Test of the dynamic calibration of the airspeed device

Bad and good news from the velodrome test today. I implemented recently in the app, a dynamic procedure for calculating the correction factor to be applied to the raw air velocity measured by the anemometer. This factor is calculated at each lap. The anemometer (blue) was placed on the left drop of the bike during the test:

Several turns are made where I changed the position of my hands (hoods then drops, again hoods). Thus, we can see that when the left hand on the hood is close to the anemometer (certainly creating a local air acceleration), the calibration factor decreases by about 2% (1.095 to 1.075), and so a similar erreor increase of ~4% on the calculated CdA:

The good new is that if we keep a same position, the factor is well calculated with acceptable variability +/- 0.5%. We can also assume that by placing the bike's anemometer in another location, the issue may be reduced.

Power meter data quality

Yesterday, for the first direct comparison during a turbo session, I got results, which confirmed my suspicions, between my two current powermeters, a Power2max NG-Eco (2 months old) and a PowerTap G3 (recently changed). Unfortunatly, I deleted some of the data. Today, during a ride with intervals of several minutes, I recorded the following averages:

One (or the two?) gave an unexplicated difference during the first lap of the two runs (the relative difference does not depend of the gear ratio and is constant at +/-0.5% during the whole lap). Auto-zero feature was activated on the two power-meters and I stopped pedalling during the laps. I have some guesses about the suspect. More to come.  

Cheapest Android phone to use CdaCrr bike computer

The app is currently tested with the following phones:

• Blackview A7
• Samsung J5, S4 mini, S4, S5
• Xiaomi Redmi Note 7
• Wiko Pulp 4G

Whereas with ANT+, you had only access to ~100 phones supporting ANT+ natively, now that the app enables BLE connection with powermeter and speed sensors, you have a much larger choice (~2000 models) to pick an Android phone under 100$*.

* You would need also a powermeter (~450$), a speed sensor (~35$), and a phone mount on your bike (~10$). You would also highly benefit from the Weatherflow anemometer (~70$) if you are seriously hooked to field testing.