike and since you are going to get more precise in your measurements but my findings both on indoor velodrome and outside it that I'm probably less precise with Notio that other measurement methods with a much longer post analysis time to get result... so feel like a LOOSE-LOOSE situation to me which I'm pretty sad about :-( .
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Re: Aero sensors for dummies thread [pyf] [ In reply to ]
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This may well be an aero dummy question but would it be better or worse if the aero sensor was attached to the head tube and therefore never moved left and right with the handlebars? but rather pointed on the same axis as the bike frame? I know everyone seems to attach to the handlebars, and that may be because it is the least problematic attachment but just curious if anyone has tried the headtube attachment?
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Re: Aero sensors for dummies thread [s5100e] [ In reply to ]
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s5100e wrote:
This may well be an aero dummy question but would it be better or worse if the aero sensor was attached to the head tube and therefore never moved left and right with the handlebars? but rather pointed on the same axis as the bike frame? I know everyone seems to attach to the handlebars, and that may be because it is the least problematic attachment but just curious if anyone has tried the headtube attachment?

If you move a pitot type device around the cockpit from "at the head tube" to "as far forward as possible" in 4 positions, then left of the left extension and right of the right extension in those same 4 (front/back) positions, so 12 positions. Then added up/down (Zaxis).

You will see a difference. If you then try to explain these differences, you will get different reasons. If you add varying wind conditions, you will get further differences. Then throw in particularities of the rider.

Simply, look around the device and imagine what components may be interacting with it.

If you've seen and understand these challenges, you can do things to account for these differences.

I compare this to the good old days when I'd calibrate (zero) my Quarq and get a 314, redo it, get a 319......redo it get a 327....314. We knew the watts/unit and it was maybe a 5w difference. It was frustrating. But they made it better with things like temperature compensation and finally we got to auto-calibrate on 0 cadence.

These calibrations can be improved.
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Re: Aero sensors for dummies thread [marcag] [ In reply to ]
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marcag wrote:
I compare this to the good old days when I'd calibrate (zero) my Quarq and get a 314, redo it, get a 319......redo it get a 327....314. We knew the watts/unit and it was maybe a 5w difference. It was frustrating. But they made it better with things like temperature compensation and finally we got to auto-calibrate on 0 cadence.


Did it become better or is the measurement error now hidden in a black box called auto-calibration?
Last edited by: BergHugi: May 31, 21 5:36
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Re: Aero sensors for dummies thread [BergHugi] [ In reply to ]
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BergHugi wrote:
marcag wrote:
I compare this to the good old days when I'd calibrate (zero) my Quarq and get a 314, redo it, get a 319......redo it get a 327....314. We knew the watts/unit and it was maybe a 5w difference. It was frustrating. But they made it better with things like temperature compensation and finally we got to auto-calibrate on 0 cadence.


Did it become better or is the measurement error now hided in a black box called auto-calibration?

Good question. Robert often refers to VE as a diagnostic tool. It definitely diagnoses that my P2Max with auto-calibration seem to be doing its job :-).

But it is true, black box auto calibration was patented by Sergeant Shultz
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Re: Aero sensors for dummies thread [marcag] [ In reply to ]
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Hi marcag, what I am really wondering about is the effect of turning the probe left and right as you turn, it is seeing the air in a way that the rest of the system is not, if you see what I mean....the bike and rider are still pointing on one vector while the probe is facing another? I know this is a transient effect and probably of no great consequence in the scheme of things, but even riding down the road straight there are minor left right adjustments at the bars that do not occur at the head tube. Of course I am also implying that the probe is out in front far enough as well. Just thinking about the effect of left right movement off axis.

RChung hit it exactly (as always) in his next response " In earlier versions, it was mounted to the head tube so it wouldn't turn with steering input -- of course, one side-effect of having a long probe is that the observed yaw in turns is greater (think what would happen if the probe were 10 meters long and how the tip would have to sweep through a turn much faster than the base) "

So that is my question if you need to get out in front of the bow wave and to do so means more sweep of the bars, why then do most probes attach to the bars? Just curious is all.
Last edited by: s5100e: May 31, 21 7:16
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Re: Aero sensors for dummies thread [pyf] [ In reply to ]
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Pierre,

The reason I asked was because of that infamous session Ray Maker, Tom Anhalt, and I had at the Specialized Wind Tunnel where we were trying to figure out the best way to test aero probes. We had a Notio, an Aeropod, and an Alphamantis Aerostick, and learned a bit about how sensitive these devices are to the exact mounting position. The Aerostick, of course, also measures yaw, and had the longest probe to get out in front of the "bow wave." In earlier versions, it was mounted to the head tube so it wouldn't turn with steering input -- of course, one side-effect of having a long probe is that the observed yaw in turns is greater (think what would happen if the probe were 10 meters long and how the tip would have to sweep through a turn much faster than the base) but the other probes didn't measure yaw so we were just trying to look at straight ahead drag.

Many years ago when we were first trying to validate aero drag measurements, Tom Compton proposed a challenge: to add objects of known shape and size to the bike and see whether the CdA changed by the predicted amount. In those photos somewhere of our day at the Specialized Tunnel you can see one photo of plastic balls hanging off a stick that were used for the Compton Challenge. In order to get clean air and avoid interaction effects, you either have to go off to the side, or way way in front, or up above. That's one of the things I think about when I see probe placement now.
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Re: Aero sensors for dummies thread [RChung] [ In reply to ]
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RChung wrote:

Many years ago when we were first trying to validate aero drag measurements, Tom Compton proposed a challenge: to add objects of known shape and size to the bike and see whether the CdA changed by the predicted amount. In those photos somewhere of our day at the Specialized Tunnel you can see one photo of plastic balls hanging off a stick that were used for the Compton Challenge. In order to get clean air and avoid interaction effects, you either have to go off to the side, or way way in front, or up above. That's one of the things I think about when I see probe placement now.

this was Hugo Houle, worldtour rider for Astana during a session to measure differences between the team bike and the new disc brake version. They needed a way to confirm the differences measured were valid. He did 3 tests, with nothing, with the stick, with the stick and ball.


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Re: Aero sensors for dummies thread [carrag340] [ In reply to ]
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carrag340 wrote:
Thanks, I found it. I expected crr to go down as the temp goes up, but this goes the other way.


https://docs.google.com/spreadsheets/d/1vTm2AQYKeDuabP8Qiv5_AjatJVNYSY_DRBOeFmO3-_8/edit#gid=2047093726


I use GC aerolab for AB testing. I generally dont compare day to day. I just do fastest previous position vs a different position. I have also used plenty of secondary options. I tried the aeropod and I was never able to get a good calibration in with it. I've also tried aerotune, which was mentioned earlier. I had good luck using it for the most part. Calibration and testing was very straightforward. A tests would be close to A and so on.

I think you might be misunderstanding the application of the temp compensation in that spreadsheet. It's being used to "normalize" the results to 20C. So, if I test at a temp higher than 20C, then the measured Crr is increased to what it would be at 20C. If tested at a temp below 20C (where measured Crr is higher), it is then decreased to predict the 20C value.

This came about from my observation that tire temperatures (both on rollers and when riding outside) basically track the ambient temperature (with an offset), and then looking at the measured Crr of a particular tire (my GP4000S "control" tire, in this case) over a wide range of ambient temps. That's all described here: http://bikeblather.blogspot.com/...ollers-chartand.html



http://bikeblather.blogspot.com/
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Re: Aero sensors for dummies thread [marcag] [ In reply to ]
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marcag wrote:
RChung wrote:


Many years ago when we were first trying to validate aero drag measurements, Tom Compton proposed a challenge: to add objects of known shape and size to the bike and see whether the CdA changed by the predicted amount. In those photos somewhere of our day at the Specialized Tunnel you can see one photo of plastic balls hanging off a stick that were used for the Compton Challenge. In order to get clean air and avoid interaction effects, you either have to go off to the side, or way way in front, or up above. That's one of the things I think about when I see probe placement now.


this was Hugo Houle, worldtour rider for Astana during a session to measure differences between the team bike and the new disc brake version. They needed a way to confirm the differences measured were valid. He did 3 tests, with nothing, with the stick, with the stick and ball.

Looks familiar :-)



Of course, this also begs the question: "What DID the results show? (i.e. which bike was faster?)" ;-)

http://bikeblather.blogspot.com/
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Re: Aero sensors for dummies thread [Tom A.] [ In reply to ]
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Tom A. wrote:
marcag wrote:
RChung wrote:


Many years ago when we were first trying to validate aero drag measurements, Tom Compton proposed a challenge: to add objects of known shape and size to the bike and see whether the CdA changed by the predicted amount. In those photos somewhere of our day at the Specialized Tunnel you can see one photo of plastic balls hanging off a stick that were used for the Compton Challenge. In order to get clean air and avoid interaction effects, you either have to go off to the side, or way way in front, or up above. That's one of the things I think about when I see probe placement now.


this was Hugo Houle, worldtour rider for Astana during a session to measure differences between the team bike and the new disc brake version. They needed a way to confirm the differences measured were valid. He did 3 tests, with nothing, with the stick, with the stick and ball.


Looks familiar :-)



Of course, this also begs the question: "What DID the results show? (i.e. which bike was faster?)" ;-)

how do you compute exactly the frontal area of the ball and the exposed stick?

E

Eric Reid AeroFit | Instagram Portfolio
Aerodynamic Retul Bike Fitting

“You are experiencing the criminal coverup of a foreign backed fascist hostile takeover of a mafia shakedown of an authoritarian religious slow motion coup. Persuade people to vote for Democracy.”
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Re: Aero sensors for dummies thread [Tom A.] [ In reply to ]
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My setup had a motor about 200watts stronger :-)
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Re: Aero sensors for dummies thread [ericMPro] [ In reply to ]
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When ever you need an answer, google your question and add RChung or Tom A to the google query

https://bikeblather.blogspot.com/...ng-chung-method.html
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Re: Aero sensors for dummies thread [marcag] [ In reply to ]
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marcag wrote:

When ever you need an answer, google your question and add RChung or Tom A to the google query

https://bikeblather.blogspot.com/...ng-chung-method.html

LOL, thanks. I've been playing around the Notio aero sensor and have been testing on a 400m athletics track. I've been using jerseys I've tested in the tunnel as "known quantities" to see if things are lining up.

E

Eric Reid AeroFit | Instagram Portfolio
Aerodynamic Retul Bike Fitting

“You are experiencing the criminal coverup of a foreign backed fascist hostile takeover of a mafia shakedown of an authoritarian religious slow motion coup. Persuade people to vote for Democracy.”
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Re: Aero sensors for dummies thread [pyf] [ In reply to ]
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pyf wrote:
- BUT, having the sensor on the side gives very suspicious low calibration factor that makes the CdA wrong if you apply the calibration factor it gives you. Factory calibration factor on a Notio is 1.39 , when I have the sensor in the middle I'm always very close to factory calibration factor (between 1.38 and 1.395) to the point that I live it at 1.39 since the repeatability at different values is not good enough that it justifies changing it. With the Notio on the left of base bar, I'm getting calibration factor between 1.32 and 1.35 (which is a WIDE range) but also very low, you would think since it is a different position it would make sense to trust that a change in calibration factor is needed BUT this change will actually give me a very CdA (increase of around 0.02), so it seems the Notio to the side ask you for a lower calibration factor that you should NOT apply...

It makes sense that "left side of basebar" would see more variability due to sidewind effects. Also, does the lower factor mean that location is less obstructed? Guessing yes, that the factor is applied to the measured dynamic pressure, and a lower number means it's less affected.

Check the distance averaged computed wind for your runs. If both directions cancel out the calibration should be good.

Ideally for the sake of measurement, we want the calibration to be independent of any changes we make. This interferes with the theme of JRA measurement taking though, since a long probe or long attachment apparatus is needed.
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Re: Aero sensors for dummies thread [rruff] [ In reply to ]
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10 years ago:


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Re: Aero sensors for dummies thread [BergHugi] [ In reply to ]
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Outdoors you'd want to measure near your drag center I think...
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Re: Aero sensors for dummies thread [BergHugi] [ In reply to ]
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BergHugi wrote:
10 years ago:

My attempt is from 8 years ago, so nearly as old ;-)

Yup...that looks similar to the setup Andy Coggan had/has. He sent it to me at one time (probably about the same 10 year time frame) to try, but I couldn't get things to work, mostly due to course difficulties (road construction had altered my original course). It wasn't until I had identified a different (and better!) course that I was able to finally attempt the Tom Compton Challenge "for score" :-)

http://bikeblather.blogspot.com/
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Re: Aero sensors for dummies thread [Tom A.] [ In reply to ]
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Thanks for clarifying and thanks for all the data. I've now got one of your data sources connected to two of your formulas.
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Re: Aero sensors for dummies thread [ericMPro] [ In reply to ]
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ericMPro wrote:


how do you compute exactly the frontal area of the ball and the exposed stick?

E


Measurements and geometry? ;-)

Seriously though, I think what you're getting at is how did I account for the stick portion as it's attached near the bike, right? Simple, I made the "baseline" the setup WITH the bare stick attached. Since I was mostly interested in relative changes from that point (to prove out the sensitivity to the various size spheres) that made sense. If you read the blog post, for the "stick only" attempt, I even place a thin washer at the end of the rod to act as sort of "endplate", mostly because I understood the spheres would end up affecting the flow over the stick in a similar manner (i.e. the flow would be mostly aligned with the direction of travel, whereas without an endplate, there would be some skewing/vortices at the rod end). I wasn't sure how much that would matter, so I decided to use the thin washer, to at least minimize any effects.

I made sure to also subtract the length of rod covered by the spheres when they were attached, to get a better "calculated" CdA difference between setups.

http://bikeblather.blogspot.com/
Last edited by: Tom A.: May 31, 21 15:40
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Re: Aero sensors for dummies thread [marcag] [ In reply to ]
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marcag wrote:
My setup had a motor about 200watts stronger :-)

Dodging the "disc vs rim brake TT bike" question, I see... ;-)

http://bikeblather.blogspot.com/
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Re: Aero sensors for dummies thread [Tom A.] [ In reply to ]
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Tom A. wrote:
marcag wrote:
My setup had a motor about 200watts stronger :-)


Dodging the "disc vs rim brake TT bike" question, I see... ;-)

The new bike with disc brakes had an effective .008 cda improvement. They published 8 watts. The wheels of course were not identical but the same generation. While stack and reach were identical, how you got to that stack and reach was a little different. There were 2 generations of bikes between the two.

The team wanted to check the results, despite the Compton proof and got exactly the same number through independent testing.

But one thing we overlooked was a ceramic speed derailleur on the rim version of the bike. It was his actual team TT bike that was brought for the test and we didn't know that would be there. A "quite high up executive" (no longer with the company) said "Ceramic speed is worth 10watts therefore we can claim we are in fact 18 watts faster". Some less creative individuals put their foot down and said no and the 8 watts stood.
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Re: Aero sensors for dummies thread [Tom A.] [ In reply to ]
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Tom A. wrote:
Yup...that looks similar to the setup Andy Coggan had/has.

Yes, Andy Coggan is older, I have it from him.
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Re: Aero sensors for dummies thread [BergHugi] [ In reply to ]
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BergHugi wrote:
Tom A. wrote:
Yup...that looks similar to the setup Andy Coggan had/has.


Yes, Andy Coggan is older, I have it from him.

That is the same bike that I test and race on. I haven't find anything faster so far, albeit I've only tested 4 other bikes from 2 manufacturers
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