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Old Feb 21, 2011, 07:24 AM
jackerbes is offline
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USA, ME, Ellsworth
Joined May 2008
18,096 Posts
On prop RPM limits, when I got interested in that and looked for it, I found that some prop makers did provide maximum RPM limitations and others did not. For example, GWS, one of the most widely prop lines, makes no recommendations. But there are some that do and there is also a lot of ancedotal evidence and experience that can be drawn on. Below are the notes I have collected on prop limits from various RC forums:

GWS Reduction Series or RS (marked EP) props = 40,000-50,000 RPM / Diameter (inches)
GWS 6" to 10" Direct Drive Series (marked HD) = 80,000-100,000 RPM / Diameter (inches)
GWS 5" or smaller Direct Drive/HD = much tested/used at 15,000-20,000, max safe RPM 80,000 RPM / Diameter (inches) or more

APC Glow/Speed 400 Electric = 190,000 RPM / Diameter (inches)
APC Thin/Folding Electric = 145,000 RPM / Diameter (inches)
APC Slow Fly = 65,000 RPM / Diameter (inches)
APC Racing (8.75 N,W,8.8,Series 40 Pylon) = 225,000 RPM / Diameter (inches)

Master Airscrew (Windsor) = 165,000 RPM / Diameter (inches)

A discussion on the Wattflyer forum on prop RPM limits:

A well known on this forum and very experienced propeller tester's opinion on prop limits:

There is no official list since GWS refuses to address the question. Since a certain lawyer tells me that if I recommend anything, I can be held liable if someone gets hurt, I can take no responsibility for these numbers below! But I have tested a LOT of props and I'm giving you what I think are reasonable limits.

The GWS RS series, especially the larger higher pitched ones (9-10-11x4.7, 11x7 etc), are very flimsy and I reckon they are good for only about 40,000-50,000rpm/diameter.

The GWS HD series are better and most of them can cope with 80,000-100,000rpm/diameter.

The tiny (<5") HD/DD props can cope with 15,000-20,000rpm...(call that 60,000-80,000rpm/diameter)... maybe a bit more.

APC Suggested RPM Limits

1. Glow Engine and Speed 400 Electric Props

Maximum RPM=190,000/prop diameter (inches)
(For example, a 10x6 glow engine prop should be limited to 19,000 RPM)

2. Thin Electrics and Folding Electric Props

Maximum RPM=145,000/prop diameter (inches)

3. Slow Flyer props

Maximum RPM=65,000/prop diameter (inches)

4. Racing Props
8.75 N,W and 8.8 series 40 Pylon props
Maximum RPM=225,000/Prop diameter (inches)

Note: In December 2010 it was noted that limits for Thin Electrics and Folding Electric props has been dropped from 190,000/prop diameter to 145,000/prop diameter. Those had formerly been included in category 1 with the Glow Engine and Speed 400 Electric Props and covered by the 190,000/prop diameter limit.

Master Airscrew limits:

RPM Operating Limit = 165,000 divided by Diameter in Inches. For example, a 10
diameter prop has an operating limit of 16,500 RPM, well above the requirement of a .40

As for the other props not mentioned above (Great Planes, E-Flite, Hoye (?), etc.) I simply compare the material in the blades and roots at the hub and think in terms of the limits I am using for the similar props above that have known limits.

And when I spin a prop up in static testing or when preparing to launch, I listen to what is going on. I have not found a prop yet that will not give you an audible warning when you start nearing the limits.

The bottom line? Keep yourself out of the swing line of all props at all times, that was drilled into me in the mid 50's when I was a 12 year old kid flying a Cox .049 on U-Control and it is still valid advice today.

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