What an intriguing concept. The following is offered as additional fodder for discussion. . .. .Might the air be used to delay retreating blade stall?. .For this, would the optimum location to discharge the air be on the aft upper surface of the tip? Will the use of discreet ports work or should it be a porous surface, to give a more even discharge? Might the roughness of this porous surface disturb the boundary layer?. .. .An addendum to your idea:. .. .If the air discharge is only required at a specific azimuth and centrifugal effect will not provide sufficient air, then the following might be considered. Provided a valve on the blade root's incoming port. The valve will cycle at the same rate as the RRPM, opening and closing at specific azimuths. This will cause the 'hollow' airfoil or spar to act as a tuned exhaust and thereby deliver pulses of air to the discharge location.. .. .An addendum to the addendum:. .. .Could pulsed ejection of air from the blade aerodynamically (as opposed to mechanically) change the angle of attack and thereby be used as a means of Higher Harmonic Control?. . . . <small>[ 18 March 2002, 02:53: Message edited by: Dave Jackson ]</small>