Outrunner EDF Versus Inrunner EDFby Motion RC
Pilots often equate 12 bladed EDFs with more speed than 5-6 bladed EDFs, but this is not always necessarily true.The thrust output and amp draw of any EDF system will vary widely based on the aircraft it's being installed in. The FSA (Fan Swept Area, the area of the opening where the air goes through the fan) of the intakes, the geometry of the ducting itself, the exit duct's length and final diameter, etc.
All these factors impact performance. Freewing's 70mm 12 bladed inrunner power system outputs ~20-25% more thrust with a 30% increase in amp draw, in Freewing aircraft such as their SU-35, when compared to the SU-35's stock plastic 70mm six bladed outrunner fan. If you are contemplating installing a 12 bladed power system, you will need to test it in the airframe to get a fully accurate observation of its performance in your specific aircraft.
It is important to note that if you decided to test it in your aircraft, that the sound will potentially be more "whoosh" and less "whine" (but that depends also on your ducting). Additionally, the amps will increase and the thrust will increase at a slightly less rate, but most importantly the top speed of the aircraft will likely not increase significantly. In most Freewing airframes, a ~5%-10% increase in speed, depending on how the aircraft is flown, can result from the 70mm 12 blade inrunner power system.
But in general, higher blade count fans sound better and give more thrust/acceleration than their 5-6 bladed counterparts, but the higher blade count fans pay for it with less efficiency and minimal speed gains. Certain changes can be made to an aircraft's ducting arrangement to fine tune the factors of static thrust versus dynamic thrust, and efficiency, speed, sound, etc.