# How much distance do I need between quadcopter propellers to avoid issues?

For a given propeller size (say 5"), what is the minimum clearance needed between propellers to ensure that not only do they not hit each other (easy to calculate), they also don't interfere too much with each other (i.e. tip vortices, airflow, etc.)

For example consider the following design: an X-shaped quad-copter where the propellers are at the end of each tip of the X - and the X across the diagonal (max distance from the center of the propellers) is 180mm - then 5" propellers will only have .279mm of clearance between them - now assuming that mechanically there are no vibrations/imperfections/etc. that cause them to run into each other, what else is there to avoid in terms of airflow? if they were raised such that two diagonal propellers are lower/higher than the others, would there be any issues? does it depend on the propeller pitch, or if it's a 2-blade or 3-blade propeller?

P.S. - I am unsure of the tags, please adjust as necessary

• I'm voting to close this question as off-topic (and too broad). It belongs to a RC site, as already pointed out.
– mins
Oct 21, 2015 at 22:57
• I agree that this would be better answered on a site more devoted to RC. But spacing of full-sized props would be on-topic here, and that is just a matter of scale.
– fooot
Oct 22, 2015 at 0:21
• I think this is a valid question for this site. The fact that another better forum might exist by itself does not seem reason enough to close it on here. Oct 22, 2015 at 1:24
• IANAAE: QC blades spin so fast that I simply cannot fathom any tip vortice issues at all, nor much, if any, interference between the rotor disks. Oct 22, 2015 at 1:53
• what else is there to avoid in terms of airflow.... On-topic. Oct 22, 2015 at 18:55