You were the one that used a ducted fan as an example to prove a point, not I. So does the ducted fan comparison make your point or not? I'm confused.
People didn't spin their 11x7 props at 15000 rpm because that was the most efficent method of providing thrust for the plane. They did it because that's where these engines made their best power. That's not true of electric power systems. So, can you do it the old way and spin a little prop like mad with an electric motor? Sure but why?
ORIGINAL: Trisquire
ORIGINAL: Mike Wiz
I'm not so certain about that. I'm no expert on ducted fans but I think there is somthing else happening there. Could you take the fan blades and attach them to the front of a plane and spin it as fast as it would in a duct and have the same thrust? I don't think so but then again, I'm not an expert in that area.
ORIGINAL: Trisquire
Turning an 11-7 at 15,000 RPM is certainly no less efficient than turning the ducted fan rotor blades on a jet. I don't know if you've seen any electric ducted fans lately, but they are not lacking in performance.
Tom
You wouldn't get the same thrust without a duct, but we're not trying to reduce the prop diameter to that of a ducted fan rotor. We're just trying to get it down to 11 inches.
Back in the glow powered ducted fan days, you had to shoehorn an O.S. 91 into a "60 sized" jet, to make up for the duct's lack of efficiency; and those engines are not covered under the O.S. 2-year warranty, because your spinning them at such high RPMs.
Tom