Coaxial ducted rotor

[stonie123]

G'day, Im building a VTOL UAV for my thesis. Unfortunatly im an electrical engineer so I have to admit I have little idea about fluid dynamics.

Ive got two power trains (Motor, LiPo, prop and ESC) am I better off running both motors seperatly (like a tilt rotor osprey) or could I use both trains running coaxial in a single duct and acheive the same (or better) thrust. Ive attached a pdf with a drawing of what I mean.

Cheers.

[AXI Motor Models]

The bottom prop will have higher airflow due to the top prop blowing air down on it, so the bottom prop should have a higher pitch.

[Peter Seddon]

How effective will the bottom prop be with the turbulent air that is enetring from the top prop? You might get some views about this issue by searching for info on Kamov coaxial helis.

regards Peter

[stonie123]

Thanks AXI and Peter, I had a look at coaxial helicopters when I was first looking into the design. Because the blades arnt ducted and they are synchronised each pair of blades produce their own thrust I think and the sychronisation prevets the blades for causing too much turbulence on eachother.
I kinda figured I would have to increase the pitch of the bottom prop, problem is finding somewhere the maufactues 3-bladed props with high pitches.
Thanks again and will keep everyone posted on how the project progresses

[stonie123]

Does anybody know if a 3-blade 14x14 propellor is manufactured by anyone?

[Peter Seddon]

The blades on a a 14 x 14 prop will be stalled until you get up to a reasonable flying speed. Three bladers tend not to be quite as effective as you might hope. The following site is quite good for props and airfoils http://www.mh-aerotools.de/airfoils/

regards Peter