What do I need for the automatic segment mode ?
You need a barometer on your smartphone, if you want to measure apparent CdA and possibly an anemometer if you want to measure CdA during a ride.
Is it possible to compare accurately position or gear during a ride ?
The training mode would give you a very good idea of your CdA on flat segments (CdA realtime feature). But in order to detect small differences between two helmets for instance, or two different positions on a time trial bike, you will investigate with the two modes (see here) where a barometer is not necessary, on a specific course. Precision will be better.
Can I use the app on the classic lap mode or velodrome mode without low wind conditions ?
It depends of the course, but according to our tests, 5 km/h of wind is the upper limit from which you should stop your field tests. Above this value, precision decreases dramatically without an anemometer.
Do I need a barometer on my smartphone for the lap modes ?
No, it is useless as the net elevation on a lap is zero.
Do I need to keep constant speed during a lap ?
No. But keeping constant from one lap to another, from one run to another is a good idea, as Cd (drag coefficient) is speed and yaw dependent.
Do I need to keep same speed at the beginning and the end of a lap ?
No. But same as before.
What is apparent CdA ?
The apparent CdA is the same than CdA if there is no wind (or drafting) and no braking. The apparent CdA is computed with no model for wind (or drafting) and/or braking effects.
How can a corrupted FIT file may be fixed ?
The .fit file may be corrupted when the phone shuts down or reboots, or during unexpected use of the app. In this case, you can fix by using this online tool (https://www.fitfiletools.com) by clicking "Corrupt Time Fixer" for instance. Several fields may be lost, typically airspeed data, though, after the operation.
7 comments:
Der Crr ist nicht konstant, sondern geschwindigkeitabhängig. Insbesondere bei Stromlinienförmigen Körpern ist auch CdA nicht konstant, sondern geschwindigkeitsabhängig. Bitte beschreiben Sie die Methode nach welcher die CdaCrr-App den angeblich konstanten Crr und CwA ermittelt ?
Indeed, Crr is speed dependent. The method: http://anonymous.coward.free.fr/wattage/cda/indirect-cda.pdf
Vielen Dank. Ich war mir nicht sicher, die Methode von R. Chung war mir bekannt.
CdA is also speed dependent. But the two coefficients are supposed constant with the method. So keeping the average speed in the same range from test to test is a good thing.
Deine Aussagen sind korrekt. Mich würde die genaue CdA(v) Kurve für ein Rennrad interessieren. Ich baue derzeit etwas damit ich CdA(v) von Bodenfahrzeugen in der Realität genau messen kann, mein Antrieb ist die Neugier die Kurven CdA(v) für Rennrad und Velomobile sehen zu können. Beim Rennrad ist die Kurve CdA(v) nicht so stark geschwindigkeitsabhängig wie beim Velomobil, aber ich möchte das sehen. Kennst Du diese Diskussion ? Da siehst Du die gemessene CdA(v) welche ich für ein Speichenlaufrad exakt gemessen habe (null Zero = Ohne Windanströmung, dreht sich auf der Stelle): https://www.velomobilforum.de/forum/index.php?threads/aerodynamik-rolltest.32880/page-51#post-791197
Thanks for the link, very interesting thread I suppose, unhappily not easy for me to read. I understand why CdA is speed dependent, Reynolds number is different on the different parts of the body or the bike, and total drag is the sum of each part drag. In my mind and for my goals, measuring CdA at race speed (which implies to find a road doing a loop where it is possible to not brake, not easy) to compare for instance 2 helmets, is the good option, even if during downhill, the result may be opposed.
Funny fact at least for me: you have the velomobile (Strada) I dreamed to buy 15 years ago... One day may be.
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