Replies to This Discussion

Permalink Reply by Helitrasher on July 29, 2012 at 5:18am

Just spin up the prop by hand or temp motor mount and feel the prop wash then add a couple of inches for luck.

But be carefull with the spining props !

Permalink Reply by Vernon Barry on July 29, 2012 at 5:25am

The aircraft industry did significant studies on thrust loss VS how close props are and further away is always better. The tips create a vortice that is cone shaped facing down. If adjacent vortexes combine, it is a loss of thrust in the swirling mass of air.

On my 3DR hexa, it's way too small with 12 inch props as they would be maybe only a few (3-5)mm apart from touching. 11 inch props work OK, but I am pretty sure longer arms would be better. 3DR just used the same arms as the quad and while it works, it's not optimal, so I would go for a slightly longer arm than what 3DR uses. The arms are ~11 inches long. but what mattters is from center to motor shaft so that is 12.5 inches from the center of the aircraft. As I said, this is too close for 12 inch props and maybe 14 inch center to motor shaft arms would make a huge difference. It's not much more weight from the added arm length. 

Permalink Reply by Rui Manuel Cravo Marques on July 29, 2012 at 7:36am

Hi Andre,

By my personal experience, the more together the props are, the worst, regarding control and stability. I had a quad with 12" props wich were about 3" appart and regarding tuning the quad was extremelly demanding on parameters. Replacing the 12" props with 10" props, left it much more tolerant and easy to control. My theory is that when leaning, the downwash from a prop was influencing the downwash of the other, causing excessive turbulence and loss of lift. So, the ideal is smaller props and the max distance between them (as long as you still have lifting power). When I passed to my hexa, this effect is much less noticeable. I have my props spinning very close to one another without  noticing any loss of controll. I think this might be from the motors not beeing perdendicular to one another, not causing too much influence in the adjacent motor, but even if it does, there's always another motor to compensate.

Permalink Reply by Andre Kotze on July 29, 2012 at 9:12am

Hi all. Thanks for the replies and advise.  I plan to use 11x4.7 props on my HEXA, so how does the idea of a 4" clearence sound to you?  Thanks

Permalink Reply by Rui Manuel Cravo Marques on July 29, 2012 at 9:21am

I believe you won't have any problem :) I'm using 10x4.7 with about the same clearence (maybe a bit less), and behaves great.