Comment by Bernard Michaud on July 16, 2011 at 11:09am

So .... this is the way the gain of efficiency is achive.

I find this an interesting combination of DIY and hands on physic concepts.

Comment by Michael Zaffuto on July 16, 2011 at 12:49pm

Vibration, prop flutter?  The prop blade tips are going into and out of different pressure zones,

curious if there is an increase in prop induced vibrations.

Comment by Henrik Ala-Uotila on July 16, 2011 at 12:57pm

Looks interesting. Have you thought of enclosing the propellers in a cylinder? Operating more like a ducted fan, the propellers' thrust should, as far as I know, improve in efficiency as the enclosure limits wingtip vortices on the rotary wings (=props).

Comment by Denny Rowland on July 16, 2011 at 9:49pm

I have tried a duct system. My conclusion was that it could not produce any more lift than it's own weight. There is however another way to do this which is where the shroud is significantly large in diameter than the prop with a large bell mouth. This is called an augmenter tube. I have not tried it yet but it could work in theory.

Comment by Denny Rowland on July 16, 2011 at 10:05pm

No vibration issues. 5 mm motor shaft, 3 bearings and 15 cm clearance on the hull. 14.4.5 props fully balanced.

Mounting the motors in this manor reduces prop overhang and thus any risk of vibration frequency oscillations.

Like I said profile drag is a square law. Put your arms under the prop wash and you incur significant drag penalty and turbulence. Because MK did it the wrong way does not mean we all have to follow!!!!

Comment by Denny Rowland on July 16, 2011 at 10:16pm

The hull sits on top of the X frame, it is mounted in only four places on small evo rubbers, so the whole hull assy. is isolated from vibration. X frame is oval section and is made from hard balsa covered with a light cabon/epoxy skin. Tip vortices go up with increased pitch angle. The best efficiency comes from absorbing the available power into the largest thrust area i.e.large dia, x small pitch angle.

Comment by Denny Rowland on July 16, 2011 at 10:25pm

The augmenter tube needs to be modeled in CFD before investing in a mold. Sadly I no longer have access to that software.

Comment by Coptaire on July 17, 2011 at 3:00am

You can use openFOAM CFD and a 10° aperture cone will produce the desired effect with a not too long tube.

Comment by nubli hashim on July 17, 2011 at 6:11pm

Interesting concept that might save loads and battery amps..way to go Denny

Comment by eduardo on July 17, 2011 at 10:44pm

have you tested this frame in wind gusts ?

i have made some test with tons of frame type and i think you will have stabilization problem when flying on the wind as i have on my tests.

 

 

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