Slow Fly Prop Questions

Hello all,


First off, I just want to introduce myself:  I am a UAV enthusiast, been involved in RC since before I can remember, an aerospace engineer working on UAVs, and just starting my first quad project.  I am guessing that probably describes 50% of the community here :)


I am currently assemblying components for my quad build, and I have run into a bit of a snag concerning the props I will be using.  I decided to go the lower kv and large dia. prop route, 750kv and 12x3.8 prop.  However, looking into the specs for the SF series of APC props, I like the low pitch for the quasi-static conditions you see with a quad (hover, low speeds), but it seems that APC puts the structural limits for RPMs quite low.  For the slow-fly series it's 65000 RPM/prop diameter:


So for a 12x3.8 prop: ~ 5000 RPM limit

 10x4.7 prop: ~ 6500 RPM limit



My rough performance estimates put me at or above those RPMs for most flight maneuvers, even hover if my quad wants to carry a medium sized payload.  Again, this is with a 750kv motor, which has a theoretical max RPM of 8300 for a 3S lipo.  For higher KV motors, it would seem that these limits are even more of a hindrance.

From my research, these APC SF props seem to be quite popular for quads.  I am assuming if there was a drastic change in performance past the limit, there would be more concern. Do most of you disregard this limit?  Do you see any flutter or vibrations beyond the RPM limit?  Does APC have a sizeable structural margin built into that number, and perhaps that's why there isn't much to worry about with our quads?


I apologize if this has been discussed before, but my searches haven't really turned up anything specific.  Thank you for the help!  Looking forward to becoming more involved in this community.


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  • Developer

    I am using 12x3.8 APC slo-fly props, and 860kv motors ( very similar to yours), and i am unable to get a reliable flight platform, despite months of attempts ( I get it flying, but never reliably ).      I also break a LOT of props ( 10+ so far. ) impacting the ground after "wobbles".    All I can say is buy at least double the number of props you think you need, and be prepared to buy more ASAP.   :-)   


  • I am also trying to use the 12x3.8 props. I was using too much throttle with the 10x4.7s (Heaver quad with gopro camera stabilazition, approx 4 lbs). I get good lift with the 12x3.8s at a lower throttle position , but getting a lot more oscillations that I can't seem to tune out.


    What should the tuning be for the larger props?

  • Hello,

    My quad has Avroto 750kv motors (4s) with APC 11x4.7-a tad heavy with a go pro/eagle tree fpv setup, and it does great at almost 7k feet in Colorado.  Took it to sea level the other day and it was a lot of fun.  With that said, prop track and balance in both low and high altitudes at power, was great. 

    I may have had one blade root failure-which could have been caused by a previous prop strike-in about 24 props, so I think there is sufficient margin built into the APC products. 

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