AeroPod as CDA measurement

[benphyr]

That looks kind of like a pitot tube like they have on aircraft. If that is so, how do they get around the low velocity limitations (very small differences in pressure such as measurement error greater than measurements)? Second, if it is measuring air velocity then I would think mounting it in a location that is in clean air or consistent air would be of paramount importance. TT location may be far enough from the wheel to avoid interactions but @Bill K the location you have it, would it be getting air buffetted by the pedals and the wheel? At least from the angle of the photo it appears that way. Regardless, I'm very interested in the results and your observations.

 

[DavidCH]

The biggest issue for an unfared recumbent rider is the size of his feet. To reduce the resistence you would need funny shaped pedals. Any edge causes turbulence so your feet being right in the front line probably is going to be the biggest resistence of all. Larry being of small size probably has small feet, and that's why Larry is fast and it's not so much down to the size of his bars.

I rest my case.

Forget about cda device and buy some funny shaped pedals

 

[ed72]

I guess that is my problem. Size 48 mega shoes. Big hands, too. Can't have everything.

I have wondered how much a pair of Giro Empire SLX paired to Speedplay Zero Aero pedals would help over my chunky pedals and fatter Sidi shoes with ratchets on the side. It is about a $450 experiment. My guess? 4-8 watts at 26 mph. It would take many runs to be sure of that, though.

0.003 to maybe 0.005 m squared?

 

[Bill K]

That looks kind of like a pitot tube like they have on aircraft. If that is so, how do they get around the low velocity limitations (very small differences in pressure such as measurement error greater than measurements)? Second, if it is measuring air velocity then I would think mounting it in a location that is in clean air or consistent air would be of paramount importance. TT location may be far enough from the wheel to avoid interactions but @Bill K the location you have it, would it be getting air buffetted by the pedals and the wheel? At least from the angle of the photo it appears that way. Regardless, I'm very interested in the results and your observations.

The cda calculation (according to their web forum) uses 60-second smoothing on the air velocity to get the signal out of all the noise. I don't know yet whether the location I have the sensor will be badly affected by pedals or the front wheel. The tip of the pitot tube (measuring velocity pressure) is about 4 inches in front of the wheel but the static pressure port is quite close to the wheel.
I plan to do some hill repeats where I can either pedal or coast at 30+ mph to see if the pedals affect wind sensor values.
I am also going to try mounting it above the boom using a go-pro mount. That will solve any wheel induced turbulence but will still be affected by the cranks.
On their forum, it looks like a few users have reported being able to do a-b testing for differences in the 5-watt range but you have to have a very good testing methodology (which involve a learning curve).

 

[Bill K]

I got a good ride in with this yesterday. Calibration followed by out and back laps across the 520 floating bridge.
https://www.strava.com/activities/2017137357

Here are the numbers it gave me for slope and ground wind speed for 4 laps across the bridge.
Slope values are % grade (+ is uphill)
Ground Wind speed is in mph (+ is headwind, - is tailwind)
The delta between the measured slope riding eastbound vs westbound (on the floating bridge which is as flat as it gets) should tell me how well it is calibrated and should give an indication of its accuracy and repeatability.

Lap Slope East Slope West Wind East Wind West
1 +.07 +.29 +3.4 -2.9
2 +.10 +.13 +2.8 -3.7
3 +.15 +.17 +1.1 -0.5
4 +.17 +.19 +0.3 -2.5

It shows me going uphill in both directions, so clearly not zeroed out.
This was my first time calibrating it and it is quite sensitive. I expect it to be better next time. There is a definite learning curve involved.
On lap 1 I stopped to take a picture of a bald eagle perched on a DOT camera pole. Not good for aero testing! But this clearly shows up in the slope data (see charts below).

The HR plot on the charts below show the encoded cda data: cda = HR * 4 / 1000.
e.g. for a HR value of 80 the calculated cda = 0.320
This is kind of a hack, but Velocomp currently has to do this because ANT+ and BLE do not support an aero data channel, so they transmit aero data using the HR channel. This is likely to change in the next year or two as there are a number of companies that want this.

Below is the data recorded for lap 1 eastbound on the floating part of the bridge:

Below is the data recorded for lap 1 westbound (this is where I stopped to take a picture).


And this is how the AeroPod is mounted on the V20:


What I learned:

Mounting the sensor below the crank (just in front of the front wheel) is bad. Turbulence from the spinning wheel fouls the static pressure sensor port and makes the data useless. I tested this 2 days ago and it thought I had a constant 20mph tailwind.

Mounting the sensor on the boom as I did for this ride appears to be a good location aerodynamically. No indication that pedaling significantly disturbs the air flow.

Cda is not calculated when you are not pedaling (such as coasting downhill, even when coasting 30 mph) or when going slow uphill.
You can see this in the cda values (in the HR data plot) when the value is completely flat and does not change at all.

Testing at 20 - 22 mph for 2 or 3 minutes is not good enough to reveal subtle changes in cda. Being adjacent to the 520 freeway is not good for wind consistency either. Maybe I should test during rush hour when the cars are moving at less than 15 mph.

Max slope values that you see in GPS data should be completely ignored.
For example, rides in Strava based on GPS data show that the climb at the east end of this bridge peaks at 15%.
I now know that the max slope of this climb is only 8.8%. Shut-up legs

The initial calibration ride calculated my cda as 0.351 m^2. This is surprisingly high for a V20 but I compared it to what CyclingPowerLab estimates from this ride data and they both agree pretty well.
I can only hope it is correct. If correct, there is lots of room for improvement and I can only get faster!
Apparently, a floppy wool shirt, loose fitting shorts, sandals, 32-spoke wheels (and who knows what else) slow you down more than you can possibly imagine!

 

[ed72]

Thanks for sharing all that, Bill.

Is the Crr user entered or calculated? 0.0032 is really low for paved roads. I have two venues that I test on. One is a flat road that was nicely asphalt paved 1 year ago. Venue 2 is a pipeline neighborhood road with rougher, course pavement. With Continental Supersonic tires (very fast tires) and latex I get 0.0045 and 0.005, approx. Vittoria tubeless Speeds are a little faster...approaching 0.004. A higher Crr would give a lower (edit) estimated CdA. You could have much better roads (concrete?) than I do.

The CdA looks reasonable from the data, I would have guessed 0.360-0.400 looking at the Strava segments. Just the Crr looks a little optimistic.

Yes, that kit has to be the culprit. LOL.

 

[Bill K]

The crr was just the default value. I did a "factory reset" on the AeroPod just before doing the calibration ride.
I was having trouble getting it to pair to the speed sensor and power meter.
It turns out that when paring to speed/power sensors (ant+), it takes about 60 seconds and the wheel has to be spinning the whole time or the AeroPod will not see it. They have not optimized the "new user" experience yet...

 

[ed72]

In 50F temperatures, tires are kinda slow. Your CdA is not as "bad" as reported. In Tom Anhalt's blog someplace, he measured 1.4% reduction in Crr per degree Celsius. This is probably why my first lap needs to be thrown out during testing but is also why I compare one change to another on the same day as a sort of control (getting precise dew point and atmospheric pressure being another factor to control). This kind of attention to detail isn't necessary for big gains but once down to smaller differences (like comparing a FLO60 wheel to the 2-Spoke wheel), it gets trickier as it is possible to fool yourself.

I found that a snug (not terribly floppy) short sleeve wool jersey cost me about 0.020 (10% reduction overall) compared to a high end tight jersey like a Castelli or Assos. It is astonishing how much my winter kit slows me down. Makes you wish for that first warm Spring day or a trip to Florida.

What would be incredible/valuable to me and get me to spend the money is if the Aeropod and a reasonably careful User would have the sensitivity and accuracy to resolve a 0.001 m² difference in just a couple of runs. 0.001 is what about the size of a mirror that hangs off the helmet or maybe a small bike headlight. If it could even do 0.002, it would be worth it. As much as I like the Chung method, it takes a lot of time and effort and essentially yields a lost training opportunity. How does one change kit in the middle of a housing development. With the Aeropod, one could station in a park with rest facilities to change and repeat runs. If my Garmin was compatible, I think I'd be inclined to shell out the $499

http://bikeblather.blogspot.com/

 

[ed72]

On sale for $399 here......I just can't pull the trigger....a new Garmin and Aeropod is in the cart.

https://powermetercity.com/

Some good points here about the challenges in any field testing. (I don't bother if I can see any movement in leaves at the top of trees)

http://www.timetriallingforum.co.uk/index.php?/topic/130737-aeropod-experiences/&

The more I look at it, $1000 for two hours in the A2 tunnel might be a better value than spending it on the aeropod and a new Garmin to find that extra 0.020 m² CdA ......or lose the extra 20 Kg or regain those lost 20 watts but those are separate old guy issues.

 

[Bill K]

That thread on timetriallingforum is an interesting read. It gives a good insight into cda testing and using the AeroPod.
BTW, you do not "need" a new Garmin to use the AeroPod. The AeroPod records all data internally, then you can download the data to your computer using the usb port when you get home.
If you want to see live AeroPod data (cda, slope, wind speed, or the results of a calibration ride) while you are riding, then you do need one of the newer Garmin's that supports "IQ Apps".
Also, clicking the Garmin "lap" button gets recorded in the AeroPod data. This is useful but I think this is part of the "IQ App" and would require the newer Garmin head unit.

Detecting cda changes of +/- .002 for a / b testing looks like it would be pushing the limits. I don't have an answer to this yet.

 

[ed72]

Thanks Bill, I somehow thought the new IQ Apps Garmin was needed. Takes the sting out a bit.

The UK time trial site and also Slowtwitch has some really smart and experienced cyclists from Andrew Coggan to Robert Chung, for example. I think "Skippy" is the designer software dude behind aerolab. +/- .002 might just take a few runs and average them. I don't bother with statistics although could do if wanted to. If I am comparing helmets and helmet 1 is consistently equal to or better than helmet 2, I go with helmet 1 especially if it ventilates heat better and is more comfy (Giro Vanquish for example) but it takes many runs and then post data analysis to determine which is better (lower CdA).

About 4 years ago I had an upright TT bike fitting by Dean Phillips at Fitwerx. He was the Masters National TT champion and owner of the shop. He did lots and lots of aero field testing using the Chung method and he told me how many runs over multiple days that it takes to determine if a new piece of gear or position change was faster. I was blown away. Now, I get it. He told me he uses his recovery ride days to test equipment and position changes. It is indeed asking too much for a Chung on a Stick to resolve a 0.001 difference real-time but if it only takes 3-5 runs (replicates) on one ride, it would be a huge time saver. I am quite confident at 0.003 A/B differences and reasonably confident at 0.002 with chung method but not 0.001.

It took me a little while to get less than lousy at testing and suspect you will get better results with the aeropod as time goes by; and, I am looking forward to reading of your results.

 

[LarryOz]

Gosh - this is a lot of stuff to read. haha!
Well - I had to give my wife something to get me for Christmas - and she said no to the Milan, so my 2nd choice was this aero-pod!
So I will be un-wrapping it next week and I will be testing it along-side my other known testing methods (primarily - fixed power and speed on a flat track under extrememly controlled conditions (as all testing should really be done. ) I don't really care about the actual Cda number - but am interested if the "changes" that I can see for what I know are "known" differences I have already tested with. . i.e helmets, and hand positions. It may be that the granularity of the data may not be great enough for testing minor changes. If it looks like it will be useful I will keep it, it not, then I will take advantage of the 60 day return and send it back. (maybe trade it in for the Milan)

 

[ed72]

I asked Santa for a Milan GT

 

[Bill K]

Gosh - this is a lot of stuff to read. haha!
Well - I had to give my wife something to get me for Christmas - and she said no to the Milan, so my 2nd choice was this aero-pod!
So I will be un-wrapping it next week and I will be testing it along-side my other known testing methods (primarily - fixed power and speed on a flat track under extrememly controlled conditions (as all testing should really be done. ) I don't really care about the actual Cda number - but am interested if the "changes" that I can see for what I know are "known" differences I have already tested with. . i.e helmets, and hand positions. It may be that the granularity of the data may not be great enough for testing minor changes. If it looks like it will be useful I will keep it, it not, then I will take advantage of the 60 day return and send it back. (maybe trade it in for the Milan)

The Milan will make you faster... way faster.
And it has 3 wheels. Get it with a roll cage and there will be no more crashing. That could be a key selling point to your wife

 

[ed72]

The Milan will make you faster... way faster.
And it has 3 wheels. Get it with a roll cage and there will be no more crashing. That could be a key selling point to your wife

Think of the money on Doctors bills I will save. I'm finally healed aside from the ruined elbow bursa after my last miscue into the desert. I'll try the safety angle, thanks..

 

[super slim]

Gosh - this is a lot of stuff to read. haha!
Well - I had to give my wife something to get me for Christmas - and she said no to the Milan, so my 2nd choice was this aero-pod!
So I will be un-wrapping it next week and I will be testing it along-side my other known testing methods (primarily - fixed power and speed on a flat track under extrememly controlled conditions (as all testing should really be done. ) I don't really care about the actual Cda number - but am interested if the "changes" that I can see for what I know are "known" differences I have already tested with. . i.e helmets, and hand positions. It may be that the granularity of the data may not be great enough for testing minor changes. If it looks like it will be useful I will keep it, it not, then I will take advantage of the 60 day return and send it back. (maybe trade it in for the Milan)

I thought you would have asked for an Alpha 7 Velo, so you could compete in the Trans AM and win it!!

 

[Bill K]

I got another good ride in with the AeroPod today.
https://www.strava.com/activities/2028737747

This time I just rode with it (no messing around with the calibration).
After I got out of the city I hit the lap button every 2 miles where I toggled the headlight (well known 5 watt dynohub resistive force) either on or off.
The best part is the four 2-mile laps in the outdoor velodrome with the 5-watt headlight load alternately on or off.
The AeroPod does appear to be sensitive enough to detect headlight-on vs headlight-off. But with only 4 6-minute laps this could very well be an anomaly.
Here is the velodrome data:


@LarryOz is an experienced tester and I'm just a guy playing with a new toy so I am looking forward to seeing what Larry can do with one.
Here is a neat way to do a/b testing and see the results as you ride:
Configure the Garmin to display AeroPod data and LapDistance.
When you hit the Garmin lap button, the AeroPod "Time Advantage" field gets reset to zero.
Make your a/b change, hit the lap button and start riding, and after a few minutes the time advantage will either go up or down, depending on whether you'r a/b change is faster or slower.

I was riding at about 20mph and you really need to be going faster than that.

 

[ed72]

5W ~= 0.5s/km time difference ~= .005 m^2

Rough rule of thumn at higher speeds (Coggan). (bigger time effect at 19 mph)

Cleaning it up (and warmer conditions...LOL) and you should be able to gain around 4 mph at the same wattage.

 

[Balor]

http://en.wellgopedal.com/products_detail_6_254.htm
Таке this pedals, maybe drill the platforms for lightness, remote studs, screw on foot fairings a-la that French hour record guy B-guy (don't ask his name, I'll never remember it). Ed, I can make this for you at half the price you stated

Anyway, currently, I'm working on a set of shoes with ultra-stiff (double-layer sandwich) soles that are molded (exactly) to my feet, midfoot cleats, uppers transplanted from old sidis. Not sure about uppers (they were damaged a bit during removal), but if it will work long term, I'll likely replicated it in carbon, not basalt fiber and use better uppers, maybe have them made from scratch.

 

[Mathew Fy]

http://en.wellgopedal.com/products_detail_6_254.htm
Таке this pedals, maybe drill the platforms for lightness, remote studs, screw on foot fairings a-la that French hour record guy B-guy (don't ask his name, I'll never remember it). Ed, I can make this for you at half the price you stated

Anyway, currently, I'm working on a set of shoes with ultra-stiff (double-layer sandwich) soles that are molded (exactly) to my feet, midfoot cleats, uppers transplanted from old sidis. Not sure about uppers (they were damaged a bit during removal), but if it will work long term, I'll likely replicated it in carbon, not basalt fiber and use better uppers, maybe have them made from scratch.

Look here for inspiration:
https://www.simmons-racing.com/cycling-2