stunthanger.com
Electric Stunt => Gettin all AMP'ed up! => Topic started by: Frank Imbriaco on July 14, 2018, 06:24:29 AM
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APC has a nice line of pusher and tractor props for multi-rotors. They are "in-between" thin electric series and slow flier series as far as construction and blade . There are more size choices, too, in the multi-rotor line.
The hubs on the thin electric and multi-rotor are similar and for the most part, so is the blade profile. Multi-rotor props are a bit lighter which is a good thing because they demand less current which theoretically, should keep the ESC happier and less likely to go into shut down or RPM limitation from load.
That said, the RPM limit is 105,000 divided by prop size (8 ", 9" , etc.) on multi-rotor as opposed to an RPM limit of 145,000 divided by prop size on thin electric. A definite negative . So, peak RPM MUST be monitored.
What I'd like to know if anyone is using multi-rotor props on their e-ships , what RPM differential exists between them and electric thin, and general experiences.
With prudent use, we shouldn't toss blades .
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I have a carbon fiber 12x4 that is very thin but has a reasonable hub and is very stiff. I only tried it once as the bite it took reduced my lap time by about 0.8 seconds. Couldn't slow my motor down enough get the lap speed down. I plan on trying it again when I have a setup that will give me an appropriate RPM.
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Kenny Stevens ran them at the World's in 2014. He broke a blade off on a tuft of grass, which caused the nose to come off in a subsequent flight. Here's part of the story (https://stunthanger.com/smf/open-forum/team-usa-and-the-world-champs/msg371222/#msg371222). Someone may have a better one to tell.
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As I recall... but Kenny would have to be the one to tell us if it was a "tuft of grass" as you assert or a turf prop strike.
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Matt Neumann tried some of the carbon multirotor props and failed them at the hub. Thankfully they only got flexible and did not separate.
APC rates their multirotor props with MUCH lower max RPM than their regular electric props, so much so that they are not suitable for our use.
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As I recall... but Kenny would have to be the one to tell us if it was a "tuft of grass" as you assert or a turf prop strike.
I may indeed have that wrong. There was an extensive discussion/report about that here when it happened, but I couldn't find it -- the best I could do was that post by Kenny that I shared a link to.
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Hello everybody,
I have used different 2 blade MR APC props for my electric models.
The main reason: they were lighter then equivalent "normal" props. The hub was less bulky and the transition between the hub and the blades was thinner.
Unfortunately, they were also less stiff than the "normal" props in the out-of-the plane of rotation direction. Simply put: the blades were more flexible. When I started flying sharp corners, the gyroscopic moment was bending the blades and I could hear the very well audible "bzzz" sound exiting the corners when the blades rebounded.
I have replaced the MP APC 2 blade props with Igor's 11x5x3 carbon composite electric and the "bzzzz" sound disappeared.
Happy Flying,
Matt
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June 2016: Symmetria, Aeronaut Cam Carbon light 14 x 6 Pusher at 8’974 RPM:
Sequence:
1. Prop noise in outside loops
2. More prop noise in outside corners
3. Sudden disintegration of fuselage nose in flight, immediate crash
4. Found both blades broken at the root, inside the 57 mm spinner
5. No blades found at place of impact
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I was inquiring about the same thing and found out that they are not rated for the kind of RPMs we are running. They might go up to 6500RPM if that.