chris collister Apr 25, 2010:

You could be right but it's not clear, is it? I'm not sure what particular curve is flat, but presumably efficiency: Efficiency vs. flowrate, vs. pressure drop,...? Even so, an efficiency of 10% is pretty poor, and surely unacceptable in these energy-conscious times.

Bourth (X) Apr 25, 2010:

Efficiency curves. If "ne s'appliquent pas aux ventilateurs (i) (axiaux) à courbes plates ou (ii) hélicoïdes", maybe?

chris collister Apr 24, 2010:

flat curves?? At first I thought this may have been referring to the efficiency curve, but the helical bit knocked that one on the head. There is a common kind of fan which consists of flat plates on the periphery of a rotating drum, but I didn't think the efficiency was as low as 10%. Sometimes very crude fans just consist of flat plates bolted onto a rim with a fixed angle of attack: no radial variation in angle of attack, no curvature, nothing. Very inefficient. Most fans or propellors are section of a helix (if you have ever seen pictures of cavitating boat propellors), so the "hélicoïde" is a bit of a problem (for me, at any rate). Maybe someone else knows better.