# Have I calculated the air flow of this fan correctly?

To calculate air flow capacity of a fan in cubic feet per minute (cfm): multiply the average air speed you measured in feet/minute (fpm) by the area of the fan face in square feet. (Area of circle =þ d2/4; where d = diameter in feet). Example: you calculated an 524.93 ft/min average air speed across the face of a 12 inch (1 foot) diameter fan. Air flow (cfm) = speed (fpm) * area (sq ft)= 524.93fpm*þ(1)2/1 sq ft =1048.78 cfm?

The fan in question is visible from this link:http://greglemond.com/#!/revolution

The diameter of the Fan is 30cm or 12inchs in diameter

The website claims the maximum airflow in meters/second^2 is 160 (in imperial 524.93ft) and the maximum newtons of resistance is 40N (I am aware that is probable not the correct phrasing?). All airflow increases in a linear fashion to this maximum point.

I fear I have got a basic fundamental wrong whilst trying to figure out the airflow capacity of this resistance trainer correctly as meters/second^2 and cubic feet per minute are not directly comparable. Can I compare the too figure or would I be better off converting the 160 meters/second^2 and cubic feet per minute to lbs/minute so I can compare this fan to others available on the market?

• The unit of airflow is $\frac{m}{s^2}$? – Wojciech Mar 24 '14 at 20:02
• yes I asked some one why this was in bicycle.stack and they said 'm/s^2 is the base unit for acceleration, so perhaps it is because the resistance (measured in newtons), varies as a function of the acceleration which you put into the pedals/trainer.' Others added 'the x-axis label should be read as (m/s)^2, not m/s^2.' – user95786 Mar 24 '14 at 20:09
• It seems that you need some mass/volume units to measure airflow: en.wikipedia.org/wiki/Airflow (unless you use another definition). – jinawee Mar 24 '14 at 20:22

and the $x$ axis is speed squared i.e. $(m/sec)^2$ not $m/(sec^2)$. Also this isn't the wind speed through the fan, it's the speed of the cyclist (squared) so $160$ means the cyclists speed is $\sqrt{160} \approx 12.6$ m/sec.
Actually $40N$ seems a very low drag - is the drag at $12.6$ m/sec ($\approx 28$ mph) really only $4$ kg?